JP2020172086A - Base material for liquid container, container for liquid and method for producing the same - Google Patents

Abstract

To provide a base material for liquid container having a paper base material which prevents delamination and is excellent in laminate workability and printability, and a container for liquid using the base material for liquid container.SOLUTION: A base material for liquid container has a paper base material containing cellulose pulp as a main component, and a thermoplastic resin layer layered on at least one surface of the paper base material, in which the paper base material is composed of three or more pulp layers, when an average value of a basis weight of the outermost layer on a surface and a rear face of the paper base material is represented by W1 and an average value of a basis weight of the first inner layer positioned immediately inside the outermost layer of the surface and the rear face is represented by W2, the relationship of W1/W2=1.1 to 2.4 is satisfied. There are also provided a container for liquid using the base material for liquid container and a method for producing the base material for liquid container.SELECTED DRAWING: None

Description

The present invention relates to a base material for a liquid container, a liquid container using the base material, and a method for producing a base material for a liquid container.

In liquid containers used for milk cartons and the like, laminated paper in which a thermoplastic resin layer such as polyethylene is laminated on a paper base material mainly composed of pulp fibers is often used. As the paper base material, since it is excellent in physical properties and productivity, a multi-layer paper base material in which a plurality of pulp layers are laminated (multi-layer structure) is preferably used.

A multi-layer paper substrate is manufactured by stacking and pressing low-weight sheets in several stages and drying them. When papermaking with a high basis weight, the papermaking method using multi-layer papermaking is advantageous from the viewpoint of productivity because the load during drying is small and the papermaking speed can be faster than that of single-layer papermaking.

However, when a multi-layer paper base material is used as a base material for a liquid container or the like, the strength between the paper layers is lower than that of the single-layer paper base material, so that there is a concern that peeling may occur between the paper layers during the molding process. ..

Various attempts to improve the molding processability of the multi-layer paper base material have already been published. For example, Patent Document 1 discloses a liquid container paper base material that is easily bent along a ruled line by containing a softener in the middle layer excluding the outer layer in a multi-layer paper base material having three or more layers. Further, Patent Document 2 describes a base paper for a paper container having a multi-layer structure, in which the outer layer has a softwood kraft pulp content of 40% by mass or more and the inner layer has a softwood kraft pulp content of 30% by mass or less. Base paper for containers is disclosed. In the base paper for paper containers of Patent Document 2, since the inner layer is broken first during the bending process, stress is concentrated on the outermost layer to prevent the resin layer from being broken.

JP-A-2010-144286 International Publication No. 2010/1183849

However, in the liquid container paper base material of Patent Document 1, since the middle layer contains a softener that inhibits interfiber bonding, the strength of the middle layer is lowered, and there is a concern that delamination may occur due to being squeezed by a roller during processing. Had. Further, even in the base paper for paper containers of Patent Document 2, the strength of the inner layer is lowered, and there is a concern that delamination due to ironing during processing is likely to occur.

When manufacturing a liquid container by laminating or printing a paper base material, the paper base material runs along the curved surface of various rollers under tension, and is curved. Since the direction is constantly changing from the front side to the back side, the paper base material is in a squeezed state. Therefore, if the interlayer strength of the paper base material is low, delamination is likely to occur when the paper substrate is squeezed.

The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide a base material for a liquid container having a paper base material which is less likely to cause delamination and has excellent laminating workability and printability, and a liquid container using the base material for the liquid container. That is.

The present inventors focused on the basis weight of each pulp layer constituting the multi-layered paper substrate. Then, when a multi-layered paper base material composed of three or more pulp layers is used as the paper base material and the basis weight of the outer layer in the paper base material is adjusted to be larger than the basis weight of the inner layer, It has been found that delamination is reduced and laminating workability and printability are improved. It was also found that a papermaking method in which pulp layers are sequentially made from one surface of a paper substrate to the other surface is effective. The present invention has been completed based on such findings. That is, the present invention has the following configuration.

(1) A base material for a liquid container having a paper base material containing cellulose pulp as a main component and a thermoplastic resin layer laminated on at least one surface of the paper base material, wherein the paper base material is It is composed of three or more pulp layers, the average value of the basis weight of the outermost layers on the front and back surfaces of the paper substrate is W1, and the average value of the basis weight of the first inner layer located immediately inside the outermost layers of the front and back surfaces is defined as W1. A base material for a liquid container, which satisfies W1 / W2 = 1.1 to 2.4 when W2 is used.

