JP7623251B2 - Paper cup base paper - Google Patents

Description

The present invention relates to a paper cup base paper that is less susceptible to top curl cracks during the molding of paper cups.

Generally, paper cups are made by using paper with a thin polyethylene laminate on the surface, printing as necessary, and then molding the paper into a cup with the polyethylene-laminated surface 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, which heats the top of the cup to become the drinking spout. The cup is then 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), can occur.

As a base paper for such paper cups, it has been proposed to make it by combining three or more layers, using LBKP with a freeness of 320 to 420 ml CSF for the outermost layer, and imparting top curl suitability by setting the ratio of the longitudinal tensile strength (front/back) of the outermost layer to the innermost layer to 1.00 or less (see, for example, Patent Document 1).

JP 2012-219381 A

However, the base paper for paper cups in Patent Document 1 is made of three or more layers, which means that 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 these problems and provide a paper cup base paper that is less susceptible to top curl cracking, and a paper cup manufactured from the paper.

After extensive research into paper cup base paper, the inventors have found that the problem can be solved 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 base paper contains 0.2 to 1.0 mass% amphoteric polyacrylamide per 100 mass parts of pulp.

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 warp 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.

The present invention further relates to a paper cup using the above-mentioned paper cup base paper as a base paper. A paper cup using the paper cup base paper of the present invention as a base paper is less likely to suffer from top curl cracks during its manufacture, and paper cups can be manufactured economically without incurring extra costs.

The present invention can provide a paper cup base paper that is less susceptible to top curl cracks. Furthermore, by using this paper cup base paper, paper cups can be produced economically without top curl cracks occurring during production.

Next, the present invention will be described in detail with reference to an embodiment, but the present invention should not be interpreted as being limited to these descriptions. Various modifications of the embodiment may be made as long as the effects of the present invention are achieved.

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 molding the paper cup, making it more likely to cause top curl cracking. If it exceeds 500 ml, the interfiber bonds become 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 "Test Method for Freeness of Pulp").

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 fibers, 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.

The base paper of the paper cup base paper according to this embodiment may contain a filler. Examples of fillers that may 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.

In the 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) that can 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 added 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 less likely 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 amphoteric polyacrylamide content is less than 0.2% by mass, sufficient paper strength cannot be obtained, and it is difficult to obtain the desired tensile breaking elongation in the transverse direction. If the amphoteric polyacrylamide content exceeds 1.0% by mass, the base paper may become too hard and top curl cracks may occur easily.

In the base paper for paper cups according to this 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% by mass of aluminum sulfate may be added to 100 parts by mass of pulp. Also, 0.2 to 0.6% by mass of an acidic rosin emulsion sizing agent may be added to 100 parts by mass 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 breaking elongation 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 breaking elongation 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.

In the paper cup base paper according to the present 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, so the degree of freedom within the layer is limited, resulting in a hard paper, and is not adopted in the present invention. In addition, the density of the base paper made by multi-layer papermaking is likely to be high, which causes the paper to become hard. In addition, when the basis weight of the paper cup base paper is 150 g/m ² or more, it is preferable to use a shaking device that applies vibration to the papermaking machine to make the base paper uniform. As a method for making the tensile breaking elongation of the paper in the lateral direction of 5% or more, as described later, in addition to using amphoteric polyacrylamide as a paper strength agent, it is also effective to control the fiber orientation of the paper and control the formation. When using a shaking device to control the formation, 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 that the inlet concentration, which is the concentration at the inlet of the papermaking machine, is 0.7 to 1.5 mass %.

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 surface sizing liquid include known water-soluble polymers such as starch, polyvinyl alcohol, polyacrylamide resin, acrylic resin, and polyamide resin. It is preferable to apply 0.1 to 2.0 g/ ^m2 in solid form per side of the base paper. Since the surface strength enhancer applied as the surface sizing liquid is unlikely to affect the tensile breaking elongation in the lateral direction of the paper, general surface strength enhancers can also be used within a range that does not impair the intended effect of the present invention.

The method of applying the surface size liquid can be, but is not limited to, a known applicator such as a pond-equipped type 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.

In the 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, and calcined kaolin. 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.

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.

In the 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 of 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, a range of 7 to 30 g/ ^m2 is preferable.

