JP2009191372A - Multilayer paperboard - Google Patents

Abstract

The present invention provides a multilayer paperboard excellent in cushioning property, anti-slip property, and surface strength, and excellent in processing, laminating and boxing suitability to a corrugated cardboard sheet, a corrugated cardboard packaging container, and an interior packaging container.
A multilayer paperboard having excellent cushioning properties and anti-slip properties is obtained by applying a coating liquid containing thermally foamed particles, pulp and binder to at least one side of a base paper comprising at least a front layer and a back layer. create.
[Selection figure] None

Description

  The present invention relates to a multilayer paperboard, and more specifically, excellent in cushioning properties, anti-slip properties, and surface strength, and also suitable for processing, bonding, and box making to corrugated cardboard sheets, corrugated packaging containers, interior packaging containers, etc. It relates to an excellent multilayer paperboard.

  Conventionally, for example, in the packaging of electrical appliances, in order to reduce the friction and impact of the internal products, the foam is foamed with good moldability, inexpensive and lightweight, and the product is fixed, and the product is packaged with a nonwoven fabric or the like. It is common.

  However, such a polystyrene foam has a problem that a large burden is placed on the environment upon disposal. As is well known, if the styrene foam is discarded by incineration, the incinerator will be damaged due to high combustion calories, and air pollution will also occur as black smoke and pollutants. On the other hand, when the expanded polystyrene is discarded by the landfill process, the expanded polystyrene is hardly decomposable and bulky, so that it remains in the soil as it is and shortens the life of the landfill disposal site. Therefore, recently, such separate collection and recycling of polystyrene foam has been studied, but the actual situation is that the fundamental measures have not yet been established due to the high cost of collection and recycling. It is.

  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.

  In particular, various types of foamed paper using foamable microcapsules that foam by heat have been proposed as paper having excellent cushioning properties and anti-slip properties. For example, as described in Patent Document 1, the foamable microcapsule has 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. A low-boiling agent such as butane gas is sealed in, and 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. .

  Conventionally, using such foamable microcapsules, as a method of imparting cushioning and anti-slip properties to paper, an internally added papermaking method for making paper by mixing thermally foamable particles with pulp raw materials, and a paper manufacturing process There is known a method of spraying or impregnating thermally foamable particles onto a wet paper that contains a lot of moisture on the way.

  As a method of internally adding thermally foamable particles, for example, in Patent Document 2, 5-30 μm foamable microcapsules are mixed with pulp, and the amount of water before heating and foaming is considerably larger than the amount of moisture in general papermaking. And the method of foaming a foamable microcapsule by heat-drying and obtaining a lightweight paper is disclosed.

  Further, Patent Document 3 discloses a paper base having a water content of 50 to 60% by weight obtained by blending foamable microcapsules with papermaking raw materials mainly composed of paper pulp, and mainly foamable microcapsules and rubber latex. And / or impregnating liquid comprising a synthetic resin emulsion is impregnated with a wet impregnation method in an amount of 5 to 40% by weight of the raw material for papermaking, and then the foamable microcapsules are foamed by heating. A manufacturing method is disclosed.

  However, in the foamed papers described in Patent Documents 2 and 3, both the foamable microcapsules are foamed and the entire paper layer is porous, and the microballoons in which the microcapsules are foamed hinders the binding between pulp fibers. However, there is a problem that the paper strength and the peel strength between the paper layers are greatly reduced, and the paper is easily torn or torn.

That is, when the paper obtained above is processed and used as a cushion / anti-slip packaging container,
(A) Foamed microballoons inhibit the bonding between fibers, and the compressive strength and burst strength of the packaging container are weak, and the packaging container is crushed because the strength required for the packaging container cannot be ensured.
(B) The peeling strength between the paper layers is low, and peeling occurs at the joint portion and the flap portion of the packaging container due to the paper peeling.
(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 box making. Therefore, the adhesive is consumed more than necessary, and the cost increases.
(E) Due to the adhesive absorbed in a large amount in the paper layer, the original heat insulating property of the foamed paper is hindered and lowered.
Therefore, it is not suitable as paper for use in cushion / anti-slip packaging containers.

