JP2018058035A - Method for producing sheet for heat insulating container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a sheet for heat insulating container, exerting favorable adiabaticity at heating by an electronic oven and suitable for a cooking container-molding material or the like.SOLUTION: A method for producing a sheet for a heat insulating container comprises a process of laminating a foamable layer comprising a composition for the foamable layer including a thermofoamable microcapsule and a binder on one face side of a paper base, and a process of laminating a coating layer comprising a composition for the coating layer on the face of the foamable layer opposite to the paper base. The basis weight of the paper base is 50 g/mor more but 600 g/mor less, and the foamable layer is laminated by a flexographic printing system. Preferably, the process of laminating the foamable layer is carried out using a flexographic press equipped with an anilox roll, and the line number engraved on the cylindrical surface of the anilox roll is preferably 80 lines/inch or more but 200 lines/inch or less. Besides, the lamination amount of the composition for the foamable layer in this layer is preferably 10 to 50 g/m.SELECTED DRAWING: None

Description

  The present invention relates to a method for manufacturing a sheet for a heat insulating container.

  Insulated containers are used as containers for hot drinks such as coffee and instant foods such as ramen, soup and miso soup. Today, using a microwave oven, heat-insulating containers containing contents such as beverages and prepared dishes are also cooked. Some heat insulating containers have a heat insulating structure that shields the heat of the contents so that they can be easily held by hand, and are formed by a paper sheet for a heat insulating container (Japanese Patent Laid-Open Nos. 8-226097 and 2008). -266-799). Such a sheet for an insulated container usually has a paper base and a foamable composition. The foamable composition contains foamable microcapsules (foaming agent) that foams when heated, and a heat insulating layer is formed by foaming of the foaming agent to exhibit heat insulation.

JP-A-8-226097 JP 2008-266799 A

  However, in a microwave cooking container (insulated container) in which the sheet for a heat insulating container is used, moisture in the sheet is dielectrically heated when heated by the microwave, and thereby the foaming agent foams. Examples of moisture in the sheet include moisture contained in the paper base material during paper making and moisture absorbed from food materials. However, since the sheet | seat for conventional heat insulation containers is not the structure which can absorb and hold | maintain sufficient water | moisture content for the heating by a microwave oven, foamability is not enough. For this reason, improvement of heat insulation is desired. Furthermore, improvement in smoothness, processability, etc. is also desired as a molding material for cooking containers.

  The present invention has been made based on the circumstances as described above, and its purpose is that it can exhibit good heat insulation properties when heated by a microwave oven, and is suitable as a molding material for cooking containers and the like. It is providing the manufacturing method of the sheet | seat for a proper heat insulation container.

The invention made to solve the above problems includes a step of laminating a foamable layer comprising a composition for a foamable layer containing a heat-foamable microcapsule and a binder on one side of a paper substrate, and the foaming And a step of laminating a coating layer made of the composition for a coating layer on the surface of the adhesive layer opposite to the paper substrate, and the basis weight of the paper substrate is 50 g / m ² or more and 600 g / m ² or less. In addition, the foamable layer is a method for manufacturing a sheet for a heat insulating container, which is laminated by a flexographic printing method.

In the method for producing a sheet for a heat insulating container, a foamable layer composed of a composition for a foamable layer containing a heat-foamable microcapsule and a binder is laminated on one surface side of a paper substrate by a flexographic printing method. Therefore, the foamable layer which consists of a convex-shaped halftone dot pattern can be formed. As a result, the thickness and specific surface area of the foamable layer can be increased. Further, since the basis weight of the paper base material is 50 g / m ² or more and 600 g / m ² or less, heat insulation, workability and the like can be improved. Therefore, it is possible to produce a sheet for a heat insulating container that exhibits good heat insulating properties and processability. Also, by laminating a coating layer on the surface of the foamable layer opposite to the paper substrate, that is, the outer surface of the foamable layer, heat dissipation is suppressed and thermal foaming of the thermally foamable microcapsules is promoted. The sheet | seat for heat insulation containers which can be made can be manufactured.

The step of laminating the foamable layer is performed using a flexographic printing machine equipped with an anilox roll, and the number of lines engraved on the cylindrical portion surface of the anilox roll is 80 lines / inch or more and 200 lines / inch or less. preferable. As the lamination amount of the foamable layer composition in the foamable layer, preferably 10 g / m ² or more 50 g / m ² or less in terms of solid content. When the number of lines is less than the lower limit, irregularities on the surface after expansion may easily occur. On the other hand, when the number of lines exceeds the above upper limit, the film thickness becomes thin and sufficient heat insulating properties and cushioning properties may not be obtained. When the amount of the foamable layer composition is less than the lower limit, sufficient heat insulating properties and cushioning properties may not be obtained. On the other hand, when the amount of the foamable layer composition exceeds the above upper limit, the heat-foamable microcapsules may easily drop off, or the surface after swelling may easily become uneven. Then, the thickness of the foamable layer of the sheet | seat for heat insulation containers manufactured by making the number of the lines engraved on the cylindrical part surface of the anilox roll and the lamination amount of the composition for the foamable layer into the above range is improved. Moreover, the sheet | seat for heat insulation containers with high heat insulation can be obtained by improving the thickness of the foamable layer after heat foaming.

As content of the said heat-foamable microcapsule with respect to the said composition for foamable layers, 20 mass% or more and 70 mass% or less are preferable, and it is No. of the said composition for foamable layers. The viscosity at 25 ° C. measured by 4 Zahn cups is preferably 5 seconds or more and 50 seconds or less. When the content of the heat expandable microcapsules to said onset foaming layer composition is less than the above lower limit, it may become impossible to obtain a sufficient heat insulating property or the like. On the other hand, when the said content exceeds the said upper limit, the unevenness | corrugation of the surface after a heating becomes large, and smoothness may fall. Furthermore, the cost increases with an increase in the amount of thermally foamable microcapsules used. Moreover, No. of the said composition for foamable layers. When the viscosity at 25 ° C. measured by a 4 Zahn cup is less than the above lower limit, there may be a case where sufficient fixability of the thermally foamable microcapsules cannot be obtained. On the other hand, when the viscosity exceeds the upper limit, smoothness may be reduced.

