JP2008031601A - Multi-layered cardboard - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layered cardboard which is used for corrugated cardboard cases used for receiving, transporting and storing individually packed frozen foods or the like, is especially excellent in a water-intercepting property, a cold-insulating property and a heat-insulating property, does not cause delamination, when adhered / processed into corrugated cardboard cases or the like or when used, and can further be recycled as a waste paper raw material. <P>SOLUTION: In the multi-layered cardboard having at least a surface layer, a back side layer, and one or more intermediate layers disposed between the surface layer and the backside layer, at least one layer of the intermediate layers is a foam layer blended with at least thermally expandable particles and thermally fusible fibers and having a water-impermeable property. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a paperboard used for corrugated cardboard cases used for transporting and storing stored items that require cold insulation and heat insulation such as frozen foods, and in particular, excellent in water shielding, cold insulation, and heat insulation. The present invention relates to a multi-layer paperboard which is excellent in bonding and box making suitability when processed into a corrugated cardboard case and can be recycled as a raw material for used paper.

  Conventionally, as a paperboard to be processed into corrugated cardboard cases used for transporting and storing frozen foods and other items that require heat retaining properties, aluminum vapor-deposited paperboard or a laminate film intervened in the paper layer Laminated sand paperboard or the like is used.

  The corrugated cardboard case formed of the aluminum vapor-deposited paperboard has almost no air permeability between the inside and the outside of the corrugated cardboard case due to the aluminum vapor-deposited layer, and exhibits water shielding and heat retaining properties.

  Further, in the corrugated cardboard case formed of laminated sand paperboard, the laminated film in the paper layer plays the same role as the aluminum vapor deposition layer, thereby having a shielding property and exhibiting a water shielding property and a heat retaining property.

  However, when such aluminum vapor-deposited paperboard and laminate sand paperboard are tried to recycle into used paper, there is a problem that it is difficult to recycle as used paper because it is difficult to remove the aluminum vapor-deposited layer and laminate film. .

  Further, particularly in the case of aluminum vapor-deposited paperboard, there is a problem that the metal foreign matter sensor may malfunction.

  In order to solve such a problem, there is a technique using a ceramic coated paperboard, but the ceramic coated paperboard has an effect of being excellent in water shielding and heat retaining properties, but has a problem that it is expensive.

For example, as shown in Patent Document 1, by heating and foaming a sheet obtained by blending foamable particles having a liquid as a core substance and making a paper, a heat insulating property having a density of 0.1 to 0.3 g / cm ³ . In addition, a method for producing a low-density base paper that is excellent in heat retention and has cushioning properties and used for cups such as instant noodles and tea has been proposed.

  However, blending foamable particles in this way reduces the bond between fibers of pulp fibers and weakens the bond strength between fibers, so the paper strength such as surface strength and interlayer strength is greatly reduced. Resulting in.

  When such a paper is used as a corrugated cardboard and processed into a corrugated cardboard case by being bonded to the core, the strength required as the corrugated cardboard case cannot be secured. Cannot play a role as a cardboard case.

  Further, since the surface of the paper is easily torn due to the influence of the expandable particles, the adhesive strength with the core is weak. Furthermore, the adhesive strength of the joint part and the flap part of the cardboard case is also weak.

  Therefore, it is difficult to use the paper obtained by such a manufacturing method for a cardboard case.

  Therefore, as shown in Patent Document 2, the applicant of the present invention has a cardboard case while having water-insulating properties and heat-retaining properties by including thermally foamable particles in an intermediate layer of a multilayer paperboard comprising at least three layers. Disclosed is a water-insulating and heat-insulating paperboard that can be used as a base paper.

  However, since this paperboard contains heat-expandable particles, the interlaminar strength is reduced compared to paperboard that does not contain heat-expandable particles. When using the corrugated cardboard case, delamination is likely to occur. In addition, the water and heat insulation properties can be significantly improved compared to general multilayer paperboard, but the water insulation and heat insulation properties are sufficient when compared with foamed polystyrene and laminates. I couldn't say that.

JP-A-5-339898 JP 2003-49400 A

  The present invention has been made in view of the above-described circumstances, and the object of the present invention is to provide a multi-layer paperboard for use in a corrugated cardboard case used for transporting, storing, etc. In particular, it has excellent water barrier properties, cold insulation properties, and heat insulation properties. Also, there is no delamination during bonding and box making when processing into corrugated cardboard cases and the like. Is to provide recyclable multilayer paperboard.

The above object of the present invention is a multilayer paperboard having at least a surface layer, a back layer, and an intermediate layer composed of one or more layers disposed between the surface layer and the back layer,
To provide a multilayer paperboard, wherein at least one of the intermediate layers is a foamed layer in which at least a heat-expandable particle and a heat-meltable fiber are blended, and the foamed layer has a water barrier property. Achieved by:

Moreover, the said objective of this invention is 1-30 mass% in conversion of solid content with respect to pulp solid content in the said foaming layer, and a thermomeltable fiber is 1-10 with respect to pulp solid content. The total basis weight of the foamed layer is 25 to 80 g / m ² . TAPPI No. This is achieved effectively by providing a multilayer paperboard characterized by having an interlayer strength defined by 18-2 of 75 mJ or more.

  The above-mentioned object of the present invention can be achieved more effectively by providing a multilayer paperboard having a thermal conductivity of 0.05 W / mk or less.

  Furthermore, the above object of the present invention can be achieved more effectively by providing a multilayer paperboard having a water shielding rate of 81% or more.

