JP7729196B2 - Packaging materials and packages - Google Patents

Description

The present invention relates to packaging materials that utilize a heat-sealing method and packaging products that use such materials.

Heat seal sheets are widely used as packaging materials for foods, medicines, industrial products, etc. Examples of usage include self-adhesive heat seal sheets formed into bags, heat seal sheets bonded to other substrates, and lid materials for molded containers such as cups and blister packs.
In addition to heat sealing properties, heat seal sheets may be required to have various barrier properties depending on the contents to be packaged. In particular, when packaging food, oil resistance is often required.

Packaging materials having heat sealability and oil resistance based on a paper base have been proposed, for example, in JP-A-2015-155582 (Patent Document 1) and JP-A-2020-183593 (Patent Document 2).
These use petrochemical materials such as styrene-adiene copolymer latex, olefin resins, and acrylic resin emulsions to achieve heat sealability and oil resistance, and have not given sufficient consideration to the environmental impact.

Japanese Patent Application Laid-Open No. 2020-183593 JP 2015-155582 A

The objective of this invention is to provide a packaging material that has excellent heat sealing properties and oil resistance while reducing the amount of petrochemical materials used, thereby resolving environmental problems such as marine pollution.

After extensive research into the use of non-petrochemical raw materials with a low environmental impact, the inventors discovered that by mixing casein or its salt with a rosin compound and using this in the heat seal layer, a heat seal sheet with good heat sealability, oil resistance, and other properties could be obtained, leading to the present invention.

The present invention has the following aspects.
[1] A packaging material having a coating layer on at least one surface of a substrate, characterized in that the coating layer contains casein and/or a salt thereof, and the coating layer further contains a rosin compound.
[2] The packaging material according to [1], wherein the content ratio of the casein and/or its salt to the rosin compound in the coating layer is 20:80 to 95:5.
[3] The packaging material according to [1] or [2], wherein the substrate comprises one or more materials selected from wood pulp, non-wood pulp, and regenerated cellulose.
[4] The packaging material according to any one of [1] to [3], wherein the substrate contains 0.01 to 2.0 g/m2 of a styrene-(meth)acrylic acid copolymer compound and/or a styrene-maleic anhydride copolymer compound.
[5] The packaging material according to any one of [1] to [4], wherein the base material has a Stockigt sizing degree of 20 seconds or more as measured in accordance with JIS P 8122:2004.
[6] A package obtained by thermally bonding at least a portion of the coating layer surface of the packaging material according to any one of [1] to [5].

The packaging material of the present invention has good thermal adhesion, excellent oil resistance, and a low environmental impact.

In the present invention, "air permeability" is a value measured in accordance with JIS P 8117:2009. In the present invention, "Stöckigt sizing degree" is a value measured in accordance with JIS P 8122:2004. In the present invention, "peel strength" is a value measured in accordance with JIS P 8113:2006. In the present invention, "oil resistance" is a value measured in accordance with TAPPI UM-557. The symbol "to" indicating a numerical range means that the values before and after it are included as the lower and upper limits.

One embodiment of the packaging material of the present invention is a packaging material comprising a substrate and a coating layer provided on at least one surface of the substrate. A primer layer may be provided between the coating layer and the substrate. Furthermore, the substrate may have a sizing agent applied to its surface.

Furthermore, the coating layer may be provided on only one side of the substrate, or on one side and the other side opposite the one side. When the coating layer is provided on only one side of the substrate, another layer may be provided on the other side of the substrate.

When the substrate is made of paper, the air permeability measured with an Oken air permeability measuring device in accordance with JIS P 8117:2009 for packaging materials, with the coating layer facing up, is preferably 10 to 100,000 seconds, more preferably 50 to 100,000 seconds, and particularly preferably 100 to 50,000 seconds. By setting the air permeability measured by the above-mentioned measurement method within the above range, sealing at the adhesive interface is less likely to be impeded by evaporation of moisture contained in the paper substrate, even when packaging materials are bonded together at high temperatures (170°C or higher). It can also be used in applications requiring the gradual release of evaporative materials contained therein, or the control of the flow of air and moisture in and out of the packaging, such as packaging materials for freshness-preserving agents and portable hand warmers.
On the other hand, it is preferable to use a substrate having an air permeability of more than 100,000 seconds as measured by the above method, since oil resistance is easily obtained.