(2) The base material for a liquid container according to (1) above, wherein the interlayer strength measured using an internal bond tester is 200 to 600 J / m ² .

(3) The base material for a liquid container according to (1) or (2) above, wherein the water content is 6.0 to 9.5%.

(4) The base material for a liquid container according to any one of (1) to (3) above, wherein the paper base material is composed of five or more pulp layers.

(5) A liquid container using the liquid container base material according to any one of (1) to (4) above.

(6) A method for producing a base material for a liquid container, which comprises a paper base material containing cellulose pulp as a main component and a thermoplastic resin layer laminated on at least one surface of the paper base material. The base material is composed of three or more pulp layers, the average value of the basis weights of the outermost layers on the front and back surfaces of the paper base material is W1, and the basis weight of the first inner layer located immediately inside the outermost layers on the front and back surfaces. A method for producing a base material for a liquid container, which comprises a laminating step of laminating the pulp layers so as to satisfy W1 / W2 = 1.1 to 2.4 when the average value is W2.

(7) The method for producing a base material for a liquid container according to (6) above, wherein the laminating step is a multi-layer bonding step of three or more pulp layers.

(8) Production of the base material for a liquid container according to (7) above, wherein in the multi-layer bonding step, one of the outermost layers on the front and back surfaces to the outermost layer on the other side are sequentially bonded. Method.

(9) The above-mentioned (7) or the above-mentioned (7) or the above-mentioned (7) or the said ( The method for producing a base material for a liquid container according to 8).

(10) The multi-layer bonding process includes a step of sandwiching and dehydrating the first wire and the second wire, and a step of laminating on a third wire or felt different from these wires. (7) or the method for producing a base material for a liquid container according to (8) above.

(11) The multi-layer bonding step is different from the step of dehydrating with at least one wire in the initial dehydration section and the step of sandwiching and dehydrating with the first wire and the second wire in the double-sided dehydration section. The method for producing a base material for a liquid container according to (7) or (8) above, which comprises a step of laminating on a third wire or felt.

The base material for a liquid container of the present invention has a paper base material having a multi-layer structure, is less likely to cause delamination, and is excellent in laminating workability and printability.

Hereinafter, embodiments of the present invention will be specifically described. The description of the constituent elements described below may be based on typical embodiments or specific examples, but the present invention is not limited to such embodiments.

The base material for a liquid container of the present invention (hereinafter, also appropriately referred to as “base material”) is laminated on a paper base material containing cellulose pulp as a main component and on at least one surface of the paper base material. It has a thermoplastic resin layer. Hereinafter, each member constituting the present embodiment will be described.

[Paper base material]
The paper base material contains cellulose pulp as a main component. Here, the main component means a component that occupies 50% by mass or more of the components constituting the paper base material.

(pulp)
The type of cellulose pulp is not particularly limited, but it is preferable to contain chemical pulp from the viewpoint of strength. The chemical pulp is not particularly limited, but preferably contains hardwood kraft pulp (LKP) or softwood kraft pulp (NKP). The pulp may be bleached pulp or unbleached pulp. Hereinafter, unless otherwise specified, LKP and NKP include bleached pulp or unbleached pulp, respectively, but hardwood bleached kraft pulp may be referred to as LBKP and softwood bleached kraft pulp may be referred to as NBKP. As LKP, acacia material, eucalyptus material and the like can be used, and as NKP, radiata pine material and the like can be used.

LKP has shorter fibers and is inferior in strength to NKP, but is excellent in the texture and smoothness of the paper made. Since good texture and smoothness of the paper base material are required to obtain good printability, the content of LKP should be 50% by mass or more with respect to the total mass of the pulp components. It is preferably 60% by mass, more preferably 70% by mass or more.

The paper base material may contain pulps other than the above NKP and LKP (hereinafter, referred to as other pulps). Other pulps include stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), thermogrand pulp (TGP), chemigrand pulp (CGP), crushed wood pulp (GP), and thermo. Manufactured from mechanical pulp such as mechanical pulp (TMP), brown waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, leaflet waste paper, office waste paper, cardboard waste paper, upper white waste paper, Kent waste paper, imitation waste paper, ground ticket waste paper, etc. Examples thereof include disintegrated waste paper pulp (DIP) and pulp chemically or mechanically produced from non-wood fibers such as kenaf, hemp and reed. The content of the other pulp is preferably less than 3% by mass, more preferably less than 2% by mass, and even more preferably less than 1% by mass with respect to the total mass of the pulp components.

