Manufacturing method of paper cups

Abstract

To provide a manufacturing method of paper cups with excellent liquid retention properties, which can reduce plastic quantity to be used.SOLUTION: A manufacturing method of paper cups has the steps of: preparing raw paper for a paper cup with one or more heat-seal layers formed by applying heat-seal layer coating liquid to at least one side of a paper base material; producing body paper and bottom paper from the raw paper for the paper cup; overlapping a part of the body paper and perform heat-seal pressure bonding to form a body part; and folding an outer periphery of the bottom paper downward, folding a lower end of the body part upward to combine it with the bottom paper, and making paper cups with a cup molding machine, wherein the heat-seal layer coating liquid contains aqueous resin dispersion containing a solvent primarily composed of resin and water, and the total heat-seal layer thickness of all heat-seal layers on one side of the raw paper for the paper cup is 2 to 15 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing paper cups that use less plastic and have excellent liquid retention properties. [Background technology]

[0002] In recent years, the problem of plastic waste has become more serious. Global plastic production is said to exceed 400 million tons per year, with a large amount of plastic produced in the packaging sector, contributing to plastic waste. The most commonly used plastics for packaging include polyethylene terephthalate (PET), used in beverage cups and bottles, and polyethylene (PE) and polypropylene (PP), used in plastic bags and container lamination. Plastics do not decompose permanently, and their waste breaks down into microplastics in the natural environment, causing serious damage to ecosystems. Marine pollution is particularly severe, and it is said that such plastic waste is impossible to recover. Reducing plastic use in the future is essential for the global environment.

[0003] One proposed solution is to replace plastic with paper, and paper is widely used in packaging containers. However, when processing paper into paper cups, large amounts of plastics such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) are used in the lamination process as heat sealants. The amount of plastic lamination varies depending on the product concept, but is generally 20 to 60 μm per side, and can be as much as 100 μm on both sides combined. For this reason, even in paper cups where plastic is replaced with paper, the amount of plastic used remains insufficient, and a means to directly reduce plastic use is needed (see Patent Document 1).

[0004] As a processing method for paper cups, Patent Document 2 proposes a method of providing a recess in the female mold portion of the bottom mold to improve the heat-sealing properties of the laminated portion of the paper cup body, as shown in Figures 4 and 5. In addition, Patent Document 2 proposes a method of providing multiple protrusions on the bottom clamping mold, as shown in Figures 7 and 8, to provide a paper cup that reliably connects the body and bottom plate and prevents leakage of contents. However, when the thickness of the heat-sealing layer of the paper cup is reduced to reduce the use of plastic, the heat-sealing of the laminated portion of the paper cup body becomes insufficient, resulting in the problem of liquid leakage. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-87983 [Patent Document 2] Japanese Patent Application Publication No. 58-216539 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention was made in response to the above-mentioned problems, and its purpose is to provide a method for manufacturing paper cups that can reduce the amount of plastic used and have excellent liquid retention properties.

[0007] Another object of the present invention is to provide a method for producing paper cups that are excellent in water repellency and oil repellency.

[0008] Other objects and advantages of the present invention will be readily apparent to those skilled in the art by reading the following description. [Means for solving the problem]

[0009] The paper cup manufacturing method of the present invention includes the steps of preparing a paper cup base paper having one or more heat-seal layers formed by applying a heat-seal layer coating liquid to at least one side of a paper substrate, producing a body paper and a bottom paper from the paper cup base paper, overlapping parts of the body paper and performing a heat-seal pressure bonding process to form a body, folding the outer periphery of the bottom paper downward, folding the lower end of the body upward to combine it with the bottom paper, and producing a paper cup in a cup forming machine.The heat-seal layer coating liquid contains an aqueous resin dispersion containing a solvent mainly composed of resin and water, and the total heat-seal layer thickness of all heat-seal layers on one side of the paper cup base paper is 2 to 15 μm.

[0010] Here, "paper cups" includes paper cups and paper bowls made of paper body and bottom. This method is effective in reducing plastic waste.

