Coated paper and paper cushioning material

Abstract

To provide coated paper which can be used as a practical cushioning material, and to provide a paper-made cushioning material comprising the coated paper.SOLUTION: The paper-made cushioning material comprises coated papers having an under layer and a top layer in this order on a paper base material, wherein both the under layer and the top layer contain resins, at least one of the under layer and the top layer has a Young modulus of 300MPa or less, and the Oken type air permeation resistance as a whole is 100,000 seconds or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to coated paper and a paper cushioning material made from this coated paper. [Background technology]

[0002] Air cushions, which are bags made of flexible plastic film filled with gas, are used to protect products from impacts during transportation, for example. Air cushions are lightweight and inexpensive, and after use, they can be punctured to release the gas, significantly reducing their volume, which helps reduce disposal costs, making them widely used. On the other hand, in recent years, environmental issues such as plastic waste and global warming have led to a growing trend toward eliminating petroleum and plastic, and it is desirable to reduce the amount of resin materials derived from fossil resources and non-biodegradable resin materials used in industrial products as much as possible. Paper has therefore been attracting attention as an alternative material to plastic.

[0003] As a paper-based cushioning material, Patent Document 1 proposes a laminated paper for cushioning material in which a water-soluble polyvinyl alcohol layer is laminated on one side of a paper base material. The laminated paper for cushioning material in Patent Document 1 is highly recyclable and biodegradable, but it easily loses gas, so it needs to be gassed just before use, and it also has poor heat-sealing strength, so it is prone to tearing when subjected to impact. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-262935 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a coated paper that can be used as a practical cushioning material, and a paper cushioning material made from this coated paper. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. A paper substrate having an under layer and a top layer in this order, Both the under layer and the top layer contain a resin, At least one of the under layer and the top layer has a Young's modulus of 300 MPa or less, A coated paper characterized by an overall Oken air resistance of 100,000 seconds or more. 2. The coated paper according to 1., wherein both the under layer and the top layer have a Young's modulus of 300 MPa or less. 3. The coating amount of the under layer is 3 g / m 2 3. The coated paper according to 1. or 2., characterized in that: 4. A paper cushioning body made of the coated paper described in any one of 1. to 3., characterized in that a gas is sealed inside. [Effects of the Invention]

[0007] The coated paper of the present invention is resistant to cracking between the under layer and top layer when bent, preventing a decrease in barrier properties due to cracking, and therefore the paper cushioning of the present invention made from this coated paper can maintain a sufficient amount of gas sealed in for a long period of time. The coated paper of the present invention has excellent heat seal strength, and therefore the paper cushioning material of the present invention made from this coated paper is resistant to tearing even when subjected to impact, making it suitable for practical use as a cushioning material. The coated paper of the present invention can be re-defibrated and therefore recycled as waste paper. DETAILED DESCRIPTION OF THE INVENTION

[0008] Coated paper The coated paper of the present invention has an under layer and a top layer in this order on a paper substrate, Both the under layer and the top layer contain a resin, At least one of the under layer and the top layer has a Young's modulus of 300 MPa or less, The overall Oken air resistance is 100,000 seconds or more. Young's modulus is the ratio of the force (stress) acting per unit cross-sectional area of ​​a sample to the rate of deformation (strain) when an external force is applied in one axis direction within the elastic range of the object, and is the initial slope of the stress-strain curve. Young's modulus is a value that indicates the resistance of a material to deformation; the higher the Young's modulus, the more difficult it is to deform.

[0009] (Paper base material) The paper base material is a sheet made of pulp, filler, and various auxiliary agents. Pulp can be selected from a wide variety of materials, including chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft 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, and the like. These materials can be used alone or in combination. Among these, chemical pulp and mechanical pulp from wood fibers are preferred, with chemical pulp being more preferred, for reasons such as reduced contamination of the paper substrate, reduced discoloration over time when used paper containers are recycled as recycled paper materials, and high whiteness, which results in a favorable surface appearance during printing and increases the useful value of the paper, particularly when used as a packaging material. Furthermore, hardwood pulp is even more preferred as the wood fiber, since it is easier to obtain a flexible paper substrate.

