JP4268980B2 - Multilayer paperboard and packaging container using this multilayer paperboard - Google Patents

Description

  The present invention relates to a multi-layer paperboard and a packaging container using this multi-layer paperboard. More specifically, the present invention has a low thermal conductivity, excellent heat insulation and heat retention, and corrugated cardboard sheets and corrugated cardboard packaging containers. The present invention relates to a multilayer paperboard having excellent processing, box making, and bonding suitability for interior packaging containers and the like, and further excellent printability, and a packaging container using the multilayer paperboard.

  Styrofoam in which polystyrene raw materials are mainly inflated with a foaming agent such as butane for packaging materials and cushioning materials for fresh products that require heat insulation and heat insulation, and insulation materials for construction, etc. has good moldability. Since it is inexpensive and lightweight, it has been used in large quantities.

  However, the foamed polystyrene has a problem that the load on the environment is large at the time of disposal.

  That is, if these sheets are disposed of by incineration, the incinerator is damaged because of the high calorie burn, and air pollution is caused by black smoke and pollutants. On the other hand, when discarded by landfill processing, it is difficult to decompose and bulky, so it remains in the soil as it is and shortens the life of the landfill site. Separate collection and recycling are also being considered, but no fundamental measures have been established from the viewpoint of collection and recycling costs.

  On the other hand, paper is low in calories burned, generates little smoke and harmful substances due to combustion, and is easily decomposable. Therefore, attempts have been made to develop paper having heat insulation properties and heat retaining properties instead of polystyrene foam. Yes.

  Various types of foamed paper using foamable microcapsules that foam by heating have been proposed as paper having excellent heat insulation and heat retention. This foamable microcapsule is one in which a low-boiling agent such as butane gas is encapsulated in a fine particle outer shell of a thermoplastic synthetic resin such as a copolymer of methacrylic acid and styrene, a copolymer of acrylonitrile and styrene, or vinylidene chloride. Yes, the outer shell is softened by heating, and a low-boiling solvent such as butane gas is vaporized and expanded to form a microballoon that is a hollow closed cell (see, for example, Patent Document 1 and Patent Document 2). .

  As a method of imparting heat insulation and heat retention to paper using foamable microcapsules, an internally added papermaking method in which paper is made by mixing thermally foamable particles with pulp raw materials, or in the middle of the paper manufacturing process There are known a method of spraying thermally impregnated particles on a wet paper wet containing a large amount of water, a method of impregnating, and the like.

  As a method for internally adding thermally foamable particles, for example, as shown in Patent Document 3 and Patent Document 4, 5-30 μm foamable microcapsules are mixed with pulp, and the water content before heating foaming is adjusted to general papermaking. A method has been proposed in which foamable microcapsules are foamed by heating and drying to a bulky and lightweight paper by making it much larger than the amount of water in the paper.

  Further, Patent Document 5 discloses a paper base having a water content of 50 to 60% by weight obtained by blending foamable microcapsules into papermaking raw materials mainly composed of paper pulp, and mainly foamable microcapsules and rubber latex. And / or impregnating liquid consisting of synthetic resin emulsion is impregnated with a wet impregnation method in an amount of 5 to 40% by weight with respect to the raw material for papermaking, and then the foamable microcapsules are foamed by heating. A manufacturing method is disclosed.

  However, all of the foamed papers described in Patent Documents 3 to 5 have foamable microcapsules foamed so that the entire paper layer is porous, and the microballoons in which the microcapsules are foamed hinders the binding between pulp fibers. There is a problem in that the strength and peel strength between paper layers are greatly reduced, and they are easily torn or torn.

In other words, when the paper obtained above is used after being processed into a packaging container that requires heat insulation and heat retention,
(A) The foamed microballoon hinders the bonding between the fibers, and the compressive strength and burst strength as a packaging container are weak, so that the strength required for the packaging container cannot be secured, and the packaging container is crushed.
(B) The peel strength between the paper layers is low, and peeling occurs due to the paper delamination at the joint portion and the flap portion of the packaging container.
(C) The surface strength is weak, and the surface of the packaging container is peeled and torn by rubbing during transportation and movement.
(D) Since the thermally foamable particles have a porous property distributed throughout the paper layer, a large amount of adhesive is absorbed during pasting and boxing. Therefore, the adhesive is consumed more than necessary, leading to an increase in manufacturing cost. Moreover, the heat insulation inherent to foamed paper is hindered and lowered by the adhesive absorbed in a large amount in the paper layer.
Such a problem arises, and it is not suitable as paper used for packaging containers that require heat insulation and heat retention.

