JP7172818B2 - Base material for cup, cup container for liquid, and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cup base material, a liquid cup container using the same, and a method for manufacturing the cup base material.

BACKGROUND ART Paper cups (liquid cup containers) are widely used in fast food restaurants, vending machines, etc. to provide purchasers with beverages such as coffee and juice.

In order to impart water resistance to the inner surface of a cup container for liquid, lamination of a thermoplastic resin layer on a paper substrate is performed. The use of laminated paper having a thermoplastic resin layer on the inner surface of the container is preferable in terms of sanitation and appearance because liquid does not come into direct contact with the paper substrate.

As the paper base material for laminated paper, a multi-layer paper base material (multilayer structure) in which a plurality of pulp layers are laminated is often used because of its excellent physical properties and productivity. A multi-layered paper substrate is produced by stacking several low basis weight sheets, pressing them, and drying them. When paper with a high basis weight is made, the multi-layer paper making method is advantageous from the viewpoint of productivity because the drying load is small and the paper making speed can be made faster than that of the single layer paper making.

Further, in the liquid cup container, the top curl portion is formed by winding the peripheral edge of the upper end opening portion outward. In addition to the role of increasing the strength of the liquid cup container, the top curl portion also has the role of functioning as a hook when mechanically supporting the liquid cup container in an automatic supply device or the like.

A general automatic supply device for a liquid cup container performs automatic supply using the top curl portion of the container. For example, an automatic paper cup feeder in a vending machine contains a large number of vertically stacked paper cups. The paper cup automatic supply device supports a large number of paper cups by engaging with the top curl portion of the lowest paper cup during standby. It engages the top curl of the paper cup. In this way, the automatic paper cup feeder utilizes the top curl section to reliably drop the paper cups one by one and provide them to the user.

Molding of the top curl portion of the liquid cup container (hereinafter sometimes referred to as top curl processing) is performed, for example, as follows. First, a mold for upper molding and a mold for lower molding of the top curl portion are prepared. Each mold has a specific curl shape. Next, a mold for upper molding is applied from the side of the upper end opening of the paper cup to curl the periphery of the upper end opening of the paper cup outward. After that, by pushing the paper cup downward, the peripheral edge of the upper end opening of the paper cup is rolled inward along the curved surface of the lower molding die set downward, and the top curl portion is formed.

As for the base material for a cup used in such a cup container for liquid, base materials having various configurations have conventionally been studied. For example, in Patent Document 1, paper is made by combining three or more layers, LBKP with a freeness of 320 to 420 ml CSF is used for the outermost layer, and the ratio of tensile strength in the longitudinal direction between the outermost layer and the outermost layer (front /back) is 1.00 or less.

JP 2012-219381 A

The base paper for paper cups of Patent Document 1 is intended to improve the top curl processability by increasing the tensile strength and basis weight of the outermost layer than the outermost layer, but delamination is not taken into consideration. However, there is still room for improvement.

When manufacturing a liquid cup container using a base material for a cup (hereinafter also referred to as "base material" as appropriate), if the base material is subjected to top curling, the outer side of the top curl part A tensile force acts and a compressive force acts on the inside. In this way, in the top curling process, forces in opposite directions (shearing force) act on the front and back surfaces of the base material. Delamination may be caused.

In particular, the top curling of the adhesive portion (seam portion) on the side surface of the liquid cup container is much more difficult than other portions. Since the seam portion is a portion where two base materials are overlapped and joined, a greater force is applied than other portions during top curl processing.

Also, at the seam portion, a force is generated to return the cup shape to its original state due to the elastic force. In addition, when the top curling process is performed, the outer diameter of the top curl becomes larger than the inner diameter of the container, so a force to expand in the circumferential direction is generated. Due to these two forces, a peeling force acts on the seam portion, and peeling is likely to occur at the adhesive surface between the base materials and within the layers of the base material itself.

