JP2019065436A - Paper base paper and paper cup - Google Patents

Abstract

To provide a base paper for paper cups which is excellent in the balance between the tensile strength of the back layer portion and the compression strength of the surface layer portion and which is easy to form the top curled portion, and a paper cup using the same.SOLUTION: Base paper for paper cups having cellulose pulp as a main component and having three or more paper layers, which has a tensile strength in the MD direction of 14.0 kN/m or more, and includes a surface layer portion including the surface in the paper thickness direction and a back layer portion including a back surface. When the specific tensile strength of the back layer portion in the MD direction is T, and the specific compressive strength of the surface layer portion in the MD direction is C when divided into two layers of equal thickness to the surface layer portion and the back layer portion by the short span method, T/C is 3.0 or more.SELECTED DRAWING: None

Description

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

  Conventionally, in a beverage paper cup, a portion serving as a mouth of the cup (hereinafter, referred to as a top curled portion) is formed by top curl processing in which a paper cup upper end opening peripheral edge is wound outward. One of the qualities required for paper cup base paper is the ease of making this top curled part.

The top curl portion plays a role of increasing the strength of the paper cup, taking on the function 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 accommodates a large number of paper cups stacked in the vertical direction. The paper cup automatic feeding device supports the cup by being engaged with the top curl portion of the lowermost paper cup at the time of standby, and at the time of sale, the paper cup is released immediately after the engagement is released. Engage with the top curl. As described above, the paper cup automatic feeding device securely uses the top curl portion to drop the paper cups one by one and provides the user with the paper cups (see Patent Document 1).

JP, 2012-219381, A

  The top curled portion of the paper cup is formed, for example, as follows. First, open the opening by placing a mold on the periphery of the top opening of the paper cup, and apply a mold with a curled shape of a specific size from the side of the top opening of the paper cup. Make it curl outward. Next, the paper cup is pushed downward to be guided along the curved surface of the curled mold set downward and rolled inward to form a top curled portion (Patent Document 1).

  As described above, when forming the top curled portion, a tensile force is applied to the outer side of the top curled portion, and a compressive force is applied to the inner side. Therefore, for example, when the outside of the top curled portion can not withstand the tensile force, the top curled 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 broken or the like. Such a cause causes problems in the formation of the top curl portion in paper cup manufacture. In the top curl portion which fails in such molding, the circumference does not follow the mold due to breakage, breakage or the like, and the circular shape is crushed and the outer periphery is reduced.

Since the top curl portion plays a role as described above, a paper cup having a defect in forming the top curl portion can not withstand practical use.
It is conceivable to increase the tensile strength of the base paper for paper cups as one of the methods of suppressing the problem of molding of the top curled part. If the tensile strength is high, even if a large tensile force is applied during molding, problems in molding the top curled portion due to breakage of the fibers of the base paper for paper cups hardly occur.

However, tensile strength and compressive strength are both indicators of paper strength, and in general, paper with high tensile strength simultaneously becomes paper with high compressive strength.
Paper with high compressive strength is paper that is hard to curl, and is not suitable for top curling, and it is easy for the top curled part to be broken. In particular, since the joint area on the side of the paper cup, that is, the seam section, has double paper base paper, and two sheets of paper are overlapped and rolled up, top curling is more difficult than other parts. Become. Therefore, if the base paper for paper cups which is hard to round is used, a problem (seam part turning up) that a part of the top curled part which is not rounding up in the seam part is turned up easily occurs easily. As described above, the base paper for paper cups, which has large compressive strength and is hard to round, has a problem of deteriorating the yield of paper cups.

  From the above, the paper layer constituting the outer side of the top curled part to which tensile force is applied in top curl processing, that is, the back side of the base paper for paper cup (inner side of paper cup) The paper layer that constitutes the inside of the top curl portion that has strength and compression force in top curl processing, that is, the surface of the base paper for paper cup (outside of the paper cup), is sufficiently sufficient to realize roundness. There is a need for a base paper for paper cups having a small compressive strength.

  The present invention has been made in view of such a situation. That is, the object of the present invention is that the balance between the tensile strength of the paper layer constituting the back surface and the compressive strength of the paper layer constituting the surface is excellent, the formation of the top curled portion is easy, and the curling is difficult to occur in the seam portion. It is providing a base paper for paper cups and a paper cup using the same.

