JP7572191B2 - Packaging paper and laminated sheet using the same - Google Patents

Description

The present invention relates to packaging paper and laminated sheets using the same, and in particular to packaging paper that has strength and flexibility suitable for pillow packaging and laminated sheets using the same.

Pillow packaging is widely used to package various items such as food and daily necessities. Resin films with a sealant layer are generally used for pillow packaging (see, for example, Patent Document 1). In recent years, there has been a demand to replace some packaging materials with paper in order to reduce environmental impact and improve recyclability.

JP 2018-58599 A JP 2007-125722 A

When pillow packaging is performed, the bag making machine applies a pulling force in the flow direction and a tearing force in the lateral direction to the packaging material. When pillow packaging is performed with a packaging material consisting of laminated paper and resin layers, if the paper is not strong enough, problems can arise in that the paper will tear, or the paper will be unable to follow the movement of the resin layer and partially peel off from the resin layer. In addition, if the paper is hard (rigid) due to a high basis weight, etc., the paper may break when folded into a cylindrical shape, causing streaky wrinkles.

Patent Document 2 describes how the structure of the sealant film can be improved to improve the ease of opening pillow packaging and lamination with a paper substrate, but there is no mention of improving the strength of the paper substrate itself, leaving room for improvement.

Therefore, the present invention aims to provide a wrapping paper that has the conflicting properties of strength and flexibility suitable for pillow packaging, and a laminated sheet using the same.

The wrapping paper according to the present invention is made by making a raw material pulp containing two kinds of kraft pulp having different freeness, the two kinds of kraft pulp including 50 to 90 mass% of a first softwood bleached kraft pulp having a Canadian standard freeness of 340 to 480 ml according to JIS P 8121 (2012) and 10 to 50 mass% of a second softwood bleached kraft pulp having a Canadian standard freeness of 640 to 660 ml according to JIS P 8121, the wrapping paper having a basis weight of 12 to 53 g/ ^m2 according to JIS P 8124 (2011), a longitudinal tensile strength of 2.0 kN/m or more according to JIS P 8113 (2006), and a transverse tear strength of 150 mN or more according to JIS P 8116 (2000), and a tensile strength of 100 kN/m or more according to JAPAN TAPPI No. The softness in the longitudinal direction measured in accordance with JIS H34 is 100 mN/100 mm or more and 2,000 mN/100 mm or less, and the softness in the transverse direction is 50 mN/ 100 mm or more and 1,000 mN/100 mm or less , and the sheet is used as a laminated sheet for vertical pillow packaging .

The laminated sheet according to the present invention is made by papermaking a raw material pulp containing two kinds of kraft pulp having different freeness, the two kinds of kraft pulp include 50 to 90 mass% of a first softwood bleached kraft pulp having a Canadian standard freeness of 340 to 480 ml according to JIS P 8121 (2012) and 10 to 50 mass% of a second softwood bleached kraft pulp having a Canadian standard freeness of 640 to 660 ml according to JIS P 8121, the basis weight according to JIS P 8124 (2011) is 12 to 53 g / m ² , the longitudinal tensile strength according to JIS P 8113 (2006) is 2.0 kN / m or more, and the transverse tear strength according to JIS P 8116 (2000) is 150 mN or more, and the laminated sheet according to JAPAN TAPPI No. The laminated sheet for vertical pillow packaging comprises wrapping paper having a longitudinal softness of 100 mN/100 mm or more and 2,000 mN/100 mm or less and a transverse softness of 50 mN/100 mm or more and 1,000 mN/100 mm or less, as measured in accordance with JIS H11134, and a sealant layer laminated on one side of the wrapping paper .

The present invention provides packaging paper with strength and flexibility suitable for pillow packaging, and a laminated sheet using the same.

The packaging paper in this embodiment is made by papermaking from raw pulp that contains two types of kraft pulp with different freeness.

