JP2009133030A - Foamed paperboard - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamed paperboard not only having excellent water-intercepting properties, cold-keeping properties and temperature-keeping properties, but also hardly causing delamination when laminating and manufacturing a box at the processing to a corrugated paperboard case or the like and when in use, and further capable of being recycled to a raw material of a waste paper, obtained while improving yield of thermally expandable particles in paper, and giving reduced environmental load. <P>SOLUTION: The foamed paperboard comprises at least a front surface layer, an intermediate layer composed of a single layer or a plurality of layers, and a back surface layer. At least one layer of the intermediate layer is formed into a foamed layer by adding a suspension of the thermally expandable particles obtained by forming a thermally expandable particle aggregate by aggregating the thermally expandable particles by previously adding a cationic polymer resin to at least one layer of the intermediate layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to foamed paperboard for use in corrugated cardboard cases used for transporting and storing cold storage, such as frozen food, storage items that require heat retention, and particularly excellent in water shielding, cold insulation, and heat retention, The present invention relates to foamed paperboard that has excellent bonding and boxing 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.

Then, for example, as shown in Patent Document 1, by heating and foaming a sheet made by blending foamable microcapsules that are thermally foamable particles having a low-boiling solvent as a core substance, a density of 0.2 to An inexpensive water-insulating and heat-insulating paperboard having a heat insulating property and a heat insulating property of 0.5 g / cm ³ and having a water shielding property has been proposed.

  However, by blending the heat-expandable particles in this way, the bonding between the fibers of the pulp fibers is reduced, and the bonding strength between the fibers is also weakened, so the paper strength such as surface strength and interlayer strength is greatly increased. Therefore, there is a problem that the use of such paper for a cardboard case is weak. That is, when such a paper is used as a corrugated cardboard, interlaminar strength is particularly weak at the joint part and the flap part of the corrugated cardboard case, and cannot serve as a corrugated cardboard case.

  In addition, since foamable capsules are ionic in anionic nature, they do not stay in paper well, and there is a problem that white water is contaminated and the environmental load (COD) is high.

  Moreover, for example, as shown in Patent Documents 2 to 4, etc., in order to obtain a foamed layer that is an air layer related to thermal conductivity, a bulking agent is contained, mechanical pulp having bulky characteristics, and softwood pulp are contained. , There are means such as increasing the raw material freeness, pressing linear pressure in the paper making process, lowering the calender linear pressure, etc., but either means weakens or reduces the entanglement between the pulp fibers. The interlaminar strength is lowered, and the interlaminar strength as foamed paperboard in this technical field cannot be secured.

JP 2003-49400 A JP-A-11-200222 JP 2004-100119 A JP 09-67790 A

  The present invention has been made in view of the above-described circumstances, and the object of the present invention is to contain frozen foods that are individually packaged, in foamed paperboard that is used for cardboard cases used for transportation, storage, etc. In particular, it has excellent water barrier properties, cold insulation properties, and heat insulation properties, and can be recycled to raw paper materials without causing delamination during bonding and box making when used in cardboard cases, etc. An object of the present invention is to provide a foamed paperboard in which the yield of thermally foamable particles in paper is improved and the environmental load is reduced.

  The above object of the present invention is to add a cationic polymer resin in advance to agglomerate thermally foamable particles in a foamed paperboard having a layer structure having at least a surface layer, a single layer or a plurality of layers, and a back layer. By providing a foamed paperboard characterized by adding a heat-expandable particle suspension in which a heat-expandable particle agglomerate is formed to at least one intermediate layer and forming the intermediate layer as a foam layer. Achieved.

  Moreover, the said objective of this invention is 1-15 mass% in conversion of solid content with respect to pulp solid content in the said foaming layer, 1-15 mass% of said heat-expandable particles, and 1-of-hot-melt fiber with respect to pulp solid content. Is contained in an amount of 10% by mass. TAPPI No. This is effectively achieved by providing a foamed paperboard having an interlayer strength defined by 18-2 of 75 mJ or more.

  The above-mentioned object of the present invention is achieved more effectively by providing a foamed 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 foamed paperboard having a water barrier property of 81% or more.

  According to the foamed paperboard of the present invention, it has excellent water shielding properties, cold insulation properties, and heat insulation properties, without causing delamination at the time of bonding / boxing when processing into a cardboard case or the like, and at the time of use. In addition, it can be recycled as a raw material for waste paper, improving the yield of thermally foamable particles in the paper and reducing the environmental burden.

