Paper cup base paper

Abstract

To provide paper cup base paper in which a top curl crack hardly occurs when molding a paper cup therefrom.SOLUTION: In paper cup base paper including pulp as a principal component and including single-layer paper-making base paper, the base paper contains amphoteric polyacrylamide, and tensile breaking elongation in a lateral direction is 5% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a paper cup base paper that is less susceptible to top curl cracks during the formation of paper cups. [Background technology]

[0002] Generally, paper cups are made by using paper with a thin polyethylene laminate on the surface, printing as necessary, and then molding the paper so that the polyethylene-laminated surface is on the inside. This cup molding process includes the steps of punching out a fan shape with a die with a blade, wrapping the paper around a cup-shaped die and gluing both ends, punching out the bottom of the cup from another roll of paper, forming the bottom of the cup to join the bottom and sides of the cup, and forming the top curl by heating the top of the cup that will become the drinking spout. After that, the paper is inspected, packaged, and shipped as a paper cup. In the top curl molding process, the paper is forcibly curled by pressing it with a heated metal called a curl iron, so if the base paper is not flexible, a phenomenon called top curl cracking, in which the curled part cracks (splits), may occur.

[0003] It has been proposed that base paper for such paper cups is made by combining three or more layers, with the outermost layer being made of LBKP with a freeness of 320 to 420 mlCSF, and the ratio of the longitudinal tensile strength (front / back) of the outermost layer to the innermost layer being 1.00 or less, thereby imparting top curl suitability (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-219381 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the paper cup base paper in Patent Document 1 is made of three or more layers, so the paper tends to be hard, and as a result, top curl cracking may not be sufficiently prevented. The object of the present invention is to solve such problems and provide a paper cup base paper that is less susceptible to top curl cracking, and a paper cup manufactured therefrom. [Means for solving the problem]

[0006] As a result of extensive research into paper cup base paper, the inventors have found that the object can be achieved by the following configuration. That is, the paper cup base paper according to the present invention is a paper cup base paper having a single-layered base paper mainly composed of pulp, characterized in that the base paper contains amphoteric polyacrylamide and has a tensile breaking elongation in the transverse direction of 5% or more. Furthermore, it is preferable that the amphoteric polyacrylamide is contained in an amount of 0.2 to 1.0 mass% relative to 100 mass parts of pulp.

[0007] In addition, in the present invention, the tensile breaking elongation in the longitudinal direction of the paper cup base paper may be 2% or more. With this configuration, the paper cup base paper is less likely to be distorted during top curl formation, and has better processability. In addition, in the present invention, the paper cup base paper may have a moisture content of 7% or more. With this configuration, the paper cup base paper is less likely to crack due to top curl.

[0008] Furthermore, the present invention relates to a paper cup using the above-mentioned paper cup base paper as a base paper. If a paper cup uses the paper cup base paper of the present invention as a base paper, top curl cracks are unlikely to occur during its production, and the paper cup can be produced economically without incurring extra costs. Effect of the Invention

[0009] The present invention can provide a paper cup base paper that is less susceptible to top curl cracking. Furthermore, by using the paper cup base paper, paper cups can be produced economically without top curl cracking during production. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] The base paper for paper cups of the present invention is made of a single-layered base paper mainly composed of pulp. The freeness of the pulp used in the base paper is preferably 200 ml to 500 ml. More preferably, it is 300 ml to 400 ml. If it is less than 200 ml, the base paper becomes too dense and becomes too hard when forming a paper cup, which makes the top curl crack more likely to occur. If it exceeds 500 ml, the interfiber bond becomes weak, the paper strength decreases, and the strength after processing into a container is low, which may cause problems in use. The freeness of the pulp in the present invention is obtained by measuring with a Canadian Standard Type Freeness Tester (based on JIS P 8121:1995 "Testing Method for Freeness of Pulp").