  In addition, in the foamed paper described in Patent Document 3 and Patent Document 4, foaming microcapsules are mixed with raw pulp to make paper, but the foaming microcapsules only physically stay in the form of pulp fibers. The yield on the paper machine wire is very poor, and the problem arises that excessively expensive foamable microcapsules must be mixed into the raw pulp.

  Further, for example, Patent Document 6 discloses a foamed paper manufacturing method in which a foamed microcapsule dispersion is spray-added to a wet paper obtained by papermaking in a paper machine wire part. , Foam for inkjet recording, in which foamed microcapsule dispersion is spray-coated on wet paper made from wood pulp as the main raw material, the foamable microcapsules are distributed in the paper layer, and the size is adjusted to a certain range The base paper is disclosed.

  However, the foamed papers described in Patent Document 6 and Patent Document 7 are both spray-coated with a dispersion of foamable microcapsules on wet paper that retains a large amount of water during the paper manufacturing process. This is a manufacturing method in which foamable microcapsules are distributed not on the paper surface but on a paper layer, and a foam base paper for ink jet recording. Similarly to the above, the microballoons in which the microcapsules are foamed prevent the binding between pulp fibers, thereby reducing paper strength and paper. Since the peel strength between the layers is low, it is easily torn or torn, and is not suitable as a packaging container.

  Moreover, although there is no prior art document, it is also conceivable to obtain foamed paper by coating a coating liquid containing thermally foamable particles on the paper surface on or off machine.

  However, in such foamed paper, since the heat-foamable particles are not fixed on the paper surface by itself, the coating liquid comprising the heat-foamable particles and the binder is applied to the paper surface by a coating machine, and then heated. Must be manufactured by foaming.

  Thus, when a binder is mix | blended in a coating liquid, foaming of a thermally foamable particle is suppressed by this binder. For this reason, the heat insulation effect and heat retention effect which are expressed when the heat-expandable particles are appropriately foamed cannot be obtained, and such paper cannot be used for a packaging container which requires heat insulation and heat retention.

  Also, if the amount of thermally foamable particles added is increased, not only will the production cost of foamed paper increase, but the heat-foamable particles will reduce the surface strength of the paper and reduce the suitability for processing, box making and bonding. At the same time, the printability also decreases.

  Furthermore, the method for producing foamed paper by applying a coating liquid containing the thermally foamable particles and the binder to the paper surface requires that the coating amount of the coating liquid be limited to a certain amount or less. The thickness of the coating layer is reduced, and the content of thermally foamable particles is reduced. For this reason, since it is thought that it is inferior to the above-mentioned internal addition method and impregnation method in terms of imparting heat insulating properties and heat retaining properties to paper, it is considered that it has not been put into practical use.

Japanese Examined Patent Publication No. 42-26524 Japanese Patent Publication No. 44-7344 JP-A-5-339898 JP-A-10-88495 JP-A-8-226097 JP 2001-98494 A JP 2002-46342 A

  The invention of the present application has been made in view of the above-mentioned circumstances, and the object is to have excellent heat insulation and heat retention, and to process / paste into a corrugated cardboard sheet, a corrugated cardboard packaging container, an interior packaging container, etc. It is an object of the present invention to provide a multi-layer paperboard having excellent suitability for box making and printing, and a packaging container using the multi-layer paperboard.

The object of the present invention is to apply a coating liquid containing at least hollow inorganic particles, thermally expandable particles, and a binder to at least one side of a base paper, and expand the thermally expandable particles by a dryer in the drying step. This is achieved by providing a multilayer paperboard characterized by providing a foamed coating layer.

Further, the object of the present invention is to provide a multilayer paperboard characterized in that the coating amount of the coating liquid is 0.4 to 10 g / m ² in terms of solid content per side. Is achieved.

  The above-mentioned object of the present invention is more effective by providing a multilayer paperboard characterized in that the multilayer paperboard has a thermal conductivity of 0.03 to 0.06 W / m · K. Is achieved.

  Furthermore, the above object of the present invention can be achieved more effectively by using the multilayer paperboard according to any one of claims 1 to 3 for a packaging container.

  According to the multilayer paperboard according to the present invention, since at least one surface of the base paper is coated with a coating solution containing at least hollow inorganic particles, thermally foamable particles, and a binder, a coating layer is formed. Insulation and heat insulation. Furthermore, it is excellent in processing, bonding, box making, and printing suitability for corrugated cardboard sheets, corrugated packaging containers, and interior packaging containers.