  It is preferable that at least one of the foamable layer composition and the coating layer composition contains a humectant. By containing the humectant, moisture from foods and the like is easily absorbed and retained in the heat insulating sheet by the humectant. For this reason, since there is much water content in the sheet | seat for heat insulation in the case of the heating by a microwave oven, the said sheet | seat for heat insulation efficiently heated can be manufactured. Moreover, since the generation | occurrence | production of the curl of the said sheet | seat for heat insulation containers is suppressed by containing a humectant, workability is also improved.

  Here, "solid content" means components other than a solvent and water.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the foamability in the case of the heating by a microwave oven, and being able to exhibit favorable heat insulation, the sheet | seat for heat insulation containers suitable as a molding material etc. of a cooking container can be manufactured. .

  Hereinafter, the manufacturing method of the sheet | seat for heat insulation containers which concerns on one Embodiment of this invention is explained in full detail.

  The manufacturing method of the sheet | seat for heat insulation containers which concerns on one Embodiment of this invention is a manufacturing method of the sheet | seat for heat insulation containers which is a layer structure provided with a paper base material, a foamable layer, and a coating layer in this order. The method for producing a sheet for a heat-insulating container includes a step of laminating a foamable layer made of a composition for a foamable layer containing a thermally foamable microcapsule and a binder on one surface side of a paper substrate, and the foamable layer. And laminating a coating layer made of the composition for a coating layer on the surface opposite to the paper substrate.

<Foaming layer lamination process>
In the foamable layer laminating step, a foamable layer made of a foamable layer composition containing a heat-foamable microcapsule and a binder is laminated on one side of the paper substrate. The foamable layer is laminated by a flexographic printing method.

[Paper base]
The paper base is so-called paper, and is a layer obtained by making pulp fibers with pulp fibers as a main component. The pulp fiber is not particularly limited, and examples thereof include wood pulp such as softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), and softwood bleached sulfite pulp (NBSP). be able to. Moreover, non-wood pulps such as hemp, cotton, straw and kenaf, synthetic pulps using polyethylene, polypropylene, polyacrylonitrile and the like as raw materials can be used in combination with these wood pulps as main materials. In addition, organic synthetic fibers such as acrylic fibers, rayon fibers, polyester fibers, and polyamide fibers, glass fibers, carbon fibers, alumina fibers, silica / alumina silicate fibers, and inorganic fibers such as rock wool can be used in combination.

  Examples of other components that may be contained in the paper substrate include, for example, a sizing agent, a dry paper strength enhancer, a wet paper strength enhancer, a dye, a pigment, a yield improver, a filler, a pH adjuster, and a slime control agent. , Stickers, preservatives, antifungal agents, flame retardants, and the like. These can be used individually by 1 type or in mixture of 2 or more types.

  The paper base material preferably has air permeability, and the paper base material has air permeability, whereby moisture in the paper base material and foodstuffs is evaporated by heating, and further promotes foaming by heating of the foamable layer. Can do. As a paper substrate having air permeability, for example, using a Gurley tester according to JIS-P8117 (2009) “Paper and paperboard—Air permeability and air resistance test method (intermediate region) —Gurley method”. It refers to a paper substrate having a measured air resistance of 200 seconds or less.

The lower limit of the basis weight of the paper base is preferably 50 g / ^{m 2,} and more preferably 150 g / ^{m 2.} When the lower limit of the basis weight of the paper substrate is less than 50 g / m ² , the moldability may be deteriorated. As said upper limit, 600 g / m < ² > is preferable and 450 g / m < ² > is more preferable. When the upper limit of the basis weight of the paper substrate exceeds 600 g / m ² , the moldability is deteriorated, the air permeability of the paper substrate is too low, and the foamability may be lowered.

[Foaming layer]
The foamable layer is a layer existing between the paper base material and the coating layer. The foamable layer is laminated on one surface side of the paper substrate using the foamable layer composition. The foamable layer composition contains at least a heat-foamable microcapsule and a binder, and preferably a moisturizing agent is contained in the foamable layer.

(Thermal foaming microcapsule)
The heat-expandable microcapsules are usually heat-expandable microcapsules in which a low-boiling solvent is enclosed in a resin-made microcapsule that forms an outer shell. When the thermally foamable microcapsules are heated to a temperature equal to or higher than the softening point of the resin forming the microcapsules, the resin softens and the vapor pressure of the low-boiling solvent encapsulated increases. As a result, closed cells are formed by expanding the resin and expanding the microcapsules. The heat insulation and cushioning properties of the heat insulating container sheet are improved by the closed cells.

  As a minimum of content of the said heat-foamable microcapsule with respect to the said composition for foamable layers, 20 mass% is preferable, 25 mass% is more preferable, and 30 mass% is further more preferable. On the other hand, the upper limit of the content is preferably 70% by mass, and more preferably 40% by mass. When the content of the heat-foamable microcapsule is less than the above lower limit, sufficient heat insulating properties may not be obtained. On the contrary, when the content exceeds the above upper limit, unevenness of the surface after heating becomes large, and smoothness may be lowered. In addition, the cost increases with an increase in the amount of thermally foamable microcapsules used.

  No. of the foamable layer composition. Although it does not specifically limit as a minimum of the viscosity in 25 degreeC measured by 4 Zahn cups, 5 seconds are preferable, 10 seconds are more preferable, and 15 seconds are further more preferable. The upper limit of the viscosity is preferably 50 seconds, more preferably 45 seconds, and even more preferably 40 seconds. If the viscosity is less than the lower limit, sufficient stickiness of the heat-foamable microcapsules may not be obtained. On the other hand, when the viscosity exceeds the upper limit, smoothness may be reduced.

  Although it does not specifically limit as said resin which forms an outer shell, For example, the thermoplastic resin which consists of copolymers, such as a vinylidene chloride, an acrylonitrile, an acrylic ester, a methacrylic ester, can be used.