In general, the smaller the freeness (degree of drainage) of the pulp component, the greater the tensile strength of the paper-made product. However, when the freeness is reduced, not only the tensile strength is increased but also the paper tends to be hard. If the paper is too hard, the moldability deteriorates. Therefore, in order to realize a paper base material having a certain degree of tensile strength and an excellent balance that does not become too hard, the pulp disintegration freeness (csf) is 410 to 600 ml. Is preferable. The dissociation freeness (csf) is more preferably 420 to 590 ml, further preferably 430 to 580 ml.

The dissociation freeness (csf) refers to a value of Canadian standard freeness measured using a pulp slurry obtained by dissociating a paper substrate. Dissolution freeness (csf) can be adjusted by increasing or decreasing the freeness of the cellulose pulp before papermaking. The freeness (csf) of the cellulose pulp before papermaking is preferably 360 to 550 ml, more preferably 370 to 540 ml, and even more preferably 380 to 530 ml.

(Filling fee)
The filler to be blended when the paper base material is made can be a filler generally used in the papermaking field, and is not particularly limited. Examples of fillers are clay, calcined kaolin, delaminated kaolin, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous. Examples thereof include inorganic fillers such as silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide and zinc hydroxide, and organic fillers such as urea-formalin resin, polystyrene resin, phenol resin and fine hollow particles. These fillers can be used alone or in combination of two or more, depending on the purpose.

(Internal aid)
When making a paper base material, various internal aids can be appropriately selected and used as needed. Examples of internal additives include sizing agents, yield improvers, water solubility improvers, paper strength enhancers, wet paper strength enhancers, starches such as cationized starch, bulkiness improvers, sulfate bands, and polyvalent values. Examples thereof include metal compounds, silica sol, defoaming agents, coloring dyes, coloring pigments, fluorescent whitening agents, pH adjusting agents, pitch control agents, slime control agents and the like.

The basis weight of the paper base material is not particularly limited, but is preferably 150 to 500 g / m ² . If it is 150 g / m ² or less, the rigidity may be insufficient when molded into a liquid container. Further, if it is 500 g / m ² or more, a large amount of raw material is used, which may increase the cost.

(Paper machine)
The paper substrate is composed of three or more pulp layers. The paper base material preferably has 5 or more layers. A paper substrate composed of a plurality of pulp layers is generally produced by multi-layer fabrication, which is performed from a plurality of inlets. As the number of layers is larger, the basis weight of each layer can be reduced, so that the formation can be easily taken, the surface property of the paper base material is improved, and the base material for a liquid container having a better surface quality can be obtained. Further, as the number of layers is larger, the bending rigidity is appropriately lowered and it is easier to bend at the ruled line portion, so that the base material for a liquid container having excellent ruled line suitability can be used.

Here, in order to specify each of the plurality of pulp layers constituting the paper base material, each pulp layer is given a name. For example, in the case of a paper base material having a multi-layer structure consisting of five layers, when each layer is from the first layer to the fifth layer from the front side to the back side, the first layer and the fifth layer located on the outermost side are front and back. I will call it the outermost layer of. Further, the second layer and the fourth layer located immediately inside the outermost layers on the front and back are referred to as the first inner layer. Further, the third layer located inside the first inner layer will be referred to as a second inner layer. Here, the front side refers to the surface that becomes the outer side when the liquid container is used, and the back side refers to the surface that becomes the inner side of the liquid container.

(Water-soluble resin layer)
A water-soluble resin layer may or may not be formed on both sides or one side of the paper base material. The water-soluble resin is not particularly limited as long as it is a water-soluble polymer having a film-forming property. Examples of the water-soluble resin include completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinyl alcohol such as modified polyvinyl alcohol, starches, polyacrylamides, polyethyleneimine, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, and carboxymethyl cellulose. Examples thereof include cellulose ethers such as acetyl cellulose and derivatives thereof. These can be used alone or in combination of two or more.

