JP7597690B2 - Manufacturing method of coated paper for heat sealing - Google Patents

Description

The present invention relates to a method for producing coated paper for heat sealing that has excellent printability and good heat sealing properties.

Heat sealing is a sealing method in which plastic films are melted and bonded by applying a certain amount of heat and pressure. Heat sealing has been used for the past for bonding bags for packaging materials and for forming paper cups. Proposals for imparting heat sealing properties to paper cups include using biaxially oriented polyethylene terephthalate as a heat seal layer and using multiple resins in specific ratios (see, for example, Patent Documents 1 to 4). However, when applying high-quality printing to the side opposite the heat seal layer, a pigment coating layer is provided, but the adhesion to this coating layer cannot be made satisfactory. There has been a proposal to provide a water-resistant and oil-resistant resin layer on top of a prescribed amount of primer layer containing pigment (see, for example, Patent Document 5). This method does not provide good print quality because there is no pigment coating layer.

JP 2017-43388 A JP 2011-79584 A JP 2009-149351 A JP 2006-256643 A Japanese Patent Application Publication No. 9-158089

The object of the present invention is to provide a method for producing coated paper for heat sealing that has excellent printability and good heat sealing properties and solves the above-mentioned problems.

Another object of the present invention is to provide a method for producing coated paper for heat sealing in which, when the coated paper for heat sealing breaks, the base paper or base paper portion and the coating layer do not peel off at the interface, but break as one piece.

Other objects and advantages of the present invention will be readily apparent to those skilled in the art by reading the following description.

After extensive research into the manufacturing method of heat-sealing coated paper, the inventors have found that the problem can be solved by the following configuration. That is, the manufacturing method of heat-sealing coated paper according to the present invention includes the steps of preparing a base paper, preparing a coating layer paint, and applying the coating layer paint to at least one surface of the base paper to provide a coating layer, and is characterized in that the coating layer paint contains a pigment and an adhesive, and the adhesive contains a styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more.

This configuration makes it possible to produce a relatively thin heat-sealable coated paper with excellent printability.

A different embodiment of the method for producing coated paper for heat sealing according to the present invention includes the steps of preparing a base paper, preparing a paint for an outermost coating layer, preparing a paint for an inner coating layer, applying the paint for the inner coating layer to at least one surface of the base paper to provide one or more inner coating layers, and applying the paint for the outermost coating layer on the inner coating layer to provide an outermost coating layer, the paint for the outermost coating layer containing a pigment and an adhesive, and the adhesive of the paint for the outermost coating layer containing a styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more.

This configuration allows the production of relatively thick heat-sealable coated paper with excellent printability.

In a preferred embodiment of the present invention, the coating layer paint and the outermost coating layer paint preferably contain 5 to 30 parts by mass of styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more per 100 parts by mass of the pigment. With this configuration, it is possible to produce a heat-sealable coated paper that has good heat-sealing suitability in addition to printability.

In a preferred embodiment of the present invention, the styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more preferably has an average particle size in the range of 100 to 200 nm. This configuration can provide better heat sealing suitability.

In a preferred embodiment of the present invention, the disintegration freeness of the base paper is preferably in the range of 300 to 550 ml. This configuration results in a heat-sealable coated paper with an excellent balance between paper strength and processing suitability.

In a preferred embodiment of the present invention, one or more intermediate coating layers may be formed between the inner coating layer and the outermost coating layer.

This invention can also be considered as an invention of coated paper for heat sealing.

The present invention can also be seen as an invention for paper cup containers and packaging paper that use coated paper for heat sealing.

The present invention can provide a method for producing coated paper for heat sealing that has excellent printability and good heat sealing properties.

FIG. 1 is a diagram showing an example of the configuration of a coated paper for heat sealing according to the present invention. FIG. 2 is a diagram showing an example of the configuration of a base paper of a heat-sealing coated paper according to the present invention. 1 is a table showing the configuration and evaluation of coated papers for heat sealing according to Examples and Comparative Examples.

Next, the present invention will be described in detail with reference to an embodiment, but the present invention should not be interpreted as being limited to this description. Various modifications of the embodiment may be made as long as the effects of the present invention are achieved.