[0012] The pulp used for the base paper may be any known pulp such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), bleached hardwood sulfite pulp (LBSP), bleached softwood sulfite pulp (NBSP), mechanical pulp (GP, TMP, BCTMP), or deinked pulp (DIP). In addition to wood pulp, non-wood pulp, synthetic pulp, synthetic fiber, etc. may be used as needed. In order to obtain whiteness and a clean feeling, it is preferable to use LBKP or NBKP. LBKP is more preferable because shorter pulp fibers are easier to impart smoothness and uniformity. The pulp blend is preferably 90-100% LBKP or 95-100% LBKP in the pulp used, and is particularly preferably 100% LBKP.

[0013] The base paper of the paper cup base paper according to this embodiment may contain a filler. Examples of fillers that can be used include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, calcined clay, titanium dioxide, and aluminum hydroxide. However, since the strength of the base paper may be reduced by adding a filler, the filler content in the base paper is preferably 2% by mass or less, and more preferably 1% by mass or less.

[0014] In the paper base paper for paper cups according to this embodiment, amphoteric polyacrylamide is contained in the base paper. The base paper for paper cups needs to have a strength (e.g., a certain tensile strength) sufficient to withstand processing during cup formation, so a paper strength enhancer is added to the base paper to improve its strength. However, as the amount of paper strength enhancer increases, the paper tends to become harder, and if a certain paper strength is sought, the paper becomes prone to top curl cracking. Therefore, in the present invention, amphoteric polyacrylamide is used as the paper strength enhancer. By blending amphoteric polyacrylamide, the strength of the base paper can be improved without the paper becoming too hard, and in addition, the tensile breaking elongation in the lateral direction can be efficiently improved. As a result, a paper that is unlikely to cause top curl cracking while obtaining a certain paper strength can be obtained. The content of amphoteric polyacrylamide is preferably blended to be 0.2 to 1.0 mass% relative to 100 mass parts of pulp in the base paper, and more preferably blended to be 0.3 to 0.7 mass%. If the content of amphoteric polyacrylamide is less than 0.2% by mass, sufficient paper strength is not obtained and it is difficult to obtain the desired tensile breaking elongation in the transverse direction.If the content of amphoteric polyacrylamide is more than 1.0% by mass, the base paper may become too hard and top curl cracks may easily occur.

[0015] In the base paper for paper cups according to the present embodiment, known papermaking additives can be used within a range that does not impair the intended effect of the present invention. For example, various auxiliaries such as aluminum sulfate, sizing agents, internal paper strength enhancers such as cationic starch and amphoteric starch, anionic or cationic polyacrylamide, retention improvers, drainage improvers, coloring dyes, coloring pigments, fluorescent brighteners, fluorescent decolorizers, charge regulators, or pitch control agents may be blended. For example, 0.3 to 1.0 mass% of aluminum sulfate may be added to 100 mass parts of pulp. Also, 0.2 to 0.6 mass% of an acidic rosin emulsion sizing agent may be added to 100 mass parts of pulp as a sizing agent. However, it is not preferable to add a large amount of internal paper strength enhancers other than amphoteric polyacrylamide, for example, starch-based internal paper strength enhancers such as cationic starch, because they tend to make the base paper hard and brittle. The amount of starch-based paper strength enhancer added is preferably 0.2% by mass or less relative to the pulp in the base paper, and more preferably none is added. In addition, anionic polyacrylamide-based paper strength enhancers have poor adhesion to the pulp, making it difficult to improve paper strength, and as a result, the tensile elongation at break in the transverse direction is also difficult to satisfy. Cationic polyacrylamide-based paper strength enhancers also have poor adhesion to the pulp, making it difficult to improve paper strength, and as a result, the tensile elongation at break in the transverse direction is also difficult to satisfy. Furthermore, excess cationic materials circulate within the system, which can easily lead to process contamination during production.

