EP4660371A1 - Heat seal paper - Google Patents

Heat seal paper

Info

Publication number
EP4660371A1
EP4660371A1 EP24750119.0A EP24750119A EP4660371A1 EP 4660371 A1 EP4660371 A1 EP 4660371A1 EP 24750119 A EP24750119 A EP 24750119A EP 4660371 A1 EP4660371 A1 EP 4660371A1
Authority
EP
European Patent Office
Prior art keywords
heat seal
paper
pulp
seal paper
mass
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24750119.0A
Other languages
German (de)
French (fr)
Inventor
Kazuyuki Abe
Tatsuya Matsumoto
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Oji Holdings Corp
Original Assignee
Oji Holdings Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Oji Holdings Corp filed Critical Oji Holdings Corp
Priority claimed from PCT/JP2024/002197 external-priority patent/WO2024162170A1/en
Publication of EP4660371A1 publication Critical patent/EP4660371A1/en
Pending legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H19/00—Coated paper; Coating material
    • D21H19/10—Coatings without pigments
    • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
    • D21H19/24—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H19/28—Polyesters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/10—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of paper or cardboard
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
    • D21H17/63—Inorganic compounds
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D21H27/10—Packing paper

Definitions

  • the present invention relates to a heat seal paper.
  • heat seal papers use a paper substrate, their environmental impact is less than that of heat seal films that use a resin substrate.
  • Polylactic acid and polybutylene succinate exhibit excellent biodegradability, and therefore by using these resins for the heat seal layer of a heat seal paper, the environmental impact can be reduced even further.
  • heat seal papers that use polylactic acid or polybutylene succinate for the heat seal layer have high rigidity, and therefore tend to be prone to wrinkling during processing, and particularly during bag production in a pillow packaging machine.
  • Pillow packaging is one packaging method employed with film-like packaging materials.
  • a roll of the wound packaging material is set in the pillow packaging machine, the packaging material is wound off the roll and transformed into a cylindrical shape using a tool known as a sailor (former), and heat sealing and cutting are then conducted to form a pillow-shape package. If wrinkling occurs during this bag production process, then the external appearance of the package is unsatisfactory.
  • the present invention has an object of providing a heat seal paper that is resistant to wrinkling even during pillow processing.
  • the present invention has the following aspects.
  • the present invention is able to provide a heat seal paper that is resistant to wrinkling even during pillow processing.
  • MD means "machine direction”.
  • the direction parallel to the direction of progression when a paper substrate is produced in a paper making machine also referred to as the longitudinal direction or flow direction.
  • the direction of alignment of the fibers of the paper substrate may also be considered to be MD.
  • the tensile strength may be measured at 22.5 degree intervals, with the direction that exhibits the highest tensile strength being deemed MD.
  • CD means "cross direction”.
  • the direction orthogonal to MD also referred to as the lateral direction.
  • the expression "to” used to indicate a numerical range means a range that includes the numerical values before and after the "to” as the lower limit and upper limit respectively.
  • the heat seal paper has a heat seal component containing a thermoplastic resin adhered to at least one surface of a paper substrate.
  • the paper substrate and the heat seal component are described below in further detail.
  • T the geometric mean of the MD and CD tear strength values (mN) of the heat seal paper
  • S the geometric mean of the MD and CD bending resistance values (mN)
  • T/S the value represented by T/S is preferably at least 10, more preferably at least 11.5, and even more preferably 13 or greater. There are no particular limitations on the upper limit for T/S, but the value is, for example, typically not more than 50, or 40 or less.
  • the tear strength is measured in accordance with JIS P 8116:2000.
  • the bending resistance is measured in accordance with JIS P 8125-1:2017.
  • T/S value of a heat seal paper affects the bag production suitability in a pillow packaging machine.
  • T is an indicator of breakage resistance
  • S is an indicator of hardness. If the value of S is too high (the paper is too hard), then breakage during bag production in a pillow packaging machine is more prevalent, even if T is high.
  • the geometric mean T of the MD and CD tear strength values (mN) of the heat seal paper is preferably at least 300 mN, more preferably at least 350 mN, and even more preferably 400 mN or greater.
  • T the geometric mean T of the MD and CD tear strength values (mN) of the heat seal paper is preferably at least 300 mN, more preferably at least 350 mN, and even more preferably 400 mN or greater.
  • the upper limit for T is, for example, typically not more than 4,000 mN, or 3,000 mN or less.
  • the geometric mean S of the MD and CD bending resistance values (mN) of the heat seal paper is preferably not more than 60 mN, more preferably not more than 50 mN, and even more preferably 40 mN or less. There are no particular limitations on the lower limit for S, but the value is, for example, typically at least 5 mN, or 10 mN or greater.
  • the peel strength (hereinafter also referred to as the "heat seal peel strength") is preferably at least 2 N/15mm, more preferably at least 2.4 N/15mm, and even more preferably 2.8 N/15mm or greater.
  • the upper limit for the heat seal peel strength is, for example, typically not more than 30 N/15mm, or 20 N/15mm or less.
  • the heat seal peel strength can be adjusted, for example, by altering the amount of the heat seal component adhered per unit area of the paper, and altering the amount of the thermoplastic resin relative to the total mass of the heat seal component.
  • the amount of the heat seal component adhered per unit area of the heat seal paper is preferably within a range from 2 to 30 g/m 2 , more preferably from 3 to 20 g/m 2 , and even more preferably from 4 to 10 g/m 2 . Ensuring that the amount adhered of the heat seal component is at least as large as the above lower limit yields superior pillow packaging suitability. Further, by ensuring that the amount adhered of the heat seal component is not more than the above upper limit, blocking and soiling during the production process can be better suppressed.
  • the thickness of the heat seal component adhered to the fibrous surface of the paper substrate is not more than about 4 ⁇ m, but there are no particular limitations on this thickness.
  • the thickness of the heat seal component on the fibrous surface of the paper substrate can be ascertained by observing a cross-section of the fibers using a microscope.
  • the heat seal layer composed of the heat seal component can sometimes be seem, but it is thought that this heat seal layer is not always clearly visible.
  • the heat seal component may be adhered to one surface or to both surfaces of the paper substrate. In terms of reducing production costs, the heat seal component is preferably adhered to only one surface of the paper substrate.
  • the heat seal component may be adhered uniformly across the paper substrate, or may be adhered in a non-uniform manner which appears as a dot-like pattern, linear pattern, or mesh-like pattern or the like when viewed from above.
  • a pulp produced by disintegrating the heat seal paper in accordance with JIS P 8220-1 exhibits a Canadian standard freeness (hereinafter also referred to as the "disintegrated freeness") measured in accordance with JIS P 8121-2:2012 that is preferably within a range from 300 to 600 mL, more preferably from 350 to 550 mL, and even more preferably from 400 to 500 mL. Provided the disintegrated freeness of the heat seal paper falls within this range, the tear strength of the heat seal paper tends to be higher.
  • the grammage of the heat seal paper is preferably within a range from 20 to 200 g/m 2 , more preferably from 35 to 150 g/m 2 , and even more preferably from 40 to 100 g/m 2 . Provided the grammage of the heat seal paper is at least as large as the above lower limit, the tear strength of the heat seal paper tends to be higher. Further, provided the grammage of the heat seal paper is not more than the above upper limit, the bending resistance of the heat seal paper tends to be lower.
  • the grammage of the heat seal paper is measured in accordance with JIS P 8124:2011.
  • the thickness of the heat seal paper is preferably within a range from 20 to 300 ⁇ m, more preferably from 35 to 220 ⁇ m, and even more preferably from 40 to 150 ⁇ m. Provided the thickness of the heat seal paper is at least as large as the above lower limit, the tear strength of the heat seal paper tends to be higher. Further, provided the thickness of the heat seal paper is not more than the above upper limit, the bending resistance of the heat seal paper tends to be lower.
  • the thickness of the heat seal paper is measured in accordance with JIS P 8118:2014.
  • the paper substrate contains pulp as the main component.
  • the expression “contains pulp as the main component” means that the amount of pulp relative to the mass of the paper substrate is at least 70% by mass.
  • the paper substrate contains from 1 to 20% by mass of an inorganic pigment. Accordingly, the amount of pulp relative to the mass of the paper substrate is within a range from 80 to 99% by mass. The amount of pulp relative to the mass of the paper substrate is preferably within a range from 85 to 97% by mass, and more preferably from 90 to 95% by mass.
  • the paper substrate may be composed of a typically used paper, and examples include paper substrates containing wood pulp as the main component.
  • the paper substrate include bleached kraft papers, unbleached kraft papers, high-quality papers, cardboards, liner papers, coated papers, single-sided glossy papers, glassine papers, and graphan papers.
  • a bleached kraft paper, unbleached kraft paper, coated paper, or single-sided glossy paper is preferred.
  • Examples of the pulp include chemical pulps such as leaf bleached kraft pulp (LBKP), northern bleached kraft pulp (NBKP), leaf bleached sulfite pulp (LBSP), and northern bleached sulfite pulp (NBSP).
  • Examples of other pulps include unbleached pulps, semi-bleached pulps and bleached pulps such as stone grand pulp (GP), pressurized stone grand pulp (PGW), refiner grand pulp (RGP), chemi-grand pulp (CGP), thermomechanical pulp (TMP) and chemi-thermomechanical pulp (CTMP). Sulfite pulps and recycled paper pulps may also be used.
  • the pulp preferably contains a hardwood pulp such as a leaf bleached kraft pulp (LBKP) or a leach bleached sulfite pulp (LBSP).
  • a hardwood pulp such as a leaf bleached kraft pulp (LBKP) or a leach bleached sulfite pulp (LBSP).
