JP7559293B2 - Heat seal paper - Google Patents

Description

The present invention relates to heat seal paper.

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.
On the other hand, poly(3-hydroxybutyrate)-based resins are microbially produced thermoplastics that are highly degradable under aerobic and anaerobic conditions, and have the remarkable ability of being decomposed by microorganisms in a short period of time even in water such as the ocean. Patent Document 1 describes that a biodegradable polyester aqueous dispersion containing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter also referred to as PHBH), which is a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate, has excellent film-forming properties and gives a resin coating film that is flexible, has good elongation, and is strong against bending when applied to paints, adhesives, fiber processing, sheet/film processing, paper processing, etc.

Patent Document 2 proposes an invention for a laminate in which this PHBH is laminated on at least one side of a lamination substrate such as paper, and describes in its examples that a laminate is obtained by melt extrusion laminating PHBH. However, when PHBH is directly laminated onto paper, there is a problem in that the adhesive strength between the paper and the PHBH layer is weak, and when PHBH layers are laminated together for use as packaging or the like, peeling is likely to occur at the interface between the paper and the PHBH layer.

International Publication No. 2004/041936 Japanese Patent Application Publication No. 10-128920

The objective of the present invention is to provide a heat seal paper having a film mainly composed of PHBH, which has excellent adhesion to the laminate layer.

The means for solving the problems of the present invention are as follows.
1. A heat seal layer made of a film mainly composed of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) is attached to at least one surface of a paper substrate via an anchor layer;
1. A heat seal paper characterized in that the anchor layer is a coating layer containing one or more thermoplastic resins selected from the group consisting of polyethyleneimine-based, styrene-acrylic, acrylic, and polyester-based thermoplastic resins.
2. The heat sealable paper according to 1., wherein the anchor layer contains one or more thermoplastic resins selected from the group consisting of acrylic and polyester resins.
3. The heat sealable paper according to 1. or 2., wherein the anchor layer is mainly composed of polylactic acid.

The heat seal paper of the present invention has excellent interlayer adhesion, and peeling is unlikely to occur between the paper base material and the anchor layer, and between the anchor layer and the heat seal layer. The heat seal paper of the present invention can be made into various types of packaging materials by heat sealing processing. The heat seal paper of the present invention, whose anchor layer is mainly composed of polylactic acid, has a high ratio of biodegradable materials to the entire heat seal paper, and even if it leaks into the environment, it decomposes quickly, so it poses a small burden on the environment.

The heat seal paper of the present invention has a heat seal layer made of a film mainly composed of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) bonded to at least one surface of a paper substrate via an anchor layer;
The anchor layer is characterized in that it is a coating layer containing one or more thermoplastic resins selected from the group consisting of polyethyleneimine-based, styrene-acrylic, acrylic, and polyester-based thermoplastic resins.
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 mainly made of pulp, and is obtained by making paper stock containing 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 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 appropriate 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 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, which 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 for packaging materials such as wrapping paper, paper bags, lid materials, and underlayment paper, and posters used outdoors, the basis weight of the paper base material 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 base material 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, particularly using thin paper of about 20 g/m ² to 100 g/m ² among packaging materials. In addition, 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.

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.

(Heat seal layer)
The heat seal layer is made of a film containing PHBH as a main component. In the present invention, "containing PHBH as a main component" means that the content is 50% by weight or more.
<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 Laid-Open Publication 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 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 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 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 weight 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 weight average molecular weight of PHBH is within the above range, a film with excellent mechanical properties can be obtained. The weight 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, two or more types of PHBH having different composition ratios, weight average molecular weights, etc. may be mixed and used.

In addition to PHBH, the heat seal layer may contain other thermoplastic resins, lubricants, inorganic fillers, plasticizers, antiblocking agents, odor absorbers, fragrances, antioxidants, weather resistance improvers, UV absorbers, crystal nucleating agents, release agents, water repellents, antibacterial agents, sliding improvers, and colorants such as pigments and dyes. However, the heat seal layer is mainly composed of PHBH, and the ratio of PHBH to the entire heat seal layer is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, even more preferably 98% by weight or more, and even more preferably 99% by weight or more.

The other thermoplastic resins are not particularly limited as long as they are compatible with PHBH, but are preferably biodegradable resins, such as aliphatic polyester resins such as polycaprolactone, polybutylene succinate adipate, polybutylene succinate, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate and polybutylene azelate terephthalate.

As the lubricant, known lubricants can be used, and examples thereof include aliphatic amide compounds such as saturated or unsaturated fatty acid amides such as lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, and erucic acid amide, alkylene fatty acid amides such as methylene bisstearic acid amide and methylene bisstearic acid amide, and pentaerythritol.
The amount of the lubricant to be added is preferably 0.1 to 2 parts by weight, more preferably 0.2 to 1 part by weight, based on 100 parts by weight of PHBH.

