JP7556495B1 - Clupak Paper and Processed Products for UV Laser Printing - Google Patents

Abstract

The present invention relates to Clupak paper for ultraviolet laser printing, which has drop impact resistance and excellent flexibility, and further allows printing with an ultraviolet laser, and exhibits excellent visibility of printed matter even after a drop test, a method for producing a printed matter using the Clupak paper for ultraviolet laser printing, and a paper product using the Clupak paper for ultraviolet laser printing or a printed matter. The Clupak paper for ultraviolet laser printing of the present invention has a print layer containing an inorganic compound that discolors when irradiated with an ultraviolet laser on a paper base material containing pulp, and has a longitudinal stiffness of 0.70 mNm or less and a lateral stiffness of 0.45 mNm or less, measured in accordance with ISO 2493-1:2010, and a puncture strength of 7.50 N or more, measured in accordance with JIS Z 1707:2019.

Description

The present invention relates to Clupak paper and processed products for UV laser printing.

Clupak paper, which has been given stretchability by minutely shrinking the paper during papermaking, has been used as packaging paper. For example, Patent Document 1 discloses Clupak paper that is resistant to tearing even in heavy packaging applications by controlling the specific tensile strength in the longitudinal and transverse directions.

On the other hand, plastic materials have been mainly used for packaging containers such as food trays and packaging bodies such as pillowcase bags. However, due to environmental concerns, there has been an investigation into using paper packaging materials instead of plastic containers.

Conventionally, labeling or inkjet printing has been used to display dates such as manufacturing dates and shipping dates, and variable information such as bar codes on packaging containers or packages.
Patent Document 2 describes an ink composition used to form a laser marking layer that contains first titanium oxide particles having an average particle size of 150 nm or less and changes color when irradiated with an ultraviolet laser, with the aim of providing a technology that generates relatively little heat and is preferably applicable to laser marking of packaging materials.

International Publication No. 2015/008703 JP 2020-75943 A

Clupak paper has excellent flexibility, but low puncture strength, and for example, when manufacturing pillow packaging bags, the drop impact resistance of the bag is insufficient when the bag is filled with a product. Normally, paper with high puncture strength tends to become hard and has poor flexibility, so it is difficult to achieve both drop impact resistance and flexibility in Clupak paper. In addition, direct laser marking on Clupak paper has not been considered.
The present disclosure relates to Clupak paper for ultraviolet laser printing that has drop impact resistance and excellent flexibility, and furthermore can be printed with an ultraviolet laser, and provides excellent visibility of printed matter even after a drop test; a method for producing a printed matter using the Clupak paper for ultraviolet laser printing; and a paper product using the Clupak paper for ultraviolet laser printing or the printed matter.

That is, the present disclosure relates to the following <1> to <12>.
<1> Clupak paper for ultraviolet laser printing, comprising a print layer containing an inorganic compound that changes color when irradiated with an ultraviolet laser on a paper base material containing pulp, the stiffness in the longitudinal direction being 0.70 mNm or less and the stiffness in the lateral direction being 0.45 mNm or less, as measured in accordance with ISO 2493-1: 2010, and the puncture strength, as measured in accordance with JIS Z 1707: 2019, being 7.50 N or more.
<2> The Clupak paper for ultraviolet laser printing according to <1>, wherein the stiffness in the longitudinal direction is 0.05 mNm or more and 0.55 mNm or less, and the stiffness in the lateral direction is 0.05 mNm or more and 0.35 mNm or less.
<3> The Clupak paper for ultraviolet laser printing according to <1> or <2>, wherein the puncture strength is 12.50 N or more.
<4> The Clupak paper for ultraviolet laser printing according to any one of <1> to <3>, wherein the length-weighted average fiber length of the pulp is 1.2 mm or more and 1.9 mm or less.
<5> The Clupak paper for ultraviolet laser printing according to any one of <1> to <4>, wherein the paper base material has a basis weight of 30 g/m2 or ^more and 120 g/ ^m2 or less.
<6> The Clupak paper for ultraviolet laser printing according to any one of <1> to <5>, having a specific puncture strength of 0.13 N·m ² /g or more.
<7> The Clupak paper for ultraviolet laser printing according to any one of <1> to <6>, further comprising at least one layer selected from a protective layer and a thermoplastic resin layer in addition to the paper base material.
<8> The Clupak paper for ultraviolet laser printing according to any one of <1> to <7>, wherein the inorganic compound that changes color when irradiated with an ultraviolet laser is at least one selected from the group consisting of titanium oxide and zinc oxide.
<9> A printed matter obtained from the Clupak paper for ultraviolet laser printing according to any one of <1> to <8>, wherein the printed layer has, at least in a part thereof, a printed area containing the inorganic compound that has been discolored by irradiation with an ultraviolet laser.
<10> A processed product obtained by using the Clupak paper for ultraviolet laser printing according to any one of <1> to <8>.
<11> A processed product obtained by using the printed matter according to <9>.
<12> A method for producing a printed matter, comprising a step of irradiating the Clupak paper for ultraviolet laser printing according to any one of <1> to <8> with an ultraviolet laser to discolor the irradiated area, thereby forming a print.

According to the present invention, there are provided Clupak paper for ultraviolet laser printing which has drop impact resistance and excellent flexibility, and furthermore can be printed with an ultraviolet laser, and which provides excellent visibility of printed matter even after a drop test; a method for producing a printed matter using the Clupak paper for ultraviolet laser printing; and a paper product using the Clupak paper for ultraviolet laser printing or the printed matter.

Schematic diagram of bag processing for evaluating drop impact resistance and bag flexibility

In the present disclosure, the description of a numerical range such as "X or more and Y or less" or "X to Y" means a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be arbitrarily combined.
The machine direction is the machine direction (MD) of the paper base material, which is the same as the direction in which the fibers are oriented, and the cross direction is the direction perpendicular to the machine direction (CD).

[Clupak paper for UV laser printing]
The Clupak paper for ultraviolet laser printing of this embodiment (hereinafter also simply referred to as "Clupak paper") has a print layer containing an inorganic compound that changes color when irradiated with an ultraviolet laser on a paper base material containing pulp, and has a longitudinal stiffness of 0.70 mNm or less and a lateral stiffness of 0.45 mNm or less, measured in accordance with ISO 2493-1:2010, and a puncture strength of 7.50 N or more, measured in accordance with JIS Z 1707:2019.
As described above, Clupak processing is a process that gives the paper stretchability by minutely shrinking it on the papermaking machine. Specifically, for example, a Clupak device equipped with an endless thick elastic rubber blanket with nip rolls is installed in a part of the papermaking machine dryer. A wet paper web is introduced into the Clupak device and compressed by the nip rolls and blanket. At this time, the blanket, which has been stretched in advance, contracts, shrinking the running paper web (creaping), thereby increasing the breaking elongation. The resulting shrinkage is dried and fixed so that it does not stretch in the subsequent process.

The present inventors have found that the above problem can be solved by providing a printed layer containing an inorganic compound that changes color when irradiated with an ultraviolet laser on a paper substrate, and controlling the stiffness and puncture strength to specific values by Clupak treatment during the manufacture of the paper substrate. Stiffness indicates how easily the paper can be folded, and puncture strength indicates how difficult the paper is to tear. Clupak paper having the above specific stiffness and puncture strength indicates that the paper is moderately easy to fold and difficult to tear. Therefore, the present inventors believe that Clupak paper with excellent flexibility and drop impact resistance can be obtained. It is also believed that printing with an ultraviolet laser is possible by providing a printed layer containing an inorganic compound that changes color when irradiated with an ultraviolet laser on the paper substrate.
The Clupak paper of this embodiment may be composed only of a paper base material and a printed layer, or may further have at least one layer selected from a thermoplastic resin layer and a protective layer in addition to the paper base material and the printed layer.

<Characteristics of Clupak paper for UV laser printing>
[Vertical and horizontal stiffness]
The Clupak paper for ultraviolet laser printing of this embodiment needs to have a stiffness in the longitudinal direction of the Clupak paper of 0.70 mNm or less and a stiffness in the transverse direction of the Clupak paper of 0.45 mNm or less, measured in accordance with ISO 2493-1:2010.
If the stiffness exceeds the upper limit, it becomes difficult to bend and flexibility decreases.
The stiffness is measured by the method described in the Examples.