An example of the configuration of the heat-sealing coated paper according to the present invention is shown in FIG. 1. In the figure, 10 is a base paper, 20 is a size layer, 30 is a base paper, 31 is a base paper surface, 40 is a coating layer, 41 is an inner coating layer, 42 is an intermediate coating layer, 43 is an outermost coating layer, 50 is an outer surface of the heat-sealing coated paper, and 100 is a heat-sealing coated paper. FIG. 1(a) is an example of the configuration of the heat-sealing coated paper when there is one coating layer, in which a size layer 20 is provided on both sides of the base paper 10, and a coating layer 40 is provided on the size layer 20. FIG. 1(b) is an example of the configuration of the heat-sealing coated paper when there are three coating layers, in which a size layer 20 is provided on one side of the base paper 10, and the base paper 30 is provided with a size layer on the surface of the base paper 10. On the base paper surface 31, the coating layers 40 are provided in the order of an inner coating layer 41, an intermediate coating layer 42, and an outermost coating layer 43. In the example of FIG. 1(b), three coating layers are provided, but if there are two coating layers, the intermediate coating layer 42 is not necessary, and conversely, if there are four or more coating layers, it is preferable to provide multiple intermediate coating layers 42. Note that FIG. 1 is a schematic representation of the structure of the heat-sealing coated paper according to the present invention, and the thickness of each layer in the figure is not based on the actual ratio of each layer.

An example of the configuration of the base paper of the heat-sealing coated paper according to the present invention is shown in Figure 2. In the figure, 10 is the base paper, 11 is the middle layer, 12 is the white underlayer, 13 is the white layer, and 14 is the surface of the base paper. The configuration shown in Figure 2 is an example of a multi-layered base paper, in which the layer exposed on both base paper surfaces 14 is the white layer 13, the layer adjacent to the inside of the white layer 13 is the white underlayer 12, and the layer provided inside the white underlayer 12 is the inner layer 11. In this example, the base paper has a five-layer structure, but if it has a three-layer structure, it is possible to omit the white underlayer 12 or the inner layer 11. On the other hand, if it has a six-layer structure or more, it is preferable to appropriately increase the number of layers of the white underlayer 12 or the inner layer 11.

In the present invention, known pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), bleached hardwood sulfite pulp (LBSP), bleached softwood sulfite pulp (NBSP), mechanical pulp (GP, TMP, BCTMP), and deinked pulp (DIP) can be used as the pulp for the base paper. In addition, in addition to wood pulp, non-wood pulp, synthetic pulp, synthetic fiber, etc. may be used as necessary. In order to give whiteness and a clean feeling to the heat-sealing coated paper, it is preferable to use LBKP or NBKP in the white layer that becomes the surface, and when using mechanical pulp, it is preferable to not mix it in the white layer but mix it in the white underlayer or middle layer from the viewpoint of fading. In addition, deinked pulp (DIP) may be mixed in the white layer if it is a high-quality waste paper, but in the case of medium-quality waste paper, it is preferable to not mix it in the white layer but mix it in the white underlayer or middle layer.

The disintegration freeness of the pulp of each layer used in the base paper of the heat-sealing coated paper is preferably in the range of 300 to 550 ml, and more preferably in the range of 350 to 500 ml. If the disintegration freeness is less than 300 ml, the base paper becomes dense and too hard, which may cause cracks when molded into a paper cup or cracks at the creases when processed into packaging paper. On the other hand, if it exceeds 550 ml, the interfiber bonds become weak, the paper strength decreases, and the strength is low after processing into a container or when used as packaging paper, which may cause problems in use. The disintegration freeness of the pulp of each layer in the present invention is obtained by measuring with a Canadian Standard Type Freeness Tester (based on JIS P 8121:1995 "Test Method for Freeness of Pulp").

The base paper of the heat-sealing coated paper of the present invention may contain a filler. Examples of fillers that may be used include light calcium carbonate, heavy calcium carbonate, talc, clay, kaolin, calcined clay, titanium dioxide, and aluminum hydroxide.

