JP2013227699A - Core for corrugated board and method for producing core for corrugated board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core for corrugated board that has sufficient compression strength and is excellent in laminating with a liner regardless of a low basis weight and a weight reduction.SOLUTION: The core for corrugated board includes base paper for core obtained by making paper from raw material pulp and is obtained by coating on at least one side of the base paper with a coating liquid including a paper-strengthening agent as a main component. The paper-strengthening agent includes hyperbranched polyacrylamide as a main component, and the core for corrugated board has a basis weight of 130 g/mor less, a compression strength (lateral) of 184 N or more, and a gas permeation resistance of 55 seconds or less. It is preferable that the hyperbranched polyacrylamide has a solid concentration of 12.5 mass%, and the aqueous solution has a viscosity of 9 mPa s or more and 25 mPa s or less at a temperature of 30°C. Also, it is preferable that the coating amount of the hyperbranched polyacrylamide is 0.5 g/mor more and 2.5 g/mor less per single surface of the core for corrugated board in terms of solid content.

Description

  The present invention relates to a corrugated core and a method for producing a corrugated core.

In general, corrugated cardboard is manufactured by pasting a liner on one or both sides of a core formed into a corrugated shape, processed into a box, a partition plate or the like and used in a wide range of fields as a packaging material. Since these cardboard boxes are often stacked in the distribution process, the cardboard is required to have high compressive strength. In recent years, the weight of corrugated cardboard has been reduced from the viewpoints of resource saving, cost reduction, transportation energy reduction, and the like, and thus a corrugated cardboard having a high compressive strength that can cope with the weight reduction is desired. In particular, the compressive strength of the core used as the core material is emphasized, and in recent years, there has been an increasing demand for a reinforced core that is lighter (low basis weight) but has the same compressive strength. For example, JIS-P3904 In the case of the MC grade described in “Core paper for corrugated cardboard”, it is desired to achieve a basis weight of 120 g / m ² with a basis weight of 160 g / m ² and a lateral compressive strength of 184 N or more. Yes.

  Examples of the method for improving the compressive strength of the corrugated cardboard include a method of internally adding a paper strength agent to a pulp slurry used as a raw material for corrugated cardboard, and a method of externally adding a paper strength agent to the surface of a base paper such as a core. It is done. Of these, the method of externally adding a paper strength agent to the surface of the base paper has the advantage that the yield of paper strength agent is higher than the method of internally adding a paper strength agent and the compression strength of the cardboard can be easily adjusted. .

  As a method for externally adding the paper strength agent as described above, for example, a method of coating a water-soluble polymer such as starch on both sides of the base paper (see JP 2008-190064 A), or starch on both sides of the base paper A method of applying an aqueous solution by a film transfer method (see JP 2009-114572 A) has been proposed.

  However, in any of the above conventional methods, the coated paper strength agent is likely to form a film on the surface of the paper, and the water absorption is likely to decrease due to an increase in the air resistance of the paper. As a result, when producing a corrugated cardboard by laminating the liner and core with a corrugator, the adhesive stays on the surface of the paper, making it difficult to penetrate inside the paper, reducing the anchor effect of the adhesive, There is a possibility that a good bonding property cannot be obtained.

JP 2008-190064 A JP 2009-114572 A

  The present invention has been made based on the above circumstances, and has a sufficient compressive strength and excellent bonding properties with a liner, despite having a low basis weight and a light weight. The purpose is to provide.

The present invention made to solve the above problems
A core for corrugated board comprising a base paper for core obtained by papermaking raw material pulp, and coating a coating liquid mainly composed of a paper strength agent on at least one side of the base paper,
The paper strength agent is mainly composed of highly branched polyacrylamide,
The basis weight is 130 g / m ² or less, the compressive strength (horizontal) is 184 N or more, and the air permeability resistance is 55 seconds or less.

The core for corrugated board uses a highly branched polyacrylamide as a main component of the paper strength agent contained in the coating liquid applied to at least one side of the core paper for the core, and therefore has a basis weight of 130 g / m. Despite being reduced in weight to ² or less, the compression strength (lateral) has a high compression strength of 184 N or more. In addition, since the corrugated core has an air resistance of 55 seconds or less, the adhesive at the time of bonding easily penetrates into the corrugated core, thereby enhancing the anchor effect of the adhesive. It has excellent bonding properties. These are presumed to be because the highly branched polyacrylamide, which is the main component of the paper strength agent, has many branched structures. In other words, the highly branched polyacrylamide, which is the main component of the paper strength agent, has a lot of branched structure, so that it becomes easy to get entangled with the raw pulp fiber of the core paper for the core, and the same paper strength enhancing effect is exhibited. First, the molecular weight of the polyacrylamide can be reduced, thereby reducing the viscosity of the coating solution. As a result, the permeability of the coating liquid is improved, so that it penetrates into the core paper for the core, and it is presumed that the formation of the coating film of the paper strength agent on the surface of the core paper for the core is suppressed. As a result, the compressive strength is increased by the paper strength agent penetrating into the core base paper and adhering the pulp fibers, and the coating film formation of the coating liquid on the surface of the core base paper is suppressed. Thus, it is presumed that it becomes difficult to inhibit the penetration of the adhesive at the time of bonding into the core for corrugated cardboard, and the anchor effect of the adhesive is enhanced.