Stiffness can be controlled by the type and blending ratio of pulp that makes up the paper base material, the basis weight and thickness of the Clupak paper, the speed difference before and after the Clupak treatment, etc. In order to increase stiffness, when hardwood kraft pulp and softwood kraft pulp are used as the raw pulp, methods such as increasing the ratio of softwood kraft pulp, increasing the basis weight, increasing the thickness, and increasing the speed difference before and after the Clupak treatment can be mentioned. On the other hand, in order to decrease stiffness, when hardwood kraft pulp and softwood kraft pulp are used as the raw pulp, methods such as decreasing the ratio of softwood kraft pulp, decreasing the basis weight, decreasing the thickness, and decreasing the speed difference before and after the Clupak treatment can be mentioned.

The stiffness of the Clupak paper in the longitudinal direction is preferably 0.05 mNm or more and 0.70 mNm or less, more preferably 0.10 mNm or more, and preferably 0.65 mNm or less, more preferably 0.55 mNm or less, even more preferably 0.30 mNm or less, and even more preferably 0.20 mNm or less.
The stiffness in the lateral direction of the Clupak paper is preferably 0.05 mNm or more and 0.45 mNm or less, more preferably 0.10 mNm or more, and preferably 0.35 mNm or less, more preferably 0.20 mNm or less.

[Puncture strength]
The Clupak paper of the present embodiment is required to have a puncture strength of 7.50 N or more as measured in accordance with JIS Z 1707:2019.
If the puncture strength is less than the lower limit, dents and tears are likely to occur, and drop impact resistance is reduced.
The puncture strength of Clupak paper is measured by the method described in the Examples.

The puncture strength can be controlled by the basis weight, the speed difference before and after Clupak treatment, the content of softwood kraft pulp, the nip pressure during Clupak treatment, etc. Methods for increasing the puncture strength include increasing the basis weight, increasing the speed difference before and after Clupak treatment, increasing the content of softwood kraft pulp, and decreasing the nip pressure during Clupak treatment. On the other hand, methods for decreasing the puncture strength include decreasing the basis weight, decreasing the speed difference before and after Clupak treatment, decreasing the content of softwood kraft pulp, and increasing the nip pressure during Clupak treatment.

The puncture strength of Clupak paper is preferably 7.50 N or more and 18.00 N or less, preferably 8.00 N or more, more preferably 10.00 N or more, and even more preferably 12.50 N or more. If the upper limit of the puncture strength is 18.00 N or less, it is preferable because it has excellent suitability for bag making.

[Length-weighted average fiber length of pulp]
The length-weighted average fiber length of the pulp obtained by disintegrating Clupak paper, measured in accordance with ISO 16065-2:2007, is preferably 1.0 mm or more and 2.0 mm or less, more preferably 1.2 mm or more, even more preferably 1.3 mm or more, and more preferably 1.9 mm or less, even more preferably 1.8 mm or less.
If the length-weighted average fiber length is less than the lower limit, the strength is weak and drop impact resistance tends to deteriorate, but on the other hand, flexibility increases. If the length-weighted average fiber length exceeds the upper limit, the strength is strong and drop impact resistance improves, but on the other hand, flexibility tends to deteriorate. In other words, within the above range, both bag flexibility and drop impact resistance can be achieved. The length-weighted average fiber length of the pulp can be controlled by the type of pulp used, etc.
The length-weighted average fiber length of the pulp is measured by the method described in the Examples.

[Specific puncture strength]
The specific puncture strength of Clupak paper is preferably 0.05 N·m ² /g or more and 0.30 N·m ² /g or less, more preferably 0.10 N·m ² /g or more, and even more preferably 0.13 N·m ² /g or more. When it is in the above range, it has excellent flexibility and drop impact resistance. Also, when it is equal to or less than the above upper limit, it has excellent suitability for bag making, which is preferable.
The specific puncture strength is a value obtained by dividing the puncture strength by the basis weight.
The specific puncture strength is measured by the method described in the Examples.

[Basis weight]
The basis weight of the paper substrate is preferably 30 g/m ² or more and 120 g/m ² or less, more preferably 60 g/m ² or more, even more preferably 70 g/m ² or more, and more preferably 110 g/m ² or less, even more preferably 90 g/m ² or less. If the basis weight of the paper substrate is less than the lower limit, the strength is weak and drop impact resistance tends to deteriorate, but on the other hand, flexibility increases. If the basis weight exceeds the upper limit, the strength is strong and drop impact resistance improves, but flexibility tends to deteriorate. Within the above range, both bag flexibility and drop impact resistance can be achieved.
The basis weight of Clupak paper is preferably 35 g/m2 or ^more and 200 g/m2 ^or less, more preferably 50 g/m2 or ^more , even more preferably 70 g/ ^m2 or more, and more preferably 160 g/ ^m2 or less, even more preferably 120 g/m2 or ^less . If the basis weight of Clupak paper is less than the above lower limit, the strength is weak and drop impact resistance tends to deteriorate, but on the other hand, flexibility increases. If the basis weight exceeds the above upper limit, the strength is strong and drop impact resistance improves, but flexibility tends to deteriorate. Within the above range, both bag flexibility and drop impact resistance can be achieved.
The basis weight of the paper base and Clupak paper is measured by the method described in the Examples.

[Thickness]
The thickness of the paper base material is preferably 50 μm or more and 300 μm or less, more preferably 60 μm or more, even more preferably 70 μm or more, still more preferably 80 μm or more, and more preferably 200 μm or less, even more preferably 160 μm or less, and still more preferably 140 μm or less.
In addition, the thickness of the Clupak paper is not particularly limited, but is preferably 55 μm or more and 400 μm or less, more preferably 65 μm or more, even more preferably 75 μm or more, still more preferably 85 μm or more, and more preferably 300 μm or less, even more preferably 240 μm or less, and still more preferably 180 μm or less.
The thickness of the paper substrate and Clupak paper is measured by the method described in the Examples.

〔density〕
The density of the paper base material is preferably 0.30 g/ ^cm3 or more and 1.00 g/ ^cm3 or less, more preferably 0.40 g/cm3 or ^more , even more preferably 0.50 g/cm3 ^or more, still more preferably 0.55 g/cm3 or ^more , and more preferably 0.90 g/cm3 or ^less , even more preferably 0.85 g/cm3 or ^less , and still more preferably 0.80 g/cm3 or ^less .
In addition, the density of Clupak paper is preferably 0.40 g/ ^cm3 or more and 1.00 g/cm3 ^or less, more preferably 0.50 g/cm3 or ^more , even more preferably 0.55 g/ ^cm3 or more, still more preferably 0.60 g/cm3 or ^more , and more preferably 0.95 g/cm3 or ^less , even more preferably 0.90 g/cm3 or ^less , and still more preferably 0.85 g/cm3 or ^less .
The density of the paper base and Clupak paper is calculated from their basis weight and thickness.

<Paper base material>
Next, materials that can be used for Clupak paper will be described.
〔pulp〕
Examples of the pulp constituting the paper base material include hardwood kraft pulps such as hardwood unbleached kraft pulp (LUKP) and hardwood bleached kraft pulp (LBKP); softwood kraft pulps such as softwood unbleached kraft pulp (NUKP) and softwood bleached kraft pulp (NBKP); mechanical pulps such as groundwood pulp (GP), pressurized groundwood pulp (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-mechanical pulp (CMP), and chemi-ground pulp (CGP); waste paper pulp; non-wood fiber pulps such as kenaf, bagasse, bamboo, and cotton; synthetic pulp, etc. These pulps may be used alone or in combination of two or more.

The pulp preferably contains at least one selected from hardwood kraft pulp and softwood kraft pulp, more preferably contains at least one selected from unbleached hardwood kraft pulp and unbleached softwood kraft pulp, even more preferably contains at least unbleached softwood kraft pulp, and even more preferably contains unbleached hardwood kraft pulp and unbleached softwood kraft pulp.

