JP7532039B2 - Packaging paper and its manufacturing method - Google Patents

Description

The present invention relates to packaging paper and its manufacturing method.

Resin sheet materials such as films and dry nonwoven fabrics are commonly used as packaging materials for various items. In recent years, from the perspective of environmental protection, there has been a demand for packaging materials that use less resin material, and packaging materials in which part of the resin material is replaced with pulp have been proposed. For example, Patent Document 1 describes a packaging material made by papermaking a material in which pulp fibers are blended with polyester fibers, which are heat-fusible fibers.

Patent No. 3991209

Packaging materials are required to have the flexibility and heat sealability of resin films, as well as strength and printability. In the packaging material described in Patent Document 1, the amount of resin used is reduced by incorporating pulp fibers, but compared to resin films and dry nonwoven fabrics, the flexibility, heat sealability, strength and printability are inferior, leaving room for improvement.

Therefore, the present invention aims to provide a packaging paper that has flexibility and heat sealability, excellent strength and printability, and uses a reduced amount of resin, and a method for manufacturing the same.

The wrapping paper according to the present invention is made of a fiber raw material containing pulp and polyolefin fibers, the blending amount of pulp is 50% by mass or more of the fiber raw material and the blending amount of polyolefin fibers is 20 to 50% by mass of the fiber raw material, the density is 0.30 to 0.65 g/ ^cm3 , the basis weight is 20.0 to 100.0 g/m2 ^, the tensile strength is 0.5 kN/m or more in the longitudinal direction and 0.1 kN/m or more in the transverse direction, the softness in the machine direction is 300 to 1200 mN/100 mm, the softness in the transverse direction is 10 to 350 mN/100 mm, and the Beck smoothness according to JIS P 8119 is 20 to 150 seconds.

In addition, the method for producing packaging paper according to the present invention comprises making a fiber raw material containing pulp and polyolefin fibers, followed by calendering, the calendering processing conditions being a linear pressure of 50 kg/cm or more and 350 kg/cm or less , and a heating temperature of 50°C or more and 160°C or less, the amount of pulp blended being 50% by mass or more of the fiber raw material, and the amount of polyolefin fiber blended being 20 to 50% by mass of the fiber raw material, the density being 0.30 to 0.65 g/ ^cm3 , the basis weight being 20.0 to ^100.0 g/m2, the tensile strength being 0.5 kN/m or more in the longitudinal direction and 0.1 kN/m or more in the transverse direction, and the Beck smoothness according to JIS P 8119 being 20 to 150 seconds.

The present invention provides a packaging paper that is flexible and heat-sealable, has excellent strength and printability, and uses a reduced amount of resin, and a method for producing the same.

The wrapping paper according to the embodiment is a mixed paper made from a fiber raw material containing pulp and polyolefin fibers. From the standpoint of flexibility, the wrapping paper according to the embodiment is preferably a single-layer wet-processed mixed paper, but may be made of two or more layers of laminated mixed paper.

(pulp)
As the pulp, for example, virgin pulp, recycled paper pulp, a combination of these pulps, etc. can be used.

Examples of virgin pulp include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), semi-bleached hardwood kraft pulp (LSBKP), semi-bleached softwood kraft pulp (NSBKP), hardwood sulfite pulp, and softwood sulfite pulp; and mechanical pulps (MP) such as stone ground pulp (SGP), pressed stone ground pulp (TGP), chemi-ground pulp (CGP), groundwood pulp (GP), and thermomechanical pulp (TMP), which may be used alone or in combination.

Examples of waste paper pulp that can be used include disintegrated waste paper pulp, disintegrated and deinked waste paper pulp (DIP), and disintegrated, deinked and bleached waste paper pulp, which are produced from, for example, brown waste paper, kraft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, cardboard waste paper, white waste paper, Kent waste paper, imitation waste paper, and land tax waste paper, and can be used alone or in combination.

The amount of pulp used is 50% or more by mass of the total amount of fiber raw materials. By using 50% or more by mass of pulp, the amount of resin used can be reduced, resulting in a wrapping paper with a reduced burden on the environment.

