JP7579944B1 - Laminate base paper and laminate paper - Google Patents

Abstract

The present invention provides a laminate base paper with excellent blocking resistance. The laminate base paper has a paper base material and, on at least one surface of the paper base material, an anchor layer which is a coating layer containing an ethylene-vinyl acetate copolymer resin and PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). [Selected Figure] Figure 1

Description

The present invention relates to laminate base paper and laminate paper.

Paper cups have traditionally been used as liquid containers. Paper cups are made up of a body and a bottom, and are manufactured by first heating both ends of the body paper with hot air in a cup-forming machine, wrapping it around a mandrel, overlapping one end of the body paper with the other, and forming the body joint using a heat sealing process to form a cylindrical body, and then punching out the bottom paper as it is wound up, to form the bottom member whose outer periphery stands downward (Patent Document 1).

Generally, the material used for paper cups is laminated paper, which is a base paper with a laminate layer attached by methods such as dry lamination and extrusion lamination. When a paper cup is manufactured using laminated paper with a laminate layer on one side of the base paper, the base paper of the inner laminate paper is heat-sealed in contact with the laminate layer of the outer laminate paper at the body bonding part, so that the bonding part has a layer structure in the thickness direction from the inside to the outside in the order of laminate layer/base paper layer/laminate layer/base paper layer (Figure 2A). Although this structure maintains a certain degree of adhesive strength, a method of providing an anchor layer made of a thermoplastic resin on the non-laminated side of the base paper can be considered as a method of further increasing the adhesive strength. By using this anchor layer, the order is laminate layer/base paper layer/anchor layer/laminate layer/base paper layer/anchor layer (Figure 2B), and the adhesive strength between the base paper layer and the laminate layer can be increased. Furthermore, in order to improve the adhesive strength of the body joint, it is also possible to consider providing an anchor layer between the laminate layer and the base paper layer in the laminate base paper (Figure 2 (c)).

When manufacturing laminated base paper in which an anchor layer is provided on such a base paper, it is first necessary to coat one surface of the base paper with the anchor layer, dry it, and wind it up as a roll, or subsequently provide a similar anchor layer on the other surface and wind it up. However, once the base paper with the anchor layer is wound up, the anchor layer on one surface of the laminated base paper may come into contact with the uncoated surface of the overlapping base paper or with the anchor layer on the other surface, resulting in blocking. In particular, when anchor layers are provided on both surfaces of the base paper, there is a high risk of blocking occurring, and a solution was desired.

JP 2015-214365 A

The objective of the present invention is to provide a laminate base paper with excellent blocking resistance.

The means for solving the problems of the present invention are as follows.
1. A laminate base paper characterized by having a paper substrate and, on at least one surface of the paper substrate, an anchor layer which is a coating layer containing an ethylene-vinyl acetate copolymer resin and PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)).
2. The laminate base paper according to 1., wherein the weight ratio of the ethylene-vinyl acetate copolymer resin to the PHBH is 30:70 to 70:30.
3. A laminated paper characterized by having a laminate layer on the anchor layer of the laminate base paper described in 1. or 2.

The laminate base paper of the present invention has excellent blocking resistance, and even if the laminate base paper is wound into a roll and stored in a high-temperature and high-humidity environment, blocking (sticking) is unlikely to occur, and problems caused by blocking can be prevented.

FIG. 2 is a schematic diagram showing the evaluation of blocking properties in the examples. Schematic diagram of a cross-section of the body of a paper cup made using laminated paper having a laminate layer on one side of the base paper (a); schematic diagram of a cross-section of the body of a paper cup made using laminated paper having a laminate layer on one side of the base paper and an anchor layer on the other side (b); schematic diagram of a cross-section of the body of a paper cup made using laminated paper having a laminate layer via an anchor layer on one side of the base paper and an anchor layer on the other side (c).

Laminate base paper
The laminate base paper of the present invention has a paper substrate and, on at least one surface of the paper substrate, an anchor layer which is a coating layer containing an ethylene-vinyl acetate copolymer resin and PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)).
In this specification, the expression "A to B" (A and B are numerical values) means a numerical range including A and B, that is, "A or more and B or less."