The content of coniferous kraft pulp in the pulp is preferably 20% by mass or more and 100% by mass or less, more preferably 30% by mass or more, even more preferably 35% by mass or more, still more preferably 40% by mass or more, and more preferably 95% by mass or less, even more preferably 90% by mass or less.

The hardwood kraft pulp content in the pulp is preferably 0% by mass or more and 80% by mass or less, more preferably 5% by mass or more, even more preferably 10% by mass or more, and more preferably 70% by mass or less, even more preferably 65% by mass or less, and even more preferably 60% by mass or less.

The degree of beating of the pulp is not particularly limited, but is preferably 200 mL or more and 800 mL or less, more preferably 300 mL or more, and more preferably 700 mL or less, in terms of Canadian Standard Freeness (CSF). CSF is measured in accordance with JIS P 8121-2:2012 "Pulp - Test method for freeness - Part 2: Canadian Standard Freeness Method."

[Method of manufacturing paper base material]
An example of a method for producing a paper base material is a method in which a stock containing pulp is made and Clupak treatment is performed during the papermaking process. The stock may further contain additives as necessary. Examples of additives include the additives described above. The stock can be prepared by adding additives to a pulp slurry as necessary. The pulp slurry can be obtained by beating pulp in the presence of water. The pulp beating method and beating device are not particularly limited, and any known beating method and beating device can be used.

The solids concentration of the pulp slurry during beating is not particularly limited, but is preferably about 0.5% by mass or more and 10% by mass or less, more preferably 1% by mass or more, and more preferably 5% by mass or less. The pulp content in the paper stock or paper base material is not particularly limited, and may be within a range that is normally used. For example, it is preferably 60% by mass or more and 100% by mass or less, more preferably 80% by mass or more, and more preferably less than 100% by mass, based on the total mass of the paper stock (solids) or paper base material.

In making paper substrates, a known wet paper machine can be appropriately selected and used. Examples of paper machines include Fourdrinier paper machines, gap former paper machines, cylinder paper machines, and short wire paper machines. These paper machines can be equipped with a Clupak device capable of performing the Clupak treatment, and the Clupak treatment can be performed.

A known Clupak device can be used. For example, a Clupak device equipped with a nip roll and an endless thick elastic rubber blanket can be mentioned. As described above, in the Clupak process, the paper web is introduced between the nip roll and the blanket, and when the paper web is compressed by the nip roll and the blanket, the blanket, which has been stretched in advance, is contracted to shrink the paper web and impart a crepe. The Clupak device is usually installed as part of the dryer device of a papermaking machine, and after creping, the paper is dried and fixed. In this manner, a paper base material can be obtained.

In papermaking using the Clupak device, the stiffness and puncture strength can be controlled by the difference in papermaking speed before and after the Clupak treatment.
The papermaking speed is not particularly limited, but is preferably 200 m/min to 1000 m/min, more preferably 300 m/min or more, even more preferably 400 m/min or more, and more preferably 800 m/min or less, even more preferably 700 m/min or less, and may be controlled within the above ranges. The speed difference before and after the Clupak treatment is not particularly limited, and may be controlled so as to obtain the desired stiffness and puncture strength depending on the basis weight and pulp material. It is preferably -5 m/min to -60 m/min, more preferably -10 m/min to -50 m/min, and even more preferably -15 m/min to -40 m/min. The minus sign "-" here indicates that the speed after the Clupak treatment is slow.

The reel moisture content is not particularly limited, and may be controlled to obtain the desired stiffness and puncture strength depending on the basis weight, pulp material, speed difference before and after Clupac treatment, etc. It is preferably 2.0% or more and 12.0% or less, more preferably 5.0% or more, and more preferably 9.0% or less.

<Printed layer>
The Clupak paper for ultraviolet laser printing of this embodiment has a printed layer containing an inorganic compound that changes color when irradiated with an ultraviolet laser (hereinafter, the "inorganic compound that changes color when irradiated with an ultraviolet laser" is also referred to as "inorganic compound A") on a paper base material. The printed layer may be provided by coating or lamination, and is not particularly limited. That is, the printed layer is preferably a coated layer containing inorganic compound A, or a laminate layer containing inorganic compound A. In the present invention, the printed layer is more preferably provided by coating from the viewpoint of ease of providing the printed layer only at desired locations and ease of production. The term "provided by coating" means that the printed layer is formed by a coating liquid (ink composition), and includes, for example, the case of forming the printed layer by gravure printing, inkjet printing, etc.
The printing layer contains an inorganic compound (inorganic compound A) that changes color when irradiated with an ultraviolet laser, and the inorganic compound A in the printing layer changes color when irradiated with an ultraviolet laser, making it possible to perform printing. Note that the discoloration of the inorganic compound A occurs due to a change in the ionic valence of the inorganic compound A contained in the printing layer, which causes oxygen defects, causing the inorganic compound A to change color from white to black, which is thought to make the ultraviolet laser irradiated area visible.
For example, when the inorganic compound A is titanium oxide, it is considered that the ionic valence of titanium oxide changes from tetravalent to trivalent by irradiation with an ultraviolet laser, and oxygen defects are generated, causing a change from white to black, which is visible. For example, the band gap of titanium oxide varies depending on the crystal system, but is generally about 3.0 eV to 3.2 eV, and the wavelength of light corresponding to this is 420 nm or less. Therefore, even if a laser beam with a wavelength exceeding 420 nm (for example, 530 nm, 1064 nm, 10600 nm) is used, it is difficult to perform printing due to the change in the ionic valence of titanium oxide as in the present invention.
The same can be said for inorganic compounds A other than titanium oxide.
In this embodiment, the printable area means an area (portion) where printing is possible due to discoloration of inorganic compound A contained in a printing layer provided on Clupak paper for ultraviolet laser printing, preferably due to irradiation with an ultraviolet laser, whereby inorganic compound A in the portion irradiated with the ultraviolet laser changes color from white to black, and the printed area means a portion in the printable area where inorganic compound A has actually changed color, preferably a portion where inorganic compound A has changed color by irradiation with an ultraviolet laser and become visible, i.e., an area irradiated with an ultraviolet laser. Also, the non-printable area means an area (portion) in the printable area where inorganic compound A has not changed color, for example, an area (portion) not irradiated with an ultraviolet laser.

The content of inorganic compound A in the printing layer is preferably 0.1 g/ ^m2 or more and 10 g/ ^m2 or less, more preferably 0.2 g/m2 or ^more , even more preferably 0.3 g/m2 or ^more , still more preferably 0.4 g/m2 or ^more , and more preferably 7.5 g/m2 or ^less , even more preferably 5 g/m2 or ^less , and still more preferably 3.5 g/m2 or ^less .
It is preferable that the content of inorganic compound A in the printing layer is equal to or more than the above-mentioned lower limit, since a sufficient printing density can be obtained, and it is also preferable that the content is equal to or less than the above-mentioned upper limit, since the printing density reaches a plateau and the increase in costs due to the inclusion of more inorganic compound A than necessary can be suppressed.
If the content of inorganic compound A in the printed layer is too high, there is a tendency for smoke to be generated during irradiation with an ultraviolet laser, which is believed to be due to scattering of inorganic compound A. Furthermore, as a result of the smoke generation, a phenomenon occurs in which discolored inorganic compound A is detached from the printed layer, and the print density also tends to deteriorate.
It is sufficient that at least the printable area of the ultraviolet laser printing paper contains inorganic compound A, and there may be a portion in the area where printing is not performed where no printed layer is provided. From the viewpoint of ease of production, it is also preferable that the entire area of the Clupak paper is provided with a printed layer containing inorganic compound A.

In this embodiment, the Clupak paper may have an undercoat layer that does not contain inorganic compound A as a layer below the printed layer that contains inorganic compound A.
Furthermore, in the case where a resin layer, which will be described later, is provided on the printed layer, the resin layer is not considered to be a printed layer.