  Although it does not specifically limit as said low boiling point solvent, For example, volatile organic solvents (swelling agent), such as isobutane, pentane, petroleum ether, hexane, a low boiling halogenated hydrocarbon, and methylsilane, can be used.

  A commercially available product can also be used as the thermally foamable microcapsule. Examples of such commercially available products include “Matsumoto Microsphere F Series” and “Matsumoto Microsphere FN Series” from Matsumoto Yushi Seiyaku Co., Ltd., “Expancel 007-40”, “Expancel WU” and “Expancel” from Akzo Nobel. DU "and the like.

  The lower limit of the average particle diameter of the thermally foamable microcapsules before foaming is preferably 5 μm, and more preferably 10 μm. Moreover, as an upper limit of the average particle diameter of the said thermally foamable microcapsule, 50 micrometers is preferable, 30 micrometers is more preferable, and 20 micrometers is more preferable. When the average particle diameter of the heat-foamable microcapsule is less than the above lower limit, the obtained closed cells are small, and thus the heat insulating property and cushioning property of the heat insulating container sheet may be insufficient. On the other hand, when the average particle size of the heat-foamable microcapsule exceeds the above upper limit, the size may cause unevenness on the surface, or it may be difficult to fix the heat-foamable microcapsule in the foamable layer. is there. The average particle diameter of the thermally foamable microcapsule refers to a value calculated from the average of the maximum diameter in plan view and the diameter in a direction orthogonal to the maximum diameter when any 10 samples are observed with a microscope. .

  The lower limit of the foaming start temperature of the heat-foamable microcapsule is preferably in the range of 75 to 101 ° C, more preferably 91 to 101 ° C, and still more preferably 91 to 99 ° C. Moreover, as a width | variety of the upper limit of the foaming start temperature of the said thermally foamable microcapsule, 120-144 degreeC is preferable, 130-140 is more preferable, 132-140 degreeC is further more preferable. When the foaming start temperature of the foamable microcapsule is less than the lower limit, foaming of the thermally foamable microcapsule may start near the temperature at which the binder starts to soften. On the other hand, when the foaming start temperature of the heat-foamable microcapsule exceeds the upper limit, the heat-foamable microcapsule may not be sufficiently foamed when the heat-insulating container sheet is used.

  The lower limit of the maximum foaming temperature of the thermally foamable microcapsule is preferably 150 ° C. Moreover, as an upper limit of the maximum foaming temperature of the said foamable microcapsule, 200 degreeC is preferable and 185 degreeC is more preferable. When the maximum foaming temperature of the thermally foamable microcapsule is less than the above lower limit, or when the maximum foaming temperature of the thermally foamable microcapsule exceeds the above upper limit, the foamability of the foamable layer due to dielectric heating such as a microwave oven May be insufficient. The maximum foaming temperature is a temperature at which the expansion rate is maximized.

  The lower limit of the ratio of volume after foaming to the volume before foaming of the thermally foamable microcapsules (volume expansion coefficient) is preferably 50 times, more preferably 65 times, and even more preferably 80 times. The upper limit of the volume expansion coefficient of the thermally foamable microcapsules is preferably 130 times. When the volume expansion coefficient of the heat-foamable microcapsule is less than the lower limit, the obtained closed cells are small, and thus the heat insulating property and cushioning property of the heat insulating container sheet may be insufficient. On the other hand, when the volume expansion coefficient of the thermally foamable microcapsule exceeds the upper limit, the smoothness of the surface after foaming may be greatly reduced.

(binder)
The binder is preferably a resin having a glass transition temperature of 30 ° C. or lower. Thus, when the glass transition temperature of the binder in a foamable layer is 30 degrees C or less, a binder softens in the case of the dielectric heating etc. by a microwave oven, and expansion | swelling of a thermally foamable microcapsule is performed effectively. In addition, as an upper limit of the glass transition temperature of the said binder, 20 degreeC is preferable from viewpoints, such as the expansibility of a thermally foamable microcapsule, and 10 degreeC is more preferable. On the other hand, the lower limit of the glass transition temperature of the binder can be, for example, −50 ° C., preferably −30 ° C., more preferably −10 ° C. By making the glass transition temperature of the said binder more than the said minimum, the adhesiveness of a thermally foamable microcapsule can be improved. Here, the glass transition temperature refers to a midpoint glass transition temperature measured according to JIS-K-7121 (1987).

  Examples of the binder include an ethylene vinyl acetate copolymer, polyvinylidene chloride, polyvinylidene fluoride, and a styrene butadiene copolymer. The binder preferably contains an ethylene vinyl acetate copolymer as a main component. By using an ethylene vinyl acetate copolymer as a binder, the thermally foamable microcapsules can be expanded more favorably. As content of the ethylene vinyl acetate copolymer in the said binder, 60 mass% or more is preferable, 80 mass% or more is more preferable, 95 mass% or more is further more preferable. In these resins, the glass transition temperature can be controlled by the molecular weight or the like. Moreover, the resin of the said binder can be used individually by 1 type or in mixture of 2 or more types.

  The lower limit of the binder content in the foamable layer is preferably 30% by mass, and more preferably 50% by mass. On the other hand, as an upper limit of this content, 80 mass% is preferable, 70 mass% is more preferable, and 65 mass% is further more preferable. When the content of the binder is less than the above lower limit, the unevenness of the surface after heating becomes large, the smoothness may be lowered, or the foamable microcapsules may be easily dropped off. On the contrary, when the content of the binder exceeds the above upper limit, sufficient foaming cannot be performed, and the heat insulating property may be lowered.

(Humectant)
It is preferable that at least one of the foamable layer composition and the coating layer composition contains a humectant. By containing a moisturizing agent in at least one of the foamable layer and the coating layer, the thermally foamable macrocapsule can be effectively expanded by heating with a microwave oven, and the heat insulation is excellent. Moreover, since the generation | occurrence | production of the curl of the said sheet | seat for heat insulation containers is suppressed by containing a humectant, workability is also improved.

