JP7729240B2 - Packaging paper with translucent area, packaging bag with translucent area, and method for manufacturing packaging paper with translucent area - Google Patents

Description

The present invention relates to wrapping paper. More specifically, it relates to wrapping paper having a translucent area in at least a portion of its surface.

Common methods for producing highly transparent paper include, for example, making paper using pulp fibers with a high degree of beating, or impregnating the spaces between the fibers of the made base paper with a resin or the like.
The method of making paper using pulp fibers with a high degree of beating is used in the manufacture of glassine paper, tracing paper, etc. These sheets are used as packaging paper for the window portions of envelopes, etc. However, because the pulp fibers are crushed and cut by the high beating, pulp fibers with a high degree of beating are generally difficult to apply to applications such as packaging bags, which require strength, even if they are used for envelope windows.

On the other hand, methods of impregnating the spaces between fibers in papermaking base paper with resins or the like are used in the manufacture of oil paper, wax paper, etc. For example, various types of packaging paper impregnated with resins or the like have been proposed for the purpose of improving transparency (e.g., Patent Documents 1, 2, and 3). Patent Document 1 proposes obtaining transparent paper using a clarifying agent made by blending paraffin wax with an organic solvent solution of resin. Patent Document 2 proposes a method of making opaque paper transparent, which involves printing and impregnating a specific surface of opaque paper with a clarifying agent primarily composed of vegetable oil, and then printing and drying an oil layer protective agent for fixing the clarifying agent on both sides of the transparent agent-impregnated layer to form an oil layer protective film. Patent Document 3 proposes transparent paper in which a paper base material is impregnated with a specific resin.

Japanese Unexamined Patent Publication No. 2-127599 Japanese Unexamined Patent Publication No. 15395/1983 Japanese Patent Application Publication No. 11-61696

In recent years, direct mailings and other mailings have seen the use of plastic film envelopes, as well as paper envelopes with the address section made of plastic film. However, as the need to eliminate the use of plastic grows, there is a demand for alternatives to plastic film. While alternatives using translucent glassine paper in place of the plastic film on envelopes are also available, there is an issue with the difficulty of seeing information such as the addressee through the glassine paper. Furthermore, when glassine paper is used to make envelopes, there are issues with the glassine paper's wrinkles and strength.

On the other hand, as described in Patent Documents 1 to 3, a method of reducing opacity has been used in which a clarifying agent is applied to a portion of the paper. While this method of using a clarifying agent is suitable for the strength of wrapping paper for applications such as envelopes, it has resulted in poor visibility of the address written inside. Therefore, the present invention aims to provide wrapping paper with a translucent region that provides excellent visibility of the interior.

After extensive research into packaging paper using a clarifying agent, the inventors discovered that impregnating a paper base with a clarifying agent reduces opacity, but reduces visibility due to light scattering caused by the paper base's texture. They then discovered that packaging paper with excellent visibility can be obtained by not only adding a clarifying agent but also by using halftone printing with a light-absorbing substance, leading to the present invention.

The present invention has the following aspects.
(1) A packaging paper having a translucent area, characterized by having a sheet whose main component is cellulose fiber, a transparent material that permeates the interior of the sheet in the entire area or in a partial area of the sheet, and a halftone printed area in which a light-absorbing substance is attached in the area of the sheet having the transparent material.
(2) A wrapping paper having a translucent region according to (1), wherein the opacity of the region permeated with the transparent material is 10 to 40%.
(3) A packaging bag having a translucent region, formed by forming the packaging paper according to (1) or (2) into a bag shape.
(4) The window envelope according to (3), wherein the packaging bag is an envelope, and a window is formed in a part of the envelope by an area permeated with a transparent material.
(5) A method for producing packaging paper having a translucent region, comprising: attaching a light-absorbing substance to the entire area or a part of a sheet whose main component is cellulose fiber by halftone printing; and then coating and impregnating the halftone-printed area with a clarifying agent.
(6) A method for producing packaging paper having a translucent region, comprising coating or impregnating a sheet whose main component is cellulose fiber with a transparentizing agent over the entire area or a portion of the sheet, then printing a halftone pattern of a light-absorbing material on the sheet, and then coating the halftone-printed area with a transparentizing agent.