[0016] For the paper cup base paper according to this embodiment, the method of manufacturing the base paper is not particularly limited as long as it is a single-layer papermaking, but for example, a single-layer papermaking is performed using a papermaking machine such as a Fourdrinier papermaking machine or a cylinder papermaking machine. In the case of multi-layer papermaking of two or more layers, the basis weight of each layer is small, limiting the degree of freedom within the layer and resulting in a hard paper, so it is not adopted in the present invention. In addition, the density of multi-layer paper is likely to be high, which causes the paper to become hard. In addition, the basis weight of the paper cup base paper is 150 g / m 2In the above cases, it is preferable to use a shaking device that vibrates the papermaking machine to make the base paper uniform. As a method for making the tensile breaking elongation of the paper in the transverse direction 5% or more, which will be described later, in addition to using amphoteric polyacrylamide as a paper strength agent, controlling the fiber orientation of the paper and controlling the formation are also effective. When controlling the formation using a shaking device, for example, the shaking conditions are preferably a shaking width of 10 to 20 mm and a vibration frequency of 2 to 4 times / second. At the same time, it is preferable to set the inlet concentration, which is the concentration at the inlet of the papermaking machine, to 0.7 to 1.5 mass%.

[0017] In the paper cup base paper according to this embodiment, a surface sizing liquid may be applied to the surface of the base paper. Examples of the surface sizing liquid include known water-soluble polymers such as starch, polyvinyl alcohol, polyacrylamide resin, acrylic resin, and polyamide resin. The amount of the surface sizing liquid is 0.1 to 2.0 g / m2 in solid form per side of the base paper. 2 Since the surface strength agent applied as the surface sizing liquid does not easily affect the tensile breaking elongation in the lateral direction of the paper, a general surface strength agent can also be used within a range that does not impair the intended effect of the present invention.

[0018] The method of applying the surface size liquid can be, but is not particularly limited to, a known applicator such as a type equipped with a pond such as a size press, a film metering type such as a gate roll size press or a shim sizer, a rod coater, or an air knife coater.

[0019] In the base paper for paper cups according to this embodiment, a coating layer containing a pigment may be provided on the surface of the base paper. The coating layer may be provided on one side of the base paper or on both sides of the base paper. Pigments used in the coating layer may include kaolin clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, talc, satin white, lithopone, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, calcined kaolin, and the like. Organic pigments may also be used. These may be used alone or in combination of two or more. When coating layers are provided on both sides of the base paper, the coating layer provided on one side and the coating layer provided on the other side may have the same composition or different compositions.

[0020] In the paper cup base paper according to this embodiment, the paint for forming the coating layer may contain various commonly used auxiliary agents such as adhesives, dispersants, defoamers, water-resistant agents, coloring dyes, coloring pigments, and thickeners, as necessary.

[0021] In the base paper for paper cups according to this embodiment, a coating layer can be provided by applying a coating material for forming a coating layer to the base paper. The method for applying the coating material for forming a coating layer to the base paper is not particularly limited, and various methods such as a metering size press, various film transfer coaters such as a gate roll or a shim sizer, an air knife coater, a rod coater, a blade coater, a direct fountain coater, a spray coater, and a curtain coater are appropriately used. There is no restriction on the dry coating amount per side of the coating layer as long as it is within a range that does not impair the intended effect of the present invention, but if the coating amount is too high, top curl cracking is likely to occur, so for example, 7 to 30 g / m 2 The range is preferably:

[0022] In the paper cup base paper according to this embodiment, the tensile breaking elongation in the transverse direction of the paper cup base paper is set to 5% or more. 5.2% or more is preferable, and 5.5% or more is more preferable. If it is less than 5.0%, the elasticity is poor and top curl cracks (splits) are likely to occur during the molding of the cup. There is no particular upper limit, but if it exceeds 7.0%, not only will the elongation plateau, but the tensile strength will tend to decrease, so 7.0% is essentially the upper limit.