The moisturizing agent is not particularly limited as long as it is a component having moisturizing properties. For example, polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, and 1,3-butylene glycol;
Polyols such as polyethylene glycol, polypropylene glycol, polyglycerin;
Sugars such as sorbitol, glucose, xylitol, maltose, maltitol, mannitol, trehalose;
Cellulose derivatives such as carboxymethylcellulose (CMC), hydroxyethylcellulose, hydroxypropylcellulose;
Higher alcohols such as cetanol, stearyl alcohol, oleyl alcohol;
Other examples include collagen, hydrolyzed collagen, hydrolyzed keratin, hydrolyzed silk, ceramide, hyaluronic acid and the like.

  Among these moisturizers, polyhydric alcohols and polyols are preferable, polyols are more preferable, and polyethylene glycol is more preferable. By using these compounds as a humectant, it is possible to exhibit better moisturizing properties and consequently heat insulating properties. In addition, these (polyethylene glycol and the like) are preferable because they make paper soft and have an effect of suppressing curling and improve surface properties after foaming. A sheet for a heat-insulating container that easily generates curl is not preferable because it affects the processability and workability of the container.

  When the foamable layer contains a humectant, the lower limit of the content of the humectant in the foamable layer may be, for example, 1% by mass, preferably 5% by mass, and more preferably 7% by mass. On the other hand, the upper limit of the content may be, for example, 50% by mass, but is preferably 30% by mass, and more preferably 15% by mass. When the content of the humectant exceeds the above upper limit, the material forming the foamable layer becomes non-uniform and the strength is lowered. As a result, the surface of the sheet after foaming is likely to be distorted or wrinkled. Moreover, when there is too much content of the moisturizer in a foamable layer, it will become impossible to make a foamable layer contain sufficient quantity of a heat-foamable microcapsule, and heat insulation will fall. For this reason, by setting the content of the moisturizing agent in the foamable layer within the above range, it is possible to exhibit sufficient water retention while suppressing deterioration of the appearance and to enhance the heat insulation after foaming.

(Other ingredients)
The foamable layer may contain components other than the heat-foamable microcapsules, the binder, and the humectant. Examples of other components include a surfactant, a sizing agent, and a pigment. However, as content of the other component in a foamable layer, 10 mass% or less is preferable, and 1 mass% or less is more preferable. In the foamable layer, if the content of components other than the heat-foamable microcapsules and the binder is increased, the foamability, and thus the heat insulation properties may be affected.

[Flexo printing]
The foamable layer is laminated on one surface side of the paper substrate by a flexographic printing method. Since the said foamable layer is laminated | stacked by a flexographic printing system, the foamable layer which consists of a convex-shaped halftone dot pattern can be formed. As a result, the layer thickness and specific surface area can be easily increased as compared to a flat coating film formed by a known coating machine. Therefore, it is possible to manufacture a heat insulating container sheet that exhibits good heat insulating properties.

  Flexographic printing consists of a relief printing plate roll made of rubber or resin, an anilox roll with fine cells engraved in parallel on the surface, and an impression cylinder roll that applies a low pressure during transfer from the printing plate roll to the substrate. This is a relief printing method using a flexographic printing machine. First, a foamable layer composition that becomes a water-based ink is supplied to an anilox roll from a fountain roll (rubber roll) or a doctor chamber. The temperature of the foamable layer composition to be supplied is adjusted by a heating tank according to the outside air temperature. Next, the anilox roll transfers a certain amount of the foamable layer composition to the printing plate roll. And a foamable layer is laminated | stacked with respect to the one surface side of the paper base material which passes between between a printing plate roll and an impression cylinder roll.

  The lower limit of the number of lines engraved on the surface of the cylindrical portion of the anilox roll is not particularly limited, but is preferably 80 lines / inch, more preferably 85 lines / inch, and even more preferably 90 lines / inch. On the other hand, the upper limit of the number of lines is not particularly limited, but is preferably 200 lines / inch, more preferably 180 lines / inch, and even more preferably 160 lines / inch. When the number of lines is less than the lower limit, irregularities on the surface after expansion may easily occur. On the other hand, when the number of lines exceeds the above upper limit, the film thickness becomes thin and sufficient heat insulating properties and cushioning properties may not be obtained.

The lower limit of the amount of lamination of the foamable layer composition in the foamable layer, is preferably 10 g / ^{m 2} in terms of solid content, more preferably 12 g / ^{m 2,} more preferably 15 g / ^{m 2.} On the other hand, the upper limit of the amount of the foamable layer composition is preferably 50 g / m ² , more preferably 45 g / m ² , and even more preferably 35 g / m ^{2 in} terms of solid content. When the mass per unit area of the foamable layer is less than the lower limit, sufficient heat insulating properties and cushioning properties may not be obtained. On the other hand, when the mass per unit area of the foamable layer exceeds the above upper limit, the heat-foamable microcapsules are likely to drop off, and the surface irregularities after expansion may be likely to occur.

  After flexographic printing, the foamable layer can be obtained by heating and drying as necessary. In addition, when performing heat drying, it carries out on the conditions on which a thermally foamable microcapsule does not foam substantially.

<Coating layer lamination process>
In the coating layer laminating step, a coating layer made of the composition for the coating layer is laminated on the surface of the foamable layer opposite to the paper substrate. That is, the coating layer is a layer that covers the outer surface of the foamable layer. By laminating a coating layer on the surface of the foamable layer opposite to the paper substrate, that is, on the outer surface side of the foamable layer, heat dissipation is suppressed and thermal foaming of the thermally foamable microcapsules is promoted. The sheet | seat for heat insulation containers which can be manufactured can be manufactured. In addition, it is possible to suppress the falling off of the heat-foamable microcapsules in the foamable layer and to improve the surface smoothness.