Furthermore, the present inventors have conducted extensive research into ways to improve the visibility of glassine paper and the like, and have discovered that by printing a halftone pattern of a light-absorbing material on translucent paper made from highly beaten pulp such as glassine paper, packaging paper with excellent visibility can be obtained, leading to the present invention.
(7) A packaging paper having a translucent area, characterized in that the sheet is primarily composed of cellulose fibers made from highly beaten pulp, and has a halftone printed area to which a light-absorbing substance is attached in at least a partial area on one side of the sheet.
(8) A window envelope,
A window envelope, wherein the window portion of the window envelope is a wrapping paper having a translucent region as described in (7).

This invention makes it possible to provide packaging paper with translucent areas that allow excellent visibility of the interior.

FIG. 1 is a cross-sectional view schematically illustrating an example of packaging paper. FIG. 1 is a cross-sectional view schematically illustrating an example of packaging paper. FIG. 1 is a schematic diagram showing how light rays travel when contents are viewed from the outside in packaging paper having a transparent resin film. FIG. 1 is a schematic diagram showing that conventional semi-transparent paper does not provide sufficient visibility. 10A and 10B are schematic diagrams illustrating a possible mechanism by which visibility is improved by a halftone printed portion.

The packaging paper having a translucent region of the present invention is characterized by having a sheet whose main component is cellulose fiber, a transparent material that has permeated into the interior of the sheet in the entire area or in a partial area of the sheet, and a cross-hatched printed area in which a light-absorbing substance is attached in the area of the sheet having the transparent material.
For example, the packaging paper 1A shown in Figure 1 has a transparent material 3 that has permeated into a portion of a sheet 2 whose main component is cellulose fiber; and a cross-hatched printed portion 4 on one side of the sheet 2 in the area having the transparent material 3, to which a light-absorbing substance has been attached.
For example, the packaging paper 1B shown in Figure 2 has, in a portion of a sheet 2 whose main component is cellulose fiber, a transparent material 3 that has permeated into the sheet 2, a coating layer 5 that covers the surface of the area having the transparent material 3, and a cross-hatched printed portion 4 on one side of the sheet 2 in the area having the transparent material, to which a light-absorbing substance is attached.

1 and 2 are schematic diagrams. In principle, it is believed that the interface between the sheet 2 and the transparentizing material 3, and the interface between the transparentizing material 3 and the coating layer 5, can be observed using an electron microscope. However, in cross-sectional views, these interfaces may not be clearly present or may be difficult to clearly identify, as shown schematically in FIGS. 1 and 2.
Furthermore, the halftone printed portion 4 is formed by adhering a plurality of dots of a light-absorbing material, and therefore the interface of the halftone printed portion 4 (light-absorbing material) in a cross-sectional view may not necessarily be as clear as in the schematic drawings.

"Sheet made primarily of cellulose fiber"
The term "sheet containing cellulose fibers as a main component" refers to a sheet having a cellulose fiber content of 50% by mass or more relative to the entire sheet. The cellulose fiber content is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass.
Examples of sheets containing cellulose fibers as a main component include substrates such as paper, paperboard, nonwoven fabric, etc. Among these, paper substrates are preferred because they can easily produce packaging paper with excellent translucent regions.

The pulp that makes up the paper base material is primarily composed of cellulose fiber. Examples of pulp include chemical pulp, mechanical pulp, recycled paper pulp, and non-wood pulp. However, the pulp in the paper base material is not limited to these examples.

Examples of chemical pulp include softwood pulp (NKP) and hardwood pulp (LKP).
Examples of pulp derived from conifers include unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), semi-bleached coniferous kraft pulp (NSB KP), and coniferous sulfite pulp (NSP).
Examples of hardwood-derived pulp include unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), semi-bleached hardwood kraft pulp (LSBKP), and hardwood sulfite pulp (LSP).

Examples of mechanical pulp include stone ground pulp (SGP), pressed stone ground pulp (PGW), refiner ground pulp (RGP), thermoground pulp (TGP), chemiground pulp (CGP), groundwood pulp (GP), and thermomechanical pulp (TMP).

Examples of waste paper pulp include disintegrated waste paper pulp, disintegrated and deinked waste paper pulp, and disintegrated, deinked, and bleached waste paper pulp. Examples of waste paper that can be used as a raw material for waste paper pulp include brown waste paper, kraft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, cardboard waste paper, white waste paper, Kent waste paper, imitation waste paper, and land certificate waste paper.
Non-wood pulp includes various pulps such as pulp produced chemically or mechanically from non-wood fibers such as kenaf, cotton, hemp, and reed.
These pulps may be used alone or in combination of two or more. Among them, chemical pulp is suitable for achieving both visibility and strength of the sheet, and is preferably used as the main component.