(Kraft pulp)
As the kraft pulp, for example, 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), sulfite hardwood pulp, and sulfite softwood pulp; mechanical pulps (MP) such as stone ground pulp (SGP), pressurized stone ground pulp (TGP), chemi-ground pulp (CGP), groundwood pulp (GP), and thermomechanical pulp (TMP) can be used alone or in combination. Among these, it is preferable to use unbleached softwood kraft pulp (NUKP) or bleached softwood kraft pulp (NBKP). Softwood kraft pulp has a longer fiber length than hardwood kraft pulp, and therefore has the advantage of increasing the bond between fibers and improving paper strength. In addition, NBKP is more preferred in the present invention because sufficient lignin is dissolved by bleaching and the fibers swell to form flexible paper.

In addition to the above kraft pulp, non-wood pulp or waste paper pulp may be blended with the raw material pulp. Examples of non-wood pulp that can be used include kenaf pulp, abaca pulp, cotton linter pulp, straw pulp, bamboo pulp, and hemp pulp. 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 paper, magazine paper, newspaper paper, flyer paper, office paper, cardboard paper, white waste paper, Kent waste paper, imitation waste paper, and land certificate waste paper, and can be used alone or in combination. When a pulp other than kraft pulp is blended with the raw material pulp, the amount of kraft pulp blended is preferably 60 to 100% by mass of the total amount of pulp.

The two types of kraft pulp having different freeness preferably include a first kraft pulp having a Canadian Standard Freeness (CSF) of 340 to 480 ml according to JIS P 8121 (2012) and a second kraft pulp having a Canadian Standard Freeness of 640 to 660 ml according to JIS P 8121 (2012). The first kraft pulp having a relatively low freeness plays a role in ensuring the elongation of the packaging paper, and the second kraft pulp having a relatively high freeness plays a role in ensuring the tensile strength and tear strength. Even within the above range, the freeness of the first kraft pulp is more preferably 645 to 655 ml. Also, the freeness of the second kraft pulp is more preferably 345 to 355 ml.

The blending ratios of the first and second kraft pulps are preferably 50-90% and 10-50% by mass, respectively, of the total mass of both, and more preferably 60-80% and 20-40% by mass. If the blending ratio of the first kraft pulp is less than 50% by mass, it is difficult to ensure sufficient elongation, and the wrapping paper is prone to tearing when used for pillow packaging. If the blending ratio of the first kraft pulp exceeds 90% by mass, the blending ratio of the second softwood kraft pulp becomes too small, resulting in a decrease in tensile strength and tear strength. By blending the first kraft pulp within the range of 50-90% by mass, the proportion of short fibers increases, which increases the density of the paper and allows the paper thickness to be reduced.

The raw pulp may contain additives such as pigments, surfactants, wax, sizing agents, fillers, rust inhibitors, conductive agents, defoamers, dispersants, viscosity regulators, flocculants, coagulants, paper strength improvers, yield improvers, paper powder shedding prevention agents, bulking agents, and thickeners.

Among these additives, it is preferable to add a sizing agent to the raw pulp. By adding a sizing agent, the water absorption of the packaging paper can be controlled and bleeding of water and ink can be suppressed, improving the printability of the packaging paper.

Examples of sizing agents include rosin-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), various emulsion sizing agents, starch, etc. Among these, rosin-based sizing agents are preferred because of their great effect of imparting water resistance and improving the smoothness of the glossy surface. Examples of such rosin-based sizing agents include modified rosin, reinforced rosin, saponified rosin, and emulsion rosin.

The amount of sizing agent is preferably 0.1% to 1.5% by mass relative to 100 parts by mass of the total amount of raw pulp. If the amount of sizing agent is less than 0.1% by mass, the effect of suppressing the water absorption of the packaging paper will not be sufficient, and printability will decrease. If the amount of sizing agent is more than 1.5% by mass, the water repellency of the packaging paper will be too high, and printability may decrease.

It is also preferable to blend a wet strength agent into the raw pulp. The wrapping paper according to this embodiment is used as an outer packaging material, and therefore may absorb moisture from the environment while in the wrapping paper state or while in the package containing the contents, or may become wet while in the package state. However, by increasing the wet strength, it is possible to prevent the wrapping paper from breaking, etc. Also, it is possible to suppress a decrease in paper strength when printing on the wrapping paper with water-based ink.

Examples of wet strength agents include epichlorohydrin-based resins such as polyamide-epichlorohydrin resin, urea resins, acid colloid-melamine resins, and thermally crosslinked polyacrylamides (thermally crosslinked PAM).

