JP2012140712A - Core base paper for cardboard sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core base paper for a cardboard sheet that can improve initial adhesion strength without coating a chemical.SOLUTION: Provided is a core base paper for a cardboard sheet that shows the maximum value of ultrasonic wave transmission intensity T of at least one of a surface 1a and a rear face 1b measured by using a dynamic penetrability tester during a measurement time of 0.1-1.0 second. The ultrasonic wave transmission intensity T is a value measured by using DPM-30-1T manufactured by EMCO as a dynamic penetrability tester.

Description

  The present invention relates to a core base paper for corrugated cardboard sheets.

  The corrugated cardboard sheet is produced by, for example, bonding (adhering) three types of paper, that is, an outer liner, a core, and an inner liner with a bonding machine (corrugator). The core is processed into a flute shape with a corrugated roll provided on the pasting machine of the core base paper, and an aqueous solution (bonding paste) containing adhesive components such as starch paste and PVA is formed on the top of the flute (step top). Manufactured by applying. After this application, the core and the exterior / interior liner are laminated and heated to about 80 ° C. with a hot plate having a surface temperature of 120 to 160 ° C. to complete the adhesion. The bonded corrugated cardboard sheet is subjected to, for example, a process of putting a crease ruled line or a process of cutting it into a predetermined size. However, if the adhesive strength (initial adhesive strength) between the core and the exterior / interior liner is insufficient, there is a possibility that the core and the exterior / interior liner will peel off when performing ruled line processing or cutting. There is a need to take measures such as reducing the bonding speed. Therefore, the initial adhesive strength between the core and the exterior / interior liner greatly affects the productivity of the cardboard sheet.

  Therefore, various proposals have been made at present for improving the initial adhesive strength. For example, Patent Document 1 proposes applying caustic soda or a mixture of caustic potash and borax to the surface of the core and the liner. Patent Document 2 proposes adjusting the surface of the core and the liner to pH 6 to 10 with borax or the like. Patent Document 3 proposes applying sodium octaborate or sodium octaborate dissolved water, or borax dissolved water adjusted to pH 6.0 to 8.5 with sulfuric acid or caustic soda to the surface of the core or liner. Moreover, patent document 4 proposes apply | coating the bonding speed improvement agent which dissolved the borax in the polyhydric alcohol aqueous solution to the surface of a center core or a liner. However, since these methods apply chemicals to the surface of the core and the liner, there is a problem that the manufacturing process of the core and the liner becomes complicated. In addition, since the chemical is applied to a portion (a portion other than the top of the step) that is not related to the adhesion between the core and the liner, there is a problem that the cost is inferior.

Therefore, the present applicant has proposed a technical idea in Patent Document 5 that improves the initial adhesive strength without applying chemicals. In this proposal, the basis weight of the liner composed of the surface layer, the middle layer and the back layer is set to 100 to 300 g / m ² , and “Cobb water absorption (10 seconds) / basis weight” is set to 0.7 to 2.5. In other words, the inner layer sizing agent is not substantially contained in the back layer of the liner involved in adhesion. Although this proposal is related to a liner, it seems to be applicable to a core base paper because it is intended to improve the initial adhesive strength by soaking the adhesive paste. However, even if the technical idea of Patent Document 5 is applied to the core base paper, the initial adhesive strength cannot be improved.

JP-A-7-195648 Japanese Patent Application Laid-Open No. 7-100977 JP 7-290622 A JP 7-238263 A JP 2005-133258 A

  The main problem to be solved by the present invention is to provide a core base paper for corrugated cardboard sheets which can improve the initial adhesive strength without applying chemicals.

