JP2020172085A - Base material for cup, cup container for liquid and method for producing the same - Google Patents

Abstract

To provide a base material for cup having a paper base material of a multilayer structure which prevents delamination and peeling in a seam part and is excellent in top curling workability, and a cup container for liquid using the base material for cup.SOLUTION: A base material for cup 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 cup container for liquid using the base material for cup and a method for producing the base material for cup.SELECTED DRAWING: None

Description

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

Paper cups (liquid cup containers) are widely used in fast food stores, vending machines, and the like to provide beverages such as coffee and juice to purchasers.

In order to impart water resistance to the inner surface of the liquid cup container, a thermoplastic resin layer is laminated on the paper base material. When laminated paper having a thermoplastic resin layer on the inner surface of the container is used, the liquid does not come into direct contact with the paper base material, which is preferable in terms of hygiene and appearance.

Further, as the paper base material of the laminated paper, since it is excellent in physical properties and productivity, a multi-layer paper base material in which a plurality of pulp layers are laminated is often 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.

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

A general automatic supply device for a cup container for liquid uses the top curl portion of the container to perform automatic supply. For example, an automatic paper cup feeder in a vending machine stores a large number of paper cups stacked in the vertical direction. The automatic paper cup supply device supports a large number of paper cups by engaging with the top curl part of the lowest paper cup during standby, and at the time of sale, the engagement is released and immediately above. Engage with the top curl of the paper cup. In this way, the automatic paper cup feeding device uses the top curl portion to reliably drop the paper cups one by one and provide them to the user.

The molding process of the top curl portion of the liquid cup container (hereinafter, may be referred to as the top curl process) is performed as follows, for example. 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 upper end opening side of the paper cup, and the peripheral edge of the upper end opening of the paper cup is curled 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 a cup base material used for such a liquid cup container, base materials having various configurations have been conventionally studied. For example, in Patent Document 1, LBKP, which is made by laminating three or more layers and has a drainage degree of 320 to 420 ml CSF, is used for the outermost layer, and the ratio of the tensile strength in the vertical direction between the outermost layer and the innermost layer (table). A base paper for a paper cup having a / back) of 1.00 or less is disclosed.

Japanese Unexamined Patent Publication No. 2012-219381

The base paper for paper cups of Patent Document 1 is intended to improve the top curl workability by increasing the tensile strength and basis weight of the backmost layer rather than the outermost layer, but delamination is taken into consideration. However, there was room for further improvement.

When a liquid cup container is manufactured using a cup base material (hereinafter, also referred to as "base material" as appropriate), when the base material is top-curled, the outside of the top curl portion is exposed. A tensile force acts, and a compressive force acts on the inside. As described above, in the top curl processing, a force (shearing force) in the opposite direction acts on the front and back surfaces of the base material. Therefore, when a paper base material having a multilayer structure is used, if the interlayer strength is not sufficiently large, the layers Peeling may be caused.

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

Further, in the seam portion, a force for returning from the cup shape to the original state is generated by the elastic force. In addition, when the top curl processing is performed, the diameter of the outside of the top curl is larger than the inner diameter of the container, so that a force is generated to extend in the circumferential direction. Due to these two forces, a force for peeling acts on the seam portion, and the peeling on the adhesive surface between the base materials and the peeling in the layer of the base materials themselves are likely to occur.

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

The present inventors focused on the basis weight of each pulp layer constituting the multi-layered paper substrate. Then, when a paper base material having a multilayer structure 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 and peeling at the seam portion are reduced, and the top curl workability is 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 cup base material 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 3. W1 is the average value of the basis weight of the outermost layers on the front and back surfaces of the paper substrate, and the average value of the basis weight of the first inner layer located immediately inside the outermost layers on the front and back surfaces is W2. When, the base material for a cup is characterized by satisfying W1 / W2 = 1.1 to 2.4.

(2) The base material for a cup according to (1) above, wherein the interlayer 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 base material according to any one of (1) to (3) above.