[Thermoplastic resin layer]
The thermoplastic resin layer is formed by laminating a thermoplastic resin layer on a paper base material. The thermoplastic resin layer may be laminated on only one side of the paper base material, or may be laminated on both sides of the paper base material. It is usually formed at least on the inner surface of the liquid container in contact with the liquid.

As the thermoplastic resin, either a crystalline resin or a non-crystalline resin can be used depending on the intended use. Examples of the thermoplastic resin include polyethylene (LDPE, MDPE, HDPE, LLDPE, etc.), polypropylene, polyolefin resin such as polymethylpentene, polyester resin such as PET and PBT, polyamide resin, polylactic acid, PHB, PBS, PBAT, PCL, etc. Examples thereof include biodegradable resins such as PHBH, polystyrenes, polyvinyl chlorides, acrylonitrile-butadiene-styrene (ABS) resins, acrylic resins, and modified polyphenylene ethers (PPE). The thermoplastic resin layer may be formed of a single layer of a single resin, may be formed of a single layer by mixing a plurality of resins, or may be formed as a plurality of layers of the same or different types of resins. You may.

The thickness of the thermoplastic resin layer is not particularly limited, but is usually about 10 to 100 μm.

The basic layer structure of the base material for liquid containers is a two-layer structure or a three-layer structure composed of a paper base material and a thermoplastic resin layer, but in addition to this, various various layer structures are used depending on the application. Can be formed. For example, a thermoplastic resin layer of the same type or a different type may be further provided on a base material for a liquid container composed of a paper base material and a thermoplastic resin layer, or a layer other than the thermoplastic resin layer may be provided between the thermoplastic resin layer and the thermoplastic resin layer. Layers can also be provided. Examples of the layer other than the thermoplastic resin include a water-soluble polymer (PVA and the like), a coating layer containing pigments and adhesives as main components, an aluminum foil (Al foil), a printing layer and the like.

[Base material for liquid containers]
The present inventors have investigated a method for suppressing the occurrence of delamination that occurs when squeezed during laminating or printing. As a result, when the average value of the basis weights of the two outermost layers on the front and back surfaces of the paper substrate is W1, and the average value of the basis weights of the two first inner layers immediately inside the outermost layers on the front and back surfaces is W2, W1 / It has been found that satisfying W2 = 1.1 to 2.4 is effective in improving the interlayer strength and suppressing delamination. When W1 / W2 is less than 1.1, the water content of the last layer to be laminated is not sufficient, and sufficient hydrogen bonds cannot be obtained on the bonded surface, resulting in a decrease in interlayer strength. On the other hand, when W1 / W2 exceeds 2.4, the layer to be laminated at the end has too much water, resulting in insufficient dehydration, which in turn causes a decrease in interlayer strength and operability. There are effects such as leading to deterioration. Therefore, when W1 / W2 = 1.1 to 2.4, the interlayer strength tends to be less than 200 J / m ² . W1 / W2 is preferably in the range of 1.2 to 2.4, and more preferably in the range of 1.3 to 1.8.

In the multi-layered paper base material, the basis weight of each of the outermost layers on the front and back is preferably 25 to 40% with respect to the total basis weight. For example, if the paper substrate of 300 g / ^{m 2,} the outermost layer is preferably a 75~120g / ^{m 2.} The basis weights of the outermost layers on the front and back may be the same or different. The basis weight of each of the first inner layers immediately inside the outermost layers of the front and back surfaces is smaller than the basis weight of the outermost layer, and for a paper substrate consisting of five layers of 300 g / m ² , 35 g / m ^{2 to} 62.5 g. It is preferably / m ² . The basis weight of the second inner layer may be the same as or smaller than the basis weight of the first inner layer.

(Interlayer strength)
As described above, when a base material having a multi-layered paper base material is squeezed during processing, a phenomenon of peeling between the layers constituting the paper base material occurs. Here, when the method for quantifying the interlayer strength of the paper substrate was examined, it was found that the measurement method using an internal bond tester was effective. Therefore, in order to suppress peeling in the layer of the paper base material itself, a numerical range to be maintained as the interlayer strength measured using an internal bond tester was examined from the base material for liquid containers, and it was found to be 200 to 600 J / m. It was found that ² is preferable.

