JP7580002B1 - Coated Paper - Google Patents

Abstract

The present invention provides a coated paper that has excellent abrasion resistance when water is attached (hereinafter, also referred to as wet rub resistance).
The present invention relates to a paper substrate and a coating layer containing PHBH and EVA on at least one of the outermost surfaces of the paper substrate.
The coating layer contains 1 part by mass or more and 250 parts by mass or less of the EVA per 100 parts by mass of the PHBH,
The coated paper has an EVA having a glass transition temperature (Tg) of -50°C or higher and 30°C or lower.
[Selection diagram] None

Description

The present invention relates to a coated paper having a coating layer containing PHBH.

In recent years, efforts have begun to prevent environmental destruction caused by plastic waste, and there is a demand to replace disposable plastic products with materials that have a smaller impact on the environment. Alternative materials to plastic include biodegradable plastics, wood, paper, etc.
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 decompose slowly in natural environments such as the ocean.

Poly(3-hydroxybutyrate) resins are microbially produced thermoplastics that are highly degradable under both aerobic and anaerobic conditions, and have the remarkable ability to be decomposed by microorganisms in a short period of time even in water, such as the ocean. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter also referred to as PHBH), a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate, has attracted attention for its biodegradability, resin properties, etc.

Patent Document 1 proposes a coated paper with few coating defects, which has a coating layer containing PHBH and an adhesive on at least one side of a paper substrate, and in which the solid mass ratio of PHBH to adhesive in the coating layer is 99.9/0.1 to 60.0/40.0, and describes that the paper can be used as heat seal paper, waterproof paper, oil-resistant paper, etc.

International Publication No. 2021/256381

The coated paper described in Patent Document 1 has excellent water resistance, as shown in the example of coated paper containing PVA as an adhesive and having a Cobb water absorbency (120 seconds) of 5 g/m2 or ^less . However, although this coating layer is resistant to water penetration and has excellent water resistance, it has been found that the surface of the coating layer may be scraped off when it is rubbed against the contents in a wet state. Specifically, when a package formed from the coated paper described in Patent Document 1 containing food is purchased as a product at a supermarket or the like and stored in a refrigerator or freezer at home or work, condensation occurs inside the package due to the cold air inside the refrigerator, and then when the food comes into contact with the wet coating layer due to vibration or impact caused by putting food in and taking it out of the refrigerator, the surface of the coating layer is scraped off. Alternatively, if a package made of the above-mentioned coated paper purchased at a different store is placed next to a plastic carrier bag containing frozen foods or other products previously purchased at the same store, the package will be cooled by contact with the frozen food or by the cold air emitted from the frozen food, causing condensation to form inside, and the surface of the coating layer will then be scraped off by vibrations such as walking when traveling to one's home or workplace.For this reason, the coated paper described in Patent Document 1 was unsuitable for use as a package for, for example, fruits and vegetables that evaporate water, foods that contain a lot of moisture, or goods that are transported at low temperatures and are prone to condensation.
The present invention has been developed against this background, and an object of the present invention is to provide a coated paper that has excellent abrasion resistance when water is attached (hereinafter also referred to as wet rub resistance).

The means for solving the problems of the present invention are as follows.
1. A paper substrate and a coating layer containing PHBH and EVA on at least one outermost surface thereof,
The coating layer contains 1 part by mass or more and 250 parts by mass or less of the EVA per 100 parts by mass of the PHBH,
The coated paper is characterized in that the EVA has a glass transition temperature (Tg) of -50°C or higher and 30°C or lower.
2. The coated paper according to 1., characterized in that the molar ratio of ethylene to vinyl acetate in the EVA (ethylene:vinyl acetate, total 100) is 1:99 to 60:40.
3. The coated paper according to 1. or 2, characterized in that the coating layer contains an inorganic pigment.
4. A packaging body having the coated paper according to any one of 1. to 3.

The coated paper of the present invention has excellent wet-rub properties, and the coating layer is not easily peeled off even when rubbed with moisture attached. The coated paper of the present invention also has excellent heat-sealing properties, and therefore the coated paper of the present invention is suitable for use in packaging foods and the like that contain a lot of moisture.
The coated paper of the present invention has excellent wet-rub properties even when the coating layer contains an inorganic pigment, and can also be imparted with functionality such as barrier properties derived from the inorganic pigment.
The coated paper of the present invention contains a high proportion of biodegradable materials and will decompose quickly even if it is released into the environment.