  The hyperbranched polyacrylamide may have a solid content concentration of 12.5% by mass and a viscosity of an aqueous solution at a temperature of 30 ° C. of 9 mPa · s to 25 mPa · s. Improve the permeability and coating properties of the paper strength agent to the core paper by using the highly branched polyacrylamide having such viscosity as the main component of the strength material under specific temperature conditions. Can do. As a result, the compressive strength can be improved without reducing the bonding property and productivity of the corrugated core.

The coating amount of the high branched polyacrylamide is 0.5 g / ^{m 2} or more 2.5 g / ^{m 2} or less is preferable in terms of solid per side content basis. By making the coating amount of the highly branched polyacrylamide within the above range, the bonding property and compressive strength of the corrugated core can be further improved.

Another invention made to solve the above problems is
A method for producing a core for corrugated board having a coating step of coating a coating liquid mainly composed of a paper strength agent on at least one side of a base paper for core obtained by papermaking raw material pulp,
The paper strength agent is mainly composed of highly branched polyacrylamide,
The solid content concentration of the coating liquid is 5% by mass or more and 20% by mass or less,
The coating step is performed by setting the temperature of the coating liquid at 26 ° C. or more and the viscosity at 9 mPa · s or more and 25 mPa · s or less.

  According to the manufacturing method of the core for corrugated cardboard, the temperature of the coating liquid in the coating process is set to 26 ° C. or more, and the viscosity is set to 9 mPa · s or more and 25 mPa · s or less. Can be improved. As a result, the paper strength agent can easily penetrate into the core paper for the core, and the increase in the air resistance of the core for the cardboard can be suppressed, so that the cardboard having excellent compressive strength and bonding property. An intermediate core can be obtained. Moreover, since the manufacturing method of the core for corrugated cardboard can increase the concentration of the paper strength agent by setting the temperature of the coating liquid in the coating process to 26 ° C. or higher, the drying load can be reduced, Productivity can be improved. Furthermore, according to the manufacturing method of the core for corrugated cardboard, since the paper strength agent is externally added, the yield strength of the paper strength agent is not lost, and the compression strength can be effectively improved.

  Here, the “highly branched polyacrylamide” is obtained by copolymerizing a monomer mixture mainly composed of a trifunctional or higher functional vinyl monomer and (meth) acrylamide.

  As described above, the core for corrugated board of the present invention has a sufficient compressive strength and excellent bonding properties with a liner, despite its low basis weight and light weight. Moreover, the manufacturing method of the core for corrugated boards of this invention can manufacture efficiently the core for corrugated boards which has the outstanding compressive strength and bonding property.

  Hereinafter, embodiments of the corrugated core for the present invention will be described in detail.

<Core for cardboard>
The core for corrugated board according to the present invention comprises a base paper for core obtained by papermaking raw material pulp, and is formed by coating a coating liquid on at least one side of the base paper. First, the coating liquid that is a feature of the present invention will be described, and then other components will be described.

[Coating fluid]
The coating liquid contains a paper strength agent as a main component.

(Paper strength agent)
The paper strength agent is mainly composed of highly branched polyacrylamide. The hyperbranched polyacrylamide can be obtained, for example, by copolymerizing a tri- or higher functional crosslinkable vinyl monomer and a monomer mixture containing a cationic vinyl monomer and / or an anionic vinyl monomer with (meth) acrylamide.

  Examples of the crosslinkable vinyl monomer include N-substituted acrylamides such as N, N-dimethylacrylamide and N-methylolacrylamide, bis (meth) acrylamides such as methylenebis (meth) acrylamide, ethylenebis (meth) acrylamide, and ethylene glycol di- Bifunctional vinyl monomers such as di (meth) acrylates such as (meth) acrylate and diethylene glycol di (meth) acrylate, divinyl esters such as divinyl adipate and divinyl sebacate, epoxy acrylates, urethane acrylates and divinylbenzene 1,3,5-triacryloylhexahydro-S-triazine, triallyl isocyanurate, triallyl trimellitate, triallylamine, N, N-diallylacrylamide, etc. Ability monomer, tetramethylolmethane tetraacrylate, tetrafunctional monomers such as tetraallyl pyromellitate and the like. Among these, N-methylolacrylamide, methylenebisacrylamide, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, 1,3,5-triacryloylhexahydro-S-triazine, tetramethylolmethane tetraacrylate, N, N-dimethylacrylamide Is preferred. These crosslinkable vinyl monomers may be used alone or in combination of two or more.

  The ratio of the crosslinkable vinyl monomer is preferably 0.001 mol% or more and 10 mol% or less, and more preferably 0.01 mol% or more and 8 mol% or less in the highly branched polyacrylamide. If the ratio of the crosslinkable vinyl monomer in the highly branched polyacrylamide exceeds the upper limit, gelation may occur. On the other hand, when the ratio of the crosslinkable vinyl monomer in the highly branched polyacrylamide is less than the lower limit, a sufficient effect as a paper strength agent may not be obtained.

