JP7542508B2 - Paper cup base paper - Google Patents

Description

The present invention relates to base paper for paper cups.

Base paper for paper cups is known (for example, Patent Documents 1 to 3). In general, paper cups can be obtained by using paper with a thin polyethylene laminate on the surface, printing if necessary, and then molding the paper into a cup with the polyethylene-laminated surface facing inside.

JP 2012-219381 A JP 2019-65436 A JP 2019-52382 A

At least one surface of the base paper for paper cups is laminated, but the edge (cross section) is not laminated. As a result, liquid poured into the cup or condensation on the surface of the cup can penetrate the base paper, causing problems such as tearing or peeling. The object of the present invention is to solve these problems and provide a base paper for paper cups that is less likely to tear or peel when liquid is absorbed from the edge, and a method for manufacturing the same.

The present inventors have found that the problem can be solved by the following configuration after extensive research into paper cup base paper. That is, the paper cup base paper according to the present invention is a single-layer paper cup base paper mainly composed of pulp and having a basis weight of less than 350 g/ ^m2 , which contains a sizing agent, has a small edge water absorbency of 0.6 g/1000 mm2 ^or less, and has a formation index of 1.2 or less measured by the total β-ray ground. In the present invention, it is preferable that the sizing agent is contained in an amount of 0.1 to 0.8 mass% per 100 mass parts of pulp, and the sizing agent is preferably one or more selected from the group consisting of reinforced rosin sizing agents, neutral rosin sizing agents, neutral rosin emulsion sizing agents, acidic rosin sizing agents, acidic rosin emulsion sizing agents, weakly acidic rosin sizing agents, weakly acidic rosin emulsion sizing agents, AKD (alkyl ketene dimer), and ASA (alkenyl succinic anhydride). Furthermore, the present invention relates to a paper cup made from the paper cup base paper of the present invention. A paper cup formed using the paper cup base paper of the present invention is a paper cup that is less likely to tear or peel off because liquid is prevented from seeping in from the cross section of the body joint even after liquid is poured into the cup.

Furthermore, it has been found that the above-mentioned problems can be solved by a method for producing base paper for single-ply paper cups having a basis weight of less than 350 g/ ^m2 , characterized in that a papermaking raw material mainly composed of pulp containing 0.1 to 0.8 mass% of a sizing agent relative to 100 mass parts of pulp is made by a papermaking machine at an inlet concentration of 0.5 to 1.5 mass%, which is the inlet concentration of the papermaking machine. Furthermore, in the production method of the present invention, it is preferable that the sizing agent is one or more selected from the group consisting of reinforced rosin sizing agents, neutral rosin sizing agents, neutral rosin emulsion sizing agents, acidic rosin sizing agents, acidic rosin emulsion sizing agents, weakly acidic rosin sizing agents, weakly acidic rosin emulsion sizing agents, AKD (alkyl ketene dimer), and ASA (alkenyl succinic anhydride).

The base paper for paper cups and the manufacturing method thereof of the present invention can provide a paper cup that is less susceptible to tearing or peeling by preventing liquid from seeping in through the cross section of the body joint after molding.

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, and synthetic fibers may be used as needed. In order to obtain whiteness and a clean look, 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 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 decrease due to the incorporation of 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, a sizing agent is contained in the base paper. By containing a sizing agent, it is possible to prevent condensation water or liquid poured into the cup from entering through the edge of the base paper. The sizing agent used is not particularly limited, and various known agents such as reinforced rosin sizing agents, neutral rosin sizing agents, neutral rosin emulsion sizing agents, acidic rosin sizing agents, acidic rosin emulsion sizing agents, weakly acidic rosin sizing agents, weakly acidic rosin emulsion sizing agents, AKD (alkyl ketene dimer), and ASA (alkenyl succinic anhydride) can be used, but acidic rosin emulsion sizing agents are preferred. The content of the sizing agent in the paper for paper cups is not particularly limited, but for example, when an acidic rosin emulsion sizing agent is used, it is preferably 0.1 to 0.8% by mass, and more preferably 0.2 to 0.6% by mass, relative to 100 parts by mass of pulp. If it is less than 0.1% by mass, it may not be possible to sufficiently prevent liquid from entering through the edge. Furthermore, if the content exceeds 0.8% by mass, the sizing agent may inhibit the entanglement of pulp fibers, leading to reduced strength, and may easily lead to process contamination, such as foaming during the papermaking process or circulation of sizing agent that has not been fully fixed, making production virtually impossible.