The coated paper of the present invention has a paper base material and a coating layer containing PHBH and EVA on at least one outermost surface,
The coating layer contains 1 part by mass or more and 250 parts by mass or less of EVA per 100 parts by mass of PHBH,
The glass transition temperature (Tg) of EVA is -50 to 30°C.
In this specification, the expression "A to B" (A and B are numerical values or ratios) means a numerical range including A and B.

The coated paper of the present invention may have a coating layer on one of the outermost surfaces, or may have coating layers on both outermost surfaces. In addition, other layers such as an anchor layer, a water vapor barrier layer, a gas barrier layer, and an ink receiving layer may be present between the paper substrate and the coating layer.

(Paper base material)
The paper base material is a sheet mainly made of pulp, and is obtained by papermaking a paper stock containing fillers, various auxiliaries, 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 waste paper pulp, and non-wood fibers obtained from kenaf, bamboo, hemp, etc., and one or more of these can be used in appropriate combination. Among these, it is preferable to use chemical pulp of wood fiber or mechanical pulp of wood fiber, and it is more preferable to use chemical pulp of wood fiber, for reasons such as the fact that foreign matter is unlikely to be mixed into the paper base material, that discoloration with time is unlikely to occur when recycled as a waste paper raw material, that the surface texture during printing is good due to the high whiteness, and that the value of use is particularly high when used as a packaging material. Specifically, the blending amount of chemical pulp of wood fibers such as LBKP and NBKP relative to the total pulp is preferably 80 mass% or more, more preferably 90 mass% or more, even more preferably 95 mass% or more, and most preferably 100 mass%.

Fillers that can be used include known fillers such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate, and organic fillers such as urea-formaldehyde resin, polystyrene resin, phenolic resin, and microhollow particles. Note that fillers are not essential materials and may not be used.

Examples of various auxiliary agents include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationic starch, various modified starches, dry strength agents such as urea-formaldehyde resin and melamine-formaldehyde resin, wet strength agents, retention agents, drainage improvers, coagulants, aluminum sulfate, bulking agents, dyes, fluorescent whitening agents, pH adjusters, defoamers, UV inhibitors, anti-fading agents, pitch control agents, slime control agents, etc., and can be selected and used as needed.

The surface of the paper substrate may be treated with various chemicals. Examples of chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water retention agents, thickeners, and lubricants, and these may be used alone or in combination of two or more. Furthermore, these various chemicals may 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, and organic pigments such as solid, hollow, and core-shell types, and these may be used alone or in combination of two or more.

The basis weight of the paper base material can be appropriately selected depending on the desired qualities and its applications, but is usually preferably 20 g/m ² or more and 600 g/m ² or less, more preferably 25 g/m ² or more and 600 g/m ² or less. When used as packaging materials such as wrapping paper, paper bags, lid materials, lining paper, liquid paper containers such as milk cartons, and posters used outdoors, the basis weight of the paper base material is preferably 20 g/m ² or more and 350 g/m ² or less. When used as a soft packaging material, the basis weight of the paper base material is preferably 20 g/m ² or more and 100 g/m ² or less, more preferably 20 g/m ² or more and 80 g/m ² or less. The soft packaging material is a packaging material that is highly flexible, using thin paper of about 20 g/m ² to 100 g/m ² among packaging materials. When used for paper cups, paper containers, paper boxes, paper plates, paper trays, etc., the basis weight of the paper base material is preferably 150 g/m ² or more and 300 g/m ² or less.
The density of the paper base material can be appropriately selected depending on the desired qualities, ease of handling, etc., but is usually preferably 0.5 g/cm ³ or more and 1.0 g/cm ³ or less.
In the present invention, the paper base material may be either a paper consisting of only a single paper layer or a multi-layer paper having two or more paper layers. When the paper base material is a multi-layer paper, the paper materials, basis weights, etc. of each paper layer may be the same or different.

The method for producing (making) the paper base material is not particularly limited, and any known production (making) method or papermaking machine can be selected, such as a Fourdrinier papermaking machine, a cylinder papermaking machine, a short wire papermaking machine, or a twin-wire papermaking machine such as a gap former type or a hybrid former type (on-top former type). The pH during papermaking may be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking), and after papermaking in the acidic range, an alkaline agent may be applied to the surface of the paper layer.
Furthermore, when treating the surface of a paper substrate with a chemical, the method of surface treatment is not particularly limited, and known coating devices such as a rod metering size press, a pond type size press, a gate roll coater, a spray coater, a blade coater, or a curtain coater can be used.