  Further, in the foamed paper described in Patent Document 2, foamable microcapsules are mixed with raw pulp to make paper, but the foamable microcapsules only physically stay in the form of pulp fibers. The yield is very poor, and there is a problem that excessively expensive foamable microcapsules must be mixed with the raw pulp.

  Further, for example, Patent Document 4 discloses a foamed paper manufacturing method in which a foamed microcapsule dispersion is externally added to a wet paper obtained by making pulp in a paper machine wire part. In the inkjet recording, the dispersion of foamable microcapsules 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 sizing degree is adjusted to a certain range. Foam base paper is disclosed.

  However, the foamed papers described in Patent Document 4 and Patent Document 5 are both foamed by spraying a dispersion of foamable microcapsules on wet paper that contains a large amount of water during the paper manufacturing process. This is a manufacturing method in which the conductive microcapsules are distributed not on the paper surface but on the paper layer, and the foamed base paper for ink jet recording. Similarly to the above, since the microballoons in which the microcapsules are foamed prevent the binding between the pulp fibers, Since the peel strength between layers is low, and the paper is easily torn or torn, it is not suitable as a packaging container.

  Although no prior art document is found, 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. In the production of foamed paper by applying such heat-expandable particles to paper, the heat-expandable particles alone are not fixed to the paper, so a coating liquid consisting of heat-expandable particles and a binder is applied to the paper by a coating machine. After coating, it must be done by heating and foaming.

  However, this method uses a binder, the expansion ratio of the heat-expandable particles is suppressed by the binder, and the cushioning properties and anti-slip properties that are manifested by appropriately foaming the heat-expandable particles are reduced. become.

  Further, when the addition ratio of the thermally foamable particles is increased, not only the cost of the foamed paper is increased, but also the surface strength of the paper and the printability are lowered by the thermally foamable particles.

  Furthermore, since the coating amount of the coating liquid containing thermally foamable particles on the paper surface is limited to a certain amount or less, the coating amount of thermally foamable particles is limited, and the coating layer Since the thickness of the film is also thin, it is considered that it is inferior to the above-described internal addition method and impregnation method in terms of cushioning properties and anti-slip properties, and thus is not yet put into practical use.

Japanese Patent Publication No. 44-7344 JP-A-10-88495 JP-A-8-226097 JP 2001-98494 A JP 2002-46342 A

  The present invention has been made in view of the above-described circumstances, and the object thereof is excellent in cushioning properties, slip resistance, surface strength, and processing into corrugated cardboard sheets, corrugated cardboard packaging containers, interior packaging containers, etc. An object of the present invention is to provide a multilayer paperboard having excellent bonding and boxing suitability.

  The above-mentioned object of the present invention is characterized in that a coating liquid containing thermally foamed particles, pulp and binder is applied to at least one side of a base paper comprising at least a surface layer and a back layer to impart cushioning properties and anti-slip properties. This is accomplished by providing a multi-layer paperboard.

Further, the above object of the present invention is such that the blend ratio of the thermally foamed particles and the pulp contained in the coating liquid is 95.0% to 99.9% (Dry%) of the thermally foamable particles, and 5.0 The thermally foamed particles contained in the coating liquid have a particle diameter of 15 to 20 μm, a foaming start temperature of 75 to 85 ° C., and a maximum expansion temperature of 105 to 120 °. C, the binder contained in the coating liquid is styrene / butadiene copolymer latex (SBR), and the coating amount of the coating liquid is 0.4 to 10 g in solid content per one side of the base paper. / effectively be achieved by providing a multi-layer paper making paperboard and respectively, characterized in that m is ^2.