(Polyolefin fiber)
As the polyolefin fiber, a sheath-core composite fiber in which the core and sheath are made of a polyolefin resin can be preferably used. The sheath-core composite fiber is a fiber having a core-sheath structure. As the polyolefin fiber, for example, a sheath-core composite fiber in which the core material is a polypropylene resin and the sheath material is a polyethylene resin or a polypropylene resin, or a sheath-core composite fiber in which the core and sheath material is a polypropylene resin can be used.

The melting point of the core of the sheath-core composite fiber is preferably 130°C or higher and 160°C or lower, and the melting point of the sheath is preferably 110°C or higher and 155°C or lower. By having the melting points of the sheath and core of the sheath-core composite fiber within these ranges, the adhesive strength between the fibers due to heating in the calendaring process is improved, and the tensile strength of the packaging paper can be improved.

The amount of polyolefin fiber blended is 20-50% by mass of the total amount of fiber raw material. If the amount of polyolefin fiber blended is within this range, the wrapping paper can be given the same flexibility and heat sealability as a resin film.

(Other fibers)
The fiber raw material may further contain other fibers in addition to the pulp and polyolefin fibers. Examples of the other fibers that can be used include unstretched polyester fibers, stretched polyester fibers, and core-sheath type composite fibers in which the core is a polyester fiber.

Unstretched polyester fibers refer to filaments of unstretched yarns that have been spun. The polyester resin that constitutes unstretched polyester fibers is basically a polycondensation product of polycarboxylic acid and polyalcohol. Specific examples of polyester resins include polyethylene terephthalate, polyethylene naphthalate, polytributylene terephthalate, polybutylene naphthalate, polytrimethylene terephthalate, polylactic acid, polyhydroxybutyrate, polycaprolactone, and polybutylene succinate. Examples of polylactic acid include condensation products of lactic acid units of either L-lactic acid or D-lactic acid, or mixtures of these condensations. Among these, polyethylene terephthalate is preferred.

The softening point of the unstretched polyester fiber is preferably 110°C or higher and 140°C or lower. The crystallinity of the unstretched polyester fiber is preferably 10% or lower. By having the softening point and crystallinity of the unstretched polyester fiber within these ranges, the adhesive strength and heat seal strength of the pulp and polyolefin fiber can be improved.

The fineness of the unstretched polyester fibers is preferably 1.0 to 2.2 dtex, and the average fiber length of the unstretched polyester fibers is preferably 3.0 to 10.0 mm.

Stretched polyester fibers are filaments that are made by stretching unstretched spun yarns at several times the normal speed in a stretching machine and then winding them up. The polyester resins that make up stretched polyester fibers can be those listed for unstretched polyester fibers. By blending stretched polyester fibers with the fiber raw material, the tensile strength of the packaging paper can be improved.

The melting point of the stretched polyester fiber is preferably 200°C or higher and 260°C or lower. The crystallinity of the stretched polyester fiber is preferably 10% or higher and 40% or lower. By having the softening point and crystallinity of the stretched polyester fiber within these ranges, the tensile strength of the wrapping paper can be improved.

The drawn polyester fiber may contain additives such as titanium oxide, and may be modified with a modifying group to impart functionality such as improved moisture absorption. The cross-sectional shape of the single fiber unit of the drawn polyester fiber is not particularly limited, and various irregular cross-section yarns such as round, triangular, octave, flat, and Y-shaped can be used. In addition, false-twisted yarns obtained by subjecting raw yarns to false-twist processing may also be used as drawn polyester fibers.

The fineness of the stretched polyester fibers is preferably 0.1 to 2.2 dtex, and the average fiber length of the stretched polyester fibers is preferably 3.0 to 10.0 mm.

As polyester-based core-sheath composite fibers, core-sheath composite fibers having a core made of a polyester resin such as polyethylene terephthalate and a sheath made of a polyolefin resin such as polyethylene or polypropylene, or core-sheath composite fibers having a core made of a polyester resin such as polyethylene terephthalate and a sheath made of a polyester resin such as low-melting polyethylene terephthalate, can be used. Core-sheath polyester fibers have heat-fusible properties. Therefore, by containing core-sheath polyester fibers in the fiber raw material, the adhesive strength between the pulp and polyolefin fibers in the wrapping paper after papermaking can be improved, and the heat-fusible properties of the core-sheath polyester fibers can improve the heat seal strength of the wrapping paper, making this particularly preferable.