(Paper base material)
The paper base material is a sheet (hereinafter also referred to as "base paper") mainly made of pulp, and is obtained by papermaking a paper stock that further contains fillers, various auxiliaries, etc.
As the pulp, chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood pulp (NUKP), sulfite pulp, mechanical pulps such as stone grind pulp and thermomechanical pulp, wood fibers such as deinked pulp and waste paper pulp, non-wood fibers obtained from kenaf, bamboo, hemp, etc. can be used, and they can be appropriately mixed and used. 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, because foreign matter is unlikely to be mixed into the paper base material, discoloration is unlikely to occur over time when recycled as a waste paper raw material, the surface texture is good when printed because of high whiteness, and the value of use is high especially when used as a packaging material. Specifically, the blending ratio of chemical pulp such as LBKP or NBKP to the total pulp is preferably 80% or more, more preferably 90% or more, even more preferably 95% or more, and particularly preferably 100%.

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. These may be used alone or in combination of two or more. Furthermore, these 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 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 applications, but is usually preferably 20 g/m ² or more and 600 g/m ² or less, and more preferably 25 g/m ² or more and 600 g/m ² or less.
For example, when used as packaging materials such as wrapping paper, paper bags, lids, and underlays, the basis weight of the paper substrate is preferably 30 g/m ² or more and 150 g/m ² or less. When used as a soft packaging material, the basis weight of the paper substrate is preferably 20 g/m ² or more and 100 g/m ² or less, and more preferably 35 g/m ² or more and 80 g/m ² or less. Note that the soft packaging material is a packaging material that is highly flexible and uses thin paper, particularly about 20 g/m ² to 100 g/m ^2. When used as a paper cup, paper container, paper box, paper plate, paper tray, etc., the basis weight of the paper substrate 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.

The method of manufacturing (papermaking) the paper base material is not particularly limited, and known manufacturing (papermaking) methods and papermaking machines can be selected, such as a Fourdrinier papermaking machine, a cylinder papermaking machine, a short wire papermaking machine, 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. The paper base material may be one layer, or may be composed of two or more layers.
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.

(Anchor layer)
The anchor layer is a coating layer formed by coating, and contains an ethylene-vinyl acetate copolymer resin and PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). From the viewpoint of reducing the environmental load during production, it is preferable that the anchor layer is a coating layer of a water-dispersed paint. Whether or not a layer is a coating layer can be determined by observing the cross section with an electron microscope or the like.

Ethylene-vinyl acetate copolymer resin Ethylene-vinyl acetate copolymer resin (hereinafter also referred to as EVA) is a copolymer containing ethylene and vinyl acetate as monomers, and may further contain other monomers as monomers. When EVA contains other monomers as monomers, the content of 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.

The glass transition temperature (Tg) of EVA is preferably -50 to 30°C. If the glass transition temperature exceeds 30°C, the adhesion to the laminate layer may decrease, resulting in insufficient interlayer adhesion. If the glass transition temperature is lower than -50°C, the EVA may become too soft and blocking may occur easily. The glass transition temperature of EVA is more preferably -40 to 20°C, and even more preferably -30 to 15°C. In this specification, the glass transition temperature refers to 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 referred to as ethylene:vinyl acetate) is preferably 50:50 to 6:94. As the molar ratio of ethylene increases, the Tg of EVA decreases, and as the molar ratio of vinyl acetate increases, the Tg increases. In addition, as the molar ratio of vinyl acetate increases, the interlayer adhesion with the laminate layer tends to increase. The improvement in interlayer adhesion is presumed to be due to the polar group of vinyl acetate. When the molar ratio of ethylene to vinyl acetate is within the above range, it is easy to obtain EVA with a glass transition temperature within the above range, and it is also easy to obtain laminate base paper with excellent adhesion to the laminate layer. The molar ratio of ethylene to vinyl acetate is more preferably 45:55 to 7:93, and even more preferably 40:60 to 8:92.

・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 are microorganisms that accumulate PHBH intracellularly, and examples of such microorganisms 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, 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 JP-A-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 78:22, and even more preferably 93:7 to 80:20. 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 excessively high film-forming processing temperature, which is undesirable. 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 flexural modulus. The composition ratio of PHBH can be measured by a known method, for example, NMR analysis.
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.