The air permeability of the packaging material measured by the above-mentioned method can be controlled by appropriately selecting the air permeability of the substrate measured by the above-mentioned method, the coating amount of the coating layer paint (mass of the coating layer per unit area), the layer structure of the coating layer, the coating and drying conditions, the freeness of the pulp of the substrate, the basis weight and density of the substrate, etc. in the manufacturing method of the packaging material described below.

(Base material)
The raw materials used for the substrate are not particularly limited, but it is preferable to use pulp, regenerated cellulose fiber, biodegradable resin, plant-derived resin, etc., in order to reduce the environmental impact. Examples of pulp include wood pulp and non-wood pulp. Examples of wood pulp include softwood pulp and hardwood pulp, and any of them may be used. Furthermore, the cooking method and bleaching method for wood pulp are not particularly limited. Examples of non-wood pulp include hemp pulp, kenaf pulp, bamboo pulp, cotton pulp, etc. These pulps may be used alone or in combination of two or more. Examples of regenerated cellulose fibers include rayon fiber, lyocell fiber, Bemberg fiber, etc.

Examples of biodegradable resins include polylactic acid, polybutylene succinate, polybutylene succinate adipate, and polybutylene succinate lactide.
Examples of plant-derived resins include ethylene glycol produced from bioethanol, polyethylene terephthalate, polyolefin, and polyethylene furanoate produced from plant-derived monosaccharides and the like.
The biodegradable resin and plant-derived resin may be formed into a film and used as a substrate, or may be formed into a fiber and included in the substrate.

The substrate is obtained by papermaking a papermaking raw material containing a slurry in which fibrous materials such as pulp and resin fibers are dispersed in water.

The substrate can be obtained, for example, by making paper from a papermaking raw material containing a pulp slurry.
The pulp slurry is obtained by beating pulp in the presence of water. The method and apparatus for beating the pulp are not particularly limited, but a double disc refiner (DDR), which has high beating efficiency, is preferably used.

The pulp is preferably beaten so that the Canadian Standard Freeness of the pulp is 250 mL CSF or more and 700 mL CSF or less, more preferably 250 mL CSF or more and 600 mL CSF or less, and particularly preferably 300 mL CSF or more and 500 mL CSF or less.
By setting the Canadian Standard Freeness of the pulp to the above lower limit or higher, the breathability of the paper base material can be more effectively improved. Also, by setting the Canadian Standard Freeness of the pulp to the above upper limit or lower, the strength of the paper can be improved, which can contribute to improving the peel strength of the heat-sealed portion.

Generally speaking, regarding the relationship between pulp beating and paper strength, it is difficult to obtain paper strength if the beating is not carried out sufficiently. This is thought to be because the pulp fibers are not entangled with each other very well and there are few points of inter-fiber bonding (hydrogen bonding). However, paper strength improves with a certain amount of beating.
On the other hand, as beating progresses, the pulp fibers become more entangled with each other, increasing the number of bonding points between the fibers, which increases the paper strength but reduces the voids between the fibers, reducing the air permeability of the base paper.
When the Canadian Standard Freeness of the pulp is within the above range, the paper strength can be sufficiently increased while maintaining the breathability of the breathable substrate, and the peel strength of the heat-sealed portion of the packaging material can be improved.

If necessary, various papermaking internal additives can be added to the pulp slurry obtained by beating to prepare a papermaking raw material. The pulp slurry can also contain the above-mentioned fibrous materials.
Examples of internal additives include sizing agents, paper strength agents, wet strength agents, aluminum sulfate, cationic starch, and other fixing agents. Other internal additives include water retention agents, retention aids, antifoaming agents, fillers, colorants, and the like, which can be arbitrarily blended into the papermaking raw materials. These internal additives can be any known ones.