The amount of other fibers, such as unstretched polyester fibers, stretched polyester fibers, and polyester-sheath core composite fibers, can be set appropriately, provided that the amount of pulp and polyolefin fibers falls within the above range.

Additional additives such as pigments, surfactants, waxes, sizing agents, fillers, rust inhibitors, conductive agents, defoamers, dispersants, viscosity regulators, flocculants, coagulants, paper strength improving agents, retention improvers, paper powder shedding prevention agents, bulking agents, thickeners, etc. can be added to the fiber raw materials.

(Production method)
The packaging paper according to the present embodiment can be manufactured by wet-laid papermaking of the above-mentioned fiber raw material, drying the obtained wet paper, and then calendering. Calendering is a process in which the dried mixed paper is heated and pressurized using a calender roll, for example, a combination of a cast steel metal roll and a resin elastic roll, to improve the smoothness of the paper surface or to fuse chemical fibers including polyolefin fibers.

The surface temperature (heating temperature) of the metal roll in the calendaring process is preferably 50°C or higher and 160°C or lower. If the surface temperature of the metal roll is less than 50°C, the smoothness or strength of the surface of the packaging paper may be insufficient. Also, if the surface temperature of the metal roll exceeds 160°C, the packaging paper will stick to the metal roll, leading to reduced production efficiency.

The linear pressure of the metal roll in the calendaring process is preferably 50 kg/cm or more and 350 kg/cm or less. From the viewpoint of improving the surface smoothness and strength of the packaging paper, the linear pressure in the calendaring process is more preferably 120 kg/cm or more and 180 kg/cm or less. If the linear pressure in the calendaring process is less than 50 kg/cm, the surface smoothness or strength of the packaging paper may be insufficient. Also, if the linear pressure in the calendaring process exceeds 350 kg/cm, the paper becomes hard and lacks flexibility.

(density)
The density of the wrapping paper according to this embodiment is 0.30 to 0.65 g/ ^cm3 . Here, the density is a value measured in accordance with "Paper and paperboard -- Test methods for thickness, density and specific volume" JIS P8118 (2014). If the density of the wrapping paper is less than 0.30, the tensile strength and smoothness of the wrapping paper may be insufficient. Also, if the density of the wrapping paper exceeds 0.65, the flexibility of the wrapping paper may be insufficient.

(Beck smoothness)
The wrapping paper according to this embodiment has a Beck smoothness of 20 to 150 seconds. Here, the Beck smoothness is a value measured in accordance with JIS P8119 (1988) "Paper and cardboard - Smoothness test method using a Beck smoothness tester." If the wrapping paper has a Beck smoothness of less than 20 seconds, the printability is significantly poor. If the wrapping paper has a Beck smoothness of more than 150 seconds, the paper surface becomes hard and lacks flexibility.

(grammage)
The basis weight (US basis weight) of the wrapping paper according to this embodiment is preferably 14.0 to 100.0 g/ ^m2 , and more preferably 20.0 to 80.0 g/ ^m2 . Here, the basis weight of the wrapping paper is a value measured in accordance with "Paper and paperboard -- Method of measuring basis weight" JIS P 8124 (2011). If the basis weight is less than 10.0 g/ ^m2 , the strength required for wrapping paper may not be obtained. On the other hand, if the basis weight exceeds 100.0 g/ ^m2 , the thickness of the wrapping paper may increase, and the flexibility of the wrapping paper may become insufficient.

(Tensile strength)
The tensile strength is a value measured in accordance with "Paper and paperboard -- Test methods for tensile properties" JIS P 8113 (2006), the longitudinal tensile strength is a value measured in the machine direction (MD direction) of the packaging paper, which is the flow (progress) direction relative to the papermaking machine, and the transverse tensile strength is a value measured in the transverse direction (CD direction) of the packaging paper, which is the direction perpendicular to the papermaking machine. When the tensile strength of the packaging paper is 0.5 kN/m or more in the machine direction and 0.1 kN/m or more in the transverse direction, the packaging paper can have the strength required for packaging materials.