(Coating layer)
The coating layer is located on at least one outermost surface of the coated paper and contains at least PHBH and EVA, with the amount of EVA being 1 part by mass or more and 250 parts by mass or less per 100 parts by mass of PHBH.

<PHBH>
PHBH is a copolymer of 3-hydroxybutyrate (hereinafter also referred to as 3HB) and 3-hydroxyhexanoate (hereinafter also referred to as 3HH), and is a biodegradable resin known to be produced by microorganisms. In the present invention, the PHBH used may be derived from microorganisms or from petroleum resources, but it is preferable to use the PHBH derived from microorganisms in terms of reducing the environmental load.

Microorganisms that produce PHBH are not particularly limited as long as they accumulate PHBH intracellularly, and examples thereof include bacteria of the genus Alcaligenes, such as A. lipolytica, A. eutrophus, and A. latus, as well as bacteria of the genus Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. Among them, in terms of productivity of PHBH, strains such as Aeromonas caviae, and Alcaligenes eutrophus AC32 into which genes of PHA synthase group have been introduced (Accession No. FERM BP-6038, Date of deposit on August 7, 1997, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, Address: Central 6, 1-1-1 Higashi, Tsukuba-shi, Ibaraki-ken, Japan) (J. Bacteriol., 179, pp. 4821-4830 (1997)) are particularly preferred. A method for obtaining PHBH from Aeromonas caviae, a microorganism of the Aeromonas genus, is disclosed, for example, in Japanese Patent Application Laid-Open No. 05-093049. These microorganisms are used by culturing them under appropriate conditions to accumulate PHBH in the cells.
The carbon source and culture conditions used in the culture can be obtained according to the methods described in JP-A-05-093049, JP-A-2001-340078, etc., but are not limited thereto.

The composition ratio (mol%) of PHBH is preferably 3HB:3HH=97:3 to 75:25, more preferably 95:5 to 85:15. If the composition of 3HH is less than 3 mol%, the characteristics of PHBH become close to those of 3HB homopolymer, resulting in loss of flexibility and an undesirable tendency for the film-forming processing temperature to become too high. If the composition of 3HH exceeds 25 mol%, the crystallization rate becomes too slow to be suitable for film-forming processing, and the degree of crystallization decreases, making the resin flexible and tending to decrease the bending modulus. The composition ratio of PHBH can be measured by NMR analysis of the powder obtained by centrifuging the aqueous dispersion and then drying it.
Microbial PHBH is a random copolymer. To adjust the molar ratio of the copolymer, there are methods such as selecting the bacterial cells, selecting the carbon source as the raw material, blending with PHBH of different molar ratios, and blending with 3HB homopolymer.

The mass average molecular weight of PHBH is preferably 50,000 to 1,500,000. If the mass average molecular weight of PHBH is within this range, a film can be formed at a low temperature when PHBH is applied, and a film with excellent mechanical properties can be obtained when PHBH is laminated. The mass average molecular weight of PHBH is more preferably 100,000 to 500,000, and even more preferably 150,000 to 450,000. The mass average molecular weight of PHBH can be determined by gel permeation chromatography (GPC, such as "Shodex GPC-101" manufactured by Showa Denko K.K.) using a polystyrene gel (such as "Shodex K-804" manufactured by Showa Denko K.K.) in a column, chloroform as the mobile phase, and the molecular weight converted into polystyrene. The measurement sample is a powder obtained by centrifuging an aqueous dispersion containing PHBH and then drying it.

The average particle size of PHBH is preferably 0.1 to 50 μm. PHBH with an average particle size of less than 0.1 μm is difficult to produce by microbial production, and even when obtained by chemical synthesis, a step of microparticulation is required. If the average particle size exceeds 50 μm, uneven coating may occur on the surface when a coating liquid containing PHBH is applied. It is more preferable that the average particle size of PHBH is 0.5 to 10 μm. The average particle size of PHBH refers to the particle size corresponding to 50% accumulation of all particles measured by adjusting an aqueous suspension of PHBH to a specified concentration using a general-purpose particle sizer such as a Microtrack particle sizer (manufactured by Nikkiso, FRA).

<EVA>
EVA (ethylene vinyl acetate copolymer) is a copolymer having ethylene and vinyl acetate as monomers, and may further have other monomers as monomers. However, the EVA of the present invention is not saponified and does not have vinyl alcohol units generated by saponification of vinyl acetate units. When EVA has other monomers as monomers, the content of the structural units derived from other monomers relative to the entire EVA is preferably 30% by mass or less. This content is not particularly limited as long as it does not impair the effects of the present invention, and can be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, etc.