Hereinafter, the direction (longitudinal direction) in which the pulp slurry flows out in the process of forming the paper layer in the paper making of the paper cup base paper is also referred to as the MD direction. In addition, the direction perpendicular to the longitudinal direction on paper, that is, the lateral direction is also referred to as the CD direction.
In the base paper for paper cup, the back side is the inner side when the paper cup is formed, and the front side is the outer side to be printed etc. That is, the back surface of the base paper for paper cups is the outside of the top curl portion, and the surface is the inside of the top curl portion.
Hereinafter, when the base paper for paper cup is equally divided into two in the paper thickness direction, the side including the front surface is also referred to as a surface layer portion, and the side including the back surface is also referred to as a back layer portion.

The inventors have found that the back layer has a tensile strength sufficient to prevent breakage of the fiber due to the tension of top curling, and the surface layer has a paper with a sufficiently small compressive strength to realize roundness. We proceeded to study the base paper for cups.
As a result, it has been found that if there is a predetermined relationship between the tensile strength of the back layer portion and the compressive strength of the surface layer portion, it is possible to realize a paper cup base paper having ease of rounding and no breakage of fibers. In particular, in the seam portion, the paper inside the top curled portion buckles and deforms in accordance with the paper outside, thereby causing cracking, peeling, etc. between the paper inside and the paper outside at the tip of the seam portion. Will not occur. Thereby, seam part turning can be suppressed.

  The present invention has been completed based on such findings. That is, the present invention has the following configuration.

(1) It is a base paper for paper cups having three or more paper layers mainly composed of cellulose pulp,
The tensile strength in the MD direction is 14.0 kN / m or more,
When divided into two by a thickness equal to the surface layer portion including the surface and the back layer portion including the back surface in the paper thickness direction, the specific tensile strength in the MD direction of the back layer portion is measured by the T and short span method T / C is 3.0 or more, wherein C is a specific compressive strength in the MD direction of the surface layer portion.

(2) The base paper for paper cups according to (1), wherein the fiber orientation ratio of the back layer portion is larger than that of the surface layer portion by 0.15 or more.

(3) Of the paper layers constituting the paper cup base paper, the number of NKP blended parts of the outermost paper layer constituting the back surface is 10 mass than the number of NKP blended parts of the outermost paper layer constituting the surface The base paper for paper cups according to (1) or (2), characterized in that the size is larger than that of the part.

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

  The base paper for paper cups of the present invention is excellent in the balance between the tensile strength of the back layer portion and the compressive strength of the surface layer portion, and is suitable for forming the top curled portion. In addition, it is possible to suppress the occurrence of seam portion curling. Since the paper cup of the present invention uses the base paper for paper cups, it is suitable for forming the top curl portion and the seam portion thereof. Further, it is possible to process with a small force when forming the top curled portion.

  Hereinafter, embodiments of the present invention will be specifically described. The description of the configuration requirements described below may be made based on typical embodiments and specific examples, but the present invention is not limited to such embodiments. In addition, the numerical range represented using "-" in this specification means the range which includes the numerical value described before and after "-" as a lower limit and an upper limit.

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

Hereinafter, each element which comprises the base paper for paper cups of this embodiment is demonstrated.
The base paper for paper cups of the present invention has three or more paper layers. The number of layers is not particularly limited, and may be four, five, or more. It is preferable that the plurality of paper layers be paper (laminated paper) of a multi-layered structure made by multi-layered paper making.

(Papermaking method)
The paper making method of the base paper for paper cups usually has a step of refining the pulp constituting each layer so as to have a desired freeness, and a step of making a pulp slurry.
As a papermaking machine for making paper for a paper cup, a papermaking machine capable of papermaking with three or more layers is used. The paper machine comprises an inlet, a wire part, a press part, a dryer part, a calendar part (smoothing processing), and a reel part. Moreover, you may include the coating part for providing functionality as the middle or the back process of these parts. The papermaking pH is not particularly limited, and may be, for example, an acidic papermaking method, or a neutral papermaking method using an alkaline filler such as calcium carbonate.

  The types of the inlet and the wire part are not particularly limited. For example, it is possible to cite a circular mesh type paper machine, a fourdrinier paper machine, a fourdrinier paper machine, a twin wire, a gap former or the like, and it is constructed by multi-layered papermaking which is made together from a plurality of inlets.