In Patent Document 5 described above, initial adhesive strength is improved by soaking (penetrating) the adhesive paste into the liner (anchor effect), and the water absorption of the liner is a large factor. However, the present inventors have found that this factor cannot be applied to the core (core core paper) as it is.
That is, the liner is not directly applied with the bonding paste, but is adhered to the liner by being laminated on the core to which the bonding paste is applied. On the other hand, bonding is performed after the paste is directly applied to the core and then the liner is laminated. Therefore, the time required for bonding is different between the liner and the core. And if initial adhesive strength improves so that a paste paste permeates into a liner or a core, it will not be a problem, but it is not so. Currently, pastes that are widely used include, for example, pregelatinized starch (heated after dispersing raw starch in water and gelatinized after swelling) and β starch (raw starch). The non-gelatinized starch that has been dispersed and swelled in water) is made of an aqueous solution in which, for example, a mass ratio of 13 to 18:87 to 82 is dispersed in 300% of water. The mechanism by which the bonding between the liner and the core is achieved by the pasting paste is first achieved by the pregelatinized starch, and then the adhesion is promoted by the β-starch that has been gelled by heat (pregelatinized). Finally, adhesion is further promoted by drying with heat. When the liner and the core are to be bonded by this bonding paste, the cause of poor adhesion (lamination failure) is considered to be insufficient moisture and excessive moisture. If the moisture is insufficient, the β starch will not gel and adhesion will not proceed. Further, even if gelation occurs, if the moisture is insufficient, the fluidity is lowered, so that it does not penetrate into the liner or the core and adhesion does not proceed. On the other hand, if the water content is excessive, heat is lost to the evaporation of water, and the amount of heat necessary for gelling β-starch is insufficient, so that β-starch does not gel (gelatinize) and adhesion does not proceed. With respect to the background and the core raw paper, the present invention as described below has solved the above problems.

[Invention of Claim 1]
The ultrasonic transmission intensity measured using at least one of the dynamic permeability tester on the front surface and the back surface shows a maximum value during a measurement time of 0.1 to 1.0 seconds.
A core base paper for corrugated cardboard sheets.
Here, the ultrasonic transmission intensity is a value measured using DPM-30-1T manufactured by emco as the dynamic permeability tester.

(Main effects)
When the ultrasonic transmission intensity shows the maximum value during the measurement time of 0.1 to 1.0 seconds, the above-described problems of insufficient moisture and excessive moisture in adhesion are prevented. Therefore, the core base paper for corrugated cardboard sheets can be improved in initial adhesive strength without applying chemicals.
In addition, the inventors of the present invention determined that the Steecht sizing degree measured in accordance with JIS P 8122: 2004 “Paper and paperboard—Sizing test method—Steecht method” and JIS P 8140: 1998 “Paper and board—Water absorption test”. It has been confirmed that there is a possibility that the initial adhesive strength may be different even with a core base paper having the same Cobb water absorption measured in accordance with “Method-Cobb method”.

[Invention of Claim 2]
Containing 0.01 to 0.2% by weight of a sizing agent,
The core base paper for corrugated cardboard sheets according to claim 1.

(Main effects)
By containing the sizing agent within the above range, the core base paper can be obtained with the effects described in claim 1 reliably.

[Invention of Claim 3]
The density measured according to JIS P 8118: 1998 is 0.60 to 0.80 g / cm ³ , and the air permeability measured according to JIS P 8117: 2009 is 30 to 100 seconds.
The core base paper for corrugated board sheets of Claim 1 or Claim 2.

(Main effects)
When the density exceeds 0.80 g / cm ³ , the water absorption rate is slow, and there is a possibility that the above-mentioned problem of excessive moisture in the bonding may occur. Moreover, there is a possibility that the problem that heat transferability is poor and the gelatinization of β-starch is difficult to proceed, and the problem that heat builds up and cooling at the cooling part cannot be performed smoothly. On the other hand, if the density is less than 0.60 g / cm ³ , the water absorption rate is high, and there is a possibility that the above-mentioned problem of insufficient moisture in the bonding may occur.
If the air permeability exceeds 100 seconds, the water absorption rate is slow, and the same problem as in the case where the density exceeds 0.80 g / cm ³ may occur. On the other hand, if the air permeability is less than 30 seconds, the water absorption rate is high, and the same problem as in the case where the density is less than 0.60 g / cm ³ may occur.

  According to the present invention, it becomes a core base paper for corrugated cardboard sheets that can improve the initial adhesive strength without applying chemicals.

It is sectional drawing of the core raw paper of this form. It is a schematic diagram of a dynamic permeability tester. It is an example which shows a time-dependent change of ultrasonic transmission intensity | strength.

Next, an embodiment of the present invention will be described.
The pulp raw material of the core raw paper in this form is not particularly limited, and for example, hardwood bleached kraft pulp, softwood bleached kraft pulp, hardwood unbleached kraft pulp, softwood unbleached kraft pulp, hardwood sulfite pulp, conifer sulfite pulp, etc. are used. be able to. Further, the pulping method such as chemical pulp, mechanical pulp, and chemi-ground pulp, and the types and blending ratios of pulp raw materials such as virgin pulp and waste paper pulp are not particularly limited.