When recycled paper pulp is used as the pulp, the recycled paper pulp content is preferably 10% by mass or less, and more preferably 5% by mass or less, based on the total mass of the pulp constituting the paper base material. When the recycled paper pulp content is below the upper limit, the translucent paper can be suitably used as a packaging material for food and beverages. The lower limit for the recycled paper pulp content is 0% by mass.

The freeness of the pulp constituting the paper base material is preferably 350 ml CSF or more, more preferably 400 to 700 ml CSF, and even more preferably 450 to 600 ml CSF. When the freeness of the pulp in the paper base material is equal to or greater than the lower limit of the above-mentioned range, the strength of the packaging paper is easily maintained. When the freeness of the pulp in the paper base material is equal to or less than the upper limit of the above-mentioned range, packaging paper with a translucent region that is excellent in transparency and visibility is easily obtained.
The freeness (unit: ml CSF) of the pulp in the paper base material is measured in accordance with JIS P8121-2.

Glassine paper, which is generally known as translucent paper, has traditionally been made from highly beaten chemical pulp, for example, chemical pulp with a freeness of 250 ml CSF or less. However, because the highly beaten pulp fibers are ground and cut, they are difficult to use for applications such as packaging bags, which require strength, even if they are used for transparent window portions of envelopes.
In contrast, in the present invention, visibility can be ensured even if the freeness of the paper substrate is kept at 350 ml CSF or more, making it easier to maintain the strength of the packaging paper. Furthermore, even a paper substrate called glassine paper can be used as a packaging paper sheet as long as it is within a range that allows the strength of the package to be maintained.

For example, paper substrates that can be used include kraft paper, one-side glossy kraft paper, one-side glossy paper, fine paper, electrophotographic paper, inkjet recording paper, thermal transfer recording paper, art paper, coated paper, cast-coated paper, white paperboard, colored paperboard, and cardboard liners. Among these, fine paper, electrophotographic paper, kraft paper, and one-side glossy kraft paper with low pigment content are preferred because they provide excellent visibility in the translucent areas.

Paper base materials may contain fillers such as talc and calcium carbonate to improve smoothness and whiteness. However, fillers can affect the transparency and visibility of the paper, so it is preferable to limit the filler content to a range that does not impair visibility, and it is preferable for the paper base material to contain no fillers.

The basis weight of the paper substrate is preferably 40 to 150 g/ ^cm² , more preferably 45 to 100 g/ ^cm² , and even more preferably 50 to 85 g/ ^cm² . If the basis weight of the paper substrate is below the upper limit, the opacity of the translucent region of the packaging paper tends to be reduced. On the other hand, if the basis weight of the paper substrate is above the lower limit, it tends to be possible to obtain good paper strength as packaging paper.
The basis weight of the paper substrate is measured in accordance with JIS P8124.

The density of the paper substrate is preferably 0.5 to 0.8 g/ ^cm3 , and more preferably 0.55 to 0.75 g/ ^cm3 . When the density of the paper substrate is equal to or less than the upper limit, it is easy to increase the content of the transparent material in the packaging paper. When the density of the paper substrate is equal to or more than the lower limit, it is easy to increase the strength of the packaging paper.
The density of the paper substrate is measured in accordance with JIS P8118.

The thickness of the paper substrate is preferably 20 to 120 μm, more preferably 20 to 80 μm, and even more preferably 30 to 70 μm. When the thickness of the paper substrate is equal to or greater than the lower limit of the above-mentioned numerical range, the strength of the packaging paper is easily increased. When the thickness of the paper substrate is equal to or less than the upper limit of the above-mentioned numerical range, excellent visibility in the translucent region is easily obtained.
The thickness of the paper substrate is determined by cutting out a cross section perpendicular to the plane and observing the cross section with an electron microscope, and measuring the maximum value in the thickness direction.

The method for producing the paper base material is not particularly limited, and examples thereof include a method including a step of beating pulp, which is the raw material for the paper base material, a step of making a pulp slurry containing the beaten pulp, and a step of drying the wet sheet obtained by papermaking.
In the beating step, it is preferable to beat the raw pulp until the disintegration freeness of the paper base material reaches a desired range. The beating machine is not particularly limited. For example, a double disc refiner or the like can be used.