[0011] In a preferred embodiment of the present invention, the base paper for paper cups preferably has two or more heat-seal layers. This method improves the air permeability of the base paper for paper cups by covering minute pinholes and cracks in the first coating layer (lower layer) with the second coating layer (upper layer). It also improves water and oil repellency.

[0012] In a preferred embodiment of the present invention, the bottom mold of the cup molding machine is provided with a recess for allowing the overlapping portion of the body paper to escape, and the recess preferably has a depth of 0 to 1.0 mm. According to this method, since the recess of the bottom mold is shallower than conventional ones, even the paper cup of the present invention, which has a thinner heat-seal layer thickness than conventional paper cups, is sufficiently pressurized during heat-sealing, thereby increasing the heat-seal strength between the bottom paper and body paper of the paper cup. In particular, since the overlapping portion of the body paper is also sufficiently pressurized, liquid leakage at the bottom of the paper cup due to poor crimping is less likely to occur.

[0013] In a preferred embodiment of the present invention, the heat-sealable layer coating solution is preferably composed of only an ionomer emulsion containing an ionomer and a solvent for the ionomer. This method makes it easy to obtain high heat-seal strength and to keep the coating amount low.

[0014] The present invention can also be seen as an invention relating to base paper for paper cups.

[0015] The base paper for paper cups according to the present invention is a base paper for paper cups in which a heat-seal layer coating liquid is applied to at least one side of a paper substrate to form two or more heat-seal layers, and the heat-seal layer coating liquid contains an aqueous resin dispersion containing a solvent mainly composed of resin and water, and the total heat-seal layer thickness of all heat-seal layers on one side is 2 to 15 μm.

[0016] This configuration allows for the production of paper cups that use less plastic and have excellent water and oil repellency. [Effects of the Invention]

[0017] The paper cup manufacturing method of the present invention reduces the amount of plastic used and makes it possible to manufacture paper cups with excellent liquid retention. In particular, the heat seal strength at the overlapping portion of the body paper and bottom paper is increased, preventing liquid leakage from the bottom. Even if the paper cup of the present invention is inappropriately disposed of as waste in nature, it is possible to reduce the negative impact of plastic waste on the natural environment, thereby helping to solve the plastic waste problem. The paper cup of the present invention is excellent as a paper cup for food products such as beverages, yogurt, ice cream (including lacto ice cream, frozen desserts, and ice milk), boxed lunches, prepared meals, hot snacks, and sweets. The statement that paper cups include paper cups and paper bowls has been moved to the previous paragraph. [Brief explanation of the drawings]

[0018] [Figure 1]1 is a cross-sectional view of a paper cup according to the present invention. [Figure 2] 2 is an enlarged view of the positional relationship between part A in FIG. 1, the bottom mold, and the bottom clamping mold, as viewed from directly above. [Figure 3] FIG. 3 is an enlarged view of part B in FIG. 2. [Figure 4] An enlarged view of the bottom mold relief processing portion and a diagram of the recess. [Figure 5] 1 is a table showing the configurations and evaluation results of base paper for paper cups according to Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] Next, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

[0020] In the present invention, the paper base material used for the base paper for paper cups is not particularly limited, and any known paper base material containing pulp as the main component can be used. Pulp as the main component of the paper base material can be chemical pulp such as LBKP (bleached hardwood kraft pulp) or NBKP (bleached softwood kraft pulp), mechanical pulp such as GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemi-mechanical pulp), or CGP (chemi-ground pulp), wood pulp such as DIP (deinked pulp), or non-wood pulp such as kenaf, bagasse, bamboo, or cotton. Unbleached pulp can also be used. These can be used alone or in any combination. For example, 90 to 100 parts by mass of LBKP (bleached hardwood kraft pulp) can be used as the pulp.

[0021] For example, in order to minimize top curl cracking and increase strength and bending resistance, it is preferable to blend softwood pulp. In such a case, for example, the total pulp content may be 50 to 95 parts by mass of softwood pulp and 5 to 50 parts by mass of hardwood pulp, or only softwood pulp may be used.

[0022] In the present invention, synthetic fibers can be further blended within a range that does not impair the intended effects of the present invention. From the viewpoint of environmental conservation, ECF (Elemental Chlorine Free) pulp, TCF (Total Chlorine Free) pulp, recycled paper pulp, and pulp obtained from planted trees are preferred.

