JP2019052382A - Paper cups and paper cups - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a base paper for a paper cup which has sufficient tensile strength to withstand the tensile force at the time of molding of a top curl portion and is easy to curl, is easy to mold the top curl portion, and is less likely to cause curling of the seam portion. Provide the paper cup that was there. SOLUTION: A base paper for a paper cup containing cellulose pulp as a main component, having a Z-axis strength of 560 kN / m2 or less, and a tensile strength in the MD direction of 14.0 to 20.0 kN / m. [Selection diagram] None

Description

  The present invention relates to a paper cup base paper and a paper cup made of the paper cup base paper.

  Conventionally, in beverage paper cups, a top curl portion (hereinafter referred to as a top curl portion) is formed by a top curl process in which the periphery of the upper end opening of the paper cup is wound outward. One of the qualities required for paper cup base paper is the ease of making this top curl section.

The top curl portion has a role of increasing the strength of the paper cup and serving as a hook when the paper cup is mechanically supported, and is particularly important in an automatic paper cup feeder.
For example, an automatic paper cup feeder in a general vending machine stores a large number of paper cups stacked in the vertical direction. The paper cup automatic supply device supports the cup by engaging with the top curl portion of the lowermost paper cup at the time of standby, and at the time of sale, the engagement of the paper cup is released immediately after the engagement is released. Engage with the top curl. As described above, the paper cup automatic supply device uses the top curl portion to reliably drop the paper cups one by one and provide them to the user (see Patent Document 1).

JP 2012-219381 A

  The top curl portion of the paper cup is, for example, widened by applying a die to the periphery of the upper end opening of the paper cup, and applied to a die having a curl shape of a specific size from the upper end opening side of the paper cup. Then, the paper cup is curled outward with respect to the peripheral edge of the upper end opening. Further, by pushing the paper cup downward, the paper cup is guided along the curved surface of the curl-shaped mold set below, and the top curl portion is formed (Patent Document 1).

  Thus, when the top curl portion is molded, a tensile force is applied to the outside of the top curl portion, and a compressive force is applied to the inside thereof. Therefore, for example, when the outer side of the top curl portion cannot withstand the tensile force, the top curl portion is broken or swollen. On the other hand, when an excessive compressive force is applied to the inside of the top curl portion, the top curl portion is bent. Due to such a cause, a problem occurs in forming the top curl portion in the paper cup manufacturing.

Since the top curl portion plays a role as described above, a paper cup in which a problem has occurred in forming the top curl portion cannot withstand practical use.
As one of the methods for suppressing the problem of forming the top curl portion, it is conceivable to increase the tensile strength of the paper cup base paper. If the tensile strength is large, even if a large tensile force is applied during molding, a problem of molding of the top curl portion due to breakage of the fibers of the paper cup base paper is unlikely to occur.

However, both the tensile strength and the compressive strength are indicators of the strength of the paper. In general, a paper having a high tensile strength is a paper having a high compressive strength at the same time.
Paper with high compressive strength is paper that is difficult to curl, lacks suitability for top curl processing, and tends to break the top curl portion. In particular, the joint part on the side of the paper cup, that is, the seam part, is made of double paper for paper cups, and two sheets of paper are overlapped, so top curl processing is more difficult than other parts. Become. Therefore, if a paper cup base paper that is difficult to be rounded is used, a problem (seam portion turning) that a part of the top curl portion that has not been rounded up at the joining portion is turned up is very likely to occur. As described above, the paper cup base paper, which has a high compressive strength and is not easily rounded, has a problem of deteriorating the yield of the paper cup.

  The present invention has been made in view of such a situation. That is, the object of the present invention is to provide a paper that has both a tensile strength sufficient to withstand the tensile force at the time of molding the top curl portion and ease of curling, can be easily molded at the top curl portion, and does not easily turn over at the seam portion. It is to provide a base paper for a cup and a paper cup using the same.

The inventors of the present invention have studied a base paper for a paper cup that has both a tensile strength sufficient to withstand the tensile force at the time of molding the top curl portion and ease of curling.
As a result, it has been found that not only a reduction in compressive strength but also a reduction in Z-axis strength (interlayer strength) is effective as a means for realizing ease of rounding. According to the present invention, if the Z-axis strength and the tensile strength are in a certain range, it is possible to realize a paper cup base paper that is easy to curl and does not cause fiber breakage. Especially in the seam part, the paper on the inside of the top curl part follows the paper on the outside and buckles and deforms, so that the paper on the inside and the paper on the outside at the end of the seam part is cracked, peeled off, etc. The seam portion can be prevented from turning over.
The present invention has been completed based on such knowledge. That is, the present invention has the following configuration.