In the paper for paper cups according to this embodiment, the tensile breaking elongation in the lateral 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. This is because if it is less than 5.0%, the paper cup base paper has poor elasticity and is prone to top curl cracking (splitting) during the molding of the cups. 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.

In the 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 distort during top curl forming, resulting in improved processing suitability. If it exceeds 3.0%, not only will the elongation plateau, but the tensile strength will tend to decrease, so 3.0% is essentially the upper limit. The tensile breaking elongation in the longitudinal and transverse directions of the 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 the paper is the papermaking direction (MD direction), and the transverse direction is the direction perpendicular to the papermaking direction (CD direction). In the 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 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 7-9%. The moisture content was measured according to JIS P8127:2010 Paper and paperboard - Lot moisture test method - Dryer method.

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 as described above, paper cups can be manufactured without top curl cracks occurring 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.

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 the solid content.

The following evaluations were carried out on the base paper for paper cups obtained in each of the examples and comparative examples shown below. The evaluation results are shown in Table 1. The evaluation methods are also described below.

<Top curl cracking>
The base paper for paper cups obtained in each Example and Comparative Example was laminated with low-density polyethylene (Petrothene DLZ19A, manufactured by Tosoh Corporation) using an extrusion coater (melt extruder) so that the coating amount was 30 g/ ^m2 , the laminated surface was placed on the inside of the cup, and top curl processing was performed using a cup forming machine so that the diameter of the curled part was 3 mm, and cracks in the top curl were visually evaluated.
⊚: No cracks were observed in the curled portion (passed).
○: Almost no cracks were observed in the curled portion (passed).
△: Cracks are observed in the curled portion, but there is no problem in actual use (pass).
×: Cracks were clearly observed in the curled portion, and the product could not actually be used (failed).

<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) was measured by the constant speed extension method.

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

Example 1
<Preparation of base paper>
Using pulp adjusted to a CSF of 350 ml consisting of 100% hardwood pulp (L-BKP), a base paper with a basis weight of 250 g/ ^m2 was made at a speed of 150 m/min using a fourdrinier papermaking machine equipped with a top wire. The raw materials for papermaking contained 0.5% amphoteric polyacrylamide (Polystron 387, manufactured by Arakawa Chemical Industries Co., Ltd.) as a paper strength enhancer, 0.6% aluminum sulfate as a flocculation aid, and 0.4% acidic rosin emulsion sizing agent (AL-1203, manufactured by Seiko PMC Co., Ltd.) as a sizing agent. The shaking conditions for the papermaking machine were 3 times/second, and the amplitude was 12 mm.

<Size Press>
A sizing solution of 2% aqueous solution of oxidized starch (MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to both sides of the base paper using a pond-type size press so that the amount of adhesion per side was 0.5 g/ ^m2 in terms of solid content, and then dried.

<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%.

Example 2
A base paper for a paper cup 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.

Example 3
A base paper for a paper cup 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.

Example 4
A base paper for a paper cup 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%.

(Comparative Example 1)
A base paper for a paper cup 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 an anionic polyacrylamide (Polystron 117, manufactured by Arakawa Chemical Industries Co., Ltd.).

(Comparative Example 2)
A base paper for a paper cup 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.).

(Comparative Example 3)
A base paper for a paper cup 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.

As is clear from Table 1, the top curl cracking evaluation was good for all of the paper cup base papers obtained in Examples 1 to 4.

On the other hand, the base paper for paper cups obtained in Comparative Examples 1 to 3, in which amphoteric polyacrylamide was not added to the base paper, did not achieve the desired lateral elongation and experienced top curl cracking.

Claims (7)

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. The base paper for paper cups according to claim 1, characterized in that the longitudinal tensile elongation at break of the base paper is 2% or more. The base paper for paper cups according to claim 1 or 2, characterized in that the moisture content is 7% or more. The paper base paper for paper cups according to any one of claims 1 to 3, characterized in that it contains 0.3 to 1.0 mass% of amphoteric polyacrylamide per 100 mass parts of pulp. The base paper for paper cups according to any one of claims 1 to 4, characterized in that the base paper is not coated with carboxymethyl cellulose. A paper base paper for paper cups according to any one of claims 1 to 5, characterized in that the freeness of the pulp used in the base paper is 200 ml or more and 500 ml or less. A paper cup having a base paper for paper cups according to any one of claims 1 to 6.