[0023] In the present invention, the beating degree of the pulp is preferably 200 to 700 ml CSF in Canadian Standard Freeness (freeness) (JIS P 8121:1995 "Testing Method for Pulp Freeness"), more preferably 250 to 520 ml CSF, and even more preferably 350 to 420 ml CSF. If the freeness is within this range, paper with appropriate bending resistance for paper packaging containers can be obtained, which makes it less likely to break, particularly during cup molding. On the other hand, if the freeness exceeds 700 ml CSF, the bending resistance of the resulting paper cup base paper may be insufficient, and it may be too soft for a paper cup.

[0024] In the present invention, the ash content of the paper base material is preferably in the range of 0 to 10%, more preferably 0 to 9%, and even more preferably 0 to 7%. If the ash content exceeds 10%, folding cracks are likely to occur during cup molding.

[0025] In the present invention, the paper base material may contain a filler within the above-mentioned ash content range. Examples of fillers used here include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, calcined clay, titanium dioxide, and aluminum hydroxide. The filler content in the paper base material is, for example, 0.2 to 10 parts by mass per 100 parts by mass of the dry mass of pulp. For example, when light calcium carbonate is used as the filler, 0.2 to 10 parts by mass of light calcium carbonate can be blended per 100 parts by mass of the dry mass of pulp. From the viewpoint of preventing breakage during molding, it is preferable to not add a filler.

[0026] In addition to pulp and fillers, the paper substrate may also contain various known papermaking additives. Examples of papermaking additives include water-soluble polymers such as starch, sizing agents, internal paper strength agents such as wet strength agents, bulking agents, retention aids, drainage aids, coloring dyes, coloring pigments, fluorescent brighteners, fluorescent decolorizers, and pitch control agents. For example, it is recommended to add 0.1 to 1.0 parts by mass of a sizing agent, particularly a rosin sizing agent, per 100 parts by mass of pulp, or 0.1 to 1.0 parts by mass of starch, particularly a cationic starch, per 100 parts by mass of pulp. Furthermore, water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide may be applied to the base paper of the paper substrate. The amount of water-soluble polymer applied is 0.5 to 5 g / m2 per both sides. 2 is preferred, and 1 to 4 g / m 2 By applying a water-soluble polymer to the base paper, cracks are less likely to occur when the paper is bent during processing.

[0027] In the present invention, the paper base material may be made by any method without particular limitation, and may be produced using various paper machines such as a Fourdrinier paper machine, a multi-layer Fourdrinier paper machine, a cylinder paper machine, a multi-layer cylinder paper machine, a multi-layer Fourdrinier cylinder combination paper machine, a twin-wire paper machine, etc. The paper base material may be a single-layer paper machine, a multi-layer paper machine, or a laminate of multiple layers.

[0028] In the present invention, a heat-seal layer can be provided by applying an aqueous heat-seal layer coating liquid to at least one surface of a paper substrate and drying it. Any aqueous resin dispersion can be used as the heat-seal layer coating liquid. Here, "aqueous" refers to a dispersion in which the solvent is primarily water. Examples of aqueous resin dispersions that can be used include acrylic dispersions, styrene-acrylic dispersions, polyvinylidene chloride (PVDC) dispersions, urethane dispersions, and ethylene vinyl acetate dispersions. However, it is preferable that the heat-seal layer coating liquid contain an ionomer emulsion because of its excellent heat-seal strength.

[0029] In the present invention, "ionomer" refers to a synthetic resin in which polymers are aggregated by utilizing the cohesive force of metal ions. It is a resin formed by combining acrylic acid or methacrylic acid with ethylene or other compounds. Specifically, metal salts of ethylene-methacrylic acid copolymers, metal salts of ethylene-acrylic copolymers, metal salts of ethylene-urethane copolymers, and metal salts of ethylene-fluorinated polymer copolymers are all included in the ionomer category. Metals that form salts include, for example, alkali metal ions and alkaline earth metal ions, specifically, sodium, potassium, calcium, magnesium, and zinc ions. In the present invention, the ionomer is preferably a self-emulsifying emulsion of a metal salt of ethylene-methacrylic acid copolymer. By including an ionomer emulsion in the heat-seal layer coating solution, a heat-seal layer with sufficient heat-seal strength can be formed even with a relatively low coating weight. Therefore, the use of an ionomer emulsion allows for the coating weight to be controlled relatively low. Furthermore, by using a water-based ionomer emulsion, VOC emissions are eliminated, reducing the burden on the natural environment.