In the paper for paper cups according to this embodiment, known additives for papermaking can be used within a range that does not impair the intended effect of the present invention. For example, it is preferable to add a paper strength enhancer to the papermaking raw material. By adding a paper strength enhancer, sufficient interlayer strength can be ensured and the occurrence of fuzz and creases can be suppressed. As the paper strength enhancer, although there is no particular limitation, cationic starch, amphoteric starch, polyacrylamide-based internal paper strength enhancers are preferable. For example, in the papermaking raw material, it is preferable to contain amphoteric polyacrylamide as a paper strength enhancer at 0.1 to 1.0 mass% relative to the pulp amount. Furthermore, various auxiliaries such as aluminum sulfate as a flocculation aid, a retention improver, a drainage improver, a coloring dye, a coloring pigment, a fluorescent brightener, a fluorescent decolorizer, a charge regulator, or a pitch control agent may be blended. For example, it is preferable to contain aluminum sulfate as a flocculation aid at 0.1 to 1.0 mass% relative to the pulp amount.

In the paper for paper cups 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, it is a single-layer papermaking using a papermaking machine such as a Fourdrinier papermaking machine or a cylinder papermaking machine. In the case of a multi-layer papermaking of two or more layers, when comparing between layers and within layers, the entanglement of fibers is clearly smaller between layers, and as a result, the density of that area is lower. This makes it easier for water to penetrate and there is a possibility of peeling, which is not preferred in the present invention.

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. For example, oxidized starch can be applied at 0.2 to 1.5 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 as long as they do 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 base paper for paper cups 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 limit to 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 this embodiment, the edge absorption of the base paper for paper cups is 0.6 g/1000 ^mm2 or less. 0.5 g/1000 ^mm2 or less is preferable, and 0.4 g/ ¹⁰⁰⁰ mm2 or ^less is more preferable. If it exceeds 0.6 g/1000 mm2, there is a possibility that liquid intrusion from the edge cannot be prevented. There is no particular lower limit, but to make it less than 0.1 g/1000 ^mm2 , a large amount of sizing agent is used, which may result in inhibition of interfiber bonding described later and lead to breakage of the base paper. Here, the edge water absorption is a measured value of the amount of water absorbed from the edge. The method for measuring the edge water absorption is to cover the entire front and back sides of the base paper for paper cups with cellophane tape to prevent pure water from penetrating from the front and back sides, and then immerse the entire base paper in water for one hour to measure the weight increase per edge cross-sectional area (total length of sample edge x paper thickness). It is calculated as follows: Edge water absorbency A (g/1000 mm ² )=weight increase (g)×1000÷edge cross-sectional area (paper thickness (mm)×edge total length (mm)).

Methods for measuring water durability generally include Stockigt sizing and Cobb water absorbency. Stockigt sizing involves floating the paper on water while simultaneously dripping a drop of water from above and measuring the time it takes for the two to come into contact. Cobb water absorbency involves covering one side of the paper surface with water and measuring the amount of water absorbed. Both methods measure the amount of water absorbed or the absorption time from a large area of the paper surface, but are not suitable for evaluating the amount of water that penetrates from the cross section of the cup base paper, which is the subject of this invention. Therefore, in this invention, we use edge water absorbency, which is suitable for evaluating the amount of water that penetrates from the cross section of the cup base paper. With this edge water absorbency, the effect of the surface tension of the liquid is accurately reflected in the measured value.

The base paper for paper cups according to this embodiment has a formation index of 1.2 or less, measured by the total of the β-rays. The formation index is preferably 1.0 or less, more preferably 0.8 or less. The lower limit of the formation index is not particularly limited, but is preferably 0.3 or more, more preferably 0.5 or more. If the formation index exceeds 1.2, the microscopic variation in basis weight increases, resulting in sparseness and density. As described above, the base paper for paper cups according to the present invention contains a sizing agent to prevent liquid from penetrating from the edge of the base paper, but since the sizing agent acts in the direction of inhibiting the interfiber bonding of pulp fibers, the paper tends to become bulky. In such bulky paper, if the microscopic variation in basis weight increases and sparseness and density occurs (poor formation), liquid is likely to penetrate from the sparse parts, and it is also thought that the paper strength, such as interlayer strength, after the liquid penetrates will decrease significantly. Also, it is possible that the surface tension of the liquid may be able to prevent the liquid poured into the cup from seeping in through the narrow edge of the paper, but condensation water can also come from the narrow edge of the paper, and the moisture in the air contained within the paper can also appear as liquid. If this water concentrates in the narrow areas, it can cause a significant decrease in paper strength. Therefore, in this invention, it is necessary to contain a sizing agent while keeping the formation index measured with the total β-rays below a certain level.