  According to the multilayer paperboard according to the present invention, at least one layer of the intermediate layer is a foamed layer imparted with water barrier properties by blending at least heat-expandable particles and heat-meltable fibers. When the paperboard is processed into, for example, a corrugated cardboard case and frozen food or the like individually packaged in the corrugated cardboard case is stored, moisture from the stored food (contained material) is blocked by the intermediate layer which is a foam layer. As a result, moisture does not ooze out to the outer surface of the cardboard case, so that the appearance of the cardboard case is reduced, the commercial value is not lowered, and the strength of the paperboard is reduced by the moisture that comes out of the contents. Therefore, strength and rigidity as a cardboard case can be secured.

  In addition, since at least one of the intermediate layers is a foamed layer, no special adhesive is required in the process of processing the paperboard into a cardboard case or the like by bonding or box making, and it can be processed in the same way as general paperboard. .

  Moreover, even when processed into a corrugated cardboard case, the adhesive strength of the joint part and the flap part of the corrugated cardboard case can be set to the same level as general paperboard.

  Also, with regard to printability, good printability can be obtained by the same method as for general paperboard.

Moreover, the foaming layer contains 1-30% by mass of thermally foamable particles in terms of solid content with respect to the pulp solid content, and 1-10% by mass of thermomeltable fiber with respect to the pulp solid content. Since the total basis weight was set to 25 to 80 g / m ² , the desired water shielding property can be imparted to the intermediate layer serving as the foam layer. Specifically, the water shielding rate of the foam layer can be 81% or more. Accordingly, it is possible to improve the water barrier property, cold insulation property, and heat insulation property of the paperboard. Specifically, the thermal conductivity can be 0.05 W / mk or less.

  In addition, J.H. TAPPI No. Since the interlayer strength defined by 18-2 is 75 mJ or more, delamination does not occur during pasting / boxing and use.

  Hereinafter, the multilayer paperboard according to the present invention will be described with reference to the drawings, taking as an example the case of a surface layer, three intermediate layers (including two foam layers), and a back layer of five paper layers. This will be described in detail. The multilayer paperboard according to the present invention is not limited to the following embodiments, and it is needless to say that the configuration can be changed as appropriate without departing from the scope of the claims.

  As shown in FIG. 1, a multilayer paperboard (hereinafter referred to as “main paperboard”) 10 according to the present invention includes a surface layer 11, an intermediate layer (foamed layer) 12, an intermediate layer (foamed layer) 13, and an intermediate layer 14. , And a back layer 15 of five paper layers.

  As shown in FIG. 2, the main paperboard 10 configured in this manner is bonded to the main paperboard 10 </ b> A, the core 16, and the main paperboard 10 </ b> B, and is processed into a cardboard case 17 as an example. explain. In the present embodiment, the surface of the surface layer 15 of the paperboard 10A is the outer surface of the cardboard case, the surface of the surface layer 15 of the paperboard 10B is the inner surface of the cardboard case 17 (the surface in contact with the contents), and the back of the paperboard 10A. This is a case where the surface of the layer 11 and the surface of the back layer 11 of the main paperboard 10 </ b> B are bonded to the core 16 and processed into a cardboard case 17.

  The surface layer 11 of the main paperboard 10 is a layer responsible for (a) ensuring good boxing suitability when processing the mainboard 10 into the cardboard case 17, and (b) ensuring good printability. .

  Therefore, the surface layer 11 of the present paperboard 10 can be manufactured by a method similar to a general outer layer liner for cardboard.

  Moreover, it is preferable that the surface layer 11 of the present paperboard 10 fulfills the roles (a) and (b) above after imparting water resistance so as not to be affected by moisture.

  In other words, the present paperboard 10 is premised on containing individually packed frozen foods and used in a corrugated cardboard case 17 used for transportation and storage. Moisture may come out. Therefore, since the surface layer 11 comes into contact with moisture, in addition to the roles (a) and (b), it is preferable to impart a predetermined water resistance.

Specifically, the surface layer 11 preferably has a water absorption of 20 to 80 g / m ² measured in accordance with JIS-P8140 paper and paperboard-water absorption test method-Cobb method. ² is more preferable.

If the water absorption exceeds 80 g / m ² , the surface strength of the surface layer 11 is reduced even if a wet paper strength enhancer is contained, and therefore, the surface layer 11 becomes fuzzy due to rubbing with the contents, Damage can occur. Moreover, since the adhesive agent at the time of bonding and box making penetrates too much into the paper layer of the surface layer 11 and the adhesiveness deteriorates, there also arises a problem that a large amount of adhesive agent must be applied.

On the other hand, if the water absorption of the surface layer 11 is less than 20 g / m ² , the adhesive at the time of bonding / boxing does not penetrate into the paper layer of the surface layer 11 and the adhesiveness deteriorates. In addition to the necessity, there is a problem that the solubility becomes worse when the paperboard 10 is recycled as used paper. Furthermore, in order to make the water absorption less than 20 g / m ² , it is necessary to add a large amount of chemicals. As a result, the operability is deteriorated and the production cost is increased.

  In order to impart such water resistance to the surface layer 11, a sizing agent is blended in the raw material pulp of the surface layer 11.

  As the sizing agent, various known ones can be used as long as they are acidic or neutral. In particular, neutral rosin sizing agents, AKD sizing agents, ASA sizing agents and the like are neutral. It is preferable to manufacture the present paperboard 10 using a sizing agent having a high size development effect in the region and setting the hot water extraction PH of the surface layer 11 to a neutral region of 5-9. This is because the effect of the fixing agent for heat-expandable particles, which will be described later, is easily exhibited in the neutral region.

  Furthermore, even if the surface layer 11 absorbs a large amount of moisture, it is necessary to maintain appropriate surface strength, compressive strength, burst strength, and the like in order to serve as the corrugated cardboard case 17, so that the wet paper It is preferable to include a force enhancer in the raw material pulp of the surface layer 11.