  According to the present invention having the configuration as described above, it is possible to obtain a multilayer paperboard having excellent cushioning properties, anti-slip properties, and surface strength, and thereby to corrugated cardboard sheets, corrugated cardboard packaging containers, interior packaging containers, and the like. A multilayer paperboard having excellent processing, laminating and boxing suitability can be obtained. Further, the multilayer paperboard according to the present invention is excellent in cushioning properties and anti-slip properties without bonding, for example, paperboard and foamed paper, so that the process can be simplified. Furthermore, since the surface strength is also excellent, corrugated cardboard packaging containers with excellent cushioning and anti-slip properties used for transportation, storage and protection, which could not be used due to weak surface strength with conventional foamed paper, It can be used for a packaging container such as an interior packaging container, and even when used for such a packaging container, problems such as ruled line cracking do not occur.

In particular, when the coating amount of the coating liquid is 0.4 to 10 g / m ² in terms of solid content on one side of the base paper, the surface hardness can be lowered, and the multi-layer paper with further improved cushioning and anti-slip properties. Paperboard can be obtained.

  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, a middle layer, and a back layer. The multilayer paperboard according to the present invention is not limited to the following embodiments, and it is needless to say that the configuration can be changed as appropriate without departing from the scope of the claims.

  The multilayer paperboard according to the present invention (hereinafter referred to as “main paperboard”) is a base paper composed of three paper layers: a surface layer, a back layer, and a single middle layer disposed between the front and back layers. And at least one surface of the base paper is coated with a coating solution containing at least thermally expandable particles, pulp, and a binder to provide a coating layer.

  The coating liquid applied to the base paper of this paperboard contains thermally foamable particles. Thereby, cushioning properties and slip resistance can be imparted to the present 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, acrylic acid ester, acrylonitrile, 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 The volume expands to 5 to 50 times and the volume to 50 to 130 times. In addition, since the temperature of the paper drying process in the paper making process and the paper processing process is 80 to 200 ° C., the thermally foamable particles in the present invention have a particle diameter of 15 to 20 μm and a foaming start temperature of 75 to 85. It is preferable that it is (degreeC) and the maximum expansion temperature is 105-120 degreeC.

  If the particle size of the thermally foamable particles is less than 15 μm, the thickness of the cushion layer cannot be sufficiently secured, and therefore it is impossible to prevent damage. If it exceeds 20 μm, the thickness of the cushion layer varies and is necessary. Since the thickness of the cushion layer is increased as described above, the cushion layer is not suitable for folding, which is not preferable. Further, when the foaming start temperature is less than 75 ° C. and the maximum expansion temperature is less than 105 ° C., the heat-expandable particles rapidly expand due to heat, thereby causing operational troubles that contaminate the dryer surface. . When the foaming start temperature is 85 ° C. and the maximum expansion temperature is more than 120 ° C., the thermally foamable particles are not sufficiently expanded, and thus cushioning properties are hindered.

  In the drying process, the thermally foamable particles are foamed and expanded by a dryer, and the paperboard is made bulky to impart cushioning properties and slip resistance. In addition, it is preferable that the heating for expanding the thermally foamable particles is expanded by foaming to a desired size of the paperboard by one heating.

  Examples of such thermally foamable particles include “Matsumoto Microsphere F-30D”, “F-30GS”, “F-20D”, and “F-50D” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. Various known products such as “Expancel WU” and “Same DU” sold by Nippon Philite Co., Ltd. can be used, but the particle size of the thermally expandable particles before expansion, coating suitability, and drying process From the viewpoint of foaming property, particularly heat-expandable particles made of an acrylic copolymer are preferable.

  Moreover, the coating liquid applied to the base paper of the present paperboard contains pulp. Thereby, cushioning properties can be imparted to the present paperboard.

  Examples of raw material pulp include hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), conifer unbleached kraft pulp (NUKP), hardwood semi-bleached kraft pulp (LSBKP), and conifer Semi-bleached kraft pulp (NSBKP), chemical pulp such as hardwood sulfite pulp, softwood sulfite pulp, stone grand pulp (SGP), pressurized stone grand pulp (PGW), refiner grand pulp (RGP), thermo ground pulp (TGP), Mechanical pulp such as Chemi-Grand Pulp (CGP), Groundwood Pulp (GP), Thermomechanical Pulp (TMP), Tea Waste Paper, Craft Envelope Waste Paper, Magazine Waste Paper, Newspaper Waste Paper, Flyer Waste Paper, Office Waste Paper, Corrugated Waste Paper, Upper White Waste Paper, Kent waste paper, imitation waste paper, Produced 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 dried pulp can be used.