The mass (solids content, basis weight) per ^m2 of the printed layer is preferably 1.0 g/ ^m2 or more and 50 g/m2 or ^less , more preferably 2.5 g/m2 ^{or more} , even more preferably 4.5 g/m2 or more, and more preferably 40 g/m2 ^{or less} , even more preferably 30 g/m2 ^{or less} , from the viewpoints of print density and suppression of smoke generation during irradiation with an ultraviolet laser.

The content of inorganic compounds in the printing layer (solids) is preferably 0.3 mass% or more and 95 mass% or less, more preferably 1.0 mass% or more, even more preferably 2.0 mass% or more, even more preferably 2.5 mass% or more, and more preferably 85 mass% or less, even more preferably 75 mass% or less, and even more preferably 60 mass% or less.
It is preferable that the content of the inorganic compound in the printing layer (solid content) is equal to or more than the above lower limit, since sufficient printing density can be obtained, and it is preferable that the content is equal to or less than the above upper limit, since the printing density reaches a plateau, and the increase in costs due to the inclusion of more inorganic compound A than necessary is suppressed, the printing layer is easily formed, and smoke generation during irradiation with an ultraviolet laser is suppressed.

The thickness of the printing layer is preferably 0.3 μm or more and 40.0 μm or less, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, still more preferably 2.0 μm or more, and more preferably 30.0 μm or less, even more preferably 25.0 μm or less, and still more preferably 20.0 μm or less.
When the thickness of the printing layer is equal to or greater than the above lower limit, sufficient printing density can be obtained and the printing layer can be easily formed, which is preferable. When the thickness of the printing layer exceeds the above upper limit, the printing density tends to plateau, and when the thickness is equal to or less than the above upper limit, the printing layer can be easily formed, which is preferable.
The thickness of the printing layer is measured from an image of a cross section of the printing paper observed under an scanning electron microscope (SEM).

The paper base material itself may contain inorganic compound A. The paper base material contains inorganic compound A, which tends to produce a clearer image. In particular, when the thickness of the printed layer is thin, the paper base material itself contains inorganic compound A, which tends to produce a clearer image. In this case, when the thickness of the printed layer is 2.0 μm or less, the effect of the paper base material containing inorganic compound A tends to be more pronounced.
When the paper base material contains inorganic compound A, the content of inorganic compound A in the paper base material is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more.

The printing layer preferably contains a thermoplastic resin in addition to the inorganic compound A. Furthermore, it may contain an inorganic pigment other than the inorganic compound A. Each component will be described in detail below.
[Inorganic compound that changes color when irradiated with an ultraviolet laser (inorganic compound A)]
Examples of the inorganic compound A contained in the print layer include metal oxides, specifically titanium oxide and zinc oxide, and among these, titanium oxide is preferred.
Titanium oxide is represented by the composition formula _TiO2 and is also called titanium dioxide or titania.
The titanium oxide may have any crystal structure, and is preferably at least one selected from rutile titanium oxide, anatase titanium oxide, and brookite titanium oxide. From the standpoints of availability and stability, it is more preferably at least one selected from rutile titanium oxide and anatase titanium oxide, and even more preferably rutile titanium oxide.
The crystal form of titanium oxide can be determined by known methods, specifically, by analysis of Raman spectrum, XRD pattern, etc. For example, when identifying from Raman spectrum, generally, peaks are observed at 447±10 cm ⁻¹ and 609±10 cm ⁻¹ for rutile type, and peaks are observed at 395±10 cm ⁻¹ , 516±10 cm ⁻¹ and 637±10 cm ⁻¹ for anatase type.
The titanium oxide may be used alone or in combination of two or more kinds.
Zinc oxide is represented by the composition formula ZnO and is also called zinc white or zinc oxide. Zinc oxide generally has a wurtzite crystal structure.
The inorganic compound A may be used alone or in combination of two or more kinds.

The shape of the inorganic compound A is not particularly limited, and may be any shape such as amorphous, spherical, rod-like, or needle-like.
When the inorganic compound A is amorphous or spherical, the average particle size of the inorganic compound A is not particularly limited, but from the viewpoint of obtaining Clupak paper having excellent surface smoothness, it is preferably from 0.01 μm to 20.0 μm, more preferably from 0.05 μm or more, even more preferably from 0.1 μm or more, still more preferably from 0.15 μm or more, even more preferably from 0.16 μm or more, and more preferably from 5.0 μm or less, even more preferably from 1.5 μm or less, and even more preferably from 0.50 μm or less.

In addition, when the inorganic compound A is needle-shaped, the major axis of the inorganic compound A is not particularly limited, but from the viewpoint of obtaining Clupak paper having excellent surface smoothness, it is preferably 0.1 μm or more and 50.0 μm or less, more preferably 0.5 μm or more, even more preferably 1.5 μm or more, and more preferably 30.0 μm or less, and even more preferably 15.0 μm or less. In addition, the minor axis is preferably 0.01 μm or more and 3.0 μm or less, more preferably 0.03 μm or more, even more preferably 0.05 μm or more, and more preferably 1.5 μm or less, and even more preferably 1.0 μm or less. In addition, when the titanium oxide is needle-shaped, the aspect ratio (major axis/minor axis) is preferably 5 or more and 300 or less, more preferably 10 or more, even more preferably 15 or more, and more preferably 100 or less, and even more preferably 30 or less.
The average particle size, major axis, and minor axis of the inorganic compound A are measured by the method described in the Examples. The values of the particle size, major axis, and minor axis of the inorganic compound A used as the raw material may be adopted, or the catalog values of the particle size, major axis, and minor axis of the inorganic compound A used as the raw material may be adopted.

[Thermoplastic resin]
The thermoplastic resin used in the printing layer functions as a binder.
The thermoplastic resin of the printing layer is not particularly limited, but when the printing layer is provided by coating, it may be applied as an aqueous coating liquid or as an organic solvent-based coating liquid (oil-based coating liquid). When the printing layer is provided by coating, the printing layer is also called a coating layer. The composition used to provide the coating layer is also called a coating liquid or an ink composition.
When the coating liquid is applied as an aqueous coating liquid, the thermoplastic resin is preferably a water-dilutable thermoplastic resin. Examples of the water-dilutable resin include water-soluble, emulsion-type, and dispersion-type resins.
The water-dilutable thermoplastic resin may be either a natural resin or a synthetic resin, and examples thereof include starch derivatives, casein, shellac, polyvinyl alcohol and its derivatives, acrylic resins, maleic acid resins, urethane resins, polyester resins, styrene-butadiene resins, vinyl chloride resins, and polyolefin resins.
More specifically, examples of the acrylic resin include an acrylic resin copolymerized with (meth)acrylic acid and its alkyl ester or styrene as a monomer component, a styrene-maleic acid resin, a styrene-acrylic acid-maleic acid resin, and an olefin-(meth)acrylic acid copolymer resin (e.g., an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer), and the like.
Among these, from the viewpoints of the stability of the coating liquid and the solvent resistance of the printed layer, at least one selected from starch derivatives, casein, shellac, polyvinyl alcohol and its derivatives, acrylic resins, maleic acid resins, and styrene-butadiene resins is preferred, at least one selected from starch derivatives, polyvinyl alcohol, polyvinyl alcohol derivatives, acrylic resins, maleic acid resins, and styrene-butadiene resins is more preferred, at least one selected from starch derivatives, polyvinyl alcohol, polyvinyl alcohol derivatives, acrylic resins, and styrene-butadiene resins is even more preferred, and at least one selected from polyvinyl alcohol, polyvinyl alcohol derivatives, acrylic resins, and styrene-butadiene resins is even more preferred.
These resins may be used alone or in combination of two or more.
In the case of an organic solvent-based coating liquid (oil-based coating liquid), it is preferable to use a known thermoplastic resin such as a cellulose-based resin (e.g., soluble cellulose, cellulose acetate, cellulose acetate propionate), a polyurethane-based resin, an acrylic-based resin, or a vinyl chloride copolymer-based resin.

The content of the thermoplastic resin is not particularly limited and may be appropriately selected depending on the type of thermoplastic resin, the content of inorganic compound A in the coating liquid and the inorganic pigment described below, etc., and is, for example, preferably 5% by mass or more and 99% by mass or less, more preferably 10% by mass or more, even more preferably 15% by mass or more, and more preferably 98% by mass or less, of the solid content of the coating liquid.