(1) A base paper for paper cups comprising cellulose pulp as a main component, having a Z-axis strength of 560 kN / m ² or less and a tensile strength in the MD direction of 14.0 to 20.0 kN / m.

(2) The base paper for paper cups according to (1), wherein the cellulose pulp contains softwood kraft pulp, and the content of softwood kraft pulp relative to the cellulose pulp is 10 to 20% by mass.

(3) The base paper for paper cups according to (1) or (2) above, wherein the disintegration freeness of the cellulose pulp measured in accordance with JIS P 8121: 2012 is 440 to 530 ml.

(4) A paper cup comprising the base paper for paper cup according to any one of (1) to (3).

  The base paper for paper cups of the present invention has a tensile strength sufficient to withstand the tensile force at the time of molding the top curl portion and ease of curling, and is suitable for molding the top curl portion. In addition, the occurrence of seam turning can be suppressed. Since the paper cup of the present invention uses the paper cup base paper, the paper cup is suitable for forming a top curl portion and a seam portion thereof. Further, it is possible to process with a small force when the top curl portion is formed.

  Hereinafter, embodiments of the present invention will be specifically described. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

The operation procedure at the time of forming the top curl portion is, for example, as follows after forming the seam portion on the side surface of the paper cup.
(1) The opening is widened by applying a mold to the periphery of the opening of the upper end of the paper cup.
(2) A curl upper molding die having a curl shape with a specific size is applied from above to the upper end opening side of the paper cup.
(3) The upper mold for curling is pushed down, and the upper end opening of the paper cup is curled outward with respect to the periphery of the opening.
(4) A curl lower molding die having a curl shape having a specific size is applied from below to the upper end opening side of the paper cup.
(5) By pushing the paper cup downward, it is guided along the curved surface of the mold for lower curl molding and is wound inward to form the top curl portion.

Hereafter, each element which comprises the base paper for paper cups of this embodiment is demonstrated.
(pulp)
The paper cup base paper is mainly composed of cellulose pulp. Although there is no restriction | limiting in particular in a cellulose pulp, It is preferable to contain a chemical pulp from a viewpoint of intensity | strength. Although it does not specifically limit as a chemical pulp, It is preferable to contain a hardwood kraft pulp (LKP) or a softwood kraft pulp (NKP). The pulp may be bleached pulp or unbleached pulp. Furthermore, it is preferable to contain both LKP and NKP. Hereinafter, unless otherwise specified, LKP and NKP include bleached pulp or unbleached pulp, respectively. Hardwood bleached kraft pulp may be referred to as LBKP, and softwood bleached kraft pulp as NBKP.

Here, in the paper cup base paper, it is preferable to blend NKP at a predetermined ratio in order to increase the tensile strength. Because NKP has long fibers, it can increase the tensile strength of the paper-made product.
However, increasing the blending amount of NKP increases the compressive strength as well as the tensile strength. Therefore, the present inventors examined the content of NKP that can obtain a sufficiently small compressive strength and at the same time obtain a tensile strength that does not break the fiber of the paper cup base paper by the tensile force at the time of forming the top curl portion. Repeated. As a result, it was found that the content of NKP is preferably 10 to 20% by mass and more preferably 13 to 18% by mass with respect to the total mass of the pulp components.

Various types of printing are performed on the surface of a general paper cup. Therefore, printability is required for the base paper for paper cups.
LKP has short fibers and is inferior in strength compared to NKP, but is excellent in the texture and smoothness of the paper made and can improve the printability. Therefore, in the base paper for paper cups, the content of LKP is preferably 40% by mass or more, more preferably 60% by mass, and 80% by mass or more with respect to the total mass of the pulp components. Is more preferable.