  Examples of the cationic vinyl monomer include tertiary amino groups such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide, allylamine, and diallylamine. Quaternizing agents such as vinyl monomers and salts thereof, tertiary amino group-containing vinyl monomers and benzyl chloride, methyl chloride, dimethyl sulfate, epichlorohydrin, glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride And vinyl monomers containing a quaternary ammonium salt obtained by the above reaction. These cationic vinyl monomers may be used alone or in combination of two or more.

  The proportion of the cationic vinyl monomer is preferably 20 mol% or less, more preferably 18 mol% or less, and even more preferably 15 mol% or less in the highly branched polyacrylamide. If the proportion of the cationic vinyl monomer in the highly branched polyacrylamide exceeds the above upper limit, gelation may occur.

  Examples of the anionic vinyl monomers include α, β-unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid, α, β-unsaturated dicarboxylic acids such as itaconic acid, maleic acid and maleic anhydride, and aconitic acid. Examples include α, β-unsaturated tricarboxylic acid, (meth) allylsulfonic acid, sulfo group-containing vinyl monomers such as 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof. These anionic vinyl monomers may be used alone or in combination of two or more.

  The proportion of the anionic vinyl monomer is preferably 20 mol% or less, more preferably 18 mol% or less, and further preferably 15 mol% or less in the highly branched polyacrylamide. If the proportion of the anionic vinyl monomer in the highly branched polyacrylamide exceeds the above upper limit, gelation may occur.

  Further, the proportion of (meth) acrylamide in the highly branched polyacrylamide is preferably from 50 mol% to 99 mol%, more preferably from 60 mol% to 98 mol%. If the proportion of (meth) acrylamide in the highly branched polyacrylamide exceeds the above upper limit, a sufficient branched structure cannot be obtained, and the viscosity of the paper strength agent may increase. On the other hand, when the proportion of (meth) acrylamide in the highly branched polyacrylamide is less than the lower limit, a sufficient effect as a paper strength agent may not be obtained.

  In addition to the monomers described above, other monomers can be copolymerized with the highly branched polyacrylamide within a range that does not impair the effects of the present invention. Examples of other monomers include styrene derivatives such as styrene and α-methylstyrene, vinyl acetate, acrylonitrile, allyl alcohol, (meth) acrylic acid ester having a hydroxyl group, methyl (meth) acrylate, and (meth) acrylic acid. Examples include (meth) acrylic acid alkyl esters such as ethyl.

  The highly branched polyacrylamide has a solid content concentration of 12.5% by mass and a viscosity of an aqueous solution at a temperature of 30 ° C., preferably 9 mPa · s to 25 mPa · s, more preferably 10 mPa · s to 20 mPa · s. . When the viscosity of the highly branched polyacrylamide aqueous solution exceeds the above upper limit, the viscosity of the paper strength agent increases, and the strength of the paper strength agent easily forms a coating film on the surface of the core paper for the core. There is a possibility that the air permeability resistance may be increased or that the coating property may be deteriorated due to contamination on the coating machine. On the other hand, when the viscosity of the highly branched polyacrylamide aqueous solution is less than the lower limit, a sufficient effect as a paper strength agent cannot be obtained, and the compressive strength of the corrugated core may be lowered.

  As a weight average molecular weight of the said highly branched polyacrylamide, 200,000 or more and 6 million or less are preferable, 300,000 or more and 4 million or less are more preferable, 350,000 or more and 2 million or less are more preferable. When the weight average molecular weight of the hyperbranched polyacrylamide exceeds the above upper limit, the viscosity of the paper strength agent is increased and the coating property may be lowered, or the air resistance of the corrugated core may be increased. On the other hand, when the weight average molecular weight of the highly branched polyacrylamide is less than the lower limit, a sufficient effect as a paper strength agent cannot be obtained, and the compression strength of the corrugated core may be lowered.

  As the method for producing the highly branched polyacrylamide, a conventionally known method can be employed. For example, the monomer components and water are added to a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube. By charging, adding a polymerization initiator such as hydrogen peroxide, and optionally using a polymerization regulator or chain transfer agent such as isopropyl alcohol, and reacting at a temperature of 40 ° C. to 95 ° C. for about 1 to 5 hours. Can be manufactured.

The coating amount of the highly branched polyacrylamide is preferably 0.5 g / m ² or more and 2.5 g / m ² or less in terms of solid content per side, and preferably 1.2 g / m ² or more and 1.8 g / m ² or less. Is more preferably 1.3 g / m ² or more and 1.7 g / m ² or less. If the coating amount of the highly branched polyacrylamide exceeds the above upper limit, the core for corrugated cardboard becomes hard and the workability may be lowered, and the bonding property of the core for corrugated cardboard may be lowered. On the other hand, when the coating amount of the highly branched polyacrylamide is less than the above lower limit, the compressive strength of the corrugated core may be lowered. In particular, a highly branched polyacrylamide having a solid content concentration of 12.5% by mass and a viscosity of an aqueous solution at a temperature of 30 ° C. of 9 mPa · s to 25 mPa · s is 0.5 g / m ^{2 to} 2. It is preferable to apply 5 g / m ² or less because a core for corrugated board is obtained which is more excellent in compressive strength and particularly excellent in bonding property with a liner despite the low basis weight.