  • the amount of the hardwood pulp relative to the total mass of the pulp is preferably at least 50% by mass, more preferably at least 70% by mass, and may be 100% by mass.
  • the pulp preferably contains a softwood pulp such as a northern bleached kraft pulp (NBKP) or a northern bleached sulfite pulp (NBSP).
  • a softwood pulp such as a northern bleached kraft pulp (NBKP) or a northern bleached sulfite pulp (NBSP).
  • the amount of the softwood pulp relative to the total mass of the pulp is preferably at least 10% by mass, more preferably at least 20% by mass, and may be 100% by mass.
  • a combination of a hardwood pulp and a softwood pulp may also be used.
  • the amount of the hardwood pulp is within a range from 50 to 90% by mass and the amount of the softwood pulp is within a range from 10 to 50% by mass, and more preferable that the amount of the hardwood pulp is from 70 to 90% by mass and the amount of the softwood pulp is from 10 to 30% by mass.
  • the paper substrate contains an inorganic pigment.
  • an inorganic pigment in the paper substrate, the ash content of the paper substrate increases and the tensile modulus of elasticity decreases.
  • the bending resistance of the paper substrate is cubically proportional to the value of tensile modulus of elasticity ⁇ thickness.
  • the inorganic pigment examples include talc, kaolin, calcium carbonate, titanium oxide, barium sulfate, calcium sulfate, zinc oxide, silica, silicates, colloidal silica, and satin white.
  • at least one inorganic pigment selected from the group consisting of talc, kaolin, calcium carbonate and titanium oxide is preferred.
  • the amount of the inorganic pigment relative to the total mass of the paper substrate is typically within a range from 1 to 20% by mass, preferably from 3 to 15% by mass, and even more preferably from 5 to 10% by mass. Provided the amount of the inorganic pigment is at least as large as the above lower limit, the bending resistance can be more easily reduced. Further, provided the amount of the inorganic pigment is not more than the above upper limit, paper powder is unlikely to form.
  • the paper substrate may also contain other internal additives besides the inorganic pigment.
  • Examples of these internal additives include sizing agents, fillers, paper strengthening agents, yield improvers, pH adjusters, freeness improvers, water resistance agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, and pigments (excluding inorganic pigments).
  • the paper substrate may also have an optional layer such as a clay coat layer on at least a portion of one surface or both surfaces of the paper substrate.
  • a clay coat layer is used for filling the paper substrate and smoothing the surface of the paper substrate. Examples of the clay include kaolin, talc and mica.
  • the density (bulk density) of the paper substrate is preferably within a range from 0.60 to 1.00 g/cm 3 , more preferably from 0.65 to 0.95 g/cm 3 , and even more preferably from 0.70 to 0.90 g/cm 3 .
  • the density of the paper substrate is at least as large as the above lower limit, excessive leaching of the heat seal component into the paper substrate can be suppressed, and the heat seal peel strength tends to improve.
  • the density of the paper substrate is not more than the above upper limit, the heat seal paper tends not to become hard, and tends to be more resistant to breakage.
  • the density of the paper substrate can be determined by dividing the grammage of the paper substrate by the thickness.
  • the methods used for measuring the grammage and thickness of the paper substrate are the same as the methods used for measuring the grammage and thickness of the heat seal paper.
  • the heat seal component contains a thermoplastic resin.
  • the heat seal paper exhibits heat sealing properties within a practical heating temperature range.
  • thermoplastic resin preferably includes at least one resin selected from the group consisting of polylactic acid and polybutylene succinate (hereinafter, also referred to as "PBS").
  • PBS polybutylene succinate
  • polylactic acid and PBS are sometimes jointly referred to as the “resin I”.
  • the resin I exhibits excellent biodegradability, meaning the heat seal paper has minimal environmental impact.
  • the polylactic acid may be a homopolymer of L-lactic acid, a homopolymer of D-lactic acid, a copolymer of L-lactic acid and D-lactic acid, or a copolymer of L-lactic acid and/or D-lactic acid and another copolymerizable monomer.
  • monomers that are copolymerizable with L-lactic acid and/or D-lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid.
  • a commercially available product may also be used as the polylactic acid.
  • Examples of commercially available products of polylactic acid include the products LANDY PL-1000 and LANDY PL-3000 (aqueous dispersions of polylactic acid) manufactured by Miyoshi Oil & Fat Co., Ltd., and the product RESEM Y225 (an aqueous dispersion of polylactic acid) manufactured by Chukyo Yushi Co., Ltd.
  • a single type of the resin I may be used alone, or a combination of two or more such resins may be used.
  • the resin I is preferably a polylactic acid.
  • the amount of the resin I namely the total amount of polylactic acid and PBS, relative to the total mass of the thermoplastic resin, is preferably at least 50% by mass, more preferably at least 70% by mass, and may be 100% by mass.
  • the thermoplastic resin may also include another thermoplastic resin besides the resin I.
  • thermoplastic resin examples include biodegradable resins other than the resin I, polyethylene, polypropylene, olefin-unsaturated carboxylic acid copolymers, acrylic resins, ethylene vinyl alcohol, polystyrene resins, polycarbonate resins, polyacetal resins, polyester resins, polyamide, styrene-butadiene latex, polyvinyl alcohol, and polyvinylidene chloride.
  • This other thermoplastic resin may also be a non-petroleum-derived resin.
  • a single other thermoplastic resin may be used alone, or a combination of two or more such resins may be used.
  • biodegradable resins examples include polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), and poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBH).
  • PBSA polybutylene succinate adipate
  • PBAT polybutylene adipate terephthalate
  • PHBH poly(3-hydroxybutyrate-co-hydroxyhexanoate)
  • One of these other biodegradable resins may be used alone, or a combination of two or more such resins may be used.
  • the olefin-unsaturated carboxylic acid copolymers are copolymers of an olefin and an unsaturated carboxylic acid-based monomer.
  • olefin examples include ethylene and propylene.
  • a single olefin may be used alone, or a combination of two or more olefins may be used.
  • the unsaturated carboxylic acid-based monomer examples include unsaturated carboxylic acids, as well as salts and esters of those acids.
  • Specific examples of the unsaturated carboxylic acid-based monomers include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid; alkyl esters of unsaturated polycarboxylic acids having at least one carboxyl group such as itaconic acid monomethyl ester, fumaric acid monobutyl ester, and maleic acid monobutyl ester; and unsaturated sulfonic acid monomers and salts thereof such as acrylamidopropanesulfonic acid, sodium sulfoethyl acrylate, and sodium sulfopropyl methacrylate.
  • a single unsaturated carboxylic acid-based monomer may be used alone, or a combination of two or
  • the olefin-unsaturated carboxylic acid copolymer can be obtained, for example, by subjecting the olefin such as ethylene and the unsaturated carboxylic acid-based monomer to emulsion polymerization.
  • olefin-unsaturated carboxylic acid copolymer Commercially available products may also be used as the olefin-unsaturated carboxylic acid copolymer.
  • olefin-unsaturated carboxylic acid copolymer product is ZAIKTHEN AC (an aqueous dispersion of an ammonium salt of an ethylene-acrylic acid copolymer, acrylic acid copolymerization ratio: 20 mol%).
  • a single olefin-unsaturated carboxylic acid copolymer may be used alone, or a combination of two or more such copolymers may be used.
  • non-petroleum-derived resins there are no particular limitations on the non-petroleum-derived resins, and all manner of thermoplastic resins may be used. Examples include biomass-derived polyolefins, biomass-derived polyesters, biomass-derived polyamides, biomass-derived polyurethane, and biomass-derived cellulose acetate.
  • the biomass is preferably of plant derivation. Examples include biomass derived from corn and biomass derived from sugar cane.
  • a single non-petroleum-derived resin may be used alone, or a combination of two or more such resins may be used.
  • biomass-derived polyolefins examples include polymers of various olefins such as ethylene and propylene, as well as copolymers of those olefins.
  • biomass-derived polypropylene and biomass-derived polyethylene are preferred, and biomass-derived polyethylene is particularly desirable.
  • biomass-derived polyolefins Commercially available products may also be used as the biomass-derived polyolefins. Examples of commercially available biomass-derived polyolefin products include SBC818 (a biomass low-density polyethylene) and SGF4950 (a biomass high-density polyethylene) manufactured by Braskem S.A.
  • either one or both of the alcohol unit and the carboxylic acid unit are derived from biomass.
  • Examples of the alcohol include diols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, decanediol, and 2-ethylbutyl-1-propanediol.
  • diols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, decanediol, and 2-ethylbutyl-1-propanediol.
  • alcohol is in no way limited to the alcohols mentioned above. Further, a single alcohol may be used alone, or a combination of two or more alcohols may be used.
  • carboxylic acid examples include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and derivatives of these acids.
  • aromatic dicarboxylic acids examples include terephthalic acid, isophthalic acid, and phthalic acid.
  • aromatic dicarboxylic acid derivatives include lower alkyl esters (such as the methyl esters, ethyl esters, propyl esters and butyl esters) of the aromatic dicarboxylic acids.
  • Examples of the aliphatic dicarboxylic acids include chain-like or alicyclic dicarboxylic acids of 2 to 40 carbon atoms. Specific examples include oxalic acid, succinic acid, glutaric acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid, azelaic acid, dodecadicarboxylic acid, and cyclohexanedicarboxylic acid.
  • Examples of aliphatic dicarboxylic acid derivatives include lower alkyl esters (such as the methyl esters, ethyl esters, propyl esters and butyl esters) of the aliphatic dicarboxylic acids. Other derivatives include acid anhydrides of aliphatic dicarboxylic acids such as succinic anhydride.
