CN115847986A

CN115847986A - Paper layer, method for producing same, composite sheet for packaging, and packaging container

Info

Publication number: CN115847986A
Application number: CN202211493658.1A
Authority: CN
Inventors: 宋强; 朱向阳; 邹义龙
Original assignee: Kangmeibao Suzhou Co ltd
Current assignee: Kangmeibao Suzhou Co ltd
Priority date: 2022-11-25
Filing date: 2022-11-25
Publication date: 2023-03-28

Abstract

The invention provides a paper layer, a manufacturing method thereof, a composite sheet for packaging and a packaging container. The paper layer comprises a first layer, a second layer and an intermediate layer positioned between the first layer and the second layer which are arranged in a stacked manner in the thickness direction of the paper layer, wherein the first layer, the intermediate layer and the second layer respectively comprise wood chemical pulp, the wood chemical pulp comprises first fiber chemical pulp with first fibers and second fiber chemical pulp with second fibers, and the fiber length of the first fibers is greater than that of the second fibers; wherein a content of the first fiber chemical pulp of at least one of the second layer and the first layer is higher than a content of the first fiber chemical pulp of the intermediate layer. The paper layer can reduce or even eliminate the bag leakage phenomenon of the packaging container and improve the quality of the packaged product.

Description

Paper layer, method for producing same, composite sheet for packaging, and packaging container

Technical Field

The invention relates to the field of packaging, in particular to a paper layer of a composite sheet for packaging, a manufacturing method of the paper layer, the composite sheet for packaging and a packaging container.

Background

Typically, the packaging sheet used to form the packaging container is formed from a plurality of layers of laminate materials including, but not limited to: paper layers for support, barrier layers for water and oxygen blocking, pattern layers for printing, encapsulation layers for sealing, etc.

In the process of forming the packaging container, the packaging sheet is firstly folded along a predetermined crease line to form a packaging sleeve with two open ends; then, sealing one end opening to form the top of the packaging container and filling through the other end opening; after the filling is finished, the other end of the bottle is sealed, and finally the packaging container filled with the contents is formed. If the performance of the packaging sheet is poor, the formed packaging container is easy to leak liquid (or called as a bag leakage phenomenon), and the quality of the packaged product is affected.

Disclosure of Invention

The embodiment of the invention provides a paper layer of a composite sheet for packaging, a manufacturing method thereof, the composite sheet for packaging and a packaging container, which can reduce or even eliminate the bag leakage phenomenon of the packaging container and improve the quality of a packaged product.

According to a first aspect of the present invention, there is provided a paper layer of a composite sheet for packaging, the paper layer including, in a thickness direction thereof, a first layer, a second layer, and an intermediate layer between the first layer and the second layer, the first layer, the intermediate layer, and the second layer each including a wood chemical pulp including a first fiber chemical pulp having first fibers and a second fiber chemical pulp having second fibers, the first fibers having a fiber length greater than a fiber length of the second fibers; wherein a content of the first fiber chemical pulp of at least one of the second layer and the first layer is higher than a content of the first fiber chemical pulp of the intermediate layer.

In at least some embodiments, the first fibers are softwood fibers and the first fiber chemical pulp is kraft softwood chemical pulp; the content of the kraft conidial pulp of at least one of the second layer and the first layer is higher than the content of the kraft conidial pulp of the intermediate layer.

In at least some embodiments, the second layer has a higher content of kraft softwood chemical pulp than the middle layer; and the mass percentage of the sulfate needle-leaved chemical pulp in the second layer is more than or equal to 70 percent of the second layer.

In at least some embodiments, the sulfate softwood chemical pulp included in the second layer is greater than or equal to 85% by mass of the second layer.

In at least some embodiments, the sulfate softwood chemical pulp included in the second layer comprises 100% by mass of the second layer.

In at least some embodiments, the first layer has a higher content of kraft conifer chemical pulp than the middle layer; and the sulfate coniferous chemical pulp in the first layer accounts for more than or equal to 70 percent of the mass of the first layer.

In at least some embodiments, the first layer has a content of kraft softwood chemical pulp equal to the content of kraft softwood chemical pulp of the second layer.

In at least some embodiments, the kraft softwood chemical pulp in the first layer comprises 75% to 85% by weight of the first layer; the sulfate needle-leaved chemical pulp in the second layer accounts for 75-85% of the second layer by mass.

In at least some embodiments, the first layer has a lower content of kraft softwood chemical pulp than the second layer.

In at least some embodiments, the kraft softwood chemical pulp in the first layer comprises 75% to 85% by weight of the first layer; the sulfate needle-leaved chemical pulp in the second layer accounts for 95-100% of the second layer by mass.

In at least some embodiments, the grammage of the at least one of the second layer and the first layer is 19% to 30% of the total grammage of the paper layer.

In at least some embodiments, the second fiber is hardwood fiber and the second fiber chemical pulp is sulfate hardwood chemical pulp; the second fiber chemical pulp is present in an amount lower than the first fiber chemical pulp in each of the first layer, the intermediate layer, and the second layer.

In at least some embodiments, the middle layer further comprises wood mechanical pulp or wood mechanochemical pulp; the wood mechanical pulp and the wood mechanochemical pulp are absent from both the second layer and the first layer.

In at least some embodiments, the middle layer further comprises the wood mechanical pulp; the wood mechanical pulp comprises a second fiber mechanical pulp having second fibers; the second fiber is hardwood fiber, and the second fiber mechanical pulp is hardwood mechanical pulp.

In at least some embodiments, the hardwood mechanical pulp in the middle layer comprises 40% to 50% by weight of the middle layer.

In at least some embodiments, the hardwood mechanical pulp in the middle layer comprises 43% to 48% by weight of the middle layer.

In at least some embodiments, the paper layer of the composite packaging sheet further comprises: a coating layer disposed on top of the first layer in a thickness direction of the paper layer and on a side opposite to the intermediate layer, wherein the coating layer is configured to have a printed pattern.

In at least some embodiments, the coating comprises an inorganic non-metallic material.

In at least some embodiments, the inorganic non-metallic material comprises china clay.

In at least some embodiments, the grammage of the coating is 6% to 9% of the total grammage of the paper layer.

In at least some embodiments, the coating has a thickness of 4% to 5% of the total thickness of the paper layer.

According to a second aspect of the present invention, there is provided a composite sheet for packaging comprising the aforementioned paper layer.