From the viewpoint of heat seal strength, the glass transition temperature of EVA is preferably −50 to 30° C. This glass transition temperature is more preferably −40° C. or higher, even more preferably −35° C. or higher, and more preferably 20° C. or lower, even more preferably 10° C. or lower. In this specification, the glass transition temperature means the midpoint glass transition temperature measured in accordance with JIS K 7121-1987.
The molar ratio of ethylene to vinyl acetate in EVA (structural units derived from ethylene:structural units derived from vinyl acetate, also expressed as ethylene:vinyl acetate, the total being 100) is preferably 1:99 to 60:40 from the viewpoint of heat seal strength, more preferably 3:97 to 50:50, and even more preferably 5:95 to 45:55.

The coating layer contains 1 to 250 parts by mass of EVA per 100 parts by mass of PHBH. By containing PHBH and EVA in this ratio, the coating layer has excellent wet-rub properties. The ratio of EVA per 100 parts by mass of PHBH is preferably 6 parts by mass or more, more preferably 11 parts by mass or more, and even more preferably 16 parts by mass or more. There is no particular upper limit to the EVA ratio, but it can be, for example, 230 parts by mass or less, 210 parts by mass or less, 190 parts by mass or less, etc.

The coating layer only needs to contain PHBH and EVA, and may also contain other thermoplastic resins and inorganic pigments.
<Other thermoplastic resins>
As the other thermoplastic resin, any resin having heat sealability at the temperature at which PHBH is fused can be used without any particular limitation, but it is preferable to use biodegradable resins such as aliphatic polyester-based resins such as polycaprolactone, polybutylene succinate adipate, polybutylene succinate, and polylactic acid, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate and polybutylene azelate terephthalate.

When the coating layer contains other thermoplastic resins, the total proportion of PHBH and EVA to the total thermoplastic resins contained in the coating layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

<Inorganic pigments>
As the inorganic pigment, those used for coating on paper can be used without any particular limitation, and examples thereof include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, bentonite, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, satin white, etc., and one or more of these can be used. Among these, one or more of kaolin, heavy calcium carbonate, light calcium carbonate, mica, talc, and bentonite are preferred.

From the viewpoint of the fixation of the coating layer, the inorganic pigment preferably has a volume 50% average particle size (D50, hereinafter also referred to as "average particle size") of 6.0 μm or less, measured by the laser diffraction/scattering method. Examples of measuring devices for the laser diffraction/scattering method include the particle size distribution measuring device "Partica" by Horiba, Ltd. and the particle size distribution measuring device "MASTER SIZER S" by Malvern Corporation. From the viewpoint of the fixation of the coating layer, the average particle size of the inorganic pigment is more preferably 5.0 μm or less, even more preferably 4.0 μm or less, even more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. There is no particular lower limit for the average particle size of the inorganic pigment, but from the viewpoint of dispersibility, etc., it is preferably 0.1 μm or more, and more preferably 0.2 μm or more. When two or more inorganic pigments are included, it is preferable that the average particle size of at least one of the inorganic pigments is within the above-mentioned numerical range, and the proportion of the inorganic pigments that satisfy this average particle size relative to the total inorganic pigments is preferably 50% by mass or more, and more preferably 70% by mass or more.

When the coating layer contains an inorganic pigment, the solid mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment, total 100) is preferably 90:10 to 0.01:99.99. By further blending an inorganic pigment into a coating liquid containing PHBH and EVA, the fixation of the resulting coating layer is improved. Although the mechanism is unclear, the present inventors speculate that this is because inorganic pigments have better thermal conductivity than organic PHBH and adhesives, so that the inorganic pigments quickly rise in temperature when heated, and this heat is transferred from the inorganic pigment to the PHBH, so that the PHBH is sufficiently heated and melted, making it easy to form a film.
The solid content mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment, total 100) is more preferably from 70:30 to 1:99, even more preferably from 60:40 to 2:98, and even more preferably from 50:50 to 3:97, from the viewpoint of the fixing property of the coating layer.

The coating layer may contain other water-soluble resins and water-dispersible resins in addition to PHBH, EVA, other thermoplastic resins, and inorganic pigments, and may further contain various auxiliaries that are blended into coating solutions in the papermaking industry, such as dispersants, viscosity modifiers, defoamers, water-resistant agents, pH adjusters, cationic resins, anionic resins, UV absorbers, metal salts, lubricants, coloring dyes, and pigments, as necessary.