  • carboxylic acid is in no way limited to the carboxylic acids mentioned above. Further, a single carboxylic acid may be used alone, or a combination of two or more carboxylic acids may be used.
  • biomass-derived polyesters may also be used as the biomass-derived polyesters.
  • An example of a commercially available biomass-derived polyester products is the product CB-602AB (a bio-polyethylene terephthalate) manufactured by FENC Corporation.
  • the other thermoplastic resin is preferably at least one resin selected from the group consisting of other biodegradable resins and non-petroleum-derived resins.
  • the melting point is preferably within a range from 80 to 180°C, more preferably from 100 to 170°C, and even more preferably from 110 to 160°C. Provided the melting point of the thermoplastic resin falls within this range, heat sealing can be conducted favorably during bag production in a pillow packaging machine.
  • thermoplastic resin melting point The melting point of the thermoplastic resin is measured using a differential scanning calorimeter (DSC). In those cases where the heat seal component contains two or more types of thermoplastic resin, the mass average value measured for the mixture of the plurality of thermoplastic resins is used as the thermoplastic resin melting point.
  • DSC differential scanning calorimeter
  • the melting point of a polylactic acid is, for example, within a range from 145 to 180°C.
  • the melting point of PBS is, for example, within a range from 100 to 120°C.
  • the amount of the thermoplastic resin in the heat seal component, relative to the total mass of the heat seal component, is preferably at least 70% by mass, more preferably at least 80% by mass, even more preferably at least 85% by mass, still more preferably at least 90% by mass, and may be 100% by mass.
  • the amount of the thermoplastic resin in the heat seal component is at least as large as the above lower limit, heat sealing can be conducted favorably during bag production in a pillow packaging machine, and the pillow packaging suitability is superior.
  • the amount of the thermoplastic resin in the heat seal component relative to the total mass of the heat seal component may be, for example, not more than 99% by mass, not more than 98% by mass, not more than 98.5% by mass, or 97% by mass or less.
  • the heat seal component may also contain a salt of an acrylic acid polymer in order to enhance the adhesive strength of the heat seal paper following heat sealing.
  • acrylic acid polymer examples include polyacrylic acid, acrylic acid-maleic acid copolymers, and acrylic acid-sulfonic acid copolymers.
  • salt examples include sodium salts, potassium salts and ammonium salts.
  • the amount of the salt of the acrylic acid polymer, relative to the mass of the thermoplastic resin in the heat seal component is preferably within a range from 0.1 to 3% by mass, more preferably from 0.2 to 2% by mass, and even more preferably from 0.5 to 1.5% by mass.
  • the amount of the acrylic acid polymer salt is at least as large as the above lower limit, favorable heat sealing properties can be more easily achieved. Further, provided the amount of the acrylic acid polymer salt is not more than the above upper limit, an improvement in the heat sealing properties consistent with the amount added can be obtained.
  • the heat seal component may also contain any of various auxiliary agents in addition to the thermoplastic resin and the acrylic acid polymer salt.
  • auxiliary agents include antifoaming agents, thickeners, polysaccharide thickeners, neutralizing agents, plasticizers, preservatives, pH adjusters, crosslinking agents, anti-blocking agents, lubricants, dyes, and pigments.
  • the pigments include the inorganic pigments mentioned above. However, the list of possible auxiliary agents is not limited to those mentioned examples.
  • the heat seal paper can be produced by producing the paper substrate described above, and then adhering the heat seal component described above to at least one surface of the paper substrate.
  • the paper substrate can be produced, for example, by making a paper from a pulp slurry containing the inorganic pigment in a paper making machine, and then drying the thus formed wet paper.
  • paper making machine There are no particular limitations on the paper making machine. Examples include a Fourdrinier paper machine, gap former paper machine, cylinder paper machine, or short net paper machine. In terms of economic viability, a paper making machine equipped with on-machine coating is preferred.
  • the pulp is preferably disintegrated, and a refiner or beater then used to beat the pulp to impart suitable levels of flexibility and fluff to the pulp.
  • a refiner or beater used to beat the pulp to impart suitable levels of flexibility and fluff to the pulp.
  • the pulp beating method There are no particular limitations on the pulp beating method.
  • the disintegrated freeness of the pulp which acts as an indicator of the degree of beating, is preferably within a range from 300 to 600 mL, more preferably from 350 to 550 mL, and even more preferably from 400 to 500 mL.
  • the beaten pulp may be mixed with the inorganic pigment and, where necessary, other internal additives such as sizing agents and paper strengthening agents, and subsequently dispersed in water to prepare a pulp slurry with a concentration suitable for paper making.
  • the wet paper obtained using the paper making machine is preferably dried using a multistage cylinder dryer, and air dryer, or a Yankee dryer.
  • One example of the method used for adhering the heat seal component to at least one surface of the paper substrate involves applying a coating liquid containing the heat seal component to at least one surface of the paper substrate, and then conducting drying.
  • the coating liquid is preferably an aqueous dispersion (for example, an aqueous emulsion) containing the thermoplastic resin.
  • the coating liquid may also contain other optional components such as a salt of an acrylic acid polymer or one or more auxiliary agents.
  • coating devices there are no particular limitations on the method used for applying the coating liquid.
  • Various widely available coating devices may be used. Examples of such coating devices include a blade coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, slot die coater, gravure coater, champlex coater, brush coater, slide bead coater, two-roll size press coater, pond size press coater, rod metaling size press coater, blade metaling size press coater, short-dwell coater, gate roll coater, and nip coater using calendering.
  • an on-machine coating device is preferred. This on-machine coating devices is, for example, preferably a blade coater, bar coater, gate roll coater, rod metaling size press coater, blade metaling size press coater, or pond size press coater.
  • the heat seal paper may, if necessary, be subjected to a smoothing treatment.
  • the smoothing treatment is typically conducted either on-machine or off-machine using a smoothing treatment device such as super calender, gloss calender or soft calender.
  • a smoothing treatment device such as super calender, gloss calender or soft calender.
  • the paper substrate may also be subjected to a smoothing treatment prior to application of the coating liquid.
  • the obtained heat seal paper may be wound into a roll form.
  • the two end portions of the roll may be removed using a slitter so as to match the width of the heat seal paper to the width required in the processing equipment of subsequent stages.
  • the heat seal paper described above because the paper substrate contains from 1 to 20% by mass of an inorganic pigment, wrinkling is unlikely during pillow processing (bag production in a pillow packaging machine). Further, the heat seal paper exhibits excellent pillow packaging suitability, and is resistant to breakage when subjected to continuous bag production in a pillow packaging machine. The heat sealing properties and printability are also excellent.
  • the heat seal paper can be used as a packaging material in a variety of fields such as paper products, foodstuffs (such as confectionery), pharmaceutical items, electronic components, hygiene products, agricultural materials, and construction materials.
  • heat seal paper When used as a packaging material, conventional packaging methods may be used as the packaging method, and examples include pillow packaging, gusset packaging, tube packaging, three-way seal packaging, four-way seal packaging, stick packaging, pouch packaging, and deep-drawn packaging.
  • the heat seal paper is ideal for pillow packaging.
  • An aqueous coating liquid was prepared by mixing 90 parts of a polylactic acid aqueous emulsion (RESEM Y225, manufactured by Chukyo Yushi Co., Ltd., melting point of polylactic acid: 150°C), 8.5 parts of kaolin (BARRISURF HX, manufactured by Imerys S.A.), 1 part of a polyacrylic acid-based sulfonate salt (SN-Thickener 615, manufactured by San Nopco Ltd.), and 0.5 parts of a mineral oil-based antifoaming agent (NOPTAM 777F, manufactured by San Nopco Ltd.).
  • RESEM Y225 manufactured by Chukyo Yushi Co., Ltd., melting point of polylactic acid: 150°C
  • BARRISURF HX 8.5 parts
  • SN-Thickener 615 manufactured by San Nopco Ltd.
  • NOPTAM 777F mineral oil-based antifoaming agent
  • a hardwood pulp (LBKP) was beaten as a pulp, and this pulp was then mixed with 5.5% of talc, 1.5% of aluminum sulfate (manufactured in-house), 0.55% of a rosin sizing agent (Sizepine G, manufactured by Arakawa Chemical Industries, Ltd.) and 0.5% of a cationized starch powder (GELTRON 18, manufactured by Oji Cornstarch Co., Ltd.) as internal additives, thus yielding a pulp slurry.
  • the blend amount (%) of each component represents a percentage relative to a value of 100% for the mass of the pulp.
  • This pulp slurry was subjected to papermaking so as to achieve a heat seal paper grammage of 50 g/m 2 , thus obtaining a paper substrate.
  • the degree of beating of the pulp was adjusted to achieve a disintegrated freeness of 500 mL for the obtained heat seal paper.
  • the aqueous coating liquid described above was applied to the felt surface of the obtained paper substrate by an on-machine process using a rod metaling size press coater, and the coating liquid was then dried to adhere the heat seal component to one surface of the substrate, thus yielding a heat seal paper.