In at least some embodiments, the composite packaging sheet includes an inner surface and an outer surface opposite in a thickness direction thereof, a first one of the paper layers being disposed adjacent the outer surface, a second one of the paper layers being disposed adjacent the inner surface, the composite packaging sheet further including: and a sealing layer which is arranged in a manner of being laminated with the second layer of the paper layer and is positioned on the opposite side of the middle layer in the thickness direction of the paper layer, wherein the sealing layer is configured to seal the composite sheet for packaging under the action of heat activation or ultrasonic activation.

According to a third aspect of the present invention, there is provided a packaging container comprising the aforementioned composite sheet for packaging.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a paper layer of a composite sheet for packaging, comprising: forming a paper layer; wherein the forming the paper layer comprises: forming a first layer, a second layer, and an intermediate layer between the first layer and the second layer, wherein the first layer, the intermediate layer, and the second layer each comprise a wood chemical pulp comprising a first fiber chemical pulp having first fibers and a second fiber chemical pulp having second fibers, the first fibers having a fiber length greater than a fiber length of the second fibers; wherein a content of the first fiber chemical pulp of at least one of the second layer and the first layer is higher than a content of the first fiber chemical pulp of the intermediate layer.

In at least some embodiments, the forming a first layer, a second layer, and an intermediate layer between the first layer and the second layer comprises: providing wet paper pulp, and adding starch and/or dry strength agent into the wet paper pulp; and applying the wet pulp to a forming device and drying.

In at least some embodiments, only dry strength agent is added into the wet pulp, and the dosage of the dry strength agent is 5-10 kg/t.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly described below, and it is apparent that the drawings in the following description only relate to some embodiments of the present invention and are not limiting on the present invention.

Fig. 1 is a photograph of the top appearance of a packaging container.

Fig. 1A isbase:Sub>A cross-sectional photograph taken along linebase:Sub>A-base:Sub>A of fig. 1.

Fig. 2 is a photograph of the appearance of the top ear flap of another packaging container.

Fig. 2A is a partial photograph of the inner surface of the ear flap of fig. 2.

Fig. 2B is an enlarged partial photograph of the inner surface of the middle ear flap of fig. 2A.

Fig. 3 is a schematic plan view of a composite sheet for packaging according to an embodiment of the present invention.

Fig. 3A is a schematic cross-sectional view taken along line B-B of fig. 3.

Fig. 4 is a schematic view of the structure of a packaging sleeve according to an embodiment of the present invention.

Fig. 5 is a schematic structural view of a packaging container according to an embodiment of the present invention.

Fig. 5A is a schematic cross-sectional view taken along line C-C of fig. 5.

Fig. 6 is another cross-sectional view taken along line B-B of fig. 3.

Fig. 7 shows a method for manufacturing a paper layer of a composite sheet for packaging according to an embodiment of the present invention.

Fig. 8 is a photograph of a cross-section of a top seal of a packaging container according to an embodiment of the invention.

Fig. 9 is a photograph of a cross-section of a top seal of a packaging container according to another embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without inventive step, are within the scope of protection of the invention.

Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by the first person of ordinary skill in the art to which this invention belongs. The use of "first," "second," and similar terms in the description and claims of the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The word "comprise" or "comprises", and the like, means that the element or item listed before "comprises" or "comprising" covers the element or item listed after "comprising" or "comprises" and its equivalents, and does not exclude other elements or items. The terms "connected" or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "upper", "lower", "left", "right", and the like are used merely to indicate relative positional relationships, which may also change accordingly when the absolute position of the object being described changes.

The packaging sheet is formed from a number of laminate layers, of which a paper layer, usually serving as a carrier layer for other material layers, provides structural stability to the packaging container. The paper layer is a sheet-like composite layer produced by depositing a suspension of suitably treated (e.g. pulped) animal or vegetable fibres onto a forming device and drying it. There are a variety of parameters used to characterize the properties of paper layers, including but not limited to: grammage, thickness, density, dust degree, color difference, porosity, tensile strength, breaking strength, folding strength, stiffness, roughness, smoothness, air permeability, water absorption, ink absorbency, brightness, internal bond strength, water content, and the like.

The inventors of the present application have found, through intensive studies, that the problem of a missing package of a packaging container is mainly determined by the properties of the paper layer. Among these performance parameters of the paper layer, the bending strength is strongly associated with the problem of missing packages. When layering appears in the paper layer, the bending strength of the paper layer can be reduced, and the problem of bag leakage is more likely to occur.

Fig. 1 isbase:Sub>A photograph showing the top appearance ofbase:Sub>A packaging container, and fig. 1A isbase:Sub>A photograph showingbase:Sub>A cross section taken along linebase:Sub>A-base:Sub>A of fig. 1. The inventors have found that in a packaging container having a top-leakage package, the top seal portion thereof usually has an uneven surface, and the foaming phenomenon shown in fig. 1 appears in appearance. The foaming phenomenon occurs because delamination occurs in the paper layers 11 and 12 laminated to each other at the foaming sites (as shown in fig. 1A). This delamination results in a reduced bending strength of the

paper layer

11 or 12 itself, which makes it easier for a breakout to occur at the seal.

Fig. 2 is an external view photograph of a top ear flap of another packaging container, fig. 2A is a partial photograph of an inner surface of the ear flap of fig. 2, and fig. 2B is a partial enlarged photograph of the inner surface of the ear flap of fig. 2A. Through the research of the inventor, when the bending strength of the paper layer is lower, the bag leakage is easier to occur at the ear wing, because the packaging sheet is folded at the ear wing for a plurality of times, and the performance requirement on the paper layer is higher. For example, as can be seen from fig. 2B, due to the low bending strength of the paper layer, the packaging container is ruptured on the inner surface of the ear flap 13, resulting in the ear flap 13 being leaky.

In order to solve at least one of the above problems, an embodiment of the present invention provides a paper layer of a composite sheet for packaging, the paper layer including, in a thickness direction thereof, a first layer, a second layer, and an intermediate layer between the first layer and the second layer, the first layer and the second layer being disposed in a stacked manner. The first layer, the middle layer, and the second layer each comprise wood chemical pulp comprising a first fiber chemical pulp having first fibers and a second fiber chemical pulp having second fibers, the first fibers having a fiber length greater than a fiber length of the second fibers. The first fiber chemical pulp content of at least one of the second layer and the first layer is higher than the first fiber chemical pulp content of the middle layer.

In the paper layer of the composite sheet for packaging provided by the embodiment of the invention, the content of the first fiber chemical pulp in at least one of the second layer and the first layer is increased to be higher than that of the first fiber chemical pulp in the middle layer, so that the bending strength of the paper layer is improved. On one hand, the product quality of the packaging container can be improved, and even if the packaging sheet is folded for multiple times, the bag leakage phenomenon can not occur; on the other hand, the packaging container can have a smoother surface at the sealing position, thereby improving the aesthetic property of the packaging product.