  The coating layer is formed by coating a composition for a coating layer that becomes a coating solution. The coating can be performed using a known coating apparatus such as a two-roll size press coater, a gate roll coater, a blade coater, or a rod metering coater. Moreover, it can also coat using printing machines, such as a flexographic printing machine, a gravure printing machine, and an offset printing machine. After coating, the coating layer is obtained by heating and drying as necessary. In addition, when heat-drying a coating layer, it carries out on the conditions on which the thermally foamable microcapsule in the foaming layer used as a lower layer does not foam substantially.

  Although the said composition for coating layers can have well-known general various resin as a main component, it is preferable to contain crystalline resin as a main component. In addition, crystalline resin means resin which can confirm a melting peak in the measurement by the differential scanning calorimeter (DSC) based on JIS-K-7121 (2012) based on JIS-K-7121 (2012). . Moreover, a main component means a component with most content on a mass basis. As a minimum of content of the above-mentioned crystalline resin in the above-mentioned composition for coating layers, 50 mass% is preferred, 80 mass% is more preferred, 90 mass% is still more preferred, and 95 mass% is especially preferred. Further, the upper limit of the content of the crystalline resin may be 100% by mass, but may be 90% by mass or 70% by mass when the coating layer contains the moisturizing agent. %.

  The crystalline resin is preferably a crystalline resin having a melting point of 120 ° C. or higher. Note that a crystalline resin that decomposes without melting at 120 ° C. or higher and does not have a melting point is also a crystalline resin having a melting point of 120 ° C. or higher. As a minimum of melting point of the above-mentioned crystalline resin, 140 ° C is preferred and 150 ° C is more preferred. In particular, the glass transition temperature of the binder in the foamable layer is preferably 30 ° C. or lower, and the melting point of the crystalline resin in the coating layer is preferably 120 ° C. or higher. In such a case, the melting point of the crystalline resin of the coating layer is sufficiently high with respect to the glass transition temperature of the binder of the foamable layer. Therefore, when the thermally foamable microcapsules are expanded by heating, the coating layer is difficult to soften, so that the surface shape is maintained and the smoothness of the surface can be maintained. The upper limit of the melting point of the crystalline resin is not particularly limited, but can be, for example, 300 ° C., 250 ° C., or 230 ° C.

  Examples of the crystalline resin include polyethylene, polypropylene, nylon, polyvinyl alcohol, carboxymethyl cellulose, starch, and the like. Water-soluble polymers such as polyvinyl alcohol, carboxymethyl cellulose, and starch are preferable, and polyvinyl alcohol is more preferable. By using a water-soluble polymer, a coating layer can be formed relatively easily by application of this aqueous solution. In particular, by using polyvinyl alcohol, a strong film can be formed, and the ability to prevent the thermally foamable microcapsules from falling off and the smoothness of the surface after foaming can be further enhanced. Further, when polyvinyl alcohol is used, even when the degree of crystallinity is low, crystallization proceeds with heating during use, so that the smoothness of the surface can be maintained well even after heating.

  Polyvinyl alcohol (PVA) can be obtained, for example, by polymerizing a vinyl ester such as vinyl acetate and saponifying the obtained polyvinyl ester.

  As a minimum of the saponification degree of PVA, although it may be 70 mol%, 85 mol% is preferable. By setting the saponification degree of PVA to the above lower limit or more, the crystallization degree of PVA forming the coating layer can be increased, and the surface smoothness after expansion of the thermally foamable microcapsules can be further increased. Moreover, by making the saponification degree of PVA more than the said minimum, the intensity | strength of a coating layer can be raised and the fall prevention ability of a thermally foamable microcapsule can be improved more. The degree of saponification of polyvinyl alcohol is the ratio (mol%) of the number of moles of vinyl alcohol units to the total number of moles of vinyl ester units and vinyl alcohol units that can be converted to vinyl alcohol units by saponification. Say.

  As a minimum of the polymerization degree of PVA, 200 is preferable and 400 is more preferable. When the degree of polymerization of PVA is less than the above lower limit, there is a possibility that the strength of the resulting coating layer is lowered, the melting point is lowered, and the like. On the other hand, the upper limit of the degree of polymerization of PVA is preferably 2500, more preferably 2000. When the degree of polymerization of PVA exceeds the above upper limit, the solution becomes highly viscous and the coatability may be reduced.

  When the said coating layer contains a moisturizer, as a minimum of content of the moisturizer in a coating layer, 1 mass% may be sufficient, but 5 mass% is preferable and 7 mass% is more preferable. On the other hand, as an upper limit of this content, 30 mass% is preferable and 15 mass% is more preferable. When the content of the humectant is less than the above lower limit, the humectant content effect may not be sufficiently achieved, and the heat insulation effect due to sufficient foaming may not be obtained. On the other hand, when the content of the humectant exceeds the above upper limit, the material forming the coating layer becomes non-uniform, the strength is reduced, and the like, and as a result, the surface of the sheet after foaming is likely to be distorted or wrinkled.

  The coating layer may contain components other than the crystalline resin and the humectant. Examples of other components include an amorphous resin, a surfactant, a sizing agent, and a pigment. However, as content of the other component in a coating layer, 10 mass% or less is preferable, and 1 mass% or less is more preferable. If the content of the component in the coating layer increases, the surface smoothness and the like may be affected.

The lower limit of the mass per unit area of the coating layer (basis weight), for example can be a 0.3 g / ^{m 2,} preferably ^{1g / m 2, 1.5g / m} 2 is more preferable. On the other hand, the upper limit of the mass per unit area of the coating layer (basis weight), preferably 10 g / ^{m 2,} more preferably ^{6g / m 2, 4g / m} 2 is more preferred. When the basis weight of the coating layer is less than the lower limit, the heat-foamable microcapsules are likely to drop off during printing or processing. On the other hand, if the basis weight of the coating layer exceeds the above upper limit, the covering property is too high, and blisters (wrinkles) may occur due to water vapor during heating.