  However, the pulp raw material conforms to JIS P 8121: 1995 “Pulp freeness test method” of disaggregated pulp obtained by disaggregating the obtained core base paper according to JIS P 8220: 1998 “pulp-disaggregation method”. It is suitable that the freeness measured in this way is adjusted to be 200 to 450 ml CSF, preferably 250 to 400 ml CSF. If the freeness is less than 200 ml CSF, the compressive strength is weak, and there is a risk of stepping. Further, if the freeness is less than 200 ml CSF, the air permeability becomes high, and there is a possibility that the above-mentioned problem of excessive moisture in the adhesion may occur. On the other hand, if the freeness exceeds 450 ml CSF, there is little entanglement between the fibers, so that the compressive strength is weak, and there is a possibility that step crushing may occur. On the other hand, if the freeness exceeds 450 ml CSF, the air permeability is lowered, and there is a possibility that the above-mentioned problem of water shortage in the adhesion may occur.

  In making the above pulp raw material, known additives can be internally added. Known additives include, for example, polyacrylamide, polyvinyl alcohol polymer, urea / formalin resin, melamine / formalin resin, paper strength enhancer such as starch, fixing agent such as sulfate band, polyacrylamide, acrylamide / amino. Methylacrylamide copolymer salt, cationized starch, polyethyleneimine, polyethylene oxide, acrylamide / sodium acrylate copolymer and other yield improvers, polyamide, polyamine, epichlorohydrin and other water-resistant agents, antifoaming agents, talc, etc. Illustrative examples include fillers, dyes, slime control agents, antibacterial agents, anti-ultraviolet agents, anti-slip agents, lubricants, oil-resistant agents, oil-repellent agents, and light / weather resistance-imparting agents. In addition to the above, a sizing agent can also be added as an additive, which will be described later.

  The above pulp raw material is made into paper using a known paper machine or the like to obtain a core base paper having a single-layer or multi-layer structure. As the core raw paper having a multilayer structure, a core raw paper having a two-layer structure consisting of only a surface layer and a back layer, and a core having a three-layer structure consisting of a surface layer 2, a middle layer 3 and a back layer 4 as shown in FIG. Examples of the base paper 1 include a core base paper having a multilayer structure of four or more layers, which is not shown, but a surface layer is provided between the surface layer 2 and the middle layer 3.

In addition, the core base paper has at least one of the front and back surfaces, and in the core base paper 1 shown in FIG. 1, at least one of the front surface 1a and the back surface 1b, preferably the front and back surfaces (both sides). It is preferable that the ultrasonic transmission intensity measured using a tester shows a maximum value during a measurement time of 0.1 to 1.0 seconds, preferably 0.2 to 0.5 seconds.
Here, the ultrasonic transmission intensity is a value measured using a DPM-30-1T manufactured by emco as a dynamic permeability tester. As shown in FIG. 2, this measurement is performed by attaching the core raw paper (test piece) 1 to the sample holder 23 with the double-sided tape 24 and immersing (immersing) it in the water W in the water tank 20. The ultrasonic wave is transmitted from 21 and the change over time of the ultrasonic intensity (ultrasonic transmission intensity) reaching the ultrasonic receiver 22 is measured. In addition, as the water W in the water tank 20, 23 degreeC distilled water is used. The ultrasonic frequency is 1 MHz. As shown in FIG. 3, the ultrasonic transmission intensity T is determined by the fact that air on the core base paper surface (1a, 1b) diffuses and the core base paper surface (1a, 1b) comes into contact with water W. As the water W penetrates into the capillaries of the base paper 1, it rises in the initial stage. However, after that, the core base paper 1 is lowered by absorbing water and decreasing the elastic modulus. The maximum value Tm of the ultrasonic transmission intensity T is recorded when this rise changes to a fall. If the measurement time tm when recording the maximum value Tm is less than 0.1 seconds, the water absorption speed is high, and there is a possibility that the above-mentioned problem of insufficient moisture in the bonding may occur. On the other hand, when the measurement time tm exceeds 1.0 seconds, the water absorption rate is slow, and there is a possibility that the above-described problem of excessive moisture in the bonding may occur. This measurement time tm can be adjusted, for example, by adding a sizing agent, adjusting the density or air permeability, and the like.