[0010] As the filler, known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers can be used as needed. In addition, aluminum sulfate and various anionic, cationic, nonionic, or amphoteric retention aids, drainage aids, paper strength agents, internal sizing agents, and other internal additives may be used as needed. Furthermore, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, pitch control agents, slime control agents, and the like may also be added as needed.

[0011] Furthermore, the surface of the paper substrate can be treated with various chemicals. Examples of chemicals that can be used include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retention agents, thickeners, and lubricants. These can be used alone or in combination of two or more. Furthermore, these various chemicals can be used in combination with pigments. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, and core-shell pigments, which can be used alone or in combination of two or more.

[0012] The paper base material has a basis weight of 20 g / m2 in terms of processability, flexibility, strength, etc. 2 More than 80g / m 2 The basis weight is preferably 24 g / m or less. 2 More preferably, 28 g / m 2 More preferably, 70 g / m 2 Less than 60 g / m is more preferable. 2 The following is even more preferred: From the viewpoint of flexibility and strength when made into a paper packaging material, the thickness of the paper substrate is preferably 20 μm or more and 100 μm or less, more preferably 26 μm or more, even more preferably 30 μm or more, and more preferably 88 μm or less, even more preferably 75 μm or less.

[0013] The paper substrate preferably has a bending hysteresis 2HB in the MD direction measured by the KES method of 0.001 g·cm / cm or more and 0.5 g·cm / cm or less. The smaller the hysteresis 2HB value, the easier it is to return to its original shape after bending. Paper substrates with a hysteresis 2HB of 0.001 g·cm / cm or more and 0.5 g·cm / cm or less have excellent processability and are less susceptible to cracking during processing or when subjected to impact, resulting in less gas escape. In the paper substrate of the present invention, the hysteresis 2HB is preferably 0.002 g·cm / cm or more, more preferably 0.004 g·cm / cm or more, even more preferably 0.006 g·cm / cm or more, even more preferably 0.008 g·cm / cm or more, and more preferably 0.46 g·cm / cm or less, even more preferably 0.42 g·cm / cm or less, and even more preferably 0.38 g·cm / cm or less.

[0014] The paper substrate has a bending stiffness B of 0.2 g cm in the MD direction according to the KES method. 2 / cm or more 1.5g·cm 2 / cm or less. The smaller the value of bending stiffness B, the softer the material. This bending stiffness B is 0.2g cm 2 / cm or more 1.5g·cm 2 When the thickness is 1 / cm or less, the paper substrate has a good balance between flexibility and strength, is excellent in processability and air sealing property, and the barrier property is not easily reduced. The KES method, an abbreviation for Kawabata Evaluation System, is a method for measuring the physical properties of flexible materials such as nonwoven fabrics and woven fabrics, and can objectively evaluate tensile, bending, and shear properties. The bending hysteresis 2HB using the KES method can be measured, for example, using an automated pure bending tester, model KES-FB2-S, manufactured by Kato Tech Co., Ltd. The bending hysteresis 2HB, which is a bending property, can be calculated from the relationship between the bending moment (M) and curvature (K) during bending deformation. The bending hysteresis 2HB represents the difference in bending moment when bending and returning, and is calculated from the difference between the two MK curves. The bending stiffness B, which is a bending property, is calculated from the increase in bending moment (M) relative to the increase in curvature (K), i.e., the slope of the MK curve.

[0015] (Underlayer and top layer) The under layer and top layer are both coating layers containing resin, and they work together to provide gas barrier properties. Whether or not a layer is a coating layer can be determined by observing the cross section with a microscope or the like. If a coating defect such as a pinhole exists in the coating layer, gas can easily escape from the defective area, resulting in a decrease in barrier properties. When a top layer is applied on an under layer, the coating defects in the under layer are covered by the top layer, preventing a decrease in barrier properties due to the coating defects and allowing the desired barrier properties to be exhibited.