As a minimum of the density of the sheet | seat for heat insulation containers manufactured with the manufacturing method of the said sheet | seat for heat insulation containers, 0.2g / cm < ³ > is preferable and 0.3g / cm < ³ > is more preferable. On the other hand, the upper limit of the density of the sheet for heat insulating containers is preferably 0.7 g / cm ³ . When the density of the sheet for heat insulating containers is less than the lower limit, the strength of the sheet for heat insulating containers may be insufficient. On the other hand, when the density of the sheet for heat-insulating containers exceeds the above upper limit, the smoothness and shape retention of the surface of the sheet for heat-insulating containers may be insufficient due to the expansion of the foamable microcapsules by heating.

The lower limit of the basis weight of the insulated container for sheet produced by the production method of the heat insulating container sheet, preferably ^{60g / m 2, 160g / m} 2 is more preferable. Moreover, as an upper limit of the basic weight of the said sheet | seat for heat insulation containers, 700 g / m < ² > is preferable and 500 g / m < ² > is more preferable. When the basis weight of the sheet for heat insulating containers is less than the lower limit, there is a possibility that the hand feeling after foaming and the strength as the heat insulating container are insufficient. On the other hand, when the basis weight of the said heat insulating container sheet | seat exceeds the said upper limit, there exists a possibility that the weight of the heat insulating container using the said heat insulating container sheet | seat may become unnecessarily large, or the productivity of the sheet | seat for heat insulating containers may fall.

  According to the method for manufacturing a sheet for a heat insulating container, it is possible to manufacture a sheet for a heat insulating container that is excellent in foamability when heated by a microwave oven and can exhibit good heat insulating properties when heated by a microwave oven. it can.

<Other embodiments>
The sheet | seat for heat insulation containers and heat insulation containers of this invention are not limited to the said embodiment. For example, in a sheet for a heat insulating container, a structure in which a foamable layer and a coating layer are provided on both sides of a paper substrate may be used. Moreover, you may have layers other than a paper base material, a foamable layer, and a coating layer. Examples of the other layer include an inorganic layer and a resin layer for the purpose of imparting functions such as water resistance (leakage resistance) and gas barrier properties to the heat insulating container.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

The thermally foamable microcapsules and the like used in Examples and Comparative Examples are shown below.
(1) Paper base material Yankee paper machine with slurry containing hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP) with sizing agent ("AL1362" by Starlight PMC), sulfate band and cationized starch Made paper. Paper base materials A1 to A5 and a1 to a2 were obtained by appropriately adjusting papermaking raw materials and papermaking conditions.
(Physical properties of paper substrate)
Table 1 shows the basis weight (g / m ² ) and air resistance (seconds) as physical properties of the paper bases A1 to A5 and a1 to a2 used. The basis weight of the sheet was measured in accordance with JIS-P8124 (2011) “Paper and paperboard—basis weight measurement method”.

(2) Foamable layer (2-1) Thermally foamable microcapsule The following B1 to B6 were used as the thermally foamable microcapsule of the foamable layer. The content (parts by mass) in the foamable layer of the thermally foamable microcapsules used is shown in Table 2 below.
・ B1 ("EXPANEL 007-40" manufactured by AkzoNobel)
Monomer of outer resin: acrylonitrile (AN) and methyl methacrylate (MMA)
Low boiling point solvent: isobutane Particle size: 10-16 μm
Foam start temperature (Ts): 91-99 ° C
Maximum foaming temperature: 132-140 ° C
Volume ratio before and after foaming: 50 times-B2 ("EXPANEL 051" manufactured by AkzoNobel)
Monomer of outer resin: acrylonitrile (AN) and methyl methacrylate (MMA)
Low boiling point solvent: isobutane Particle size: 9-15 μm
Foam start temperature (Ts): 106-111 ° C
Maximum foaming temperature: 138-147 ° C
Volume ratio before and after foaming: 130 times B3 ("EXPANEL 053" manufactured by AkzoNobel)
Monomer of outer resin: acrylonitrile (AN) and methyl methacrylate (MMA)
Low boiling point solvent: isobutane Particle size: 10-16 μm
Foam start temperature (Ts): 94-101 ° C
Maximum foaming temperature: 136-144 ° C
Volume ratio before and after foaming: 65 times B4 ("Microsphere-F36" manufactured by Matsumoto Yushi Co., Ltd.)
Monomer of outer resin: Acrylonitrile (AN) copolymer Low boiling point solvent: Isobutane Particle size: 10-16μm
Foam start temperature (Ts): 75-85 ° C
Maximum foaming temperature: 120-130 ° C
Volume ratio before and after foaming: 60 times B5 ("Microsphere-F30VS" manufactured by Matsumoto Yushi Co., Ltd.)
Monomer of outer resin: acrylonitrile (AN) copolymer and vinylidene chloride (PVDC)
Low boiling point solvent: Isobutane Particle size: 3-7μm
Foam start temperature (Ts): 91-99 ° C
Maximum foaming temperature: 110-120 ° C
Volume ratio before and after foaming: 30 times-B6 ("Microsphere-F793" manufactured by Matsumoto Yushi Co., Ltd.)
Monomer of outer resin: Acrylonitrile (AN) copolymer Low boiling point solvent: Isobutane Particle size: 25-35 μm
Foam start temperature (Ts): 110-120 ° C
Maximum foaming temperature: 160-165 ° C
Volume ratio before and after foaming: 50 times

(2-2) Binder As the binder, the following C1 to C4 were used. The content (parts by mass) of the binder used in the foamable layer is shown in Table 2 below. The glass transition temperature (Tg) was measured using a differential scanning calorimeter (DSC) using a film obtained by flowing an emulsion solution of a binder on a glass plate and drying at 100 ° C. as a sample. Measured.
・ C1 (Kuraray "Panflex OM4000NT")
Ethylene vinyl acetate copolymer Glass transition temperature (Tg): 5 ° C
・ C2 (Sumikaflex 753 manufactured by Sumitomo Chemical Co., Ltd.)
Ethylene vinyl acetate copolymer resin emulsion Glass transition temperature (Tg): -20 ° C
・ C3 (“SBR0589” manufactured by Nippon Synthetic Rubber Co., Ltd.)
Styrene butadiene latex Glass transition temperature (Tg): 8 ° C
・ C4 ("Saran Latex L411A" manufactured by Asahi Kasei Corporation)
Polyvinylidene chloride Glass transition temperature (Tg): -18 ° C

(2-3) Moisturizer The following D1 to D3 were used as the moisturizer for the foamable layer. In addition, Table 2 below shows the content (parts by mass) of the moisturizer used in the foamable layer.
D1: Polyethylene glycol (PEG200) manufactured by Toho Chemical Co., Ltd.
D2: Glycerol manufactured by Toho Chemical Co., Ltd. D3: Propylene glycol manufactured by Toho Chemical Co., Ltd.