  As the wet paper strength enhancer, amphoteric polyacrylamide, polyamide epichlorohydrin, starch, starch starch such as oxidized starch, carboxymethylated starch, plant gum, polyvinyl alcohol, carboxymethylcellulose, etc. can be used. Even when a large amount of moisture is absorbed as in the present paperboard 10, it is preferable to add a polyamide epichlorohydrin wet paper strength enhancer in order to maintain an appropriate strength.

  The content of the wet paper strength enhancer is preferably 0.1 to 1.2% by mass with respect to the pulp solid content of the surface layer.

  That is, when the content of the wet paper strength enhancer exceeds 1.2% by mass, the wet paper strength of the surface layer 11 is improved, but it becomes difficult to recycle as used paper. On the other hand, when the content of the wet paper strength enhancer is less than 0.1% by mass, the wet paper strength is often insufficient when the surface layer 11 absorbs a large amount of water. The strength cannot be ensured, and there is a possibility that the surface of the surface layer 11 is fluffed and damaged due to rubbing with the contents.

  In addition, as raw material pulp of the surface layer 11, for example, hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), hardwood semi-bleached kraft pulp (LSBKP), softwood semi-bleached kraft pulp (NSBKP), chemical pulp such as hardwood sulfite pulp, coniferous sulfite pulp, stone grand pulp (SGP), pressurized stone grand pulp (PGW), refiner grand pulp (RGP), thermo ground Pulp (TGP), Chemi-Grand Pulp (CGP), Crushed Wood Pulp (GP), Thermomechanical Pulp (TMP) and other mechanical pulp, tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, leaflet waste paper, office waste paper, cardboard waste paper , On white old paper, Kent Chemically from disaggregated waste paper pulp, disaggregated / deinked waste paper pulp, or disaggregated / deinked / bleached waste paper pulp, or non-wood fibers such as kenaf, hemp, cocoon, etc. Alternatively, various known pulps such as mechanically produced pulp can be used.

  Next, the intermediate layer 12 and the intermediate layer 13 will be described.

  As shown in FIG. 1, the present paperboard 10 has three intermediate layers 12 to 14. Among these, the intermediate layer 12 and the intermediate layer 13 are foamed layers imparted with water shielding properties.

  That is, in the intermediate layers 12 and 13, the moisture absorbed in the surface layer 11 passes through the intermediate layer 14, passes through the back layer 15, and penetrates to the outer surface of the cardboard case 17. It is a layer that plays the role of preventing exudation, and in order to fulfill this role, water shielding is provided.

  As a result, moisture from the stored food is absorbed by the surface layer 11, but the moisture absorbed by the surface layer 11 can be shielded in the thickness direction of the paperboard 10. Accordingly, it is possible to prevent moisture from seeping out from the intermediate layer 14 to the outer surface of the cardboard case 17.

  By providing the intermediate layer 12 and the intermediate layer 13 with a water shielding function, the paperboard 10 can have a water shielding rate of 81% or more, preferably 85% or more, as will be described later.

  In order to impart such a water barrier property to the intermediate layers 12 and 13 and to make the intermediate layers 12 and 13 into foamed layers, at the time of making the paperboard 10, at least the thermal foaming property in the raw pulp of the intermediate layers 12 and 13 Blend particles and hot melt fibers.

  The heat-expandable particles are blended in an amount of 1 to 30% by mass, preferably 3 to 20% by mass in terms of solid content with respect to the pulp solid content of each layer of the intermediate layers 12 and 13.

  That is, the blending amount of the heat-expandable particles per layer is preferably less than 30% by mass, and it is preferable to provide two or more intermediate layers, which are foam layers, as required, like the present paperboard 10. Thereby, it is possible to efficiently obtain a paperboard that has excellent interlayer strength and does not cause delamination at the time of bonding / boxing and use while obtaining predetermined water shielding properties, cold insulation properties, and heat retention properties.

  When the amount of the heat-expandable particles is less than 1% by mass per layer, the distance between the heat-expandable particles becomes long and the voids increase even if the heat-expandable particles are expanded. It becomes difficult to provide the water barrier property. On the other hand, even if the blending amount of the heat-expandable particles exceeds 30% by mass per layer, the improvement of the water shielding function of the paperboard cannot be expected and only the production cost is increased. In addition, the greater the amount of thermally foamable particles, the lower the interlaminar strength of the paperboard. However, if the amount of thermally foamable particles exceeds 30% by mass, even if the heat-fusible fiber described later is blended, it is predetermined. It is difficult to obtain the interlayer strength of the paperboard, which reduces the strength and rigidity of the paperboard.

  The thermally foamable particles that can be used for the present paperboard 10 are those in which a low-boiling solvent is enclosed in a fine particle outer shell made of a thermoplastic synthetic resin. The thermally foamable particles have an average particle size of 5 to 30 μm, and expand by 4 to 5 times in diameter and 50 to 130 times in volume when heated at 90 to 200 ° C.

  Examples of the thermoplastic synthetic resin constituting the outer shell include copolymers such as vinylidene chloride, acrylonitrile, acrylic acid ester, and methacrylic acid ester.

  Examples of the low boiling point solvent enclosed in the outer shell include isobutane, pentane, petroleum ether, hexane, low boiling point halogenated hydrocarbon, and methylsilane.

  Examples of such thermally expandable particles include “Matsumoto Microsphere F-20 Series”, “F-30 Series”, “F-36 Series”, and “F-46” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. "Expancel WU" and "Same DU" sold by Nippon Philite Co., Ltd. can be used, but the heat-expandable particles used for the present paperboard 10 are not limited to these.