Fig. 3 is a schematic plan view of a composite sheet for packaging according to an embodiment of the present invention. Fig. 3A is a schematic cross-sectional view taken along line B-B of fig. 3. Fig. 4 is a schematic view of the structure of a packaging sleeve according to an embodiment of the present invention. Fig. 5 is a schematic structural view of a packaging container according to an embodiment of the present invention.

As shown in fig. 3, the composite sheet 1 for packaging according to the embodiment of the present invention includes a crease line pattern including a plurality of intersecting crease lines, such as

crease lines

901 and 902. When the ends of the composite sheet for packaging 1 on the left and right sides are folded along a plurality of crease lines and bonded to each other, a packaging sleeve as shown in fig. 4 can be formed. For purposes of simplicity, only a portion of the crease lines are shown in FIG. 1, it being understood that embodiments of the present invention are not limited to the crease line pattern shown in FIG. 1.

As shown in FIG. 4, the embodiment of the present invention provides a packaging sleeve having a sleeve-like structure comprising a top opening 9A and a bottom opening 9B disposed opposite to each other. Before filling, one of the top opening 9A and the bottom opening 9B may be sealed, filling may be performed through the other opening, and then the other opening may be sealed to form the packaging container with contents shown in fig. 5. In embodiments of the present invention, the contents may be food or industrial products, including but not limited to liquids, solids, and mixtures thereof.

As shown in fig. 3A, the composite sheet for packaging 1 includes a paper layer 100 and a sealing layer 200. The sealing layer 200 is arranged in a layer with the paper layer 100 such that when sealing the top opening 9A and the bottom opening 9B of the packaging sleeve, the sealing layer 200 can be heated to effect adhesion.

As shown in fig. 3A, in the thickness direction D of the paper layer 100, the paper layer 100 includes an outer layer 10 (i.e., a first layer), an inner layer 30 (i.e., a second layer) and an intermediate layer 20 between the outer layer 10 and the inner layer 30. For example, the paper layer 100 comprises a first side S1 and a second side S2 in the thickness direction D, the first side S1 being the side of the paper layer 100 facing the outside of the packaging container 9, and the second side S2 being the side of the paper layer 100 facing the inside of the packaging container 9 (i.e. facing the contents). The outer layer 10 is for example located on a first side S1 of the paper layer 100 and the inner layer 30 is for example located on a second side S2 of the paper layer 100. The intermediate layer 20 is sandwiched between the outer layer 10 and the inner layer 30.

As shown in fig. 3A, the composite sheet for packaging 1 includes an outer surface 1A and an inner surface 1B opposed in a thickness direction D thereof. For example, the outer layer 10 of the paper layer 100 is disposed adjacent to the outer surface 1A, and the inner layer 30 of the paper layer 100 is disposed adjacent to the inner surface 1B.

In at least some embodiments, the sealing layer 200 may be located on at least one of the first side S1 and the second side S2 of the paper layer 100. For example, as shown in fig. 3A, the sealing layer 200 is located on the second side S2 of the paper layer 100 in the thickness direction D of the paper layer 100 and is laminated with the inner layer 30 of the paper layer 100. That is, the sealing layer 200 and the intermediate layer 20 are respectively located on opposite sides of the inner layer 30 in the thickness direction D.

It is understood that in other embodiments of the present invention, the sealing layer 200 may be located on the first side S1 of the paper layer 100, or may also be located on the first side S1 and the second side S2 of the paper layer 100, which is not limited by the present invention.

Fig. 5A is a schematic cross-sectional view taken along line C-C of fig. 5. As shown in fig. 5, the packaging container 9 includes a top portion 91 and a bottom portion 92, the top portion 91 being obtained by sealing the top opening 9A, and the bottom portion 92 being obtained by sealing the bottom opening 9A. Crease line 901 defines the top perimeter of packaging container 9 and crease line 902 defines the bottom perimeter of packaging container 9.

When the top opening 9A is sealed, the composite sheet for packaging 1 on both opposite sides of the top opening 9A is bonded to each other, as shown in fig. 5A, wherein two sealing layers 200 are disposed to be attached to each other, and then the two sealing layers 200 are heat-activated or ultrasonically activated to be melted, thereby achieving sealing of the top opening 9A. The sealing of the bottom opening 9B is performed in the same manner as described above and will not be repeated here.

In at least some embodiments, the outer layer 10, the middle layer 20, and the inner layer 30 each comprise wood chemical pulp. That is, the outer layer 10, the middle layer 20 and the inner layer 30 have the same wood chemical pulp.

Generally, pulp can be divided into wood mechanical pulp, wood chemical pulp and wood chemical mechanical pulp, which are obtained by different process techniques. Mechanical wood pulp is made by mechanical pulping, for example, by pressing wood segments lengthwise against a wet, coarse, uniformly rotating grindstone to separate fibers from the wood segments, screening and concentrating the separated fibers to make pulp. The mechanical pulp of wood has the characteristics of low density, high bulk, low price and the like. Chemical pulping of wood is produced by chemical pulping, for example, by immersing wood chips in an aqueous solution of a suitable chemical and cooking the wood chips at elevated temperature and pressure to dissolve out the lignin from the wood chips and obtain intact cellulose. The chemical pulp for wood has the characteristics of low bulk, high cost and the like. Wood chemi-mechanical pulp is produced by a semi-chemical pulping process combining chemical and mechanical processes, for example, by partially softening or cooking wood chips with chemicals and then mechanically gelatinizing the chips.

In at least some embodiments, the wood chemical pulp in the outer layer 10, the middle layer 20, and the inner layer 30 includes a first fiber chemical pulp having first fibers and a second fiber chemical pulp having second fibers, the first fibers having a fiber length greater than the second fibers

For example, the first fibers are softwood fibers and the second fibers are hardwood fibers. The softwood fibers have a fiber length greater than the hardwood fibers. In one example, softwood fibers have a length of 2.5 to 4 millimeters and a width of 41 to 55 microns with an aspect ratio of less than 70, while hardwood fibers have a length of about 1 millimeter and a shorter width of 60 times less than their length.

For example, softwood includes, but is not limited to, masson pine, larch, red pine, spruce, and the like, and hardwood includes, but is not limited to, birch, poplar, basswood, eucalyptus, maple, and the like. The needle-leaved wood has a tight tissue structure, so that the pulp has good quality, high lignin content and low pentosan content, fibers are not easy to absorb water and swell, and pulping is difficult. The tissue structure of the broad-leaved wood has lower lignin content than that of the needle-leaved wood, but has high pentosan content, so the beating is easy.