  The relationship between the measurement time tm of the core base paper surface (1a) and the measurement time tm of the core base paper back surface (1b) is not particularly limited, but the difference between the measurement times is within 0.2 seconds (preferably Is preferably 0 to 0.1 seconds). The normal laminating machine can use either the front or back side of the core base paper for the single side or the backer side, and it is optional whether the pasting paste is applied to the front or back side first. . However, if the difference in the measurement time is within 0.2 seconds, the above problem is surely solved no matter how the core raw paper is used.

  The core base paper of this embodiment preferably contains a sizing agent. Particularly in the case of a core base paper 1 having a multilayer structure as shown in the illustrated example, it is preferable that at least the surface layer 2 and the back layer 4 contain a sizing agent. . Since the surface layer 2 and the back layer 4 contain a sizing agent, the initial water absorption speed can be adjusted easily and inexpensively, so that the core base paper is inexpensive and can reliably solve the above problems. Become. Moreover, as this sizing agent, well-known sizing agents, such as rosin size, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), can be used, for example. However, it is preferable to use at least one of a rosin emulsion sizing agent and an alkyl ketene dimer sizing agent. Further, the content of these sizing agents is 0.01 to 0.2% by mass (preferably 0.015 to 0.15% by mass) based on the solid content with respect to the pulp raw material (solid content standard). It is more preferable to use for. Since the sizing agent is at least one of the rosin emulsion sizing agent and the alkyl ketene dimer sizing agent, the initial water absorption rate can be finely adjusted, so that the core base paper can reliably achieve the above-described problem. In this respect, for example, alkenyl succinic anhydride (ASA) and the like have no problem in size, but the yield is relatively large depending on other operating conditions such as the concentration of pulp raw material and the addition rate of filler. For fine adjustment of the water absorption rate, it is preferable to use a rosin emulsion sizing agent or an alkyl ketene dimer sizing agent. In particular, when an alkyl ketene dimer sizing agent is used, the sliding angle (dynamic / static friction coefficient) of the core base paper is lowered, so that the frictional force with the corrugated roll is lowered and step cracking is prevented. In addition, the said effect is reliably show | played because content of a sizing agent is 0.01-0.2 mass%. In the case of the core base paper 1 having a multilayer structure as shown in the illustrated example, the content of the sizing agent in each layer (surface layer 2, middle layer 3 and back layer 4) can be adjusted as appropriate. It is preferable to adjust the difference in measurement time at which the ultrasonic transmission intensity reaches the maximum value by adjusting the layer 4 separately.

  When these sizing agents are contained (added), when a sulfuric acid band is added in an amount of 0.3 to 2.0% by mass (preferably 0.5 to 1.0% by mass) based on the pulp raw material, it is initial. This is preferable because fine adjustment of the water absorption speed can be easily performed. If the addition amount of the sulfuric acid band is less than 0.3% by mass, the fixing effect of the sizing agent is low. On the other hand, if it exceeds 2% by mass, the initial water absorption rate is affected and fine adjustment may be difficult. . For example, some water-resistant cores (paper) used for water-resistant corrugated cardboard used in fisheries boxes, fruit and vegetable boxes, etc. use a sizing agent, but the sizing agent provides water resistance. It is not used for adjusting the time until the ultrasonic transmission intensity reaches the maximum value. Therefore, the technical significance of using the sizing agent differs between the two.

The density measured in accordance with JIS P 8118: 1998 “Test method of thickness and density” of the core raw paper of the present embodiment is preferably 0.60 to 0.80 g / cm ³ , more preferably 0.65 to 0.75 g / cm ³ . When the density exceeds 0.80 g / cm ³ , the water absorption rate is slow, and there is a possibility that the above-mentioned problem of excessive moisture in the bonding may occur. Moreover, there is a possibility that the problem that heat transferability is poor and the gelatinization of β-starch is difficult to proceed, and the problem that heat builds up and cooling at the cooling part cannot be performed smoothly. On the other hand, if the density is less than 0.60 g / cm ³ , the water absorption rate is high, and there is a possibility that the above-mentioned problem of insufficient moisture in the bonding may occur.

The air permeability measured in accordance with JIS P 8117: 2009 “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method” of the core raw paper of this embodiment is preferably 30 to 100 seconds, more preferably 50 to 85 seconds. If the air permeability exceeds 100 seconds, the water absorption rate is slow, and the same problem as in the case where the density exceeds 0.80 g / cm ³ may occur. On the other hand, if the air permeability is less than 30 seconds, the water absorption rate is high, and the same problem as in the case where the density is less than 0.60 g / cm ³ may occur.