(2-4) Foamable layer composition Foamable layer compositions G1 to G38 were prepared using the thermally foamable microcapsules, the binder, and the humectant. The content (parts by mass) in the foamable layer composition of each component and the No. of the foamable layer composition. The viscosities at 25 ° C. measured by 4 Zahn cups are shown in Table 2 below.

(3) Covering layer (3-1) Crystalline resin As crystalline resin of the composition for coating layers, the following E1-E5 was used. Table 3 below shows the means for laminating the coating layer resin used and the content (parts by mass) in the coating layer.
・ E1 ("PVA205" manufactured by Kuraray)
Polyvinyl alcohol Saponification degree: 88 mol%
Degree of polymerization: 500
・ E2 (Kuraray "PVA105")
Polyvinyl alcohol Saponification degree: 98.5 mol%
Degree of polymerization: 500
・ E3 (Kuraray "PVA405")
Polyvinyl alcohol Saponification degree: 81.5 mol%
Degree of polymerization: 500
・ E4 ("PVA110" manufactured by Kuraray Co., Ltd.)
Polyvinyl alcohol Saponification degree: 98 mol%
Degree of polymerization: 1000
・ E5 (Kuraray "PVA224")
Polyvinyl alcohol Saponification degree: 88 mol%
Degree of polymerization: 2400

(3-2) Moisturizing agent As the moisturizing agent for the coating layer composition, D1 to D3 were used in the same manner as the moisturizing agent for the foamable layer.

(3-3) Other components The following compounds were used as other components of the composition for a coating layer. In addition, Table 3 below shows the content (parts by mass) of each component in the coating layer.
Surfactant: “Cathogen DDM” manufactured by Daiichi Pharmaceutical Co., Ltd., which is a cationic dodecyl ammonium chloride
Sizing agent: “AL1200” manufactured by Seiko PMC Co., Ltd., a rosin emulsion sizing agent

(3-4) Composition for Coating Layer Compositions H1 to H38 for the coating layer were prepared using the crystalline resin, the humectant and other components. The contents (parts by mass) in the composition for the coating layer of each component are shown in Table 3 below.

[Example 1]
The foamable layer was formed by laminating 20 g / m ² of the foamable layer composition G1 on a paper substrate A1 in terms of solid content using a flexographic printing machine.
The conditions for flexographic printing are as follows.
Supply of composition for foaming layer: Doctor chamber method Number of wires of anilox roll: 120 lines / inch Temperature of composition for foaming layer: 25 ° C
Printing speed: 110 m / min Next, the surface of the foamable layer was coated with 2 g / m ² of the coating layer composition H1 in terms of solid content by a flexographic printing machine in the same manner as the foamable layer composition G1. And a sheet for a heat insulating container of Example 1 was obtained.

[Examples 2 to 25, Comparative Examples 1 and 2]
Except having made the conditions of a foamable layer and a coating layer as shown in following Table 4, it carried out similarly to Example 1, and obtained the sheet | seat for heat insulation containers of Examples 2-15 and Comparative Examples 1-2.

[Comparative Example 3]
The foamable layer was formed by laminating 2 g / m ² of the foamable layer composition G18 on the paper base material A3 in terms of solid content using a coating machine (2-roll size press coater). Next, 2 g / m ² of the coating layer composition H18 was applied to the surface of the foamable layer by a flexographic printing machine in terms of solid content to form a coating layer, and a heat insulating container sheet of Comparative Example 3 was obtained.

[Comparative Examples 4 to 13]
Heat insulation container sheets of Comparative Examples 4 to 11 were obtained in the same manner as Comparative Example 3 except that the conditions of the foamable layer and the coating layer were as shown in Table 4 below.

<Evaluation>
About the obtained sheet | seat for heat insulation containers, the thickness of a foamable layer, a density (g / m < ³ >), a heat insulation test, drop-off evaluation of a heat-foamable microcapsule, smoothness evaluation (blister evaluation), Curl evaluation and container processability evaluation were performed. The evaluation results are shown in Table 5.

[Thickness of foamable layer]
The thickness (μm) of the insulating container sheet before and after foaming was measured with a length measuring SEM.

[density]
The density of the sheet | seat for heat insulation containers obtained based on JIS-P8118 (1998) "" Test method of thickness and density "was measured.

[Insulation test]
The heat insulation property of the sheet | seat for heat insulation containers after foaming was evaluated in the following procedures. The sheet for an insulated container was immersed in water for 1 minute, then wrapped in Saran Wrap (registered trademark), heated in a microwave oven at 600 W for 3 minutes, and foamed. The sheet | seat for heat insulation containers after foaming was cut | judged to 65 mm x 50 mm, and the paper base material side was affixed on the paper cup outer side. Hot water of 90 ° C. was poured into this paper cup, and the maximum temperature (° C.) reached by the outer surface of the sheet for heat insulating container was measured with a thermocouple. This maximum temperature is preferably 80 ° C. or lower, and very preferably 70 ° C. or lower.