In one embodiment of the present invention, the mass average molecular weight of PHBH is preferably 50,000 to 700,000, more preferably 100,000 to 600,000, and even more preferably 200,000 to 400,000. When the mass average molecular weight of PHBH is within the above range, a film with excellent mechanical properties can be obtained. 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, using chloroform as the mobile phase, and converting the molecular weight into polystyrene. As the measurement sample, a powder obtained by centrifuging an aqueous dispersion containing PHBH and then drying it is used.
In the present invention, as the PHBH, a mixture of two or more types having different composition ratios, mass average molecular weights, etc. can be used.

The weight ratio (solids content) of EVA to PHBH in the anchor layer is not particularly limited as long as the effects of the present invention are achieved, but is preferably 20:80 to 70:30, more preferably 25:75 to 60:40, and even more preferably 30:70 to 50:50.

In the present invention, the average particle size of the PHBH in the coating material for forming the anchor layer is preferably 0.1 to 50 μm, more preferably 0.5 to 10 μm, and even more preferably 1 to 5 μm, from the viewpoint of blocking resistance. PHBH with an average particle size of less than 0.1 μm is difficult to achieve by microbial production, and even when obtained by chemical synthesis, a microparticulation operation is required. If the average particle size exceeds 50 μm, uneven coating may occur. The average particle size of PHBH refers to the particle size corresponding to 50% accumulation of all particles in a normal distribution, measured by adjusting an aqueous suspension of PHBH to a specified concentration using a general-purpose particle sizer such as a Microtrac particle sizer (manufactured by Nikkiso Co., Ltd., FRA).

In addition to EVA and PHBH, the anchor layer may contain other water-soluble resins and water-dispersible resins, and may further contain various auxiliaries that are blended into coating solutions in the papermaking field, such as dispersants, viscosity improvers, water retention agents, defoamers, water resistance agents, pH adjusters, cationic resins, anionic resins, UV absorbers, metal salts, lubricants, coloring dyes, and pigments, as necessary. However, the anchor layer is preferably composed mainly of EVA and PHBH, and the ratio of the total amount of EVA and PHBH to the entire anchor layer (solid content) is preferably 70% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

The anchor layer can be formed by a known coating method. The coating amount (dry mass) of the anchor layer is not particularly limited as long as the performance can be exhibited, but is, for example, 0.1 g/ ^m2 or more and 10.0 g/m2 ^{or less} per one side, preferably 0.5 g/m2 ^{or more} and 8 g/m2 ^{or less} , and more preferably 1 g/m2 or ^more and 5 g/m2 or ^less .

"Laminated paper"
The laminate paper of the present invention has a laminate layer on the anchor layer of the laminate base paper described above.
The method for forming the laminate layer is not particularly limited, and the laminate layer can be formed by a known method such as extrusion lamination or dry lamination.
The material forming the laminate layer is not particularly limited, and known materials can be used. In the case of dry lamination in which a resin film is bonded, the resin film can be a film containing a material other than resin, such as an aluminum deposition film, an inorganic oxide deposition film, or a laminate film in which a metal foil such as aluminum foil and a resin film are laminated. In addition, the laminate layer can contain a lubricant, an inorganic filler, a plasticizer, an antiblocking agent, an odor absorber, a fragrance, an antioxidant, an antioxidant, a weather resistance improver, an ultraviolet absorber, a crystal nucleating agent, a release agent, a water repellent, an antibacterial agent, a sliding property improver, a colorant such as a pigment or a dye, etc.

By using a biodegradable resin such as the above-mentioned PHBH, polylactic acid, polycaprolactone, polybutylene succinate, or polybutylene succinate adipate as the main component of the laminate layer, it is possible to reduce the adverse effects if the laminate layer is discharged into the environment as waste. When the laminate layer is mainly composed of a biodegradable resin, it is preferable that the aerobic ultimate biodegradability in an aqueous culture medium according to JIS K6950 (evaluation device OxiTOP-IDS, value after 7 days at a test temperature of 33°C) is 40% or more. In this specification, "main component" means 50% by weight or more.

The laminated paper of the present invention can be used for a variety of purposes because the laminate layer can impart various properties to it. The laminated paper of the present invention can be used, for example, as waterproof paper, greaseproof paper, waterproof and greaseproof paper, heat seal paper, cup base paper, paper container base paper, etc.

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.