The sizing agent was adjusted to 0.01 so that the ultrasonic transmission intensity measured using at least one of the dynamic permeability tester on the front surface and the back surface showed a maximum value during the measurement time of 0.1 to 1.0 seconds. The density measured according to JIS P 8118: 1998 “Test method of thickness and density” is 0.60 to 0.80 g / cm ³ , and JIS P 8117 is contained. : 2009 "Paper and paperboard-Test method for air permeability and resistance (intermediate region)-Gurley method" Applying chemicals by adjusting the air permeability to 30 to 100 seconds Even if not, the initial adhesive strength can be improved, and the core base paper for corrugated cardboard sheets can be improved, and the speed at which the core and the liner are bonded can be improved.

The basis weight measured in accordance with JIS P 8124: 1998 “Paper and board—Method for measuring basis weight” of the core raw paper of this embodiment is preferably 80 to 200 g / m ² , more preferably 110 to 190 g / m ^2. It is. If the basis weight is less than 80 g / m ² , step cracks may occur. On the other hand, when the basis weight exceeds 200 g / m ² , there is a risk that the step-feeding ability is lowered.

The specific compressive strength in the transverse direction (CD) measured in accordance with JIS P 8126: 2005 “Paper and paperboard—Compressive strength test method—Ring crush method” of the core raw paper of this embodiment is preferably 180 N · m. ² / g or more, more preferably 190 to 220 N · m ² / g. If the specific compressive strength is less than 180 N · m ² / g, step cracks may occur. This specific compressive strength can be adjusted, for example, by adjusting the fiber orientation and selecting the pulp raw material.

(Other)
The present invention relates to a core base paper, but a cardboard sheet can be manufactured in combination with the liner disclosed in Patent Document 5 described above, and the productivity of the cardboard sheet is greatly improved by this combination.

  A method for producing a core and a corrugated cardboard sheet from the core core paper of this embodiment is not particularly limited. For example, first, a core base paper is formed into a corrugated shape by a single facer (rolling process) to form a core, and a paste is applied to one top of the core, and then bonded to an interior liner, and single-sided cardboard Get a sheet. This single-sided corrugated cardboard sheet is sent to a double facer after applying a paste to the other top of the middle core by a glue machine. This double facer consists of a heating part and a cooling part. In the heating part, an exterior liner is pasted on the other step top side of the core and heated by a hot plate or the like to form a corrugated cardboard sheet. . Moreover, in the cooling part, the corrugated board sheet in the heated state is radiated. Thereafter, the corrugated cardboard sheet is subjected to a process of putting a crease ruled line, or a process of cutting it into a predetermined size, and the corrugated cardboard sheets after being cut can be stacked to be ready for shipment.

  The pasting paste used when bonding the core and the liner is not particularly limited, and for example, inexpensive starch can be used as a raw material. The pasting paste using starch includes, for example, water, gelatinized starch called carrier (pregelatinized starch), ungelatinized main starch (beta starch), alkali compound, boron compound, and the like. Examples of β starch (main starch) include various raw starches such as corn starch, wheat starch, potato starch, tapioca starch, and cationized starch in which starch is chemically modified with a cationic group such as phosphate esterified starch and aminated starch. , Oxidized starch hydrolyzed with acid to control molecular weight, chemically modified starch such as enzyme-modified starch hydrolyzed with α-amylase to control molecular weight, high amylose starch collected from genetically manipulated corn, etc. Can be used. On the other hand, as the pregelatinized starch (carrier starch), for example, modified starch such as acid hydrolyzed starch, cationized starch, enzyme-modified starch, high amylose starch and the like can be used. In addition, for water-resistant corrugated cardboard that requires water resistance, synthetic resin emulsions such as acrylic and SBR, and pastes mixed with starch and synthetic resin emulsions are used, but the present invention is particularly bonded with starch. It is preferably used when glue is used.

  Next, examples of the present invention will be shown to describe the present invention more specifically, but the present invention is not limited to these. In the following, unless otherwise specified,% means mass%, and the chemical addition amount means the solid content addition amount (mass%) per pulp dry mass.

  A sulfuric acid band and a sizing agent were added to the pulp raw material, and paper making was performed to produce a core base paper having a two-layer structure consisting of a surface layer and a back layer. Furthermore, a corrugated cardboard sheet was produced using this core raw paper, and various evaluations were performed. Details are as shown in Tables 1 and 2 and below.