There are no particular limitations on the paper machine used for papermaking, and examples thereof include a Fourdrinier paper machine, a short wire paper machine, and a cylinder paper machine.
After papermaking, the surface of the paper substrate obtained through a drying process may be subjected to a smoothing treatment.
Smoothing treatment can improve surface strength, printability, etc. An example of a smoothing treatment is a method in which the paper substrate is pressurized between pressurizable reels. The apparatus for smoothing treatment is not particularly limited. For example, the paper is passed through a machine calender, gloss calender, soft nip calender, etc. before the winder section to perform product finishing. A machine calender and a super calender may be used together, or a super calender may be used instead of a machine calender.

"Transparent material"
The wrapping paper of the present invention has a translucent region formed by permeating a transparent material into the entire surface or a part of the sheet, the transparent region being composed mainly of cellulose fiber. When the wrapping paper is used to make a packaging bag, the contents and address can be seen through the translucent region from the outside of the packaging bag.
The shape and area ratio of the translucent region in a planar view are not limited in any way. They can be set or changed as appropriate depending on the application of the wrapping paper, etc. In another example, the translucent region may be the entire area in the planar direction of the sheet. The number of translucent regions is not particularly limited, and may be one or more. In the case of wrapping paper with multiple translucent regions, the size and shape of each translucent region are also not particularly limited.

The opacity of the translucent region permeated with the transparency-imparting material is not particularly limited, but is preferably about 10 to 40%. If it is 10% or more, visibility tends to decrease due to light scattering within the sheet, but the light-absorbing material is able to absorb scattered light sufficiently, enhancing the visibility effect. If the opacity of the translucent region is equal to or less than the upper limit of the above numerical range, the transparency of the translucent region is improved.
The opacity of the semi-transparent area is measured according to JIS P 8138:1976.

The haze of the semi-transparent region is preferably 80% or less. When the haze of the semi-transparent region is 80% or less, the transparency of the semi-transparent region is improved. The lower limit of the haze of the semi-transparent region is not particularly limited, but is, for example, 10% or more, preferably 20% or more. When the haze of the semi-transparent region is the lower limit or more, the strength of the packaging paper is easily increased.
The haze of the semi-transparent area is measured in accordance with JIS-K7136.

The density of the semi-transparent region is preferably 0.7 to 1.2 g/ ^cm3 , more preferably 0.8 to 1.2 g/ ^cm3 , and even more preferably 0.8 to 1.1 g/ ^cm3 . When the density of the semi-transparent region is equal to or greater than the lower limit of the above-mentioned range, it is believed that the air spaces between the fibers are sufficiently eliminated by impregnation with the resin component. When the density of the semi-transparent region is equal to or less than the upper limit of the above-mentioned range, the processability of the packaging paper 1A when it is made into packaging materials, etc. is improved.
The density of the translucent region is measured in accordance with JIS P8118.

The transparent material is not particularly limited, and examples of the transparent material include transparent resins such as acrylic resin, polyethylene resin, polyester resin, urethane resin, nitrocellulose, shellac, and rosin; vegetable oils such as tung oil, linseed oil, castor oil, hydrophilic castor oil, coconut oil, soybean oil, and commercially available salad oil; and waxes such as carnauba wax, palm wax, beeswax, spermaceti, and Japan wax.
The transparent material may be used alone or in combination of two or more kinds.

Among these, a transparentizing resin that is stable over time is preferred, and an acrylic resin is more preferred. Among the acrylic resins, an ultraviolet-curable acrylic resin is particularly preferred because it has excellent surface coating properties and makes the interface of the region impregnated with the transparentizing material 3 clear in cross-sectional view.
Examples of ultraviolet-curing acrylic resins include those disclosed in paragraphs 0025 and 0026 of JP-A-2021-91481.

From the above-listed materials, it is preferable to select a material with a refractive index in the range of 1.4 to 1.6, preferably 1.45 to 1.58, more preferably 1.48 to 1.58, even more preferably 1.50 to 1.58, and particularly preferably 1.52 to 1.58, as the refractive index of cellulose fibers is generally said to be in the range of 1.4 to 1.6. When the refractive index of the transparent material is within this range, the difference with the refractive index of the cellulose fibers is small, making it easy to improve the transparency and visibility of the translucent region. The refractive index may also be adjusted by appropriately blending a substance with a high refractive index, such as zirconium or titanium.
The refractive index of the transparentizing material 3 is measured in accordance with JIS K7142.

Since the clarifying material is to be permeated into the cellulose fibers, it is preferably liquid at room temperature or in a heated state. Furthermore, from the perspective of permeability, materials that are soluble in liquid media such as organic solvents at room temperature or in a heated state are also preferred. In other words, the clarifying material is preferably one that can be impregnated into the sheet as a permeable liquid clarifying agent during production. The translucent region primarily contains the clarifying material, but other components derived from the clarifying agent used during production may also be present.