(5) A method for producing a base material for a cup 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 material 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 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 cup, which comprises a laminating step of laminating the pulp layers so as to satisfy W1 / W2 = 1.1 to 2.4 when the value is W2.

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

(7) The method for producing a base material for a cup according to (6) above, wherein in the multi-layer bonding step, the outermost layer of one of the front and back surfaces is sequentially bonded to the outermost layer of the other. ..

(8) The above-mentioned (6) or the above-mentioned (6) or the said (8) said that the said multi-layer paper-making step includes the step of dehydrating with at least one wire, and the step of laminating on a wire or felt different from the wire. The method for producing a base material for a cup according to 7).

(9) 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. (6) or the method for producing a base material for a cup according to (7) above.

(10) 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 cup according to the above (6) or (7), which comprises a step of laminating on a third wire or felt.

The base material for a cup of the present invention has a paper base material having a multi-layer structure, is less likely to cause delamination and peeling at the seam portion, and is excellent in top curl workability.

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 cup of the present invention has 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. 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 60% by mass or more with respect to the total mass of the pulp components. It is preferably 80% by mass, more preferably 90% 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 cup 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 surface quality can be made into a better base material for cups.

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 outer surface of the liquid cup container, and the back side refers to the inner surface 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 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 cup 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 cups 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 available depending on the application. Can be formed. For example, the same or different types of thermoplastic resin layers may be further provided on the cup base material composed of the paper base material and the 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 cup]
When 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-mentioned multi-layer structure, they came into contact with the adhesive surface (seam portion) or the adhesive surface of the two base materials. It was found that a lot of peeling occurred near the boundary between the outermost layer and the first inner layer. Shear force is applied to the inside of the base material by the top curl processing, and this shear force is applied to the adhesive surface or the adhesive surface of the two base materials near the center of the thickness of the laminate composed of the two base materials. It is estimated to be the strongest at the interface between the inner layers of nearby substrates. Therefore, the present inventors make the basis weight of the outermost layer larger than the basis weight of the first inner layer in order to suppress the occurrence of peeling from the vicinity of the boundary between the outermost layer and the first inner layer in the top curl portion. It was investigated.

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 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 base material close to the adhesive surface is separated from the adhesive surface of the base material. It is presumed that a large shearing force is less likely to be applied to the surface. Further, 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. When the paper base material has three layers, the average value of the basis weight of the first inner layer means the basis weight of the first inner layer of one layer. When W1 / W2 exceeds 2.4, the boundary surface is concentrated in the central portion of the paper base material. At this time, it is presumed that a large shearing force is applied to the central portion of the paper base material, so that it is considered that delamination is likely to occur during the top curl processing.

From the viewpoint of improving the interlayer strength, W1 / W2 = 1.1 to 2.4 is preferable. 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.

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, in the top curl portion of the base material having the multi-layered paper base material, a force (shearing force) in the opposite direction acts on the front and back surfaces of the paper base material, and the phenomenon of peeling between the layers constituting the paper base material. Will occur. 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 cups and found to be 200 to 800 J / m ^2. It was found that it is preferable.

When the interlayer strength is 200 J / m ² or more, delamination is unlikely to occur in the top curl portion. In addition, delamination due to vaporization of moisture in the paper base material during heating in laminating or printing and delamination due to ironing during processing are less likely to occur. On the other hand, when the interlayer strength is 800 J / m ² or less, the paper base material is not hard, so that surface cracking is unlikely to occur during top curl processing. The interlayer strength is more preferably 250 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 by 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 separation freeness of the paper base material, and the paper strength enhancement 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 cup base material 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, 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 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 cup]
The paper base material constituting the base material for the cup 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 cup 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 cup container]
The liquid cup container of the present embodiment is manufactured using a cup base material. The method for producing the liquid cup container using the cup base material is not particularly limited, and the liquid cup container can be produced by using a known method.