[0023] In the base paper for paper cups according to this embodiment, the tensile breaking elongation in the longitudinal direction is preferably 2.0% or more. More preferably, it is 2.2% or more. By having a sufficiently large tensile breaking elongation in the longitudinal direction as well as in the transverse direction, the paper is less likely to be distorted during top curl forming, resulting in improved processability. If it exceeds 3.0%, not only does the elongation plateau, but the tensile strength tends to decrease, so 3.0% is essentially the upper limit. The tensile breaking elongation in the longitudinal and transverse directions of paper is a value measured in accordance with JIS P8113:2006 Paper and paperboard - Test method for tensile properties - Part 2: Constant speed extension method. In addition, in the present invention, the longitudinal direction of paper is the papermaking direction (MD direction), and the transverse direction is the direction perpendicular to the papermaking direction (CD direction). In the base paper for paper cups according to this embodiment, the moisture content is preferably about 6.5% to 9%, for example, 7% or more. By making the moisture content 7% or more, the flexibility of the paper increases, making it possible to produce a paper cup base paper that is less susceptible to top curl cracking. If the moisture content exceeds 9%, the strength of the paper tends to decrease, so it is more preferable to make the moisture content 7 to 9%. The moisture content was measured according to JIS P8127:2010 Paper and paperboard - Lot moisture test method - Dryer method.

[0024] In one embodiment, the present invention relates to a paper cup using a base paper for a paper cup. By using the paper cup base paper of the present invention obtained above, a paper cup can be manufactured without top curl cracks during manufacturing. For example, it is preferable to use a paper cup base paper in which at least one side of the paper cup base paper is thinly laminated with polyethylene. This makes it possible to obtain a paper cup that can be used appropriately as a paper cup. EXAMPLES

[0025] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of parts added is a value calculated as a solid content.

[0026] The base paper for paper cups obtained in each of the Examples and Comparative Examples shown below was evaluated as follows. The evaluation results are shown in Table 1. The evaluation methods are as follows.

[0027] <Top curl cracking> The base paper for paper cups obtained in each Example and Comparative Example was coated with low-density polyethylene (Petrosen DLZ19A, manufactured by Tosoh Corporation) in an amount of 30 g / m using an extrusion coater (melt extruder). 2 The laminated surface was placed inside the cup, and top curling was performed using a cup forming machine so that the diameter of the curled part was 3 mm. The cracks in the top curl were visually evaluated. ◎: No cracks were observed in the curled portion. (Pass) ○: Almost no cracks were observed in the curled portion. (Pass) △: Cracks are observed in the curled portion, but there is no problem in actual use. (Pass) ×: Cracks are clearly observed in the curled portion, and the product cannot actually be used (failed).

[0028] <Longitudinal and transverse tensile elongation at break> JIS P8113:2006 Paper and paperboard-Test methods for tensile properties-Part 2: The tensile breaking elongation in the machine direction (tensile breaking elongation T) and the transverse direction (tensile breaking elongation Y) were measured by the constant speed extension method.

[0029] <Moisture content> The measurement was performed according to JIS P8127:10, Paper and paperboard - Lot moisture test method - Dryer method.

[0030] Example 1 <Preparation of base paper> The pulp was adjusted to 350 ml of CSF consisting of 100% hardwood pulp (L-BKP), and a basis weight of 250 g / m was produced on a fourdrinier papermaking machine equipped with a top wire. 2 The base paper was made at a speed of 150 m / min. The raw materials for papermaking contained amphoteric polyacrylamide (Polystron 387, manufactured by Arakawa Chemical Industries Co., Ltd.) at 0.5% of the pulp weight as a paper strength enhancer, aluminum sulfate at 0.6% of the pulp weight as a flocculation aid, and acidic rosin emulsion sizing agent (AL-1203, manufactured by Seiko PMC Co., Ltd.) at 0.4% of the pulp weight as a sizing agent. The shaking conditions for the papermaking machine were 3 times / second, with an amplitude of 12 mm.