A clarifying agent is a liquid containing a clarifying material. If the clarifying material is solid at room temperature, a liquid medium capable of dissolving the clarifying material is used to prepare a liquid clarifying agent. If the clarifying material is liquid at room temperature, the concentration of the clarifying material may be changed using a liquid medium, or it may be used as is as a clarifying agent without using a liquid medium.

The liquid medium is not particularly limited. Either an aqueous solvent or an organic solvent can be used. If the liquid medium contains water, the water will likely cause the sheet to swell. Furthermore, the sheet will likely shrink when it is subsequently dried. This can lead to curling, lumps, and unevenness. Therefore, it is preferable that the liquid medium does not contain water, and organic solvents are more preferable.

The organic solvent may be a polar solvent or a non-polar solvent.
Examples of polar solvents include alcohols, ethers, esters, and non-polar solvents.
Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, and n-hexanol.
Examples of ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diethylene glycol monopropyl ether, triethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, triethylene glycol monoisopropyl ether, tetraethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monoisobutyl ether, tetraethylene glycol monoisobutyl ether, ethylene glycol monotertiary butyl ether, diethylene glycol Examples of glycol ethers include propylene glycol monotertiary butyl ether, triethylene glycol monotertiary butyl ether, tetraethylene glycol monotertiary butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monoethyl ether, tetrapropylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monopropyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monoisopropyl ether, tripropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, propylene glycol monoisobutyl ether, dipropylene glycol monoisobutyl ether, tripropylene glycol monoisobutyl ether, propylene glycol monotertiary butyl ether, dipropylene glycol monotertiary butyl ether, and tripropylene glycol monotertiary butyl ether.
Examples of the esters include diethylene glycol monoethyl ether acetate and diethylene glycol monobutyl ether acetate.
Examples of non-polar solvents include paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, and dodecane; isoparaffinic hydrocarbons such as isohexane, isooctane, and isododecane; alkylnaphthenic hydrocarbons such as liquid paraffin; aromatic hydrocarbons such as benzene, toluene, xylene, alkylbenzene, and solvent naphtha; and silicone oil.

The clarifying agent may further contain other components in addition to the clarifying material and liquid medium. Examples of other components include basic substances such as ammonia, ethylenediamine, and triethylamine; viscosity modifiers such as glycerin and ethylene glycol; high refractive index substances such as zirconium and titanium; antifoaming agents; and mold release agents. However, the other components are not limited to these examples.

"Shaded printing area"
The packaging paper of the present invention is characterized by having a halftone printed area with a light-absorbing material attached to the transparent material area. The halftone printed area with a light-absorbing material functions to absorb light scattered within the sheet, so although the amount of light transmitted through the sheet is reduced, the scattered light is suppressed, improving visibility.

The light-absorbing material is not particularly limited as long as it has a high absorption coefficient. Since the light-absorbing material 7 is formed by halftone printing, the ink used for printing can be prepared and used. For example, black components, particularly black ink, are preferred because of their excellent light absorption properties. Black ink may be either a black ink used in single-color printing or a composite black made using multiple colors. However, the color of the light-absorbing material is not limited to black.

The halftone print area is formed by a collection of dots. There are no particular restrictions on the shape of the dot pattern. For example, the area may be filled with patterns such as halftone dots, grids, diagonal lines, circles, rings, and polygons. The shape of the dot pattern can be changed as appropriate depending on the settings for halftone printing.

The area ratio of the halftone printed portion is preferably 20% to 80%, and more preferably 25% to 75%.
When the area ratio is equal to or greater than the lower limit of the above-mentioned range, the halftone printed portion is likely to absorb scattered light.When the area ratio is equal to or less than the upper limit of the above-mentioned range, it is thought that the halftone printed portion is unlikely to affect the color tone or color impression of the translucent region.
The area ratio here refers to the area of halftone dots per unit area expressed as a percentage. In the case of solid printing, the area ratio is 100%, and in the case of no dots, the area ratio is 0%. The area ratio can be changed as appropriate depending on the settings for halftone printing.

The size of the dots in the halftone printing is not particularly limited. For example, it is preferably 40 to 100 μm, and more preferably 50 to 80 μm. If the dot size is equal to or greater than the lower limit of the above-mentioned numerical range, the halftone printing portion is likely to absorb scattered light. If the dot size is equal to or less than the upper limit of the above-mentioned numerical range, it is thought that the halftone printing portion is unlikely to affect the color tone and color impression of the semi-transparent region.
The dot size is the diameter or minor axis of the circumscribing circle or circumscribing ellipse that has the smallest area among the circumscribing circles or circumscribing ellipses that contain one dot. The dot size can be changed as appropriate by changing the settings for halftone printing.