(Production method)
The coating layer can be produced by a conventionally known coating method. For example, the coating device may be a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, a curtain coater, a spray coater, a size press coater, a gate roll coater, etc. In addition, the coating system may be an aqueous coating using a solvent such as water, a solvent coating using a solvent such as an organic solvent, etc., and the aqueous coating is preferable.

The coating amount of the coating layer is preferably 1 g/ ^m2 or more and 50 g/ ^m2 or less in terms of dry mass. If the coating amount is less than 1 g/ ^m2 , it may be difficult to form a uniform coating film. On the other hand, if it is more than 50 g/ ^m2 , the drying load during coating increases. The coating amount of the coating layer is more preferably 3 g/m2 or ^more , even more preferably 5 g/m2 or ^more , more preferably 40 g/m2 or ^less , and even more preferably 30 g/m2 or ^less .

The coated paper of the present invention has excellent wet-love properties and is easy to heat seal, making it suitable for use as packaging material, and can also be used for refrigeration and freezing of foods that contain a lot of moisture or for which condensation is likely to occur.
When the coated paper of the present invention is used for a package, the shape of the package is not particularly limited. When it is a flexible package, it can be a vertical pillow package bag, a horizontal pillow package bag, a side seal bag, a two-sided seal bag, a three-sided seal bag, a four-sided seal bag, a gusset bag, a bottom gusset bag, a stand-up bag, a blister package (blister pack), etc. When it is a package consisting of multiple cylindrical or cup-shaped members, it can be used for one or more of the members constituting the package, such as a body member, a bottom plate member, and a lid member.

The coated paper of the present invention has a heat seal strength, measured in accordance with JIS Z1707:2019 7.4 "Heat seal strength test", when heat sealed at a pressing temperature of 160°C, a pressing pressure of 0.2 MPa (20.0 N/cm ² ), and a pressing time of 1.0 second and T-peeled off, of preferably 4.0 N/15 mm or more, more preferably 5.0 N/15 mm or more, even more preferably 6.0 N/15 mm or more, and even more preferably 6.5/15 mm or more.
Furthermore, the heat seal strength of the coated paper of the present invention, measured in the same manner except that the pressing temperature is 180°C, is preferably 4.0 N/15 mm or more, more preferably 5.0 N/15 mm or more, even more preferably 6.0 N/15 mm or more, and even more preferably 6.5/15 mm or more.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and % in the examples indicate parts by mass and % by mass, respectively.

(Evaluation Method)
Wet Rub: The prepared coated paper was placed on a horizontal table and conditioned for at least 24 hours (conditions: 23°C, humidity 50%), after which a cross pattern was drawn on the coated surface of the coated paper with a new oil-based marker (ZEBRA Makie Extra Fine) that had been opened just before the test, and allowed to dry for 5 minutes. The pattern was then lightly traced back and forth 50 times with a wet finger, and the remaining state of the pattern and the peeling state of the coating layer were evaluated according to the following criteria. If the evaluation was 5 or 4, there was no problem in practical use.
5: No change 4: White spots occur in less than 10% 3: White spots occur in 10% to less than 50% 2: White spots occur in 20% to less than 50% + coating layer dissolution 1: White spots occur in 50% to 100% + coating layer dissolution <Judgment sample>

- Tape pick The prepared coated paper was placed on a horizontal table and conditioned for at least 24 hours (conditions: 23 ° C., humidity 50%), and then a 12 mm wide mending tape (3M Japan, Scotch (registered trademark) Mending Tape 810-1-12) was applied to the coating layer surface of the coated paper, and a rubber roller with a width of 130 mm and a weight of 1.8 kg was reciprocated 20 times under its own weight on the mending tape to adhere the mending tape to the coating layer surface. Immediately after, the mending tape was vigorously peeled off, and the ratio of the area where the coating layer was peeled off from the paper substrate surface by adhering to the mending tape (area of interface destruction) to the area where the mending tape was applied, or the ratio of the area where a part of the paper substrate was attached to the mending tape together with the coating layer and the paper substrate was destroyed (area of internal destruction of the paper substrate) was calculated, and the adhesion to the paper substrate was evaluated according to the following criteria. If the evaluation is 5 or 4, there is no problem in practical use.
5: No peeling 4: Peeling occurred on 0 to less than 10% of the applied surface 3: Peeling occurred on 10 to less than 50% of the applied surface 2: Peeling occurred on 50 to less than 90% of the applied surface 1: Peeling occurred on 90 to 100% of the applied surface

