Coating agent for heat-resistant paper sheet and printed paper sheet for packaging material

Abstract

To provide a coating agent for a heat-resistant paper sheet capable of protecting ink printed on a printing surface of a heat-resistant paper layer.SOLUTION: There is provided a coating agent for a heat-resistant paper sheet having a heat-resistant paper layer, which has heat resistance to heat treatment and is made of a material mainly composed of paper on a printing surface, in which a sealant layer is provided on the opposite side of the printing surface, wherein the coating agent is constituted by adding an isocyanate-based curing agent and a wax-based additive to a varnish used to coat the printing surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a coating agent for heat-resistant paper sheets and printed paper sheets for packaging, in particular a coating agent for heat-resistant paper sheets having a heat-resistant paper layer made of a paper-based material on the printed surface, which has heat resistance against heat treatment, and a sealant layer on the surface opposite the printed surface. [Background technology]

[0002] When constructing a packaging material from laminated sheets in which resin layers are laminated, it is common to provide a sealant layer on the joining surfaces of the sheets and heat-seal the sealant layers to join the sheets. On the other hand, when the packaging material is heat-treated after the contents are placed inside, the packaging material may be formed using a sheet having a paper layer with excellent heat resistance on its outer surface. Such a sheet having a heat-resistant paper layer on its outer surface is called a heat-resistant paper sheet. Such a paper layer having heat resistance (hot water resistance) is described, for example, in Patent Document 1 below. When this heat-resistant paper sheet is used to make a packaging material, a sealant layer (resin layer) for heat fusion is provided on one side of the heat-resistant paper sheet, which will be the inner surface of the packaging material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-219745 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, when printing is performed on a heat-resistant paper sheet having a paper layer on its outer surface, the outer surface of this paper layer becomes the printing surface since the paper layer is generally opaque. The paper layer constituting the outer surface layer of such a heat-resistant paper sheet has a lower thermal conductivity than the resin layer. In addition, since a heat treatment is performed, a resin with a high melting point is also used for the sealant layer used in the heat-resistant paper sheet. Therefore, the temperature of the seal bar used for heat-sealing the heat-resistant paper sheets is set to a higher temperature than the temperature of the seal bar used for heat-sealing the resin laminated sheets. When heat-sealing the heat-resistant paper sheets having the outer surface of the paper layer printed thereon, the ink on the outer surface, that is, the printing surface, comes into contact with the high-temperature seal bar, and a problem occurs in that part of the ink adhering to the printing surface is transferred to the seal bar.

[0005] The present invention has been made in consideration of the above problems, and its object is to provide a coating agent for heat-resistant paper sheets that can protect ink printed on the printing surface of a heat-resistant paper layer. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, one embodiment of the present invention provides a coating agent for heat-resistant paper sheets, which has a heat-resistant paper layer made of a paper-based material on its printed surface and is resistant to heat treatment, and has a sealant layer on the surface opposite the printed surface, and is composed of a varnish that coats the printed surface to which an isocyanate-based curing agent and a wax-based additive have been added. Effect of the Invention

[0007] According to the coating agent for heat-resistant paper sheets of the present invention, the strength of the hardened varnish is improved by the isocyanate-based curing agent, and the wax-based additive reduces the contact area between the seal bar and the hardened varnish, thereby reducing the heat shock of the ink caused by the seal bar and protecting the ink by preventing transfer of the ink to the seal bar. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view of a heat-resistant paper layer showing one embodiment of a coating agent for a heat-resistant paper sheet and a printed paper sheet for packaging material of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The embodiments of the coating agent for heat-resistant paper sheets of the present invention will be described in detail below with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not specify the materials, shapes, structures, arrangements, etc. of the components to the embodiments below. In addition, the drawings are schematic. Therefore, it should be noted that the relationship and ratio between thickness and planar dimensions are different from the actual ones, and the drawings also include parts where the relationship and ratio of dimensions are different from each other.

[0010] FIG. 1 is a cross-sectional view of the surface of a heat-resistant paper layer 1 of a heat-resistant paper sheet (printed paper sheet for packaging material) in a state in which a coating agent for heat-resistant paper sheets is applied to the printed surface and hardened. The hatched portion in the figure is the paper layer 1 arranged on the outer surface of the heat-resistant paper sheet, and in this embodiment, it has heat resistance and water resistance (hot water resistance) corresponding to hot water treatment. As the paper layer 1 having heat resistance and water resistance in this way, the one described in the above-mentioned Patent Document 1 can be applied. This paper layer 1 is, for example, a fiber structure such as virgin pulp used as a processed base paper, which is impregnated or coated with a resin that can impart hot water resistance. This heat-resistant paper sheet is used as a packaging material for retort foods, for example, and therefore a barrier film layer is laminated on the inside of the paper layer 1 with an adhesive layer sandwiched therebetween, and a sealant layer is laminated on the inside of that with an adhesive layer sandwiched therebetween. As described above, the sealant layer is arranged to heat-seal the heat-resistant paper sheets together.