Examples of sizing agents include alkenyl succinic anhydride, alkyl ketene dimer, and rosin compounds. These sizing agents may be used alone or in combination of two or more. Among these, the use of rosin compounds derived from natural products is preferred, as this increases the proportion of non-petrochemical materials used in the packaging material.

It is preferable that the surface of the substrate on which the coating layer is to be formed is coated with a styrene-(meth)acrylic acid copolymer compound and/or a styrene-maleic anhydride copolymer compound in an amount of 0.01 to 2.0 g/m ² .

The primer layer can be applied to the base paper obtained in the papermaking process using a size press or gate roll, which are processes subsequent to the papermaking process, to coat the above-mentioned styrene-(meth)acrylic acid copolymer compound or styrene-maleic anhydride copolymer compound alone or as a mixture with a binder such as starch. Alternatively, the substrate can be formed by applying a primer containing a styrene-(meth)acrylic acid copolymer compound or a styrene-maleic anhydride copolymer compound to at least one surface of the substrate.

The sizing property of the substrate is preferably 50 seconds or more in terms of Stockigt sizing degree measured in accordance with JIS P 8122:2004, since this improves the heat sealability and oil resistance of the packaging material, and more preferably 100 seconds or more.
Examples of the paper strength agent include polyacrylamide resin, cationized starch, and polyvinyl alcohol. These paper strength agents may be used alone or in combination of two or more.

Examples of the wet strength agent include polyamide epoxy resin, epichlorine resin, and melamine resin. These wet strength agents may be used alone or in combination of two or more.
An example of a water-retaining agent is carboxymethyl cellulose.
An example of the filler is talc.

When the packaging material is to be given easy-peel openability, the substrate preferably contains a polyacrylamide resin, which enhances the easy-peel property.
In particular, by adding polyacrylamide resin to the substrate as a paper strength enhancer, the strength of the substrate can be more effectively improved, preventing destruction of the substrate when the heat-sealed portion is opened after heat sealing processing, and further improving the easy-peel properties.

In order to maintain the strength of the packaging material, the basis weight of the substrate is, for example, preferably 30 g/m ² or more, more preferably 40 g/m ² or more, and even more preferably 45 g/m ² or more.
The upper limit of the basis weight of the substrate is not particularly limited, but when used as a bag-shaped self-adhesive packaging material, it is, for example, preferably 300 g/m2 or ^less , more preferably 250 g/ ^m2 or less, and even more preferably 200 g/ ^m2 or less.

The density of the substrate is preferably 0.50 to 1.20 g/ ^cm3 , and more preferably 0.65 to 1.10 g/ ^cm3 . When the density of the substrate is equal to or greater than the lower limit, high adhesive strength is easily obtained at the heat-sealed portion. When the density of the substrate is equal to or less than the upper limit, sufficient breathability can be maintained.

(Coating layer)
The coating layer of the present invention contains casein and/or a salt thereof, and also contains a rosin compound.
The packaging material of the present invention contains a mixture of casein and/or a salt thereof and the rosin compound in the coating layer, thereby significantly improving the heat seal strength compared to when casein (salt) or the rosin compound is contained alone.

The content ratio of the casein and/or its salt to the rosin compound in the coating layer of the present invention is preferably in the range of 20:80 to 95:5.
By setting the content ratio of casein and/or its salt to the rosin compound within the above range, excellent heat seal strength and oil resistance can be obtained.
By setting the content ratio of the rosin compound to casein and/or its salt to 80 or less, excellent heat seal strength and oil resistance can be obtained.

The coating layer of the present invention more preferably contains the rosin compound in an amount of 5.0 to 80% by mass of the total solid content of the coating layer.
It is more preferable that the total amount of casein and/or its salt and rosin compound in the coating layer of the present invention is 80% by mass or more of the total solid content of the coating layer.
Of the casein salts used in the coating layer of the present invention, sodium salts are particularly preferred because they cause little increase in viscosity of the coating material for the coating layer when mixed with a rosin compound, thereby broadening the range of coating method options.

The casein used in the present invention is not particularly limited, and rennet casein and acid casein can be used. As a raw material for casein, cow's milk caseinate is preferred.
Alternatively, milk from other ungulates may be used, particularly milk from ungulates (eg, sheep, goats, horses, camels, and buffalo).