The present invention has been made in view of such circumstances. That is, an object of the present invention is to provide a cup base material having a multi-layered paper base material which is less likely to cause delamination of the top curl part and peeling of the top curl part from the seam part and which has excellent top curl processability; An object of the present invention is to provide a liquid cup container using a cup base material. Here, the term "excellent top curl workability" means that delamination and peeling from the adhesive portion are unlikely to occur at the top curled portion between layers and the top curled seam portion, as described later, and the top curled portion It is a characteristic that cracks are less likely to occur on the surface of the part.

The present inventors paid attention to the basis weight of each pulp layer that constitutes the paper base material of the multilayer structure. 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 was found that delamination and delamination at seams were reduced, and top curl workability was improved. The inventors have also found that a paper-making method in which pulp layers are successively combined from one side of a paper base material to the other side is effective. The present invention has been completed based on such findings. That is, the present invention has the following configurations.

(1) A cup substrate comprising a paper substrate containing cellulose pulp as a main component and a thermoplastic resin layer laminated on at least one surface of the paper substrate, wherein the paper substrate comprises three W1 is the average basis weight of the outermost layers on the front and back sides of the paper substrate, and W2 is the average basis weight of the first inner layer positioned just inside the outermost layers on the front and back sides. A cup base material satisfying W1/W2=1.1 to 2.4.

(2) The base material for a cup according to (1) above, characterized in that the interlaminar strength measured using an internal bond tester is 200 to 800 J/m ² .

(3) The base material for a cup according to (1) or (2) above, wherein the paper base material is composed of five or more pulp layers.

(4) A liquid cup container using the cup substrate according to any one of (1) to (3) above.

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

(6) The method for producing a cup base material according to (5) above, wherein the lamination step is a multi-layer papermaking step of three or more pulp layers.

(7) The method for producing a cup base material according to (6) above, wherein in the multi-layer paper-making step, the outermost layer on one of the front and back sides to the outermost layer on the other side are sequentially made. .

(8) The above (6) or ( 7) The method for producing a cup base material.

(9) The multi-layer combining step includes a step of sandwiching and dehydrating with a first wire and a second wire, and a step of laminating on a third wire or felt different from these wires. (6) or the method for producing a cup substrate according to (7) above.

(10) The multi-layer combining step includes a step of dewatering with at least one wire in the initial dewatering section and a step of sandwiching and dewatering with the first wire and the second wire in the double-sided dewatering section, and these wires are different. and laminating on a third wire or felt.

The cup base material of the present invention has a multi-layered paper base material, is resistant to delamination and delamination at seams, and is excellent in top curl processability.

Embodiments of the present invention will be specifically described below. Although the constituent elements described below may be described based on representative embodiments and specific examples, the present invention is not limited to such embodiments.

The cup substrate of the present invention comprises a paper substrate containing cellulose pulp as a main component, and a thermoplastic resin layer laminated on at least one surface of the paper substrate. Each member constituting the present embodiment will be described below.

[Paper substrate]
The paper substrate is mainly composed of cellulose pulp. Here, the main component means a component that accounts for 50% by mass or more of the components that constitute the paper substrate.

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

LKP has shorter fibers than NKP and is inferior in strength, but is excellent in formation and smoothness of the paper produced. In order to obtain good printability, the paper substrate must have good formation and smoothness, so the content of LKP should be 60% by mass or more based on the total mass of the pulp components. It is preferably 80% by mass, more preferably 90% by mass or more.

The paper substrate may contain pulp other than the above NKP and LKP (hereinafter referred to as other pulp). Other pulps include stone ground pulp (SGP), pressure stone ground pulp (PGW), refiner ground pulp (RGP), thermo ground pulp (TGP), chemi ground pulp (CGP), ground wood pulp (GP), thermo Manufactured from mechanical pulp such as mechanical pulp (TMP), waste tea paper, waste kraft envelope paper, waste magazine paper, waste newspaper paper, waste leaflet paper, waste office paper, waste cardboard, waste white paper, waste paper for Kent, waste imitation paper, waste paper for certificates, etc. Examples include defiberized waste paper pulp (DIP), or pulp chemically or mechanically produced from non-wood fibers such as kenaf, hemp, reeds, and the like. 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, relative to the total mass of the pulp components.