  However, in the present invention, since the temperature of the paper drying step is generally about 130 ° C., the low temperature expansion type in which the expansion start temperature of the thermally foamable particles is 90 to 130 ° C. is preferable.

  Thermally foamable particles are heated above the softening point of the thermoplastic synthetic resin that constitutes the outer shell, and at the same time, the low-boiling solvent encapsulated is vaporized, the vapor pressure rises, the outer shell expands, and the particles expand. During expansion, the internal pressure and the tension / external pressure of the shell are balanced to maintain the expanded state. The thermally foamable particles are generally expanded to this state and used as a lightening agent, a bulking agent, a cushioning agent, a heat insulating agent and the like. If additional heat is applied to the expanded thermally expandable particles, the gas permeates and diffuses from the expanded and thinned shell, and the tension and external pressure of the shell become larger than the internal pressure. As a result, the foamed particles shrink.

  The thermally foamable particles used in the present paperboard 10 are foamed by a dryer in the drying step. For the above reason, it is preferable to use low-temperature expansion type thermally foamable particles having an expansion start temperature of 90 to 130 ° C. . That is, when the expansion start temperature is less than 90 ° C., when the foaming is performed by the dryer in the drying process, the particles once expanded are contracted again as described above, and the predetermined water-impervious property is obtained. It becomes difficult to give to 12 and 13.

  In addition, the intermediate layers 12 and 13 are provided with a water-impervious layer and used as a foam layer to form a paperboard having excellent interlaminar strength that does not cause delamination at the time of bonding / boxing or use. Hot melt fibers are also blended in the pulp.

  1 to 10 mass%, Preferably 3 to 8 mass% is mix | blended with respect to the pulp solid content of each layer of the intermediate | middle layers 12 and 13.

  When the blending amount of the heat-meltable fiber is less than 1% by mass, it is difficult to suppress a decrease in the bond between pulp fibers caused by blending the heat-foamable particles, and it becomes difficult to obtain a predetermined interlayer strength. On the other hand, even if the blending amount of the hot-melt fiber exceeds 10% by mass, the effect of improving the interlaminar strength cannot be expected, and only the production cost increases.

  Examples of heat-meltable fibers include polyethylene terephthalate (PET) fibers, polyethylene (PE) fibers, EVA vinylon (PVA fibers) fibers, polyester fibers, aramid fibers, carbon fibers, rayon fibers, acrylic fibers, Various materials such as polyamide fibers and glass fibers are known.

  However, in the present paperboard 10, the adhesiveness with the heat-expandable particles, the adhesiveness with the pulp fibers, the paperboard can be mixed with the raw material pulp, and the paperboard 10 can be melted appropriately in the drying process of the papermaking machine. From the standpoint of bonding to fibers, it is preferable to use hot-melt fibers made mainly of PET, vinylon, PE, EVA, etc. Among these, the hot-melt fibers made mainly of PET are mainly used for this paperboard. It is preferable because it has an excellent effect of improving the interlayer strength of 10.

  The melting temperature of the heat-meltable fiber is preferably that having a fiber surface of 90 to 130 ° C. Specifically, Sophit N720 / Kuraray, TJ04CN / Teijin, Vinylon Binder SML / Unitika, EA-CHOP / Chisso, Ester 4080 / Unitika, NBF / Daiwabo and the like can be suitably used.

  As the raw material pulp for the intermediate layers 12 and 13, various known pulps can be used in the same manner as the raw material pulp for the surface layer 11 described above. In particular, it is preferable to contain 30% by mass or more of softwood kraft pulp.

  That is, since the heat-expandable particles are blended in the raw material pulp of the intermediate layers 12 and 13, the interfiber bond between the pulp fibers is weakened, and there arises a problem that the interlayer strength of the obtained paperboard is lowered. In order to prevent the occurrence of this problem, it is preferable to contain a predetermined amount of softwood kraft pulp having a long fiber length and high strength. The softwood kraft pulp may be virgin pulp or may be derived from waste paper.

The total basis weights of the intermediate layers 12 and 13 which are foamed layers to which water shielding is imparted are 25 to 80 g / m ² , preferably 30 to 70 g / m ² .

That is, if the total basis weight of the intermediate layers 12 and 13 as the foam layer is less than 25 g / m ² , the foam layer is thin even if a predetermined amount of thermally foamable particles is blended, so that it is desirable. There are cases where water impermeability cannot be imparted.

On the other hand, if the total basis weight of the intermediate layers 12 and 13 that are foam layers exceeds 80 g / m ² , the basis weight of the present paperboard 10, that is, the basis weight of the entire paperboard, is almost excellent in terms of imparting water shielding. Since it is determined, the basis weight of layers other than the foam layer is inevitably reduced. For this reason, it becomes difficult to ensure the strength required for the cardboard case 17 for protecting and storing the contents. Although it is possible to increase the basis weight of the layers other than the intermediate layers 12 and 13 which are the foam layers, problems such as an increase in manufacturing cost occur, which is not practical.

  Next, the intermediate layer 14 and the back layer 15 will be described.

  The intermediate layer 14 and the back layer 15 of the paperboard 10 ensure (a) good bonding and boxing suitability when processing the paperboard 10 into the cardboard case 17, and (b) strength as the cardboard case 17. It is a layer that plays a role such as securing.

  In addition, since the present paperboard 10 stores frozen foods and the like in which a lot of moisture is contained, it plays the roles of (a) and (b) described above, and affects the suitability for bonding with the core 16 when processed into the cardboard case 17. It is preferable to impart water resistance to the intermediate layer 14 and the back layer 15 within a range where no water is generated.