Caseinates that can be used in the present invention are not particularly limited and can be obtained by acid precipitation from a liquid containing soluble casein (casein micelles), such as milk, followed by neutralization with a base such as a hydroxide (e.g., NaOH, KOH, Mg(OH) ₂ , Ca(OH _{) 2} , _NH4OH , or a basic salt, such as CaCO3 _{, Na2CO3} , or _{K2CO3 ,} and mixtures thereof). The term caseinate also includes modified cases (e.g., saccharified caseinate or deamidated caseinate).

Deamidated caseinate can be obtained, for example, by subjecting caseinate to the deamidating activity of an enzyme (e.g., deamidase or transglutaminase). During this process, some or all of the amide groups in the glutamine and/or asparagine side chains are deamidated to form carboxyl groups. Like casein, caseinate is composed of a mixture of four major casein types (alpha S1, alpha S2, bata, and kappa casein).

However, (micellar) casein contains calcium and phosphate bound to the protein structure, stabilizing the micellar structure. While calcium or phosphate may be included in caseinate preparations, caseinate need not contain either calcium or phosphate. Among caseinates, the sodium salt is preferred, as it is the most widely available.

The rosin compounds used in the coating layer of the present invention include reinforced rosin, acid-value-imparted rosin, and rosin-modified phenol. When the coating layer of the present invention contains a so-called reinforced rosin obtained by reacting rosin with an α,β-unsaturated carboxylic acid such as fumaric acid, the heat sealability and oil resistance can be further improved. Furthermore, those with a low content of residual terpene compounds are preferred because they produce a mild cypress odor. Specific examples include the Super Ester series (Arakawa Chemical Industries, Ltd.). These rosin compounds may be used alone or in combination of two or more.

The coating layer may further contain other components as long as the effects of the present invention are not impaired. There are no particular limitations on the other components, and any components that are commonly used to impart heat sealability and oil resistance to packaging materials can be used.

The mass of the coating layer per unit area may be, for example, 0.1 to 30 g/m ² , 0.3 to 20 g/m ² , 1 to 10 g/m ² , or 3 to 10 g/m ² .

(Undercoat layer)
Examples of the undercoat layer include the above-mentioned styrene-(meth)acrylic acid copolymer compound, styrene-maleic anhydride copolymer compound and polyacrylamide resin, as well as various barrier layers, printed coating layers, light-shielding layers and the like.

(Back layer)
In the present invention, a backside layer can be provided as needed. Examples include various barrier layers, printed coating layers, and light-shielding layers. Printing can be performed, and an overprint layer may be provided on the printed layer.

(Method for manufacturing packaging material)
The packaging material is produced by forming a coating layer on at least one surface of a substrate.
An example of a method for producing a packaging material is the following packaging material production method A.

Packaging material manufacturing method A:
A method for producing a packaging material, comprising the steps of applying a coating material for a coating layer to at least one surface of a substrate and drying the coating material, wherein the content of casein and/or a salt thereof in the coating material for a coating layer is 20% by mass or more of the total solid content of the coating layer, and the content of a rosin compound in the coating layer is 10 to 500% by mass of the casein and/or a salt thereof.

The paint for the coating layer may be applied to only one surface of the substrate, or may be applied to one surface and the other surface of the substrate.
If necessary, the surface of the substrate may be smoothed before applying the coating material for the coating layer. After forming the thermal adhesive layer, the surface of the obtained heat seal sheet may be smoothed.
The Oken smoothness of the surface of the substrate on which the coating layer is to be formed, as measured in accordance with JIS P 8155:2010, is preferably 30 to 5000 seconds, since this provides good adhesion during heat sealing and is less likely to cause adhesion inhibition due to an increase in air permeability, and is more preferably 50 to 3000 seconds.