The base paper of the heat-sealing coated paper of the present invention may contain raw materials other than pulp and fillers. Such raw materials may include, for example, aluminum sulfate, sizing agents, internal paper strength enhancers such as cationic starch or polyacrylamide, retention improvers, drainage improvers, coloring dyes, coloring pigments, fluorescent brighteners, fluorescent decolorizers, and other auxiliary agents that may be suitably blended according to each product. In addition, chemicals required in the papermaking process, such as pitch control agents and defoamers, may be used as necessary.

In the case of the heat-sealing coated paper of the present invention, when the application is to be wrapping paper, the base paper is preferably made of a single layer or two layers, and the basis weight of the finished heat-sealing coated paper is preferably in the range of 50 to 150 g/ ^m2 . If the basis weight is less than 50 g/ ^m2 , the strength sufficient for wrapping paper is not obtained and it is prone to tearing. On the other hand, if the basis weight exceeds 150 g/ ^m2 , the thickness of the base paper also increases, so the heat-sealing coated paper becomes hard and may lack flexibility as wrapping paper. If the basis weight is less than 150 g/ ^m2 , the base paper is preferably made of a single layer or two layers, and the more layers there are, the harder the paper itself becomes, and in the case of a multi-layer structure, there is a possibility of delamination due to the formation of gaps between the layers, so a single layer is more preferable.

In addition, when the application is paper cups, the base paper is preferably made of three or more layers, and the basis weight of the finished heat-seal coated paper is preferably in the range of 150 to 400 g/m ^2. If the basis weight is less than 150 g/m ² , sufficient strength cannot be obtained, and the paper cup may be crushed when gripped. On the other hand, if the basis weight exceeds 400 g/m ² , the thickness of the base paper also increases, so the heat-seal coated paper becomes hard, and the flexibility suitable for processing into paper cups cannot be obtained, and processing defects may occur. In addition, when trying to obtain a thickness suitable for paper cup applications with a single-layer or two-layer base paper, it is necessary to increase the inlet concentration, which is the concentration at the inlet of the paper machine, to increase the basis weight per layer, which results in large flocks of the raw material, poor texture, and poor printability. For this reason, when increasing the basis weight of the base paper for use in applications such as paper cups, it is preferable to make it of three or more layers.

The method of manufacturing the base paper for the heat-sealing coated paper according to the present invention is not particularly limited and can be manufactured by known manufacturing methods, but when manufacturing a relatively thin heat-sealing coated paper for use in packaging paper, etc., it is preferable to use a papermaking machine suitable for single-layer or two-layer papermaking. On the other hand, when manufacturing a relatively thick heat-sealing coated paper for use in paper cups, etc., among these known manufacturing methods, various devices that are papermaking machines capable of multi-layer papermaking of three or more layers, such as a Fourdrinier multi-layer papermaking machine, a cylinder wire multi-layer papermaking machine, and a Fourdrinier cylinder wire combination multi-layer papermaking machine, are preferred.

In the heat-sealing coated paper according to the present invention, a surface sizing liquid may be applied to the front and/or back surface of the base paper. The surface sizing liquid used here is not particularly limited, but examples include known water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide. There is also no particular limit to the method of applying the surface sizing liquid, and known applicators such as a type equipped with a pond such as a size press, a film metering type such as a gate roll size press or a shim sizer, a rod coater, or an air knife coater can be used.

In the heat-sealing coated paper 100 according to the present invention, the coating layer 40 is provided on the front and/or back surface of the base paper 10 or base paper 30. The coating layer 40 may be provided directly on either the front or back outer surface 14 of the base paper 10, or the outer surface 14 of the base paper 10 may be subjected to a surface sizing treatment to provide a size layer 20, and the coating layer 40 may be provided on the outer surface 31 of the base paper 30 including the size layer 20. When coating layers are provided on both the front and back surfaces, the compositions of the coating layers on the front and back sides may be the same or different depending on the purpose.

In the present invention, when the coating layer has a single layer structure or a multilayer structure, the pigments used in the outermost coating layer are preferably kaolin clay, which is flat and therefore oriented on the coating layer surface to improve smoothness and printability, heavy calcium carbonate (ground calcium carbonate), light calcium carbonate, titanium oxide, etc., which have high whiteness, and it is desirable to use one or more of these in combination. In particular, when the product to be packaged is a white food such as yogurt or ice cream, a high whiteness is often required for the packaging container.