The top curl process that wraps the peripheral edge of the upper end opening of the cup to the outside is performed by, for example, applying a mold to the peripheral edge of the upper end opening of the cup to widen the opening and curl shape of a specific size from the upper end opening side of the cup. Apply the mold and curl outward with respect to the periphery of the top opening of the cup. Further, by pushing the cup downward, it may be guided along the curved surface of the mold having the curl shape set downward and wound inward to form the top curl 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. 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) 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)
100 parts of LBKP was beaten to obtain a pulp slurry. 0.5% by mass of sulfate band, 0.40% by mass of cationized starch, 0.35% 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 237 g / m ² . The dissociation freeness (csf) of the obtained pulp obtained by re-dissociating the paper substrate was 480 ml.

(Base material for cup)
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 cup of Example 1.

[Example 2]
In Example 1, three layers were made instead of five layers, 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 235 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 cup 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 cup of Example 3.

[Example 4]
In Example 1, a paper substrate having a basis weight of 296 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 cup of Example 4.

[Example 5]
100 parts of LBKP was beaten to obtain a pulp slurry. 0.5% by mass of sulfuric acid band, 0.40% by mass of cationized starch, 0.10% 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 cup of Example 5.

[Example 6]
100 parts of LBKP was beaten to obtain a pulp slurry. 0.5% by mass of sulfate band, 0.40% by mass of cationized starch, and 1.00% 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 cup 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 cup 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 cup of Comparative Example 2.

Using each of the obtained base materials for cups, a cup container for liquid was molded so that the inner diameter of the upper part was 85 mm and the diameter of the top curl portion was 3 mm.

[Evaluation method]
The liquid cup container and the cup base material obtained as described above were evaluated as follows. The evaluation results are as shown in Table 1. In terms of top curl workability, ○ and Δ were judged to be acceptable, and × was determined 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 turning up is seen in the seam part.
Δ: Some distortion is seen in the seam part, but almost no turning up is seen.
×: The seam part is very often turned up.

(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 seen in the layer of the top curl part.
Δ: Some strain is observed in the layer at the top curl portion, but almost no peeling is observed.
X: Very much 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.
◯: No surface cracks are seen on the top curl part.
Δ: Some wrinkles are seen on the top curl part, but almost no surface cracks are seen.
X: Very many surface cracks are seen in the top curl part.

As can be seen from the results in Table 1, the cup base materials of Examples 1 to 4 all satisfy the provisions of the basis weight ratio W1 / W2 and are excellent in top curl workability. It was. Although the cup base material of Example 5 satisfies the provision of the basis weight ratio W1 / W2, since the amount of the paper strength enhancer added is smaller than that of Example 1, the interlayer strength is small and the strain is slightly observed. Was done. Further, although the base material for the cup of Example 6 satisfies the regulation of the basis weight ratio W1 / W2, since the amount of the paper strength enhancer added is larger than that of Example 1, the interlayer strength is excessive and the paper The base material became hard, and some wrinkles were seen on the top curl part.
On the other hand, the base materials for cups of Comparative Example 1 and Comparative Example 2 were inferior in top curl workability because they did not satisfy the regulation of the basis weight ratio W1 / W2.

Claims (10)

A base material for a cup 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 cup, which is characterized by satisfying 1 to 2.4. The base material for a cup according to claim 1, wherein the interlayer strength measured using an internal bond tester is 200 to 800 J / m ² . The base material for a cup according to claim 1 or 2, wherein the paper base material is composed of five or more pulp layers. A liquid cup container using the cup base material according to any one of claims 1 to 3. A method for producing a base material for a cup, 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 cup, 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 cup according to claim 5, 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 cup according to claim 6, 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 sixth or seventh aspect of the 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 cup. 6. or claim 6, wherein the multi-layer bonding step includes a step of sandwiching and dehydrating between 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 cup according to claim 7. 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 cup according to claim 6 or 7, further comprising a step of laminating on a felt.