[0030] In the present invention, it is most preferable that the coating liquid for the heat-seal layer contains only the ionomer emulsion without adding any other raw materials such as auxiliaries, but various auxiliaries may be added as necessary. Examples of such auxiliaries include lubricants, viscosity modifiers, antifoaming agents, leveling agents such as surfactants and alcohols, color pigments, and color dyes. However, since the addition of these auxiliaries tends to reduce the heat-seal strength, it is preferable that they be added in small amounts, even if they are added at all.

[0031] In the present invention, the smoothness of the heat-seal layer coating surface of the paper substrate is preferably 10 seconds or more, and more preferably 20 seconds or more. The smoother the paper substrate, the less likely fine irregularities will occur, and the more likely the thickness of the heat-seal layer formed by coating will be uniform. This results in less variation in heat-seal strength, and uniform heat-seal strength can be imparted to the flat surface. The method for increasing the smoothness of the paper substrate is not particularly limited, and examples include calendering using known calendering devices such as super calenders, gloss calenders, shoe-nip calenders, and soft calenders. Paper with a Yankee dryer mirror finish, such as one-sided gloss kraft paper, is also suitable as a highly smooth paper substrate. While pinholes and cracks invisible to the naked eye may be present in the heat-seal layer, these do not adversely affect heat-sealability. Furthermore, a leveling agent for preventing pinholes may be added to the heat-seal layer coating solution within a range that does not impair the effects of the present invention.

[0032] In the present invention, the method for applying the coating liquid for the heat seal layer is not particularly limited, and any commonly used coating device can be used, such as an air knife coater, blade coater, gravure coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, spray coater, gate roll coater, or lip coater.

[0033] In the present invention, it is preferable that the heat seal layer is formed of two or more layers. By forming two or more heat seal layers, water repellency and oil repellency can be imparted, and properties similar to or close to those of plastic film-laminated paper can be obtained. When the heat seal layer has two or more layers, it is preferable that the coating weight of the bottom heat seal layer closest to the paper substrate is greater than the total coating weight of the other heat seal layers. This is because the water repellency and oil repellency of the paper cup are further improved.

[0034] The thickness of the heat seal layer in the present invention is preferably 2 to 15 μm, more preferably 3 to 14 μm, in total for all layers on one side of the paper substrate. If the total thickness of the heat seal layer is less than 2 μm, sufficient heat seal strength may not be obtained. Conversely, if it exceeds 15 μm, the effect of reducing plastics will be poor.

[0035] In the present invention, the heat seal layer is provided on at least one surface of the paper substrate not only in a portion thereof but also over the entire surface thereof, i.e., not only in a net-like, island-like, or linear shape, but also in a portion necessary for adhesion by heat sealing, but is provided so as to cover the entire surface of at least one side of the paper substrate. I was told that the entire page is required, so I have corrected it. Please check that the content is correct.

[0036] In the present invention, the paper substrate may have one or more coating layers other than the heat-seal layer. Examples of such coating layers include pigment coating layers containing a pigment and an adhesive. Pigments for the pigment coating layer can be those commonly used in coating layers of coated printing paper, such as calcium carbonate (heavy calcium carbonate, light calcium carbonate, etc.), kaolin (including clay), calcined clay, talc, magnesium carbonate, barium sulfate, calcium sulfate, titanium dioxide, zinc oxide, zinc sulfate, zinc carbonate, calcium silicate, aluminum silicate, magnesium silicate, diatomaceous earth, aluminum hydroxide, and magnesium hydroxide. Examples include inorganic pigments such as acrylic, styrene, vinyl chloride, and nylon, as well as organic pigments obtained by copolymerizing these (so-called plastic pigments). For example, a combination of 20 to 40 parts by weight of kaolin and 60 to 80 parts by weight of heavy calcium carbonate can be used.