[0011] The outer surface (top surface of the figure) of the paper layer 1 in FIG. 1 is printed with ink (ink is not shown). A coating agent is applied to the surface (top surface) of this printed surface and hardened. The main agent of this coating agent is varnish 2. Varnish 2 refers to a paint that does not contain pigment (colored material) and is mainly composed of resin and solvent, and forms a resin film on the surface of the material when the solvent evaporates and dries. In this embodiment, varnish 2 is used to mix the ink to dilute its concentration, and therefore the resin system of varnish 2 and the resin system of ink are the same. This varnish 2 is added with an isocyanate-based hardener, for example, polyisocyanate, a wax-based additive 3, and an additive mainly composed of a matte component 4. For example, natural wax is used for the wax-based additive 3. For example, silica, i.e., silicon dioxide, is used as the main component for the additive mainly composed of the matte component 4. The amount of the hardener, the wax-based additive 3, and the additive mainly composed of the matte component 4 is 3% by weight of the amount of the varnish 2 applied. The recommended pot life of the coating is three months.

[0012] The isocyanate-based hardener is used to improve the cohesive force of the varnish 2 itself and to improve its heat resistance, thereby improving durability during heat sealing with a seal bar. In addition, by using a urethane-based ink as the ink, it is firmly bonded to the varnish 2 and prevented from being transferred to the seal bar. The wax-based additive 3 has a relatively large particle diameter, and these large particles reduce the contact area with other objects and improve slipperiness, resulting in improved friction resistance. In this embodiment, by protruding the particles of the wax-based additive 3 from the cured layer of the varnish 2, the contact area with other objects, particularly the seal bar, can be reduced, and durability against thermal shock during heat sealing can be improved. Additives mainly composed of the matte component 4 are often used literally for the purpose of matting, but this is because they form small irregularities on the surface of the resin to which they are added. The surface of the coating agent layer in Figure 1 is uneven due to the additive mainly composed of the matte component 4. The isocyanate-based hardener has a low viscosity, and the surface of the cured varnish 2 is easily smoothed. Since a smooth surface is easy to adhere to, the addition of an additive mainly composed of matte component 4 forms unevenness on the surface of the coating agent layer, thereby reducing adhesion between sheets (preventing blocking) and preventing them from sticking together, making it easier to wind the product when it is processed. A synthetic resin is added to the additive mainly composed of matte component 4 to improve the processing suitability during processing. A fatty acid amide may be added to further enhance the blocking prevention effect.

[0013] Thus, in the coating agent for heat-resistant paper sheets of this embodiment, by adding an isocyanate-based curing agent and a wax-based additive 3 to the varnish 2, which is the main agent used to coat the printed surface, it is possible to improve the cohesive strength and heat resistance of the cured varnish 2 as well as improve its durability against thermal shock during heat sealing, thereby preventing the transfer of ink to the seal bar during heat sealing and providing protection.

[0014] Furthermore, by adding an additive mainly consisting of a matte component 4 to the base varnish 2, it is possible to prevent the heat-resistant paper sheets from sticking together, facilitating processes such as winding. The above describes the coating agent for heat-resistant paper sheets according to the embodiment, but the present invention is not limited to the configuration described in the above embodiment, and various modifications are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0015] 1 paper layer 2. Varnish 3. Wax-based additives 4. Matte Ingredients

Claims

1. A coating agent for a heat-resistant paper sheet, the heat-resistant paper layer being made of a material mainly composed of paper and having heat resistance against heat treatment, on a printed surface, and a sealant layer being provided on a surface opposite to the printed surface, The coating agent for heat-resistant paper sheets is composed of a varnish for coating the printed surface, to which an isocyanate-based hardener and a wax-based additive have been added.

2. 2. The coating agent for heat-resistant paper sheets according to claim 1, wherein the varnish contains an additive mainly composed of a matte component.

3. 3. The coating agent for heat-resistant paper sheets according to claim 2, wherein the amounts of the isocyanate-based hardener, the wax-based additive and the additive mainly composed of a matte component are all 3% by weight of the varnish.

4. A printed paper sheet for packaging material, comprising the coating agent for heat-resistant paper sheets according to any one of claims 1 to 3 applied to an upper surface of a printed surface and cured.

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