When the interlayer strength is 200 J / m ² or more, delamination is unlikely to occur in the squeezed portion. In addition, there is little concern that delamination will occur due to the vaporization of moisture in the paper substrate during heating during lamination or printing. On the other hand, when the interlayer strength is 600 J / m ² or less, the paper base material is less likely to be hardened, and ruled line cracking is less likely to occur during bending. When manufacturing a liquid container using a liquid container base material, a ruled line is provided at a necessary position on the base material and bending is performed. However, when the base material becomes hard, a ruled line is added or when bending. , The ruled line part may be cracked. The interlayer strength is more preferably 300 to 500 J / m ² . Here, the interlayer strength is a numerical value obtained as a geometric mean of the numerical value of the interlayer strength measured in the vertical direction and the numerical value of the interlayer strength measured in the horizontal direction. The method for measuring the interlayer strength using an internal bond tester is described in J.I. Measured according to TAPPI 18-2.

As a method for controlling the interlayer strength measured using the internal bond tester of the base material within the above-mentioned predetermined numerical range, the linear pressure in the pressing process during the papermaking process, the freeness of separation of the paper base material, and the improvement of the paper strength are used. There are methods for adjusting the amount of an internal additive such as an agent, the amount and concentration of water, starch, or paper strength agent sprayed between the layers of the papermaking process.

(Basis weight)
The base material composed of the paper base material and the thermoplastic resin layer preferably has a basis weight of 150 to 500 g / m ² , and more preferably 200 to 400 g / m ² .

(moisture)
The water content of the base material is the water content contained in the base material for a liquid container composed of the paper base material and the thermoplastic resin layer. The water content of the base material is preferably 6.0 to 9.5%, more preferably 6.2 to 8.0%. When the water content of the base material is 6.0% or more, wrinkles are less likely to occur on the paper base material, so that the operability is less likely to deteriorate. On the other hand, when the water content of the base material is 9.5% or less, there is little concern that the water content in the paper base material will vaporize during heating in laminating or printing and delamination will occur. The water content of the base material is measured according to JIS P8127; 2010 after humidity control.

[Manufacturing method of base material for liquid containers]
The paper base material constituting the base material for a liquid container is composed of three or more pulp layers. Further, in the method for manufacturing a paper base material, when the average value of the basis weight of the outermost layer on the front and back of the paper base material is W1, and the average value of the basis weight of the first inner layer located immediately inside the outermost layer is W2. , W1 / W2 = 1.1 to 2.4, including a laminating step of laminating the pulp layers.

The laminating step is preferably a multi-layered laminating step of laminating three or more pulp layers together. In the multi-layer bonding step, it is preferable to sequentially combine the outermost layer of one of the front and back surfaces to the outermost layer of the other. In addition, it is preferable that the basis weight of the outermost layer, which will be the last to be assembled, is larger than the basis weight of the other pulp layers. As a result, a sufficient amount of water can be retained in each layer when they are squeezed together, sufficient hydrogen bonds can be obtained on the squeezed surface, and the interlayer strength can be improved.

In the multi-layer bonding step, wet paper dehydrated by at least one wire is transferred onto a flat surface of a wire or felt different from the wire, and one layer at a time on the flat surface of the other wire or felt. It is preferable to stack them by a method of combining them in order. In other words, the multi-layer bonding step preferably includes a step of dehydrating with at least one wire and a step of laminating on a wire or felt different from the wire.

Further, in the multi-layer bonding step, the wet paper sandwiched between the first wire and the second wire and dehydrated is transferred onto a third wire or a flat surface of felt different from these wires, and the other third wire is transferred. It is preferable to stack the layers one by one on the flat surface of the wire or felt in order. In other words, the multilayer bonding step preferably includes a step of sandwiching and dehydrating the first wire and the second wire, and a step of laminating on a third wire or felt different from these wires.

Further, in the multi-layer laminating step, the wet paper that has been dehydrated with at least one wire in the initial dehydration section and further sandwiched between the first wire and the second wire in the double-sided dehydration section is separated from these wires. It is preferable to transfer the material onto a flat surface of the third wire or felt of the above material and to laminate the layers on the flat surface of the other third wire or felt layer one by one in order. In other words, the multi-layer bonding step is different from the step of dehydrating with at least one wire in the initial dehydration section and the step of sandwiching and dehydrating with the first wire and the second wire in the double-sided dehydration section. It is preferable to include a step of laminating on a third wire or felt. By these methods, the formation can be improved and the interlayer strength can be increased.
Further, it is preferable that the length of the initial dehydration portion of the outermost layer is longer than the length of the initial dehydration portion of any other pulp layer excluding the outermost layer.