  The pulp component may contain pulp other than NKP and LKP (hereinafter referred to as other pulp). Other pulps include Stone Grand Pulp (SGP), Pressurized Stone Grand Pulp (PGW), Refiner Grand Pulp (RGP), Thermo Grand Pulp (TGP), Chemi Grand Pulp (CGP), Ground Pulp (GP), Thermo Manufactured from mechanical pulp such as mechanical pulp (TMP), tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, Kami white waste paper, Kent waste paper, imitation waste paper, old paper waste paper, etc. Examples include pulp that has been chemically or mechanically produced from non-wood fibers such as disintegrated waste paper pulp (DIP), kenaf, hemp, and straw. The content of the other pulp is preferably less than 3% by mass, more preferably less than 2% by mass, and even more preferably less than 1% by mass with respect to the total mass of the pulp components.

Generally, if the beating degree (freeness) of the pulp component is reduced, the tensile strength of the paper-made product can be increased.
However, reducing the freeness increases the compressive strength as well as the tensile strength. Therefore, the present inventors obtain sufficiently small compressive strength for the paper cup base paper that has been made, and at the same time obtain a tensile strength that does not break the fiber of the paper cup base paper due to the tensile force at the time of molding the top curl portion. We studied the disintegration freeness that can be done. As a result, it was found that the disaggregation freeness measured in accordance with JIS P 8121: 2012 is preferably 440 to 530 mlcsf. The disaggregation freeness is more preferably 460 to 510 mlcsf, and further preferably 460 to 500 mlcsf. Here, the disaggregation freeness is a Canadian standard freeness value measured according to the method of JIS P 8121: 2012 using pulp slurry obtained by disaggregating the paper cup paper according to the method of JIS P 8220: 2012. Point to.
The disaggregation freeness can be adjusted by adjusting the freeness of the cellulose pulp before papermaking. It has been found that the freeness of the cellulose pulp before papermaking is preferably 390 to 480 mlcsf, more preferably 410 to 460 mlcsf.

  In addition to pulp, internal chemicals can be added to the paper cup base paper of the present invention as required. For example, known chemicals such as a yield improver, a drainage improver, a sizing agent, a paper strength enhancer, a sulfuric acid band, a dye, and a pitch control agent can be used.

  The paper cup base paper of the present invention is not particularly limited as long as it is produced by a generally used paper machine. The paper machine is composed of an inlet, a wire part, a press part, a dryer part, and a reel part, and may include a coating part for imparting functionality in the middle or as a subsequent process.

  The form of the inlet and wire part is not particularly limited. For example, a circular net paper machine, a short net paper machine, a long net paper machine, a twin wire, and a gap former can be used. Moreover, it may consist of one layer, and may be comprised by the multi-layered making which is made up from several inlets.

  The paper cup base paper of the present invention can be coated on the surface as necessary. It is coated or impregnated with various surface binders such as starch, polyvinyl alcohol, polyacrylamide, surface sizing agents such as rosin sizing agents, synthetic sizing agents, and neutral sizing agents, and conductive agents such as sodium chloride and sodium sulfate. Also good.

(Basis weight)
The basis weight of base paper for paper cups is preferably 180~240g / ^{m 2,} more preferably from 200~240g / ^{m 2,} further preferably 220~240g / ^{m 2.} When the basis weight is 240 g / m ² or less, there is no possibility that the paper becomes too heavy and the workability at the time of manufacturing the paper cup decreases. On the other hand, when the basis weight is 180 g / m ² or more, the strength of the paper cup can be improved.

(Paper thickness)
The paper thickness of the paper cup base paper is preferably 210 to 290 μm, more preferably 260 to 290 μm. When the paper thickness is 290 μm or less, there is no possibility that workability at the time of manufacturing the paper cup is lowered due to being too bulky. On the other hand, when the paper thickness is 210 μm or more, the strength as a paper cup can be improved.

(density)
The density of base paper for paper cups is preferably 0.82~0.85g / cm ^3, more preferably 0.83~0.84g / cm ^3. When the density is 0.85 g / cm ³ or less, it is not necessary to extremely reduce the paper thickness, and the productivity is improved. On the other hand, when the density is 0.82 g / cm ³ or more, the strength as a paper cup can be improved.