(Other additives)
The coating liquid is within the range not affecting the effects of the present invention, in addition to the highly branched polyacrylamide, for example, polyacrylamide other than the highly branched polyacrylamide, polyvinyl alcohol (PVA), starch, sizing agent , Various known additives such as pH adjusters, antifoaming agents, antifoaming agents, penetrating agents, coloring dyes, preservatives, water-proofing agents, fluorescent quenching agents, alone or in combination. It may also be applied separately.

  The solid concentration of the coating liquid is preferably 5% by mass or more and 20% by mass or less, more preferably 10% by mass or more and 15% by mass or less, and further preferably 11% by mass or more and 14% by mass or less. When the solid content concentration of the coating liquid exceeds the above upper limit, the coating property may be lowered, or the air resistance of the corrugated core may be increased. On the other hand, when the solid content concentration of the coating liquid is less than the above lower limit, the coating amount of the paper strength agent is lowered and the compression strength may be lowered.

  The viscosity of the coating solution is preferably 9 mPa · s to 25 mPa · s, and more preferably 10 mPa · s to 20 mPa · s. If the viscosity of the coating liquid exceeds the above upper limit, the coating property may be lowered, or the air resistance of the corrugated core may be increased. On the other hand, when the viscosity of the coating liquid is less than the above lower limit, sufficient compression strength may not be obtained.

[Core paper for core]
The core paper for the core is usually obtained by making a pulp slurry containing raw pulp and the like. The core base paper may have a single layer structure or a multilayer structure.

(Raw pulp)
As said raw material pulp, a well-known thing can be used and used paper pulp, virgin pulp, or these combined things can be used suitably. In addition, it is preferable from the viewpoint of resource saving to use more waste paper pulp than virgin pulp.

  Waste paper pulp, for example, tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, upper white waste paper, Kent waste paper, imitation waste paper, ground ticket waste paper, etc. Examples include disaggregation / deinked waste paper pulp (DIP) and disaggregation / deinking / bleached waste paper pulp. Among these waste paper pulps, waste paper pulp produced from corrugated waste paper is preferable.

  Examples of virgin pulp include hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), conifer unbleached kraft pulp (NUKP), hardwood semi-bleached kraft pulp (LSBKP), conifer Chemical pulp such as semi-bleached kraft pulp (NSBKP), hardwood sulfite pulp, coniferous sulfite pulp, etc .; Mechanical pulp (MP) such as mechanical pulp (TMP); pulp chemically or mechanically produced from non-wood fibers such as kenaf, hemp, and straw.

  As content rate of the used paper pulp in raw material pulp, 50 mass% or more is preferable, 60 mass% or more is more preferable, and 70 mass% or more is further more preferable. By setting the content ratio of the used paper pulp in the raw material pulp to the above range, environmental properties such as effective use of resources can be improved.

(Inner paper strength agent)
In addition to the raw material pulp, an internal paper strength agent may be further added to the pulp slurry. Examples of the internal paper strength agent include a dry paper strength agent and a wet strength paper strength. Examples of the dry paper strength agent include cationic starch, polyacrylamide (PAM), carboxymethylcellulose (CMC), and the like. Examples of the agent include polyamide / epichlorohydrin resin, urea resin, acid colloid / melamine resin, thermal crosslinkability imparting PAM and the like. Of these, polyacrylamide having excellent yield is preferable.

  The charge of the internal paper strength agent is not particularly limited, and any of cationic, anionic or amphoteric may be used. Among these, an amphoteric internal paper strength agent is preferable in that the generation of minute foreign matters is small, the effect of improving the compressive strength is excellent, and the absorbability of the adhesive for bonding is excellent, and amphoteric polyacrylamide is particularly preferable.

  The amount of the internal paper strength agent added is preferably 2 kg or more and 10 kg or less, more preferably 3 kg or more and 8 kg or less in terms of solid content per ton of pulp (absolutely dry amount) contained in the pulp slurry. If the added amount of the internal paper strength agent exceeds the above upper limit, the paper strength agent may be deposited in the papermaking system and fine foreign matter may be generated. On the other hand, when the addition amount of the internal paper strength agent is less than the lower limit, a sufficient paper strength improvement effect may not be obtained.

In the present invention, the highly branched polyacrylamide is used as an external paper strength agent to be applied, and this highly branched polyacrylamide is applied to 0.5 g / m ² or more and 2.5 g / m ² or less per side. In addition, it is preferable to add amphoteric polyacrylamide to the pulp slurry as an internal paper strength agent because a core for corrugated cardboard having excellent compressive strength and excellent adhesive absorbability can be obtained. In general, internal paper strength agents have poor yield and circulate in the system, causing foaming.If foaming occurs, problems with drainage and operability are likely to occur. By using acrylamide, foaming can be suppressed as compared with an anionic or cationic internal paper strength agent, so that the compressive strength can be improved without reducing the production efficiency. In this way, in addition to improving the compressive strength of the core base paper itself using the internal paper strength agent, the highly branched polyacrylamide is coated with the highly branched polyacrylamide so that the highly branched polyacrylamide becomes the base paper. Since it can penetrate | invade inside and can improve the adhesive force of a pulp fiber further, compressive strength can be improved more.