In general, the lower the freeness (freeness) of the pulp component, the higher the tensile strength of the paper-made product. However, when the freeness is reduced, not only does the tensile strength increase, but the paper tends to become harder. If the paper is too hard, the molding processability will be poor, so in order to achieve a paper base material that has an excellent balance of tensile strength and does not become too hard, the pulp has a defibration freeness (csf) of 410 to 600 ml. is preferred. The disaggregation freeness (csf) is more preferably 420-590 ml, even more preferably 430-580 ml.

The disaggregation freeness (csf) refers to the Canadian standard freeness value measured using a pulp slurry obtained by disaggregating a paper substrate. The defibration 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 360-550 ml, more preferably 370-540 ml, even more preferably 380-530 ml.

(filler)
There are no particular restrictions on the fillers that are added when the paper substrate is made, and fillers that are commonly used in the papermaking field can be used. Examples of fillers include clay, calcined kaolin, delaminated kaolin, ground calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous Inorganic fillers such as silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide and zinc hydroxide, and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin and fine hollow particles. These fillers can be used alone or in combination of two or more, depending on the purpose.

(Internal auxiliary agent)
When the paper substrate is made into paper, it is possible to appropriately select and use various internal additives as necessary. Examples of internal additives include sizing agents, yield improvers, freeness improvers, paper strength enhancers, wet paper strength enhancers, starches such as cationized starch, bulkiness improvers, aluminum sulfate, polyvalent Metal compounds, silica sol, antifoaming agents, coloring dyes, coloring pigments, fluorescent whitening agents, pH adjusters, pitch control agents, slime control agents and the like.

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

(papermaking)
The paper substrate is composed of three or more pulp layers. The paper substrate preferably has 5 or more layers. A paper base material composed of a plurality of pulp layers is generally produced by multi-layer papermaking in which a plurality of inlets are used. As the number of layers increases, the basis weight of each layer can be reduced, so that formation can be easily removed, the surface properties of the paper base material can be improved, and a cup base material with better surface quality can be obtained.

Here, each pulp layer is given a name in order to identify each of the plurality of pulp layers that constitute the paper substrate. For example, in the case of a paper substrate having a multilayer structure consisting of 5 layers, when each layer is 1st to 5th layers from the front side to the back side, the 1st layer and the 5th layer located on the outermost side are the front and back. will be called the outermost layer of Also, the second layer and the fourth layer positioned just inside the outermost layer on the front and back are called the first inner layer. Furthermore, the third layer positioned inside the first inner layer will be referred to as the second inner layer. Here, the front side refers to the outer side of the liquid cup container, and the back side refers to the inner side of the liquid cup 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 substrate. The water-soluble resin is not particularly limited as long as it is a water-soluble polymer having film-forming properties. Examples of water-soluble resins include polyvinyl alcohol such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and modified polyvinyl alcohol, starches, polyacrylamides, polyethyleneimine, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, Cellulose ethers such as acetyl cellulose and derivatives thereof are included. 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 substrate. The thermoplastic resin layer may be laminated on only one side of the paper substrate, or may be laminated on both sides of the paper substrate. Usually, it is formed at least on the inner surface of the liquid cup container that comes into contact with the liquid.

Either a crystalline resin or an amorphous resin can be used as the thermoplastic resin depending on the application. Thermoplastic resins include polyethylene (LDPE, MDPE, HDPE, LLDPE, etc.), polyolefin resins such as polypropylene and polymethylpentene, polyester resins such as PET and PBT, polyamide resins, polylactic acid, PHB, PBS, PBAT, PCL, Biodegradable resins such as PHBH, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene (ABS) resins, acrylic resins, modified polyphenylene ethers (PPE), and the like. The thermoplastic resin layer may be formed as a single layer of a single resin, may be formed as a single layer by mixing a plurality of resins, or may be formed as a plurality of layers made of the same or different resins. You may

Although the thickness of the thermoplastic resin layer is not particularly limited, it is usually about 10 to 100 μm thick.