When the printed layer is provided by coating, the coated layer is preferably provided by applying a coating liquid and drying it.
The coating liquid is preferably an aqueous coating liquid, and the aqueous medium used may be water or a mixture of water and a water-miscible solvent.
Examples of the water-miscible solvent include lower alcohols, polyhydric alcohols, and their alkyl ethers or alkyl esters.Specific examples of the water-miscible solvent include lower alcohols such as methyl alcohol, ethyl alcohol, normal propyl alcohol, and isopropyl alcohol, polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and glycerin, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoacetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monoacetate, diethylene glycol monomethyl ether, and dipropylene glycol monomethyl ether.
In the case of an organic solvent-based coating liquid, examples of the solvent include known solvents such as aromatic organic solvents such as toluene and xylene, ester-based organic solvents such as ethyl acetate, n-propyl acetate, isobutyl acetate, ester-based organic solvents, ketone-based organic solvents such as methyl ethyl ketone and methyl isobutyl ketone, alcohol-based organic solvents such as methanol, ethanol, isopropanol, and n-butanol, and hydrocarbon-based solvents such as methylcyclohexane.

The solids concentration of the coating liquid is not particularly limited, but from the viewpoints of obtaining the desired coating layer thickness, giving the coating liquid a viscosity that is easy to apply, and ease of drying, it is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more, even more preferably 30% by mass or more, and more preferably 75% by mass or less, even more preferably 70% by mass or less, and even more preferably 65% by mass or less.

The viscosity of the coating liquid, as measured with a Brookfield viscometer, from the viewpoints of suitability for coating, obtaining the desired coating layer thickness, and ease of drying, is preferably 10 mPa·s (20°C) or more and 5000 mPa·s (20°C) or less, more preferably 15 mPa·s (20°C) or more, even more preferably 20 mPa·s (20°C) or more, more preferably 4000 mPa·s (20°C) or less, even more preferably 3000 mPa·s (20°C) or less, and even more preferably 2000 mPa·s (20°C) or less.

When the printed layer is provided by lamination, it is preferable to laminate on the substrate a film containing the inorganic compound A. When the printed layer is provided by lamination, the printed layer is also called a laminate layer.
The thermoplastic resin constituting the laminate layer is not particularly limited, and may be appropriately selected from known thermoplastic resins as long as it can be processed into a film by incorporating inorganic compound A. Specific examples include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin resins such as polyvinyl chloride, polyvinylidene chloride, polybutene, polybutadiene, ethylene-vinyl acetate copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, and polymethylpentene; polycarbonate; polyurethane; polyamide; polyacrylonitrile; and poly(meth)acrylate.
Among these, the resin constituting the laminate layer is preferably a polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polybutylene terephthalate, polylactic acid, polybutylene succinate, etc., from the viewpoint of being versatile and having high UV transmittance, and enabling the discoloration of the inorganic compound A to the inside of the film, more preferably at least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polylactic acid, and polybutylene succinate, and even more preferably at least one selected from the group consisting of polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene terephthalate, polylactic acid, and polybutylene succinate. The resin constituting the laminate layer is even more preferably a polyolefin, and even more preferably at least one selected from the group consisting of polyethylene and polypropylene. Polyethylene (PE) is roughly classified into linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE). Among these, low density polyethylene (LDPE) is preferred because of its excellent extrusion lamination properties.
In addition, it is preferable to use a biodegradable polyester resin as the resin constituting the laminate layer in terms of reducing the environmental load. Examples of such resins include polylactic acid and polybutylene succinate.
These resins may be used alone or in combination of two or more.

From the viewpoint of suppressing smoke generation during irradiation with an ultraviolet laser, the content of thermoplastic resin in the laminate layer is preferably 20% by mass or more and 99% by mass or less, more preferably 30% by mass or more, even more preferably 50% by mass or more, still more preferably 70% by mass or more, even more preferably 80% by mass or more, and more preferably 98% by mass or less, and even more preferably 95% by mass or less.

The printing layer may contain other components in addition to the inorganic compound A and the thermoplastic resin described above. Examples of other components include inorganic pigments other than the inorganic compound A (hereinafter, also simply referred to as "inorganic pigments"). By containing an inorganic pigment other than the inorganic compound A, scattering of the inorganic compound A is suppressed, smoke generation during irradiation with an ultraviolet laser is suppressed, and as a result, the printing density is improved, which is preferable.
The inorganic pigments may be used alone or in combination of two or more kinds.

In addition to the components mentioned above, the printing layer may contain film-forming agents, pigment dispersants, pigment dispersing resins, anti-blocking agents, wetting agents, viscosity adjusters, pH adjusters, defoamers, general surfactants, etc.

(Coating Fluid)
When the printing layer is provided by coating, if the coating liquid (ink composition) is an aqueous coating liquid, it is preferable to obtain it by mixing the above-mentioned various materials with an aqueous medium. Note that, prior to mixing with the aqueous medium, inorganic compound A, thermoplastic resin, water, and if necessary, inorganic pigments other than inorganic compound A, water-miscible solvents, pigment dispersants, pigment dispersing resins, etc. may be mixed and kneaded, and water, if necessary, water-miscible solvents, and the remaining predetermined materials may be added and mixed thereto.
Furthermore, when the coating liquid is an oil-based coating liquid, inorganic compound A or a pigment other than inorganic compound A may be added after mixing the organic solvent and the resin, and a pigment dispersant, pigment dispersing resin, etc. may be added in advance to the mixed liquid of the organic material and the resin, or may be added later.
The coating liquid can be obtained by mixing and dispersing the above-mentioned components using a high-speed stirrer such as a homomixer or a lab mixer, or a dispersing machine such as a Coles disperser, a three-roll mill or a bead mill.

The method for applying the coating liquid is not particularly limited, and the coating liquid may be applied to the substrate using flexographic printing, inkjet printing, gravure printing, screen printing, pad printing, spray coating, a Mayer bar, a gravure coater, an air knife coater, a blade coater, a rod coater, a die coater, a bar coater, etc.

(Laminate layer)
When the printed layer is a laminate layer, the film to be laminated is obtained by preparing a raw material composition by melt-kneading at least inorganic compound A and a thermoplastic resin, and, if necessary, materials such as an inorganic pigment, forming this into a film, and then stretching it if necessary.
In preparing the raw material composition, a master batch containing the inorganic compound A or the inorganic pigment at a high concentration may be prepared and then mixed with the resin.
Alternatively, materials that have been uniformly mixed in advance may be charged into the molding machine, or the materials may be mixed in a hopper or kneader that is integrated with the molding machine.
The method for forming the composition into a film may be appropriately selected from conventionally known methods, such as melt extrusion, melt casting, and calendering.

The substrate and the film may be attached via an adhesive layer or may be laminated, with lamination being preferred.
The adhesive layer is not particularly limited and may be appropriately selected from known adhesive layers. Specific examples include the pressure-sensitive adhesive layer described in JP 2012-57112 A.
Specific examples of the lamination process include laminating a paper base material and a laminate layer by a thermal lamination method, a dry lamination method, a wet lamination method, an extrusion lamination method, or the like.
Among these, the extrusion lamination method is preferred from the viewpoint of the manufacturing process since it does not require a step of bonding the laminate layer and the paper base material.

<Other demographics>
Clupak paper for ultraviolet laser printing having a printed layer provided on a paper base material can be used as it is as Clupak paper for ultraviolet laser printing. It may further have at least one layer selected from a protective layer and a thermoplastic resin layer. Here, the protective layer is provided on the printed layer, for example, for the purpose of improving water resistance and functioning as a protective layer for the printed layer. The thermoplastic resin layer is provided on the surface opposite to the surface on which the printed layer is provided, from the viewpoint of improving waterproofness and antifouling properties, etc.
That is, Clupak paper for UV laser printing on which a protective layer or a resin layer has been previously provided may be used. The Clupak paper for UV laser printing may have a protective layer on the printing layer and a thermoplastic resin layer on the side opposite to the printed side, may have a protective layer on the printed side of the paper base material and no thermoplastic resin layer on the opposite side, or may not have a protective layer on the printed side of the paper base material and a thermoplastic resin layer on the opposite side.
Furthermore, the Clupak paper may be provided with other layers, for example, printed layers printed by printing methods other than ultraviolet laser printing, such as gravure printing, to the extent that the above-mentioned effects are not impaired.