  • Example 2 With the exception of using titanium oxide instead of talc, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • Example 1 With the exception of altering the blend amount of talc so that the amount of inorganic pigment in the paper substrate satisfied the value shown in Table 1, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • Example 1 With the exception of altering the degree of beating of the pulp so that the disintegrated freeness of the paper substrate satisfied the value shown in Table 1, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • Example 1 With the exception of using the aqueous emulsion of polylactic acid (RESEM Y225, manufactured by Chukyo Yushi Co., Ltd.) alone as the aqueous coating liquid, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • RESEM Y225 aqueous emulsion of polylactic acid
  • Example 1 With the exception of using a mixture of 60 parts of the hardwood pulp (LBKP) and 40 parts of a softwood pulp (NBKP) as the pulp, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • LKP hardwood pulp
  • NNKP softwood pulp
  • An aqueous coating liquid was prepared by mixing 70 parts of a polylactic acid aqueous emulsion (RESEM Y225, manufactured by Chukyo Yushi Co., Ltd., melting point of polylactic acid: 150°C), 28.5 parts of kaolin (BARRISURF HX, manufactured by Imerys S.A.), 1 part of a polyacrylic acid-based sulfonate salt (SN-Thickener 615, manufactured by San Nopco Ltd.), and 0.5 parts of a mineral oil-based antifoaming agent (NOPTAM 777F, manufactured by San Nopco Ltd.). With the exception of using this aqueous coating liquid, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • RESEM Y225 manufactured by Chukyo Yushi Co., Ltd., melting point of polylactic acid: 150°C
  • BARRISURF HX kaolin
  • SN-Thickener 615 manufactured by San Nop
  • Example 1 With the exceptions of altering the degree of beating of the pulp so that the disintegrated freeness of the paper substrate was 280 mL, and adjusting the grammage of the paper substrate to 40 g/m 2 , the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • Example 1 With the exception of using a styrene-butadiene-based latex (LX407-S12, manufactured by Zeon Corporation) instead of the aqueous emulsion of polylactic acid, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • a styrene-butadiene-based latex LX407-S12, manufactured by Zeon Corporation
  • Example 1 With the exceptions of altering the degree of beating of the pulp so that the disintegrated freeness of the paper substrate was 200 mL, and not adding the talc, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • Example 2 With the exception of not adding the talc, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • Example 1 With the exception of altering the blend amount of the talc so that the amount of talc was 25% by mass relative to the mas of the paper substrate, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
  • the grammage of the heat seal paper was measured in accordance with JIS P 8124:2011.
  • the heat seal paper was disintegrated in accordance with JIS P 8220-1, the Canadian standard freeness of the resulting pulp was measured in accordance with JIS P 8121-2:2012, and that value was recorded as the disintegrated freeness.
  • the MD and CD tear strength values (mN) for the heat seal paper were measured in accordance with JIS P 8116:2000, and the geometric mean T of the two values was determined.
  • the MD and CD bending resistance values (mN) for the heat seal paper were measured in accordance with JIS P 8125:2017, and the geometric mean S of the two values was determined.
  • a heat seal tester (TP-701-B, manufactured by Tester Sangyo Co., Ltd.) was used to conduct heat sealing under conditions including 140°C and 0.2 MPa for one second, yielding a test piece.
  • the resulting test piece was left to stand indoors at a temperature of 23 ⁇ 1°C and a humidity of 50% ⁇ 2% for at least four hours. Subsequently, the test piece was cut to a width of 15 mm, a peel tester was used to conduct a T-peel test at a tensile speed of 300 mm/minute, and the maximum load recorded was deemed the heat seal peel strength.
  • aqueous gravure ink ("Surf WH Process Black", manufactured by DIC Corporation) was printed onto the wire surface of the heat seal paper of each example using a gravure printing tester (manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions including a printing pressure of 30 kg/cm and a printing speed of 60 m/min. The printed surface was inspected visually, and the printability was evaluated against the following criteria.
  • bag production was conducted using the heat seal paper from each example, and the state of wrinkling occurrence at the sailor unit of the bag production device (wrinkling during bag production) was evaluated against the following criteria.
  • bag production was conducted using the heat seal paper from each example, and the bag production suitability was evaluated against the following criteria.
  • the bag production suitability indicates the suitability to continuous bag production. Any breakage or other problem resulting in impaired bag performance impacts continuous production.
  • the heat seal papers of Examples 1 to 10 suppressed wrinkling during bag production. Further, the papers of the examples also had satisfactory heat sealing properties and exhibited excellent printability.
  • Comparative Example 1 which used a thermoplastic resin other than the resin I in the heat seal component was inferior in terms of environmental impact.
  • Comparative Examples 2 and 3 which did not contain an inorganic pigment in the paper substrate suffered from significant wrinkling during bag production. Further, the bag production suitability was also inferior.
  • the present invention is able to provide a heat seal paper that is resistant to wrinkling even during pillow processing.

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  • Inorganic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
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Abstract

The heat seal paper according to one embodiment of the present invention is obtained by adhering a heat seal component containing a thermoplastic resin to at least one surface of a paper substrate having pulp as the main component, wherein the thermoplastic resin contains at least one type of resin selected from the group consisting of polylactic acid and polybutylene succinate, the paper substrate contains an inorganic pigment, and the amount of the inorganic pigment is within a range from 1 to 20% by mass relative to the total mass of the paper substrate.

Description

    [Technical Field]
  • The present invention relates to a heat seal paper.
  • Priority is claimed on Japanese Patent Application No. 2023-012730, filed January 31, 2023 , the content of which is incorporated herein by reference.
    • [Background Art]
  • Film-like packaging materials that have been processed into bag-like forms (bag production) are frequently used in packaging for foodstuffs and the like. Heat seal films having a heat seal layer containing a thermoplastic resin formed on at least one surface of a resin substrate are widely used as these packaging materials, but in recent years, heat seal papers having a heat seal layer formed on at least one surface of a paper substrate are also becoming increasingly common (Patent Documents 1 and 2).
    • [Citation List] [Patent Documents
    • [Patent Document 1]
      Japanese Unexamined Patent Application, First Publication No. 2021-188241
    • [Patent Document 2]
      Japanese Unexamined Patent Application, First Publication No. 2022-018160
    [Summary of Invention] [Technical Problem]
  • Because heat seal papers use a paper substrate, their environmental impact is less than that of heat seal films that use a resin substrate.
  • Polylactic acid and polybutylene succinate exhibit excellent biodegradability, and therefore by using these resins for the heat seal layer of a heat seal paper, the environmental impact can be reduced even further.
  • However, heat seal papers that use polylactic acid or polybutylene succinate for the heat seal layer have high rigidity, and therefore tend to be prone to wrinkling during processing, and particularly during bag production in a pillow packaging machine.
  • Pillow packaging is one packaging method employed with film-like packaging materials. In pillow packaging, a roll of the wound packaging material is set in the pillow packaging machine, the packaging material is wound off the roll and transformed into a cylindrical shape using a tool known as a sailor (former), and heat sealing and cutting are then conducted to form a pillow-shape package. If wrinkling occurs during this bag production process, then the external appearance of the package is unsatisfactory.
  • The present invention has an object of providing a heat seal paper that is resistant to wrinkling even during pillow processing.
    • [Solution to Problem]
  • The present invention has the following aspects.
    1. [1] A heat seal paper having a heat seal component containing a thermoplastic resin adhered to at least one surface of a paper substrate having pulp as the main component, wherein
      • the thermoplastic resin contains at least one type of resin selected from the group consisting of polylactic acid and polybutylene succinate,
      • the paper substrate contains an inorganic pigment, and
      • the amount of the inorganic pigment is within a range from 1 to 20% by mass relative to the total mass of the paper substrate.
    2. [2] The heat seal paper according to [1], wherein the inorganic pigment is at least one type of pigment selected from the group consisting of talc, kaolin, calcium carbonate and titanium oxide.
    3. [3] The heat seal paper according to [1] or [2], wherein the amount of the thermoplastic resin is at least 90% by mass relative to the total mass of the heat seal component.
    4. [4] The heat seal paper according to any one of [1] to [3], wherein if the geometric mean of the MD and CD tear strength values (mN) measured in accordance with JIS P 8116:2000 is deemed T, and the geometric mean of the MD and CD bending resistance values (mN) measured in accordance with JIS P 8125-1:2017 is deemed S, then the value represented by T/S is 10 or greater.
    5. [5] The heat seal paper according to any one of [1] to [4], wherein when two surfaces of the heat seal paper having the heat seal component adhered thereto are heat sealed together under conditions including 140°C and 0.2 MPa for one second, and a T-peel test is then conducted at a tensile speed of 300 mm/minute, the peel strength is 2 N/15mm or greater.
    6. [6] The heat seal paper according to any one of [1] to [5], wherein a pulp produced by disintegrating the heat seal paper in accordance with JIS P 8220-1:2012 exhibits a Canadian standard freeness measured in accordance with JIS P 8121-2:2012 of 300 to 600 mL.
    7. [7] The heat seal paper according to any one of [1] to [6], wherein the heat seal paper is used for pillow packaging.
    [Advantageous Effects of Invention]
  • The present invention is able to provide a heat seal paper that is resistant to wrinkling even during pillow processing.
    • [Description of Embodiments]
  • In this description, "MD" means "machine direction". In other words, the direction parallel to the direction of progression when a paper substrate is produced in a paper making machine, also referred to as the longitudinal direction or flow direction. The direction of alignment of the fibers of the paper substrate may also be considered to be MD. In those cases where MD is unclear, the tensile strength may be measured at 22.5 degree intervals, with the direction that exhibits the highest tensile strength being deemed MD.
  • Further, "CD" means "cross direction". In other words, the direction orthogonal to MD, also referred to as the lateral direction.
  • In this description, the expression "to" used to indicate a numerical range means a range that includes the numerical values before and after the "to" as the lower limit and upper limit respectively.
  • The lower limits and upper limits of numerical ranges described in this description may also be combined as desired to create new numerical ranges.
    • <Heat Seal Paper>
  • The heat seal paper according to one embodiment of the present invention has a heat seal component containing a thermoplastic resin adhered to at least one surface of a paper substrate. The paper substrate and the heat seal component are described below in further detail.