  In addition, the multilayer paperboard according to the present invention can obtain excellent heat insulation and heat retention without bonding, for example, paperboard and foamed paper. Simplification can be achieved.

  Furthermore, since the multilayer paperboard according to the present invention has excellent surface strength, it is difficult to cause ruled line cracking or the like when processing the paperboard into a corrugated cardboard sheet, a corrugated cardboard packaging container, an interior packaging container, etc. It is difficult for paper to be peeled off or torn due to rubbing when transporting, storing or protecting containers.

Moreover, since the thermal conductivity can be further lowered by setting the coating amount of the coating liquid to 0.4 to 10 g / m ^{2 in} terms of solid content per side, a multilayer having superior heat insulation and heat retention. It becomes paperboard.

  Furthermore, by setting the thermal conductivity of the multilayer paperboard to 0.03 to 0.06 W / m · K, more excellent heat insulation and heat retention can be imparted.

  Hereinafter, the multilayer paperboard according to the present invention will be described in detail, taking as an example the case where the base paper is composed of three paper layers, a surface layer, an intermediate layer, and a back layer. The multilayer paperboard according to the present invention is not limited to the following embodiments, and it goes without saying that the configuration can be changed as appropriate without departing from the scope of the claims.

  The multilayer paperboard according to the present invention (hereinafter referred to as “main paperboard”) is a base paper made up of three paper layers: a surface layer, a back layer, and a single middle layer disposed between the front and back layers. And a coating layer containing at least hollow inorganic particles, thermally foamable particles, and a binder is applied to at least one side of the base paper.

  The coating liquid applied to at least one surface of the base paper of the present paperboard contains hollow inorganic particles. As the hollow inorganic particles, inorganic materials such as silicon, aluminum, titanium, calcium, and magnesium are baked. Hollow shaped inorganic pigments are used.

  Moreover, such hollow inorganic particles have an average particle diameter of 0.1 to 40 μm. Thereby, since the hollow inorganic particles can be satisfactorily applied to the surface of the base paper of the paperboard, desired heat insulation can be imparted to the paperboard.

  When the average particle diameter exceeds 40 μm, problems such as low heat insulation and low surface strength occur.

  On the other hand, if the average particle size is less than 0.1 μm, the surface strength is increased, and in order to obtain the desired processing, box making, pasting suitability, and printing suitability, the blending amount of the binder must be increased. As a result, the coating amount of the coating solution must be increased. Such an increase in the coating amount of the coating liquid causes a problem that the viscosity of the coating liquid increases with an increase in the concentration of the coating liquid and the drying property is deteriorated.

  Further, the porosity of the hollow inorganic particles is preferably 93 to 20%, and more preferably 90 to 48%, in order to improve the heat insulating property of the present paperboard.

  Examples of such hollow inorganic particles include hollow silica particles, hollow alumina particles, and hollow magnesium particles. Specific examples include “Senolite M-732C”, “SZ-3”, “DH” and the like manufactured by Sakai Kogyo Co., Ltd.

  Moreover, the coating liquid applied to the base paper of the present paperboard also contains thermally foamable particles. Thereby, heat insulation and heat retention can be provided to this paperboard.

  The heat-expandable particles used in the coating liquid applied to this paperboard are those in which a low-boiling solvent is enclosed in a fine particle outer shell composed of a thermoplastic synthetic resin. The average particle diameter of the heat-expandable particles is 5 to 30 μm.

  Examples of the thermoplastic synthetic resin constituting the outer shell of the thermally foamable particles 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.

  Such heat-expandable particles are heated at 80 to 200 ° C. to evaporate the low-boiling solvent encapsulated to increase the vapor pressure, expand the outer shell to form closed cells, and have a diameter of 4 to 5 times, volume expands 50-130 times. In addition, since the temperature of the drying process in the paper making process and the paper manufacturing process is 80 to 200 ° C., the foaming start temperature of the thermally foamable particles is more preferably 80 to 60 ° C., and the maximum expansion is achieved. The temperature is preferably 120 to 190 ° C.

  In the drying step, the thermally foamable particles are expanded and foamed by a drier so that the board becomes bulky, and heat insulation and heat retention are imparted to the board. The heat for expanding and foaming the thermally foamable particles may be expanded by a single heating to a desired size of the paperboard, or expanded to a certain size by a dryer, and thereafter By heating again, the thermally foamable particles may be expanded to a desired size and foamed.