[0037] The adhesive can be any known adhesive used in coating layers of general coated printing papers, including starches such as butadiene copolymer latex, crosslinker-modified starch, oxidized starch, enzyme-modified starch, esterified starch, cationic starch, and amphoteric starch; water-soluble polymers such as gelatin, casein, soy protein, and polyvinyl alcohol; and synthetic resins such as vinyl acetate, ethylene vinyl acetate, polyurethane resins, acrylic resins, polyester resins, and polyamide resins. The blending ratio of pigment and adhesive in the pigment coating layer is not particularly limited, but a ratio of 5 to 50 parts by weight of adhesive per 100 parts by weight of pigment is preferred. For example, a combination of 1 to 5 parts by weight of phosphated starch and 5 to 15 parts by weight of styrene-butadiene latex per 100 parts by weight of pigment can be used as the adhesive.

[0038] The pigment coating layer may contain various auxiliaries within the range that does not impair the intended effects of the present invention, such as viscosity adjusters, softeners, gloss-imparting agents, water-resistant agents, dispersants, flow modifiers, UV absorbers, stabilizers, antistatic agents, crosslinking agents, sizing agents, fluorescent whitening agents, colorants, pH adjusters, antifoaming agents, plasticizers, and preservatives. The coating weight of such a pigment coating layer is, for example, 2 to 40 g / m2 in terms of solid content per side of the paper substrate. 2 In one embodiment of the base paper for paper cups of the present invention, a heat seal layer may be provided on such a pigment coating layer, and in another embodiment, a heat seal layer may be provided on the side of a paper base material having a pigment coating layer on only one side, where the pigment coating layer is not provided.

[0039] The base paper for paper cups according to the present invention has a basis weight of 30 to 400 g / m2, which is the total weight of the paper base material, heat seal layer, and other coating layers. 2 If the basis weight is within this range, the sheet is less likely to break during molding. 2 If the basis weight exceeds 30 g / m, the sheet becomes too rigid and the bending resistance increases too much, which may result in dimensional defects. 2 If it is less than this, the base paper for paper cups may be easily torn.

[0040] The specific volume of the base paper for paper cups according to the present invention is 0.8 to 1.8 cm 3 / g, and 0.9 to 1.7 cm 3 / g is more preferable. 3 If the specific volume is less than 1.8 cm / g, there is a risk that cracks may easily occur during cup molding. 3 If it exceeds 1 / g, there is a risk that sufficient rigidity as a cup cannot be obtained.

[0041] In the base paper for paper cups according to the present invention, the longitudinal tensile elongation at break (JIS P-8113) is preferably 1% or more, and more preferably 1.2% or more. If the tensile elongation at break is less than 1%, folding and cracking are likely to occur during molding. Note that in the present invention, the longitudinal direction refers to the longitudinal grain direction (MD), and the transverse direction refers to the cross grain direction (CD).

[0042] The paper base paper for paper cups according to the present invention preferably has an air permeability of more than 10,000 seconds, more preferably an air permeability of 12,000 seconds or more, and even more preferably an air permeability of 15,000 seconds or more. By making the air permeability of the paper base paper for paper cups 10,000 seconds or more, the barrier properties in terms of blocking air are further improved, and the water repellency and oil repellency are further improved.

[0043] In the present invention, the method for achieving an air permeability of 10,000 seconds or more for the paper cup base paper is not particularly limited, but can be achieved, for example, by using a paper substrate with high air permeability. The air permeability of the paper cup base paper can also be increased by increasing the smoothness of the heat-seal layer coating surface. This is because a high smoothness of the heat-seal layer coating surface can further reduce pinholes and cracks in the subsequently formed heat-seal layer, thereby improving the air permeability. Examples of methods for increasing the smoothness of the heat-seal layer coating surface include providing a pigment coating layer on the heat-seal layer coating surface and then performing a calendering treatment, etc.