  • If the geometric mean of the MD and CD tear strength values (mN) of the heat seal paper is deemed T, and the geometric mean of the MD and CD bending resistance values (mN) is deemed S, then the value represented by T/S is preferably at least 10, more preferably at least 11.5, and even more preferably 13 or greater. There are no particular limitations on the upper limit for T/S, but the value is, for example, typically not more than 50, or 40 or less. The tear strength is measured in accordance with JIS P 8116:2000. The bending resistance is measured in accordance with JIS P 8125-1:2017.
  • As a result of intensive investigation, the inventors of the present invention discovered that the T/S value of a heat seal paper affects the bag production suitability in a pillow packaging machine. T is an indicator of breakage resistance, whereas S is an indicator of hardness. If the value of S is too high (the paper is too hard), then breakage during bag production in a pillow packaging machine is more prevalent, even if T is high. By ensuring that T/S is 10 or greater, the bag production suitability in a pillow packaging machine can be improved, and breakage of the heat seal paper during bag production in the pillow packaging machine can be suppressed.
  • Examples of techniques that can be used to ensure a T/S value of 10 or greater include the techniques below. The disintegrated freeness is described below in further detail.
    • Include 1 to 20% by mass of an inorganic pigment in the heat seal paper.
    • Adjust the disintegrated freeness of the heat seal paper to a value of 300 to 600 mL.
  • In terms of increasing T/S, the geometric mean T of the MD and CD tear strength values (mN) of the heat seal paper is preferably at least 300 mN, more preferably at least 350 mN, and even more preferably 400 mN or greater. There are no particular limitations on the upper limit for T, but the value is, for example, typically not more than 4,000 mN, or 3,000 mN or less.
  • In terms of increasing T/S, the geometric mean S of the MD and CD bending resistance values (mN) of the heat seal paper is preferably not more than 60 mN, more preferably not more than 50 mN, and even more preferably 40 mN or less. There are no particular limitations on the lower limit for S, but the value is, for example, typically at least 5 mN, or 10 mN or greater.
  • When two of the surfaces of the heat seal paper having the heat seal component adhered thereto are heat sealed together under conditions including 140°C and 0.2 MPa for one second, and a T-peel test is then conducted at a tensile speed of 300 mm/minute, the peel strength (hereinafter also referred to as the "heat seal peel strength") is preferably at least 2 N/15mm, more preferably at least 2.4 N/15mm, and even more preferably 2.8 N/15mm or greater. By ensuring that the heat seal peel strength is at least as large as the above lower limit, heat sealing can be conducted favorably during bag production in a pillow packaging machine, meaning superior pillow packaging suitability.
  • There are no particular limitations on the upper limit for the heat seal peel strength, but the value is, for example, typically not more than 30 N/15mm, or 20 N/15mm or less.
  • The heat seal peel strength can be adjusted, for example, by altering the amount of the heat seal component adhered per unit area of the paper, and altering the amount of the thermoplastic resin relative to the total mass of the heat seal component.
  • The amount of the heat seal component adhered per unit area of the heat seal paper, expressed as an amount per single surface, is preferably within a range from 2 to 30 g/m2, more preferably from 3 to 20 g/m2, and even more preferably from 4 to 10 g/m2. Ensuring that the amount adhered of the heat seal component is at least as large as the above lower limit yields superior pillow packaging suitability. Further, by ensuring that the amount adhered of the heat seal component is not more than the above upper limit, blocking and soiling during the production process can be better suppressed.
  • It is thought that in those cases where the amount adhered of the heat seal component falls within the above range, the thickness of the heat seal component adhered to the fibrous surface of the paper substrate is not more than about 4 µm, but there are no particular limitations on this thickness. The thickness of the heat seal component on the fibrous surface of the paper substrate can be ascertained by observing a cross-section of the fibers using a microscope.
  • In a cross-sectional view perpendicular to the plane of the heat seal paper, the heat seal layer composed of the heat seal component can sometimes be seem, but it is thought that this heat seal layer is not always clearly visible.
  • In the heat seal paper, the heat seal component may be adhered to one surface or to both surfaces of the paper substrate. In terms of reducing production costs, the heat seal component is preferably adhered to only one surface of the paper substrate.
  • In the heat seal paper, the heat seal component may be adhered uniformly across the paper substrate, or may be adhered in a non-uniform manner which appears as a dot-like pattern, linear pattern, or mesh-like pattern or the like when viewed from above.
  • A pulp produced by disintegrating the heat seal paper in accordance with JIS P 8220-1 exhibits a Canadian standard freeness (hereinafter also referred to as the "disintegrated freeness") measured in accordance with JIS P 8121-2:2012 that is preferably within a range from 300 to 600 mL, more preferably from 350 to 550 mL, and even more preferably from 400 to 500 mL. Provided the disintegrated freeness of the heat seal paper falls within this range, the tear strength of the heat seal paper tends to be higher.
  • The grammage of the heat seal paper is preferably within a range from 20 to 200 g/m2, more preferably from 35 to 150 g/m2, and even more preferably from 40 to 100 g/m2. Provided the grammage of the heat seal paper is at least as large as the above lower limit, the tear strength of the heat seal paper tends to be higher. Further, provided the grammage of the heat seal paper is not more than the above upper limit, the bending resistance of the heat seal paper tends to be lower.
  • The grammage of the heat seal paper is measured in accordance with JIS P 8124:2011.
  • The thickness of the heat seal paper is preferably within a range from 20 to 300 µm, more preferably from 35 to 220 µm, and even more preferably from 40 to 150 µm. Provided the thickness of the heat seal paper is at least as large as the above lower limit, the tear strength of the heat seal paper tends to be higher. Further, provided the thickness of the heat seal paper is not more than the above upper limit, the bending resistance of the heat seal paper tends to be lower.
  • The thickness of the heat seal paper is measured in accordance with JIS P 8118:2014.
    • (Paper Substrate)
  • The paper substrate contains pulp as the main component. Here, the expression "contains pulp as the main component" means that the amount of pulp relative to the mass of the paper substrate is at least 70% by mass.
  • In one embodiment of the present invention, the paper substrate contains from 1 to 20% by mass of an inorganic pigment. Accordingly, the amount of pulp relative to the mass of the paper substrate is within a range from 80 to 99% by mass. The amount of pulp relative to the mass of the paper substrate is preferably within a range from 85 to 97% by mass, and more preferably from 90 to 95% by mass.
  • The paper substrate may be composed of a typically used paper, and examples include paper substrates containing wood pulp as the main component.
  • Specific examples of the paper substrate include bleached kraft papers, unbleached kraft papers, high-quality papers, cardboards, liner papers, coated papers, single-sided glossy papers, glassine papers, and graphan papers. Among these, in terms of the heat sealing properties of the resulting heat seal paper, a bleached kraft paper, unbleached kraft paper, coated paper, or single-sided glossy paper is preferred.
  • Examples of the pulp include chemical pulps such as leaf bleached kraft pulp (LBKP), northern bleached kraft pulp (NBKP), leaf bleached sulfite pulp (LBSP), and northern bleached sulfite pulp (NBSP). Examples of other pulps include unbleached pulps, semi-bleached pulps and bleached pulps such as stone grand pulp (GP), pressurized stone grand pulp (PGW), refiner grand pulp (RGP), chemi-grand pulp (CGP), thermomechanical pulp (TMP) and chemi-thermomechanical pulp (CTMP). Sulfite pulps and recycled paper pulps may also be used.
  • In terms of enhancing the printability, the pulp preferably contains a hardwood pulp such as a leaf bleached kraft pulp (LBKP) or a leach bleached sulfite pulp (LBSP).
  • The amount of the hardwood pulp relative to the total mass of the pulp is preferably at least 50% by mass, more preferably at least 70% by mass, and may be 100% by mass.
  • In terms of improving the tear strength, the pulp preferably contains a softwood pulp such as a northern bleached kraft pulp (NBKP) or a northern bleached sulfite pulp (NBSP).
  • The amount of the softwood pulp relative to the total mass of the pulp is preferably at least 10% by mass, more preferably at least 20% by mass, and may be 100% by mass.
  • A combination of a hardwood pulp and a softwood pulp may also be used.
  • In those cases where a hardwood pulp and a softwood pulp are combined, then relative to the total mass of the pulp, it is preferable that the amount of the hardwood pulp is within a range from 50 to 90% by mass and the amount of the softwood pulp is within a range from 10 to 50% by mass, and more preferable that the amount of the hardwood pulp is from 70 to 90% by mass and the amount of the softwood pulp is from 10 to 30% by mass.
  • The paper substrate contains an inorganic pigment. By including an inorganic pigment in the paper substrate, the ash content of the paper substrate increases and the tensile modulus of elasticity decreases. The bending resistance of the paper substrate is cubically proportional to the value of tensile modulus of elasticity × thickness. By reducing the tensile modulus of elasticity, the bending resistance of the paper substrate, and therefore the bending resistance of the heat seal paper, can be lowered, meaning wrinkling is less likely to occur, even during pillow processing. Further, the pillow packaging suitability also improves.
  • Examples of the inorganic pigment include talc, kaolin, calcium carbonate, titanium oxide, barium sulfate, calcium sulfate, zinc oxide, silica, silicates, colloidal silica, and satin white. Among these, in terms of economic viability, at least one inorganic pigment selected from the group consisting of talc, kaolin, calcium carbonate and titanium oxide is preferred.
  • The amount of the inorganic pigment relative to the total mass of the paper substrate is typically within a range from 1 to 20% by mass, preferably from 3 to 15% by mass, and even more preferably from 5 to 10% by mass. Provided the amount of the inorganic pigment is at least as large as the above lower limit, the bending resistance can be more easily reduced. Further, provided the amount of the inorganic pigment is not more than the above upper limit, paper powder is unlikely to form.