(grammage)
The basis weight (US basis weight) of the wrapping paper according to this embodiment is 12.0 to 53.0 g/ ^m2 . The basis weight is a value measured in accordance with "Paper and paperboard -- Method of measuring basis weight" JIS P8124 (2011). If the basis weight is less than 12.0 g/ ^m2 , the wrapping paper will not have enough strength and will not be suitable for pillow packaging. Also, if the basis weight exceeds 53.0 g/ ^m2 , the rigidity will be too high, and wrapping paper of any configuration will break, reducing the processing suitability when performing pillow packaging.

(Tear strength)
The tear strength in the lateral direction of the packaging paper according to this embodiment is 150 mN or more. The tear strength is a value measured in accordance with "Paper and cardboard-Testing method for tear strength" JIS P 8116 (2000), and the tear strength in the lateral direction is a value measured with the direction of a pre-inserted cut being the lateral direction (CD direction) of the packaging paper. A twisting force is applied to the packaging paper during pillow packaging, but if the tear strength of the packaging paper is 150 mN or more, the pillow packaging can be performed without tearing. There is no particular limit to the upper limit of the tear strength in the lateral direction of the packaging paper, but it is, for example, 1,000 mN or less.

(Tensile strength)
The wrapping paper according to this embodiment has a longitudinal tensile strength of 2.0 kN/m or more. The tensile strength is a value measured in accordance with "Paper and paperboard -- Test method for tear strength" JIS P 8113 (2006). If the wrapping paper has a longitudinal tensile strength of 2.0 kN/m or more, pillow packaging can be performed without breakage. There is no particular upper limit to the longitudinal tensile strength of the wrapping paper, but it is, for example, 12.0 kN/m or less.

(Softness)
The softness of the wrapping paper according to this embodiment is 100 mN/100 mm to 2000 mN/100 mm in the longitudinal direction and 50 mN/100 mm to 1,000 mN/100 mm in the transverse direction. If the upper limit of each value is exceeded, the paper becomes too stiff and loses its conformability, resulting in creases when folded. If the lower limit of each value is exceeded, the paper becomes too soft, leading to wrinkles and breakage of the sheet.

(Beck smoothness)
It is preferable that the Beck smoothness of one side of the packaging paper according to this embodiment is 40 seconds or less. If there is a side with a Beck smoothness of 40 seconds or less, a sealant or a laminated film having a sealant can be laminated on this side to form a laminated sheet. When a sealant or a laminated film is laminated on a side with a Beck smoothness of 40 seconds or less, the adhesion between the packaging paper and the sealant or laminated film is excellent, and interlayer peeling can be suppressed when used for pillow packaging. In addition, it is preferable that the difference between the front and back of the Beck smoothness is 20 seconds or more. If the difference between the front and back of the Beck smoothness is 20 seconds or more, the printability of the other side of the packaging paper (the side opposite to the side on which the sealant is laminated) is improved.

(Weight average fiber length)
The weight average fiber length of the wrapping paper according to this embodiment is preferably 1.0 to 5.0 mm. This range allows the strength of the wrapping paper and the index of stiffness and softness, such as softness, to be optimized. This unique effect is thought to be related to the fiber length distribution obtained by containing two types of kraft pulp with different freeness.

(Production method)
The wrapping paper according to the present embodiment can be manufactured by wet-laid papermaking of a raw material containing pulp raw material and various additives added as necessary, and drying the wet-laid paper. The dried paper is preferably dried using a Yankee dryer. When dried using a Yankee dryer, the wrapping paper is obtained as a one-sided glossy paper with one glossy side. By laminating a sealant or a laminated film containing a sealant on the non-glossy side, the adhesion between the wrapping paper and the sealant or laminated film is excellent, and the glossy side is smooth, so that the printability required for the wrapping paper is excellent. By performing a calendaring process after the drying process, the smoothness of the wrapping paper can be increased and the printability can be further improved. However, the calendaring process is not necessarily required and may be omitted.