The preferred blend ratios of these pigments are as follows. Kaolin clay is preferably in the range of 10-30% of the total pigment amount. If the blend ratio of kaolin clay is less than 10%, sufficient ink receptivity may not be obtained and printability may decrease. If the blend ratio of kaolin clay is more than 30%, the blend ratio of pigments that contribute to whiteness will decrease relatively, resulting in a decrease in whiteness, and depending on the application, the required whiteness may not be obtained. Heavy calcium carbonate is preferably in the range of 50-90% of the total pigment amount. If the blend ratio of heavy calcium carbonate is less than 50%, the whiteness may decrease and depending on the application, the required whiteness may not be obtained. If the blend ratio of heavy calcium carbonate is more than 90%, the blend ratio of kaolin clay will decrease relatively, resulting in a decrease in sufficient ink receptivity and printability may decrease. Light calcium carbonate is preferably in the range of 0-20% of the total pigment amount. If the blending ratio of light calcium carbonate exceeds 20%, the blending ratio of kaolin clay decreases relatively, so that sufficient ink receptivity may not be obtained, and printability may decrease, and the fluidity of the paint may decrease, and the processing suitability may also decrease. The blending of light calcium carbonate is not essential, but if the blending ratio of pigments that contribute to whiteness, including light calcium carbonate, is small, the required whiteness may not be obtained depending on the application. The titanium oxide is preferably in the range of 5 to 30% of the total pigment. If the blending ratio of titanium oxide is less than 5%, the whiteness may decrease and the required whiteness may not be obtained depending on the application. If the blending ratio of titanium oxide exceeds 30%, the blending ratio of kaolin clay decreases relatively, so that sufficient ink receptivity may not be obtained, and printability may also decrease, and the fluidity of the paint may also decrease, and the processing suitability may also decrease.

In the present invention, the pigment used in the intermediate coating layer or the inner coating layer is not particularly limited, and any general pigment can be used as appropriate, but since it is desirable for the pigment in these layers to improve whiteness and have an anchoring effect on the overcoated layer, it is preferable that 90% or more of the total amount of pigment contained in the layer is heavy calcium carbonate.

In the present invention, other pigments may be used in each coating layer as necessary. Such pigments are not particularly limited, but examples include talc, satin white, lithopone, titanium dioxide, silica, alumina, aluminum hydroxide, zinc oxide, magnesium carbonate, calcined kaolin, and colored pigments.

In the heat-sealing coated paper according to the present invention, the adhesive used in the coating layer includes a styrene-butadiene copolymer latex having an average particle size of 100 nm or more (hereinafter, styrene-butadiene copolymer latex will be referred to as SBR latex). In addition, adhesives other than SBR latex may be used alone or in combination of two or more types as long as the effects of the present invention are not impaired. Other adhesives that can be used here include various copolymer latexes such as acrylic, polyvinyl acetate, or ethylene-vinyl acetate, polyvinyl alcohol, modified polyvinyl alcohol, polyacrylamide, urea or melamine/formalin resin, polyethyleneimine or polyamidepolyamine/epichlorohydrin, and other water-soluble synthetic materials. Further examples include starch refined from natural plants, hydroxyethylated starch, oxidized starch, etherified starch, phosphate esterified starch, enzyme-modified starch, cold water soluble starch obtained by flash drying these, natural polysaccharides such as dextrin, mannan, chitosan, arabinogalactan, glycogen, inulin, pectin, hyaluronic acid, carboxymethylcellulose, hydroxyethylcellulose, or their oligomers or modified forms. Other examples include natural proteins such as casein, gelatin, soybean protein, collagen, or their modified forms, and synthetic polymers or oligomers such as polylactic acid and peptides. When the coating layer has a multi-layer structure, the SBR latex having an average particle size of 100 nm or more may be contained in the outermost coating layer.