[0044] Another method for improving the air permeability of paper cup base paper is to coat it with two or more heat-seal layers. The reason for the improved air permeability when two or more heat-seal layers are coated is thought to be that the second coating layer (upper layer) applied on top of the first coat increases air permeability by covering minute pinholes and cracks present in the first coat (lower layer). Increasing the amount of coating liquid for the heat-seal layer also has an effect on improving air permeability. In terms of film formation of the heat-seal layer, air permeability is likely to be improved by setting the drying temperature after coating of the heat-seal layer coating liquid to a temperature above the melting point of the aqueous resin.

[0045] The structure and molding process of the paper cup according to the present invention will be described in detail with reference to Figures 1 to 4. In Figures 1 to 4, 1 denotes a paper cup, 11 denotes a body paper, 111 denotes a body paper overlapping portion, 12 denotes a bottom paper, 2 denotes a bottom mold, 21 denotes a bottom mold recess, 22 denotes an outer wall of the bottom mold, 23 denotes an inner wall of the bottom mold, and 3 denotes a bottom clamping mold. Note that Figures 1 to 4 are intended to explain the approximate positional relationship of each part, and the size of each part does not strictly reflect the actual scale. In this example, the body paper 11 and bottom paper 12 are made from the same base paper for paper cups, and therefore have the same thickness.

[0046] An example of a cross-sectional view of a paper cup according to the present invention is shown in Figure 1. As shown in Figure 1, the paper cup 1 is made up of a body paper 11 and a bottom paper 12, and is formed by folding the body paper 11 over.

[0047] Figure 2 shows an enlarged view from directly above of the positional relationship between part A in Figure 1, the bottom mold, and the bottom clamping mold. When heat-sealing the body paper 11 and the bottom paper 12, the overlapping portion 111 of the body paper 11 is sandwiched between the bottom mold 2 and the bottom clamping mold 3, as shown in the figure. This body paper overlapping portion 111 is the thickest, and in conventional laminated paper processing, it is also the part that receives the most mechanical load on the bottom mold 2.

[0048] Next, an enlarged view of part B in Figure 2 is shown in Figure 3. This figure shows the positional relationship of the bottom mold offset processing portion near the overlapping portion of the body paper, i.e., the recess. In the present invention, in order to reduce the mechanical load on the overlapping portion 111 of the body paper, as shown in Figure 3, the bottom mold 2 is offset processed so that the inner wall 23 is recessed toward the outside of the bottom mold, forming a recess 21. This "recess" of the bottom mold is sometimes referred to as the "offset processing portion near the overlapping portion of the body paper" or the "relief processing portion."

[0049] An enlarged view of the bottom mold relief processing portion and the bottom mold recess is shown in Figure 4. The offset processing referred to in this invention refers to a processing that includes processing that shifts the portion outward in the normal direction on the mold drawing. In other words, in Figure 4, it includes processing that shifts the bottom mold inner wall 23 outward in the normal direction (toward the bottom mold outer wall 22). The recess depth here refers to the maximum value d (mm) of the length shifted by the bottom mold relief processing, i.e., the distance between the deepest part of the bottom mold inner wall 23 and the bottom mold recess 21. Furthermore, in this invention, a conventional mold can be used as the mold for the body paper 11.

[0050] In the present invention, the heat seal layer is thinner than conventional paper cup base paper, and a bottom mold recess 21 is provided in the bottom mold 2. All of these measures also reduce the pressure applied to the body paper overlap portion 111 during heat sealing. Therefore, if the recess depth d of the bottom mold recess 21 is made too large, the pressure from the bottom clamping mold 3 will escape too much at the body paper overlap portion 111, reducing the heat seal strength of the bottom body paper overlap portion 111 and potentially causing liquid leakage at the bottom. To prevent such liquid leakage, in the present invention, the recess depth of the bottom mold recess 21 of the cup molding machine is set to 0 to 1.0 mm, which is shallower than conventional methods. A recess depth of 0 to 0.5 mm is more preferable.