  • The paper substrate may also contain other internal additives besides the inorganic pigment.
  • Examples of these internal additives include sizing agents, fillers, paper strengthening agents, yield improvers, pH adjusters, freeness improvers, water resistance agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, and pigments (excluding inorganic pigments).
  • If necessary, the paper substrate may also have an optional layer such as a clay coat layer on at least a portion of one surface or both surfaces of the paper substrate. A clay coat layer is used for filling the paper substrate and smoothing the surface of the paper substrate. Examples of the clay include kaolin, talc and mica.
  • The density (bulk density) of the paper substrate is preferably within a range from 0.60 to 1.00 g/cm3, more preferably from 0.65 to 0.95 g/cm3, and even more preferably from 0.70 to 0.90 g/cm3. Provided the density of the paper substrate is at least as large as the above lower limit, excessive leaching of the heat seal component into the paper substrate can be suppressed, and the heat seal peel strength tends to improve. Provided the density of the paper substrate is not more than the above upper limit, the heat seal paper tends not to become hard, and tends to be more resistant to breakage.
  • The density of the paper substrate can be determined by dividing the grammage of the paper substrate by the thickness. The methods used for measuring the grammage and thickness of the paper substrate are the same as the methods used for measuring the grammage and thickness of the heat seal paper.
    • (Heat Seal Component)
  • The heat seal component contains a thermoplastic resin. As a result, the heat seal paper exhibits heat sealing properties within a practical heating temperature range.
  • Further, the thermoplastic resin preferably includes at least one resin selected from the group consisting of polylactic acid and polybutylene succinate (hereinafter, also referred to as "PBS"). In the following description, polylactic acid and PBS are sometimes jointly referred to as the "resin I". The resin I exhibits excellent biodegradability, meaning the heat seal paper has minimal environmental impact.
  • The polylactic acid may be a homopolymer of L-lactic acid, a homopolymer of D-lactic acid, a copolymer of L-lactic acid and D-lactic acid, or a copolymer of L-lactic acid and/or D-lactic acid and another copolymerizable monomer. Examples of monomers that are copolymerizable with L-lactic acid and/or D-lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid.
  • A commercially available product may also be used as the polylactic acid. Examples of commercially available products of polylactic acid include the products LANDY PL-1000 and LANDY PL-3000 (aqueous dispersions of polylactic acid) manufactured by Miyoshi Oil & Fat Co., Ltd., and the product RESEM Y225 (an aqueous dispersion of polylactic acid) manufactured by Chukyo Yushi Co., Ltd.
  • A single type of the resin I may be used alone, or a combination of two or more such resins may be used. In terms of ease of availability, the resin I is preferably a polylactic acid.
  • The amount of the resin I, namely the total amount of polylactic acid and PBS, relative to the total mass of the thermoplastic resin, is preferably at least 50% by mass, more preferably at least 70% by mass, and may be 100% by mass.
  • The thermoplastic resin may also include another thermoplastic resin besides the resin I.
  • Examples of this other thermoplastic resin include biodegradable resins other than the resin I, polyethylene, polypropylene, olefin-unsaturated carboxylic acid copolymers, acrylic resins, ethylene vinyl alcohol, polystyrene resins, polycarbonate resins, polyacetal resins, polyester resins, polyamide, styrene-butadiene latex, polyvinyl alcohol, and polyvinylidene chloride. This other thermoplastic resin may also be a non-petroleum-derived resin. A single other thermoplastic resin may be used alone, or a combination of two or more such resins may be used.
  • Examples of other biodegradable resins include polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), and poly(3-hydroxybutyrate-co-hydroxyhexanoate) (PHBH). One of these other biodegradable resins may be used alone, or a combination of two or more such resins may be used.
  • The olefin-unsaturated carboxylic acid copolymers are copolymers of an olefin and an unsaturated carboxylic acid-based monomer.
  • Examples of the olefin include ethylene and propylene. A single olefin may be used alone, or a combination of two or more olefins may be used.
  • Examples of the unsaturated carboxylic acid-based monomer include unsaturated carboxylic acids, as well as salts and esters of those acids. Specific examples of the unsaturated carboxylic acid-based monomers include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid; alkyl esters of unsaturated polycarboxylic acids having at least one carboxyl group such as itaconic acid monomethyl ester, fumaric acid monobutyl ester, and maleic acid monobutyl ester; and unsaturated sulfonic acid monomers and salts thereof such as acrylamidopropanesulfonic acid, sodium sulfoethyl acrylate, and sodium sulfopropyl methacrylate. A single unsaturated carboxylic acid-based monomer may be used alone, or a combination of two or more such monomers may be used.
  • The olefin-unsaturated carboxylic acid copolymer can be obtained, for example, by subjecting the olefin such as ethylene and the unsaturated carboxylic acid-based monomer to emulsion polymerization.
  • Commercially available products may also be used as the olefin-unsaturated carboxylic acid copolymer. One example of a commercially available olefin-unsaturated carboxylic acid copolymer product is ZAIKTHEN AC (an aqueous dispersion of an ammonium salt of an ethylene-acrylic acid copolymer, acrylic acid copolymerization ratio: 20 mol%).
  • A single olefin-unsaturated carboxylic acid copolymer may be used alone, or a combination of two or more such copolymers may be used.
  • There are no particular limitations on the non-petroleum-derived resins, and all manner of thermoplastic resins may be used. Examples include biomass-derived polyolefins, biomass-derived polyesters, biomass-derived polyamides, biomass-derived polyurethane, and biomass-derived cellulose acetate. The biomass is preferably of plant derivation. Examples include biomass derived from corn and biomass derived from sugar cane. A single non-petroleum-derived resin may be used alone, or a combination of two or more such resins may be used.
  • Examples of the biomass-derived polyolefins include polymers of various olefins such as ethylene and propylene, as well as copolymers of those olefins. Among the various possibilities, biomass-derived polypropylene and biomass-derived polyethylene are preferred, and biomass-derived polyethylene is particularly desirable.
  • Commercially available products may also be used as the biomass-derived polyolefins. Examples of commercially available biomass-derived polyolefin products include SBC818 (a biomass low-density polyethylene) and SGF4950 (a biomass high-density polyethylene) manufactured by Braskem S.A.
  • In a biomass-derived polyester, either one or both of the alcohol unit and the carboxylic acid unit are derived from biomass.
  • Examples of the alcohol include diols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, decanediol, and 2-ethylbutyl-1-propanediol.
  • However the alcohol is in no way limited to the alcohols mentioned above. Further, a single alcohol may be used alone, or a combination of two or more alcohols may be used.
  • Examples of the carboxylic acid include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and derivatives of these acids.
  • Examples of the aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, and phthalic acid. Examples of aromatic dicarboxylic acid derivatives include lower alkyl esters (such as the methyl esters, ethyl esters, propyl esters and butyl esters) of the aromatic dicarboxylic acids.
  • Examples of the aliphatic dicarboxylic acids include chain-like or alicyclic dicarboxylic acids of 2 to 40 carbon atoms. Specific examples include oxalic acid, succinic acid, glutaric acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid, azelaic acid, dodecadicarboxylic acid, and cyclohexanedicarboxylic acid. Examples of aliphatic dicarboxylic acid derivatives include lower alkyl esters (such as the methyl esters, ethyl esters, propyl esters and butyl esters) of the aliphatic dicarboxylic acids. Other derivatives include acid anhydrides of aliphatic dicarboxylic acids such as succinic anhydride.
  • However the carboxylic acid is in no way limited to the carboxylic acids mentioned above. Further, a single carboxylic acid may be used alone, or a combination of two or more carboxylic acids may be used.
  • Commercially available products may also be used as the biomass-derived polyesters. An example of a commercially available biomass-derived polyester products is the product CB-602AB (a bio-polyethylene terephthalate) manufactured by FENC Corporation.
  • In terms of environmental compatibility, the other thermoplastic resin is preferably at least one resin selected from the group consisting of other biodegradable resins and non-petroleum-derived resins.
  • In those cases where the thermoplastic resin has a melting point, the melting point is preferably within a range from 80 to 180°C, more preferably from 100 to 170°C, and even more preferably from 110 to 160°C. Provided the melting point of the thermoplastic resin falls within this range, heat sealing can be conducted favorably during bag production in a pillow packaging machine.
  • The melting point of the thermoplastic resin is measured using a differential scanning calorimeter (DSC). In those cases where the heat seal component contains two or more types of thermoplastic resin, the mass average value measured for the mixture of the plurality of thermoplastic resins is used as the thermoplastic resin melting point.
  • The melting point of a polylactic acid is, for example, within a range from 145 to 180°C. The melting point of PBS is, for example, within a range from 100 to 120°C.
  • The amount of the thermoplastic resin in the heat seal component, relative to the total mass of the heat seal component, is preferably at least 70% by mass, more preferably at least 80% by mass, even more preferably at least 85% by mass, still more preferably at least 90% by mass, and may be 100% by mass. Provided the amount of the thermoplastic resin in the heat seal component is at least as large as the above lower limit, heat sealing can be conducted favorably during bag production in a pillow packaging machine, and the pillow packaging suitability is superior.
  • In those cases where the heat seal component contains one or more components other than the thermoplastic resin, the amount of the thermoplastic resin in the heat seal component relative to the total mass of the heat seal component may be, for example, not more than 99% by mass, not more than 98% by mass, not more than 98.5% by mass, or 97% by mass or less.
  • The heat seal component may also contain a salt of an acrylic acid polymer in order to enhance the adhesive strength of the heat seal paper following heat sealing.