The layer structure of the base material for cups is basically a two-layer structure or a three-layer structure consisting of a paper base material and a thermoplastic resin layer. can be formed. For example, a thermoplastic resin layer of the same or different type may be further provided on a cup base material composed of a paper base material and a thermoplastic resin layer, or a layer other than a thermoplastic resin layer may be provided between the thermoplastic resin layers. Layers can also be provided. Layers other than the thermoplastic resin include water-soluble polymers (PVA, etc.), coating layers containing pigments and adhesives as main components, aluminum foil (Al foil), printing layers, and the like.

[Base material for cup]
The present inventors observed the occurrence of peeling in the top curl portion of the base material made of the paper base material having the above multilayer structure, and found that the adhesive surface (seam portion) of the two substrates and the adhesive surface are in contact with each other. It was found that many peelings occurred near the boundary between the outermost layer and the first inner layer. A shearing force is applied to the base material by the top curling process. It is assumed to be strongest at the interfaces of the inner layers of the adjacent substrates. Therefore, in order to suppress the occurrence of delamination near the boundary between the outermost layer and the first inner layer in the top curl portion, the inventors have found that the basis weight of the outermost layer is larger than that of the first inner layer. It was investigated.

As a result, when the average value of the basis weights of the two outermost layers on the front and back 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 is W2, W1/ It was found that satisfying W2=1.1 to 2.4 is effective in suppressing peeling. When W1/W2=1.1 to 2.4, the basis weight of the outermost layer is sufficiently large, and the boundary surface of the inner layer of the substrate close to the bonding surface is kept away from the bonding surface of the substrate, so that the boundary surface It is presumed that this is because large shear forces are less likely to be applied to Also, W1/W2 is preferably in the range of 1.2 to 2.4, more preferably in the range of 1.3 to 1.8. When the paper substrate has three layers, the average value of the basis weight of the first inner layer means the basis weight of one first inner layer. If W1/W2 exceeds 2.4, the interface will be concentrated in the center of the paper substrate. At this time, it is presumed that a large shearing force is applied to the central portion of the paper base material, so that delamination is likely to occur during top curling.

W1/W2=1.1 to 2.4 is preferable also from the viewpoint of improving the interlayer strength. If W1/W2 is less than 1.1, the water content of the layer that is finally combined is not sufficient, and sufficient hydrogen bonding cannot be obtained at the combined surfaces, resulting in a decrease in interlaminar strength. On the other hand, when W1/W2 exceeds 2.4, the layer to be combined at the end has too much moisture, resulting in insufficient dehydration, leading to a decrease in interlaminar strength and workability. There is an impact such as leading to deterioration.

In the multi-layered paper substrate, the basis weight of each of the front and back outermost layers is preferably 25 to 40% of the total basis weight. For example, for a paper substrate of 300 g/m ² , the outermost layer is preferably 75 to 120 g/m ² . The basis weights of the outermost layers on the front and back sides may be the same or different. The basis weight of each of the ^first inner layers immediately inside the front and back outermost layers is smaller ^than the basis weight of the outermost layer. /m ² is preferred. The basis weight of the second inner layer may be equal to or smaller than the basis weight of the first inner layer.