(Z-axis strength)
In order to facilitate the formation of the top curl portion, a paper cup base paper that is easy to curl is required.
The Z-axis strength refers to strength in a direction perpendicular to the paper surface, that is, strength between paper layers, in other words, internal bond strength within the paper layers. If the bond between the paper layers is weak, the Z-axis strength decreases. When the top curl part is formed on the base paper for paper cups with low Z-axis strength, each paper layer slides away from the adjacent paper layer, and the top curl part is easily formed by slipping and curling each paper layer. can do.
The reduction of the Z-axis strength can be realized by appropriately reducing and adjusting the linear pressure, for example, in the pressing step during the paper making step. Other adjustment methods include methods such as adjusting the NKP blending amount relative to the pulp blending amount and adjusting the disaggregation freeness. The inventors of the present invention repeatedly studied a sufficiently small Z-axis strength to facilitate the formation of the top curl portion. As a result, if the Z-axis strength is greater than 560 kN / m ² , sufficient curling ease cannot be ensured, and seam turning is significantly generated. From the viewpoint of suppressing the curling seam effectively, Z axis strength preferably not more than 540kN / ^{m 2,} was found more preferable if 500 kN / ^{m 2} or less.
On the other hand, if the Z-axis strength is too small, it is difficult to maintain sufficient tensile strength. Therefore, it is preferable that the Z-axis strength is 400 kN / ^{m 2} or more, more preferably 460kN / ^{m 2} or more.

(Tensile strength)
The tensile strength of the paper cup base paper needs to be 14.0 to 20.0 kN / m in order to withstand the tensile force while ensuring the ease of curling of the top curl portion. The tensile strength is preferably 15.0 to 20.0 kN / m, more preferably 15.0 to 18.0 kN / m, and further preferably 16.0 to 18.0 kN / m.
In order to control the tensile strength in the range of 14.0 to 20.0 kN / m, adjust the blending amount of NKP with respect to the blending amount of pulp, adjust the disaggregation freeness, adjust the degree of fiber orientation, and press pressure in the press part. There are methods such as adjusting and changing the internal chemicals. Further, regardless of whether the paper layer of the paper cup is single-layered or multi-layered, there are methods such as adding a large amount of paper strength agent on the surface layer side of the paper and making the fiber orientation different from front to back.
In any case, the tensile strength is measured in the MD direction (paper machine flow direction) in principle. However, when it is unclear whether the direction is the MD direction, the tensile strength is measured every angle of 22.5 degrees, and the direction showing the strongest tensile strength is taken as the MD direction.

  The paper cup base paper of the present embodiment can be suitably used as a paper cup base paper.

  Examples and comparative examples are shown below. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

Example 1 15 parts of NBKP and 85 parts of LBKP were mixed and beaten to obtain a pulp slurry. For 100 parts of the obtained pulp slurry, 0.55 parts (in terms of solid content) as an internal paper strength enhancer, 1.45 parts (in terms of solid content) as an internal additive size agent, 2.5 parts of sulfuric acid band ( Solid content) was added to prepare a paper stock. The paper stock was used to make a paper using a long sheet paper machine. During the paper making process, 0.7 g / m ² of polyvinyl alcohol is applied with a size press and smoothed with a calendar to obtain a paper cup base paper having a basis weight of 226 g / m ² and a density of 0.84 g / cm ^3. It was. The disaggregation freeness of the pulp obtained by reaggregating this base paper was 480 ml.

(Example 2) 20 parts of NBKP and 80 parts of LBKP were mixed and beaten, and paper was made in the same manner as in Example 1 to obtain a paper cup base paper having a basis weight of 225 g / m ² and a density of 0.84 g / cm ³ . The disaggregation freeness of the pulp obtained by reaggregating this base paper was 530 ml.

(Example 3) 10 parts of NBKP and 90 parts of LBKP were mixed and beaten, and paper was made in the same manner as in Example 1 to obtain a paper cup base paper having a basis weight of 223 g / m ² and a density of 0.84 g / cm ³ . The disaggregation freeness of the pulp obtained by reaggregating this base paper was 440 ml.

(Example 4) 10 parts of NBKP and 90 parts of LBKP were mixed and beaten, and paper was made in the same manner as in Example 1 to obtain a paper cup base paper having a basis weight of 230 g / m ^{2 and a} density of 0.84 g / cm ³ . The disaggregation freeness of the pulp obtained by reaggregating this base paper was 530 ml.

(Comparative Example 1) 100 parts of LBKP was beaten and paper was made in the same manner as in Example 1 to obtain a paper cup base paper having a basis weight of 218 g / m ² and a density of 0.84 g / cm ³ . The disaggregation freeness of the pulp obtained by reaggregating this base paper was 520 ml.