  In the papermaking method of the base paper for paper cup, the above-mentioned smoothing treatment may be applied to the surface in order to improve the surface strength or enhance the printability. The smoothing treatment is preferably performed, for example, by pressing the paper cup base paper between the pressable reels. There are no particular restrictions on various finishing devices for smoothing, but for example, the product finish is applied by passing through a machine calendar in front of the winder, and / or a super calender, a gloss calender, a soft nip calender, etc. .

  The base paper for paper cups of the present invention can also be coated on the surface as needed. Coating or impregnating various surface binders such as starch, polyvinyl alcohol and polyacrylamide, surface sizing agents such as rosin based sizing agents, synthetic sizing agents and neutral sizing agents, and conductive agents such as sodium chloride and sodium sulfate it can.

(pulp)
The base paper for paper cups is mainly composed of cellulose pulp. The cellulose pulp is not particularly limited, but it is preferable to contain a chemical pulp from the viewpoint of strength. The chemical pulp is not particularly limited, but it is preferable to contain hardwood kraft pulp (LKP) or softwood kraft pulp (NKP). The pulp may be bleached pulp or unbleached pulp. Furthermore, it is preferable to contain both LKP and NKP. Hereinafter, although LKP and NKP contain bleached pulp or unbleached pulp, respectively, unless otherwise specified, hardwood bleached kraft pulp may be referred to as LBKP, and softwood bleached kraft pulp may be referred to as NBKP.

Here, in the base paper for paper cups, it is preferable to blend NKP at a predetermined ratio in order to increase the tensile strength. NKPs have the effect of increasing the tensile strength and compressive strength of the machined product due to the long fibers.
Therefore, if the NKP content of the pulp constituting the back layer portion of the paper base paper for papermaking exceeds the NKP content of the pulp constituting the surface layer portion, a tensile force of top curling is applied. It was thought that the tensile strength of the back layer part could be increased and the compressive strength of the surface layer part to which a compressive force is applied could be reduced.

The inventors of the present invention have studied the NKP blending of pulp for increasing the tensile strength of the back layer and reducing the compressive strength of the surface layer. Hereinafter, among a plurality of paper layers of multilayer paper, the outermost paper layer constituting the surface is also referred to as a surface layer. Further, the outermost paper layer constituting the back surface is also referred to as a back layer.
The present inventors examined the difference in the number of NKP blended parts of the pulp constituting the surface layer and the pulp constituting the back layer. As a result, it has been found that the number of NKP blended parts of the pulp constituting the backing layer is preferably 10 parts by mass or more more than the surface layer, and more preferably 15 parts by mass or more. Here, the difference in the number of blended parts means the difference between the content rate (parts by mass) of NKP in 100 parts by mass of all pulps in the backing layer and the content rate (parts by mass) of NKP in 100 parts by mass of all pulps in the surface layer. Point to.

  The pulp constituting the backing layer of the base paper for paper cups preferably contains 10 to 30 parts by mass of NKP, and more preferably 15 to 30 parts by mass, in order to obtain a backing layer having a sufficiently large tensile force. Preferably, 15 to 25 parts by mass is more preferable. In addition, in order to obtain a surface layer portion with a sufficiently small compressive force, it is preferable that the pulp constituting the surface layer of the base paper for paper cups contains 1 to 15 parts by mass of NKP, and more preferably 5 to 15 parts by mass preferable. Within these ranges, the difference in the number of NKP parts may be adjusted to a preferable range.

In addition, various printings are applied to the surface of a general paper cup. Therefore, printability is required for the base paper for paper cups.
LKP has short fibers and inferior strength as compared to NKP, but it is excellent in formation and smoothness of paper made of paper and can make printability good. Therefore, in the surface layer of the base paper for paper cup, the content of LKP is preferably 81 parts by mass or more, and more preferably 85 parts by mass or more, based on 100 parts by mass of the total mass of pulp components. In the present invention, since the paper layer has a multilayer structure, the strength can be maintained to increase the content of LKP in the surface layer.