(Other additives)
In addition to the internal paper strength agent, for example, a lubricant, a sizing agent, a filler dispersant, a pH adjuster, a thickener, a fluidity improver, an antifoaming agent, an antifoaming agent, Various known additives such as mold release agents, penetrating agents, coloring dyes, coloring pigments, ultraviolet absorbers, antioxidants, preservatives, antibacterial agents, water-proofing agents, and fluorescent quenching agents may be used alone or in combination. More than one seed may be mixed and added.

<Quality etc.>
The basis weight measured according to JIS-P8124 (1998) “Paper and paperboard—basis weight measurement method” of the core for corrugated cardboard is 130 g / m ² or less, and 115 g / m ² or more and 125 g / m ² or less. 116.4 g / m ² or more and 123.6 g / m ² or less is more preferable. If the basis weight of the core for corrugated board exceeds the above upper limit, it is contrary to the recent demand for light weight and resource saving. On the other hand, if the basis weight of the core for corrugated cardboard is less than the above lower limit, sufficient compressive strength may not be obtained.

The compressive strength (lateral) measured in accordance with JIS-P8126 (2005) “Paper and paperboard—Compressive strength test method—Ring crush method” of the corrugated core is 184 N or more, and 184 N or more and 220 N or less. Is preferable, and 195N or more and 210N or less is more preferable. If the compressive strength (horizontal) of the corrugated core exceeds the above upper limit, workability may be reduced. On the other hand, if the compressive strength (horizontal) of the corrugated core is less than the above lower limit, there is a risk of step cracking, for example, MC grade described in JIS-P3904 “Corrugated cardboard base paper” at a basis weight of 120 g / m ^2. There is a possibility that the compressive strength of 160 g / m ² cannot be satisfied. The compressive strength (horizontal) is adjusted by adjusting, for example, the type and amount of the paper strength agent to be applied, the type and amount of the internal strength agent, the orientation of the fibers, and the type of raw pulp. However, by using the highly branched polyacrylamide as the paper strength agent to be applied, the compression strength (lateral) can be more easily achieved.

  The air resistance measured in accordance with JIS-P8117 (2009) “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method” of the corrugated core is 55 seconds or less. Yes, it is preferably 35 seconds or longer and 55 seconds or shorter, and more preferably 40 seconds or longer and 50 seconds or shorter. If the air permeability resistance exceeds the above upper limit, the adhesive for bonding hardly penetrates into the corrugated core and the anchor effect may be lowered. On the other hand, when the air permeability resistance is less than the above lower limit, the bonding property between the corrugated core and the liner is reduced by excessively penetrating the bonding adhesive into the corrugated core. There is a fear. The air resistance can be adjusted, for example, by adjusting the type and amount of the paper strength agent to be applied, the type and amount of the internal strength agent, the type and freeness of the raw pulp, etc. It is preferable that the highly branched polyacrylamide is used as the paper strength agent to be used because it has excellent compressive strength and can easily achieve the air resistance.

  The time until the signal intensity reaches the maximum value in the corrugated cardboard core dynamic liquid permeability measurement apparatus is preferably 0.5 seconds or less, and more preferably 0.2 seconds or less. The inventors of the present invention indicate that the time until the signal strength reaches the maximum value in the dynamic permeability test of the core for corrugated board is an index of water absorption of the paste for corrugated core in the corrugator. It has been found that it becomes an index of water absorption of the paste paste on the facer side. When the time until the signal intensity in the dynamic liquid permeability measuring device reaches the maximum value exceeds the above upper limit, the adhesive used to bond the corrugated core and the liner is inside the corrugated core. It may become difficult to penetrate and the anchor effect of the adhesive may be reduced. In addition, time until the said signal strength shows the maximum value is the value measured using "SURFACE AND SIZING TESTER (EST-12)" by Emtec as a dynamic liquid permeability measuring apparatus.

  In the corrugated cardboard core dynamic liquid permeability measuring apparatus, the signal intensity after one second from the start of penetration is preferably 50% or less, more preferably 40% or less with respect to the maximum value of the signal intensity. More preferred. The inventors of the present invention determined that the ratio (%) to the maximum value of the signal intensity 1 second after the start of penetration in the dynamic permeability test of the core for corrugated board is the water absorption property of the paste for corrugated core in the corrugator. It has been found that it becomes an index, in particular, an index of water absorption of the adhesive paste on the double facer side. If the signal intensity after 1 second from the start of penetration in the dynamic liquid permeability measurement apparatus exceeds the above upper limit, the bonding property between the corrugated core and the liner may be lowered. In addition, time until the said signal strength shows the maximum value is the value measured using "SURFACE AND SIZING TESTER (EST-12)" by Emtec as a dynamic liquid permeability measuring apparatus.