The method for applying the coating material for the coating layer is not particularly limited, and various known wet application methods can be used.
For example, application can be carried out using an on-machine size press device of a paper machine, a transfer roll coater (such as a shim sizer or gate roll coater), a spray device, etc. Off-machine application can be carried out using a common coating device, such as a blade coater, air knife coater, roll coater, reverse roll coater, shim sizer, gate roll coater, bar coater, curtain coater, slot die coater, gravure coater, champlex coater, brush coater, two-roll coater, bill blade coater, short dwell coater, etc. Application can also be carried out using a printing machine such as a gravure printing machine or a flexographic printing machine.

The device for drying the applied coating layer paint may be a cylinder dryer that comes into contact with the coating surface, but from the viewpoint of preventing contamination of the device, an air dryer, an infrared heater, or the like that does not come into contact with the coating surface is preferred. Considering operability and productivity, the application and drying of the coating layer paint are preferably carried out on-machine.
The type of paper machine used to make the substrate is not particularly limited, and examples include a Fourdrinier paper machine, a short wire paper machine, a cylinder paper machine, an inclined paper machine, etc. An on-machine type paper machine equipped with a coating device and a dryer is preferred.

Drying conditions after applying the coating layer paint include, for example, 60 to 160°C and 20 seconds to 5 minutes.

(Action and effect)
The packaging material is self-adhesive or adheres to other materials by heat sealing to encase the contents.
The adhesive strength of the heat-sealed portion can be measured by heat-sealing a test piece by applying heat and pressure so that the coating layers of the packaging material are in contact with each other, cutting the heat-sealed piece to a width of 15 mm, and peeling it at a peel rate of 300 mm/min using a tensile tester by the 180-degree peel method in accordance with JIS P 8113: 2006. Alternatively, the adhesive strength can be measured in the same way between the packaging material and other materials.
The peel strength is preferably 0.5 N/15 mm or more, more preferably 1.0 N/15 mm or more, even more preferably 2.0 N/15 mm or more, and most preferably 5.0 N/15 mm or more.

Furthermore, the packaging material can also exhibit oil resistance. Oil resistance can be evaluated by dropping a kit solution of each grade prepared in accordance with TAPPI UM-557 onto the coating surface of the coating layer and determining whether or not a stain appears after 15 seconds. Oil resistance (kit) of grade 2 or higher is preferred, more preferably grade 5 or higher, even more preferably grade 8 or higher, and most preferably grade 10 or higher.

The present invention will be explained in more detail below using examples. However, the present invention is not limited to these examples in any way. Unless otherwise specified, % means % by mass and parts means parts by mass. The measurement and evaluation methods used in each example are shown below.

[Oken air permeability measurement]
The Oken air permeability of the substrate and packaging material was measured in accordance with JIS P 8117: 2009. The air permeability of the substrate was measured with the surface to be provided with the coating layer facing up, and the air permeability of the packaging material was measured with the surface to be provided with the coating layer facing up.

[Peel test]
The packaging materials were stacked so that the coated surfaces were in contact with each other, and then heat-pressed using a heat press tester under heat-pressing conditions of 150° C., 0.2 MPa, and 1.0 second to produce a heat-pressed product.
The thermocompression-bonded product prepared by the above method was cut into a width of 15 mm to prepare a sample for measuring peel strength. The peel strength (N/15 mm) of the obtained sample for measuring peel strength was measured in accordance with JIS P 8113:2006 using a tensile tester (model: Tensilon RTC-1250A, manufactured by Orientec Co., Ltd.) by chucking the edges of the composite film and heat seal sheet of the sample and peeling them at a peel rate of 300 mm/min using the 180-degree peel method. The higher the peel strength, the better the thermal adhesiveness.

[Oil resistance of coating layer surface]
Each grade of kit solution prepared in accordance with TAPPI UM-557 was dropped onto the coating surface of the packaging material, and the coating was evaluated based on whether stains occurred after 15 seconds.