In the embodiment of the invention, the outer layer 10, the middle layer 20 and the inner layer 30 are made of wood chemical pulp with two different fiber lengths, so that the pulping difficulty of paper pulp is reduced, the good quality of pulp can be ensured, and the manufactured paper layer is not easy to break.

For example, the first fiber chemical pulp is a sulfate softwood chemical pulp and the second fiber chemical pulp is a sulfate hardwood chemical pulp.

The kraft process and the sulfite process are two basic chemical pulping processes, the chemical pulp produced by the kraft process is called kraft chemical pulp and the pulp produced by the sulfite process is called sulfite chemical pulp.

For example, kraft pulp uses a mixture of sodium hydroxide and sodium sulfide as the cooking agent. In the cooking process, because the liquid medicine has relatively mild action and the fibers are not strongly corroded, the paper is tough and powerful, and the manufactured paper has better folding resistance, breaking resistance and tearing strength; generally, the method can be divided into bleaching and unbleached.

For example, sulfite wood pulp uses a mixture of sulfurous acid and acid sulfite as a cooking agent. The pulp has longer fiber, soft property, good toughness, high strength, easy bleaching and excellent interweaving capability; it can be generally divided into unbleached, half-bleached and bleached.

In the embodiment of the present invention, the folding endurance and the bursting endurance of each of the outer layer 10, the middle layer 20 and the inner layer 30 can be improved by setting the first fiber chemical pulp in the outer layer 10, the middle layer 20 and the inner layer 30 as the sulfate needle-leaved chemical pulp and the second fiber chemical pulp as the sulfate broadleaf chemical pulp.

In one example, the sulfate softwood chemical pulp is a softwood bleached sulfate chemical pulp and the sulfate hardwood chemical pulp is a hardwood bleached sulfate chemical pulp.

In at least some embodiments, at least one of the inner layer 30 and the outer layer 10 has a higher content of kraft coniferous chemical pulp than the middle layer 20.

Herein, "content" of a substance refers to a mass percentage or mass fraction (also referred to as a proportion or a proportion) of the substance, for example, "a content in B is higher than a content in C" means that a mass percentage in B is higher than a mass percentage in C.

For example, the content of the chemical pulp of sulfate needle in the inner layer 30 is higher than that of the chemical pulp of sulfate needle in the middle layer 20, so that the bending strength of the inner layer 30 can be improved and the inner layer 30 can be prevented from cracking by improving the proportion of the chemical pulp of sulfate needle in the inner layer 30 under the condition that the fiber proportion of the middle layer 20 is not changed.

In one example, the kraft coniferous chemical pulp in the middle layer 20 accounts for 40-60% of the mass of the middle layer 20; the mass percentage of the sulfate needle-leaved chemical pulp in the inner layer 30 is 70% or more, more preferably 75% or more, still more preferably 85% or more, still more preferably 95% or more, and still more preferably 100% or more of the inner layer 30. If it is less than 70%, the folding resistance of the inner layer 30 is deteriorated, and the inner layer 30 is easily broken to cause a pouch leakage. The larger the above value, the better without considering the cost.

For another example, the content of the chemical pulp of sulfate needles in the outer layer 10 is higher than that of the chemical pulp of sulfate needles in the middle layer 20, so that the blending ratio of the chemical pulp of sulfate needles in the outer layer 10 is increased under the condition that the fiber blending ratio of the middle layer 20 is not changed, the bending strength of the outer layer 10 is increased, and the outer layer 10 is prevented from cracking.

In one example, the sulfate needle-leaved chemical pulp in the middle layer 20 accounts for 40% to 60% by mass of the middle layer 20; the mass percentage of the sulfate needle-leaved chemical pulp in the outer layer 10 is greater than or equal to 70%, more preferably greater than or equal to 75%, and still more preferably greater than or equal to 80% of the outer layer 10. If it is less than 70%, the folding resistance of the outer layer 10 is deteriorated, which easily causes the outer layer 10 to be broken to cause a breakout.

For another example, the content of the chemical pulp of the sulfate needles in the inner layer 30 and the outer layer 10 is higher than that of the chemical pulp of the sulfate needles in the middle layer 20, so that under the condition that the fiber proportion of the middle layer 20 is not changed, the proportion of the chemical pulp of the sulfate needles in the outer layer 10 and the inner layer 30 is increased, the bending strength of the outer layer 10 and the inner layer 30 is improved, and the outer layer 10 and the inner layer 30 are prevented from cracking.

In one example, the mass percentage of the kraft softwood chemical pulp in the inner layer 30 to the inner layer 30 is greater than or equal to 70%, more preferably greater than or equal to 75%, still more preferably greater than or equal to 85%, more preferably greater than or equal to 95%, and still more preferably 100%; the mass percentage of the sulfate needle-leaved chemical pulp in the outer layer 10 is greater than or equal to 70%, more preferably greater than or equal to 75%, and still more preferably greater than or equal to 80%.

In the embodiment of the present invention, the content of the sulfate needle chemical pulp in the inner layer 30 and the content of the sulfate needle chemical pulp in the outer layer 10 may be the same or different. That is, the percentage by mass of the kraft coniferous chemical pulp in the inner layer 30 to the inner layer 30 and the percentage by mass of the kraft coniferous chemical pulp in the outer layer 10 to the outer layer 10 may be the same or different. The person skilled in the art can select the paper layer by taking into account the manufacturing costs, various properties of the pulp and paper layer, etc.

In at least some embodiments, the outer layer 10 has a content of kraft coniferous chemical pulp equal to the content of kraft coniferous chemical pulp of the inner layer 30. That is, the mass percentage of the kraft needle chemical pulp in the outer layer 10 to the outer layer 10 is equal to the mass percentage of the kraft needle chemical pulp in the inner layer 30 to the inner layer 30.

For example, the chemical pulp of the sulfate needles in the outer layer 10 accounts for 75-85% of the outer layer 10 by mass, and the chemical pulp of the sulfate needles in the inner layer 30 accounts for 75-85% of the inner layer 30 by mass; correspondingly, the sulfate broadleaf chemical pulp in the outer layer 10 accounts for 15-25% of the mass of the outer layer 10, and the sulfate broadleaf chemical pulp in the inner layer 30 accounts for 15-25% of the mass of the inner layer 30. By setting the content of the chemical pulp of the sulfate needle blade in the outer layer 10 to be equal to the content of the chemical pulp of the sulfate needle blade in the inner layer 30, the manufactured paper layer 100 can be more flat and is not easy to warp or curl.