  The pulp component may contain pulp other than the above NKP and LKP (hereinafter referred to as other pulp). Other pulps include stone ground pulp (SGP), pressed stone ground pulp (PGW), refiner ground pulp (RGP), thermoground pulp (TGP), chemiground pulp (CGP), ground pulp (GP), thermo Manufactured from mechanical pulp (TMP) and other mechanical pulp, waste paper, kraft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, white waste paper, white waste paper, Kent waste paper, imitation waste paper, ground paper waste paper, etc. Examples thereof include disintegrated paper pulp (DIP), and pulp chemically or mechanically produced from non-wood fibers such as kenaf, hemp, straw and the like. The content of the other pulp is preferably less than 3% by mass, more preferably less than 2% by mass, and still more preferably less than 1% by mass, based on the total mass of the pulp components.

In general, if the freeness of the pulp component is in an appropriate range, the tensile strength and compressive strength of the papermaking product will increase.
Therefore, the present inventors examined the appropriateness of the back layer freeness and the surface layer freeness. As a result, in order to obtain a backing layer having a sufficiently large tensile force, the disintegration-freeness of the pulp constituting the backing layer of the base paper for paper cup is preferably 470 to 520 mlcsf, more preferably 480 to 510 mlcsf. It turned out to be preferable. It is preferable that it is 420 ml-470 mlcsf, and, as for the freeness (Canadian standard freeness) of the cellulose pulp which comprises the back layer before being paper-made, it is more preferable that it is 430 ml-460 mlcsf.

Further, in order to obtain a surface layer portion with a sufficiently small compressive force, the disintegration freeness of the pulp constituting the surface layer of the base paper for paper cup is preferably 480 to 540 mlcsf, more preferably 490 to 540 mlcsf, 500 It turned out that it is further preferable that it is -530 mlcsf. The freeness of the cellulose pulp constituting the surface layer before papermaking is preferably 440 to 490 mlcsf, and more preferably 450 to 480 mlcsf.
Here, disaggregation freeness refers to Canadian Standard Freeness (Canadian Standard Pulp Freeness) measured according to JIS P 8121: 2012 using pulp slurry obtained by disaggregation according to JIS P 8220: 2012. Points to the value of The disaggregation freeness in a specific paper layer is the freeness obtained by separating the paper layer of the paper cup base paper. The disaggregation freeness can be adjusted by adjusting the freeness of the cellulose pulp before papermaking. On the other hand, the freeness of the pulp before papermaking may be adjusted to the above-mentioned range by beating the at least one kind of pulp described above. When two or more types of pulp are used, the pulps that have been separately beaten may be mixed to make the above-mentioned range, or the pre-mixed pulp may be beaten and adjusted to the above-mentioned range.

  In addition to pulp, internally added chemicals can be added to the paper base paper of the present invention as required. For example, known chemicals such as retention aids, drainage improvers, sizing agents, strength agents, sulfuric acid bands, dyes, pitch control agents and the like can be mentioned.

(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. If the basis weight is 240 g / m ² or less, there is no possibility that the paper will be too heavy to lower the workability at the time of paper cup manufacture. On the other hand, when the basis weight is 180 g / m ² or more, the strength as a paper cup can be improved.

(Paper thickness)
It is preferable that it is 210-290 micrometers, and, as for the paper thickness of the base paper for paper cups, it is more preferable that it is 260-290 micrometers. If the paper thickness is 290 μm or less, there is no possibility of lowering the workability at the time of paper cup manufacture due to the bulk being too high. 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 0.82~0.87g / cm ^3, more preferably 0.82~0.85g / cm ^3, 0.83~0.84g / cm More preferably, it is ³ . When the density is 0.87 g / cm ³ or less, it is not necessary to make the paper thickness extremely thin, 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.

(Fiber orientation ratio)
The fiber orientation is a tendency of pulp slurry to flow out on a wire of a paper machine, to be dewatered, and to be aligned in the flow direction (MD direction) in the process of forming a paper layer. The fiber orientation ratio can be adjusted by changing the jet wire ratio (raw material ejection velocity ratio).
The jet wire ratio is the ratio of the outflow velocity of the pulp slurry to the traveling velocity of the wire, and is expressed by the outflow velocity of the slurry / the traveling velocity of the wire.