In order to provide such water resistance, the sizing agent is 0.3 to 1.5% by mass in terms of solid content, preferably 0.6 to the raw material pulp of each layer of the intermediate layer 14 and the back layer 15. was added 1.5 wt%, it is preferable that the water absorption measured according to JIS-P8140 is adjusted to 30 to 80 g / ^{m 2,} and more preferably a 30 to 50 g / ^{m 2.}

That is, if the water absorption is less than 30 g / m ² , the adhesiveness of the adhesive during the bonding / boxing of the intermediate layer 14 or the back layer 15 is deteriorated, and a special adhesive is required. When recycled as used paper, the solubility becomes worse. In addition, the operability is deteriorated and the manufacturing cost is increased. On the other hand, when the water absorption exceeds 80 g / m ² , the adhesive at the time of bonding and box making penetrates into the paper layer of the intermediate layer 14 or the back layer 15, and the adhesiveness with the core 16 is deteriorated. . In addition, a problem arises in that a large amount of adhesive must be applied.

  As the raw material pulp for the intermediate layer 14 and the back layer 15, various known pulps can be used in the same manner as the raw material pulp for the surface layer 11 described above. However, in the range that does not impair the water resistance performance and does not impair the purpose of maintaining the strength of the paperboard 10, it is possible to blend as much wastepaper pulp as possible in terms of reducing the load on the energy intensity and the environment, Moreover, since it is advantageous also in cost, it is preferable.

Although the total basis weight of the intermediate | middle layer 14 and the back layer 15 changes also with the layer structure of this paperboard 10, and the basis weight of each other layer, it is preferable to set it as 60-175 g / m < ² >. However, it is preferable to make the total basis weight of the intermediate layer 14 and the back layer 15 as large as possible within the range not impairing the effects of the present invention, because it is advantageous in terms of cost.

  The paperboard 10 is manufactured by laminating raw material pulp of the surface layer 11, the intermediate layer 12, the intermediate layer 13, the intermediate layer 14, and the back layer 15 in this order by a paper machine. That is, as shown in FIG. 1, the present paperboard 10 is a paper machine in which an intermediate layer 12 is laminated on the surface of the surface layer 11, an intermediate layer 13 is laminated on the surface of the intermediate layer 12, and the surface of the intermediate layer 13 The intermediate layer 14 is laminated thereon, and the back layer 15 is laminated on the surface of the intermediate layer 14. Depending on the type of the paper machine, the layers may be stacked in the reverse order.

  The present paperboard 10 configured as described above is disclosed in J. Pat. TAPPI No. The interlayer strength based on 18-2 is 75 mJ or more. When the interlayer strength is less than 75 mJ, when the paperboard is processed into a cardboard case, the predetermined strength cannot be maintained, and it becomes difficult to play a role as a cardboard case.

  Further, the present paperboard 10 has a water shielding rate of 81% or more, preferably 85% or more, measured by a water shielding test method described later.

  When the water barrier rate of the present paperboard 10 is less than 81%, when the surface layer 11 is in contact with moisture for 24 hours or more, the moisture absorbed by the surface layer 11 passes through the intermediate layers 12 and 13, and further, the intermediate layer 14 and The back layer 15 also permeates and penetrates to the outer surface of the cardboard case 17. As a result, the appearance of the cardboard case 17 is lowered, and the commercial value is lowered. Further, when the surface layer 11 is in contact with moisture for a longer time, the strength and rigidity of the cardboard case 17 is lowered, and the role as the cardboard case 17 cannot be performed.

  Further, the present paperboard 10 has a thermal conductivity of 0.05 W / mk or less based on the heat flow meter method of JIS-A1412. As described above, the main paperboard 10 contains frozen foods that are individually packaged, and is often used for the cardboard case 17 used for transportation and storage. Therefore, when the thermal conductivity becomes higher than 0.05 W / mk. The temperature of the outside air or the like is transmitted to the inside of the cardboard case 17 and the frozen food may be melted, so that it is not possible to ensure cold insulation and heat insulation.

The basis weight of the paperboard 10 is also changed depending on the size and intended use of the corrugated board, preferably in the range of 160~300g / ^{m 2,} more preferably in the range of 160~230g / ^{m 2} . When the basis weight of the paperboard 10 is less than 160 g / m ² , it is difficult to ensure strength and rigidity as a cardboard case. On the other hand, even if the basis weight of the main paperboard 10 is larger than 300 g / m ² , the quality becomes excessive and the manufacturing cost only increases.

  The papermaking method of the present paperboard 10 is not particularly limited, and may be any of acidic papermaking, neutral papermaking, and alkaline papermaking, but the intermediate layers 12 and 13 that are foam layers. In order to fix the heat-expandable particles with a fixing agent and to effectively exhibit the water shielding function, it is preferable to produce the paper with neutral paper making the hot water extraction PH to be 5-9.

  Also, since the paper machine is not particularly limited, for example, various known paper machines such as a long net paper machine, a twin wire paper machine, a circular net paper machine, and a short net combination machine can be used. it can.

  In addition, since the surface layer 11 of the main paperboard 10 is often printed, the surface of the mainboard paper 10 is water-soluble as necessary in order to improve the printing gloss and surface strength and adjust the slipperiness. It is preferable to apply various means for improving the printability, for example, by applying a coating liquid containing a functional substance as a main component.

  Examples of such water-soluble substances include polyacrylamide and derivatives thereof, polyvinyl alcohol, cellulose derivatives, starch, modified starch, polystyrene-butadiene-based, acrylic-based, polyvinyl acetate-based latex, wax emulsion, and the like. Various known materials that are commonly used in the field can be used alone or in admixture of two or more.

For example, good printability can be obtained by applying polyvinyl alcohol to the surface of the surface layer 11 by 0.5 to 3.5 g / m ² , preferably 0.7 to ² g / m ² .