The color of the light-absorbing material is preferably changed appropriately depending on the use of the wrapping paper, the contents when the wrapping is completed, the color of the sheet, and the color of the contents. For example, this is because the visibility and color can be changed to suit the preferences of users and consumers. In commercialization, for example, a light-absorbing material of a color similar to the color of the contents of the wrapping may be used, or a light-absorbing material of a color complementary to the color of the contents of the wrapping may be used.
It is also preferable to change the shape of the dot pattern of the halftone printed portion, the size of each dot, and the area ratio as appropriate depending on the use of the wrapping paper, the contents of the wrapping, and the color of the contents, since this allows the visibility and color impression to be adjusted to suit the preferences of users and consumers.

"Coating layer"
The wrapping paper of the present invention preferably has a coating layer provided on the surface of the sheet in the translucent region, which further improves the visibility of the translucent region.
In the example shown in Figure 2, i.e., in packaging paper 1B, coating layer 5 is provided on the entire surface of the translucent region in the planar direction, but in other examples, the coating layer may be provided on only a part of the translucent region in the planar direction. Also, the number of coating layers may be one or more.

The material of the coating layer is preferably a transparent material from the standpoint of visibility. Examples of materials for the coating layer include a transparent material and OP varnish. Examples of transparent materials include the same materials as those described for the translucent region. When the coating layer contains a transparent material, the transparent material of the coating layer and the transparent material of the translucent region may be the same type or different types. Furthermore, one type of material for the coating layer may be used alone, or two or more types may be used in combination.

OP varnish is sometimes called overprint varnish. The components of OP varnish vary depending on the product, manufacturer, etc., but OP varnishes containing at least one selected from the group consisting of linseed oil, tung oil, and soluble nitrocellulose are preferred. Commercially available OP varnishes include products from Toyo Ink Co., Ltd., T&K Toka Corporation, and Fuji Ink Mfg. Co., Ltd.
The OP varnish may be used alone or in combination of two or more kinds.

The thickness of the coating layer is preferably 0.5 to 2.5 μm, more preferably 0.5 to 2.5 μm, and even more preferably 0.7 to 2.0 μm. When the thickness of the coating layer is equal to or greater than the lower limit of the above-mentioned range, the surface irregularities of the translucent region are reduced, making it easier to increase smoothness and achieve excellent visibility in the translucent region. When the thickness of the coating layer is equal to or less than the upper limit of the above-mentioned range, the processability of the packaging paper when it is made into packaging materials and the like is improved.
The thickness of the coating layer is determined by cutting out a cross section perpendicular to the plane and observing the cross section with an electron microscope, and measuring the maximum value in the thickness direction.

"Wrapping paper manufacturing method"
The method for producing the packaging paper of the present invention is not particularly limited, but for example,
(1) A method for producing packaging paper having a translucent region, characterized by performing halftone printing of a light-absorbing material on the entire area or a portion of a sheet whose main component is cellulose fiber, and then coating, impregnating, and covering the halftone-printed area with a clarifying agent.
(2) A method for producing packaging paper having a translucent region, characterized by coating or impregnating the entire area or a part of the area of a sheet whose main component is cellulose fiber with a clarifying agent, then performing halftone printing of a light-absorbing material, and then covering the halftone-printed area with a clarifying agent.
etc. can be adopted.

By penetrating the clarifying agent into the sheet, the voids within the sheet are filled with the agent, which has a refractive index close to that of cellulose, thereby suppressing refraction within the sheet. More preferably, by covering the entire surface of the sheet, refraction due to unevenness on the sheet surface can be suppressed. The clarifying agent may be applied to and impregnated into the sheet in one step, or in multiple steps. It may also be applied to and impregnated on both sides of the sheet. When forming the sheet in multiple steps, different clarifying agents may be used. For example, the sheet may be impregnated with a vegetable oil such as linseed oil and then coated with a resin such as an acrylic resin. There are no particular limitations on the method for applying and impregnating the clarifying agent into the sheet, but a coating machine or printer can be used. Furthermore, since a light-absorbing material is printed in a halftone pattern in the areas where the clarifying agent is applied, it is preferable to use a printer for the clarifying agent as well.