  Examples of such thermally foamable particles include “Matsumoto Microsphere F-30D”, “F-30GS”, “F-20D”, “F-50D” manufactured by Matsumoto Yushi Seiyaku Co., Ltd., Various known products such as “Expancel WU” and “Same DU” manufactured by Nippon Philite Co., Ltd. can be used. However, synergistically enhancing the heat insulating property imparted to the paperboard together with the heat insulating property imparted to the paperboard by the hollow inorganic particles, the particle size of the thermally foamable particles before expansion, the coating suitability of the coating liquid, and drying From the viewpoint of foamability in the process, heat-expandable particles made of an acrylic copolymer are particularly preferable.

  In this way, in addition to the hollow inorganic particles, by containing thermally foamable particles in the coating liquid, the coating layer can be made bulky and more thick, so that heat insulation and heat retention can be added to the main paperboard. Can be granted.

  Furthermore, the coating liquid applied to the base paper of the present paperboard contains a binder. As a result, the surface strength of the paperboard can be improved, and the ruled line breakage when the paperboard is processed into a corrugated cardboard sheet, a corrugated cardboard packaging container, an interior packaging container, etc. (hereinafter simply referred to as “container etc.”) Occurrence, paper peeling due to rubbing during transportation and storage of processed containers, tearing, etc. can be prevented.

  As the binder of the coating liquid for the board, various known ones such as vinyl acetate, acrylic, polyvinyl alcohol (PVA), styrene / butadiene copolymer latex (SBR), starch, polyacrylamide (PAM), and the like can be used. Can be used.

  However, since the coating liquid applied to the paperboard also contains hollow inorganic particles and thermally foamable particles as described above, the surface strength of the paperboard may be reduced depending on the type and properties of the binder. is there.

  Although the binder having high hardness is excellent in the effect of improving the surface strength, it inhibits the expansion and foaming of the thermally foamable particles. That is, the heat-expandable particles can be heated and expanded to be foamed to make the coating layer bulky, thereby imparting heat insulation and heat retention to the paperboard. Therefore, if the expansion / foaming of the thermally foamable particles is hindered, it becomes impossible to impart heat insulation and heat retention to the paperboard.

  Furthermore, this paperboard is premised on processing into a container etc. which require heat insulation and heat retention. For this reason, when this paperboard is processed into a container or the like, a strong bending force is applied to the ruled line part (folded part), but even in this case, the coating layer does not break, that is, the ruled line crack occurs. It is required not to.

  For this reason, it is particularly preferable to use SBR among the various binders described above. That is, SBR has good adhesion to hollow inorganic particles and thermally foamable particles, does not hinder expansion and foaming of thermally foamable particles, and has a soft property (hereinafter referred to as “elongation”). Therefore, the problem of ruled line cracking when processing the paperboard into a container or the like is less likely to occur.

  Furthermore, when the glass transition temperature of the binder is −50 to 30 ° C., more preferably −30 to 20 ° C., the viscosity of the coating liquid at the time of coating is low, and the expansion / foaming of the thermally foamable particles is inhibited. In addition, the sheet is excellent in bendability, and after drying, the effect of improving the surface strength of the paperboard can be obtained, and the paperboard processing, box making and bonding suitability are further improved.

  As described above, the coating liquid to be applied to the surface of the base paper of the present paperboard may be a known one such as a pigment as long as it contains at least hollow inorganic particles, thermally foamable particles, and a binder. Various things may be contained.

The hollow inorganic particles and the thermally expandable particles can be internally added to the raw material pulp of each layer constituting the base paper, but the specific gravity of the hollow inorganic particles is 0.5 to 0.9 g / cm ³ . The specific gravity of the thermally foamable particles is 0.9 to 1.2 g / cm ³ . Therefore, when these are added internally, it is difficult to uniformly disperse in the thickness direction during papermaking, and heat insulation (including heat insulation by a synergistic effect of hollow inorganic particles and thermally foamable particles) is effectively imparted to the paperboard. I can't.

  In addition, when hollow inorganic particles or heat-expandable particles are internally added to the raw material pulp, it is necessary to increase the blending amount of the hollow inorganic particles or heat-expandable particles in order to give the paperboard the desired heat insulation. Such an increase in the amount of particles causes an increase in production cost, and in terms of quality, the surface strength decreases, various strengths such as compressive strength, burst strength, tensile strength, and tear strength, and printability decrease. Problems such as the occurrence of curling due to the difference between the front and back sides arise.