(interlayer strength)
As described above, in the top curl portion of a substrate having a paper substrate with a multilayer structure, a force (shear force) in the opposite direction acts on the front and back surfaces of the paper substrate, causing the layers constituting the paper substrate to separate. will occur. Here, when a method for quantifying the interlaminar strength of a paper base material was investigated, it was found that a measuring method using an internal bond tester was effective. Therefore, in order to suppress the peeling in the layers of the paper base material itself, the numerical range that should be maintained as the interlaminar strength measured using an internal bond tester was examined from the base material for cups, and it was 200 to 800 J / m ² It has been found that it is preferable that

When the interlaminar strength is 200 J/m ² or more, delamination is less likely to occur in the top curl portion. In addition, delamination due to vaporization of moisture in the paper base material during heating during lamination or printing and delamination due to ironing during processing is less likely to occur. On the other hand, when the interlaminar strength is 800 J/m ² or less, the paper base material is not hard, so surface cracks are less likely to occur during top curling. More preferably, the interlayer strength is 250 to 500 J/m ² . Here, the interlaminar strength is a numerical value obtained as a geometric mean of the numerical value of the interlaminar strength measured in the longitudinal direction and the numerical value of the interlaminar strength measured in the lateral direction. A method for measuring interlaminar strength using an internal bond tester is described in J. Am. Measured according to TAPPI 18-2.

As a method for controlling the interlaminar strength measured using the internal bond tester of the base material within the above specified numerical range, the linear pressure in the press process during the papermaking process, the deaggregation freeness of the paper base material, and the paper strength enhancement There is a method of adjusting the added amount of internal additives such as agents, and the amount and concentration of water, starch, and paper strength agent sprayed between layers of papermaking.

(basis weight)
The basis weight of the substrate comprising a paper substrate and a thermoplastic resin layer is preferably 150-500 g/m ² , more preferably 200-400 g/m ² .

(moisture)
The water content of the base material is the water contained in the base material for a cup composed of a paper base material and a thermoplastic resin layer. The moisture content of the substrate is preferably 6.0-9.5%, more preferably 6.2-8.0%. When the water content of the base material is 6.0% or more, wrinkles are less likely to occur in the paper base material, and the workability is less likely to deteriorate. On the other hand, if 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 evaporate during heating during lamination or printing, causing delamination. The moisture content of the substrate is measured according to JIS P8127;2010 after conditioning.

[Method for producing base material for cup]
The paper substrate constituting the cup substrate is composed of three or more pulp layers. Further, in the paper base material manufacturing method, when W1 is the average value of the basis weights of the outermost layers on the front and back of the paper base material, and W2 is the average value of the basis weights of the first inner layer positioned immediately inside the outermost layer. , W1/W2=1.1 to 2.4.

The lamination step is preferably a multi-layer papermaking step in which three or more pulp layers are combined and papered together. In the multi-layer paper-making step, it is preferable to make paper in order from the outermost layer on one of the front and back to the outermost layer on the other side. Moreover, it is preferable that the basis weight of the outermost layer, which is to be finally combined, is larger than the basis weight of the other pulp layers. As a result, each layer can retain a sufficient amount of water when the sheets are combined, sufficient hydrogen bonding can be obtained at the surfaces of the sheets combined, and the interlaminar strength can be improved.

In the multi-layer combining step, the wet paper web dehydrated with at least one wire is transferred onto a plane of a wire or felt separate from the wire, and layer by layer on the plane of the separate wire or felt. It is preferable to laminate by the method of paper-making in order. In other words, it is preferable that the step of combining multiple layers 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 combining step, the wet paper web sandwiched between the first wire and the second wire and dewatered is transferred onto a third wire separate from these wires or onto the plane of the felt, and It is preferable to stack the sheets one by one on a flat surface of a wire or felt by a method of laminating them one by one. In other words, it is preferable that the multi-layer combining step includes a step of sandwiching and dehydrating with a first wire and a second wire, and a step of laminating on a third wire or felt different from these wires.