  Among these raw material pulps, waste paper pulp produced from LBKP, NBKP, LUKP, NUKP in order to achieve a balanced and efficient achievement of the role of cushioning of this board and various quality characteristics as this board. Is preferably used.

  When the content of NKP exceeds 5% by mass, unevenness in strength due to coating unevenness and a decrease in cushioning properties are caused.

  In this way, by adding the heat-foamable particles and pulp to the coating liquid, the coating layer can be made thicker, thereby obtaining a synergistic effect of cushioning properties and anti-slip properties.

  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, the occurrence of ruled line cracks when the paperboard is processed into a packaging container, etc., and the paper is peeled or torn due to rubbing with the contents during transportation, storage, etc. Can be prevented.

  Examples of the binder used in the coating liquid for the paperboard include various known materials such as vinyl acetate, acrylic, polyvinyl alcohol (PVA), styrene / butadiene copolymer latex (SBR), starch, and polyacrylamide (PAM). Things can be used.

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

  Moreover, although a binder with high hardness is excellent in the improvement effect of surface strength, it will inhibit expansion | swelling of a thermally foamable particle. That is, as described above, the heat-expandable particles exhibit cushioning properties and anti-slip properties by being heated and expanded to be foamed. Therefore, if the expansion of the heat-expandable particles is inhibited, the cushioning properties and The slip resistance cannot be obtained.

  Furthermore, this paperboard is often processed into a packaging container, but it is required that the coating layer does not break when it is processed into a packaging container and a strong bending force is applied to the ruled line portion (folded portion). The

  For this reason, it is particularly preferable to use SBR among the various binders described above. That is, SBR has good adhesiveness to thermally foamable particles and pulp, and is excellent in elongation at the time of bending, so it does not hinder expansion and foaming of thermally foamable particles, and the paperboard is packaged. The problem of ruled line cracking when processed into a container is less likely to occur.

  Furthermore, the glass transition temperature is -50 to 30 ° C., which is a soft property having a low viscosity at the time of coating of the coating liquid and excellent in bendability and can obtain an appropriate surface strength improving effect after drying. More preferably, the temperature is −30 to 20 ° C. When such a binder is used, the foamability of the thermally foamable particles and the processability of the paperboard are further improved.

  As described above, the coating liquid applied to the surface of the base paper of the present paperboard contains at least thermally foamable particles, pulp, and a binder.

Although the heat-expandable particles can be internally added to the raw material pulp of each layer constituting the base paper, the specific gravity of the heat-expandable particles is 0.9 to 1.2 g / cm ^3. When it is added internally, it is difficult to uniformly disperse in the thickness direction during paper making, and cushioning properties cannot be obtained effectively.

  Moreover, in order to obtain desired cushioning properties and anti-slip properties, it is necessary to add excessively heat-expandable particles. Excessive addition of such heat-expandable particles leads to an increase in manufacturing cost, and in terms of quality, surface strength is reduced, compressive strength, burst strength, tensile strength, tensile strength, various strengths such as cleaving strength, printability, etc. Therefore, it is preferable to form a coating layer by applying a coating liquid containing at least thermally foamable particles, pulp, and a binder.

  The blending ratio of the heat-expandable particles and the pulp is preferably heat-expandable particles: pulp = 95.0 to 99.9% (Dry%): 5.0 to 0.1% (Dry%). : Pulp = 98.5 to 99.5% (Dry%): 1.5 to 0.5% (Dry%) is more preferable.

  When the pulp content is less than 0.1%, the entanglement between the foamed particles and the pulp fibers is deteriorated and the surface strength is weakened. When the pulp content exceeds 5.0%, the coating liquid is increased. It becomes sticky and cannot be applied.