The paper-based paper-making method and the type of paper-making machine are not particularly limited, and are long-net paper machines, twin-wire paper machines, circular-net paper machines, gap formers, hybrid formers (on-top formers), etc. A known papermaking method and papermaking machine can be selected. As a multi-layer papermaking machine, an on-top former having a long net type initial dehydration portion that dehydrates with at least one wire is preferable.

The pH at the time of papermaking may be any of an acidic region (acidic papermaking), a pseudo-neutral region (pseudo-neutral papermaking), a neutral region (neutral papermaking), and an alkaline region (alkaline papermaking).

The paper substrate is smoothed as necessary after papermaking. The smoothing process is performed on-machine or off-machine using a smoothing process device such as a normal super calendar, gloss calendar, or soft calendar.

The base material for a liquid container is manufactured by laminating a thermoplastic resin layer on at least one surface of the paper base material obtained by the above-mentioned manufacturing method. As a method of laminating the thermoplastic resin layer on the paper base material, various known methods such as an extrusion laminating method, a dry laminating method, a wet laminating method, and a thermal laminating method can be appropriately used.

[Manufacturing method of liquid container]
The liquid container of the present embodiment is manufactured using a liquid container base material. The method for producing the liquid container using the liquid container base material is not particularly limited, and the liquid container can be produced by using a known method.

The liquid container of the present embodiment can be suitably used as a packaging container filled with various liquids such as a milk carton and a sake pack.

Hereinafter, the effects of the present invention will be described in detail with reference to Examples. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples indicate "parts by mass" and "% by mass", respectively.

The raw materials used in the examples and comparative examples are as follows.
(1) Pulp: NBKP, LBKP
(2) Paper strength enhancer: Polyacrylamide-based paper strength enhancer (PAM)
(3) Wet paper strength enhancer: Polyamide polyamine Epichlorohydrin-based (PAE-based) resin (4) Catylated starch (5) Sulfuric acid band (6) Sizing agent: Alkyl ketene dimer-based sizing agent (AKD)
(7) Thermoplastic resin: Low density polyethylene (LDPE)

The measurement methods for various performances are as follows.
(1) Pulp Dissolution Freeness (csf): The pulp slurry obtained by dissociating the base material according to JIS P8212: 2012 was measured according to JIS P8121-2: 2012.
(2) Basis weight: The basis weight of the paper base material was measured according to JIS P8124: 2011.
(3) Moisture: After humidity control, the moisture content of the base material was measured according to JIS P8127; 2010.
(4) Interlayer strength: According to JAPAN TAPPI 18-2, the vertical and horizontal directions of the base material were measured, and the geometric mean value thereof was obtained. As the double-sided tape, 400 manufactured by 3M Co., Ltd. was used.

The basis weight in each layer is measured by dividing one sheet of paper substrate into each layer. The division into layers is performed as follows.
1) Soak a sample cut into a size of 28 cm x 28 cm in hot water at 80 ° C. for 24 hours.
2) Take the sample out of the hot water and place it on a water-moistened absorbent paper. The blotting paper used is that specified in JIS P 8222: 2015.
3) Place the absorbent paper on the sample and lightly press it by hand to remove excess water.
4) Remove the blotting paper on the sample and slowly peel it off one by one from the edge of the paper. At that time, the sample is appropriately wetted with water so that the paper does not dry.
5) Separately, restrain the peeled paper between the drying plate specified in JIS P 8222: 2015 and the hand-made paper fixing device for the drying plate, and dry it for 1 day or more.

[Example 1]
(Paper base material)
70 parts of LBKP and 30 parts of NBKP were beaten to obtain a pulp slurry. 0.5% by mass of sulfate band, 0.40% by mass of cationized starch, and 0.25% by mass of paper strength enhancer (PAM-based paper strength enhancer) with respect to 100% by mass (solid content equivalent) of the obtained pulp slurry. , 0.23% by mass of an alkyl keten dimer-based sizing agent and 0.07% by mass of a PAE-based wet paper strength enhancer were added to obtain a paper material slurry. Using the obtained paper slurry, a five-layer papermaking process was performed using an on-top former having a long net type initial dehydration section, and papermaking was performed. At the time of papermaking, each layer was dehydrated with one wire each in the initial dehydration section, and then sandwiched between the first wire and the second wire different from the wires in the initial dehydration section in the double-sided dehydration section to form dehydrated wet paper, in order. One layer at a time was transferred onto the same felt plane, and the layers were laminated. The order of abstraction was the order of the first layer, the second layer, the third layer, the fourth layer, and the fifth layer. The basis weights from the first layer to the fifth layer were adjusted as shown in Table 1 to prepare a paper base material.