The ground total used in the measurement of the formation index in this embodiment is a β-ray ground total, that is, a ground total using a β-ray radiation source, which indicates the distribution of basis weight (sometimes called U.S. basis weight). The widely used ground total is based on light transmission, but pulp components, type and amount of filler, hue, whiteness, degree of beating of pulp, etc. are variable factors and are not suitable for formation evaluation. As mentioned above, the paper cup base paper is more likely to absorb liquid from the base paper edge than the sparse and dense parts of the basis weight, which results in breakage, etc. The formation index measured using the β-ray ground total is an index of the difference in basis weight (referred to as unit basis weight) measured at a diameter of 1 mm of the cup base paper. Since the β-ray ground total lacks accuracy for basis weights of 350 g/ ^m2 or more, this embodiment targets paper cup base paper with a basis weight of less than 350 g/ ^m2 .

As a method for making the formation index measured by the total β-rays less than 1.2, for example, the concentration of the raw material at the inlet of the papermaking machine (hereinafter, sometimes referred to as raw material concentration) can be reduced. Therefore, in the manufacturing method of the single-layer paper cup base paper of the present invention having a basis weight of less than 350 g/ ^m2 , the papermaking raw material mainly composed of pulp is made by a papermaking machine at an inlet concentration of 0.5 to 1.5 mass%, which is the inlet concentration of the paper cup base paper. By reducing the raw material concentration, the formation of the paper cup base paper can be improved, and as a result, the formation index can be reduced. In the case of a fourdrinier papermaking machine, the inlet concentration of the head box is preferably 1.5 mass% or less, more preferably 1.3 mass% or less, and even better 1.1 mass% or less. If it exceeds 1.5 mass%, the formation index does not fall within the desired range, and the variation in density tends to become large. If the raw material concentration is less than 0.5% by mass, the sheet becomes difficult to peel off from the wire and the yield on the wire also decreases, so 0.5% by mass is the actual lower limit. In addition, when the basis weight of the base paper for paper cups is 150 g/ ^m2 or more, it is preferable to use a shaking device that applies vibration to the papermaking machine to make the base paper uniform. 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 to set the inlet concentration, which is the concentration at the inlet of the papermaking machine, to 0.7 to 1.5% by mass.

In this embodiment, the formation index is calculated, for example, as follows: The basis weight (referred to as unit basis weight) measured at a diameter of 1 mm of the paper cup base paper is measured at a pitch of 3.5 mm x 3.5 mm over a measurement area of 70 mm x 70 mm, and the standard deviation of the basis weight and the weighted average value of the basis weight are calculated for the 400 unit basis weight values obtained. The normalized standard deviation of the basis weight (n.s.d. = normalized standard deviation) calculated according to the following formula (Equation 1) is determined as the formation index.
(Formula 1) Standard deviation of basis weight (g/m)=Standard deviation of basis weight (g/m ² )/Weighted average value of basis weight (g/m ² ) ^1/2

In the paper for paper cups according to this embodiment, the moisture content is preferably about 6% to 9%, for example 9% or less. If the moisture content exceeds 9%, the amount of water contained in the paper becomes liquid, which tends to lead to a decrease in paper strength. If the moisture content is less than 6%, the amount of water contained in the paper decreases, but on the other hand the paper becomes hard and brittle, which tends to lead to a decrease in paper strength such as cracking. The moisture content was measured according to JIS P8127:2010 Paper and cardboard - Lot moisture test method - Dryer method.

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.

＜Edge torn＞
Both sides of the paper cup base paper obtained in each Example and Comparative Example were 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 , and paper cups were molded using a cup molding machine. The molded paper cups were immersed in pure water for 1 hour to remove excess water, and the edge was turned over with a finger to evaluate the degree of peeling.
◎: No peeling at all, good condition (passed)
○: Good, no peeling (Pass)
△: Slight peeling (lower limit of use)
×: Large tear due to peeling (failed)

<Water absorption at edge>
The base paper for paper cups obtained in each of the Examples and Comparative Examples was measured according to the following procedures.
- Apply 75 mm wide cellophane tape to both sides to prevent pure water from penetrating from the front and back.
Cut into a length of 50 mm and a width of 125 mm. Then measure the weight a before immersion.
- Immerse in pure water for 1 hour.
- Wipe off excess water and measure the weight b after immersion.
・Water absorption at the edge g/1000mm ² = (ba) x 1000 ÷ (B x D)
B: Paper thickness (mm), D: Total length of fore-edge (mm) = 350 mm