  Furthermore, if the coating liquid which has a pigment and a binder as a main component is applied to a surface layer using a coating apparatus, a more beautiful printing can be achieved.

  Further, the surface of the main paperboard 10 may be smoothed. This smoothing process is preferably performed by, for example, pressing the paperboard 10 between pressurizable rolls. When performing the smoothing treatment, it is preferable that the roll in contact with the surface of the surface layer 11 of the paperboard 10 is a metal roll that has a smooth surface and can be heated.

  In addition, the smoothing process in the main paperboard 10 is a process of making the main paperboard 10 in addition to the above-described smoothing process, for example, a calendar process using a calendar roll provided with one or more pairs of metal rolls (according to a machine calendar). Calendar processing), calendar processing with a calendar roll provided with one or a plurality of metal rolls and resin rolls (calendar processing with a soft calendar), drying processing with a Yankee dryer, and the like.

  Further, the present paperboard 10 may contain starch, filler, antifoaming agent, paper strength enhancer, anti-slip agent, pH adjuster and the like in addition to the above-mentioned oilproofing agent, fixing agent and sizing agent.

  In the above, the case where the paper layer is composed of five layers of the surface layer 11, the intermediate layer 12, the intermediate layer 13, the intermediate layer 14, and the back layer 15 has been described for the present paperboard 10. However, the present invention is not limited to such a paperboard. For example, a paperboard made of four paper layers as shown in FIG. 3 and a paperboard made of three paper layers as shown in FIG. 4 may be used.

  That is, the paperboard 10 ′ shown in FIG. 3 is composed of a surface layer 11, two intermediate layers 12 and 13, which are foam layers provided with water shielding properties, and a four-layered paper layer. Thus, it is possible to obtain the paperboard 10 'to which the desired effect of the present invention is imparted without providing the intermediate layer 14 to which no water shielding is imparted.

  Further, the paperboard 10 ″ shown in FIG. 4 is composed of three paper layers: a surface layer 11, an intermediate layer 12 which is a foam layer provided with water shielding properties, and a back layer 15. Even with such a configuration, it is possible to obtain the paperboard 10 ″ to which the desired effect of the present invention has been imparted.

  The paperboard according to the present invention may be a paperboard made up of six layers, seven layers,... By increasing the number of intermediate layers. In this case, at least one of the intermediate layers is shielded. If it is a foamed layer to which aqueous property is given, the effect which this invention desires can be acquired.

  Further, although the case where the paperboard according to the present invention is processed into the corrugated cardboard case 17 has been described, the present invention is processed into a paper container or the like so that the surface layer 11 of the paperboard becomes the inner surface and the back layer 15 becomes the outer surface. Even so, the desired effect of the present invention can be obtained.

  In order to confirm the effect of the multilayer paperboard according to the present invention, the following various samples were prepared, and a test for evaluating the quality of each sample was performed. In addition, in a present Example, the numerical value which shows a mixing | blending, a density | concentration, etc. is a numerical value of the solid content or the mass reference | standard of an active ingredient. Moreover, since the pulp, chemical | medical agent, etc. which are shown in a present Example are only examples, it cannot be overemphasized that this invention is not restrict | limited by these Examples, and can be selected suitably.

  24 types of paperboards according to the present invention (referred to as “Example 1” to “Example 24”) and three types of paperboards (referred to as “Example 1” to “Example 24”) “Comparative Example 1” to “Comparative Example 3”) were prepared in the configuration shown in Table 1. Moreover, a general exterior cardboard was evaluated as a reference example.

［実施例１］
＜１＞表層
広葉樹晒クラフトパルプ（ＬＢＫＰ）７０質量％と上白古紙パルプ３０質量％とを配合した後に、離解フリーネスを４００ｃｃに調整した表層用の原料パルプに、硫酸バンドを０．５質量％、サイズ剤（商品名：Ｒ−２２、近代化学株式会社製）を固形分換算で０．５質量％、乾燥紙力増強剤（商品名：ハーマイドＲＢ−３２、ハリマ化成株式会社製）を固形分換算で０．３質量％、湿潤紙力増強剤（星光ＰＭＣ株式会社製 エピクロロヒドリン）を固形分換算で０．１８質量％添加して表層用の原料スラリーを調整した。
＜２＞中間層（１）
針葉樹晒クラフトパルプ（ＮＢＫＰ）３０質量％と、広葉樹晒クラフトパルプ（ＬＢＫＰ）１０質量％と、上白古紙パルプ（ＬＢＫＰ）６０質量％とを配合した後に、離解フリーネスを４００ｃｃに調整した中間層（１）用の原料パルプに、硫酸バンドを０．７質量％、サイズ剤（商品名：Ｒ−２２、近代化学株式会社製）を固形分換算で０．５質量％、乾燥紙力増強剤（商品名：ハーマイドＲＢ−３２、ハリマ化成株式会社製）を固形分換算で０．７質量％、湿潤紙力増強剤（星光ＰＭＣ株式会社製 エピクロロヒドリン）を固形分換算で０．３質量％添加する。また、中間層（１）用の原料パルプには、熱発泡性粒子（商品名：マツモトマイクロフェアー Ｆ−４６、松本油脂製薬株式会社製）を、その含有量がパルプの固形分に対して１０質量％となるように添加し、さらにこの熱発泡性粒子の定着剤として、セラフィックスＳＴ（明成化学工業社製）を有姿１００％として１質量％、ファイレックスＭ（明成化学工業社製）を有姿１００％として２質量％添加する。さらにまた、熱溶融性繊維（クラレ社製 ソフィットＮ７２０）を５質量％添加する。その後、中間層（１）用の原料パルプのＰＨを６．８に調整し、中間層用の原料スラリーを調整した。