Hereinafter, the foamed paperboard according to the present invention will be described in detail.
As shown in FIG. 1, the foamed paperboard 10 (hereinafter referred to as “the present foamed paperboard”) 10 according to the present invention includes a surface layer 11, two middle layers 12 and 13, and two back layers 14 and 15. It is composed of five paper layers. Further, the foamed paperboard 10 is obtained by adding a cationic polymer resin in advance to the raw pulp of at least one middle layer (in this embodiment, the middle layers 12 and 13) to agglomerate the heat-expandable particles. A thermally foamable particle suspension in which an aggregate is formed is added, and the middle layers 12 and 13 are formed as foamed layers.

  Thus, by adding the heat-foamable particle suspension in which the aggregates of heat-foamable particles are formed to form the middle layers 12 and 13 as the foam layer, the yield of the heat-foamable particles is improved, It is excellent in cold insulation and heat retention, satisfies both conflicting properties of improving interlayer strength, and can further reduce the environmental load. That is, after securing the entanglement between the pulp fibers in the wire part and press part of the paper making process, it is possible to obtain a foamed layer (air layer) related to thermal conductivity by foaming the thermally foamable particles in the drying process. This is particularly useful in the usage method and required quality of the foamed paperboard 10. Moreover, by previously aggregating the thermally foamable particles with the cationic polymer resin, the remaining foamed particles in the white water can be reduced, and the environmental load can be reduced. In addition, the fewer foam particles remaining in white water, the higher the yield rate of thermally foamable particles in the paper, preventing the heat foamable particles from flowing into the wastewater, reducing the drainage load, and reducing the environmental impact. Can even be reduced.

  Below, the aggregate of the thermally foamable particles added to the foamed paperboard 10 will be described. The aggregate of thermally foamable particles added to the foamed paperboard 10 is formed by previously adding a cationic polymer resin to the thermally foamable particle suspension to aggregate the thermally foamable particles as described above. Is done.

  Thus, in order to agglomerate the thermally foamable particles with the cationic polymer resin, the concentration of the slurry composed of the thermally foamable particles, the cationic polymer resin, and water is preferably 5 to 30%, preferably 10 to 20%. If the slurry concentration is less than 5%, the viscosity of the slurry is low, and aggregates of thermally expandable particles cannot be formed, so that the yield is lowered. On the other hand, if the slurry concentration exceeds 30%, the viscosity becomes too high, the dispersion state is poor, and it is blended in granular form, so that it is detected as a foreign object when the foamed paperboard is manufactured.

  Further, the heat-expandable particles (heat-expandable particle aggregates) are contained in an amount of 1 to 15 mass%, preferably 2.1 to 7 mass% in terms of solid content with respect to the pulp solid content of each of the middle layers 12 and 13. . That is, when the content of the heat-expandable particles per layer is less than 1% by mass, the distance between the heat-expandable particles becomes long even when the aggregate of the heat-expandable particles is in a foamed state. Therefore, the foamed layer (air layer) desired by the present foamed paperboard 10 cannot be obtained, and it becomes difficult to impart water shielding properties, cold insulation properties, and heat insulation properties. On the other hand, even if the content of the heat-expandable particles per layer exceeds 15% by mass, improvement of the water-blocking property, cold-retaining property, and heat-retaining property of the foamed paperboard 10 cannot be expected, and the manufacturing cost only increases. . Moreover, even if a heat-meltable fiber, which will be described later, is blended, it becomes difficult to obtain a predetermined interlayer strength. Therefore, the interlayer strength of the present foamed paperboard 10 is reduced, and the paste when processing the foamed paperboard into a corrugated cardboard case or the like. Delamination will occur during box making and when using cardboard cases.

  The thermally foamable particles that can be used for the foamed paperboard 10 are those in which a low boiling point solvent is enclosed in a fine particle outer shell made of a thermoplastic synthetic resin. The thermally foamable particles have an average particle diameter 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 thermally foamable particles used for the foamed paperboard 10 are not limited to these. .

  However, in the present foamed paperboard 10, since the temperature of the paper drying process 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 foamed paperboard 10 are foamed by a dryer in the drying process, but for the above reasons, it is preferable to use low-temperature expansion type thermally foamable particles having an expansion start temperature of 90 to 130 ° C. is there. That is, when the expansion start temperature is less than 90 ° C., when the particles are expanded by a dryer in the drying process, the expanded particles once again contract as described above, and the middle layer is related to the thermal conductivity. It becomes difficult to create an air layer.