Example 1
(Production of substrate)
Hardwood bleached kraft pulp (LBKP) was beaten in a DDR to a Canadian standard freeness (freeness) of 320 mL as described in JIS P 8121-2: 2012 to obtain a pulp slurry. The pulp slurry was internally added with the following chemicals, based on the pulp mass: 1.0% aluminum sulfate on an oven-dry basis, 0.05% alkenyl succinic anhydride sizing agent (Fibran 81K, manufactured by Arakawa Chemical Industries Co., Ltd.) previously dispersed with cationized starch (Pillar 3YK, manufactured by Pillar Starch Co., Ltd.), 0.7% amphoteric polyacrylamide resin paper strength enhancer (PAM) (trade name: Polystron OFT-3, manufactured by Arakawa Chemical Industries Co., Ltd., mass average molecular weight 3,000,000), and 0.4% epichlorine resin wet strength enhancer, to obtain a papermaking raw material. The papermaking raw material was made into paper on a Fourdrinier paper machine, dried in a cylinder dryer, and then coated with 40 g/m2 of a 6.0% by mass solution of a 95:5 solids mixture of hydrophobized starch (product name: GRS- ^T110 , manufactured by Oji Cornstarch Co., Ltd.) and a styrene-acrylic acid copolymer surface sizing agent (product name: Polymaron E-109, manufactured by Arakawa Chemical Industries Co., Ltd.) in a solids ratio of 6.0% by mass. The coated paper was then dried in a cylinder dryer to obtain a substrate. The resulting substrate had a basis weight of 120 g/ ^m2 , a density of 0.74 g/ ^cm3 , an Oken air permeability of 23 seconds, an Oken smoothness of 16 seconds for the felt side (the side on which the coating layer was formed) and 11 seconds for the wire side, and a Stockigt sizing degree of 117 seconds.

(Dissolution of casein)
550 parts by mass of water was heated, and when the temperature reached 45°C, 30 parts by mass of 25% by mass ammonia was added. After further heating to 50°C, 125 parts by mass of casein was added and stirred to dissolve the casein. After dissolution, the casein was diluted with adjusted water to obtain a 10% by mass casein solution.
(Preparation of coating material for coating layer)
A coating layer paint with a solids concentration of 10% by mass was obtained by mixing and stirring 400 parts by mass of water, 500 parts by mass of the 10% by mass casein obtained by dissolving the casein described above, and 100 parts by mass of a 50% by mass reinforced rosin emulsion (product name: Sizepine N-775, manufactured by Arakawa Chemical Industries, Ltd.). The viscosity of the resulting coating layer paint at 10% by mass was 90 mPa s as measured with a Brookfield viscometer.

(Manufacturing of packaging materials)
The coating material for the coating layer was applied to the F side of the substrate obtained above using a bar coater, and then dried in a blower dryer at 110°C for 2 minutes to form a thermal adhesive layer. Here, the coating material for the thermal adhesive layer was applied so that the coating amount after drying was 3.3 g/ ^m2 . This resulted in a packaging material.

Example 2
A packaging material was obtained in the same manner as in Example 1, except that in preparing the coating layer paint of Example 1, 40 parts by weight of water, 950 parts by weight of 10% by weight casein, and 10 parts by weight of 50% by weight reinforced rosin emulsion (product name: Sizepine N-775, manufactured by Arakawa Chemical Industries, Ltd.) were mixed and stirred to use a coating layer paint with a solids concentration of 10% by weight. The viscosity of the resulting coating layer paint at 10% by weight was 1245 mPa s as measured by a Brookfield viscometer. A weak streak pattern was observed on the coated surface.

Example 3
A packaging material was obtained in the same manner as in Example 1, except that a coating layer paint with a solids concentration of 10% by mass was used by mixing and stirring 640 parts by mass of water, 200 parts by mass of 10% by mass casein, and 160 parts by mass of 50% by mass reinforced rosin emulsion (product name: Sizepine N-775, manufactured by Arakawa Chemical Industries, Ltd.) in preparation of the coating layer paint of Example 1. The viscosity of the resulting coating layer paint at 10% by mass measured with a Brookfield viscometer was 10 mPa s.

Example 4
(Dissolution of sodium caseinate)
150 parts by mass of sodium caseinate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was dispersed in 850 parts by mass of water, heated to 90°C with stirring, and then maintained at 90°C for 30 minutes. The mixture was then cooled and diluted with adjusted water to obtain a 10% by mass sodium caseinate solution.