  The binder content is preferably 20 to 60 parts by weight (Dry) and more preferably 40 to 50 parts by weight (Dry) with respect to 100 parts by weight (Dry) of the mixture of thermally foamable particles and pulp. preferable.

  When the binder content is less than 20 parts by weight (Dry) with respect to the heat-expandable particles and the pulp, the adhesiveness of the heat-expandable particles and the pulp decreases. On the other hand, when the content of the binder exceeds 60 parts by weight (Dry), the adhesiveness of the heat-foamable particles and pulp and the foaming effect of the heat-foamable particles are hardly improved, and only the production cost is increased.

Such coating liquid, on at least one surface of the base paper, 0.4~10g / ^{m 2} on one surface per solids, preferably 1 to 6 g / ^{m 2} coating. When the coating amount is less than 0.4 g / m ² , the cushioning property is deteriorated, and when it exceeds 10 g / m ² , the cushion layer becomes thick, and the expansion of the thermally foamed particles is not preferable.

  In addition, as a method of applying a coating liquid, it can apply by well-known coating means, such as a bar coater, a rod coater, and 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 the present paperboard can be made more excellent in cushioning properties.

  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 processed and used for packaging containers such as cardboard packaging containers and interior packaging containers with excellent heat insulation and heat retention used for transportation, storage and protection. It is required to have excellent strength and suitable strength as a packaging container.

  Therefore, the surface layer of this paperboard (1) prevents cracking of ruled lines during processing into cardboard packaging containers, interior packaging containers, etc., (2) has high surface strength, transports, stores and protects the contents. (3) It is a layer that bears the role of having coating suitability for a coating liquid containing hollow inorganic particles, thermally foamable particles, and a binder, and (4) ensuring printability.

  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 known pulps such as the pulp produced in the above can be used.

  Among these raw material pulps, LBKP, NBKP, LUKP, NUKP, Kamihaku old paper, Kent used paper, in order to achieve the balanced and efficient achievement of the role of the surface layer of this paperboard, various quality characteristics as the main paperboard, 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, and further, when the content of NKP is 25-70 mass%, the rupture strength is improved and ruled line cracks are caused. Since it can prevent effectively, it is more preferable.

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

  On the other hand, if the content of NKP exceeds 70% by mass, it causes variations in strength due to unevenness in texture and a decrease in appearance. In addition, when applying a coating liquid containing thermally foamable particles, pulp and binder, the coating liquid penetrates very much into the surface of the base paper. There is also a possibility that the problem that the construction layer cannot be efficiently formed may occur.

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 , an expensive raw material pulp is used for the surface layer with respect to the middle layer, which causes an increase in cost.

In addition, “attachment amount (g / m ² )” is a value obtained by performing layer peeling according to the following, and measuring the basis weight of each layer in accordance with “Paper and paperboard—basis weight measurement method” described in JIS-P8124. It is.

  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 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.

  In other words, if the freeness of the raw material pulp of the surface layer is less than 280 cc, the fiber length of the raw material pulp is shortened, so that the burst strength is reduced, and ruled line cracks and square cracks are likely to occur during box making. If it exceeds 530 cc, the fiber length is long, the binder contained in the coating liquid will permeate the surface layer excessively, making it difficult to keep the thermally foamable particles on the surface, and the thermally foamable particles may peel off. There is.

  Although it is possible to increase the coating amount of the coating liquid, excessive coating reduces the production efficiency, and a lot of expensive thermally foamable particles are applied. There is a risk of significant cost increase.

  Here, “freeness” means that after the sample was disaggregated with a standard disaggregator according to JIS-P8220, the freeness was measured with a Canadian standard freeness tester according to JIS-P8121. Value.

  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 a balanced and efficient achievement of the role of the back layer of this paperboard, various quality characteristics, etc., LBKP, NBKP, LUKP, NUKP, LSBKP, NSBKP, or used tea paper, It is preferable to use waste paper pulp produced from kraft 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 Since the ruled line crack and the square crack at the time of container packaging processing of this paperboard can be prevented effectively, it is more preferable.

  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, etc. during container packaging processing as in the case of the surface layer. It is more preferable to set it as 300-440 cc for prevention of a fall.