The halftone printing can be performed using any known printing method, such as offset printing, gravure printing, flexographic printing, screen printing, inkjet printing, or electrophotographic printing. It may be performed using the same printing machine as that used for applying and impregnating the clarifying agent. It may also be printed on the sheet in advance.

"Packaging bag and manufacturing method for packaging bag"
The packaging paper of the present invention can be formed into a bag shape to form a packaging bag. The resulting packaging bag has both strength and visibility. In addition, in the case of a packaging paper having a transparent agent in a partial area, the translucent area can be used as a window for checking the contents.
When making a packaging bag, the packaging paper can be formed into a bag shape by adhering it by a known method such as an adhesive or heat sealing agent.
The shape of the packaging bag is not particularly limited and may be an envelope, a flat bag, a square-bottom bag, a gusseted bag, a carrier bag, or the like, and may be selected as appropriate.

(Mechanism of action)
The mechanism of action of the present invention will be explained using Figures 3 to 5. In Figures 3 to 5, a transparent resin film F (Figure 3), semi-transparent paper 21 (Figure 4), and packaging paper 1A (1B) (Figure 5) are placed on top of a package 10 having an object image 11 printed on its upper surface. Arrows indicate the direction of light reflected from the object image 11 when the object image 11 is perceived as a visual image 12 from above the semi-transparent region of the packaging paper.
3, the light reflected from the target image 11 travels in a straight line toward the visual position, i.e., the position of the visually recognized image, so the outline of the visually recognized image 12A is clear. Therefore, the printed information of the target image 11 can be seen through the film.
In the case of the translucent paper 21 shown in Figure 4, the light reflected from the target image 11 is refracted by the resin 23 impregnated in the sheet 22, and much of the light is scattered. As a result, the printed information of the target image 11 can be seen through the translucent paper 21. However, due to the large amount of light scattering, the visible image 12B is an unclear image with an indistinct outline. It is difficult to say that sufficient visibility has been achieved.
In the case of the packaging paper of the present invention shown in Figure 5, the light-absorbing material is printed in a halftone pattern to absorb scattered light generated within the sheet. Therefore, among the light rays reflected from the target image 11, those that travel in a straight line toward the visual position tend to selectively pass through the translucent region. As a result, the outline of the visual image 12C is clearer than that of the visual image 12B. This improves the visibility of the contents even through the translucent region.

So far, we have discussed transparent paper impregnated with a clarifying agent such as resin, but this technical concept can also be applied to paper made from highly beaten pulp fibers, such as glassine paper. Specifically, this is a packaging paper sheet primarily composed of cellulose fibers made from highly beaten pulp, with a translucent region characterized by a halftone print of a light-absorbing material on at least a portion of one side of the sheet. Even glassine paper and other paper have scattering within the sheet, so providing a halftone print of a light-absorbing material on one side improves visibility through the glassine paper compared to when a halftone print of a light-absorbing material is not provided. The mechanism of action in this case is thought to be the same as that described above.

(Application)
The packaging paper of the present invention can be used for packaging bags, envelopes, envelope windows, packaging materials, clear files, labels, and the like.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following description.

"Seat"
As a sheet mainly composed of cellulose fibers, one-side glossy kraft paper with a basis weight of 45 g/m ² was prepared. The density of this one-side glossy kraft paper was 0.75 g/cm ³ and the thickness was 67 μm.

"Clarifying agent"
For Examples 1 to 6, an acrylic paraffin solvent (product name: Clariten DC, manufactured by Yamato Chemical Industry Co., Ltd.) was prepared as the clarifying agent. Clariten DC has a refractive index of 1.50. A paraffin solvent (product name: Clariten S) was added as the solvent to prepare a clarifying agent with a concentration of the clarifying material of 90% by mass.
Furthermore, an ultraviolet-curing acrylic resin-based OP varnish (product name: DC Gloss OP Varnish UV-20N) was prepared for Example 7. The refractive index of DC Gloss OP Varnish UV-20N is 1.53.
As the solvent, ethylene glycol monotertiary butyl ether (trade name: UV Fresh Echo II, manufactured by Morita Fine Chemicals) was added to form a clarifying agent having a concentration of 95% by mass.

"Light-absorbing materials"
Black ink (trade name: NCP Matte Ink, manufactured by DIC Corporation) was used.