Even if SBR latex is blended into the coating layer, if the average particle size of the SBR latex is less than 100 nm, the desired heat seal strength will not be achieved. There is no particular upper limit to the average particle size, but if the maximum particle size of the SBR latex exceeds 200 nm, there is a risk of a decrease in print strength, so it is preferable to set the upper limit at 200 nm.

In the present invention, the coating layer may contain SBR latex with an average particle size of less than 100 nm, as long as the effect of the invention is not impaired. The average particle size of the SBR latex in the present invention can be measured by a known method. As an example, in this embodiment, the measurement was performed using an ELSZ-1000 (manufactured by Otsuka Electronics Co., Ltd.) using the dynamic light scattering method, and the volume average value D50 was taken as the average particle size.

In the present invention, it is preferable that 5 to 30 parts by weight of SBR latex is added per 100 parts by weight of pigment. If the amount of SBR latex with an average particle size of 100 nm or more is less than 5 parts by weight, sufficient coating layer strength cannot be obtained, and there is a risk that interfacial peeling will occur between the coating layer and the base paper, resulting in material breakage from the base paper or base paper. On the other hand, if the amount exceeds 30 parts by weight, the ink absorbency of the coating layer will decrease during printing, which may cause problems in terms of printability.

In the present invention, the paint for forming the coating layer may suitably contain various commonly used auxiliaries such as dispersants, defoamers, water-resistant agents, coloring dyes, coloring pigments, and thickeners, or cationized versions of these auxiliaries, as necessary.

In the present invention, the coating layer may be formed in one layer or in two or more layers. When the coating layer is a multi-layer structure of two or more layers, it is composed of an inner coating layer 41 provided on the front and back surfaces of the base paper or raw paper, one or more intermediate layers 42 provided as necessary on the inner coating layer 41, and an outermost coating layer 43 provided on the inner coating layer 41 or the intermediate layer 42. When two or more layers are used, the inner coating layer 41 and the outermost coating layer 43 are essential, but the intermediate layer 42 is not essential. The inner coating layer 41, the intermediate layer 42, and the outermost coating layer 43 may all have the same composition, or each layer may have a different composition. When the coating layer is two or more layers, it is preferable to form the coating layer so that the total coating amount of all the coating layers is within the range of the dry coating amount per one side described later. When no coating is required on the back surface, a water-soluble polymer such as starch may be applied to prevent curling and dried only.

In the present invention, the method of applying the coating material for forming the coating layer is not particularly limited, and various methods such as a size press with a liquid pool, a metering size press, various film transfer coaters such as a gate roll or a shim sizer, an air knife coater, a rod coater, a blade coater, a direct fountain coater, a spray coater, and a curtain coater can be used as appropriate. In addition, when the coating layer has a multi-layer structure, the coating method may be different for each layer.

In the present invention, the dry coating weight of the coating layer per side is preferably 7 to 30 g/ ^m2 , and more preferably 12 to 26 g/ ^m2 . If the desired coating weight cannot be achieved by one coating, the desired coating weight may be achieved by applying two or more coats. If the dry coating weight per side is less than 7 g/ ^m2 , the desired whiteness may not be achieved. On the other hand, if the dry coating weight per side is more than 30 g/ ^m2 , the strength of the coating layer decreases, which may cause paper dust or powder falling during processing, which may be a serious problem.

In the mainstream heat-sealing coated paper, one side is printed and the other side is laminated with polyethylene or the like. In such a configuration, it is preferable that the printed side has two or more coating layers in consideration of the finish of the printed side, and the dry coating amount per side is 17 to 28 g/ ^m2 . On the other hand, the laminated side has one coating layer in order to provide a certain degree of whiteness and lamination processability, and the dry coating amount per side is 7 to 15 g/ ^m2 .

The internal bond strength of the heat-sealable coated paper is preferably 100 to 500 mJ, and more preferably 200 to 400 mJ. If the internal bond strength is less than 100 mJ, the paper is more likely to tear during processing, such as when it is molded into a packaging bag, or to crack when the top curl of a cup is molded. On the other hand, if the internal bond strength exceeds 500 mJ, the material may be less likely to tear, which is a requirement for heat sealing.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of parts added is a value calculated as the solid content.