[Example 1]
<1> Surface Layer After blending 70% by mass of hardwood bleached kraft pulp (LBKP) and 30% by mass of Kamikoshi old paper pulp, 0.5% by mass of sulfuric acid band is added to the raw material pulp for surface layer whose disintegration freeness is adjusted to 400cc. , Sizing agent (trade name: R-22, manufactured by Modern Chemical Co., Ltd.) 0.5% by mass in terms of solid content, dry paper strength enhancer (trade name: Hermide RB-32, manufactured by Harima Kasei Co., Ltd.) The raw material slurry for the surface layer was prepared by adding 0.38% by weight in terms of minutes and 0.18% by weight of wet paper strength enhancer (Epichlorohydrin manufactured by Seiko PMC Co., Ltd.) in terms of solids.
<2> Intermediate layer (1)
After blending 30% by weight of softwood bleached kraft pulp (NBKP), 10% by weight of hardwood bleached kraft pulp (LBKP), and 60% by weight of upper white waste paper pulp (LBKP), an intermediate layer having a disaggregation freeness adjusted to 400 cc ( 1) For the raw material pulp, 0.7% by mass of a sulfuric acid band and 0.5% by mass of a sizing agent (trade name: R-22, manufactured by Modern Chemical Co., Ltd.) in terms of solid content, a dry paper strength enhancer ( Product name: Hermide RB-32, manufactured by Harima Kasei Co., Ltd.) 0.7 mass% in terms of solid content, and wet paper strength enhancer (Epichlorohydrin, manufactured by Seiko PMC Co., Ltd.) 0.3 mass in terms of solid content %Added. In addition, the raw material pulp for the intermediate layer (1) contains thermally foamable particles (trade name: Matsumoto Microsphere F-46, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) with a content of 10 based on the solid content of the pulp. 1% by mass with 100% solid SERAFIX ST (manufactured by Meisei Chemical Co., Ltd.) as a fixing agent for the thermally expandable particles, Phyrex M (manufactured by Meisei Chemical Co., Ltd.) Is added as 2% by mass. Furthermore, 5% by mass of a heat-meltable fiber (Kuraray Sophit N720) is added. Then, PH of the raw material pulp for intermediate | middle layer (1) was adjusted to 6.8, and the raw material slurry for intermediate | middle layers was adjusted.

<3> Back layer After blending 70% by weight corrugated cardboard pulp and 30% by weight waste paper pulp, 0.5% by weight sulfuric acid band is added to the pulp for the back layer whose disaggregation freeness is adjusted to 300cc. Agent (trade name: R-22, manufactured by Modern Chemical Co., Ltd.) in terms of solid content is 0.5% by mass, and dry paper strength enhancer (trade name: Hermide RB-32, manufactured by Harima Kasei Co., Ltd.) is converted into solid content. The raw material slurry for the back layer was prepared by adding 0.4% by mass.

Using these raw material slurries, the surface layer, the intermediate layer (1), and the back layer paper layer are made together by a circular net three-layer paper machine, and the basis weight of the surface layer is 30 g / m ² , and the intermediate layer (1) A three-layered multilayer paperboard (Example 1) having a basis weight of 60 g / m ² , a basis weight of the back layer of 130 g / m ² , and a basis weight of the entire multilayer paperboard of 220 g / m ² Obtained.

[Examples 2 to 6]
A multilayer paperboard obtained in the same manner as in Example 1 except that the content of the heat-expandable particles is as shown in Table 1.

[Examples 7 to 11]
A multilayer paperboard obtained in the same manner as in Example 1 except that the content of the heat-meltable fiber is as shown in Table 1.

[Examples 12 to 13]
A multilayer paperboard obtained in the same manner as in Example 1 except that thermally expandable particles having an expansion start temperature shown in Table 1 were added.

[Examples 14 to 15]
A multilayer paperboard obtained in the same manner as in Example 1 except that a hot-melt fiber having a melting start temperature shown in Table 1 was added.

[Example 16]
Multilayer paperboard obtained in the same manner as in Example 1 except that heat-expandable particles having an expansion start temperature of 130 ° C. and heat-meltable fibers having a melting start temperature of 130 ° C. were added. .

[Examples 17 to 19]
A multilayer paperboard obtained in the same manner as in Example 1 except that the type of the hot-melt fiber was changed as shown in Table 1.

[Examples 20 to 24]
As shown in Table 1, the intermediate layer is composed of two layers of the intermediate layers (1) and (2) which are foamed layers imparted with water shielding properties, and the total basis weight of the intermediate layers (1) and (2) which are foamed layers is Except for the change to, the multilayer paperboard obtained in the same manner as in Example 1. The raw material slurry for the intermediate layer (2) was the same as the raw material slurry for the intermediate layer (1) described above.

[Comparative Example 1]
A multilayer paperboard obtained in the same manner as in Example 1 except that no heat-foamable particles were added to the raw material pulp of the intermediate layer (1).

[Comparative Example 2]
A multilayer paperboard obtained in the same manner as in Example 1 except that the hot-melt fiber was not added to the raw material pulp of the intermediate layer (1).

[Comparative Example 3]
A multilayer paperboard obtained in the same manner as in Example 19 except that the heat-expandable particles and the heat-meltable fibers were not added to the raw material pulps of the intermediate layers (1) and (2).

[Reference Example 1]
A commercially available general cardboard base paper for exterior 220 g / m ² was evaluated in the same manner as in the examples.

The “foamed layer total basis weight (g / m ² )” in Table 1 refers to delamination of each of the above samples, and the intermediate layer (1), or the intermediate layers (1) and (2), which are foam layers. It is a value measured in accordance with “paper and paperboard—basis weight measurement method” described in JIS-P8142.