The calendaring process can be carried out using calendaring equipment such as a hard nip calendar, soft calendar, or super calendar. The drying process can also be carried out using calendaring equipment that combines a metal roll and an elastic roll. The metal roll is a calendar roll made of cast steel that is heated. The elastic roll is a calendar roll on the non-heated side that is made of materials such as cotton, epoxy resin, special polyester, and aramid. The Shore hardness of the elastic roll is preferably D80 or more and D95 or less. If it is less than D80, the nip width during pressure application is wide and the pressure is dispersed, which may result in insufficient adhesion between the fibers. If it exceeds D95, the elastic roll itself tends to retain heat, which may make it difficult to peel off the lamination wrapping paper, resulting in a poor appearance.

The linear pressure in the calendaring process is preferably 50 kg/cm or more and 350 kg/cm or less. From the viewpoint of improving the uniformity of the thickness of the wrapping paper for lamination, 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 adhesion between the fibers may be insufficient. Furthermore, if it exceeds 350 kg/cm, the bonds between the fibers of the wrapping paper may be destroyed, the tear strength may decrease significantly, and the appearance may become poor.

The surface temperature (heating temperature) of the metal roll in the calendaring process is preferably 90°C or higher and 200°C or lower. From the viewpoint of preventing a decrease in the tensile strength of the packaging paper, it is more preferable that the surface temperature of the metal roll in the calendaring process is 100°C or higher and 160°C or lower.

(Laminated sheet)
The laminated sheet according to the present invention is obtained by laminating a sealant on one side of the above-mentioned packaging paper. This laminated sheet can be used as a packaging material for pillow packaging. The sealant can be laminated by extrusion lamination of a thermoplastic resin or dry lamination of a film. It is also possible to apply a resin-based coating chemical that imparts heat sealability. The material that can be used for the laminated sheet is not particularly limited, and LDPE, LLDPE, HDPE, CPP, OPP, EVA, PET, PVC, PVDC, EVOH, OPS (polystyrene), PVA, CNY (unstretched nylon), ONY (stretched nylon), cellophane, PBS, PLA, VM (vapor-deposited) PET, VMCPP, VMOPP, etc. can be used in a single layer or in a laminated state. The laminated sheet may have one or more paper layers or resin layers other than the packaging paper and the sealant. In particular, it is preferable to provide a vapor-deposited film from the viewpoint of barrier properties and heat seal strength. Furthermore, when laminating to a film (extrusion, dry lamination, coating, etc.), laminating to the non-glossy side of one-sided glossy paper increases the interlayer strength, so it is preferable to use one-sided glossy paper with a difference in smoothness between the front and back.

As described above, the packaging paper according to this embodiment has both vertical tensile strength and horizontal tear strength, and is flexible (conformable). When used in pillow packaging, the packaging paper is less likely to break, tear, delaminate, or develop creases, making it ideal for use as a paper layer in a laminated sheet for pillow packaging.

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

Raw pulp containing the pulp shown in Table 1 was fed to a papermaking machine and wet-laid, and the wet-laid paper was dried in a Yankee dryer to produce the packaging paper of Examples 1 to 4 and Comparative Example 1. A laminate film of VMCPP or VMPET and LLDPE was dry-laminated to the non-glossy side of the produced packaging paper via a dry lamination adhesive to produce a heat-sealable laminate.

Table 2 shows the measured values of basis weight, thickness, density, tensile strength, tensile elongation, tear strength, average fiber length, Beck smoothness (front, back, front/back difference), and softness of the packaging paper of the examples and comparative examples. Table 3 also shows the type of film laminated to the packaging paper and the lamination method, as well as the evaluation results of the processing suitability when the laminate produced was used for vertical pillow packaging.