  Generally, as a method of measuring fiber orientation of paper etc., for example, thermal expansion method, mechanical breaking strength method, X-ray diffraction method, ultrasonic method, microwave method, NMR method, polarization fluorescence method, dielectric measurement method etc. are mentioned. Be In the present invention, the ultrasonic method is employed to measure the longitudinal ultrasonic wave propagation velocity (Vmd) and the transverse ultrasonic wave propagation velocity (Vcd), and the ratio (Vmd / Vcd) is taken as the fiber orientation ratio to determine fiber orientation It was used as an index to evaluate randomness. When the fiber orientation ratio is 1.0, the fibers are completely randomly oriented.

  In top curling, since the base paper for paper cups is wound in the MD direction, tensile force and compressive force are applied in the MD direction. Therefore, the tensile strength and the compressive strength that affect top curling are the tensile strength and the compressive strength in the MD direction. Adjustment of fiber orientation ratio is mentioned as one of the methods of adjusting the tensile strength and compressive strength of MD direction. For example, when a tensile force in the MD direction is applied to a base paper for paper cups in which the fiber orientation ratio is large, that is, the fiber orientation is biased in the MD direction, the tensile force acts in the fiber orientation direction. It is hard to occur. That is, the deviation of the fiber orientation in the MD direction increases the tensile strength in the MD direction.

Therefore, in order to increase the tensile strength of the back layer of the paper cup base paper and reduce the compressive strength of the surface layer, the fibers of the back layer should be oriented in the MD direction more than the fibers of the surface layer. preferable. That is, the fiber orientation ratio of the back layer portion is preferably 0.15 or more larger than that of the surface layer portion, more preferably 0.20 or more, and still more preferably 0.30 or more.
The fiber orientation ratio of the surface layer portion is preferably in the range of 1.20 to 1.40, and more preferably in the range of 1.20 to 1.35. On the other hand, the fiber orientation ratio of the back layer portion is preferably in the range of 1.50 to 1.90, and more preferably in the range of 1.60 to 1.80. By adjusting the fiber orientation ratio within these ranges, it is possible to stably adjust the difference between the fiber orientation ratio of the back layer portion and the fiber orientation ratio of the surface layer portion.

(Tensile strength)
In order not to break the top curled portion during top curling, it is necessary to secure the tensile strength in the MD direction of the back layer portion of the base paper for paper cup.
Therefore, the specific tensile strength in the MD direction of the backing layer portion of the paper base paper for papermaking is preferably 60.0 N · m / g or more, and more preferably 65.0 N · m / g or more, More preferably, it is 67.0 N · m / g or more. Here, the specific tensile strength is a value obtained by dividing the tensile strength by the basis weight of the measurement sample.
The tensile strength in the MD direction of the base paper for the paper cup needs to be 14.0 kN / m or more, preferably 15.0 kN / m or more, and 16.0 kN / m or more. More preferable. Thereby, processing aptitude can be improved and the strength as a paper cup can be maintained.

(Compression strength)
In order to facilitate forming at the time of top curling, a base paper for paper cup that is easily rounded, that is, has a small compressive strength in the surface layer, is required. Therefore, the specific compressive strength of the surface layer of the base paper for paper cups measured according to the short span method defined in JIS P 8156: 2012 is preferably 23.0 N · m / g or less, 22.0 N ·· It is more preferable that it is m / g or less. Thereby, seam turn-over can be effectively suppressed. Here, the specific compressive strength is a value obtained by dividing the compressive strength by the basis weight of the measurement sample.

(The ratio of the specific tensile strength of the back layer to the specific compressive strength of the surface layer)
The present inventors, based on the relationship between the specific compressive strength and the specific tensile strength of the base paper for paper cup, increase the tensile strength of the back layer portion to which top curling is applied and the surface layer to which the compression is applied. A study was conducted on the ratio between the specific tensile strength of the back layer and the specific compressive strength of the surface layer, which can reduce the compressive strength of the part. As a result, when the specific tensile strength of the back layer portion is T and the specific compressive strength of the surface layer portion is C, if T / C is 3.0 or more, the tensile strength of the top curling process causes the base paper for paper cup It has been found that it is possible to obtain a base paper for paper cups in which the fibers do not break and which are easily rounded. T / C is preferably 3.05 or more, more preferably 3.10 or more, and still more preferably 3.20 or more. Thereby, seam turn-over can be effectively suppressed.
In order to control T / C to 3.0 or more, as described above, the amount of NKP blended relative to the blended amount of the pulp constituting the backing layer is larger than that of the surface layer, and the pulp constituting the backing layer and the surface layer is disintegrated There is a method of providing a difference in freeness between front and back, and a method of providing a difference in fiber orientation between front and back. It is also possible to increase the content of the paper strength agent in the back layer more than in the surface layer, or change the internal additives.