Time until signal intensity reaches the maximum value in the dynamic liquid permeability measuring device for the corrugated core and the signal strength signal one second after the start of penetration in the dynamic liquid permeability measuring device for the corrugated core. The ratio (%) to the maximum strength value is adjusted by adjusting the type and amount of the paper strength agent to be applied, the internal strength of the paper strength agent, the type and amount of the sizing agent, the type and the freeness of the raw pulp, etc. However, it is preferable to use the highly branched polyacrylamide as a paper strength agent to be applied because it has excellent compressive strength and can be easily adjusted to the above numerical range. Note that the sizing agent added internally or externally may not be added. A highly branched polyacrylamide having a solid content concentration of 12.5% by mass and a viscosity of an aqueous solution at a temperature of 30 ° C. of 9 mPa · s or more and 25 mPa · s or less is 0.5 g / m ² or more and 2.5 g / m in solid content per side. m ² or less, the time required for the signal strength to reach the maximum value in the dynamic liquid permeability measuring apparatus for the corrugated core is 0.5 seconds or less, and the dynamic liquid permeation of the corrugated core is 0.5 seconds or less. By setting the signal intensity one second after the start of penetration in the property measuring device to 50% or less with respect to the maximum value of the signal intensity, the liner strength is further improved even though the basis weight is particularly low. A core for corrugated cardboard that is particularly excellent in the pasting property is obtained and is preferable.

  As the freeness measured in accordance with JIS-P8121 (1995) "Method for testing the freeness of pulp" of the disaggregated pulp obtained by disaggregating the core for corrugated board according to JIS-P8220 (1998) "pulp-disaggregation method" Is preferably 250 ml CSF or more and 500 ml CSF or less, more preferably 300 ml CSF or more and 400 ml CSF or less. When the freeness exceeds the above upper limit, the fibers are less entangled and the compressive strength is reduced, so that there is a possibility that step crushing is likely to occur. On the other hand, if the freeness is less than the lower limit, the air permeability resistance is increased, and the adhesive at the time of bonding is less likely to penetrate into the core for corrugated cardboard, thereby reducing the anchor effect of the adhesive, There exists a possibility that pasting property may fall. In addition, the said freeness can be adjusted by changing the kind and compounding quantity of a raw material pulp, the grade of the beating of a pulp, etc., for example. In addition to using the above highly branched polyacrylamide as a paper strength agent to be applied, the freeness of the disaggregated pulp obtained by disaggregating the core for corrugated cardboard is 250 ml CSF or more and 500 ml CSF, so that the compression strength is further improved. It becomes the core for corrugated cardboard which is excellent in pasting property, and is preferred.

The density measured in accordance with JIS-P8118 (1998) “Testing method for thickness and density” of the core for corrugated cardboard is preferably 0.55 g / cm ³ or more and 0.75 g / cm ³ or less. , 0.60 g / cm ³ or more 0.70 g / cm ³ or less is more preferable. If the density exceeds the above upper limit, the adhesive effect at the time of bonding may not easily penetrate into the inside of the corrugated core, which may reduce the anchor effect. On the other hand, when the density is less than the above lower limit, the adhesive may soak into the corrugated core and the bonding property may be lowered, and the compression strength may be lowered.

<Method for producing core for corrugated cardboard>
The method for producing a corrugated core has a coating step in which a paper strength agent is applied to at least one side of a core base paper obtained by papermaking raw pulp. The core for corrugated board can be manufactured by a system generally used for papermaking. Specifically, for example, a papermaking system including a wire part, a press part, a pre-dryer part, a coater part, a calendar part, a reel part, etc. Can be used. In addition to this, a paper making system comprising an off-machine coater in which the paper machine and the coater part are separated may be used, and a paper making system comprising an off-machine calendar in which the paper machine and the soft calendar are separated may be used.

  As a coating machine for applying a paper strength agent, for example, a gate roll coater, roll size press, film press, shim sizer, blade coater, calendar, bar coater, knife coater, air knife coater, curtain coater, etc. are used. Can do. Moreover, you may apply to the base paper surface for cores with a spray coating machine. Among these, a gate roll coater and a roll size press that can uniformly apply a paper strength agent to the surface of the core paper for the core are preferable.

  The coating liquid in the coating process is heated and applied when the temperature of the coating liquid is low in order to increase the permeability of the paper strength agent and increase the compressive strength while suppressing the formation of the film of the paper strength agent. It is preferable to increase the working temperature. The coating temperature of the coating liquid is 26 ° C. or higher, and preferably 28 ° C. or higher and 40 ° C. or lower. When the coating temperature of the coating liquid is lower than the above lower limit, the viscosity of the paper strength agent increases, so that the coating liquid jumps (boiling) or mist between the inner roll and the outer roll of the gate roll coater or roll size press. Occurrence of this may reduce the operability in the coating process or increase the air resistance of the core for corrugated cardboard and may reduce the bonding property. Moreover, when the said upper limit is exceeded, there exists a possibility that the component of a coating liquid may modify | denature.

  In addition, the viscosity of the coating liquid in the coating step is preferably 9 mPa · s to 25 mPa · s, and more preferably 10 mPa · s to 20 mPa · s. If the viscosity of the coating liquid exceeds the above upper limit, the operability of the coating machine in the coating process may be lowered, or the air resistance of the core for corrugated cardboard may be increased and the bonding property may be lowered. On the other hand, when the coating viscosity of the paper strength agent is less than the lower limit, there is a risk that the compressive strength is reduced or the moisture is excessive, the drying time is increased, and the productivity is lowered. The viscosity of the coating liquid can be adjusted by adjusting the type and concentration of the paper strength agent to be applied, the temperature of the coating strength, etc. Use is preferable because it is excellent in compressive strength and can be more easily adjusted to the above numerical range.