Example 1
<Preparation of base paper>
Pulp consisting of 90% hardwood pulp (L-BKP) and 10% softwood pulp (N-BKP) was adjusted to a CSF of 450 ml, to which was added 0.5% cationic starch (Neotac 40T, manufactured by Nihon Shokuhin Kako Co., Ltd.) as a paper strength enhancer, 0.5% aluminum sulfate as a flocculation aid, and 0.5% neutral rosin emulsion sizing agent (New Size 738, manufactured by Harima Kasei Co., Ltd.) as a sizing agent to prepare the raw material for the white layer.
Next, pulp consisting of 100% hardwood pulp (L-BKP) was adjusted to a CSF of 450 ml, and 0.5% cationic starch (Neotac 40T, manufactured by Nihon Shokuhin Kako Co., Ltd.) as a paper strength enhancer, 0.5% aluminum sulfate as a flocculation aid, and 0.5% neutral rosin emulsion sizing agent (New Size 738, manufactured by Harima Kasei Co., Ltd.) as a sizing agent were added to prepare the raw material for the intermediate layer.
The prepared white layer raw material and intermediate layer raw material were used to make a three-layer base paper consisting of one intermediate layer and two white layers on both sides of the intermediate layer, for a total of three layers. The total basis weight of this base paper was 200 g/ ^m2 .

<Size press treatment (formation of size layer)>
A 7% paste solution of oxidized starch (MS3800, manufactured by Nippon Shokuhin Kako Co., Ltd.) was applied to both sides of the obtained base paper using a pond size press so that the solid content per side was 2 g/ ^m2 , and then dried to form a size layer, thereby obtaining a base paper.

<Formation of coating layer on the surface side>
An inner coating layer paint was prepared by blending 100 parts of wet heavy calcium carbonate (Carbital 90, manufactured by Imerys Minerals Japan Co., Ltd.) as a pigment, 8 parts of a styrene-butadiene rubber latex (BA-333, average particle size 90 nm, manufactured by Asahi Kasei Chemical Co., Ltd.) which is a styrene-butadiene copolymer latex as an adhesive, and 3 parts of starch phosphate. The inner coating layer paint was applied to the front side of the base paper with a rod coater to a solid content of 10 g/ ^m2 , and dried to form an inner coating layer.
Next, 15 parts of kaolin (Amazon SB, manufactured by Kadam) as a pigment, 65 parts of wet heavy calcium carbonate (Carbital 90, manufactured by Imerys Minerals Japan Co., Ltd.), 20 parts of titanium oxide (RPS-Vantage, manufactured by DuPont) were mixed, and 18 parts of styrene-butadiene rubber latex (B-1230, average particle size 150 nm, manufactured by Asahi Kasei Chemical Co., Ltd.), which is a styrene-butadiene copolymer latex, were mixed as an adhesive to prepare a paint for the outermost coating layer. The paint for the outermost coating layer was applied to the inner coating layer with a rod coater so as to have a solid content of 10 g/m ² , and dried to form a coating layer on the surface side.

<Formation of coating layer on the back side>
The outermost coating layer paint was applied to the back side of the base paper with a rod coater to a solid content of 10 g/ ^m2 , and then dried to form a coating layer on the back side. The basis weight of the completed heat-sealing coated paper was 234 g/ ^m2 .

<Smoothing processing>
A calendaring treatment was carried out at a linear pressure of 50 kg/cm, and then the surface was treated with a luster press at 80 kg/cm and 140° C. to obtain a heat-sealable coated paper according to Example 1.

Example 2
A heat-sealable coated paper according to Example 2 was obtained in the same manner as in Example 1, except that the amount of the styrene-butadiene rubber latex added in the paint for the outermost coating layer was changed from 18 parts to 5 parts.

Example 3
A heat-sealable coated paper according to Example 3 was obtained in the same manner as in Example 1, except that the amount of the styrene-butadiene rubber latex added in the paint for the outermost coating layer was changed from 18 parts by mass to 30 parts by mass.