For another example, the chemical pulp of the sulfate needles in the outer layer 10 accounts for 80-85% of the mass of the outer layer 10, and the chemical pulp of the sulfate needles in the inner layer 30 accounts for 80-85% of the mass of the inner layer 30; correspondingly, the sulfate broadleaf chemical pulp in the outer layer 10 accounts for 15-20% of the mass of the outer layer 10, and the sulfate broadleaf chemical pulp in the inner layer 30 accounts for 15-20% of the mass of the inner layer 30. Thus, by increasing the ratio of the sulfate needle chemical pulp in the outer layer 10 and the inner layer 30, the bending strength of the outer layer 10 and the inner layer 30 can be further increased on the premise of ensuring the flatness of the paper layer 100.

For another example, during the folding process of the packaging container, the external force for folding is mainly borne on the outer layer 10 or the inner layer 30, and in order to ensure that no missing package occurs during the folding forming process of the packaging container, it is necessary to ensure the bending strength of the outer layer 10 and the inner layer 30, in one example, the sulfate coniferous chemical pulp in the outer layer 10 accounts for 100% by mass of the outer layer 10, and the sulfate coniferous chemical pulp in the inner layer 30 accounts for 100% by mass of the inner layer 30. Therefore, the packet leakage rate can be greatly reduced, and the risk of customer complaints is reduced.

In at least some embodiments, the outer layer 10 has a lower content of kraft coniferous chemical pulp than the inner layer 30. That is, the mass percentage of the kraft needle chemical pulp in the outer layer 10 to the outer layer 10 is lower than the mass percentage of the kraft needle chemical pulp in the inner layer 30 to the inner layer 30.

For example, the chemical pulp of the sulfate needles in the outer layer 10 accounts for 75-85% of the outer layer 10 by mass, and the chemical pulp of the sulfate needles in the inner layer 30 accounts for 95-100% of the inner layer 30 by mass; correspondingly, the mass percentage of the sulfate broadleaf chemical pulp in the outer layer 10 accounts for 15-25% of that of the outer layer 10, and the mass percentage of the sulfate broadleaf chemical pulp in the inner layer 30 accounts for 0-5% of that of the inner layer 30.

During the forming process of the packaging container 9, the inner layer 30 is subjected to a much larger force than the outer layer 10, so that the inner layer 30 is further prevented from cracking by properly increasing the ratio of the sulfate needle chemical pulp of the inner layer 30. In addition, considering the higher cost of the needle-leaved chemical pulp, the arrangement can also reduce the material cost of the paper layer as much as possible on the premise of ensuring the performance of the paper layer.

In at least some embodiments, the content of the sulfate hardwood chemical pulp is lower than the content of the sulfate softwood chemical pulp in each of the outer layer 10, the middle layer 20, and the inner layer 30. That is, in each of the outer layer 10, the middle layer 20 and the inner layer 30, the sulfate broadleaf chemical pulp is less in mass percentage than the sulfate coniferous chemical pulp. Because the strength of the needle chemical pulp is far better than that of the broadleaf chemical pulp, the bending strength of the paper layer 100 is improved by improving the proportion of the needle chemical pulp, and the phenomena of layering and foaming are avoided.

Although the strength of the needle chemical pulp is high, the cost is high, and if the needle chemical pulp is used on the inner layer 30 and the outer layer 10, the cost of paper is greatly increased, and the problem of the thickness reduction of the paper layer is caused. In the process of manufacturing the packaging container, in addition to consideration of material costs and properties of the selected material, the thickness of the packaging sheet 1 is also required. In the field of packaging, the thickness is usually characterized by grammage, and when selecting pulp fibers, not only the components and the proportion of the pulp, etc. but also whether the grammage of the finally manufactured paper layer 100 can meet certain specific requirements or not is considered.

In the embodiment of the present invention, wood mechanical pulp or wood mechanical chemical pulp may be added to the intermediate layer 20, because the wood mechanical pulp and the wood mechanical chemical pulp have low cost and high bulk, the gram weight of the paper layer may be increased by adding the wood mechanical pulp or the wood mechanical chemical pulp to the intermediate layer 20 on the premise of ensuring that the paper layer has good bending resistance, so as to meet the gram weight requirements of the packaging container in different use environments.

It should be noted that, in the embodiment of the present invention, wood mechanical pulp or wood mechanical chemical pulp is only added to the middle layer 20, and there is no wood mechanical pulp or wood mechanical chemical pulp in both the outer layer 10 and the inner layer 30, that is, neither wood mechanical pulp nor wood mechanical chemical pulp is included in the outer layer 10 nor the inner layer 30.

In at least some embodiments, the middle layer 20 comprises a wood mechanical pulp comprising a second fiber mechanical pulp having second fibers. For example, the second fiber is hardwood fiber and the second fibrous mechanical pulp is hardwood mechanical pulp. Hardwood mechanical pulps are preferred over softwood mechanical pulps because of their lower price.

For example, the amount of the hardwood mechanical pulp in the intermediate layer 20 is 40% to 50% by mass, and more preferably 43% to 48% by mass, based on the mass of the intermediate layer 20. If the proportion of the mechanical pulp is too low, the bulk of the paper layer 100 is insufficient, so that the stiffness of the paper layer 100 cannot reach the standard; if the proportion of the mechanical pulp is too high, paper powder is increased, and the food safety control is not facilitated.

In at least some embodiments, at least one of the inner layer 30 and the outer layer 10 has a grammage of 19% to 30% of the total grammage of the paper layer 100. In the embodiments of the present invention, the total gram weight of the paper layer refers to an absolute dry gram weight of the paper layer, where absolute dry value (gram weight) = gram weight of paper (1-moisture%), and moisture% refers to a mass percentage of moisture, for example, about 7%.

For example, the total grammage of the paper layer 100 is 195 to 205g/m ³ The gram weight of the inner layer 30 is 37 to 62g/m ³ The gram weight of the outer layer 10 is 37-62 g/m ³ 。

In the embodiment of the present invention, the grammage of the inner layer 30 and the grammage of the outer layer 10 may be the same or different. Preferably, the grammage of the inner layer 30 is less than that of the outer layer 10, so that the grammage of the inner layer 30 can be reduced as much as possible while ensuring that the packing material is not leaking, and more intermediate layers are used to maintain the grammage, thereby ensuring more bulk and reducing the cost of the whole packing material, so that the whole packing material is more competitive.