  Further, the cationic polymer resin used for the foamed paperboard 10 is not particularly limited as long as it is an electrolyte exhibiting a cationic property. For example, polyamine polyamide epichlorohydrin, polydiallylmethylamine epichlorohydrin, glyoxal Various types such as water-soluble resins such as those based on cationic, polyacrylamide, polyethyleneimine, and polyamine can be used.

  Further, the cationic polymer resin that can be used for the foamed paperboard 10 preferably has a molecular weight of 1,000,000 to 12 million, more preferably 3 million to 10 million.

  Moreover, in order to effectively agglomerate 1 to 15% by mass of the above-mentioned heat-expandable particles in advance, the aggregating agent is 0.5 to 3% by mass in terms of solid content as the cationic polymer resin, preferably 0.8. It is preferable to add 7 to 2.1% by mass to the thermally foamable particle suspension. When the content of the flocculant is less than 0.5% by mass, the yield of the heat-expandable particles is deteriorated, and the foamed layer cannot be formed into the desired air layer of the present application. If it exceeds 3% by mass, the agglomeration effect becomes too high, and the pulp becomes floc and the formation becomes worse. As a flocculant, Hakutron KC100 manufactured by Hakuto Co., Ltd. can be used.

  Alternatively, a paper strength enhancer can be used for the foamed paperboard 10 as a cationic polymer resin, and RB-33 manufactured by Harima Kasei Co., Ltd. can be used as the paper strength enhancer.

  Further, the foamed paperboard 10 contains at least one middle layer (in this embodiment, middle layers 12 and 13) of raw material pulp mixed with a specific hot-melt fiber. Since the foamed paperboard 10 is a multi-layer paperboard, it can be manufactured while containing the heat-meltable fibers only in the middle layers 12 and 13 and melting the heat-meltable fibers of the middle layers 12 and 13 in the papermaking process. . It is conceivable that the hot-melt fiber is mixed not only in the middle layers 12 and 13 but also in the surface layer 11. However, when the hot-melt fiber is mixed in the surface layer 11, in the dryer part or the like, Because of the possibility of adhering to tools or the like, it is preferable to mix only the middle layers 12 and 13. Also in the case of a single paper layer, the meltable hot melt fiber on the paper surface adheres to a dryer roll or the like.

  The heat-meltable fiber is contained in an amount of 1 to 10% by mass, preferably 3 to 10% by mass, more preferably 4 to 7% by mass with respect to the pulp solid content of each of the middle layers 12 and 13. By setting the content of the heat-meltable fiber to 1% by mass or more, an effect of improving the interlayer strength can be obtained. Moreover, it can avoid that recyclability falls by setting it as 10 mass% or less.

  The heat-meltable fibers include polyethylene terephthalate (PET) fiber, polyethylene (PE) fiber, EVA fiber, vinylon fiber, PVA fiber, aramid fiber, carbon fiber, rayon fiber, acrylic fiber, polyamide Various fibers such as fiber and glass fiber are known. However, in the present foamed paperboard 10, the adhesiveness with the heat-expandable particles, the adhesiveness with the pulp fiber, that the paperboard can be mixed and mixed in the raw material pulp, and melted appropriately in the paper machine drying process, From the viewpoint of adhering to pulp fibers, it is preferable to use heat-meltable fibers whose main raw materials are PET, vinylon, PE, EVA, PVA, etc. Among these, PET fibers and PVA fibers are mainly used as main raw materials. A hot-melt fiber is preferable because it does not hinder foaming of the heat-expandable particles.

  The melting temperature of the heat-meltable fiber is preferably that having a fiber surface melting temperature 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.

  Thus, the present foamed paperboard 10 does not cause trouble due to interlayer strength only when it contains a heat-meltable fiber and heat-expandable particles that are not used in ordinary paper in at least one layer of raw material pulp. In addition, it is possible to satisfy the conflicting quality of being excellent in water shielding, heat retaining properties, and cold retaining properties.

  The pulp used as the raw material for the foamed paperboard 10 is hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), hardwood sulfite. Pulp, softwood sulfite pulp, etc., chemically treated pulp, pulp treated chemically using non-wood fibers such as kenaf, hemp, straw, etc., which are fiber materials other than wood. Ground pulp that has been mechanically pulped and chips, chemi-ground pulp that has been mechanically pulped with chemicals added to wood or chips, and semi-chemical that has been cooked until softened and then refined, etc. Including virgin pulp such as pulp, kraft pulp, semi-chemical pulp, enzyme bleached pulp Used office waste paper deinked, bleached pulp, milk-packed waste paper, high-quality cut-off waste paper, coat cut-off waste paper, upper white, special white, medium white, etc., unprinted, lottery, new stage, newspaper, craft envelope, imitation, magazine Recovered pulp obtained from used paper.