"Production of packaging paper 1: Examples 1 to 7, Comparative Examples 1 to 3"
The glossy side of one-sided gloss kraft paper was screen-printed with black ink using a sheet-fed offset printing machine (RYOBI 300ACCD) in the six patterns shown in Table 1. A Matsuo Sangyo micrometer-adjustable applicator was used to coat and print the clarifying agent in the screened areas at a coating weight of 1.2 g/ ^m² . In the case of the acrylic paraffin solvents in Examples 1 to 6, the varnish was dried for 30 seconds using a hot air dryer at 120°C. In the case of the UV-curable acrylic resin-based OP varnish in Example 7, UV curing was performed using a Nippon Bunka Seiko Co., Ltd. NPT-453 (4.8 kW, two lamps).
In Comparative Example 1, the same operation as in Example 1 was carried out, except that a clarifying agent was applied/printed in the area where no halftone printing had been carried out. In Comparative Example 2, the same operation as in Example 1 was carried out, except that a clarifying agent was applied/printed in the area where solid printing had been carried out instead of halftone printing. In Comparative Example 3, halftone printing was carried out, but no clarifying agent was used.

<Evaluation method>
The transparency paper of each example was measured and evaluated by the following methods. The results are shown in Table 1.

(opacity of transparent areas)
Measurement was carried out in accordance with JIS P8138:1976 using a color meter SC-WT manufactured by Suga Test Instruments.

(Evaluation of visibility)
An A4-sized printed matter with a 10.5-point Word document printed on it was placed on a horizontal table, and the obtained wrapping paper was placed on top of it. Visibility was evaluated by whether the printed matter could be read through the semi-transparent area of the wrapping paper from a position 30 cm above it.
◎: Characters are not missing and can be recognized. ○: Characters are missing in some places but can be recognized. ×: Characters are missing in various places and are difficult to read. ××: Characters are missing in various places and are extremely difficult to recognize as characters.

As shown in Table 1, the semi-transparent areas of Examples 1 to 7, which were subjected to halftone printing, had improved visibility compared to Comparative Examples 1 to 3.

"Production of packaging paper 2: Example 8, Comparative Examples 4 and 5"
In Example 8, a clarifying agent was applied to the glossy side of one-sided gloss kraft paper using a Matsuo Sangyo micrometer-adjustable applicator at a coating weight of 1.2 g/ ^m² and then dried for 30 seconds in a hot air dryer at 120°C to form a translucent area. A black ink halftone pattern was then printed using a sheet-fed offset printing press (RYOBI 300ACCD). The Matsuo Sangyo micrometer-adjustable applicator was used to apply and impregnate the clarifying agent to the halftone printed area at a coating weight of 1.2 g/ ^m² , and the paper was then dried for 30 seconds in a hot air dryer at 120°C to form a coating layer with a thickness of 1.0 μm.

In Comparative Example 4, the same procedure as in Example 8 was performed, except that a clarifying agent was applied and printed in areas where no halftone printing had been performed. In Comparative Example 5, the same procedure as in Example 8 was performed, except that a clarifying agent was applied and printed in areas where solid printing had been performed instead of halftone printing.

The evaluation results for opacity and visibility for each example are shown in Table 2. The measurement and evaluation methods were the same as those for Examples 1 to 7.

As shown in Table 2, excellent visibility was obtained in the translucent region of Example 8.

1A, 1B: Packaging paper having a translucent region 2: Sheet 3: Transparent material 4: Halftone printed portion 5: Coating layer 10: Package 11: Object image 12: Visual image F: Resin film 21: Translucent paper 22: Sheet 23: Transparent material

Claims (6)

A sheet mainly composed of cellulose fiber;
a transparent material permeating the interior of the sheet in the entire area or a part of the area of the sheet;
a halftone printed portion in which a light absorbing material is attached to the area of the sheet having the transparent material;
A wrapping paper having a translucent region, characterized in that it has The wrapping paper having a translucent region according to claim 1, wherein the opacity of the region permeated with the transparent material is 10 to 40%. A packaging bag having a translucent region, formed from the packaging paper of claim 1 or 2. The packaging bag according to claim 3, wherein the packaging bag is an envelope having a window formed in a portion thereof by an area permeated with a transparent material. A method for producing packaging paper with translucent regions, characterized by applying a light-absorbing substance to all or part of a sheet made primarily of cellulose fiber using halftone printing, and then coating and impregnating the halftone-printed areas with a clarifying agent. A method for producing packaging paper with translucent regions, comprising coating or impregnating a sheet whose main component is cellulose fiber with a clarifying agent over the entire surface or a portion of the sheet, then printing a light-absorbing material over the cross-hatched area, and then coating the cross-hatched area with the clarifying agent.