[0031] <Size press> A 2% aqueous solution of oxidized starch (MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) is applied to the base paper using a pond-type size press until the amount of adhesion per side is 0.5 g / m2 (solids equivalent). 2 The mixture was applied to both sides so as to obtain the above-mentioned result, and then dried.

[0032] <Smoothing processing> The dried base paper was subjected to a calendering treatment at a linear pressure of 50 kg / cm to obtain a paper cup base paper, which had a moisture content of 7.2%.

[0033] Example 2 A base paper for paper cups was obtained in the same manner as in Example 1, except that the amount of amphoteric polyacrylamide (Polystron 387, manufactured by Arakawa Chemical Industries Co., Ltd.) added as a paper strength enhancer was changed from 0.5% to 0.3% relative to the amount of pulp.

[0034] Example 3 A base paper for paper cups was obtained in the same manner as in Example 1, except that the amount of amphoteric polyacrylamide (Polystron 387, manufactured by Arakawa Chemical Industries Co., Ltd.) added as a paper strength enhancer was changed from 0.5% to 0.7% relative to the amount of pulp.

[0035] Example 4 A base paper for paper cups was obtained in the same manner as in Example 1, except that the drying conditions after the size press in Example 1 were changed and the moisture content after the smoothing process was changed from 7.2% to 6.8%.

[0036] Comparative Example 1 A base paper for paper cups was obtained in the same manner as in Example 1, except that the amphoteric polyacrylamide (Polystron 387, manufactured by Arakawa Chemical Industries Co., Ltd.) used as the paper strength enhancer was changed to anionic polyacrylamide (Polystron 117, manufactured by Arakawa Chemical Industries Co., Ltd.).

[0037] Comparative Example 2 A base paper for paper cups was obtained in the same manner as in Example 1, except that the amphoteric polyacrylamide (Polystron 387 manufactured by Arakawa Chemical Industries Co., Ltd.) used as the paper strength enhancer was changed to a cationic polyacrylamide (Polystron 705 manufactured by Arakawa Chemical Industries Co., Ltd.).

[0038] Comparative Example 3 A base paper for paper cups was obtained in the same manner as in Example 1, except that the amphoteric polyacrylamide (Polystron 387, manufactured by Arakawa Chemical Industries Co., Ltd.), which is a paper strength enhancing agent, was not added.

[0039] [Table 1]

[0040] As is clear from Table 1, the base papers for paper cups obtained in Examples 1 to 4 all had good evaluations for top curl cracking.

[0041] On the other hand, the base papers for paper cups obtained in Comparative Examples 1 to 3, in which no amphoteric polyacrylamide was added to the base paper, did not achieve the desired lateral elongation and suffered from top curl cracking.

Claims

1. A base paper for paper cups having a single-layer base paper whose main component is pulp, characterized in that the base paper contains 0.3 mass% or more of amphoteric polyacrylamide per 100 mass parts of pulp, and has a tensile breaking elongation in the lateral direction of 5% or more.

2. 2. The base paper for a paper cup according to claim 1, wherein the base paper has a longitudinal tensile breaking elongation of 2% or more.

3. 3. The paper base paper for paper cups according to claim 1, wherein the moisture content is 7% or more.

4. 4. The paper base paper for paper cups according to claim 1, further comprising 0.3 to 1.0% by mass of amphoteric polyacrylamide per 100 parts by mass of pulp.

5. 5. The paper base for paper cups according to any one of claims 1 to 4, characterized in that the base paper is not coated with carboxymethyl cellulose.

6. 6. The paper base for paper cups according to claim 1, wherein the freeness of the pulp used in the base paper is 200 ml or more and 500 ml or less.

7. A paper cup using the base paper for paper cups according to any one of claims 1 to 6 as a base paper.

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