[0051] Known pressure application methods, such as the divided pressure application method and the rotary pressure application method, can be used to heat-seal the body paper 11 and bottom paper 12 of a paper cup. The divided pressure application method is preferred because it allows for high-speed processing. The divided pressure application method, as shown in Figure 2, is a method in which a bottom clamping die 3 is arranged along the circumference of the bottom and pressurized by pushing the bottom clamping die 3 outward. A stronger heat seal can be achieved by rotating the bottom clamping die 3 to apply pressure to the unpressurized portions, or by providing multiple bottom clamping die parts and applying pressure multiple times. The rotary pressure application method is a method in which pressure is applied by rotating a circular bottom clamping die 3 along the circumference of the bottom. Furthermore, the bottom clamping die 3 used for pressure application can be processed in any way to improve heat sealing properties. [Example]

[0052] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. Furthermore, "parts" and "%" in the examples represent "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of added parts is a value calculated on a solid content basis.

[0053] Example 1 (Preparation of paper substrate) A paper stock was prepared by adding 100 parts of Canadian Standard freeness 420 mlcsf hardwood bleached kraft pulp, 0.2 parts of cationic starch (trade name: Neotack 40T, manufactured by Nippon Shokuhin Kako Co., Ltd.), and 0.5 parts of neutral rosin size (trade name: Hersize AN-300, manufactured by Harima Kasei Co., Ltd.) with water, and the paper was spun using a fourdrinier multi-cylinder paper machine to produce a paper stock with a basis weight of 198 g / m 2 A base paper of 2 g / m2 was prepared. Oxidized starch (product name: SK-20, manufactured by Nippon Corn Starch Co., Ltd.) was applied to this base paper by a size press in a dry coating amount of 2 g / m2 on both sides. 2 and dried to a density of 200 g / m 2 The paper base material was obtained (ash content 0.2%).

[0054] (Production of base paper for paper cups) A water-based ionomer emulsion (product name: Chemipearl S-300, manufactured by Mitsui Chemicals, Inc., composition: metal salt of ethylene-methacrylic acid copolymer, self-emulsifying emulsion, average particle size measured by Microtrac method: 0.5 μm) was applied to one side of the paper substrate obtained above, with a dry coating weight of 6 g / m for the first layer (lower layer). 2 , 2nd layer (top layer) dry coating weight 2g / m 2 (Total 8g / m 2 ) using an air knife coater, and dried to form a heat seal layer. 2 A base paper for a paper cup with a heat seal layer thickness of 8 μm was produced.

[0055] (Paper cup production) Using the base paper for paper cups obtained above, 16 oz cups were molded at a rate of 200 cups / min using a commercially available cup molding machine. The recess depth of the mold relief processing part on the bottom was 0 mm.

[0056] Example 2 Base paper for paper cups was prepared in the same manner as in Example 1, except that the pulp was 100 parts of unbleached softwood kraft pulp with a Canadian Standard Freeness of 550 ml csf (ash content of the paper base material: 0.1%).

[0057] Example 3 Base paper for paper cups was prepared in the same manner as in Example 1, except that the pulp was 30 parts softwood bleached kraft pulp, 70 parts hardwood bleached kraft pulp, and the Canadian Standard Freeness of the pulp slurry was 410 mlcsf (ash content of the paper base material: 0.2%).

[0058] Example 4 A paper cup was produced in the same manner as in Example 1, except that the recess depth of the mold relief processing portion on the bottom was set to 0.5 mm.

[0059] Example 5 A paper cup was produced in the same manner as in Example 1, except that the recess depth of the mold relief processing portion on the bottom was set to 1.0 mm.

[0060] Example 6 In Example 1, the heat seal layer was formed with a first layer (lower layer) dry coating amount of 1 g / m 2 , 2nd layer (upper layer) dry coating weight 1g / m 2 (Total 2g / m 2 ) using an air knife coater, and dried to form a heat seal layer. 2 A paper cup was produced in the same manner as in Example 1, except that a base paper for a paper cup with a heat seal layer thickness of 2 μm was produced.

[0061] Example 7 The coating amount of the water-based ionomer emulsion was set at 3 g / m for the first layer (bottom layer) dry coating amount. 2 , 2nd layer (upper layer) dry coating weight 1g / m 2 (Total 4g / m 2 ) was applied using an air knife coater to a basis weight of 204 g / m 2A paper cup was produced in the same manner as in Example 1, except that a base paper for a paper cup with a heat seal layer thickness of 4 μm was produced.