(Pulp raw material (surface layer))
A blend of 80% corrugated waste paper pulp and 20% kraft waste paper pulp was used. This pulp raw material was adjusted to the freeness shown in Table 1 by beating and classification. The freeness is a value measured according to JIS P 8121: 1995 “Method for testing the freeness of pulp”.

(Pulp raw material (back layer))
Corrugated used paper pulp was used 100%. This pulp raw material was adjusted to the freeness shown in Table 1 by beating and classification. The freeness is a value measured according to JIS P 8121: 1995 “Method for testing the freeness of pulp”.

(Sulfuric acid band)
A liquid sulfuric acid band (solid content 28%) manufactured by Asahi Chemical Industry Co., Ltd. was used. In addition, the addition amount of Table 1 is a solid addition amount.

(Rosin sizing agent)
R1600 (solid content 50%) manufactured by Toho Chemical Co., Ltd. was used.

(AKD sizing agent)
AD-1624 (solid content 30%) manufactured by Seiko PMC was used.

(Basis weight)
Measured according to JIS P 8124: 1998 “Paper and paperboard—basis weight measurement method”.

(Paper thickness / density)
Measured according to JIS P 8118: 1998 “Paper and paperboard—Test methods for thickness and density”.

(Air permeability)
Measured according to JIS P 8117: 2009 “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method”.

(Measurement time)
This is the measurement time when the ultrasonic transmission intensity reaches the maximum value. This measurement method is the same as described above. The “front surface” in Table 2 means the measurement time when the sample is set on the sample holder so that the surface of the core raw paper is positioned on the ultrasonic wave transmitting part side of the dynamic permeability tester. Indicates the measurement time when the sample is set in the sample holder so that the back surface of the core raw paper is located on the ultrasonic wave transmitting part side of the dynamic permeability tester. In Table 2, “impossible to measure” refers to a case where the water absorption is too good and the ultrasonic transmission intensity decreases immediately (from the beginning), and the time to reach the maximum value is less than the measurement limit.

(Bonding speed)
It is the speed when the core and the liner are bonded together by a bonding machine. In addition, the following were used as a liner, a bonding machine, and bonding paste.
Liner: JEK 210 g / m ² manufactured by Iwaki Daio Paper Co., Ltd. was used.
Bonding machine: Agnati GO-14 QRC (design bonding speed 250 m / min) manufactured by Daio Engineering Co., Ltd. was used.
Paste paste: Lowcons made by Nippon Starch Co., Ltd. was used. Coating amount (front side 3.2 g / m ² , back side 5.0 g / m ² ), concentration (front side 3.2%, back side 3.0%).

(Peeling evaluation)
The corrugator width direction both ends of the completed corrugated cardboard sheet after bonding were folded by hand, and three-step sensory evaluation was performed according to the following criteria.
○: When completely adhered to both ends in the width direction and no peeling was observed.
Δ: When peeling sound with “crisp” occurs when bent, and slight peeling is observed.
X: When clear peeling was seen before bending.

(Adhesive strength)
Measured according to JIS Z 0402: 1995 “Testing method for adhesive strength of corrugated cardboard”.

  The present invention is applicable as a core base paper for corrugated cardboard sheets.

  DESCRIPTION OF SYMBOLS 1 ... Core raw paper, 1a ... Front surface, 1b ... Back surface, 2 ... Surface layer, 3 ... Middle layer, 4 ... Back layer, 20 ... Water tank, 21 ... Ultrasonic transmission part, 22 ... Ultrasonic reception part, 23 ... Sample holder, 24 double-sided tape, W ... water.

Claims (3)

The ultrasonic transmission intensity measured using at least one of the dynamic permeability tester on the front surface and the back surface shows a maximum value during a measurement time of 0.1 to 1.0 seconds.
A core base paper for corrugated cardboard sheets.
Here, the ultrasonic transmission intensity is a value measured using DPM-30-1T manufactured by emco as the dynamic permeability tester. Containing 0.01 to 0.2% by weight of a sizing agent,
The core base paper for corrugated cardboard sheets according to claim 1. The density measured according to JIS P 8118: 1998 is 0.60 to 0.80 g / cm ³ , and the air permeability measured according to JIS P 8117: 2009 is 30 to 100 seconds.
The core base paper for corrugated board sheets of Claim 1 or Claim 2.

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