In the multi-layer paper combining step, the wet paper web dewatered by at least one wire in the initial dewatering section and further dehydrated by sandwiching it between the first wire and the second wire in the double-sided dewatering section is separated from these wires. It is preferable that the sheet is transferred onto the plane of the third wire or felt and laminated one by one on the plane of the separate third wire or felt in order. In other words, the multi-layer combining step includes a step of dewatering with at least one wire in the initial dewatering section, and a step of sandwiching and dewatering with the first wire and the second wire in the double-sided dewatering section, and these wires are different. and laminating on a third wire or felt. By these methods, formation can be improved and interlaminar strength can be increased.
Furthermore, it is preferable that the length of the initial dewatering portion of the outermost layer is longer than the length of the initial dewatering portion of any pulp layer other than the outermost layer.

The method of making the paper substrate and the model of the paper machine are not particularly limited, and include fourdrinier paper machines, twin wire paper machines, cylinder paper machines, gap formers, hybrid formers (on-top formers), and the like. known papermaking methods and machines can be selected. As the multi-layer paper machine, an on-top former having a fourdrinier initial dewatering section for dewatering with at least one wire is preferred.

The pH during papermaking may be in an acidic range (acidic papermaking), a pseudo-neutral range (quasi-neutral papermaking), a neutral range (neutral papermaking), or an alkaline range (alkaline papermaking).

After paper making, the paper substrate is subjected to a smoothing treatment, if necessary. The smoothing process is performed on-machine or off-machine using a smoothing apparatus such as a normal super calender, gross calender, or soft calender.

The cup substrate is produced by laminating a thermoplastic resin layer on at least one surface of the paper substrate obtained by the above production method. Various known methods such as extrusion lamination, dry lamination, wet lamination, and heat lamination can be appropriately used as methods for laminating the thermoplastic resin layer on the paper substrate.

[Method for manufacturing liquid cup container]
The liquid cup container of the present embodiment is manufactured using a cup base material. The method of manufacturing the liquid cup container using the cup base material is not particularly limited, and it can be manufactured using a known method.

In the top curling process, which rolls the rim of the cup top opening outward, for example, the opening is widened by applying a mold to the rim of the cup top opening, and a curl shape of a specific size is applied from the cup top opening side. Apply the mold and curl outward against the rim of the cup top opening. Further, by pushing the cup downward, the cup is guided along the curved surface of the curled mold set downward and rolled inward to form the top curled portion.

The liquid cup container of the present embodiment can be suitably used as a packaging container filled with various liquids such as paper cups, foam cups, yogurt cups, ice cream cups, and foods.

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

Raw materials used in Examples and Comparative Examples are as follows.
(1) Pulp: NBKP, LBKP
(2) paper strength agent: polyacrylamide-based paper strength agent (PAM)
(3) Wet strength agent: polyamide polyamine epichlorohydrin (PAE) resin (4) cationized starch (5) aluminum sulfate (6) sizing agent: alkyl ketene dimer sizing agent (AKD)
(7) Thermoplastic resin: low density polyethylene (LDPE)

The measurement methods for various performances are as follows.
(1) Pulp defibration freeness (csf): Pulp slurry obtained by defibrating the base material according to JIS P8220:2012 was measured according to JIS P8121-2:2012.
(2) Basis weight: The basis weight of the paper substrate was measured according to JIS P8124:2011.
(3) Interlaminar strength: Based on JAPAN TAPPI 18-2, the longitudinal and transverse directions of the substrate were measured, and the geometric mean value was obtained. The double-sided tape used was 400 manufactured by 3M.

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

[Example 1]
(Paper substrate)
100 parts of LBKP was beaten to obtain a pulp slurry. 0.5% by mass of aluminum sulfate, 0.40% by mass of cationized starch, and 0.35% by mass of a paper strength agent (PAM-based paper strength agent) with respect to 100% by weight of the obtained pulp slurry (in terms of solid content) , 0.23% by mass of an alkylketene dimer-based sizing agent, and 0.07% by mass of a PAE-based wet strength agent were added to obtain a stock slurry. Using the obtained stock slurry, an on-top former having a Fourdrinier type initial dewatering section was used to combine five layers to make paper. When making paper, each layer is dewatered with a wire in the initial dewatering section, and further sandwiched between a first wire and a second wire separate from the wires in the initial dewatering section in the double-sided dewatering section to form a dehydrated wet paper. Each layer was transferred onto the same felt plane, and the sheets were combined and laminated. The paper-making order was the first layer, the second layer, the third layer, the fourth layer, and the fifth layer. The basis weights of the 1st to 5th layers were adjusted as shown in Table 1, and paper substrates were prepared.