  For this reason, it is preferable to apply a coating liquid containing at least hollow inorganic particles, thermally foamable particles, and a binder to at least one surface of the base paper to form a coating layer.

  The blending ratio of the hollow inorganic particles and the thermally expandable particles is preferably absolutely dry weight%, and is preferably hollow inorganic particles: thermally expandable particles = 5 to 90%: 95 to 10%, and hollow inorganic particles: thermally expandable particles = 20 to 80%: 80 to 20% is more preferable.

  The content of the binder is preferably 5 to 30 parts by weight (absolutely dry parts) with respect to 100 parts by weight (absolutely dry parts) of the mixture of hollow inorganic particles and thermally foamable particles, and 8 to 20 parts by weight. It is more preferable to contain (absolute dry weight part).

  When the binder content is less than 5 parts by weight with respect to the hollow inorganic particles and the heat-expandable particles, the adhesion between the hollow inorganic particles and the heat-expandable particles is lowered. On the other hand, even if the binder content exceeds 30 parts by weight, the adhesiveness of the hollow inorganic particles and the thermally foamable particles and the foaming effect of the thermally foamable particles are hardly improved, and only the production cost is increased.

Such coating solution on at least one surface of the base paper, 0.4~10g / ^{m 2} on one surface per solids, preferably to form a coating layer by coating 1 to 6 g / ^{m 2.}

  In addition, as a method of applying the coating liquid, it can be applied to the surface of the base paper by a known coating means such as a bar coater, a rod coater, or an air knife. Moreover, it can also print by well-known printing means, such as a gravure printing machine and a flexographic printing machine. Among these, a coating machine such as a rod coater or an air knife capable of arbitrarily changing the coating amount of the coating liquid is preferable.

  Moreover, it is preferable to perform a calendar process on the base paper in the previous step of applying the coating liquid. As a result, the surface of the base paper becomes dense and the coating liquid can be efficiently retained on the surface of the base paper, so that excellent heat insulation can be imparted to the present paperboard.

  In addition, after applying the coating liquid in the paper making process and foaming the thermally foamable particles, calendering is performed, and the smoothness of the paperboard is 5 to 50 seconds, preferably 10 to 50 seconds. Suitability can be imparted to the paperboard.

  In addition, it is preferable that the calendar process performed after apply | coating a coating liquid is a soft calendar process rather than the calendar process using a steel roll.

  In other words, in order not to impair the heat insulating property imparted to the present paperboard, it is necessary to ensure a sufficient thickness of the coating layer, and in the case of soft calendering, printing is performed while suppressing a decrease in paper thickness. The aptitude can be increased. Thereby, printability can be improved without deteriorating the heat insulating property and heat retaining property imparted to the paperboard.

Moreover, the density of this paperboard after apply | coating a coating liquid is 0.7-0.9 g / cm < ³ >.

  Thereby, this paperboard can make thermal conductivity 0.03-0.06 W / m * K, and has the outstanding heat insulation and heat retention. Although it is possible to set the thermal conductivity to less than 0.03 W / m · K, there is a risk of increasing the manufacturing cost, lowering operability, and lowering the quality of the product such as surface strength and surface property. In addition, when the thermal conductivity exceeds 0.06 W / m · K, the heat insulating property and the heat retaining property are deteriorated, and the synergistic effect by the combination of the hollow inorganic particles and the thermally foamable particles of the present invention may be reduced. is there.

  Below, the base paper of this paperboard is demonstrated.

  As described above, the base paper of the present paperboard is composed of three paper layers including a front layer, a back layer, and a single middle layer disposed between the front and back layers.

  This paperboard is premised on being processed into a container used for transportation, storage and protection.

  Therefore, the surface layer of this paperboard is (1) excellent in processing, box making and pasting suitability, and prevents cracking of ruled lines when processing paperboard into containers, etc. (2) It has high surface strength and content Transport, storage, protection, (3) It has coating suitability for coating liquid containing hollow inorganic particles, heat-foamable particles and binder, (4) It is a layer responsible for functions such as ensuring printing suitability. is there.

  Examples of surface pulp include hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), and hardwood semi-bleached kraft pulp (LSBKP). Chemical pulps such as softwood semi-bleached kraft pulp (NSBKP), hardwood sulfite pulp, softwood sulfite pulp, stone grand pulp (SGP), pressurized stone grand pulp (PGW), refiner grand pulp (RGP), thermo grand 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, corrugated waste paper, upper white Waste paper, Kent waste paper, imitation Chemically or mechanically 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, straw, etc. Various well-known pulps such as the pulp produced in the above can be used.