Paper base material: Cup base paper with a basis weight of 220 g/ ^m2 (product name: CUP-HD, manufactured by Nippon Paper Industries Co., Ltd.)
EVA1: Sumika Chemtex Co., Ltd., Sumika Flex S-408HQE, Tg-30°C, ethylene:vinyl acetate=40:60
EVA2: Sumika Chemtex Co., Ltd., Sumika Flex S-410HQ, Tg-18°C, ethylene:vinyl acetate=30:70
EVA3: Sumika Chemtex Co., Ltd., Sumika Flex S-401HQ, Tg-18°C, ethylene:vinyl acetate=30:70
EVA4: Sumika Chemtex Co., Ltd., Sumika Flex S-400HQ, Tg 0°C, ethylene:vinyl acetate=20:80
EVA5: Sumika Chemtex Co., Ltd., Sumika Flex S-355HQ, Tg 10°C, ethylene:vinyl acetate=10:90
PHBH: Kaneka Corporation, mass average molecular weight 600,000, average particle size 2 μm

A 23% by mass aqueous dispersion containing ethylene-vinyl acetate copolymer resin and PHBH in a weight ratio (solid content) of 50:50 was applied to one or both sides of the paper substrate by the bar blade method, and the resulting coating was dried at 105°C for 1 minute to form an anchor layer, thereby preparing a laminate base paper. In the case of double-sided coating, the coating amount was the same on both sides.
On the anchor layer of the obtained laminate base paper, PHBH having a mass average molecular weight of 600,000 was laminated by melt extrusion to a film thickness of 30 μm, to obtain a heat seal paper.

(Evaluation Method)
The laminate base paper and heat seal paper obtained were evaluated as follows, and the results are shown in Tables 1 to 3.
Blocking properties: Two square test pieces with sides of 40 mm were cut out from the obtained laminate base paper, and the anchor layers were brought into contact with each other (Figure 1A) or with the anchor layer and the paper substrate (Figure 1B). The test pieces were then left to stand for 24 hours under conditions of 40°C and 80% RH with a load of 50 N/ ^cm2 applied.
After standing, the appearance when peeling off the laminate base paper and the condition after peeling were visually checked and evaluated according to the following criteria.
[Evaluation Criteria]
5: Peels off naturally.
4: There is weak resistance but it peels off.
3: The surface becomes rough after peeling.
2: Material fracture occurs over less than 50% of the surface.
1: Cannot be peeled off or more than 50% of the surface is damaged.
- Laminate Layer Adhesion Two square test pieces with sides of 40 mm were cut out from the obtained heat seal paper, and the heat seal layers were brought into contact with each other and heat sealed at a pressure temperature of 130°C, a pressure of 1.5 kgf/cm ² and a pressure time of 3.0 seconds.
A cutter blade was used to make a horizontal cut 2 mm deep between the opposing heat seal layers at the end of the test piece, and the heat seal layer was manually peeled off from the cut. The force felt when peeling and the condition after peeling were visually confirmed and evaluated according to the following criteria.
[Evaluation Criteria]
5: Material breakage occurs (paper base material is destroyed).
4: Partial material failure occurs (paper base material is destroyed).
3: There is a strong sense of resistance, but no breakage of the material occurs.
2: There is some resistance, but it can be easily peeled off.
1: No resistance was felt and it was very easy to peel off.

The laminate base paper obtained in the examples, in which the anchor layer contained EVA and PHBH, had excellent blocking resistance, whereas the laminate base paper obtained in the comparative examples, in which the anchor layer was made only of EVA, had poor blocking resistance.
The laminate base paper obtained in the comparative example, in which the anchor layer was made of only EVA, had excellent adhesion to the laminate layer. In Examples 1 to 5 and Comparative Examples 1 to 5, it was found that the adhesion to the laminate layer tended to decrease when the anchor layer contained PHBH, but in Example 5, which used EVA with a high molar ratio of vinyl acetate, no decrease in adhesion to the laminate layer was observed.

Claims (3)

A laminate base paper characterized by having a paper substrate and an anchor layer, which is a coating layer containing ethylene-vinyl acetate copolymer resin and PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), on at least one side of the paper substrate. The laminate base paper according to claim 1, characterized in that the weight ratio of the ethylene-vinyl acetate copolymer resin to the PHBH is 30:70 to 70:30. 3. A laminated paper comprising a laminate layer on the anchor layer of the laminate base paper according to claim 1 or 2.