The obtained paper substrate had a basis weight of 296 g / m ² . The dissociation freeness (csf) of the obtained pulp obtained by re-dissociating the paper substrate was 510 ml.

(Base material for liquid containers)
LDPE was laminated as a thermoplastic resin layer on both sides of the paper base material. Lamination was carried out by an extrusion laminating method under the conditions of a laminating temperature of 330 ° C. and a laminating speed of 200 m / min to form a thermoplastic resin layer to obtain a base material for a liquid container of Example 1.

[Example 2]
In Example 1, paper was made in the same manner as in Example 1 except that three layers were assembled instead of five layers and the basis weight ratio was adjusted as shown in Table 1, and the basis weight was 300 g / m. ² paper substrates were obtained. The order of abstraction was the first layer, the second layer (corresponding to the second-4 layers in the table), and the third layer (corresponding to the fifth layer in the table).
Then, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a base material for a liquid container of Example 2.

[Example 3]
In Example 1, a paper substrate having a basis weight of 315 g / m ² was obtained by papermaking in the same manner as in Example 1 except that the basis weight ratio was adjusted as shown in Table 1.
Then, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a base material for a liquid container of Example 3.

[Example 4]
In Example 1, 70 parts of LBKP and 30 parts of NBKP were replaced with 100 parts of LBKP, and the paper was made in the same manner as in Example 1 except that the basis weight ratio was adjusted as shown in Table 1, and the basis weight was 301 g / m. ² paper substrates were obtained. The dissociation freeness (csf) of the pulp obtained by re-dissociating the obtained paper substrate was 480 ml.
Then, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a base material for a liquid container of Example 4.

[Example 5]
70 parts of LBKP and 30 parts of NBKP were beaten to obtain a pulp slurry. 0.5% by mass of sulfuric acid band, 0.40% by mass of cationized starch, 0.85% by mass of paper strength enhancer (PAM-based paper strength enhancer) with respect to 100% by mass (solid content equivalent) of the obtained pulp slurry. , 0.23% by mass of an alkyl keten dimer-based sizing agent and 0.07% by mass of a PAE-based wet paper strength enhancer were added to obtain a paper material slurry. Using the obtained paper slurry, paper was made in the same manner as in Example 1 except that the basis weight ratio was adjusted as shown in Table 1, to obtain a paper substrate having a basis weight of 300 g / m ^2. It was.
Then, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a base material for a liquid container of Example 5.

[Example 6]
In Example 1, the same as in Example 1 except that the basis weight ratio was adjusted as shown in Table 1 and the vapor pressure of the dryer was adjusted so that the water content was 9.5% or more. A paper substrate having a basis weight of 300 g / m ² was obtained.
Then, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a base material for a liquid container of Example 6.

[Comparative Example 1]
In Example 1, a paper substrate having a basis weight of 300 g / m ² was obtained by papermaking in the same manner as in Example 1 except that the basis weight ratio was adjusted as shown in Table 1.
Then, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a base material for a liquid container of Comparative Example 1.

[Comparative Example 2]
In Example 1, a paper substrate having a basis weight of 300 g / m ² was obtained by papermaking in the same manner as in Example 1 except that the basis weight ratio was adjusted as shown in Table 1.
Then, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a base material for a liquid container of Comparative Example 2.

After offset printing was applied to the surface of the obtained base material for a liquid container, it was cut and punched into a predetermined shape, and at the same time, a ruled line was provided at a necessary position to obtain a blank material. Next, a part of the resin material of the blank material was melted by the frame seal, and the body portion was bonded to obtain a tubular sleeve. Subsequently, this tubular sleeve was supplied to a liquid filling machine, a bottom portion was formed on the filling machine, and then the top portion was sealed to obtain a gable top type liquid container.