Examples of inorganic fillers include talc, calcium carbonate, mica, silica, clay, kaolin, titanium oxide, alumina, and zeolite, all of which have an average particle size of 0.5 μm or more.
The amount of the inorganic filler to be blended is preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight, based on 100 parts by weight of PHBH.

(Anchor layer)
The anchor layer is a coating layer and contains one or more thermoplastic resins selected from the group consisting of polyethyleneimine, styrene acrylic, acrylic, and polyester. The anchor layer is preferably a coating layer of a water-dispersed paint in which a thermoplastic resin is dispersed in water, from the viewpoint of reducing the environmental load during production. Whether or not the layer is a coating layer can be determined by observing the cross section with an electron microscope or the like.
The anchor layer contains one or more thermoplastic resins selected from the group consisting of polyethyleneimine, styrene acrylic, acrylic, and polyester. Among these, from the viewpoint of interlayer adhesive strength, one or more selected from the group consisting of acrylic and polyester is preferred, and polylactic acid, which is a polyester, is more preferred because it is biodegradable.

In addition to the thermoplastic resins described above, 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, it is preferable that the anchor layer is mainly composed of a thermoplastic resin, and the ratio of the thermoplastic resin to the entire anchor layer (solid content) is preferably 70% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, even more preferably 98% by weight or more, and even more preferably 99% by weight or more.

<Method of manufacturing heat seal paper>
The heat seal paper of the present invention can be produced by laminating a film containing PHBH as a heat seal layer to a paper substrate via an anchor layer. The heat seal layer can be provided on only one side or both sides of the paper substrate.

The coating method of the anchor layer is not particularly limited, and coating can be performed using a known coating device and coating system. For example, the coating device can be a blade coater, a bar coater, an air knife coater, a curtain coater, a spray coater, a roll coater, a reverse roll coater, a size press coater, a gate roll coater, etc., and the viscosity, solid content concentration, etc. of the coating liquid for the anchor layer can be appropriately adjusted depending on the coating device, coating system, etc. used.
The coating amount (dry weight) of the anchor layer is not particularly limited as long as the performance can be exhibited, but is, for example, 0.1 g/m ² or more and 10.0 g/m ² or less per side.

The film containing PHBH as a main component can be laminated onto the anchor layer by melt extrusion lamination.
The thickness of the heat seal layer is not particularly limited, but is preferably, for example, 5 μm or more and 300 μm or less. If the thickness of the heat seal layer is less than 5 μm, the heat sealability may not be fully exhibited. If the thickness of the heat seal layer exceeds 300 μm, the heat seal layer becomes too rigid, which may reduce the processability as a heat seal paper and increase the cost. The thickness of the heat seal layer is preferably 10 μm or more, more preferably 20 μm or more, and preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 60 μm or less.

The heat seal paper of the present invention is easy to mold, maintain its shape, and ensure airtightness, and can therefore be suitably used for paper bags, paper containers, paper boxes, paper cups, (soft) packaging materials, lid materials, and the like.
The heat seal paper of the present invention, in which the heat seal layer is also a water resistant layer, can be suitably used as wrapping paper, paper bags, paper containers, paper boxes, paper cups, (soft) packaging materials, paper plates, paper trays, posters for outdoor use, etc.
The heat seal paper of the present invention, in which the heat seal layer is also an oil-resistant layer, can be suitably used as (soft) packaging materials or wrapping paper for foods that contain a lot of oil, such as hamburgers, hot dogs, French fries, fried chicken, potato chips, etc., paper linings for fried foods such as tempura, paper plates, paper trays, paper cups, 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 percentages in the examples are by weight and weight percentages, respectively.

[Example 1]
A 10% by weight aqueous dispersion of polyethyleneimine resin (Nippon Shokubai Co., Ltd., P-1000) was applied onto a paper substrate (a cup base paper with a basis weight of 170 ^g / ^m2 coated with a starch-based sizing agent at 2 g/m2 per side by a size press) using a bar blade method so that the coating amount was 2.3 g/ ^m2 on a dry basis, and the substrate was dried at 105°C for 1 minute to form an anchor layer.
On this anchor layer, PHBH having a weight average molecular weight of 600,000 was laminated by melt extrusion to a thickness of 30 μm to obtain a heat seal paper.