  As described above, since it is the tensile force and compressive force in the MD direction that affect top curling, tensile strength and compressive strength are measured in principle in both directions in the MD direction. However, when it is unknown whether it is in the MD direction, the tensile strength is measured every 22.5 degrees, and the direction showing the strongest tensile strength is taken as the MD direction.

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

  Examples and comparative examples are shown below. The materials, amounts used, proportions, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as limited by the specific examples shown below.

Example 1
15 parts of NBKP and 85 parts of LBKP were mixed and refined to a disintegration freeness of 500 ml csf to obtain a pulp slurry. With respect to 100 parts of the obtained pulp slurry, 0.55 parts (in terms of solid content) as an internal paper strengthening agent, 1.45 parts (in terms of solid content) as an internally added sizing agent, 2.5 parts of sulfuric acid band ( Solid content conversion was added to prepare a five-layer stock for surface layer, front lower layer, middle layer, back lower layer, and back layer. Using this stock, paper was prepared using a five-layer twin-wire paper machine with a set basis weight of all five layers set to 46 g / m ² . During the papermaking process, 0.7 g / m ² of polyvinyl alcohol is applied with a size press and smoothed with a calender to a basis weight of 225 g / m ² , paper thickness 268 μm, density 0.84 g / cm ³ , surface layer A base paper for paper cups having a fiber orientation ratio of 1.29, a fiber orientation ratio of the back layer portion of 1.70, and a tensile strength of 16.8 kN / m in the MD direction was obtained. The freeness of the pulp before paper making was 450 ml csf.

(Example 2)
The same pulp as in Example 1 was prepared as a three-layer stock for the surface layer, the middle layer, and the back layer. Using this stock, the set basis weight of the surface layer and the back layer is 46 g / m ² , and the set basis weight of the middle layer is 138 g / m ² as in Example 1 using a triple-layer twin-wire paper machine And paper making, basis weight 226 g / m ² , paper thickness 269 μm, density 0.84 g / cm ³ , fiber orientation ratio of surface layer 1.26, fiber orientation ratio of back layer 1.55, tensile strength in MD direction A base paper for paper cup of 16.9 kN / m was obtained.

(Example 3)
5 parts of NBKP and 95 parts of LBKP were mixed and refined so as to have a disintegration freeness of 490 ml csf to obtain a pulp slurry for surface layer. 15 parts of NBKP and 85 parts of LBKP were mixed and refined so as to have a disintegration freeness of 500 ml csf to obtain pulp slurries for the front lower layer, the middle layer, and the back lower layer. 25 parts of NBKP and 75 parts of LBKP were mixed and refined to a disintegration freeness of 510 ml csf to obtain a pulp slurry for the back layer.
A stock is prepared from these pulp slurries in the same manner as in Example 1, and papermaking is carried out. Basic weight 229 g / m ² , paper thickness 265 μm, density 0.86 g / cm ³ , fiber orientation ratio of surface layer 1.24, back A base paper for paper cup was obtained, which had a fiber orientation ratio of 1.69 in the layer portion and a tensile strength of 16.3 kN / m in the MD direction. The freeness of the pulp before papermaking was 440 mlcsf for surface layer, 450 mlcsf for front layer, middle layer and back layer, and 460 ml csf for back layer.

(Example 4)
The pulp slurry for surface layer was obtained by mixing and refining 5 parts of NBKP and 95 parts of LBKP so that the disaggregation freeness would be 480 ml csf. 15 parts of NBKP and 85 parts of LBKP were mixed and refined to a disintegration freeness of 500 ml csf to obtain a pulp slurry for the middle layer. 25 parts of NBKP and 75 parts of LBKP were mixed and refined to a disintegration freeness of 510 ml csf to obtain a pulp slurry for the back layer.
A stock is prepared from this pulp slurry in the same manner as in Example 2 to make a paper, and the basis weight is 228 g / m.
² , base paper for paper cups, paper thickness 267 μm, density 0.85 g / cm ³ , fiber orientation ratio of the surface layer portion 1.25, fiber orientation ratio of the back layer portion 1.67, tensile strength 16.6 kN / m in MD direction I got The freeness of the pulp before paper making was 430 mlcsf for the surface layer, 450 mlcsf for the middle layer, and 460 mlcsf for the back layer.