[0016] In the coated paper of the present invention, at least one of the under layer and the top layer has a Young's modulus of 300 MPa or less. Since at least one of the under layer and the top layer has a Young's modulus of 300 MPa or less, the coated paper of the present invention is less likely to crack when bent, preventing a decrease in barrier properties due to cracking. It is preferable that both the under layer and the top layer have a Young's modulus of 300 MPa or less. The Young's modulus of at least one of the under layer and the top layer is preferably 200 MPa or less, more preferably 150 MPa or less, even more preferably 100 MPa or less, even more preferably 60 MPa or less, even more preferably 40 MPa or less, and even more preferably 20 MPa or less.

[0017] The resins contained in the under layer and top layer are not particularly limited, as long as at least one of the layers has a Young's modulus of 300 MPa or less, the coated paper as a whole achieves an Oken air resistance of 100,000 seconds or more, and the top layer can be heat-sealable. Examples of such resins include acrylic resins, styrene-acrylic resins, ethylene-acrylic resins (including ionomers), ethylene-vinyl acetate resins, polyolefin resins (polyethylene, polypropylene, etc.), polyester resins (polyethylene terephthalate, polyethylene succinate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), etc.), polyvinyl alcohol resins, polyvinyl acetate resins, and modified versions thereof. One or more of these resins can be used in combination. The under layer and top layer can be made of the same or different resins. The term "same resin" simply means that the resin type is the same, and does not mean that the monomer ratio, molecular weight distribution, number average molecular weight, etc. are completely the same.

[0018] In addition to resins, the under layer and the top layer may contain various commonly used auxiliaries such as pigments, crosslinking agents, surfactants, dispersants, thickeners, water retention agents, antifoaming agents, water-resistant agents, dyes, fluorescent dyes, etc. The top layer may also contain antiblocking agents such as pigments, waxes, and metal soaps.

[0019] The underlayer and top layer may each independently contain up to 20% by weight of pigment based on the dry weight of each layer. Pigment is optional and may be absent. Pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as solid, hollow, and core-shell organic pigments, which can be used alone or in combination. Among these, from the perspective of gas barrier properties, flat pigments with an average particle size of 3 μm or more and an aspect ratio of 10 or more are preferred, and flat pigments with an average particle size of 5 μm or more and an aspect ratio of 30 or more are more preferred. In this specification, the term "average particle size" refers to the 50% volume average particle size (D50).

[0020] The higher the pigment content, the better the barrier properties, but the lower the flex resistance and the more susceptible the coating layer is to cracking during processing, etc., which in turn leads to a decrease in barrier properties. Therefore, the pigment content in the under layer and top layer is preferably 16 wt% or less, more preferably 12 wt% or less, even more preferably 8 wt% or less, even more preferably 4 wt% or less, even more preferably 2 wt% or less, even more preferably 1 wt% or less, and most preferably 0 wt% based on the weight of each layer, on a dry weight basis.

[0021] The coating amount of the undercoat is 3g / m per side in dry weight. 2 The coating weight of the under layer is preferably 3 g / m or more. 2 If the thickness is less than this, the coating film will not be thick enough, the barrier properties will be insufficient, and the injected gas may easily escape over time. The coating amount of the underlayer should be 4 g / m2 per side in dry weight. 2 More preferably, 5 g / m 2 More preferably, 6 g / m 2 More preferably, 7 g / m 2 More preferably, 8 g / m 2 More preferably, 9 g / m 2 More preferably, 10 g / m 2The upper limit of the coating amount of the under layer is not particularly limited, but since the barrier property does not improve much beyond this limit and reaches saturation, and the cost becomes high, it is preferable to set the upper limit to 20 g / m. 2 The following is preferable.