The evaluation values in Tables 2 and 3 were measured as follows.
(1) Basis weight was measured in accordance with JIS P 8124 (2011).
(2) The thickness and density were measured in accordance with JIS P 8118 (2014).
(3) Tensile strength was measured in accordance with JIS P 8113 (2006).
(4) Tensile elongation was measured in accordance with JIS P 8113 (2006).
(5) Tear strength was measured in accordance with JIS P 8116 (2000) with a pre-inserted cut aligned in the horizontal direction (CD) of the packaging paper.
(6) Average fiber length (weight average) was measured in accordance with JIS P 8226.
(7) Beck smoothness was measured in accordance with JIS P 8119 (1998).
(8) Softness was measured in accordance with JAPAN TAPPI No. 34.
(9) Processing suitability: The adhesion to the sealant layer and the presence or absence of breakage or tearing were confirmed by visually inspecting the package obtained in vertical pillow packaging.
◯: The sealant layer was not peeled off or lifted, nor was it broken or torn, and the laminate sheet was excellent.
Δ: There is no peeling, lifting, or breakage or rupture of the sealant layer, but wrinkles and creases are noticeable, but the laminate sheet can be used.
×: The sealant layer peeled off or floated, or was torn or broken, and the laminate sheet could not be used.

The wrapping paper in Examples 1 to 4 was made from a raw pulp blend of two types of kraft pulp with different freeness, and the basis weight, tensile strength (vertical and horizontal directions), and softness (vertical and horizontal directions) were all within appropriate ranges, the difference in smoothness between the front and back sides was also within appropriate ranges, and the wrapping paper had the strength and adhesion to the sealant layer required.

In contrast, the wrapping paper of Comparative Example 1 had a difference in smoothness between the front and back sides that was outside the range, and although it had the strength required of wrapping paper, laminating a sealant layer reduced its processing suitability.

The present invention can be used for packaging materials for pillow packaging.

Claims (9)

The paper is made by making a raw pulp containing two kinds of kraft pulp having different freeness,
The two types of kraft pulp include 50 to 90% by mass of a first softwood bleached kraft pulp having a Canadian standard freeness of 340 to 480 ml according to JIS P 8121 (2012) and 10 to 50% by mass of a second softwood bleached kraft pulp having a Canadian standard freeness of 640 to 660 ml according to JIS P 8121;
The basis weight according to JIS P 8124 (2011) is 12 to 53 g/ ^m2 ,
The longitudinal tensile strength according to JIS P 8113 (2006) is 2.0 kN / m or more,
The transverse tear strength according to JIS P 8116 (2000) is 150 mN or more ,
The softness in the longitudinal direction measured in accordance with JAPAN TAPPI No. 34 is 100 mN/100 mm or more and 2,000 mN/100 mm or less, and the softness in the transverse direction is 50 mN/ 100 mm or more and 1,000 mN/100 mm or less ,
Packaging paper used as a laminated sheet for vertical pillow packaging . The wrapping paper according to claim 1, in which the Beck smoothness of one side is 40 seconds or less. Basis weight: 40-53g/m ² The wrapping paper according to claim 1 or 2, The wrapping paper according to any one of claims 1 to 3, having a tensile strength in the machine direction of 4.93 kN/m or more. The wrapping paper according to any one of claims 1 to 4, having a tear strength in the transverse direction of 268 mN or more. The wrapping paper according to any one of claims 1 to 5, having a tensile elongation in the machine direction of more than 3.6%. The wrapping paper according to any one of claims 1 to 6 , wherein the average fiber length (weight average) is 1.0 to 5.0 mm. The packaging paper according to any one of claims 1 to 7 , wherein the raw pulp contains a sizing agent. The paper is made by making a raw pulp containing two kinds of kraft pulp having different freeness,
The two types of kraft pulp include 50 to 90% by mass of a first softwood bleached kraft pulp having a Canadian standard freeness of 340 to 480 ml according to JIS P 8121 (2012) and 10 to 50% by mass of a second softwood bleached kraft pulp having a Canadian standard freeness of 640 to 660 ml according to JIS P 8121;
The basis weight according to JIS P 8124 (2011) is 12 to 53 g/ ^m2 ,
The longitudinal tensile strength according to JIS P 8113 (2006) is 2.0 kN / m or more,
The transverse tear strength according to JIS P 8116 (2000) is 150 mN or more,
A wrapping paper having a longitudinal softness of 100 mN/100 mm or more and 2,000 mN/100 mm or less and a transverse softness of 50 mN/100 mm or more and 1,000 mN/100 mm or less, as measured in accordance with JAPAN TAPPI No. 34;
A laminated sheet for vertical pillow packaging, comprising the packaging paper and a sealant layer laminated on one side thereof.