(Comparative Example 2) 15 parts of NBKP and 85 parts of LBKP were mixed and beaten, and paper was made in the same manner as in Example 1 to obtain a paper cup base paper having a basis weight of 225 g / m ² and a density of 0.84 g / cm ³ . The disaggregation freeness of the pulp obtained by reaggregating this base paper was 420 ml.

(Comparative Example 3) 10 parts of NBKP and 90 parts of LBKP were mixed and beaten, and paper was made in the same manner as in Example 1 to obtain a paper cup base paper having a basis weight of 230 g / m ² and a density of 0.84 g / cm ³ . The disaggregation freeness of the pulp obtained by reaggregating the base paper was 410 ml.

The basis weight, paper thickness, density, Z-axis strength, tensile strength, and disaggregation freeness were measured for the obtained paper cup base papers of Examples and Comparative Examples. In addition, in order to examine the suitability as a base paper for paper cups, top curl treatment was performed, and top curl formability and seam turning were evaluated.
The evaluation method for each item is as follows.

<Basis weight>
Basis weight was measured according to JIS P 8124: 2011. The weight was measured using an electronic balance capable of measuring up to the last 4 digits, and the basis weight was calculated.

<Paper thickness>
Measurement was performed using a paper thickness meter in accordance with JIS P 8118: 2014.

<Density>
The density was measured according to JIS P 8118: 1998.

<Z-axis strength>
JAPAN TAPPI Paper Pulp Test Method No. 18-1: 2000 Paper and paperboard-Internal bond strength test method-Part 1: Measured according to the Z-axis direction tensile test method. As a measuring machine, Tensilon universal material testing machine RTC-1250A manufactured by A & D Corporation was used.

<Tensile strength>
Based on the method prescribed | regulated to JISP8113: 2006, the tensile strength of MD direction of the paper cup base paper after humidity control was performed in the humidity control environment prescribed | regulated to JISP8111: 1998. A horizontal tensile tester (manufactured by L & W, CODE SE-064) was used as a measuring machine.

<Disaggregation freeness>
The obtained base paper for paper cup was disaggregated according to the method of JIS P 8220: 2012, and the disaggregation freeness of the obtained pulp slurry was measured by a method based on JIS P 8121: 2012. As a measuring machine, a Canadian freeness tester manufactured by Kumagai Riki Kogyo was used.

<Top curl formability>
The top curl portion when the obtained paper cup base paper was made was visually observed and evaluated according to the following criteria.
○: No breakage, swelling, tearing, breakage, or the like is observed in the top curl portion.
Δ: Some breakage, swelling, tearing, breakage, etc. are observed in the top curl portion, but it is at a practical level.
X: Breaking, swelling, tearing, folding, etc. are very conspicuous in the top curl portion.

<Seam part turning>
When the obtained paper cup base paper was produced, the seam portion of the top curl portion was visually observed and evaluated according to the following criteria.
○: No turning up is seen in the seam part.
(Triangle | delta): Although some turning up is seen in a seam part, it is a practical use level.
X: The seam part is conspicuously turned up.

  The measurement and evaluation results for Examples 1 to 4 and Comparative Examples 1 to 3 were as shown in Table 1. In the evaluation of the characteristics, it was determined to be acceptable when the mark was ◯ and △.

  As can be seen from Table 1, in Examples where the Z-axis strength is low and the tensile strength in the MD direction is appropriate, the top curl can be molded without any problem, and the seam portion has no problem. On the other hand, in Comparative Example 1 with low tensile strength, the top curl portion is torn due to low tensile strength, and in Comparative Examples 2 and 3 with high Z-axis strength, a strong force is required at the time of curl molding. As a result, the top curl portion was bent and the seam portion was turned up.

Claims (4)

Cellulose pulp is the main component,
The Z-axis strength is 560 kN / m ² or less,
A base paper for a paper cup, wherein the tensile strength in the MD direction is 14.0 to 20.0 kN / m.   The base paper for paper cups according to claim 1, wherein the cellulose pulp contains softwood kraft pulp, and the content of softwood kraft pulp with respect to the cellulose pulp is 10 to 20% by mass.   The base paper for paper cups according to claim 1 or 2, wherein a disaggregation freeness of the cellulose pulp measured in accordance with JIS P 8121: 2012 is 440 to 530 ml.   The paper cup which consists of the base paper for paper cups of any one of Claims 1-3.