<Corrugated cardboard manufacturing method>
The method for producing corrugated cardboard using the corrugated core is not particularly limited. For example, the corrugated core is formed into a corrugated shape with a single facer (rolling process), and bonded to one top of the core. After applying the adhesive for bonding, it is bonded to the liner to make a single-sided cardboard, and then the adhesive for bonding is applied to the other top of the core of the single-sided cardboard sheet with a glue machine. Corrugated cardboard can be obtained by sending it to a sir, attaching a liner to the other top of the core at the heating part, heating it with a hot plate or the like, and then cooling it with the cooling part.

  Examples of the adhesive for pasting include starch and the like. Specifically, the adhesive is composed of water, gelatinized starch (α-modified starch), non-gelatinized starch (β-starch), alkali compound, boron compound and the like. The As non-gelatinized starch (β starch) as the main component, for example, starch is chemically treated with various raw starches such as corn starch, wheat starch, potato starch, tapioca starch, and cationic groups such as phosphated starch and aminated starch. Various chemically modified starches such as modified cationized starch, oxidized starch hydrolyzed with acid and adjusted in molecular weight, and enzyme-modified starch hydrolyzed with α-amylase and adjusted in molecular weight can be used. Examples of gelatinized starch (α-modified starch) include processed starch such as acid-hydrolyzed starch, cationized starch, and enzyme-modified starch, and high amylose starch. In addition, for a water-resistant corrugated cardboard requiring water resistance, for example, a synthetic resin such as acrylic or SBR, or an adhesive mixed with starch and a synthetic resin can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. In the following, unless otherwise specified,% means mass%, and the chemical addition amount means solid mass (kg) per pulp dry mass (t).

  In addition, each measured value in a present Example is a value measured with the following method.

[Basis weight (unit: g / m ² )]
It was measured according to “Paper and paperboard—basis weight measurement method” described in JIS-P8124 (1998).

[Air permeability resistance (unit: seconds)]
It measured using the Gurley test machine based on "Paper and paperboard-Air permeability and air resistance test method (intermediate area)-Gurley method" of JIS-P8117 (2009).

[Compressive strength (horizontal) (unit: N)]
It was measured in the transverse direction of the core for corrugated board according to “Paper and paperboard—Compression strength test method—Ring crush method” described in JIS-P8126 (2005). In addition, as a test piece, the thing of width 12.7mm and length 152.4mm was used.

[Peak appearance time (unit: seconds)]
As a dynamic liquid permeability measuring apparatus, “SURFACE AND SIZING TESTER (EST-12)” manufactured by Emtec was used, and the peak appearance time at which the signal intensity reached the maximum value was measured. Distilled water having a temperature of 23 ° C. was used as a test solution, and measurement was performed at an ultrasonic frequency of 2 MHz. In addition, it means that liquid permeability (water absorption) is so low that peak appearance time is late.

[Signal strength after 1 second (unit:%)]
As a dynamic liquid permeability measurement device, the signal strength after 1 second in the penetration characteristic curve obtained using “SURFACE AND SIZING TESTER (EST-12)” manufactured by Emtec is used, and the signal strength at the peak is 100%. As relative. The measurement conditions are the same as the measurement conditions for the peak appearance time.

[Viscosity (unit: mPa · s)]
The viscosity of the paper strength agent was measured using a digital B-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TVB-10M) at a solid content concentration of 12.5%, a rotor rotation speed of 60 rpm, and 30 ° C. The viscosity of the coating solution was measured at a coating temperature using a digital B-type viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TVB-10M) at a rotor rotational speed of 60 rpm.

[Evaluation of operability with coating machine]
The degree of coating liquid splashing (boiling) between the inner roll and outer roll of the gate roll coater and the amount of mist generated around the gate roll were visually evaluated, and the operability in the coating machine was evaluated according to the following evaluation criteria. .
(Evaluation criteria)
◎: Extremely good ○: Good △: Slightly inferior ×: Inferior

[Evaluation of bonding properties of cardboard]
JEK (basis weight: 210 g / m ² ) manufactured by Daio Paper Co., Ltd. is used as a liner on both sides of the core for corrugated cardboard under conditions of a laminating speed of 170 m / min and 250 m / min. It produced and used for evaluation. Specifically, the adhesive strength between the liner and the core of the obtained corrugated cardboard sheet was measured by JIS-Z0402 “corrugated cardboard adhesive strength test method” and evaluated according to the following criteria. In addition, the corrugator uses “Agnati GO-14 QRC (design bonding speed 250 m / min)” manufactured by Daio Engineering Co., Ltd., and the test is performed on 10 test pieces for each of the single facer and the double facer. The average value was obtained.
(Evaluation criteria)
A: Adhesive strength is 270 N or more.
○: Adhesive strength is 250N or more and less than 270N.
(Triangle | delta): Adhesive force is 230N or more and less than 250N.
X: Adhesive strength is less than 230N.