[Example 2]
A heat seal paper was obtained in the same manner as in Example 1, except that a styrene-acrylic resin (Kusumoto Chemicals, A-2091) was applied as the anchor layer so that the coating amount was 1.0 g/ ^m2 on a dry basis.
[Example 3]
A heat seal paper was obtained in the same manner as in Example 1, except that a styrene-acrylic resin (Kusumoto Chemicals, A-2092) was applied as the anchor layer so that the coating amount was 1.1 g/ ^m2 on a dry basis.
[Example 4]
A heat seal paper was obtained in the same manner as in Example 1, except that a styrene-acrylic resin (Seiko PMC Co., Ltd., NE2260) was applied as the anchor layer so that the coating amount was 1.2 g/ ^m2 on a dry basis.
[Example 5]
A heat seal paper was obtained in the same manner as in Example 1, except that a styrene-acrylic resin (Seiko PMC, XP8829) was applied as the anchor layer so that the coating amount was 1.1 g/ ^m2 on a dry basis.
[Example 6]
A heat seal paper was obtained in the same manner as in Example 1, except that a styrene-acrylic resin (GS400, Toyo Adle Co., Ltd.) was applied as the anchor layer so that the coating amount was 1.0 g/ ^m2 on a dry basis.

[Example 7]
A heat seal paper was obtained in the same manner as in Example 1, except that an acrylic resin (Henkel, BC910F) was applied as the anchor layer so that the coating amount was 1.2 g/ ^m2 on a dry basis.
[Example 8]
A heat seal paper was obtained in the same manner as in Example 1, except that a polyester resin (polybutylene succinate adipate) was applied as the anchor layer so that the coating amount was 0.9 g/ ^m2 on a dry basis.
[Example 9]
A heat seal paper was obtained in the same manner as in Example 1, except that a polyester resin (polylactic acid A) was applied as the anchor layer so that the coating amount was 0.9 g/ ^m2 on a dry basis.
[Example 10]
A heat seal paper was obtained in the same manner as in Example 1, except that a polyester resin (polylactic acid B) was applied as the anchor layer so that the coating amount was 1.0 g/ ^m2 on a dry basis.
[Example 11]
A heat seal paper was obtained in the same manner as in Example 1, except that a polyester resin (polylactic acid C) was applied as the anchor layer so that the coating amount was 1.4 g/ ^m2 on a dry basis.

[Comparative Example 1]
A heat seal paper was obtained in the same manner as in Example 1, except that a heat seal layer was formed on a paper substrate without an anchor layer.
[Comparative Example 2]
A heat seal paper was obtained in the same manner as in Comparative Example 1, except that a paper substrate (a cup base paper having a basis weight of 170 g/ ^m2 coated with a PVA-based sizing agent (Nippon Synthetic Chemical Industry Co., Ltd., P-7100) at 2 g/ ^m2 per side by a size press) was used.
[Comparative Example 3]
A heat seal paper was obtained in the same manner as in Example 1, except that a polyvinyl alcohol resin (VC10, Japan Vinyl Acetate & Poval Co., Ltd.) was applied as the anchor layer so that the coating amount was 1.9 g/ ^m2 on a dry basis.
[Comparative Example 4]
A heat seal paper was obtained in the same manner as in Example 1, except that a polyolefin resin (Unitika, AA1220) was applied as the anchor layer so that the coating amount was 1.1 g/ ^m2 on a dry basis.
[Comparative Example 5]
A heat seal paper was obtained in the same manner as in Example 1, except that a polyolefin resin (Unitika Ltd., SD1015J2) was applied as the anchor layer so that the coating amount was 1.0 g/ ^m2 on a dry basis.

(Evaluation Method)
The heat seal paper thus obtained was subjected to the following evaluations, and the results are shown in Table 1.
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 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 slit 2 mm deep in the heat seal layer, and the heat seal layer was manually peeled off from the slit. The force felt when the heat seal layer was peeled off 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 heat seal papers obtained in Examples 1 to 11 of the present invention had excellent adhesion to the laminate layer. In particular, the heat seal papers obtained in Examples 9 to 11 had strong adhesion to the laminate layer, and material failure (destruction of the paper substrate) occurred. Among these, the anchor layer in Examples 9 to 11 was a polylactic acid-based resin, and the heat seal paper as a whole was biodegradable.
The heat seal papers obtained in Comparative Examples 1 to 5 had poor adhesion between the heat seal layer and the laminate layer of the paper substrate, and the heat seal layer and the paper substrate could be easily peeled off.

Claims (3)

A heat seal layer made of a film having a thickness of 5 μm to 300 μm and mainly composed of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) is attached to at least one surface of the paper substrate via an anchor layer;
1. A heat seal paper characterized in that the anchor layer is a coating layer containing one or more thermoplastic resins selected from the group consisting of polyethyleneimine-based, styrene-acrylic, acrylic, and polyester-based thermoplastic resins. The heat seal paper according to claim 1, characterized in that the anchor layer contains one or more thermoplastic resins selected from the group consisting of acrylic and polyester resins. The heat seal paper according to claim 1 or 2, characterized in that the anchor layer is mainly composed of polylactic acid.