  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, 150-400 g / m < ² > is preferable and it is more preferable in it being 170-300 g / m < ² >. In addition, this "basis weight" is the value of the basic weight measured based on JIS-P8113. If the basis weight is less than 100 g / m ² , there is a concern of poor coating suitability at the time of manufacturing the paperboard. On the other hand, when the basis weight exceeds 400 g / m ² , it is not preferable because it is difficult to process because the thickness is too thick when processing the packaging container.

  The papermaking method of 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 case where the paper layer is composed of the three paper layers of the front layer, the back layer, and the middle layer has been described above. It is good also as a paperboard which has four paper layers of the middle layer and back layer, and also a paperboard which has five or more paper layers by increasing the number of layers of the middle layer.

  In order to confirm the effect of the multilayer paperboard according to the present invention, the following various samples were prepared, and a test for evaluating the quality of each sample was performed. In addition, in a present Example, the numerical value which shows a mixing | blending, a density | concentration, etc. is a numerical value based on the weight of a solid content or 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.

  In order to compare with 28 types of multilayer paperboards (referred to as “Example 1” to “Example 28”) according to the present invention and these Examples 1 to 28, three types of multilayer paperboards are used. Paperboard (this is referred to as “Comparative Example 1” to “Comparative Example 3”) was prepared in the configuration shown in Table 1.

  The production conditions for each sample are shown below. Unless otherwise noted, 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, 4% by mass of a sulfuric acid band and 0.3% by mass of a sizing agent (R50 manufactured by Modern Chemical Industry Co., Ltd.) were added to produce a raw material slurry for the surface layer. Here, “disaggregation freeness (cc)” means that each sample is cut into a size of about 3 cm ² to give a test piece having a weight of about 25 g, and this test piece is immersed in 1 liter of water for 24 hours. , In accordance with JIS-P8220, after 15 minutes of disaggregation with a standard disaggregator, visually confirm that the test piece is completely disaggregated, and then in accordance with JIS-P8121, a Canadian standard freeness tester The freeness value measured in the above.
<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 Industries, Ltd.) Was added to produce a raw material slurry.
<3> Middle layer (2), (3) and back layer 100% by mass of the old paper pulp is adjusted to a disintegration freeness of 230 cc, and 4% by mass of a sulfuric acid band and 0.3% by mass of a sizing agent (R50) are added. A raw slurry was produced.

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 is 30 g / m ² , the middle layer (1) is 40 g / m ² , the middle layer (2), the middle layer (3), the back layer is 50 g / m ² , and the basis weight of the entire paperboard is 220 g / m ^2. A base paper was obtained.

[Adjustment of coating solution]
A mixture of heat-expandable particles (Matsumoto Yushi Seiyaku Co., Ltd., Matsumoto Microsphere F-46) having an average particle size of 20 μm and pulp is prepared, and the glass transition temperature (Tg) is −5 with respect to 100 parts by weight of the mixture. A coating solution containing 50 parts by weight of styrene / butadiene copolymer latex (SBR) at a temperature of 0 ° C. was prepared.

[Manufacture of multilayer paperboard]
After applying the coating liquid prepared as described above to one side of the base paper with an on-machine rod coater installed in the paper machine on a single side at a solid content of 5 g / m ² , the surface temperature of the dryer cylinder is about The thermally foamable particles were foamed with an after dryer at 100 ° C., and then surface-treated with a soft calender to obtain a multilayer paperboard [Example 1].

[Examples 2 to 28]
Fix the particle size of the thermally foamable particles contained in the coating liquid, the type of binder, the Tg value, the foaming start temperature of the thermally foamable particles in the coating liquid, the maximum expansion temperature, the content, the binder content, A multilayer paperboard obtained in the same manner as in Example 1 except that the coating amount of the coating liquid was changed as shown in Table 1.

[Comparative Examples 1-2]
A multilayer paperboard obtained in the same manner as in Example 5 except that the particle diameter of the thermally foamable particles contained in the coating solution was changed as shown in Table 1.