  In addition, as the raw material pulp used for the middle layers 12 and 13 of the present foamed paperboard 10, the above-described various known pulps can be used, and the middle layers 12 and 13 of the present foamed paperboard 10 are made of 100% used paper pulp. Even when raw pulp is used, the interlayer strength can be maintained without affecting the expansion of the thermally foamable particles. However, if waste paper pulp is 100% blended, the drainage becomes worse due to the large number of fine fibers, and the production speed decreases. Therefore, 50% NBKP is blended in the raw pulp of the middle layers 12 and 13. Is preferred.

  Moreover, although the well-known various thing mentioned above can be used also as raw material pulp used for the back layers 14 and 15, the range which does not impair the objective of maintaining the intensity | strength of this foamed paperboard 10, without impairing water resistance performance. Therefore, it is preferable to add as much waste paper pulp as possible because it is advantageous in terms of reducing energy consumption and the burden on the environment and in terms of cost.

  The back layers 14 and 15 of the foamed paperboard 10 are (a) ensuring good bonding and boxing suitability when the foamed paperboard 10 is processed into a cardboard case, (b) ensuring strength as a cardboard case, etc. It is a layer that bears the role of. Further, since the foamed paperboard 10 accommodates frozen foods and the like that generate a lot of moisture, the foamed paperboard 10 fulfills the roles (a) and (b) described above, and affects the suitability for bonding with the core when processed into a cardboard case. It is preferable to impart water resistance to the back layers 14 and 15 within a range that does not come out.

In order to provide such water resistance, the sizing agent is 0.3 to 1.5% by mass, preferably 0.6 to 1.5% in terms of solid content, with respect to the raw material pulp of each layer of the back layers 14 and 15. was added mass%, 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.} When the water absorption is less than 30 g / m ² , the adhesiveness of the adhesive particularly during bonding between the back layer 15 and the core or during box making deteriorates, and a special adhesive is required. The solubility also deteriorates when the foamed paperboard 10 is recycled as used paper. Further, the operability is deteriorated and the manufacturing cost is increased. On the other hand, if the water absorption exceeds 80 g / m ² , the adhesive at the time of bonding and box making penetrates into the paper layers of the back layers 14 and 15, and the adhesiveness with the core becomes poor. In addition, a problem arises in that a large amount of adhesive must be applied.

  Moreover, the raw material pulp of each layer of the foamed paperboard 10 may contain an oil resistance agent, a fixing agent, a sizing agent, starch, a filler, an antifoaming agent, a paper strength enhancer, an anti-slip agent, a pH adjuster, and the like. In addition, from the viewpoint of water shielding, it is preferable that the pH of the paper surface of the foamed paperboard 10 is about 4-5. When the pH of the paper is in a neutral range, the effectiveness of the sizing agent is deteriorated, and water permeation from the surface is accelerated, resulting in poor water shielding.

  Using the above-described raw material pulp, the foamed paperboard 10 is manufactured through a known papermaking process, for example, a wire part, a press part, a dryer part, a size press, a calendar part, and the like.

  The foamed paperboard 10 is manufactured by laminating raw material pulp of the surface layer 11, the middle layers 12 and 13, and the back layers 14 and 15 in this order by a paper machine. That is, as shown in FIG. 1, the foamed paperboard 10 is a paper machine in which a middle layer 12 is laminated on the surface of the surface layer 11, a middle layer 13 is laminated on the surface of the middle layer 12, and a back surface on the surface of the middle layer 13. The layer 14 is laminated, and the back layer 15 is laminated on the surface of the back layer 14. Depending on the model of the paper machine, the layers may be stacked in the reverse order. Since the paper machine is not particularly limited, 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.

The basis weight of the foam board 10 is also changed depending on the intended use or the like, preferably in the range of 120~300g / ^{m 2,} more preferably in the range of 150 to 250 g / ^{m 2.} When the basis weight of the foamed paperboard 10 is less than 120 g / m ² , it is difficult to ensure the strength as the cardboard case when the foamed paperboard 10 is processed into a cardboard case. On the other hand, even if the basis weight is larger than 300 g / m ² , the quality is excessive and the manufacturing cost is increased.