Example 4
A heat-sealable coated paper according to Example 4 was obtained in the same manner as in Example 1, except that the adhesive in the paint for the outermost coating layer was changed from a styrene-butadiene rubber-based latex (B-1230 manufactured by Asahi Kasei Chemical Corporation) to a styrene-butadiene rubber-based latex (L1432X manufactured by Asahi Kasei Chemical Corporation, average particle size 170 nm).

(Example 5)
A heat-sealable coated paper according to Example 5 was obtained in the same manner as in Example 1, except that the adhesive in the paint for the outermost coating layer was changed from a styrene-butadiene rubber-based latex (B-1230 manufactured by Asahi Kasei Chemicals Corporation) to a styrene-butadiene rubber-based latex (B1335 manufactured by Asahi Kasei Chemicals Corporation, average particle size 130 nm).

Example 6
A heat-sealable coated paper according to Example 6 was obtained in the same manner as in Example 1, except that the adhesive in the coating material for the outermost coating layer was changed from a styrene-butadiene rubber-based latex (B-1230 manufactured by Asahi Kasei Chemical Corporation) to a styrene-butadiene rubber-based latex (T2788K manufactured by JSR Corporation, average particle size 130 nm).

(Example 7)
A heat-sealable coated paper according to the present embodiment was obtained in the same manner as in Example 1, except that no inner coating layer was provided on the surface side, and only one coating layer was provided using the paint for the outermost coating layer.

(Example 8)
The heat-sealing coated paper of the present embodiment was obtained in the same manner as in Example 1, except that the base paper was changed from a three-ply paper with a total basis weight of 200 g/ ^m2 to a single-ply paper with a basis weight of 200 g/ ^m2 .

Example 9
The heat-sealing coated paper of the present embodiment was obtained in the same manner as in Example 1, except that the base paper was changed from a three-ply paper with a total basis weight of 200 g/ ^m2 to a single-ply paper with a basis weight of 67 g/ ^m2 .

(Comparative Example 1)
A heat-sealable coated paper according to the present embodiment was obtained in the same manner as in Example 1, except that the adhesive in the paint for the outermost coating layer was changed from a styrene-butadiene rubber-based latex (B-1230 manufactured by Asahi Kasei Chemical Co., Ltd.) to a styrene-butadiene rubber-based latex (PA6033 manufactured by Japan A&L Co., Ltd., average particle size 95 nm).

(Comparative Example 2)
A coated paper for heat sealing according to the present example was obtained in the same manner as in Example 1, except that no coating layer was formed on the surface layer.

The heat-sealing coated papers obtained in each Example and Comparative Example were evaluated under the following conditions. The evaluation results are shown in Figure 3.

<Heat seal suitability evaluation>
The heat-sealing coated paper obtained in each Example and Comparative Example was cut into two pieces with a width of 8 mm and a length of 15 cm, and the two pieces of heat-sealing coated paper were overlapped with their front and back sides and heat-sealed using a heat-sealing device (Palmec, model number: PTS-100) under the following conditions: adhesion width: 4 mm, temperature: 180°C, pressure: 0.4 MPa, pressing time: 0.5 seconds, pitch: 4 mm to obtain each sample. Next, each sample was peeled using a peel strength tester (Shimadzu, model number: Autograph AGS-X) under the following conditions: peel speed: 100 mm/min, peel length: 10 cm, and the peeled surface was visually evaluated.
⊚: The entire seal portion is broken away from the base paper of the paper substrate and can be used for practical purposes.
◯: Most of the seal portion is torn from the base paper of the paper substrate, and is usable.
△: Part of the seal is torn from the base paper of the paper base material, and it is still usable (lower limit of usability).
×: The seal portion is peeled off at the interface between the coating layer and the size layer, or is not adhered (not practical).

<Printability Evaluation 1: Smoothness>
For the heat-sealing coated papers obtained in each Example and Comparative Example, the total area of the non-contact parts was measured using PST2600 (manufactured by FIBRO System ab) under the following conditions: clamping pressure: 7.6 MPa, clamping time: 0.02 seconds. This measurement was performed on the front side.
⊚: The total area of non-contact portions is 6% or less, which is very good.
◯: The total area of the non-contact portions is 6 to 7%, which is good.
△: The total area of non-contact parts is 7 to 8% (lower practical limit).
×: The total area of non-contact parts is 8% or more (not practical).