<Condition Index>
The basis weight measured at a diameter of 1 mm (referred to as unit basis weight) of the paper cup base paper is measured by a ground weight calculator at a pitch of 3.5 mm x 3.5 mm for a measurement area of 70 mm x 70 mm, and the standard deviation of the basis weight and the weighted average value of the basis weight are calculated for the 400 obtained unit basis weight values. The basis weight normalized standard deviation (n.s.d = normalized standard deviation) calculated according to the following formula (Equation 1) is regarded as the formation index. The ground weight calculator was measured using a β-ray ground weight calculator (model BFT-1) manufactured by Ambertec.
(Equation 1)
Standard deviation of basis weight (g/m)=Standard deviation of basis weight (g/m ² )/Weighted average value of basis weight (g/m ² ) ^1/2

Example 1
<Preparation of base paper>
Using pulp adjusted to 350 ml of CSF consisting of 100% hardwood pulp (L-BKP), a base paper with a basis weight of 230 g/ ^m2 was made in a single layer at a speed of 150 m/min using a fourdrinier papermaking machine equipped with a top wire. The raw paper material 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 of the papermaking machine were 3 times/second, the amplitude width was 12 mm, and the inlet concentration was 1.1%.

<Size Press>
A sizing solution of 5% 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 1.0 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 inlet concentration was changed from 1.1% to 0.9%.

Example 3
A base paper for a paper cup was obtained in the same manner as in Example 1, except that the inlet concentration was changed from 1.1% to 1.3%.

Example 4
A base paper for a paper cup was obtained in the same manner as in Example 1, except that the content of the acidic rosin emulsion sizing agent was changed from 0.4% to 0.2%.

Example 5
A base paper for a paper cup was obtained in the same manner as in Example 1, except that the content of the acidic rosin emulsion sizing agent was changed from 0.4% to 0.6%.

(Comparative Example 1)
A base paper for a paper cup was obtained in the same manner as in Example 1, except that the content of the acidic rosin emulsion sizing agent was changed from 0.4% to no addition.

(Comparative Example 2)
A base paper for a paper cup was obtained in the same manner as in Example 1, except that the inlet concentration was changed from 1.1% to 1.6%.

As is clear from Table 1, the base papers for paper cups obtained in Examples 1 to 5 all absorbed little liquid from the edge and almost no edge tears occurred.

On the other hand, the base paper for paper cups obtained in Comparative Examples 1 and 2, in which no sizing agent was added to the base paper, absorbed a lot of liquid from the edge, causing the edge to tear and making it unusable.

Claims (6)

The paper cup base paper is a single-layer paper base paper mainly composed of pulp and having a basis weight of less than 350 g/ ^m2 , which contains a sizing agent, has a water absorption rate at the edge of 0.6 g/1000 ^mm2 or less, and has a formation index of 1.2 or less as measured by the total β-ray ground. The base paper for paper cups according to claim 1, characterized in that it contains 0.1 to 0.8% by mass of a sizing agent per 100 parts by mass of pulp. The base paper for paper cups according to claim 1 or 2, characterized in that the sizing agent is one or more selected from the group consisting of reinforced rosin sizing agents, neutral rosin sizing agents, neutral rosin emulsion sizing agents, acidic rosin sizing agents, acidic rosin emulsion sizing agents, weakly acidic rosin sizing agents, weakly acidic rosin emulsion sizing agents, AKD (alkyl ketene dimer), and ASA (alkenyl succinic anhydride). A paper cup made from the base paper for paper cups according to any one of claims 1 to 3. A method for producing a single-ply paper base paper for a paper cup having a basis weight of less than 350 g/ ^m2 , comprising the steps of:
The method is characterized in that a papermaking raw material mainly composed of pulp containing 0.1 to 0.8 mass% of a sizing agent per 100 mass parts of pulp is made into paper by a papermaking machine at an inlet concentration of 0.5 to 1.5 mass%, which is the concentration at the inlet of the papermaking machine. The method for manufacturing base paper for paper cups according to claim 5, characterized in that the sizing agent is one or more selected from the group consisting of reinforced rosin sizing agents, neutral rosin sizing agents, neutral rosin emulsion sizing agents, acidic rosin sizing agents, acidic rosin emulsion sizing agents, weakly acidic rosin sizing agents, weakly acidic rosin emulsion sizing agents, AKD (alkyl ketene dimer), and ASA (alkenyl succinic anhydride).