Moreover, the total basic weight of the middle layers 12 and 13 which are the foaming layers to which water shielding was given is 25-80 g / m < ² >, Preferably it is 30-70 g / m < ² >. That is, when the total basis weight of the middle layers 12 and 13 as the foam layer is less than 25 g / m ² , even if a predetermined amount of thermally foamable particles is blended, the thickness of the foam layer is thin. In some cases, the desired water barrier cannot be provided. On the other hand, if the total basis weight of the middle layers 12 and 13 exceeds 80 g / m ² , the basis weight of the present foamed paperboard 10, that is, the basis weight of the entire paperboard is almost clear, although it is excellent in terms of imparting water shielding properties. The basis weight of the layers other than the middle layers (foamed layers) 12 and 13, that is, the surface layer 11 and the back layers 14 and 15 inevitably decreases in this embodiment. For this reason, it becomes difficult to ensure the strength required for a cardboard case for protecting and storing the contents. Although it is possible to increase the basis weight of the layers other than the middle layers 12 and 14 which are the foam layers, problems such as an increase in manufacturing cost occur, which is not practical.

The total basis weight of the backing layer 15 is also changed by the basis weight of the layer structure and other layers of the foam board 10, preferably in a 60~175g / ^{m 2,} 60~150g / ^{m 2} is more preferable. It is preferable to make the basis weight of the back layers 14 and 15 as large as possible because it is advantageous in terms of cost.

Moreover, it is preferable that the density after foaming of this foamed paperboard 10 shall be 0.35-0.6 g / cm < ³ >. More preferably, it is 0.35-0.45 g / cm < ³ >. When the density is less than 0.35 g / cm ³ , the foamed paperboard 10 is excellent in water shielding properties, but even when a predetermined heat-meltable fiber is contained, the interlayer strength is weak and a desired effect can be obtained. Can not. On the other hand, if the density exceeds 0.6 g / cm ³ , the water shielding effect is low, and it is difficult to solve the problems of the present invention.

Further, since the surface layer 11 of the present foamed paperboard 10 is often printed, the surface of the surface layer 11 of the present foamed paperboard 10 is adjusted as necessary in order to improve the surface strength or adjust the slipperiness. It is preferable to apply a coating solution containing a water-soluble 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 in this field. A variety of commonly used known materials can be used alone or in admixture of two or more. In addition, favorable printability can be obtained by setting the coating amount of the water-soluble substance to 0.5 to 3.5 g / m ² , preferably 0.7 to ² g / m ² .

  Further, if a coating liquid mainly composed of a pigment and a binder is applied on the surface of the present foamed paperboard 10 by using a coating apparatus, more beautiful printing can be performed.

  Further, the surface of the foamed paperboard 10 may be smoothed. This smoothing treatment is preferably performed, for example, by subjecting the foamed paperboard to a pressure treatment between rolls that can be pressurized. When performing the smoothing treatment, the roll in contact with the surface of the surface layer 11 of the foamed paperboard 10 preferably has a smooth surface and is a heatable metal roll. In addition, the smoothing process in the foamed paperboard 10 is a process of making the foamed paperboard 10 in the process of making the foamed paperboard 10 in addition to the smoothing process described above, for example, a calendar process (machine) with a pair of metal rolls or a pair of metal rolls. Calendar processing using a calendar), calendar processing using a calendar roll provided with one or more metal rolls and resin rolls (calender processing using a soft calendar), drying processing using a Yankee dryer, and the like.

  The foamed 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 foamed 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 foamed 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 middle layers 12 and 13 and further the back layers 14 and 15. Also penetrates to the outer surface of the cardboard case. As a result, the appearance of the corrugated cardboard case 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 of the cardboard case is reduced, and the role as the cardboard case cannot be achieved.

  The foamed 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 foamed paperboard 10 contains frozen foods that are individually packaged and is often used in cardboard cases used for transportation and storage. Therefore, when the thermal conductivity is higher than 0.05 W / mk, The temperature of the outside air is transmitted to the inside of the corrugated cardboard case, and the frozen food may be melted, so that it is not possible to ensure cold insulation and heat insulation.