(Comparative example 1)
20 parts of NBKP and 80 parts of LBKP are mixed and refined so as to have a disintegration freeness of 520 mlcsf, and papermaking is carried out in the same manner as Example 1; basis weight 226 g / m ² , paper thickness 270 μm, density 0.84 g / cm ³ , surface layer A base paper for paper cups having a fiber orientation ratio of 1.40, a fiber orientation ratio of the back layer portion of 1.44 and a tensile strength of 17.3 kN / m in the MD direction was obtained. The freeness of the pulp before paper making was 470 ml csf.

(Comparative example 2)
The stock prepared in the same manner as in Example 1 is made into a paper sheet by adjusting the jet wire ratio, and basis weight 225 g / m ² , paper thickness 265 μm, density 0.85 g / cm ³ , fiber orientation ratio of the surface layer portion 1.33 A base paper for paper cup was obtained, which had a fiber orientation ratio of 1.33 in the back layer portion and a tensile strength of 16.2 kN / m in the MD direction.

(Comparative example 3)
The stock prepared in the same manner as in Example 1 was made into a paper sheet by adjusting the jet wire ratio, and basis weight 226 g / m ² , paper thickness 268 μm, density 0.84 g / cm ³ , fiber orientation ratio of surface layer 1.70, A base paper for paper cup was obtained, which had a fiber orientation ratio of 1.29 in the back layer portion and a tensile strength of 16.5 kN / m in the MD direction.

(Comparative example 4)
15 parts of NBKP and 85 parts of LBKP were mixed and refined to a disintegration freeness of 400 ml csf to obtain a pulp slurry. The obtained pulp slurry is paper-made in the same manner as in Example 1 and has a basis weight of 226 g / m ² , a paper thickness of 262 μm, a density of 0.86 g / cm ³ , a fiber orientation ratio of the surface layer of 1.31, fibers of the back layer An original paper for paper cups having an orientation ratio of 1.61 and a tensile strength of 17.1 kN / m in the MD direction was obtained. The freeness of the pulp before paper making was 350 ml csf.

(Comparative example 5)
100 parts of LBKP is mixed and refined to a disintegration freeness of 480 mlcsf, and papermaking is carried out in the same manner as in Example 1; basis weight 220 g / m ² , paper thickness 260 μm, density 0.85 g / cm ³ , fiber orientation ratio of surface layer The base paper for paper cups of 1.18, fiber orientation ratio 1.55 of back layer part, and tensile strength 13.3 kN / m of MD direction was obtained. The freeness of the pulp before paper making was 430 ml csf.

With respect to the base paper for paper cups of the obtained Examples and Comparative Examples, the overall basis weight, paper thickness, density and tensile strength, disintegration freeness, fiber orientation ratio, specific tensile strength of the back layer, specific compressive strength of the surface layer Etc. were measured. In addition, in order to check the suitability as a paper cup base paper, top curl processing was performed, and top curl suitability and seam curling were evaluated. In addition, printability was also evaluated.
The evaluation method of each item is as shown below.

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

<Paper thickness>
It measured using the paper thickness meter based on JISP 8118: 2014.

<Density>
The density was measured in accordance with JIS P 8118: 1998.

<Dissolving freeness>
The obtained base paper for paper cup was impregnated in hot water at 80 ° C. for 4 hours, and the surface layer and the back layer were slowly peeled off using tweezers before the sample was dried to obtain a measurement sample. Each of the obtained layers was disintegrated according to the method of JIS P 8220: 2012, and the obtained pulp slurry was subjected to measurement of disintegration freeness by the method according to JIS P 8121: 2012. As a measuring machine, a Canadian freeness tester manufactured by Kumagai Riki Kogyo Co., Ltd. was used.

<Fiber orientation ratio>
It measured using the apparatus (SST-2500, Nomura Corporation make) which measures the fiber orientation of a sheet | seat from the angular distribution of the propagation speed of an ultrasonic wave.