For example, the grammage of the inner layer 30 is 19% to 23% of the total grammage of the paper layer 100, and the grammage of the outer layer 10 is 26% to 20% of the total grammage of the paper layer 100.

Fig. 6 is another cross-sectional view taken along line B-B of fig. 3. In contrast to fig. 3A, the paper layer 100 of the composite packaging sheet 1 of fig. 6 further comprises a coating 40. The coating layer 40 is disposed to be laminated with the outer layer 10 and on the opposite side of the intermediate layer 20 in the thickness direction D of the paper layer 100. That is, the outer layer 10 is sandwiched between the coating layer 40 and the intermediate layer 20, with the coating layer 40 and the intermediate layer 20 being located on opposite sides of the outer layer 10, respectively.

For example, the coating layer 40 is configured to have a printed pattern, and by disposing the coating layer 40 on the paper layer 100, the printing performance of the packaging container can be improved, and the cost can be reduced.

For example, the coating 40 includes an inorganic non-metallic material including, for example, china clay. Porcelain clay is preferable as the pigment coating because it has characteristics of high strength, good printing property, high glossiness, and the like.

For example, the pigment may also include calcium carbonate, with precipitated calcium carbonate typically being used. In another example, the coating 40 may also include latex, lubricants, thickeners, and the like. For example, the latex is preferably 1:1 mixing styrene-butadiene latex and styrene-acrylic latex, wherein the styrene-butadiene latex can improve the strength of the coating, and the styrene-acrylic latex can reduce the smell of the coating.

As described above, the two sealing layers 200 of fig. 5A are fused by means of a heat-or ultrasonic-activation process when the top or bottom opening of the packaging sleeve is sealed. The region where the two sealing layers 200 directly contact is defined as a weld 200S.

The inventors have found that in packaging containers in which delamination occurs, the heat energy generated by the ultrasonic waves is absorbed for the most part by the intermediate layer 20 in the paper layer 100, resulting in severe separation of the intermediate layer 20 from the outer and

inner layers

10, 30.

As a result of the research of the inventor, the weld seam 200S can be promoted to absorb more heat by increasing the thickness (i.e. grammage) of the coating layer 40, and the delamination phenomenon inside the paper layer 1 is also improved due to the reduction of the heat absorbed by the intermediate layer 20.

In at least some embodiments, the grammage of the coating 40 is 6% to 9%, preferably 6% to 7%, of the total grammage of the paper layer 100. By setting the gram weight range, the heat energy generated by ultrasonic waves can be mostly absorbed by the welding line 200S in the activation process of the packaging container, so that the layering phenomenon in the paper layer 1 is reduced, and the bag leakage is avoided. If the grammage of the coating 40 is too high, it will result in a reduction in the strength of the entire paper layer, and if it is too low, it will not work.

In at least some embodiments, the coating 40 has a thickness of 4% to 5% of the total thickness of the paper layer 100. For example, the thickness of the coating layer 40 is 13-15 microns and the total thickness of the paper layer 100 is 280-300 microns.

The embodiment of the invention also provides a manufacturing method of the paper layer of the composite sheet material for packaging. For example, the manufacturing method may be used to manufacture the paper layer of any of the packaging composite sheets of the previous embodiments.

Fig. 7 is a method for manufacturing a paper layer of a composite sheet for packaging according to an embodiment of the present invention, including: forming a paper layer 100. For example, forming the paper layer 100 includes: forming an outer layer 10 (i.e., a first layer), an inner layer 30 (i.e., a second layer), and an intermediate layer 20 positioned between the outer layer 10 and the inner layer 30, wherein the outer layer 10, the intermediate layer 20, and the inner layer 30 each comprise a wood chemical pulp comprising a first fiber chemical pulp having first fibers and a second fiber chemical pulp having second fibers, the first fibers having a fiber length greater than the second fibers; the content of the first fiber chemical pulp of at least one of the inner layer 30 and the outer layer 10 is higher than the content of the first fiber chemical pulp of the middle layer 20.

In the method for manufacturing the paper layer of the composite sheet for packaging according to the embodiment of the present invention, the content of the first fiber chemical pulp in at least one of the inner layer and the outer layer is increased to be higher than the content of the first fiber chemical pulp in the intermediate layer, so that the bending strength of the paper layer is increased. On one hand, the product quality of the packaging container can be improved, and even if the packaging sheet is folded for multiple times, the bag leakage phenomenon can not occur; on the other hand, the packaging container can have a smoother surface at the sealing position, thereby improving the aesthetic property of the packaging product.

For example, in the above-described manufacturing method, the step of forming the outer layer 10, the inner layer 30, and the intermediate layer 20 between the outer layer 10 and the inner layer 30 includes: providing wet paper pulp, and adding starch and/or dry strength agent into the wet paper pulp; and applying the wet pulp to a forming device and drying.

For example, delamination of the paper layer 100 may be avoided by at least one of the following: mode 1: controlling the proportion between needle leaf pulp and broad leaf pulp in wet paper pulp; mode 2: the amount of starch and/or dry strength agent added to the wet pulp is controlled. In the above manufacturing method, only the dry strength agent is added into the wet pulp without adding starch, so as to avoid the delamination of the paper layer 100.

Dry strength agents are chemicals that enhance the bonding between fibers to increase the physical strength (stiffness, tensile strength, ring crush strength, burst strength, etc.) of the paper without affecting its wet strength. The application of the dry strength agent can avoid the problems of the increase of the tightness of paper, the increase of wet deformation, the reduction of opacity, absorptivity, air permeability and tearing strength and the like caused by the improvement of the beating degree. The dry strength agent is mainly amphoteric multi-component copolymer polyacrylamide, and can be better combined with fibers to more effectively improve the strength of paper.

For example, the dry strength agent of starch is used in an amount of 5 to 10kg/t, for example 5kg/t, 6kg/t, 7kg/t, 8kg/t, 9kg/t, 10kg/t.

The following samples 1 to 3 are examples of paper layers of the present invention. Table 1 shows the grammage of each layer in samples 1-3. Table 2 shows the fiber compositions and ratios of the outer layer, the middle layer, and the inner layer in samples 1-2.

TABLE 1

TABLE 2

The fiber composition and the ratio of each layer in the

above samples

1 and 2 were obtained by:

1. analytical method

The fibre composition and the proportion of the samples were analysed with reference to analysis of the paper, cardboard and pulp-fibre compositions of GB/T4688-2020.