  As described above, the foamed paperboard 10 has been described with respect to the case where the paper layer is composed of five paper layers of the surface layer 11, the middle layers 12, 13 and the back layers 14, 15 as shown in FIG. Not limited to the paper layer configuration, for example, a foamed paperboard 10 ′ composed of four paper layers as shown in FIG. 2 and a foamed paperboard 10 ″ composed of three paper layers as shown in FIG. 3 may be used. That is, the foamed paperboard 10 ′ shown in FIG. 2 is composed of four paper layers: a surface layer 11, two middle layers 12 and 13 which are foamed layers with water shielding properties, and a single back layer 15. Yes. Thus, even if the back layer is a single layer, it is possible to obtain foamed paperboard having the desired effect of the present invention. Also, the foamed paperboard 10 ″ shown in FIG. 3 is composed of three paper layers: a surface layer 11, one middle layer 12 which is a foamed layer provided with water barrier properties, and one back layer 15. . Even with such a configuration, it is possible to obtain foamed paperboard to which the desired effect of the present invention has been imparted. In addition, the foamed paperboard according to the present invention may be a paper layer of 6 layers, 7 layers,... By increasing the number of middle layers. In this case, at least one of the middle layers is provided with water shielding properties. If it is the made foam layer, the effect which this invention desires can be acquired.

  In addition, the case where the foamed paperboard 10 is processed into a corrugated cardboard case has been described. However, the foamed paperboard 10 is processed into a paper container or the like so that the surface layer 11 is an inner surface and the back layer 15 is an outer surface. Also, the desired effect of the present invention can be obtained.

  In order to confirm the effect of the foamed 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.

  29 types of paperboards according to the present invention (referred to as “Example 1” to “Example 29”) were prepared as shown in Table 1, and compared with Examples 1 to 29. In order to study, three types of paperboards (referred to as “Comparative Example 1” to “Comparative Example 3”) were prepared in the configuration shown in Table 2. Further, as a reference example, a general corrugated base paper for exterior was evaluated.

[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> Middle layer (1) (2)
Middle layer (1 ) And (2), 0.7% by mass of sulfuric acid band and 0.5% by mass of sizing agent (trade name: R-22, manufactured by Modern Chemical Co., Ltd.) in terms of solid content, dry paper strength An enhancer (trade name: Hermide RB-32, manufactured by Harima Chemicals Co., Ltd.) is 0.7 mass% in terms of solid content, and a wet paper strength enhancer (Epichlorohydrin manufactured by Seiko PMC Co., Ltd.) is 0 in terms of solid content. Add 3 wt%. In addition, in the raw pulp for the middle layer (1) (2), a thermally foamable particle suspension in which thermally foamable particles (trade name: Matsumoto Microsphere F-46, manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) are blended, A cationic polymer resin (trade name: Haktron KC100, Hakuto Co., Ltd.) is mixed in advance to agglomerate the heat-expandable particles to form a heat-expandable particle aggregate. It should be noted that 4.2% by mass of thermally foamable particles are added to the solid content of the pulp, 1.4% by mass of the cationic polymer resin is added to the solid content of the pulp, and further, a hot-melt fiber. (Kuraray Sophit N720) is added in an amount of 5% by mass. Then, the pH of the raw material pulp for the middle layer (1) (2) was adjusted to 4.5, and the raw material slurry for the middle layer 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 raw material pulp for the back layer with the disaggregation freeness 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 middle layer (1) and (2), and the back layer paper layer are made together by a circular four-layer paper machine, and the basis weight of the surface layer is 30 g / m ² , the middle layer ( 1) and a basis weight of 60 g / ^{m 2} (2), a basis weight of 80 g / ^{m 2} of the backing layer, foam board having a basis weight of entire foamed paperboard paper making four layers is 170 g / ^{m 2} (example 1 )

  [Examples 2 to 7] Foamed paperboard obtained in the same manner as in Example 1 except that the content of thermally expandable particles added to the middle layers (1) and (2) was changed as shown in Table 1. .

  [Examples 8 to 12] Foamed paperboard obtained in the same manner as in Example 1 except that the content of the hot-melt fiber added to the middle layers (1) and (2) was changed as shown in Table 1. .

  [Examples 13 to 14] Example 1 is the same as Example 1 except that the heat-expandable particles added to the middle layers (1) and (2) were those whose expansion start temperature was changed as shown in Table 1. Foamed paperboard obtained in the same manner.

  [Examples 15 to 18] Foamed paperboard obtained in the same manner as in Example 1 except that the content of the cationic synthetic resin added to the middle layers (1) and (2) was changed as shown in Table 1. .