[Evaluation method]
The liquid container and the base material for the liquid container obtained as described above were evaluated as follows. The evaluation results are as shown in Table 1. In the performance evaluation, ○ and △ were judged to be acceptable, and × was judged to be unacceptable.

(Printing / laminating workability: peeling due to squeezing and peeling during heating)
When the base material for liquid containers was printed and laminated, the base material for liquid containers was visually observed and evaluated according to the following criteria.
◯: No peeling between layers is observed on the paper substrate.
Δ: Some strain is observed in the layer of the paper substrate itself, but no peeling between layers is observed.
X: Very much peeling between layers is conspicuous on the paper substrate.

(Rules crack)
The base material for liquid containers was visually observed when the base material for liquid containers was lined, and the evaluation was performed according to the following criteria.
◯: No cracks are found in the ruled lines of the liquid container base material.
Δ: Some wrinkles are seen on the ruled lines of the base material for the liquid container, but almost no cracks are seen.
X: Very many cracks are seen in the ruled line portion of the base material for liquid containers.

As can be seen from the results in Table 1, the base materials for liquid containers of Examples 1 to 6 satisfy the provisions of the basis weight ratio W1 / W2, and in terms of printability / laminating workability and ruled line cracking. It was excellent. In the base material for a liquid container of Example 5, since the amount of the paper strength enhancer added was large, the interlayer strength was large, and some wrinkles were observed in the ruled line portion. In the base material for a liquid container of Example 6, the water content of the base material is large, and the water content in the base material is vaporized during heating in the printing / laminating process, and some strain is observed in the layer of the paper base material itself. It was.
On the other hand, the base materials for liquid containers of Comparative Example 1 and Comparative Example 2 are inferior in printing / laminating workability, such as low interlayer strength and conspicuous delamination during processing because they do not satisfy the regulation of basis weight ratio W1 / W2. It was a thing.

Claims (11)

A base material for a liquid container having a paper base material containing cellulose pulp as a main component and a thermoplastic resin layer laminated on at least one surface of the paper base material.
The paper base material is composed of three or more pulp layers.
When the average value of the basis weight of the outermost layers of the front and back surfaces of the paper substrate is W1, and the average value of the basis weight of the first inner layer located immediately inside the outermost layer of the front and back surfaces is W2, W1 / W2 = 1 A base material for a liquid container, which is characterized by satisfying 1 to 2.4. The base material for a liquid container according to claim 1, wherein the interlayer strength measured using an internal bond tester is 200 to 600 J / m ² . The base material for a liquid container according to claim 1 or 2, wherein the water content of the paper base material is 6.0 to 9.5%. The base material for a liquid container according to any one of claims 1 to 3, wherein the paper base material is composed of five or more pulp layers. A liquid container using the liquid container base material according to any one of claims 1 to 4. A method for producing a base material for a liquid container, which comprises a paper base material containing cellulose pulp as a main component and a thermoplastic resin layer laminated on at least one surface of the paper base material.
The paper base material is composed of three or more pulp layers.
When the average value of the basis weight of the outermost layers of the front and back surfaces of the paper substrate is W1, and the average value of the basis weight of the first inner layer located immediately inside the outermost layer of the front and back surfaces is W2, W1 / W2 = 1 .. A method for producing a base material for a liquid container, which comprises a laminating step of laminating the pulp layers so as to satisfy 1 to 2.4. The method for producing a base material for a liquid container according to claim 6, wherein the laminating step is a multi-layer bonding step of three or more pulp layers. The method for producing a base material for a liquid container according to claim 7, wherein in the multi-layer bonding step, one of the outermost layers on the front and back surfaces to the outermost layer on the other side are sequentially bonded. The seventh or eighth aspect of the present invention, wherein the multilayer bonding step includes a step of dehydrating with at least one wire and a step of laminating on a wire or felt different from the wire. A method for manufacturing a base material for a liquid container. 7. The step 7 or the present invention is characterized in that the multilayer bonding step includes a step of sandwiching and dehydrating the first wire and the second wire, and a step of laminating on a third wire or felt different from these wires. The method for producing a base material for a liquid container according to claim 8. The multi-layer bonding step is a step of dehydrating with at least one wire in the initial dehydration section, a step of sandwiching and dehydrating with the first wire and the second wire in the double-sided dehydration section, and a third wire different from these wires. The method for producing a base material for a liquid container according to claim 7 or 8, further comprising a step of laminating on a felt.