The principle is as follows: the fiber composition analysis is performed by taking a small representative amount of the fiber from the sample to be measured, dyeing the fiber, and observing the fiber with a microscope. And carrying out qualitative analysis according to the dyeing reaction of the fiber and the morphological characteristics of the fiber. And measuring and counting the number of crossing points of various fibers and counting lines, and converting the number of crossing points into mass fractions by using a quality factor for quantitative analysis.

2. Preparation of samples

5 specimens of about 50mm by 50mm are cut from different parts of the sample and soaked with hot water at about 70 ℃ until the layers are completely separated. If the separating layer carries fibers from adjacent layers, care must be taken to remove them during the separation process. A proper amount of each layer of sample is put into a test tube, water is added to the test tube until the concentration is about 0.1 percent, and fiber suspension is prepared for fiber morphology observation.

3. Dyeing and sheeting

1. Dyeing process

For the analysis, the Herzberg (Hertzerg) stain and the Selleger (Serpentine) stain were selected for staining.

The Herzberg stain can be used for qualitatively and quantitatively distinguishing chemical pulp, mechanical pulp and cotton-flax pulp, and can also be used for qualitatively distinguishing semi-chemical pulp and distinguishing viscose fiber and synthetic fiber. Color development reaction of Herzberg stain:

A. chemical pulp fibers (softwood, hardwood, reed, bagasse, straw, wheat straw, sorghum stalk, devil's rush): bluish violet.

B. Mechanical pulp fiber: bright yellow.

C. Cotton fiber: wine red, bast fiber (flax hemp): dark wine red.

In addition to the above main color differences, the Herzberg staining can determine the presence or absence of sulfite softwood pulp based on the characteristic that the wood ray cells in sulfite softwood pulp appear yellow due to the presence of resin.

The Selleger stain is used for the identification of softwood pulp from hardwood pulp. Can also be used for distinguishing wood pulp from straw pulp. Color development reaction of Selleger stain:

A. bleaching acid softwood pulp: clear, light rose color.

B. Bleaching alkaline softwood pulp: light dark brownish red.

C. Hardwood pulp: bluish violet.

D. Wood grinding: dark yellow.

E. Cotton and hemp pulp: wine red to reddish brown.

2. Tabletting

Diluting a proper amount of fiber suspension with water to the concentration of about 0.05% (mass fraction), dripping 1.0mL of the suspension on a clean and grease-free microscope slide glass by a dropper, uniformly dispersing fibers by a dissecting needle, drying the slide glass on a heating plate, and selecting a corresponding coloring agent for dyeing after cooling. After 1-2 minutes of staining the best product in the 1-cover surface, covering a microscope cover glass, avoiding bubbles between the glass slide and the cover glass as much as possible, inclining the glass slide, sucking redundant staining agent by using filter paper, and observing and analyzing the test piece.

4. Observation and analysis of sample

1. Qualitative analysis

The test piece is moved regularly along the horizontal or vertical direction on the stage of the test piece microscope, and the whole test piece is observed. And identifying the fiber type and the pulping method according to the fiber morphological characteristics and the dyeing condition. At least 2 test pieces were observed per sample.

2. Quantitative analysis

The analysis distinguishes the fiber types according to different fiber dyeing and fiber morphological characteristics by means of a microscope. And counting by adopting a root method.

The test piece is placed on an object stage of a microscope, and the test piece is moved by the object stage, so that the center point of the visual field is positioned at a position 3 mm-5 mm away from the edge above the cover glass. And then regularly moving the test piece along the horizontal or vertical direction, counting the number of various fibers, after counting the number of the fibers on one observation line, parallelly moving the test piece for about 5mm to another observation line, and recording each fiber on each line in the same way. During the continuous counting process, the counting should not be repeated on the original row bit. Fiber fragments smaller than 0.1mm in the statistical process are ignored, but those with larger longitudinal cracks are counted, and the fibers in the fiber bundle are counted each time. Two or more test pieces should be measured to ensure that the number of fibers is more than 600. After the measurement was completed, the mass fraction of each component was calculated according to the following formula.

Wherein Wi is mass fraction (%); fi is a quality factor; ni is the total number of each fiber; k is the fiber component number. Table 3 shows the allowable error of the fiber proportioning measurement. The calculation result is accurate to an integer, and if the mass fraction is less than 2%, the calculation result is recorded as trace.

TABLE 3 fibre proportioning measurement tolerance GB/T4688-1984

The experiment shows that the samples 1 to 3 have no bag leakage at the top, the bottom or the ear wing, and the surfaces of the top and the bottom are relatively flat.

Fig. 7 is a photograph of the top appearance of a packaging container according to an embodiment of the present invention. Fig. 8 is a photograph of a cross-section of a top seal of a packaging container according to an embodiment of the invention. Fig. 7 and 8 represent the test results of sample 1.

As can be seen from fig. 7, the top surface of the packaging container manufactured using the composite sheet for packaging of sample 1 was flat and no foaming occurred. As can be seen from fig. 8, no delamination occurred in sample 1 and the bag leakage preventing effect was better, mainly due to the higher ratio (up to 99%) of the kraft needle chemical pulp in the inner layer of sample 1.

Fig. 9 is a photograph of a cross-section of a top seal of a packaging container according to another embodiment of the invention. Figure 9 represents the test results for sample 2. As can be seen from fig. 9, no delamination occurred in sample 2. Compared with fig. 8, the activation temperature and pressure used in fig. 9 are higher, so that the weld is burnt. However, even in this case, no delamination occurred in sample 2.

In the paper layer of the composite sheet for packaging and the manufacturing method thereof, the composite sheet for packaging and the packaging container provided by the embodiment of the invention, the content of the first fiber chemical pulp in at least one of the inner layer and the outer layer is increased to be higher than that of the first fiber chemical pulp in the middle layer, so that the bending strength of the paper layer is improved. On one hand, the phenomenon of layering at the sealed positions of the top and the bottom can be avoided, so that the bag leakage at the top, the bottom or the ear wings is avoided, and the product quality of the packaging container is improved; on the other hand, the top and the bottom of the formed packaging container have relatively flat surfaces at the sealing position, and the attractiveness of the packaging product is improved.

Herein, the following points need to be noted:

(1) The drawings of the embodiments of the invention only relate to the structures related to the embodiments of the invention, and other structures can refer to common designs.

(2) Without conflict, embodiments of the present invention and features of the embodiments may be combined with each other to arrive at new embodiments.

The above description is intended to be illustrative of the present invention and not to limit the scope of the invention, which is defined by the claims appended hereto.