(Softness)
The softness in the machine direction of the wrapping paper according to this embodiment is preferably 300 to 1200 mN/100 mm, and the softness in the width direction is preferably 100 to 350 mN/100 mm. Here, the machine direction refers to the direction along the papermaking flow of the papermaking machine, and the width direction refers to the direction perpendicular to the papermaking flow of the papermaking machine. It is known that the softness of a single sheet of thin paper such as tissue paper is 5 to 10 mN/100 mm, and the inventors have found that by making the conversion value of the softness of a laminate of several hundred sheets of this thin paper and the softness of the wrapping paper close to a numerical value, a wrapping body with a good feel can be obtained when wrapping a laminate of thin paper. Therefore, the wrapping paper according to this embodiment is suitable for packaging a laminate of multiple thin papers such as tissue paper.

The softness of the packaging paper was measured using the handle-o-meter method in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 34 (2000) Paper - Softness Test Method. However, the test piece was 100 mm x 100 mm in size, with the smoothest surface facing outward and a clearance of 6.25 mm. Measurements were taken 10 times in each of the machine direction and width direction, and the average value was expressed in units of mN/100 mm.

As described above, the wrapping paper according to this embodiment has excellent flexibility and heat sealability by using pulp as the main fiber and containing a predetermined amount of polyolefin-based fibers. In addition, the wrapping paper according to this embodiment has excellent strength and printability by having density and Beck smoothness within the above-mentioned ranges. Therefore, according to this embodiment, a wrapping paper and a manufacturing method thereof that have flexibility and heat sealability, excellent strength and printability, and reduced resin usage can be provided. By having the above characteristics, the wrapping paper according to this embodiment can be suitably used for packaging bags in which the contents are individually packaged in units of several hundred sheets of thin paper such as tissue. The embodiment of the packaging bag can be used for caramel-type packaging, vertical/horizontal pillow packaging, shrink packaging, etc., but due to the characteristics of this wrapping paper, it can be suitably used for caramel-type packaging.

Below, we will explain specific examples of packaging paper according to the present invention. However, the present invention is not limited to these examples.

The fiber raw materials shown in Table 1 were wet-laid and calendered using a pair of metal rolls under the processing conditions shown in Table 2 to obtain packaging papers according to Examples 1 to 7 and Comparative Examples 1 to 6. In Table 1, "PP/HDPE" indicates a core-sheath type composite fiber in which the core is polypropylene and the sheath is high-density polyethylene, "PP/PP" indicates a core-sheath type composite fiber in which the core and sheath are polypropylene, and "PET (core-sheath)" indicates a core-sheath type composite fiber in which the core is polyethylene terephthalate and the sheath is low-melting polyethylene terephthalate. Table 2 shows the processing conditions (temperature and linear pressure) in the calendering process, as well as the measured values of the basis weight, thickness, density, tensile strength, softness, Beck smoothness, and heat seal strength of the obtained packaging papers. In addition, "-" in the table indicates that the results have not been evaluated.

The evaluation values shown in Table 2 were measured as follows.
(1) Basis weight was measured in accordance with JIS P 8124 (2011).
(2) The thickness was measured in accordance with JIS P 8118 (2014) at a measurement pressure of 50 kPa.
(3) Density was measured in accordance with JIS P 8118 (2014).
It was calculated from the measured values.
(4) Tensile strength was measured in accordance with JIS P 8113 (2006). (5) Softness was measured according to the handle-o-meter method in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 34 (2000) Paper - Softness Test Method. However, the test piece was 100 mm x 100 mm in size, the smooth surface was the front side, and the clearance was 6.25 mm. Measurements were made 10 times each in the machine direction and the width direction, and the average value was used as the evaluation value, expressed in mN/100 mm units.
(6) Smoothness (Beck smoothness) was measured in accordance with JIS P 8119 (1988) using a highly smooth surface as the test surface.
(7) Heat seal strength was measured in accordance with JIS Z 0238 (1998) using a sample obtained by heat sealing the wrapping paper under conditions of 160°C and a pressure of 0.5 kg/ ^cm2 . From the viewpoint of the flexibility and usage form of the wrapping paper, it is preferably 20 N/m or more and 350 N/m or less.