[Protective Layer]
The Clupak paper for ultraviolet laser printing of this embodiment may further have a protective layer on the printing layer of the paper base material from the viewpoint of improving water resistance and for the purpose of functioning as a protective layer for the printing layer.

The total light transmittance of the protective layer is preferably 40% or more and 100% or less, more preferably 60% or more, even more preferably 70% or more, still more preferably 80% or more, and even more preferably 90% or more, from the viewpoint of good transmission of ultraviolet laser and visibility of printed matter. The upper limit is not particularly limited.
The total light transmittance is measured in accordance with JIS K 7361-1:1997.

The resin constituting the protective layer is not particularly limited as long as it preferably has a total light transmittance of 40% or more and can be provided on a paper base material; however, from the viewpoint of transparency and ease of providing the protective layer, when the protective layer and the paper base material are attached via an adhesive layer or laminated by lamination, the resin is preferably at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polyvinyl alcohol, and starch, more preferably at least one selected from polyethylene, polypropylene, polyethylene terephthalate, and polyvinyl alcohol, even more preferably polyethylene or polypropylene, and particularly preferably polyethylene.
When the protective layer is provided by coating, examples of the material include acrylic resins, styrene-maleic acid resins, water-soluble polyurethane resins, and water-soluble polyester resins.
Examples of acrylic resins include resins obtained by copolymerizing (meth)acrylic acid with other monomers, such as alkyl esters thereof, styrene, unsaturated carboxylic acids other than (meth)acrylic acid, ethylene, and propylene. Specific examples of the acrylic resin include ethylene-(meth)acrylic acid copolymers and styrene-acrylic acid-maleic acid resins, with ethylene-(meth)acrylic acid copolymers being preferred.

The protective layer and the paper base material may be laminated by any method, and there is no particular limitation. However, from the viewpoint of ease of production, it is preferable that the protective layer and the paper base material are attached via an adhesive layer, or laminated, or a transparent coating is applied in the form of a liquid coating.
When the protective layer is provided locally, it is preferable to attach it via an adhesive from the viewpoint of ease of production, whereas when the protective layer is provided over a wide area, it is preferable to use a lamination process.
The adhesive layer is not particularly limited and may be appropriately selected from known adhesive layers. Specific examples include the pressure-sensitive adhesive layer described in JP 2012-57112 A.

The thickness of the protective layer is not particularly limited, but from the viewpoint of obtaining a printed matter with high print density and from the viewpoint of the handleability of the printed matter and the Clupak paper for ultraviolet laser printing, it is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more, even more preferably 12 μm or more, and more preferably 75 μm or less, even more preferably 50 μm or less.

[Thermoplastic resin layer]
The thermoplastic resin used in the thermoplastic resin layer is not particularly limited, and may be appropriately selected from known thermoplastic resins.
Specific examples of the resin include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate; polyolefin resins such as polyvinyl chloride, polyvinylidene chloride, polybutene, polybutadiene, ethylene-vinyl acetate copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, and polymethylpentene; polycarbonate; polyurethane; polyamide; polyacrylonitrile; and poly(meth)acrylate.

Among these, polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate; and polyamides such as nylon are preferred, with polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, and polybutylene succinate being more preferred, polyethylene and polypropylene being even more preferred, and polyethylene being even more preferred.
In addition to the above materials, biomass resin or biodegradable resin may be used as the resin.
These resins may be used alone or in combination of two or more.

The thermoplastic resin is preferably one that can be laminated to the sheet substrate as a lamination layer. Among thermoplastic resins, polyethylene is preferred because of its excellent extrusion lamination properties and barrier properties.
Polyethylene (PE) is roughly classified into linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE). Among these, low density polyethylene (LDPE) is preferred because of its excellent extrusion lamination property and foaming property.

The thermoplastic resin layer and the paper substrate may be attached via an adhesive layer.
The adhesive layer is not particularly limited and may be appropriately selected from known adhesive layers. Specific examples include the pressure-sensitive adhesive layer described in JP 2012-57112 A.

The thermoplastic resin layer may be produced by a known production method, such as a melt extrusion method, a melt casting method, a calendar method, etc. The thickness of the thermoplastic resin layer is not particularly limited, but from the viewpoint of improving waterproofness and antifouling properties, and from the viewpoint of ease of forming the thermoplastic resin layer, it is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more, even more preferably 15 μm or more, and more preferably 80 μm or less, even more preferably 50 μm or less, and even more preferably 30 μm or less.

<Applications>
The use of the obtained Clupak paper for ultraviolet laser printing is not particularly limited, and by forming it into an appropriate molded product, it can be used for paper products such as packaging materials such as wrapping paper, packaging bags, and packaging containers, and various containers such as cups and trays. For example, it can be used for paper containers such as paper plates, paper cups, and paper trays, bags for horizontal pillow packaging, vertical pillow packaging, three-sided seal packaging, four-sided seal packaging, bag-feed filling packaging, tube packaging, and stick packaging. In particular, since it has excellent flexibility and drop impact resistance, it can be suitably used in the above-mentioned bag applications.
The use of the Clupak paper for ultraviolet laser printing of this embodiment is not limited to packaging materials and containers, and it may also be used for, for example, labels, adhesive tapes, and the like.

[Printed matter and method for producing printed matter]
The printed matter of the present embodiment is a printed matter obtained from the above-mentioned Clupak paper for ultraviolet laser printing, and has at least a part of a printed area containing inorganic compound A discolored by ultraviolet laser irradiation. The printed area containing discolored inorganic compound A is an area containing inorganic compound A discolored by ultraviolet laser irradiation, and is an ultraviolet laser irradiated area, i.e., a printed area.
The method for producing a printed matter of the present embodiment includes a step of irradiating the above-mentioned Clupak paper for ultraviolet laser printing with an ultraviolet laser to discolor the irradiated area, thereby printing.
The Clupak paper for ultraviolet laser printing used in the method for producing a printed matter of this embodiment is exemplified by the Clupak paper for ultraviolet laser printing described above, and the preferred ranges are also the same.

When inorganic compound A is titanium oxide, the ultraviolet laser is preferably irradiated so that the ratio of the Raman intensity derived from titanium oxide in the printed area to the Raman intensity derived from titanium oxide in the non-printed area is 0.70 or less. That is, in the printed matter of this embodiment, the ratio of the Raman intensity derived from titanium oxide in the printed area to the Raman intensity derived from titanium oxide in the non-printed area is preferably 0.70 or less.
In addition, in the printed matter, the printed area means an area (portion) containing discolored titanium oxide in the printable area, and is an area (portion) printed by an ultraviolet laser. The non-printed area means an area (portion) not printed in the printable area. Furthermore, the printable area means the entire area containing titanium oxide, including the area printable by ultraviolet laser and the area (portion) printed by ultraviolet laser, if any, in the Clupak paper for ultraviolet laser printing or the printed matter, and the non-printable area means an area other than the printable area in the Clupak paper for ultraviolet laser printing or the printed matter.
When inorganic compound A is titanium oxide, it is preferable to print so that the ratio of the Raman intensity derived from titanium oxide in the printed area to the Raman intensity derived from titanium oxide in the non-printed area (Raman intensity of the printed area/Raman intensity of the non-printed area) is 0.70 or less. By keeping the ratio of Raman intensities within the above range, a printed matter with excellent visibility can be obtained.
The above Raman intensity ratio (Raman intensity of printed area/Raman intensity of non-printed area) is the maximum Raman intensity in the wavenumber range of 447±10 cm ^-1 as the Raman intensity derived from titanium oxide when rutile titanium oxide is used as the titanium oxide, and is the maximum Raman intensity in the wavenumber range of 516±10 cm ^-1 as the Raman intensity derived from titanium oxide when anatase titanium oxide is used as the titanium oxide.
When rutile titanium oxide and anatase titanium oxide coexist, the Raman intensity derived from rutile titanium oxide is used for comparison.