<Separation method of surface layer and back layer>
The paper thickness of all layers was measured, and ground and removed using a surface grinding apparatus (manufactured by Sagawa Seisakusho) to a thickness of half excluding the side including the surface to be measured. The grindstone to be used used the thing of cylindrical grindstone 550.8x12.7 mm.

<Compression strength>
The compressive strength in the MD direction of the base paper for paper cups was measured in accordance with the short span method defined in JIS P 8156: 2012.

<Tensile strength>
According to the method defined in JIS P 8113: 2006, the tensile strength in the MD direction of the base paper for paper cup after humidity control was measured in a humidity controlled environment defined in JIS P 8111: 1998. As a measuring machine, a horizontal tensile tester (CODE SE-064, manufactured by L & W) was used.

<Top curl aptitude>
The top curled portion was visually observed when producing the obtained paper cup base paper, and was evaluated based on the following criteria.
:: The top curled portion has a large circular shape along the mold, which is a desirable shape.
Δ: The top curled part is slightly crushed and slightly deviates from the mold but the circular outer periphery becomes smaller, but at a practical level.
X: The top curled part is crushed and does not conform to the mold, and the circular outer periphery becomes so small that it can not withstand practical use.

<Seam part turn over>
The seam portion of the top curled portion was visually observed when producing the obtained paper cup base paper, and evaluation was performed based on the following criteria.
○: The seam part is not seen to curl up.
Fair: some curling up is observed at the seam portion, but this is a practical level.
X: Very many curling up at the seam portion is noticeable.

<Printability>
Gravure printing was performed on the obtained base paper for paper cups, and the printing state was visually evaluated.
:: Good with almost no printing unevenness and density reduction.
X: Unfavorably inferior in printing unevenness and density reduction.

The measurement and evaluation results for Examples 1 to 4 and Comparative Examples 1 to 5 are as shown in Table 1. In the evaluation of the characteristics, it was judged as pass when と and の.

As apparent from Table 1, in the embodiment in which the tensile strength in the MD direction is large and the tensile strength of the back layer is sufficiently larger than the compressive strength of the surface layer, the top curl along the mold without problems. The part was formed.
On the other hand, in Comparative Example 1, the specific tensile strength ratio of the back layer part to the specific compressive strength ratio of the surface layer part is less than 3.0, the content of the NKP of the pulp constituting the paper cup base paper is large, and the tensile strength is high. Therefore, although it is difficult to curl, breakage of the fiber due to tensile force is difficult to occur, and although it is provided with a top curl aptitude of practical level, seam part curling is noticeable, and the evaluation is inferior to the example. In addition, the printability was inferior because the surface layer contained a large amount of NKP. In Comparative Examples 2 and 3, since the ratio of the specific tensile strength of the back layer part to the specific compressive strength ratio of the surface layer part is small, it is weak to the tensile force and hardly rounds, and the molded top curled part is crushed.
In Comparative Example 4, by strengthening the beating, both the tensile strength and the compressive strength are high, and the specific compressive strength ratio of the specific tensile strength of the back layer part to the surface part is less than 3.0. Although the top curl aptitude is at a practical level due to high tensile strength, it is difficult to round due to high compressive strength, and seam portion curling occurs, resulting in a poor evaluation.
Comparative Example 5 did not contain NKP, and the tensile strength of the entire base paper for paper cup was too low, so that the formed top curled part was crushed.

Claims (4)

It is a base paper for paper cups having cellulose pulp as a main component and three or more paper layers,
The tensile strength in the MD direction is 14.0 kN / m or more,
When divided into two by a thickness equal to the surface layer portion including the surface and the back layer portion including the back surface in the paper thickness direction, the specific tensile strength in the MD direction of the back layer portion is measured by the T and short span method T / C is 3.0 or more, wherein C is a specific compressive strength in the MD direction of the surface layer portion.   The base paper for paper cup according to claim 1, wherein the fiber orientation ratio of the back layer portion is larger than that of the surface layer portion by 0.15 or more.   Among the paper layers constituting the paper cup base paper, the number of NKP blended parts of the outermost paper layer constituting the back surface is 10 mass parts or more larger than the number of NKP blended parts of the outermost paper layer constituting the surface The base paper for paper cups according to claim 1 or 2, characterized in that   A paper cup comprising the base paper for paper cup according to any one of claims 1 to 3.