The resulting paper substrate had a basis weight of 237 g/m ² . Further, the pulp freeness (csf) obtained by re-macring the obtained paper substrate was 480 ml.

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

[Example 2]
In Example 1, paper was made in the same manner as in Example 1 except that three layers were combined instead of five layers and the basis weight ratio was adjusted as shown in Table 1, and the basis weight was 235 g / m No. ² paper substrate was obtained. The order of papermaking was 1st layer, 2nd layer (corresponding to 2nd to 4th layers in the table), and 3rd layer (corresponding to 5th layer in the table).
Thereafter, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a cup substrate of Example 2.

[Example 3]
In Example 1, 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 base material having a basis weight of 315 g/m ² .
Thereafter, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a cup substrate of Example 3.

[Example 4]
In Example 1, 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 base material having a basis weight of 296 g/m ² .
Thereafter, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a cup substrate of Example 4.

[Example 5]
100 parts of LBKP was beaten to obtain a pulp slurry. 0.5% by mass of aluminum sulfate, 0.40% by mass of cationized starch, and 0.10% by mass of a paper strength agent (PAM-based paper strength agent) with respect to 100% by weight of the obtained pulp slurry (in terms of solid content) , 0.23% by mass of an alkylketene dimer-based sizing agent, and 0.07% by mass of a PAE-based wet strength agent were added to obtain a stock slurry. Using the obtained stock 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 base material having a basis weight of 300 g/m ² . rice field.
Thereafter, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a cup substrate of Example 5.

[Example 6]
100 parts of LBKP was beaten to obtain a pulp slurry. 0.5% by mass of aluminum sulfate, 0.40% by mass of cationized starch, and 1.00% by mass of a paper strength agent (PAM-based paper strength agent) to 100% by weight of the obtained pulp slurry (in terms of solid content) , 0.23% by mass of an alkylketene dimer-based sizing agent, and 0.07% by mass of a PAE-based wet strength agent were added to obtain a stock slurry. Using the obtained stock 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 base material having a basis weight of 300 g/m ² . rice field.
Thereafter, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a cup substrate of Example 6.

[Comparative Example 1]
In Example 1, 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 base material having a basis weight of 300 g/m ² .
Thereafter, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a cup substrate of Comparative Example 1.

[Comparative Example 2]
In Example 1, 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 base material having a basis weight of 300 g/m ² .
Thereafter, a thermoplastic resin layer was formed in the same manner as in Example 1 to obtain a cup substrate of Comparative Example 2.

Using each of the obtained cup base materials, liquid cup containers were formed so that the upper inner diameter was 85 mm and the diameter of the top curl portion was 3 mm.

[Evaluation method]
The liquid cup container and cup base material thus obtained were evaluated as follows. The evaluation results were as shown in Table 1. In terms of top curl workability, ◯ and Δ were judged to be acceptable, and × was judged to be unacceptable.

(Top curl workability: peeling on the adhesive surface)
When the liquid cup container was manufactured, the top curl portion of the seam portion was visually observed and evaluated according to the following criteria.
◯: No curling up is observed in the seam portion.
Δ: Some distortion is observed in the seam portion, but almost no curling is observed.
x: A large amount of curling up is conspicuous at the seam portion.

(Top curl workability: delamination)
When the liquid cup container was manufactured, the top curl portion of the seam portion was visually observed and evaluated according to the following criteria.
◯: No peeling is observed in the layer of the top curled portion.
Δ: Some strain is observed in the layer at the top curl portion, but almost no peeling is observed.
x: A large amount of peeling in the layer is conspicuous in the top curl portion.