- Heat seal strength This was performed in accordance with JIS Z1707:2019 7.4 "Heat seal strength test". Two square test pieces with a side of 100 mm were cut out from the obtained coated paper, and the coating layers were brought into contact with each other and heat sealed at a pressure temperature of 160°C or 180°C, a pressure of 0.2 MPa (20.0 N/cm ² ), and a pressure time of 1.0 second. The test pieces were then left to stand for 24 hours at 23°C and a humidity of 50%, and a measurement sample was cut out from the heat-sealed 100 mm square test piece so that the long side was 100 mm and the short side was 15 mm.
Thereafter, the peeled long side end was clamped between the upper and lower jigs of a vertical tensile testing machine (Tensilon, manufactured by A&D Co., Ltd.), and the measurement sample was peeled (T-type) from the long side end side at a speed of 200 mm/min, while measuring the peel strength, i.e., HS strength (N/15 mm).
The peeled surface was visually observed and evaluated according to the following criteria.
The measurement was carried out twice, and the peel strength was shown as an average value. When the evaluation results differed based on visual observation, both the average values were shown.
◯: Breakage on the entire heat-sealed surface △: Breakage partially on the heat-sealed surface ×: Peeling occurs between the coating layers (no breakage)
-: Not heat sealed

(material)
Paper base material: Nippon Paper Industries Co., Ltd., cup base paper with a basis weight of 220 g/ ^m2 , CUP-HD
PHBH: Kaneka Corporation, mass average molecular weight 600,000 Inorganic pigment: Shiraishi Kogyo Co., Ltd., kaolin, KCS, average particle size 3.6 μm, aspect ratio 10 to 15

PVA1: Kuraray Co., Ltd., 28-98, fully saponified PVA
PVA2: Kuraray Co., Ltd., HR3010, Highly water-resistant partially saponified EVA: Kuraray Co., Ltd., RS-1713
EVA1: Sumika Chemtex Co., Ltd., S-400HQ, Tg 0°C, ethylene:vinyl acetate=20:80
EVA2: Sumika Chemtex Co., Ltd., S-305HQ, Tg 7°C, ethylene:vinyl acetate=10:90
EVA3: Sumika Chemtex Co., Ltd., S-410HQ, Tg-18°C, ethylene:vinyl acetate=30:70
EVA4: Sumika Chemtex Co., Ltd., S-408HQE, Tg-30°C, ethylene:vinyl acetate=40:60

(Formation of coating layer)
PHBH, EVA or PVA, and an inorganic pigment were mixed and stirred in the parts by mass shown in Table 1 to obtain a coating liquid with a solid content concentration of 40% by mass.
The coating liquid was applied onto one side of the paper substrate by the bar blade method so as to obtain the dry mass shown in Table 1, and then dried at 105°C for 1 minute. After that, heat treatment was performed at 140°C for 1 minute to form a coating layer on the outermost surface of one side of the paper substrate.

The wet rub rating of Comparative Example 1, which had a coating layer of only PHBH, was "3," and the wet rub ratings of Comparative Examples 2 and 3, which added general-purpose PVA or highly water-resistant PVA, were also "2," and the wet rub rating of Comparative Example 4, which further added a pigment, was "1," showing no improvement. Also, the wet rub rating of Comparative Example 5, which added partially saponified EVA to PHBH, was "2," showing no improvement.
However, surprisingly, the wet rub evaluation of Examples 1 to 3 in which unsaponified EVA was added was "5," confirming an improvement.
From Examples 4 to 8, it was confirmed that the ratio of EVA to 100 parts by mass of PHBH was effective in the range of 20 to 235 parts by mass, and from Examples 9 to 11, it was confirmed that unsaponified EVA with different Tg also had an effect of improving wet rub.
Although the mechanism of action for improving wet rub is unclear, it is believed that the random presence of CH ₃ COO- groups in the polymer at a ratio of 60 to 90% (ratio to all monomers) contributes to the wet rub evaluation.

Claims (4)

A paper substrate and a coating layer containing PHBH and EVA on at least one outermost surface thereof,
The coating layer contains 1 part by mass or more and 250 parts by mass or less of the EVA per 100 parts by mass of the PHBH,
The coated paper is characterized in that the EVA has a glass transition temperature (Tg) of -50°C or higher and 30°C or lower. 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 1:99 to 60:40. The coated paper according to claim 1, characterized in that the coating layer contains an inorganic pigment. A packaging body having the coated paper according to any one of claims 1 to 3.