<Printability Evaluation 2: Ink setting ability>
For the heat-sealing coated paper obtained in each Example and Comparative Example, 0.4 cc of process ink red (manufactured by Toyo Ink Co., Ltd.) was used to print once on the front side at a printing speed of 30 rpm using an RI printing machine (manufactured by Mei Seisakusho). After that, a transfer paper (Mu Coat Neos, manufactured by Hokuetsu Corporation) was placed on the front side (printed surface) of the heat-sealing coated paper, and the rubber roll and metal roll of the printing machine were pressed against the impression cylinder, and the state of ink transfer to the transfer paper was visually confirmed. The impression cylinder was rotated by 1/3 (about 10 cm) at 30 seconds, 60 seconds, and 90 seconds after printing, and the measurement was performed three times. Note that this measurement was performed on the front side.
.circle.: The transfer of ink to the transfer paper is minimal and good.
◯: Some ink transfer onto the transfer paper, but good.
△: Ink transfer onto transfer paper (lower limit of practical use)
×: A large amount of ink was transferred to the transfer paper. (Not practical)

As is clear from Figure 3, all of the heat-sealable coated papers obtained in Examples 1 to 9 had good printability and heat-sealability.

On the other hand, the heat-sealing coated paper obtained in Comparative Example 1 had poor heat-sealing suitability because the average particle size of the SBR latex used was smaller than 100 nm. The heat-sealing coated paper obtained in Comparative Example 2 had a large surface irregularity because no coating layer was provided on the surface side where printing was performed, and the ink setting was slow, resulting in poor printability.

Claims (9)

providing a base paper;
A step of preparing a paint for an outermost coating layer;
A step of preparing a paint for an inner coating layer;
applying the inner coating paint to the printing surface of the base paper to provide one or more inner coating layers;
A step of applying the paint for the outermost coating layer onto the inner coating layer on the printed surface to provide an outermost coating layer ;
and applying the outermost coating layer paint to a non-printing surface side of the base paper to provide a non-printing surface coating layer ,
the paint for the outermost coating layer contains a pigment and an adhesive, and the adhesive of the paint for the outermost coating layer contains a styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more;
a dry coating weight of the coating layer provided on the printed side is 17 to 28 g/m2 in total ^, and a dry coating weight of the coating layer provided on the non-printed side is 7 to 15 g/ ^m2 . 2. The method for producing coated paper for heat sealing according to claim 1, characterized in that the paint for the outermost coating layer contains 5 to 30 parts by mass of the styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more per 100 parts by mass of the pigment. The method for producing coated paper for heat sealing according to claim 1, characterized in that the styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more has an average particle size in the range of 100 to 200 nm. 2. The method for producing coated paper for heat sealing according to claim 1 , wherein the disintegrated freeness of the base paper is in the range of 300 to 550 ml. 2. The method for producing coated paper for heat sealing according to claim 1, further comprising forming one or more intermediate coating layers between the inner coating layer and the outermost coating layer. In heat-sealing coated paper with one side printed and the other side non-printed,
The printed surface is provided with two or more coating layers including one or more inner coating layers obtained by applying an inner coating paint to a base paper, and an outermost coating layer obtained by applying an outermost coating paint onto the inner coating layer,
The non-printing surface is provided with one non-printing surface coating layer obtained by applying a coating material to a base paper,
the paint for the outermost coating layer contains a pigment and an adhesive, and the adhesive of the paint for the outermost coating layer contains a styrene-butadiene rubber copolymer latex having an average particle size of 100 nm or more;
The total dry coating amount of the coating layer provided on the printing surface side is 17 to 28 g/m ² and the dry coating amount of the coating layer provided on the non-printing surface is 7 to 15 g/m ² The coated paper for heat sealing is characterized in that 7. The heat-sealing coated paper according to claim 6, wherein the coating layer paint used for the non-printing surface coating layer is the outermost coating layer paint. A paper cup container using the heat-sealable coated paper according to claim 6 or 7. A packaging paper using the heat-sealable coated paper according to claim 6 or 7.

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