[0022] The top layer coating weight is 2g / m2 per side in dry weight. 2 It is preferable that the dry weight is 2 g / m or more. 2 If the thickness is less than this, the heat sealability may be insufficient. The coating weight of the top layer should be 3 g / m2 per side in dry weight. 2 More preferably, 4 g / m 2 More preferably, 5 g / m 2 More preferably, 6 g / m 2 More preferably, 7 g / m 2 More preferably, 8 g / m 2 More preferably, 9 g / m 2 More preferably, 10 g / m 2 The upper limit of the coating amount of the top layer is not particularly limited, but the heat sealability does not improve much beyond that limit and reaches saturation, and the cost becomes high. 2 The following is preferable.

[0023] The total coating weight of the undercoat and topcoat is 10g / m2 on each side in dry weight. 2 The total coating amount is preferably 11 g / m2 or more per side in dry weight. 2 More preferably, 12 g / m 2 More preferably, 13 g / m 2 More preferably, 14 g / m 2 More preferably, 15 g / m 2 The above is even more preferable.

[0024] The coated paper of the present invention is made by pressing the top layers of the coated paper together at a pressing temperature of 130°C and a pressing pressure of 2 kgf / cm. 2When a test piece is heat-sealed with a pressure application time of 0.5 seconds and peeled off at a tensile speed of 200 mm / min, the heat seal strength is preferably 2.0 N / 15 mm, more preferably 2.5 N / 15 mm, even more preferably 3.0 N / 15 mm, and even more preferably 3.5 N / 15 mm.

[0025] The method for applying the under layer and the top layer is not particularly limited, and they can be applied using a known coating device and coating system, such as a blade coater, a bar coater, an air knife coater, a curtain coater, a spray coater, a roll coater, a reverse roll coater, a size press coater, or a gate roll coater. The coating system may be either aqueous coating using a solvent such as water or solvent-based coating using a solvent such as an organic solvent, but aqueous coating is preferred from the viewpoint of safety and hygiene. When aqueous coating is used, the resin contained in the under layer and the top layer is preferably a water-dispersible resin or a water-soluble resin.

[0026] The coated paper of the present invention has an under layer and a top layer in this order on a paper substrate. The coated paper of the present invention may have other layers between the paper substrate and the underlayer, such as a filling layer, an ink-receiving layer, a water-resistant layer, an oil-resistant layer, or a water vapor barrier layer.

[0027] Paper cushioning The paper cushioning of the present invention can be produced by heat-sealing the edges of the coated paper described above to form a bag and then sealing the gas in. The shape of the paper cushioning can be any of the known bag-shaped packaging shapes, such as vertical pillow packaging bags, horizontal pillow packaging bags, side-sealed bags, two-sided sealed bags, three-sided sealed bags, and four-sided sealed bags. [Example]

[0028] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and % in the examples represent parts by weight and % by weight, respectively. The resulting coated paper and paper cushioning were tested according to the following evaluation methods. The results are shown in Table 1.

[0029] (Evaluation method) Young's modulus For each composition forming the under layer and the top layer, a test piece having a thickness of 50 μm and a width of 15 mm was prepared, and the thickness was measured in accordance with ASTM D882 using a gauge length of 50 mm. ·2HB by KES method For paper substrates, a KES type pure bending tester (KES-FB2-S) manufactured by Kato Tech Co., Ltd. was used to hold a sample of 100 mm long x 100 mm with a clamp width of 1.0 cm and bend it at a bending speed of 0.5 cm. -1 / sec, maximum curvature 2.5cm -1 The measurement was carried out under the following conditions. The MK curves were measured at two locations within the curvature range of 0.5 to 1.5 (front bending) and -0.5 to -1.5 (back bending), and the average value was taken as the bending rigidity B in the MD direction. The difference in bending moment during reciprocation was measured at two locations, one with a curvature of 1.0 (front bending) and one with a curvature of -1.0 (reverse bending), and the average value was taken as the bending hysteresis 2HB.