  • Examples of the acrylic acid polymer include polyacrylic acid, acrylic acid-maleic acid copolymers, and acrylic acid-sulfonic acid copolymers. Examples of the salt include sodium salts, potassium salts and ammonium salts.
  • In those cases where the heat seal component contains a salt of an acrylic acid polymer, the amount of the salt of the acrylic acid polymer, relative to the mass of the thermoplastic resin in the heat seal component, is preferably within a range from 0.1 to 3% by mass, more preferably from 0.2 to 2% by mass, and even more preferably from 0.5 to 1.5% by mass. Provided the amount of the acrylic acid polymer salt is at least as large as the above lower limit, favorable heat sealing properties can be more easily achieved. Further, provided the amount of the acrylic acid polymer salt is not more than the above upper limit, an improvement in the heat sealing properties consistent with the amount added can be obtained.
  • If necessary, the heat seal component may also contain any of various auxiliary agents in addition to the thermoplastic resin and the acrylic acid polymer salt. Examples of these auxiliary agents include antifoaming agents, thickeners, polysaccharide thickeners, neutralizing agents, plasticizers, preservatives, pH adjusters, crosslinking agents, anti-blocking agents, lubricants, dyes, and pigments. Examples of the pigments include the inorganic pigments mentioned above. However, the list of possible auxiliary agents is not limited to those mentioned examples.
    • (Production Method for Heat Seal Paper)
  • The heat seal paper can be produced by producing the paper substrate described above, and then adhering the heat seal component described above to at least one surface of the paper substrate.
  • The paper substrate can be produced, for example, by making a paper from a pulp slurry containing the inorganic pigment in a paper making machine, and then drying the thus formed wet paper.
  • There are no particular limitations on the paper making machine. Examples include a Fourdrinier paper machine, gap former paper machine, cylinder paper machine, or short net paper machine. In terms of economic viability, a paper making machine equipped with on-machine coating is preferred.
  • In order to prepare a pulp slurry for the paper making process, the pulp is preferably disintegrated, and a refiner or beater then used to beat the pulp to impart suitable levels of flexibility and fluff to the pulp. There are no particular limitations on the pulp beating method. As mentioned above, the disintegrated freeness of the pulp, which acts as an indicator of the degree of beating, is preferably within a range from 300 to 600 mL, more preferably from 350 to 550 mL, and even more preferably from 400 to 500 mL.
  • The beaten pulp may be mixed with the inorganic pigment and, where necessary, other internal additives such as sizing agents and paper strengthening agents, and subsequently dispersed in water to prepare a pulp slurry with a concentration suitable for paper making.
  • The wet paper obtained using the paper making machine is preferably dried using a multistage cylinder dryer, and air dryer, or a Yankee dryer.
  • One example of the method used for adhering the heat seal component to at least one surface of the paper substrate involves applying a coating liquid containing the heat seal component to at least one surface of the paper substrate, and then conducting drying.
  • The coating liquid is preferably an aqueous dispersion (for example, an aqueous emulsion) containing the thermoplastic resin.
  • In addition to the thermoplastic resin, the coating liquid may also contain other optional components such as a salt of an acrylic acid polymer or one or more auxiliary agents.
  • There are no particular limitations on the method used for applying the coating liquid. Various widely available coating devices may be used. Examples of such coating devices include a blade coater, air knife coater, roll coater, reverse roll coater, bar coater, curtain coater, slot die coater, gravure coater, champlex coater, brush coater, slide bead coater, two-roll size press coater, pond size press coater, rod metaling size press coater, blade metaling size press coater, short-dwell coater, gate roll coater, and nip coater using calendering. In terms of productivity, an on-machine coating device is preferred. This on-machine coating devices is, for example, preferably a blade coater, bar coater, gate roll coater, rod metaling size press coater, blade metaling size press coater, or pond size press coater.
  • The heat seal paper may, if necessary, be subjected to a smoothing treatment. The smoothing treatment is typically conducted either on-machine or off-machine using a smoothing treatment device such as super calender, gloss calender or soft calender. Provided the effects of the present invention are not impaired, the paper substrate may also be subjected to a smoothing treatment prior to application of the coating liquid.
  • The obtained heat seal paper may be wound into a roll form.
  • Subsequently, the two end portions of the roll may be removed using a slitter so as to match the width of the heat seal paper to the width required in the processing equipment of subsequent stages.
  • In the heat seal paper described above, because the paper substrate contains from 1 to 20% by mass of an inorganic pigment, wrinkling is unlikely during pillow processing (bag production in a pillow packaging machine). Further, the heat seal paper exhibits excellent pillow packaging suitability, and is resistant to breakage when subjected to continuous bag production in a pillow packaging machine. The heat sealing properties and printability are also excellent.
  • There are no particular limitations on the applications for the heat seal paper. For example, the heat seal paper can be used as a packaging material in a variety of fields such as paper products, foodstuffs (such as confectionery), pharmaceutical items, electronic components, hygiene products, agricultural materials, and construction materials.
  • When the heat seal paper is used as a packaging material, conventional packaging methods may be used as the packaging method, and examples include pillow packaging, gusset packaging, tube packaging, three-way seal packaging, four-way seal packaging, stick packaging, pouch packaging, and deep-drawn packaging.
  • Because of the effects described above, the heat seal paper is ideal for pillow packaging.
    • [Examples]
  • The present invention is described below in further detail using a series of examples, but the present invention is not limited to the following examples. In the following description, "parts" and "%" indicate "parts by mass" and "% by mass" respectively.
    • <Example 1>
  • An aqueous coating liquid was prepared by mixing 90 parts of a polylactic acid aqueous emulsion (RESEM Y225, manufactured by Chukyo Yushi Co., Ltd., melting point of polylactic acid: 150°C), 8.5 parts of kaolin (BARRISURF HX, manufactured by Imerys S.A.), 1 part of a polyacrylic acid-based sulfonate salt (SN-Thickener 615, manufactured by San Nopco Ltd.), and 0.5 parts of a mineral oil-based antifoaming agent (NOPTAM 777F, manufactured by San Nopco Ltd.).
  • One hundred parts of a hardwood pulp (LBKP) was beaten as a pulp, and this pulp was then mixed with 5.5% of talc, 1.5% of aluminum sulfate (manufactured in-house), 0.55% of a rosin sizing agent (Sizepine G, manufactured by Arakawa Chemical Industries, Ltd.) and 0.5% of a cationized starch powder (GELTRON 18, manufactured by Oji Cornstarch Co., Ltd.) as internal additives, thus yielding a pulp slurry. The blend amount (%) of each component represents a percentage relative to a value of 100% for the mass of the pulp. This pulp slurry was subjected to papermaking so as to achieve a heat seal paper grammage of 50 g/m2, thus obtaining a paper substrate. The degree of beating of the pulp was adjusted to achieve a disintegrated freeness of 500 mL for the obtained heat seal paper.
  • The aqueous coating liquid described above was applied to the felt surface of the obtained paper substrate by an on-machine process using a rod metaling size press coater, and the coating liquid was then dried to adhere the heat seal component to one surface of the substrate, thus yielding a heat seal paper.
    • <Example 2>
  • With the exception of using titanium oxide instead of talc, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Examples 3 and 4>
  • With the exception of altering the blend amount of talc so that the amount of inorganic pigment in the paper substrate satisfied the value shown in Table 1, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Examples 5 and 6>
  • With the exception of altering the degree of beating of the pulp so that the disintegrated freeness of the paper substrate satisfied the value shown in Table 1, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Example 7>
  • With the exception of using the aqueous emulsion of polylactic acid (RESEM Y225, manufactured by Chukyo Yushi Co., Ltd.) alone as the aqueous coating liquid, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Example 8>
  • With the exception of using a mixture of 60 parts of the hardwood pulp (LBKP) and 40 parts of a softwood pulp (NBKP) as the pulp, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Example 9>
  • An aqueous coating liquid was prepared by mixing 70 parts of a polylactic acid aqueous emulsion (RESEM Y225, manufactured by Chukyo Yushi Co., Ltd., melting point of polylactic acid: 150°C), 28.5 parts of kaolin (BARRISURF HX, manufactured by Imerys S.A.), 1 part of a polyacrylic acid-based sulfonate salt (SN-Thickener 615, manufactured by San Nopco Ltd.), and 0.5 parts of a mineral oil-based antifoaming agent (NOPTAM 777F, manufactured by San Nopco Ltd.). With the exception of using this aqueous coating liquid, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Example 10>
  • With the exceptions of altering the degree of beating of the pulp so that the disintegrated freeness of the paper substrate was 280 mL, and adjusting the grammage of the paper substrate to 40 g/m2, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Comparative Example 1>
  • With the exception of using a styrene-butadiene-based latex (LX407-S12, manufactured by Zeon Corporation) instead of the aqueous emulsion of polylactic acid, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Comparative Example 2>
  • With the exceptions of altering the degree of beating of the pulp so that the disintegrated freeness of the paper substrate was 200 mL, and not adding the talc, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Comparative Example 3>
  • With the exception of not adding the talc, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Comparative Example 4>
  • With the exception of altering the blend amount of the talc so that the amount of talc was 25% by mass relative to the mas of the paper substrate, the same method as Example 1 was used to obtain a heat seal paper having a heat seal component adhered to one surface.
    • <Measurements and Evaluations> (Grammage)
  • The grammage of the heat seal paper was measured in accordance with JIS P 8124:2011.
    • (Disintegrated Freeness)
  • The heat seal paper was disintegrated in accordance with JIS P 8220-1, the Canadian standard freeness of the resulting pulp was measured in accordance with JIS P 8121-2:2012, and that value was recorded as the disintegrated freeness.