(Manufacturing of packaging materials)
A packaging material was obtained in the same manner as in Example 1, except that a coating layer paint with a solids concentration of 14% by mass was used by mixing and stirring 160 parts by mass of water, 700 parts by mass of 10% by mass sodium caseinate obtained by dissolving the sodium caseinate described above, and 140 parts by mass of 50% by mass reinforced rosin emulsion (product name: Sizepine N-775, manufactured by Arakawa Chemical Industries, Ltd.) was used. The viscosity of the resulting coating layer paint at 14% by mass was 70 mPa s as measured by a Brookfield viscometer.

Example 5
A packaging material was obtained in the same manner as in Example 1, except that a coating layer paint with a solids concentration of 10% by mass was used by mixing and stirring 720 parts by mass of water, 100 parts by mass of 10% by mass casein, and 180 parts by mass of 50% by mass reinforced rosin emulsion (product name: Sizepine N-775, manufactured by Arakawa Chemical Industries, Ltd.) in preparation of the coating layer paint of Example 1. The viscosity of the resulting coating layer paint at 10% by mass measured with a B-type viscometer was 7 mPa s.

Example 6
A packaging material was obtained in the same manner as in Example 1, except that the amount of alkenyl succinic anhydride sizing agent (Fibran 81K, manufactured by Arakawa Chemical Industries, Ltd.) previously dispersed with cationic starch (Pillar 3YK, manufactured by Pillar Starch Co., Ltd.) used was 0.03% in the production of the substrate of Example 1. The basis weight of the substrate obtained above was 120 g/m ² , the density was 0.74 g/cm ³ , the Oken air permeability was 23 seconds, the Oken smoothness was 16 seconds for the felt side and 11 seconds for the wire side, and the Stockigt sizing degree was 52 seconds.

Example 7
A packaging material was obtained in the same manner as in Example 1, except that coating using a size press device was not performed in the production of the substrate of Example 1. The basis weight of the substrate obtained above was 117.6 g/m ² , the density was 0.74 g/cm ³ , the Oken air permeability was 23 seconds, the Oken smoothness was 16 seconds for the felt side and 11 seconds for the wire side, and the Stockigt sizing degree was 25 seconds.

Example 8
A packaging material was obtained in the same manner as in Example 1, except that in the production of the substrate of Example 1, an alkyl ketene dimer sizing agent (trade name: Sizepine K-287, manufactured by Arakawa Chemical Industries, Ltd.) was used at 0.5% instead of an alkenyl succinic anhydride sizing agent (Fibran 81K, manufactured by Arakawa Chemical Industries, Ltd.) previously dispersed with cationized starch (Pillar 3YK, manufactured by Pillar Starch Co., Ltd.). The basis weight of the substrate obtained above was 120 g/m ² , density was 0.74 g/cm ³ , Oken air permeability was 23 seconds, Oken smoothness was 16 seconds for the felt side and 11 seconds for the wire side, and Stockigt sizing degree was 110 seconds.

Example 9
A packaging material was obtained in the same manner as in Example 1, except that in the production of the substrate of Example 1, a rosin sizing agent (trade name: Sizepine N111-50, manufactured by Arakawa Chemical Industries Co., Ltd.) was used at 0.9% instead of the alkenyl succinic anhydride sizing agent (Fibran 81K, manufactured by Arakawa Chemical Industries Co., Ltd.) previously dispersed with cationized starch (Pillar 3YK, manufactured by Pillar Starch Co., Ltd.). The basis weight of the substrate obtained above was 120 g/m ² , density was 0.74 g/cm ³ , Oken air permeability was 23 seconds, Oken smoothness was 16 seconds for the felt side and 11 seconds for the wire side, and Stockigt sizing degree was 125 seconds.

< Reference example 10>
A packaging material was prepared in the same manner as in Example 1, except that the coating layer paint for Example 1 was prepared by mixing and stirring 400 parts by weight of water, 500 parts by weight of 10% by weight casein, and 100 parts by weight of a 50% by weight rosin resin emulsion (Super Ester NS-100H, manufactured by Arakawa Chemical Industries, Ltd.) for use as a tackifier in a rosin compound. This resulted in a coating layer paint with a solids concentration of 10% by weight. The viscosity of the resulting coating layer paint at 10% by weight was 45 mPa s as measured by a Brookfield viscometer. The cypress odor of the coating layer paint was also milder than that of the coating layer paints used in Examples 1 to 9.