Claims

1. A paper layer of a composite sheet for packaging, the paper layer comprising in its thickness direction a first layer, a second layer and an intermediate layer between the first layer and the second layer, which are arranged one above the other, wherein the first layer, the intermediate layer and the second layer each comprise a wood chemical pulp comprising a first fiber chemical pulp having first fibers and a second fiber chemical pulp having second fibers, the fiber length of the first fibers being greater than the fiber length of the second fibers;

wherein a content of the first fiber chemical pulp of at least one of the second layer and the first layer is higher than a content of the first fiber chemical pulp of the intermediate layer.

2. The paper layer of the packaging composite sheet according to claim 1, wherein:

the first fiber is softwood fiber, and the first fiber chemical pulp is sulfate softwood chemical pulp;

the content of the sulfate coniferous chemical pulp of at least one of the second layer and the first layer is higher than that of the sulfate coniferous chemical pulp of the middle layer.

3. The paper layer of the packaging composite sheet according to claim 2, wherein:

the content of the sulfate coniferous chemical pulp of the second layer is higher than that of the sulfate coniferous chemical pulp of the middle layer; and is

The mass percentage of the sulfate coniferous chemical pulp in the second layer is more than or equal to 70 percent.

4. The paper layer of the composite sheet for packaging as claimed in claim 3, wherein the sulfate softwood chemical pulp comprised in the second layer is greater than or equal to 85% by mass of the second layer.

5. The paper layer of the packaging composite sheet according to claim 4, wherein the sulfate needle chemical pulp included in the second layer accounts for 100% by mass of the second layer.

6. The paper layer of the packaging composite sheet according to claim 2, wherein:

the content of the sulfate coniferous chemical pulp of the first layer is higher than that of the sulfate coniferous chemical pulp of the middle layer; and is

The sulfate coniferous chemical pulp in the first layer accounts for more than or equal to 70% of the mass of the first layer.

7. The paper layer of the packaging composite sheet according to claim 6, wherein:

the content of the sulfate coniferous chemical pulp of the first layer is equal to that of the sulfate coniferous chemical pulp of the second layer.

8. The paper layer of the packaging composite sheet according to claim 7, wherein:

the sulfate needle-leaved chemical pulp in the first layer accounts for 75-85% of the mass of the first layer;

the sulfate needle-leaved chemical pulp in the second layer accounts for 75-85% of the second layer by mass.

9. The paper layer of the packaging composite sheet according to claim 6, wherein:

the first layer has a lower content of kraft softwood chemical pulp than the second layer.

10. The paper layer of the packaging composite sheet according to claim 9, wherein:

the sulfate coniferous chemical pulp in the first layer accounts for 75-85% of the first layer by mass;

the sulfate needle-leaved chemical pulp in the second layer accounts for 95-100% of the second layer by mass.

11. The paper layer of the packaging composite sheet according to claim 1, wherein the grammage of the at least one of the second layer and the first layer is 19% to 30% of the total grammage of the paper layer.

12. The paper layer of the packaging composite sheet according to claim 1, wherein:

the second fiber is hardwood fiber, and the second fiber chemical pulp is sulfate hardwood chemical pulp;

the second fiber chemical pulp is present in an amount lower than the first fiber chemical pulp in each of the first layer, the intermediate layer, and the second layer.

13. The paper layer of the packaging composite sheet according to claim 1, wherein:

the middle layer further comprises wood mechanical pulp or wood mechanochemical pulp;

the wood mechanical pulp and the wood mechanochemical pulp are absent from both the second layer and the first layer.

14. The paper layer of the packaging composite sheet according to claim 13, wherein:

the middle layer further comprises the wood mechanical pulp;

the wood mechanical pulp comprises a second fiber mechanical pulp having second fibers;

the second fiber is hardwood fiber, and the second fiber mechanical pulp is hardwood mechanical pulp.

15. The paper layer of the packaging composite sheet according to claim 14, wherein the hardwood mechanical pulp in the middle layer is 40-50% by mass of the middle layer.

16. The paper layer of the composite sheet for packaging as claimed in claim 15, wherein the hardwood mechanical pulp in the middle layer is 43-48% by mass of the middle layer.

17. The paper layer of the packaging composite sheet according to claim 1, further comprising:

a coating layer disposed on the first layer in a stacked manner in a thickness direction of the paper layer and on a side opposite to the intermediate layer,

wherein the coating is configured with a printed pattern.

18. The paper layer of the packaging composite sheet material of claim 17 wherein the coating comprises an inorganic non-metallic material.

19. The paper layer of the packaging composite sheet according to claim 18, wherein the inorganic non-metallic material comprises china clay.

20. The paper layer of the packaging composite sheet according to claim 17, wherein the grammage of the coating layer is 6% to 9% of the total grammage of the paper layer.

21. The paper layer of the packaging composite sheet according to claim 20, wherein the thickness of the coating layer is 4 to 5% of the total thickness of the paper layer.

22. A composite sheet for packaging comprising a paper layer according to any one of claims 1 to 21.

23. The packaging composite sheet material as claimed in claim 22, wherein the packaging composite sheet material comprises an inner surface and an outer surface opposed in a thickness direction thereof, a first one of the paper layers being disposed adjacent the outer surface and a second one of the paper layers being disposed adjacent the inner surface, the packaging composite sheet material further comprising:

a sealing layer disposed on the second layer of the paper layer in a stacked manner in a thickness direction of the paper layer and on a side opposite to the intermediate layer,

wherein the sealing layer is configured to seal the packaging with the composite sheet under the action of heat activation or ultrasonic activation.

24. A packaging container comprising the composite sheet for packaging according to claim 22.

25. A method of manufacturing a paper layer of a composite sheet for packaging, comprising: forming a paper layer; wherein the forming the paper layer comprises:

forming a first layer, a second layer, and an intermediate layer between the first layer and the second layer, wherein the first layer, the intermediate layer, and the second layer each comprise a wood chemical pulp comprising a first fiber chemical pulp having first fibers and a second fiber chemical pulp having second fibers, the first fibers having a fiber length greater than a fiber length of the second fibers;

26. The method of manufacturing a paper layer of a composite packaging sheet according to claim 25, wherein said forming a first layer, a second layer and an intermediate layer between the first layer and the second layer comprises:

providing wet paper pulp, and adding starch and/or dry strength agent into the wet paper pulp; and

the wet pulp is applied to a forming device and dried.

27. The method for manufacturing a paper layer of a composite sheet for packaging according to claim 26, wherein only a dry strength agent is added to the wet pulp, and the amount of the dry strength agent is 5 to 10kg/t.