  Among these raw material pulps, LBKP, NBKP, LUKP, NUKP, or upper white waste paper, Kent waste paper, in order to achieve the balanced and efficient achievement of the role of the surface layer of the present paperboard, various quality characteristics as the bookboard, etc. It is preferable to use waste paper pulp manufactured from waste tea paper and kraft envelope waste paper.

  Moreover, it is preferable to contain 5-70 mass% of conifer kraft pulp (NKP) in the raw material pulp of the surface layer. Furthermore, when the content of NKP is 25-70 mass%, with the improvement of bursting strength, Boxing / bonding suitability can be improved, and the occurrence of ruled line cracks can be effectively prevented, which is more preferable.

  In addition, if the content of NKP in the raw material pulp of the surface layer is less than 5%, the fiber length is long and the content of NKP with thick fibers decreases, so that the bursting strength is reduced, and ruled line cracking occurs during box making. It tends to occur.

  On the other hand, if the content of NKP exceeds 70% by mass, strength variation due to formation unevenness and appearance deterioration are caused. In addition, when applying a coating liquid containing hollow inorganic particles, thermally foamable particles, and a binder, the coating liquid penetrates very much into the surface of the base paper. There also exists a possibility that the problem that the coating layer which it has cannot be formed efficiently will arise.

Moreover, 15-45 g / m < ² > is preferable and the addition amount of the surface layer of this paperboard is more preferable in it being 25-40 g / m < ² >. When the amount of the surface layer is less than 15 g / m ² , the strength of the surface layer is reduced, and therefore, ruled line cracks, square cracks, and the like are likely to occur during box making. On the other hand, when the amount of the surface layer exceeds 45 g / m ² , the manufacturing cost increases because an expensive raw material pulp is used for the surface layer with respect to the middle layer.

“Amount (g / m ² )” means delamination as follows, and the basis weight of each layer is measured in accordance with “paper and paperboard—basis weight measurement method” described in JIS-P8124. It is the value.

  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 of each sample is peeled off, and this is used to separate the layers into layers. After delamination, each layer of each sample was sufficiently dried with a hot air dryer or the like and used for the test.

  Furthermore, the freeness of the raw material pulp is preferably 280 to 530 cc, more preferably 320 to 430 cc.

  If the freeness of the surface pulp is less than 280 cc, the fiber length of the raw pulp is shortened, so the bursting strength is reduced, and the suitability for processing, boxing and bonding is reduced. Cracks are likely to occur.

  On the other hand, when the freeness exceeds 530 cc, the fiber length is long, and the coating liquid containing hollow inorganic particles, thermally foamable particles, and a binder excessively penetrates into the surface layer, and efficiently heat insulation and heat retention. There is also a possibility that the problem that the coating layer having the above cannot be formed may occur.

  Although it is possible to increase the coating amount of the coating liquid, excessive coating will reduce the production efficiency, and more expensive hollow inorganic particles and thermally foamable particles will be applied. In any case, the manufacturing cost is greatly increased.

  In addition, freeness is the value which measured the freeness by the Canadian standard freeness tester based on JIS-P8121, after disintegrating the sample by the standard breaker based on JIS-P8220. (The same applies hereinafter).

  Next, the raw material composition of the middle layer and the back layer of the present paperboard will be described.

  As a raw material pulp for the middle layer and the back layer of the present paperboard, various known pulps can be used as in the case of the surface layer. Among these, in particular, as with the surface layer, in order to achieve the role and various quality characteristics of this paperboard in a balanced and efficient manner, LBKP, NBKP, LUKP, NUKP, LSBKP, NSBKP, or tea waste paper, craft It is preferable to use waste paper pulp produced from waste paper.

  Moreover, it is preferable to contain 10-80 mass% of NKP in the raw material pulp in the middle layer and the back layer of the present paperboard, and when the content of NKP is 40-60 mass%, an improvement in bursting strength and It is more preferable because it can effectively prevent ruled line cracks and square cracks when processing the present paperboard into a container or the like.

  Further, the freeness of the raw pulp of the middle layer and the back layer is preferably 280 to 480 cc in order to effectively prevent rupture, ruled line cracking, square cracking and the like when processing paperboard into a container or the like, like the surface layer. Moreover, it is more preferable to set it as 300-440 cc for prevention of the fall of tensile strength.