<UV laser irradiation conditions>
From the viewpoint of improving the visibility of the printed area, the wavelength of the ultraviolet laser is preferably 260 nm or more and 370 nm or less, more preferably 365 nm or less, even more preferably 360 nm or less, and more preferably 340 nm or more, even more preferably 350 nm or more.

From the viewpoint of improving the visibility of the printed area and from the viewpoint of economy, the average output power of the ultraviolet laser is preferably 0.3 W or more and 30 W or less, more preferably 0.8 W or more, even more preferably 1.2 W or more, even more preferably 1.8 W or more, and more preferably 25 W or less, even more preferably 20 W or less, even more preferably 15 W or less, even more preferably 10 W or less, and even more preferably 6 W or less.

From the viewpoint of improving the visibility of the printed area, the repetition frequency (frequency) of the ultraviolet laser is preferably 10 kHz or more and 100 kHz or less, more preferably 20 kHz or more, even more preferably 30 kHz or more, and more preferably 80 kHz or less, even more preferably 60 kHz or less.

From the standpoint of obtaining a clear image and ease of printing, the spot diameter of the ultraviolet laser is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more, even more preferably 30 μm or more, and more preferably 240 μm or less, even more preferably 180 μm or less, and even more preferably 120 μm or less.

From the standpoint of high-speed printing and visibility of the printed area, the scanning speed of the ultraviolet laser is preferably 500 mm/sec or more and 7000 mm/sec or less, more preferably 1000 mm/sec or more, even more preferably 2000 mm/sec or more, and more preferably 6000 mm/sec or less, even more preferably 5000 mm/sec or less.

From the standpoint of obtaining a clear image and the ease of obtaining the equipment, the filling interval (line pitch) of the ultraviolet laser is preferably 10 μm or more and 300 μm or less, more preferably 20 μm or more, even more preferably 30 μm or more, and more preferably 250 μm or less, even more preferably 200 μm or less.

<Embodiments of the method for producing printed matter>
The method for producing a printed matter of the present invention can be carried out in various modes.
Various examples of the printed matter manufacturing method of the present embodiment are described below, but the printed matter manufacturing method of the present embodiment is not limited to the following examples. The information to be printed is not particularly limited, but is preferably variable information.
The method for producing a printed matter according to the present embodiment is preferably carried out in-line.
(1) Direct Printing on Packaging A first embodiment of the method for producing a printed matter of the present embodiment is a method for printing information on packaging having the Clupak paper for UV laser printing of the present embodiment, and includes a step of printing directly on the packaging using an UV laser while it is moving on a packaging line or while it is intermittently stopped.
In the first method for producing a printed matter, a package is produced using the Clupak paper for ultraviolet laser printing of the present embodiment, and is directly printed with an ultraviolet laser. Note that it is sufficient that at least the outermost layer of the region to be printed on the package is produced using the Clupak paper for ultraviolet laser printing.
Examples of packaging materials include cardboard, boxes, packaging bags, etc., and it is preferable to print directly on the side or top surface of the packaging material using an ultraviolet laser.

In addition, the method for producing a printed matter of this embodiment is not limited to the above-mentioned aspects, and may be a method for printing information on a label having the Clupak paper for ultraviolet laser printing of this embodiment. In addition, it is preferable to use the Clupak paper for ultraviolet laser printing as an adhesive tape and print with an ultraviolet laser before or after attaching it to an article (package).

The method for producing printed matter of this embodiment is not limited to the above-mentioned aspects and can be applied to various uses where printing is required.

[Processed products]
The Clupak paper for ultraviolet laser printing and the printed matter of the present embodiment are applied to various processed products. That is, the processed products of the present embodiment are made using the Clupak paper for ultraviolet laser printing of the present embodiment or the printed matter of the present embodiment.
The processed product of this embodiment is preferably a package, a label, or an adhesive tape. Among these, the present invention can be preferably used for paper processed products such as packages such as wrapping paper, packaging bags, and packaging containers, and various containers such as cups and trays. The packaging products can be used, for example, for paper containers such as paper plates, paper cups, and paper trays, and for bags for horizontal pillow packaging, vertical pillow packaging, three-sided seal packaging, four-sided seal packaging, bag-feed filling packaging, tube packaging, and stick packaging.
Examples of the label include label base paper, adhesive labels, and adhesive sheets, and examples of the adhesive tape include adhesive tape and craft tape.
Among these, since it has particularly excellent flexibility and drop impact resistance, it can be suitably used in the above-mentioned bag applications.

The features of the present invention are explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Furthermore, unless otherwise specified, "parts" refers to "parts by mass". Furthermore, the operations of the examples and comparative examples were carried out at room temperature (20-25°C) and normal humidity (40-50% RH) unless otherwise specified.

Example 1
[Production of paper base material]
Pulp was prepared by using NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) in a ratio of 55:45, which were made by pulping (cooking) wood, and beating the slurry to a CSF (Canadian Standard Freeness) of 600 mL at a slurry concentration of 2% by mass.
Using the above pulp, 0.15 parts by mass of a synthetic sizing agent (SPS400, manufactured by Arakawa Chemical Industries, Ltd.), 1.2 parts by mass of aluminum sulfate, 0.65 parts by mass of a polyacrylamide resin (DS4433, manufactured by Seiko PMC Corporation) as a retention agent, and 0.035 parts by mass of nonionic polyacrylamide (Percoll 47, manufactured by Allied Colloids) as a polymer flocculant (retention agent) were added per 100 parts by mass of pulp in terms of solid content to prepare a paper stock.
Using the above-mentioned paper material, paper was made on a wet papermaking machine (Bellform III type, manufactured by Mitsubishi Heavy Industries, Ltd.) equipped with an expansion device (manufactured by Clupac) at a papermaking speed of 600 m/min, a reel moisture content of 7.0%, and a speed difference before and after the Clupac treatment of -20.0 m/min, to obtain a paper base material with a basis weight of 80 g/ ^m2 and a crepe applied to the paper surface.

[Preparation of Coating Liquid]
As a solid content, 68 parts of titanium oxide (manufactured by Kanto Chemical Co., Ltd., rutile type, special grade, product number: 40982-00, amorphous, average particle size 0.20 μm) and 32 parts of ion-exchanged water were mixed to adjust the solid content concentration to 68%. Thereafter, a pigment dispersion was prepared using a Coles disperser, and 1748.6 parts (612 parts as solid content) of an ethylene-acrylic emulsion (manufactured by Mitsui Chemicals, Inc., Chemipearl S-300, solid content concentration 35%, ethylene-methacrylic acid copolymer ionomer) was added as an emulsion to prepare a coating liquid with a solid content concentration of 36.8%. Thereafter, the solid content concentration was adjusted to 35.0% by dilution with ion-exchanged water.
[Production of ultraviolet laser printing paper]
The coating liquid prepared as described above was applied to a paper substrate using an air knife coater so that the coating amount of titanium oxide was 1 g/ ^m2 , and then dried at 140°C for 1 minute to form a printed layer, thereby obtaining Clupak paper for ultraviolet laser printing.

Example 2
A paper base material was produced under the same conditions as in Example 1, except that the speed difference before and after the Clupak treatment was changed to -28.0 m/min, to obtain Clupak paper for ultraviolet laser printing.

Example 3
A paper base material was produced under the same conditions as in Example 1, except that the speed difference before and after the Clupak treatment was changed to -30.0 m/min, to obtain Clupak paper for ultraviolet laser printing.

Example 4
A paper base material was produced under the same conditions as in Example 1, except that the speed difference before and after the Clupak treatment was changed to -20.0 m/min and the basis weight was changed to 100 g/ ^m2 by adjusting the discharge amount of the pulp slurry, to obtain Clupak paper for ultraviolet laser printing.

Example 5
A paper base material was obtained under the same conditions as in Example 1, except that the speed difference before and after the Clupac treatment was changed to -15.0 m/min and the basis weight was changed to 120 g/ ^m2 by adjusting the discharge amount of the pulp slurry.