[Evaluation of dropout of thermally foamable microcapsules]
The sheet for an insulated container was immersed in water for 1 minute, then wrapped in Saran Wrap (registered trademark), heated in a microwave oven at 600 W for 3 minutes, and foamed. The foamed heat insulation container sheet (A5 size) was folded in half so that the coated surface (coating layer surface) was on the outside. Next, the sheet for the heat insulating container is placed on the upper side of the funnel installed in the suction port of the glove box (“SS-MAC” of Japan Airtech Co., Ltd.), and the sheet for the heat insulating container is once per second with the index finger from the upper side. Tapped for a predetermined time (30 seconds, 10 seconds × 3 times) at intervals of. And the particle | grains which generate | occur | produced from the sheet | seat for heat insulation containers were attracted | sucked, and the number of particles with a particle size of 1 micrometer or more was measured using "Particle counter KC-32" of Rion Corporation. This measurement was repeated 5 times, the average value was calculated, and evaluated based on the following evaluation criteria. In addition, (double-circle), (circle), and (triangle | delta) are the ranges which can be actually used.
(Evaluation criteria)
A: The number of particles is less than 50, and it is considered that the heat-foamable microcapsules are very little detached.
A: The number of particles is 50 or more and less than 100, and it is considered that the heat-foamable microcapsules are less dropped.
Δ: The number of particles is 100 or more and less than 200, and it is considered that the thermally foamable microcapsules are often dropped.
X: The number of particles is 200 or more, and it is considered that the thermally foamable microcapsules are very often dropped.

[Smoothness evaluation (blister evaluation)]
The sheet for an insulated container was immersed in water for 1 minute, then wrapped in Saran Wrap (registered trademark), heated in a microwave oven at 600 W for 3 minutes, and foamed. The surface of the coating layer side of the heat insulating container sheet after foaming was observed and evaluated according to the following evaluation criteria. In addition, (double-circle), (circle), and (triangle | delta) are the ranges which can be actually used.
(Evaluation criteria)
A: Blisters could not be visually confirmed, and the smoothness was extremely high.
○: A small number of small folds (blisters) were present.
Δ: Small creases (blisters) were present overall.
×: A large number of blisters including large ones were present.

[Curl evaluation]
The ease of curling was evaluated in the following order. The sheet for a heat-insulating container before foaming was cut so as to form a 300 mm square with one side as the paper making direction, and left for 1 hour in an environment of a temperature of 23 ° C. and a humidity of 50%. Then, the said heat insulation container sheet | seat was set | placed on the flat surface (plate), the height (mm) from the surface (plate) of four corners was measured, and the average of four corners was taken.

[Evaluation of container moldability]
The ease of forming the heat insulating container sheets of Examples and Comparative Examples into containers was evaluated in the following order.
After a heat insulating container sheet is punched into a predetermined shape to produce a molding sheet, it is used in accordance with JIS-P-8111 (1998) using a thermo-hygrostat, (23 ± 1) ° C., (50 ± 2)% RH. Was conditioned. Using a hot plate pressure forming machine, a cup-shaped molded body was obtained from the humidity-controlled molding sheet. And the presence or absence of the mold retainability of the moldability and the obtained molded body was visually evaluated according to the following criteria.
(Evaluation criteria)
A: Can be easily molded into a cup shape, the surface of the molded body is smooth, and the mold retainability is very good.
○: Can be easily molded into a cup shape, and has good mold retention.
Δ: Can be molded into a cup shape, but slightly inferior to the surface state of the molded body.
X: Difficult to mold in cup shape or large irregularities on the surface of the molded body.

  The evaluation results of the above characteristics are shown in Table 5.

  As shown in Table 5, the heat-insulating container sheets of Examples 1 to 15 in which the foamable layer is laminated by the flexographic printing method have a good thickness in the foamable layer before foaming and after foaming. Was also good. Moreover, it has confirmed that the sheet | seat for heat insulation containers of Examples 1-15 was favorable in all of the low density, heat insulation, drop-off evaluation of a thermally foamable microcapsule, smoothness, curl evaluation, and container moldability. On the other hand, the sheet | seat for heat insulation containers of Comparative Examples 1-13 was inferior in any one item among said items. In addition, the sheets for heat-insulating containers of Comparative Examples 3 to 13 in which the foamable layer was coated with a 2-roll size press coater did not have sufficient thickness in the foamable layer before foaming and after foaming, and the curl evaluation was poor. It was. Moreover, the sheet | seat for heat insulation containers of Comparative Examples 1-2 and 5-6 is especially inferior in a container moldability compared with an Example, and the sheet | seat for heat insulation containers of Comparative Examples 1 and 3-13 is also inferior in curl evaluation. It was. The sheets for heat insulating containers of Comparative Examples 4, 6 to 8, and 11 to 12 were particularly inferior in dropping evaluation and smoothness of the thermally foamable microcapsules.

  The manufacturing method of the sheet | seat for heat insulation containers of this invention can manufacture the sheet | seat for heat insulation containers suitable as a molding material etc. of the container for cooking heated with a microwave oven etc.

Claims (4)

Laminating a foamable layer comprising a composition for a foamable layer containing a thermally foamable microcapsule and a binder on one side of a paper substrate;
A step of laminating a coating layer made of the composition for a coating layer on the surface of the foamable layer opposite to the paper substrate,
The basis weight of the paper substrate is 50 g / m ² or more and 600 g / m ² or less,
The manufacturing method of the sheet | seat for heat insulation containers in which the said foamable layer is laminated | stacked by a flexographic printing system. The step of laminating the foamable layer is performed using a flexographic printing machine equipped with an anilox roll,
The number of lines engraved on the surface of the cylindrical portion of the anilox roll is 80 lines / inch or more and 200 lines / inch or less,
The laminate of foamable layer above foamable layer composition in the method of producing a heat-insulating container sheet of claim 1, wherein in terms of solid content is 10 g / m ² or more 50 g / m ² or less.   Content of the said thermally foamable microcapsule with respect to the said composition for foamable layers is 20 mass% or more and 70 mass% or less, and No. of the said composition for foamable layers. The manufacturing method of the sheet | seat for heat insulation containers of Claim 1 or Claim 2 whose viscosity in 25 degreeC measured by 4 Zahn cups is 5 second or more and 50 second or less. The manufacturing method of the sheet | seat for heat insulation containers of Claim 1, Claim 2 or Claim 3 in which at least one of the said composition for foamable layers and the said composition for coating layers contains a moisturizer.