Example 11
A packaging material was obtained in the same manner as in Example 1, except that a 20 μm thick biodegradable polylactic acid film (Palgreen BO, manufactured by Mitsui Chemicals Tocello Co., Ltd.) was used instead of the substrate of Example 1.

<Comparative Example 1>
A packaging material was obtained in the same manner as in Example 1, except that only a 10% by mass aqueous casein solution was used as the coating layer paint in Example 1. The viscosity of the resulting coating layer paint at 10% by mass measured with a Brookfield viscometer was 1750 mPa s. Coating with a bar coater produced streak-like defects.

<Comparative Example 2>
A packaging material was obtained in the same manner as in Example 1, except that a coating layer paint with a solids concentration of 10% by mass was used by mixing and stirring 800 parts by mass of water and 200 parts by mass of a 50% by mass reinforced rosin emulsion (product name: Sizepine N-775, manufactured by Arakawa Chemical Industries, Ltd.) in preparation of the coating layer paint of Example 1. The viscosity of the resulting coating layer paint at 10% by mass, measured with a Brookfield viscometer, was 5 mPa s.

<Evaluation>
The following evaluations were carried out on each of the packaging materials of Examples 1 to 9, Reference Example 10 , and Comparative Examples 1 and 2. The configuration of each packaging material is shown in Table 1, and the results of the evaluation of the heat seal properties and oil resistance properties of the packaging materials are shown in Table 2.

As shown in the above results, the packaging materials of Examples 1 to 11 had a heat seal strength of 1.20 N/15 mm or more in the peel test. On the other hand, the packaging material of Comparative Example 1 had a weak heat seal strength of 0.96 N/15 mm due to a streak-like coating defect in the coating layer. The heat seal strength of Comparative Example 2 was 0.25 N/15 mm, which may cause problems in use, such as accidental opening.
Regarding oil resistance, the packaging materials of Examples 1 to 9 have a kit value of grade 2 or higher and are considered to have no problems in use. Comparative Examples 1 and 2 have poor oil resistance.

Furthermore, the packaging material in Example 4, in which sodium caseinate was added to the coating layer, maintained a coating concentration of 100 mPa s or less even when prepared with a coating concentration 4% higher than that of the other packaging materials. This is preferable because it reduces the drying load after coating and improves production efficiency.
Furthermore, the packaging material using the rosin emulsion for tackifier as the rosin compound of Example 10 is preferable because the paint viscosity is lower than that of reinforced rosin, and the cypress odor of the coating layer paint as determined by sensory evaluation is reduced compared to other packaging materials.

The packaging material of the present invention has sufficient heat sealing properties and oil resistance, and is an excellent packaging material that has a low environmental impact as it is primarily made from non-petrochemical materials.

Claims (6)

A packaging material having a coating layer on at least one surface of a substrate, the coating layer containing casein and/or a salt thereof, the coating layer further containing a rosin compound, the coating layer being a heat seal layer, and the rosin compound being a reinforced rosin . The packaging material according to claim 1, wherein the content ratio of the casein and/or its salt to the rosin compound in the coating layer is 20:80 to 95:5. The packaging material according to claim 1 or 2, wherein the substrate contains one or more materials selected from wood pulp, non-wood pulp, and regenerated cellulose. The packaging material according to any one of claims 1 to 3, wherein the substrate contains 0.01 to 2.0 g/ ^m2 of a styrene-(meth)acrylic acid copolymer compound and/or a styrene-maleic anhydride copolymer compound. The packaging material according to any one of claims 1 to 4, wherein the substrate has a Stockigt sizing degree of 20 seconds or more as measured in accordance with JIS P 8122:2004. A package in which at least a portion of the coating layer surface of the packaging material according to any one of claims 1 to 5 is heat-bonded.