[0062] Example 8 The coating amount of the water-based ionomer emulsion was 13 g / m for the first layer (bottom layer) dry coating amount. 2 , 2nd layer (top layer) dry coating weight 2g / m 2 (Total 15g / m 2 ) was applied using an air knife coater to a basis weight of 215 g / m 2 A paper cup was produced in the same manner as in Example 1, except that a base paper for a paper cup with a heat seal layer thickness of 15 μm was produced.

[0063] Example 9 The same paper stock as in Example 1 was prepared, and the first layer was 60 g / m using a fourdrinier paper machine. 2 , second layer 70g / m 2 , 3rd layer 68g / m 2 , and a three-layer paper with a basis weight of 198 g / m 2 A base paper of 2 g / m2 was prepared, and oxidized starch (product name: SK-20, manufactured by Nippon Corn Starch Co., Ltd.) was applied to the base paper by a size press in a dry coating amount of 2 g / m2 on both sides. 2 The paper is impregnated to a basis weight of 200 g / m 2 A paper cup was produced in the same manner as in Example 1, except that the paper base material (ash content: 0.3%) was prepared.

[0064] (Comparative Example 1) A paper cup was produced in the same manner as in Example 1, except that the recess depth of the bottom mold relief processing portion was set to 1.2 mm.

[0065] (Comparative Example 2) A paper cup was produced in the same manner as in Example 8, except that the recess depth in the bottom mold relief processing portion was set to 1.2 mm.

[0066] The paper cups obtained in each of the Examples and Comparative Examples were evaluated by the methods described below, and the results are shown in Figure 5.

[0067] (Leaking at the bottom) 100cc of 90°C hot coffee (commercially available instant coffee) was poured into the resulting paper cup and left to stand for 30 minutes in an environment of 23°C and 50%RH. After 30 minutes, the coffee was discarded and the area around the bottom of the paper cup was visually inspected for coffee leakage and evaluated as follows: ◎: No coffee leakage or coffee stains, and practical. Good: Coffee stains have occurred but are not noticeable and there is no coffee leakage, so it is usable. △: No coffee leakage, but noticeable coffee stains, making it unusable. ×: Coffee leaks and is not practical.

[0068] As is clear from Figure 5, according to Examples 1 to 9 of the present invention, paper cups with excellent liquid retention properties can be manufactured even with a reduced amount of plastic used. On the other hand, in Comparative Examples 1 and 2, in which the recess depth of the bottom mold relief processing part was 1.2 mm, liquid stains and leakage occurred, making them unsuitable for practical use.

Claims

1. A step of preparing a base paper for a paper cup, the base paper having one or more heat seal layers formed by applying a coating liquid for a heat seal layer to at least one surface of a paper substrate; a step of producing a body paper and a bottom paper from the paper cup base paper; a step of overlapping parts of the body paper and performing a heat-sealing and pressure-bonding process to form a body; and a step of folding the outer periphery of the bottom paper downward, folding the lower end of the body upward to combine it with the bottom paper, and producing a paper cup using a cup forming machine. the heat-seal layer coating liquid contains an aqueous resin dispersion containing a resin and a solvent mainly composed of water, The method for producing a paper cup, wherein the total thickness of all heat-seal layers on one side of the base paper for the paper cup is 2 to 15 μm.

2. 2. The method for manufacturing a paper cup according to claim 1, wherein the base paper for the paper cup has two or more heat seal layers.

3. The method for manufacturing a paper cup according to claim 1, characterized in that a recess is provided in the bottom mold of the cup molding machine to allow the overlapping portion of the body paper to escape, and the recess has a depth of 0 to 1.0 mm.

4. 2. The method for manufacturing a paper cup according to claim 1, wherein the coating liquid for the heat seal layer is composed of only an ionomer emulsion containing an ionomer and a solvent for the ionomer.

5. A paper cup base paper in which a heat-seal layer coating liquid is applied to at least one surface of a paper substrate to provide two or more heat-seal layers, the heat-seal layer coating liquid contains an aqueous resin dispersion containing a resin and a solvent mainly composed of water, A base paper for paper cups, characterized in that the total thickness of all heat-sealable layers on one side is 2 to 15 μm.

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