  [Examples 19 to 23] Except for changing the kind of the cationic synthetic resin added to the middle layers (1) and (2) to a paper strength enhancer and changing the content as shown in Table 1, Foamed paperboard obtained in the same manner as in Example 1. In addition, RB-33 by Harima Kasei Co., Ltd. was used as a paper strength enhancer.

  [Examples 24 to 25] As the hot-melt fiber added to the middle layers (1) and (2), except that the melt start temperature was changed as shown in Table 1, and Example 1 was used. Foamed paperboard obtained in the same manner.

  [Example 26] A heat-meltable fiber added to the middle layer (1) having a melting start temperature of 130 ° C is used. For the middle layer (2), heat-expandable particles, a cationic polymer resin, and heat-melting are used. A foamed paperboard obtained in the same manner as in Example 1 except that the synthetic fiber was not added.

  [Example 27] Foamed paperboard obtained in the same manner as in Example 1 except that the heat-expandable particles, the cationic polymer resin, and the heat-meltable fiber were not added to the middle layer (2).

  [Examples 28 to 29] Foamed paperboard obtained in the same manner as in Example 1 except that the total basis weight of the middle layers (1) and (2) was changed as shown in Table 1.

  [Comparative Example 1] As shown in Table 2, Example 1 except that the thermally foamable particles and the cationic polymer resin in the middle layers (1) and (2) were not added and the middle layer was not made into a foamed layer. Paperboard obtained in the same way.

  [Comparative Example 2] As shown in Table 2, foamed paperboard obtained in the same manner as in Example 1 except that the cationic polymer resins of the middle layers (1) and (2) were not added.

  [Comparative Example 3] Without adding the cationic polymer resin to the heat-expandable particle suspension in advance, the heat-expandable particle suspension is added to the raw materials of the middle layers (1) and (2), and then the raw materials A foamed paperboard obtained in the same manner as in Example 1 except that a cationic polymer resin was added to the paperboard.

  [Reference Example] “Just K Liner” made by Daio Paper Co., Ltd., which is a general corrugated base paper for exterior use, was used.

In Table 1 and Table 2, “total basis weight of foamed layer (g / m ² )” means that each sample was delaminated according to the following procedure, and “paper and paperboard—basis weight measurement” described in JIS-P8142. It is the value of the total basis weight of the middle layer (1) or the middle layers (1) and (2), which is a foamed layer, measured according to “Method”.

  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 peels off, and this is used to separate the layers into the back layer, the middle layer (1) (2), and the surface layer. After delamination, each layer of each sample was sufficiently dried with a hot air dryer or the like and used for the test.

  Quality evaluation for all of these examples, comparative examples, and reference examples, that is, evaluation tests for basis weight, density, interlayer strength, water shielding, cold insulation, heat insulation, and remaining amount of foamed particles in white water of paperboard (all layers) The results of performing are as shown in Table 3.

In addition, “basis weight (g / m ² )” in Table 3 is the basis weight of all the layers of each sample, that is, the entire foamed paperboard, and “paper and paperboard—basis weight measuring method” described in JIS-P8142. It is a value measured in compliance.

“Density (g / cm ³ )” refers to the basis weight measured in accordance with “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)” means “J. 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. That is, the water-impervious evaluation test is a method of folding, vertical, horizontal, and height so that there is no seam 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. Made a container of 15 cm each, then put 200 cc of distilled water into this container, capped the container with a polyethylene sheet, transferred the distilled water in the container to a graduated cylinder after 20 hours, and distilled The remaining amount of water was measured and evaluated, and the water shielding rate (%) of foamed paperboard = [residual amount of distilled water / 200 cc] was measured from the remaining amount of distilled water. The distilled water was adjusted to 23 ° C. ± 1 ° C., and the water-imperviousness evaluation test was performed at a temperature of 23 ° C. ± 1 ° C. and a humidity of 50% ± based on the “standard state of test place” described in JIS-Z8703. Performed under 2% condition.

  “Cold insulation rate (%)” is a value measured based on the following cold insulation evaluation test. In other words, the cold insulation evaluation test is a method of folding, vertical, horizontal, and height so that there is no seam between the four side surfaces and the side surface and the bottom surface so that the surface layer of each sample, which is foam paperboard, is the inner surface of the container. Make a 5cm rectangular parallelepiped container, put 27g ice prepared by freezing distilled water in a freezer for 24 hours in this container, cover the container, and after 90 minutes the ice remaining in the container This is a test in which the mass (remaining amount of ice) was calculated by mass%. 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 thermal conductivity, 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.