  In addition, when selecting raw material pulp, it is preferable to mix | blend as much waste paper pulp as possible from the reduction of the energy unit and the load given to an environment.

  Used paper pulp includes tea waste paper, kraft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated waste paper, Kamihaku waste paper, Kent waste paper, imitation waste paper, and old paper waste paper, etc.・ Deinked waste paper pulp or disaggregation / deinking / bleached waste paper pulp can be used.

Moreover, although the basic weight of this paperboard is not specifically limited, For example, 100-400 g / m < ² > is preferable and it is more preferable in it being 140-300 g / m < ² >. In addition, this basic weight is the value of the basic weight measured based on JIS-P8113. If the basis weight is less than 100 g / m ² , the coating suitability of the coating liquid during the production of the present paperboard may be lowered, or the printability of the produced paperboard may be lowered. On the other hand, when the basis weight exceeds 400 g / m ² , when the paperboard is processed into a container or the like, the thickness of the paperboard is too thick, which is not preferable.

  The papermaking method for the present paperboard is not particularly limited, and any of an acidic papermaking method, a neutral papermaking method, and an alkaline papermaking method may be used. Also, the paper machine is not particularly limited, and 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. .

  As described above, the present paperboard has been described with respect to the case where the paper layer is composed of the three paper layers of the front layer, the back layer, and the middle layer. However, the present invention is not limited to such a paperboard, and other than this, for example, the front layer, the two layers A paperboard having four paper layers as the middle layer and the back layer, or a paperboard having five or more paper layers by increasing the number of middle layers may be used.

  In order to confirm the effect of the multilayer paperboard according to the present invention, various samples as described below were prepared, and tests for evaluating the quality of these samples were performed. In addition, in a present Example, the numerical value which shows a mixing | blending, a density | concentration, etc. is a numerical value based on the weight of a solid content or an active ingredient. Moreover, since the pulp, chemicals, and the like shown in this embodiment are merely examples, it goes without saying that the present invention is not limited by these embodiments and can be appropriately selected.

  In order to compare with 13 types of multilayer paperboards (referred to as “Example 1” to “Example 13”) according to the present invention and these Examples 1 to 13, four types of multilayer paperboards are used. Paperboard (this is referred to as “Comparative Example 1” to “Comparative Example 4”) was prepared in the configuration shown in Table 1.

  The production conditions for each sample are shown below. Unless otherwise specified, the raw material composition, drainage, chemical addition conditions, etc. of the surface layer, middle layer (3 layers), and back layer are the same.

[Example 1]
[Manufacture of base paper]
<1> Surface layer After blending 30% by weight of softwood bleached kraft pulp (NBKP), 30% by weight of hardwood bleached kraft pulp (LBKP), and 40% by weight of high-quality waste paper pulp, sulfuric acid was added to the raw material pulp whose disintegration freeness was adjusted to 380cc. A material slurry for the surface layer was produced by adding 4% by mass of a band and 0.3% by mass of a sizing agent (R50, manufactured by Modern Chemical Industry Co., Ltd.). The “disaggregation freeness (cc)” is obtained by cutting each sample into a size of about 3 cm ² to prepare a test piece having a weight of about 25 g, and immersing the test piece in 1 liter of water for 24 hours, and then JIS. -Measured with a Canadian standard freeness tester in accordance with JIS-P8121, after visually confirming that the test piece was completely disaggregated in accordance with JIS-P8121. The freeness value obtained (the same applies hereinafter).
<2> Middle layer (1)
After blending 60% by weight of Kent waste paper pulp (NBKP) and 40% by weight of high quality waste paper pulp, 4% by weight of sulfuric acid band and sizing agent (R50 manufactured by Modern Chemical Industry Co., Ltd.) Was added to produce a raw material slurry for the middle layer (1).
<3> Middle layer (2), (3) and back layer Raw material pulp prepared by adjusting 100% by weight of old paper pulp to 230 cc of disaggregation freeness, 4% by weight of sulfuric acid band and 0.3% by weight of sizing agent (R50) The raw material slurry for the middle layer (2), (3) and the back layer was produced by adding.

Using these raw material slurries, the surface layer, the middle layer (1), the middle layer (2), the middle layer (3) and the back layer of the five paper layers are combined with an ultra former (manufactured by Kobayashi Manufacturing Co., Ltd.). The surface layer weight is 30 g / m ² , the middle layer (1) weight is 40 g / m ² , the middle layers (2) and (3), and the back layer weight is 50 g / m ² , A base paper having an amount of 220 g / m ² was obtained.