(Top curl workability: surface cracking)
When the liquid cup container was manufactured, the top curl portion was visually observed and evaluated according to the following criteria.
◯: Surface cracks are not observed in the top curl portion.
Δ: Some wrinkles are observed in the top curl portion, but almost no surface cracks are observed.
x: A large number of surface cracks are observed in the top curl portion.

As can be seen from the results in Table 1, the cup substrates of Examples 1 to 4 all satisfied the basis weight ratio W1/W2 and were excellent in top curl workability. rice field. The base material for a cup of Example 5 satisfies the stipulation of the basis weight ratio W1/W2. was taken. In addition, although the cup base material of Example 6 satisfies the stipulation of the basis weight ratio W1/W2, the amount of the paper strength enhancer added is larger than that of Example 1, so the interlaminar strength is excessive. The base material became hard, and some wrinkles were observed in the top curl portion.
On the other hand, the base materials for cups of Comparative Examples 1 and 2 did not satisfy the stipulation of the basis weight ratio W1/W2, so they were inferior in top curl workability.

Claims (13)

A cup substrate comprising a paper substrate containing cellulose pulp as a main component and a thermoplastic resin layer laminated on at least one surface of the paper substrate,
The paper substrate is composed of three or more pulp layers,
W1/W2=1, where W1 is the average basis weight of the outermost layer on the front and back of the paper base material, and W2 is the average basis weight of the first inner layer located immediately inside the outermost layer on the front and back of the paper base material. .1 to 2.4 are satisfied ,
A base material for a cup, characterized by having an interlaminar strength of 200 J/m ² or more as measured using an internal bond tester . 2. The cup substrate according to claim 1, wherein the interlaminar strength measured using an internal bond tester is 200 to 800 J/m ² . 3. The base material for a cup according to claim 1, wherein the paper base material is composed of five or more pulp layers. The cup substrate according to any one of claims 1 to 3, wherein the inner layer of the paper substrate contains a polyacrylamide-based paper strength enhancer and cationic starch. A liquid cup container using the cup substrate according to any one of claims 1 to 4 . It has a paper base mainly composed of cellulose pulp and a thermoplastic resin layer laminated on at least one surface of the paper base, and has an interlaminar strength of 200 J/m measured using an internal bond tester. A method for producing a cup base material having ² or more ,
The paper substrate is composed of three or more pulp layers,
W1/W2=1, where W1 is the average basis weight of the outermost layer on the front and back of the paper base material, and W2 is the average basis weight of the first inner layer located immediately inside the outermost layer on the front and back of the paper base material. A method for producing a cup base material, comprising a step of laminating the pulp layers so as to satisfy 1 to 2.4. Interlayer strength measured using an internal bond tester is 200 to 800 J / m ² The method for producing a cup base material according to claim 6, characterized in that: 8. The method for producing a cup base material according to claim 6 or 7, wherein the inner layer of the paper base material contains a polyacrylamide-based paper strength enhancer and cationic starch. The method for producing a cup base material according to any one of claims 6 to 8, wherein the lamination step is a multi-layer papermaking step of three or more pulp layers. 10. The method for producing a cup base material according to claim 9 , wherein in the multi-layer paper-making step, the outermost layer on either one of the front and back sides to the outermost layer on the other side are sequentially made. 11. The method according to claim 9 or 10 , wherein the step of combining multiple layers 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 producing a base material for a cup. 10. The step of laminating multiple layers includes a step of sandwiching between a first wire and a second wire and dewatering , and a step of laminating on a third wire or felt different from these wires. The method for producing a cup substrate according to claim 10 . The multi-layer combining step includes a step of dewatering with at least one wire in the initial dewatering section, a step of sandwiching and dewatering with the first wire and the second wire in the double-sided dewatering section, and a third wire different from these wires. or a step of laminating on felt.