Further, the “foamed particle residual amount (white water)” is an evaluation visually determined based on the following foamed particle residual amount test in white water. In the white water test, the remaining amount of foamed particles is obtained by collecting 300 cc of white screened water collected during paper making using a paper machine into a glass graduated cylinder. In this test, only residual particles are removed from the filter paper No. 2 and the filter paper is heated for 1 minute with a dryer at 100 to 130 ° C. to evaluate the remaining amount of the expanded particles. The evaluation criteria were the following three levels.
(Evaluation criteria)
A: A small amount of thermally foamable particles remain on the filter paper.
○: A small amount of thermally foamable particles remain on the filter paper.
X: A large amount of thermally foamable particles remain on the filter paper.

As shown in Table 3, the foamed paperboard according to the present invention, i.e., the paperboard according to Examples 1 to 26, is excellent in quality evaluation, i.e., excellent in water-insulating properties, cold-retaining properties, and heat-retaining properties, and thermal foaming. It can be seen that the yield of the conductive particles is high, and further, 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 which shows the layer structure of the foamed paperboard which concerns on this invention. It is a schematic sectional drawing which shows the layer structure of the foamed paperboard which concerns on the example of a change of this invention. It is a schematic sectional drawing which shows the layer structure of the foamed paperboard which concerns on the other modification of this invention.

Explanation of symbols

10, 10 ', 10 "Foamed paperboard 11 Surface layer 12, 13 Middle layer 14, 15 Back layer

The object of the present invention is to form a cationic polymer resin in advance in terms of solid content in an amount of 0.5 to 3 in a foamed paperboard having a layer structure having at least a surface layer, a single layer or a plurality of layers, and a back layer. It was added mass%, by aggregating heat expandable particles of thermally foamable particle suspension to form a heat-expandable particles aggregate, was added to the middle layer at least one layer, the intermediate layer and the foam layer, The foamed layer contains 1 to 15% by mass of the 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. And J. TAPPI No. This is achieved by providing a foamed paperboard having an interlayer strength defined by 18-2 of 75 mJ or more .

An object of the present invention is to provide a cationic polymer resin having a molecular weight of 1,000,000 to 12 million in advance in a foamed paperboard having a layer structure having at least a surface layer, a single layer or a plurality of layers, and a back layer. Thermally expandable particle suspension having a slurry concentration of 5 to 30%, in which 0.5 to 3% by mass in terms of solid content is added to aggregate the thermally expandable particles to form a thermally expandable particle aggregate. and the intermediate layer of at least one layer, on pulp solids, the heat expandable particles was added to a 1 to 15 wt% in terms of solid content, the intermediate layer and the foam layer, emitting foam layer to the thermally fusible fibers containing 1 to 10 wt% on pulp solids, also a total basis weight of the foam layer and 25~80g / ^{m 2,} further J. TAPPI No. This is achieved by providing a foamed paperboard having an interlayer strength defined by 18-2 of 75 mJ or more and a water shielding rate of 81 to 92% .

In addition, the object of the present invention is that the heat-meltable fiber is a heat-meltable fiber mainly made of PET fiber, and a sizing agent is added to the raw material pulp of the back layer in a solid content conversion of 0.3. was added to 1.5 wt%, by providing a foam paperboard, characterized in that a 30 to 80 g / ^{m 2} and the water absorption degree measured according to JIS-P8140, is more effectively achieved.

Furthermore, the above object of the present invention can be achieved more effectively by providing a foamed paperboard having a thermal conductivity of 0.05 W / mk or less .

Claims (4)

In the foam paperboard having a layer structure having at least a surface layer, a single layer or a plurality of layers, and a back layer,
A heat-expandable particle suspension prepared by adding a cationic polymer resin in advance to agglomerate the heat-expandable particles to form a heat-expandable particle aggregate is added to at least one intermediate layer, and the intermediate layer is A foamed paperboard characterized by having a foamed layer. The foamed layer contains the heat-foamable particles in an amount of 1 to 15% by mass in terms of solid content with respect to the pulp solid content, and 1 to 10% by mass of the hot-melt fiber in the pulp solid content. J. et al. TAPPI No. 2. The foamed paperboard according to claim 1, wherein the interlayer strength defined by 18-2 is 75 mJ or more. The foamed paperboard according to claim 1 or 2, wherein the thermal conductivity is 0.05 W / mk or less. The foamed paperboard according to any one of claims 1 to 3, wherein the water barrier property is 81% or more.

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