    • (Tear Strength of Heat Seal Paper)
  • Using an Elmendorf tear tester, the MD and CD tear strength values (mN) for the heat seal paper were measured in accordance with JIS P 8116:2000, and the geometric mean T of the two values was determined.
    • (Bending Resistance of Heat Seal Paper)
  • The MD and CD bending resistance values (mN) for the heat seal paper were measured in accordance with JIS P 8125:2017, and the geometric mean S of the two values was determined.
    • (Heat Seal Peel Strength)
  • For each example, two sheets of the heat seal paper were stacked together with the surfaces having the heat seal component adhered thereto facing each other, and a heat seal tester (TP-701-B, manufactured by Tester Sangyo Co., Ltd.) was used to conduct heat sealing under conditions including 140°C and 0.2 MPa for one second, yielding a test piece. The resulting test piece was left to stand indoors at a temperature of 23±1°C and a humidity of 50%±2% for at least four hours. Subsequently, the test piece was cut to a width of 15 mm, a peel tester was used to conduct a T-peel test at a tensile speed of 300 mm/minute, and the maximum load recorded was deemed the heat seal peel strength.
    • (Printability)
  • An aqueous gravure ink ("Surf WH Process Black", manufactured by DIC Corporation) was printed onto the wire surface of the heat seal paper of each example using a gravure printing tester (manufactured by Kumagai Riki Kogyo Co., Ltd.) under conditions including a printing pressure of 30 kg/cm and a printing speed of 60 m/min. The printed surface was inspected visually, and the printability was evaluated against the following criteria.
    1. A: no missing dots, favorable external appearance
    2. B: missing dots, partially faded
    (Heat Sealing Properties)
  • Using a high-speed horizontal pillow packaging machine FW3410/B (manufactured by Fuji Machinery Co., Ltd.), bag production using the heat seal paper from each example was conducted at a rate of 100 bags/minute, and the heat sealing properties were evaluated against the following criteria.
    1. A: adhesion occurred at a sealing temperature of 150°C, and when the sealed portion was peeled apart, the paper substrate was destroyed (material failure)
    2. B: adhesion occurred at a sealing temperature of 180°C, and when the sealed portion was peeled apart, the paper substrate was destroyed (material failure)
    3. C: adhesion occurred at a sealing temperature of 180°C, but when the sealed portion was peeled apart, the paper substrate was not destroyed (interface peeling or poor adhesion)
    (Wrinkling during Bag Production)
  • Using a high-speed horizontal pillow packaging machine FW3410/B (manufactured by Fuji Machinery Co., Ltd.), bag production was conducted using the heat seal paper from each example, and the state of wrinkling occurrence at the sailor unit of the bag production device (wrinkling during bag production) was evaluated against the following criteria.
    1. A: no wrinkling occurrence
    2. B: some fine wrinkling
    3. C: obvious wrinkling occurrence, impairing the external appearance
    (Bag Production Suitability)
  • Using a high-speed horizontal pillow packaging machine FW3410/B (manufactured by Fuji Machinery Co., Ltd.), bag production was conducted using the heat seal paper from each example, and the bag production suitability was evaluated against the following criteria. The bag production suitability indicates the suitability to continuous bag production. Any breakage or other problem resulting in impaired bag performance impacts continuous production.
    1. A: production possible with no problems
    2. B: bag production rate must be reduced to ensure stable bag production, but production is possible
    3. C: problems such as bag breakage occur, making continuous production problematic
    <Results>
  • The measurement results and evaluation results for each example are shown below in Tables 1 and 2.
  • In Tables 1 and 2, "PLA" indicates polylactic acid. [Table 1]
    Example
    1 2 3 4 5 6 7 8
    Paper substrate Pulp Hardwood pulp parts 100 100 100 100 100 100 100 60
    Softwood pulp parts 0 0 0 0 0 0 0 40
    Inorganic pigment Amount % 5 5 1.5 19 5 5 5 5
    Type - talc titanium oxide talc talc talc talc talc talc
    Density g/cm3 0.90 0.90 0.90 0.92 0.90 0.90 0.90 0.90
    Heat seal component Adhered amount g/cm2 4 4 4 4 4 4 4 4
    Amount of thermoplastic resin % 90 90 90 90 90 90 100 90
    Heat seal component - PLA PLA PLA PLA PLA PLA PLA PLA
    Heat seal paper Grammage g/m2 50 50 50 50 50 50 50 50
    Disintegrated freeness mL 500 500 500 500 320 590 500 500
    Tear strength T mN 350 320 370 300 300 420 350 1050
    Bending resistance S mN 30 24 36 18 27 36 30 54
    T/S - 11.7 13.3 10.3 16.7 11.1 11.7 11.7 19.4
    Heat seal peel strength N/15mm 3.0 2.8 3.3 2.4 3.5 3.3 4.0 3.5
    Evaluations Printability - A A A A A A A B
    Heat sealing properties - A A A A A A A A
    Wrinkling during bag production - A A A A A A A B
    Bag production suitability - A A B A B A A A
    [Table 2]
    Example Comparative Example
    9 10 1 2 3 4
    Paper substrate Pulp Hardwood pulp parts 100 100 100 100 100 100
    Softwood pulp parts 0 0 0 0 0 0
    Inorganic pigment Amount % 5 5 5 0 0 25
    Type - talc talc talc - - talc
    Density g/cm3 0.90 0.90 0.90 0.90 0.90 0.93
    Heat seal component Adhered amount g/cm2 4 4 4 4 4 4
    Amount of thermoplastic resin % 70 90 90 90 90 90
    Heat seal component - PLA PLA latex PLA PLA PLA
    Heat seal paper Grammage g/m2 50 40 50 50 50 50
    Disintegrated freeness mL 500 280 500 200 500 500
    Tear strength T mN 360 220 420 500 470 240
    Bending resistance S mN 33 24 22 72 65 16
    T/S - 10.9 9.2 19.1 6.9 7.2 15.0
    Heat seal peel strength N/15mm 2.1 3.0 2.7 3.3 3.4 2.5
    Evaluations Printability - A A A A A A
    Heat sealing properties - B A B A A C
    Wrinkling during bag production - A A A C C A
    Bag production suitability - B C A C C C
  • The heat seal papers of Examples 1 to 10 suppressed wrinkling during bag production. Further, the papers of the examples also had satisfactory heat sealing properties and exhibited excellent printability. The heat seal papers of Examples 1 to 9 which had disintegrated freeness values within a range from 300 to 600 mL also exhibited superior bag production suitability.
  • In contrast, Comparative Example 1 which used a thermoplastic resin other than the resin I in the heat seal component was inferior in terms of environmental impact.
  • Comparative Examples 2 and 3 which did not contain an inorganic pigment in the paper substrate suffered from significant wrinkling during bag production. Further, the bag production suitability was also inferior.
  • Comparative Example 4 in which the amount of the inorganic pigment in the paper substrate was 25% by mass exhibited poor heat sealing properties and was unsuitable as a heat seal paper. Further, the bag production suitability was also inferior.
    • [Industrial Applicability]
  • The present invention is able to provide a heat seal paper that is resistant to wrinkling even during pillow processing.

Claims (7)

  1. A heat seal paper having a heat seal component containing a thermoplastic resin adhered to at least one surface of a paper substrate having a pulp as the main component, wherein
    the thermoplastic resin comprises at least one type of resin selected from the group consisting of polylactic acid and polybutylene succinate,
    the paper substrate contains an inorganic pigment, and
    an amount of the inorganic pigment is within a range from 1 to 20% by mass relative to a total mass of the paper substrate.
  2. The heat seal paper according to Claim 1, wherein the inorganic pigment is at least one type of pigment selected from the group consisting of talc, kaolin, calcium carbonate and titanium oxide.
  3. The heat seal paper according to Claim 1 or 2, wherein an amount of the thermoplastic resin is at least 90% by mass relative to a total mass of the heat seal component.
  4. The heat seal paper according to Claim 1 or 2, wherein if a geometric mean of MD and CD tear strength values (mN) measured in accordance with JIS P 8116:2000 is deemed T, and a geometric mean of MD and CD bending resistance values (mN) measured in accordance with JIS P 8125-1:2017 is deemed S, then a value represented by T/S is 10 or greater.
  5. The heat seal paper according to Claim 1 or 2, wherein when two surfaces of the heat seal paper having the heat seal component adhered thereto are heat sealed together under conditions including 140°C and 0.2 MPa for one second, and a T-peel test is then conducted at a tensile speed of 300 mm/minute, a peel strength is 2 N/15mm or greater.
  6. The heat seal paper according to Claim 1 or 2, wherein a pulp produced by disintegrating the heat seal paper in accordance with JIS P 8220-1:2012 exhibits a Canadian standard freeness measured in accordance with JIS P 8121-2:2012 of 300 to 600 mL.
  7. The heat seal paper according to Claim 1 or 2, wherein the heat seal paper is used for pillow packaging.
EP24750119.0A 2023-01-31 2024-01-25 Heat seal paper Pending EP4660371A1 (en)

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JP2021188241A (en) 2020-05-27 2021-12-13 王子ホールディングス株式会社 Heat seal paper and packaging bag
JP2022018160A (en) 2020-07-15 2022-01-27 日本製紙株式会社 Heat seal paper
JP2023012730A (en) 2021-07-14 2023-01-26 グローリー株式会社 Paper sheet receiver

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CN116669947A (en) * 2021-01-15 2023-08-29 王子控股株式会社 Evaporated paper and its manufacturing method
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JP2022018160A (en) 2020-07-15 2022-01-27 日本製紙株式会社 Heat seal paper
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