<Manufacture of core for corrugated cardboard>
[Example 1]
After mixing 60% by weight of cardboard waste paper pulp and 40% by weight of magazine waste paper pulp, the freeness measured with a double disc refiner in accordance with JIS-P8121 (1995) “Pulp Freeness Test Method” is 360 ml CSF. Beating was performed to prepare a raw pulp slurry. An internal paper strength agent (amphoteric PAM, product number: TDS232, manufactured by Seiko PMC Co., Ltd.) is added to the raw pulp slurry at a solid content of 6 kg / ton per pulp solid content, and a single-layer wet paper is formed using an on-top former. After that, the wet paper was squeezed and dried with a predryer. Next, as shown in Table 1, a paper strength agent (highly branched PAM, product number: T-ST132, manufactured by Seiko PMC Co., Ltd.) is used as the core for corrugated board so that the solid content is 1.5 g / m ² per side in terms of solid content. The both sides of the base paper were coated with a gate roll coater and dried to obtain the core for corrugated board of Example 1. The basis weight of the core for corrugated board of Example 1 was 120 g / m ² . The paper strength agent (highly branched PAM, product number: T-ST132, manufactured by Seiko PMC Co., Ltd.) has a solid content concentration of 12.5%, a rotor rotation speed of 60 rpm, a viscosity at 30 ° C. of 15 mPa · s, and a mass average. The molecular weight was 400,000.

[Examples 2 to 6, Comparative Examples 1 to 4, Reference Example]
Except that the type, properties, concentration, coating temperature, coating viscosity, and coating amount of the paper strength agent were changed as shown in Table 1, the same operations as in Example 1 were performed, and Examples 2 to 6 and Corrugated cores for Comparative Examples 1 to 4 were obtained. In Comparative Example 4, no paper strength agent was applied. Further, a corrugated core for reference example was obtained by performing the same operation as in Example 1 except that the paper strength agent was not applied and the basis weight was 160 g / m ² . However, in Examples 2 to 5 and Comparative Example 4, the basis weight of the core base paper was changed in accordance with the change in the coating amount, and the cores for corrugated board having the basis weight shown in Table 1 were obtained. In addition, the following chemical | medical agents were used as a paper strength agent of Comparative Examples 1-3.
(Comparative Example 1)
Linear PAM, product number: Haricoat G35, manufactured by Harima Kasei Co., Ltd. The shape of the molecular chain was linear, the solid content concentration was 12.5%, and the viscosity at a temperature of 30 ° C. was 90 mPa · s.
(Comparative Example 2)
Reticulated PAM, product number: Haricoat GA25, manufactured by Harima Kasei Co., Ltd. The shape of the molecular chain was reticulated, the solid content concentration was 12.5%, and the viscosity at a temperature of 30 ° C. was 100 mPa · s.
(Comparative Example 3)
Oxidized starch, product number: MS # 3800, manufactured by Nippon Shokuhin Kako Co., Ltd. The solid content concentration was 18%, and the viscosity at a temperature of 50 ° C. was 82 mPa · s.

<Quality evaluation>
About each obtained core for corrugated cardboard, basic weight, compressive strength (horizontal), air permeability resistance (Gurley method), dynamic permeability test (peak appearance time, signal intensity after 1 second) by the above methods , And adhesiveness when processed into corrugated cardboard were evaluated. The results are shown in Table 1.

  As shown in Table 1 above, it can be seen that the core for corrugated board of the present invention has excellent compressive strength and bonding properties.

  The core for corrugated cardboard of the present invention has a sufficient compressive strength and excellent bonding properties with a liner, despite having a low basis weight and being lightened. Therefore, the corrugated core can be suitably used as a corrugated core that meets the demand for weight reduction while considering environmental issues.

Claims (4)

A core for corrugated board comprising a base paper for core obtained by papermaking raw material pulp, and coating a coating liquid mainly composed of a paper strength agent on at least one side of the base paper,
The paper strength agent is mainly composed of highly branched polyacrylamide,
A core for corrugated board having a basis weight of 130 g / m ² or less, a compressive strength (horizontal) of 184 N or more, and an air resistance of 55 seconds or less.   The core for corrugated board according to claim 1, wherein the highly branched polyacrylamide has a solid content concentration of 12.5 mass% and a viscosity of the aqueous solution at a temperature of 30 ° C is 9 mPa · s to 25 mPa · s. The core for corrugated board according to claim 1 or 2, wherein the coating amount of the highly branched polyacrylamide is 0.5 g / m ² or more and 2.5 g / m ² or less in terms of solid content per side. A method for producing a core for corrugated board having a coating step of coating a coating liquid mainly composed of a paper strength agent on at least one side of a base paper for core obtained by papermaking raw material pulp,
The paper strength agent is mainly composed of highly branched polyacrylamide,
The solid content concentration of the coating liquid is 5% by mass or more and 20% by mass or less,
A method for producing a core for corrugated board, wherein the coating step is carried out at a temperature of the coating liquid of 26 ° C. or more and a viscosity of 9 mPa · s to 25 mPa · s.