As shown in Table 2, the wrapping papers of Examples 1 to 7 used fiber raw materials containing the materials in the ratios shown in Table 1, and the softness was within the preferred range. The wrapping papers of Examples 1 to 7 also had tensile strength, smoothness, and heat sealability that were within the preferred ranges. Thus, the wrapping papers of Examples 1 to 7 had both flexibility and heat sealability, and were excellent in strength and printability. Furthermore, the wrapping papers of Examples 1 to 7 contained 50% or more pulp, and the amount of resin used was reduced.

In contrast, the wrapping paper in Comparative Example 1 was made from 100% pulp fiber material, so it had no heat sealability, the measured softness value was outside the preferred range, and it had insufficient flexibility.

The wrapping paper of Comparative Example 2 had too much polyolefin fiber, so the measured softness was below the preferred range and did not provide adequate flexibility. In addition, the measured smoothness was below the preferred range and printability was insufficient. The wrapping paper of Comparative Example 2 had a pulp content of less than 50%, which is undesirable from the perspective of reducing the resin content.

The wrapping paper of Comparative Example 3 did not have the necessary heat sealability for wrapping paper because the blending ratio of polyolefin-based fibers was too low. In Comparative Example 3, the measured softness value exceeded the preferred range, and the flexibility of the wrapping paper was insufficient.

The wrapping paper of Comparative Example 4 did not contain polyolefin fibers in the raw fiber, and therefore had insufficient heat seal strength. In Comparative Example 4, the softness exceeded the preferred range, and flexibility was also insufficient.

The wrapping paper of Comparative Example 5 did not contain polyolefin fibers in the raw fiber, and therefore had insufficient heat seal strength. In addition, Comparative Example 5 had a smoothness below the preferred range, and was unsuitable for printing.

The wrapping paper of Comparative Example 6 had a basis weight below the preferred range, and therefore had tensile strength and smoothness below the preferred range, making it unfavorable in terms of strength and printability.

The present invention can be used in packaging materials for packaging various items and in methods for manufacturing the same.

Claims (3)

A wrapping paper made of a fiber raw material containing pulp and polyolefin fiber,
The blending amount of the pulp is 50% by mass or more of the fiber raw material, and the blending amount of the polyolefin fiber is 20 to 50% by mass of the fiber raw material,
The density is 0.30 to 0.65 g/ ^cm3 ,
The basis weight is 20.0 to 100.0 g/ ^m2 ,
The tensile strength is 0.5 kN/m or more in the longitudinal direction and 0.1 kN/m or more in the transverse direction;
The softness in the machine direction is 300 to 1200 mN/100 mm, and the softness in the width direction is 10 to 350 mN/100 mm;
A packaging paper having a Beck smoothness according to JIS P 8119 of 20 to 150 seconds. The packaging paper according to claim 1 is a single-layer mixed paper made by wet-processing the fiber raw material. A method for manufacturing packaging paper, comprising the steps of:
A fiber raw material containing pulp and polyolefin fibers is made into paper and then calendered.
The calendering treatment is carried out under a linear pressure condition of 50 kg/cm or more and 350 kg/cm or less ,
The heating temperature of the calendering process is 50° C. or higher and 160° C. or lower;
A method for producing wrapping paper, wherein the blending amount of the pulp is 50% by mass or more of the fiber raw material, and the blending amount of the polyolefin fiber is 20 to 50% by mass of the fiber raw material, the density is 0.30 to 0.65 g/ ^cm3 , the basis weight is 20.0 to 100.0 g/ ^m2 , the tensile strength is 0.5 kN/m or more in the longitudinal direction and 0.1 kN/m or more in the transverse direction, and the Beck smoothness according to JIS P 8119 is 20 to 150 seconds.