[Adjustment of coating solution]
The blending ratio of hollow inorganic particles having an average particle size of 25 μm (manufactured by Sakai Kogyo Co., Ltd., Cenolite M-732C) and thermally foamable particles (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., Matsumoto Microsphere F-46) is 5 mass%: A mixture of hollow inorganic particles and thermally foamable particles was prepared at 95% by mass, and a styrene / butadiene copolymer latex (SBR) having a glass transition temperature (Tg) of −5 ° C. with respect to 100 parts by weight of the mixture. A coating solution containing 12 parts by weight was prepared and adjusted.

[Manufacture of multilayer paperboard]
The surface temperature of the dryer cylinder is about 100 after applying the coating liquid adjusted as described above to 5 g / m ^{2 in} terms of solid content per side on one side of the base paper with an on-machine rod coater installed in the paper machine. The thermally foamable particles were expanded and foamed with an after dryer at 0 ° C., and then subjected to surface treatment with a soft calender to obtain a multilayer paperboard (Example 1).

[Examples 2 to 5]
A multilayer paperboard obtained in the same manner as in Example 1 except that the blending ratio of the hollow inorganic particles and the thermally foamable particles was changed as shown in Table 1.

[Examples 6 to 9]
A multilayer paperboard obtained in the same manner as in Example 3 except that the binder content was changed as shown in Table 1.

[Examples 10 to 13]
A multilayer paperboard obtained in the same manner as in Example 3 except that the coating amount of the coating solution was changed as shown in Table 1.

[Comparative Examples 1-2]
A multilayer paperboard obtained in the same manner as in Example 3 except that the mixing ratio of the hollow inorganic particles and the thermally foamable particles in the coating solution was changed as shown in Table 1.

[Comparative Example 3]
A multilayer paperboard obtained in the same manner as in Example 3 except that the binder content in the coating solution was changed as shown in Table 1.

[Comparative Example 4]
A multilayer paperboard obtained in the same manner as in Example 3 except that the coating liquid was not applied to the surface of the base paper.

  Table 1 shows the results of tests for evaluating the basis weight, thermal conductivity, and surface strength of all the Examples and Comparative Examples. This evaluation test was performed under environmental conditions of a temperature of 23 ° C. ± 1 ° C. and a humidity of 50 ± 2% in accordance with JIS-P8111.

The “basis weight (g / m ² )” in Table 1 is the total basis weight of each sample, that is, the multilayer paperboard, and “paper and paperboard—basis weight measuring method” described in JIS-P8142. It is a value measured according to.

  The “thermal conductivity (W / m · K)” is a value measured by a heat flow meter method according to JIS-A1412.

  The “surface strength (A)” was evaluated as a multilayer paperboard used for a packaging container based on a value measured according to JIS-P8129. The evaluation criteria are as follows: “Surface strength is 14A or more” marked with ◎, “Surface strength is 12A to 13A” with ◯, “Surface strength is 10A to 11A” with △, “Surface strength is less than 10A” 4 levels.

表１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１３に係る多層抄き板紙は品質評価に優れる。すなわち、本発明に係る多層抄き板紙は、優れた断熱性、保温性を有し、また表面強度が強く、加工・製函・貼合適性にも優れるので断熱性、保温性を必要とする容器等に加工しても罫線割れが発生しにくく、さらにまた印刷適性にも優れる。

As shown in Table 1, the multilayer paperboard according to the present invention, that is, the multilayer paperboard according to Examples 1 to 13, is excellent in quality evaluation. That is, the multilayer paperboard according to the present invention has excellent heat insulation and heat retention, has high surface strength, and is excellent in processing, box making and bonding suitability, and therefore requires heat insulation and heat retention. Even if processed into a container or the like, ruled line cracks are less likely to occur, and it is also excellent in printability.

Claims (4)

A coating in which at least one surface of a base paper is coated with a coating liquid containing at least hollow inorganic particles, heat-expandable particles, and a binder, and the heat-expandable particles are expanded by a dryer in a drying step and foamed. A multilayer paperboard characterized by providing a layer. The multilayer paperboard according to claim 1, wherein the coating amount of the coating liquid is 0.4 to 10 g / m ² in terms of solid content per side.   The multilayer paperboard according to claim 1 or 2, wherein the multilayer paperboard has a thermal conductivity of 0.03 to 0.06 W / m · K. A packaging container using the multilayer paperboard according to any one of claims 1 to 3.