[0030] Basis weight, coating amount The basis weight was measured in accordance with JIS P 8124. In addition, the basis weight was measured before and after coating, and the coating amount (g / m 2 ) was calculated. Air permeability (Oken air resistance) The air permeability (Oken air resistance) of the prepared coated paper was measured using an Oken air permeability and smoothness tester (manufactured by Asahi Seiko Co., Ltd.) according to JAPAN TAPPI No. 5.

[0031] Load testing A pressure strength test jig manufactured by our company was used to apply a load and evaluate air escape. This pressure strength test jig fixes the metal plate so that it can move only in the vertical direction, and it is possible to apply a predetermined load depending on the weight and number of metal plates. The buffer was placed flat and a 150g metal plate was placed on top of it. The height of the metal plate was measured every 24 hours and the number of days until the height fell to 30% or less compared to the start of the test was measured.

[0032] Heat sealability Two square test pieces with sides of 100 mm were cut out from the obtained coated paper, and the top layers were placed in contact with each other and pressed at a temperature of 130°C and a pressure of 2 kgf / cm. 2 The heat-sealed test piece was cut into a width of 15 mm and tested at a tensile speed of 200 mm / min using a tensile tester, and the maximum load when peeled off was taken as the heat-seal strength. Regarding peelability, the heat-sealed test piece was peeled off by hand, and the peeled portion was visually observed, and the heat-sealability was evaluated according to the following criteria: ◯ or △ indicates no practical problems. [Evaluation criteria] ○: Peeling occurs within the paper substrate (paper substrate is destroyed). △: Most of the peeling occurs within the paper substrate (paper substrate is destroyed). ×: Peeling occurs between the coating layers.

[0033] Recyclability Samples measuring 40 mm on a side were cut from the resulting coated paper, and the degree of disintegration of each sample was evaluated using a TAPPI disintegrator at a concentration of 2.5 wt %, in 40°C water, for 10 min at 3000 rpm. [Evaluation criteria] Good: Pulp fibers are dispersed and disintegration is good. ×: Lumps and bundles of pulp fibers remain, and the defibration properties are poor.

[0034] [Example 1] Paper base material (Nippon Paper Industries Co., Ltd., basis weight 38.5 g / m 2 , LBKP100%, MD direction 2HB0.12g·cm / cm, B0.56g·cm by KES method 2 Resin 1 (product name: FILLHARMO GS411, styrene-acrylic resin, manufactured by Toyochem Co., Ltd.) was applied to one side of the 1000 mm square meter (1.25 m² / cm²) with a target coating weight of 8.0 g / m² (solids).2 The resin was then coated on one side of the underlayer so that the thickness was 9.5 g / m2, and the underlayer was air-dried to form an underlayer. Resin 2 (product name: Brightone FC640V, styrene-acrylic resin, manufactured by Sakata Inx Corporation) was then coated on the underlayer to a target coating weight of 9.5 g / m2 in solid content. 2 The mixture was then air-dried to form a top layer, thereby obtaining a coated paper. A square test piece measuring 200 mm on a side was cut out from the resulting coated paper and folded in half (200 mm x 100 mm) with the coated side facing inward. The three open sides were pressed at a temperature of 130°C and a pressure of 2 kgf / cm, leaving about 5 mm on the folded short side. 2 The paper was heat-sealed over a width of 5 mm with a pressure application time of 0.5 seconds. 300 mL of air was injected through the gap that was not heat-sealed, and then this gap was sealed using a soldering iron to obtain a paper cushioning body.