[Comparative Example 3]
Except for the fact that the coating liquid was changed so as not to contain pulp, multilayer paperboard obtained in the same manner as in Example 5 and others was used.

Table 1 shows the results of tests for evaluating the basis weight, surface strength, and slip angle quality for all of these 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 entire multilayer paperboard, and is described in “Paper and paperboard—basis weight measurement” described in JIS-P8142. It is a value measured according to “Method”.

In addition, in the cushioning property and the feeling of touch in quality evaluation, “◯” indicates good, “◎” indicates excellent, and “×” indicates poor.

表１の品質評価欄に示されるように、本発明に係る多層抄き板紙、すなわち実施例１〜実施例２８に係る多層抄き板紙は、品質面において比較例１〜３に係る多層抄き板紙より優れていることが判明した。とくに、クッション性、手触り感に関しては、表１に◎印で示されるように、熱発泡粒子の発泡開始温度が７５〜８５°Ｃであり、最高膨張温度が１０５〜１２０°Ｃである場合、熱発泡粒子に対するパルプの含有量（配合比率）が９９．９〜９５．０：０．１〜５．０（Ｄｒｙ％）である場合、バインダの含有量が２０〜６０重量部である場合、塗工液の塗工量が０．４〜１０ｇ／ｍ^２である場合に、夫々優れたものとなっている。すなわち、本発明に係る多層抄き板紙は、クッション性、防滑性に優れ、また表面強度にも優れているものであり、これにより従来の発泡紙では表面強度が弱いために用いることができなかった輸送、保管、保護のために用いられるクッション性、防滑性に優れた段ボールシート、段ボール包装容器、内装包装容器等の包装容器に用いることができ、実際に用いて包装容器を作製してみたところ、罫線割れ等の問題は全く発生しないことが確認された。

As shown in the quality evaluation column of Table 1, the multilayer paperboard according to the present invention, i.e., the multilayer paperboard according to Examples 1 to 28, is a multilayer paperboard according to Comparative Examples 1 to 3 in terms of quality. It turned out to be better than paperboard. In particular, regarding the cushioning property and the touch feeling, as indicated by ◎ in Table 1, when the foaming start temperature of the thermally foamed particles is 75 to 85 ° C and the maximum expansion temperature is 105 to 120 ° C, When the content (blending ratio) of the pulp with respect to the thermally foamed particles is 99.9 to 95.0: 0.1 to 5.0 (Dry%), when the content of the binder is 20 to 60 parts by weight, When the coating amount of the coating liquid is 0.4 to 10 g / m ² , each is excellent. That is, the multilayer paperboard according to the present invention is excellent in cushioning property, anti-slip property, and excellent in surface strength, and thus cannot be used because conventional foamed paper has low surface strength. Can be used for packaging containers such as corrugated cardboard sheets, cardboard packaging containers, interior packaging containers, etc. that are excellent in cushioning and anti-slip properties used for transport, storage, protection, and actually tried to produce packaging containers However, it was confirmed that problems such as ruled line cracking did not occur at all.

Claims (5)

  A multilayer paperboard, wherein a coating liquid containing thermally foamed particles, pulp and binder is applied to at least one side of a base paper comprising at least a surface layer and a back layer to impart cushioning properties and anti-slip properties.   The blending ratio of the thermally foamed particles and the pulp contained in the coating liquid is 5.0 to 0.1% (Dry%) of pulp with respect to 95.0 to 99.9% (Dry%) of thermally foamable particles. The multilayer paperboard according to claim 1, wherein   The thermally expanded particles contained in the coating liquid have a particle diameter of 15 to 20 µm, a foaming start temperature of 75 to 85 ° C, and a maximum expansion temperature of 105 to 120 ° C. The multilayer paperboard described.   The multilayer paperboard according to any one of claims 1 to 3, wherein the binder contained in the coating liquid is styrene / butadiene copolymer latex (SBR). The multilayer paperboard according to any one of claims 1 to 4, wherein a coating amount of the coating liquid is 0.4 to 10 g / m ² in terms of solid content per one side of the base paper.