  The delamination was performed according to the following procedure. First, each sample obtained from each sample is immersed in water at room temperature for about 1 hour. Each sample immersed in water is wound around a round bar of about 10 mmΦ starting from a corner, and then the round bar is rolled to squeeze each sample. This operation is repeated starting from all four corners of each sample, and the ironing force is applied to the sample from each direction. As a result, a part of the layers between the samples is peeled off, and this is used to separate the back layer, the intermediate layer (1), the (intermediate layer (2)), and the surface layer to separate the layers. . After delamination, each layer of each sample was sufficiently dried with a hot air dryer or the like and used for the test.

  Table 2 shows the results of quality evaluation for all of the examples, comparative examples, and reference examples, that is, the basis weight, density, interlayer strength, water shielding, cold insulation, and heat insulation of the paperboard (all layers). It was as shown in.

The “basis weight (g / m ² )” in Table 2 is the basis weight of each sample, that is, the entire paperboard, and conforms to “paper and paperboard—basis weight measurement method” described in JIS-P8142. It is the value measured.

“Density (g / cm ³ )” means the basis weight measured according to “Paper and paperboard—basis weight measurement method” described in JIS-P8142, and “paper and paperboard—thickness” described in JIS-P8118. It is a value calculated from the thickness measured according to the “Test method for thickness and density”.

  “Interlaminar strength (mJ)” refers to JAPAN TAPPI No. It is a value measured by the internal bond tester method specified in 18-2.

  “Water shielding rate (%)” is a value measured based on the following water shielding evaluation test. In the water-imperviousness evaluation test, first, folding, vertical, horizontal, and height are set so that there is no joint between the four side surfaces and the side surface and bottom surface so that the surface layer of each sample, which is paperboard, becomes the inner surface of the container. A 15 cm container was made. Next, 200 cc of distilled water was put into the container, the container was covered with a polyethylene sheet, and after 20 hours, the distilled water in the container was transferred to a graduated cylinder, and the remaining amount of distilled water was measured. The distilled water is adjusted to 23 ° C. ± 1 ° C. This test was evaluated by measuring the water shielding rate (%) [distilled water remaining amount / 200 cc] of the multilayer paperboard from this distilled water remaining amount. The water-impervious evaluation test was performed under conditions of a temperature of 23 ° C. ± 1 ° C. and a humidity of 50% ± 2% based on “standard state of test place” described in JIS-Z8703.

  “Cold insulation rate (%)” is a value measured based on the following cold insulation evaluation test. The cold insulation evaluation test is a folding, vertical, horizontal, and height of 5 cm each so that there is no joint between the four side surfaces and the side surface and bottom surface so that the surface layer of each sample, which is paperboard, becomes the inner surface of the container A rectangular parallelepiped container was created. Next, 27 g of ice prepared by freezing distilled water in a freezer for 24 hours is put in this container, the container is covered, and the mass of ice remaining in the container after 90 minutes (the remaining amount of ice) ) Is calculated by mass% and evaluated. The cold insulation evaluation test was performed under the conditions of a temperature of 23 ° C. ± 1 ° C. and a humidity of 50% ± 2% based on “standard state of test place” described in JIS-Z8703.

“Thermal insulation (W / mk)” is a heat transfer rate, and is a value measured using a thermal conductivity measuring device HC-110 manufactured by Eihiro Seiki Co., Ltd. based on the heat flow meter method of JIS-A1412. The measurement was performed under the condition of a temperature of 20 ° C.

表２に示すように、本発明に係る多層抄き板紙、すなわち実施例１〜実施例２２に係る板紙であると品質評価に優れる、すなわち遮水性、保冷性、及び保温性に優れ、また、板紙を段ボールケースなどに加工する際の貼合・製函時、また使用時において層間剥離が発生することがないことが分かる。

As shown in Table 2, the multilayer paperboard according to the present invention, that is, the paperboard according to Examples 1 to 22, is excellent in quality evaluation, that is, excellent in water shielding, cold insulation, and heat retention, It can be seen that delamination does not occur at the time of bonding and box making when processing a paperboard into a corrugated cardboard case or the like.

It is a schematic sectional drawing of the multilayer paperboard based on this invention. It is a fragmentary sectional view of the cardboard case formed using the multilayer paperboard based on this invention. It is a schematic sectional drawing of the multilayer paperboard based on the example of a change of this invention. It is a schematic sectional drawing of the multilayer paperboard based on the other modification of this invention.

Explanation of symbols

10, 10 A, 10 B, 10 ′, 10 ″ Paperboard 11 Surface layers 12, 13 Water barrier layer 14 Intermediate layer 15 Back layer 16 Core 17 Cardboard case

Claims (4)

A multilayer paperboard having at least a surface layer, a back layer, and an intermediate layer composed of one or more layers disposed between the surface layer and the back layer,
A multilayer paperboard, wherein at least one of the intermediate layers is a foamed layer in which at least a heat-expandable particle and a heat-meltable fiber are blended, and the foamed layer has a water barrier property. The foam layer contains 1 to 30% by mass of thermally foamable particles in terms of solid content with respect to the pulp solid content, and 1 to 10% by mass of heat-meltable fiber with respect to the pulp solid content. The total basis weight of the foam layer is 25 to 80 g / m ² . TAPPI No. The multilayer paperboard according to claim 1, wherein the interlayer strength defined by 18-2 is 75 mJ or more. The multilayer paperboard according to claim 1 or 2, wherein the thermal conductivity is 0.05 W / mk or less. The multilayer paperboard according to any one of claims 1 to 3, wherein the water shielding rate is 81% or more.

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