[0035] [Example 2] The target coating weight for the underlayer is 5.0 g / m2 in solids. 2 A coated paper and a paper cushioning body were obtained in the same manner as in Example 1, except that the coating was carried out so that the thickness of the coated paper was as follows: [Example 3] Coated paper and a paper cushioning body were obtained in the same manner as in Example 2, except that Resin 3 (manufactured by Sakata Inx Corporation, trade name: Brightone FC641V, styrene-acrylic resin) was used as the resin for the top layer. [Example 4] The target coating weight for the underlayer is 4.0 g / m2 in solids. 2 A coated paper and a paper cushioning body were obtained in the same manner as in Example 3, except that the coating was carried out so that the thickness of the coated paper was as follows: [Example 5] The target coating weight for the top layer is 7.5 g / m2 in solids. 2 A coated paper and a paper cushioning body were obtained in the same manner as in Example 3, except that the coating was carried out so that the thickness of the coated paper was as follows:

[0036] [Example 6] Coated paper and a paper cushioning body were obtained in the same manner as in Example 1, except that Resin 4 (manufactured by Mitsui Chemicals, Inc., trade name: Bonlon XAS-030, acrylic resin) was used as the resin for the underlayer. [Example 7] The target coating weight for the underlayer is 6.5g / m2 in solids. 2 A coated paper and a paper cushioning body were obtained in the same manner as in Example 6, except that Resin 3 was used as the resin for the top layer. [Example 8] A coated paper and a paper cushioning body were obtained in the same manner as in Example 6, except that Resin 4 was used as the resin for the top layer. [Example 9] Coated paper and a paper cushioning body were obtained in the same manner as in Example 1, except that Resin 5 (manufactured by Mitsui Chemicals, Inc., trade name: Chemipearl S500, ethylene-acrylic resin) was used as the resin for the top layer. [Example 10] A coated paper and a paper cushioning body were obtained in the same manner as in Example 6, except that Resin 1 was used as the resin for the top layer.

[0037] [Comparative Example 1] A coated paper and a paper cushioning body were obtained in the same manner as in Example 1, except that Resin 1 was used as the resin for the top layer. Comparative Example 2 No underlayer is formed (coating amount 0g / m 2 ) Coated paper and paper cushioning were obtained in the same manner as in Example 1. Comparative Example 3 A commonly available PE film air cushioning material (product name: ACF100, manufactured by Aswill Co., Ltd.) was used. Note that this comparative example was not evaluated for heat sealability or recyclability.

[0038] [Table 1]

[0039] The coated papers of Examples 1 to 10, in which at least one of the under layer and top layer had a Young's modulus of 300 MPa or less, were able to produce paper cushioning that was less susceptible to air escaping. In particular, Examples 6 to 8, in which both the under layer and top layer had a Young's modulus of 300 MPa or less, achieved the same level of air escaping resistance as the PE cushioning of Comparative Example 3. In contrast, the coated paper of Comparative Example 1, in which both the under layer and the top layer had a Young's modulus of over 300 MPa, and the coated paper of Comparative Example 2, in which only one coating layer with a Young's modulus of 300 MPa or less was formed, were prone to air leakage, and it was not possible to obtain a practical paper cushioning body. These results show that the coated papers obtained in Examples 1 to 10 of the present invention, which have a coating layer with a Young's modulus of 300 MPa or less, are less likely to crack when bent during molding into paper cushioning, and are able to prevent a decrease in barrier properties due to cracking of the coating layer. The results of Examples 1 to 2 and 3 to 5 confirmed that the greater the coating weight, the more difficult it is for air to escape. The results of Examples 1 and 9, 2 and 3 confirmed that the smaller the Young's modulus of the under layer and top layer, the more difficult it is for air to escape.

Claims

1. The paper substrate has an under layer and a top layer in this order, Both the under layer and the top layer contain a resin, At least one of the under layer and the top layer has a Young's modulus of 300 MPa or less, A coated paper characterized in that the overall Oken air resistance is 100,000 seconds or more.

2. 2. The coated paper according to claim 1, wherein both the under layer and the top layer have a Young's modulus of 300 MPa or less.

3. The coating amount of the under layer is 3 g / m ２ 2. The coated paper according to claim 1, wherein:

4. A paper cushioning body made of the coated paper according to any one of claims 1 to 3, wherein a gas is sealed inside.

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