Example 6
A paper base material was produced under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 40:60, and the paper was made at a speed difference of -25.0 m/min before and after the Clupak treatment. Clupak paper for UV laser printing was obtained.

Example 7
A paper base material was produced under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 90:10, and the paper was made at a speed difference of -40.0 m/min before and after the Clupak treatment. Clupak paper for UV laser printing was obtained.

Example 8
A paper base material was produced under the same conditions as in Example 1, except that the speed difference before and after the Clupak treatment was -16.0 m/min and the basis weight was changed to 50 g/ ^m2 by adjusting the discharge amount of the pulp slurry, to obtain Clupak paper for ultraviolet laser printing.

<Example 9>
A paper base material was produced under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 30:70, and the paper was made at a speed difference of -25.0 m/min before and after the Clupak treatment. Clupak paper for UV laser printing was obtained.

Example 10
A paper base material was produced under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 100:0, and the paper was made at a speed difference of -40.0 m/min before and after the Clupak treatment. Clupak paper for UV laser printing was obtained.

Example 11
Clupak paper for ultraviolet laser printing was obtained in the same manner as in Example 2, except that in preparing the coating solution, the titanium oxide used was changed to zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., zinc oxide type 1, shape: irregular, average particle size: 0.6 μm).

Example 12
[Formation of protective layer]
PE resin (manufactured by Japan Polyethylene Corporation, product number: LC522) was charged into a single-screw extruder (manufactured by Toyo Seiki Seisakusho, 50C150) and melt-laminated on the printed layer of the Clupak paper for UV laser printing obtained in Example 2 to a resin thickness of 15 μm, and then it was quickly quenched while being sandwiched between cooling rolls adjusted to 20° C., thereby obtaining Clupak paper for UV laser printing further having a protective layer on the printed layer. The melting temperature was 320° C.

Example 13
A coating liquid prepared by mixing 100 ^parts by mass of an aqueous acrylic adhesive (EA-G34, manufactured by Toyo-Morton Co., Ltd.) and 3 parts by mass of a curing agent (CAT-EP8, manufactured by Toyo-Morton Co., Ltd.) was applied to the side opposite the printed layer of the Clupak paper for ultraviolet laser printing in Example 8 using a reverse roll coater so that the coating amount after thermal drying would be 10 g/m2, and then dried at 105° C. Next, a linear low density polyethylene film (LL-XLTN, manufactured by Futamura Chemical Co., Ltd., 25 μm) was laminated onto the side coated with the adhesive.

<Example 14>
A coating liquid prepared by mixing 100 parts by mass of an aqueous acrylic adhesive (EA-G34, manufactured by Toyo-Morton Co., Ltd.) and 3 parts by mass of a curing agent (CAT-EP8, manufactured by Toyo-Morton Co., Ltd.) was applied to the side opposite the printed layer of the Clupak paper for ultraviolet laser printing in Example ² using a reverse roll coater so that the coating amount after thermal drying would be 10 g/m2, and then dried at 105° C. Next, a linear low density polyethylene film (LL-XLTN 20 μm, manufactured by Futamura Chemical Co., Ltd.) was laminated onto the side coated with the adhesive.

Example 15
[Method for producing master batch]
Following the teachings of JP 2015-96568 A, a master batch was prepared by the following procedure.
60 parts of PE resin (polyethylene resin, Japan Polyethylene Corporation, LC522) and 40 parts of titanium oxide were mixed in a tumbler mixer (Eishin Co., Ltd., TM-65S) at 45 rpm for 1 hour, and then melt-kneaded in a twin-screw extruder (The Japan Steel Works, Ltd., TEX30XCT, L/D=42) at a screw rotation speed of 250 rpm and a cylinder temperature of 200° C., extruded into a strand shape, cooled in a water tank, and then pelletized using a pelletizer into columnar shapes with an average shaft diameter of 2.0 mm and an average shaft length of 3.0 mm to obtain a master batch.
[Adding a Laminate Layer (Film)]
The master batch and the PE resin were put into a single screw extruder (50C150, manufactured by Toyo Seiki Seisakusho Co., Ltd.) so that the content of titanium oxide in the printed layer when a 20 μm printed layer was formed was 1.0 g/ ^m2, and melt-laminated by extrusion lamination on the surface of the paper base material of Example 2 so that the laminate layer, which is the printed layer, had a thickness of 20 μm. The laminate layer was then quickly cooled while being sandwiched between cooling rolls adjusted to 20 ° C. to obtain an ultraviolet laser printing paper having a laminate layer, which is the printed layer. The melting temperature was 320 ° C.

<Comparative Example 1>
A paper base material was obtained under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 45:55, Clupak treatment was not performed, and the discharge rate of the pulp slurry was adjusted to change the basis weight to 50 g/ ^m2 .

<Comparative Example 2>
A paper base material was obtained under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 45:55, and Clupak treatment was not performed.

<Comparative Example 3>
A paper base material was obtained under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 60:40, Clupak treatment was not performed, and the discharge rate of the pulp slurry was adjusted to change the basis weight to 100 g/ ^m2 .

<Comparative Example 4>
A paper base material was obtained under the same conditions as in Example 1, except that NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood were used in a ratio of 45:55, and the speed difference before and after the Clupak treatment was -10.0 m/min.

<Comparative Example 5>
The same preparation as in Example 13 was carried out except that Clupak paper of Comparative Example 1 was used.

<Comparative Example 6>
The preparation was carried out in the same manner as in Example 13, except that the Clupak paper of Comparative Example 2 was used.

The obtained Clupak paper or paper base material was used to carry out the following evaluations.
＜Fear＞
The stiffness of Clupak paper in the machine and cross directions was measured as per ISO 2493-1:2010 (Paper and paperboard-Bending resistance test method-Part 1: Constant rate of deflection).
Specifically, Clupak paper was left to stand for one day in an environment of 23±5°C and 50±10% humidity as a temperature and humidity conditioning treatment, and then cut into a sample with a width of 38 mm and a length of 70 mm to prepare a sample. Using a stiffness tester (L&W BENDING RESISTANCE TESTER Code No. 16-D, manufactured by Lorentzen & Wattre), the bending length was set to 10 mm and the bending angle to 15°, and the bending resistance in each of the MD (machine direction) and CD (cross direction) was measured, and the stiffness was calculated using the following formula.

<Puncture strength/specific puncture strength>
The puncture strength of Clupak paper was measured in accordance with JIS Z 1707:2019 (General rules for plastic films for food packaging).
Specifically, the Clupak paper was left to stand for one day in an environment of 23±5°C and 50±10% humidity as a temperature and humidity control treatment, and then subjected to a tensile test using a tensile tester (model RTC-1210A, A&D Co., Ltd.). The puncture strength was measured using a puncture jig (manufactured by A&D Co., Ltd.) at a puncture speed of 50 mm/min.
Furthermore, the specific puncture strength was calculated by dividing the puncture strength by the basis weight.

<Length-weighted average fiber length of pulp>
The length-weighted average fiber length of the pulp in Clupak paper was measured in accordance with ISO 16065-2:2007, specifically as follows:
The Clupak paper was cut into 40 cm square pieces, immersed in ion-exchanged water, and adjusted to a solids concentration of 2% by mass, and then soaked for 24 hours. After soaking for 24 hours, the paper was defibrated for 30 minutes using a standard defibrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) to defibrate the pulp into fibers. In cases where the Clupak paper had a thermoplastic resin layer or a protective layer, the slurry (dispersion of pulp fibers) after defibration was removed from the thermoplastic resin layer or protective layer.
The obtained pulp fiber samples were used to measure the "length-weighted average fiber length (ISO)" using a fiber length measuring instrument (model FS-5 with UHD base unit, manufactured by Valmet Co., Ltd.). The "length-weighted average fiber length (ISO)" is the length-weighted average fiber length calculated by selecting fibers having a length of 0.2 mm or more and 7.6 mm or less.

<Basance weight>
The basis weight of the paper base material was measured in accordance with JIS P 8124:2011.
In addition, when the Clupak paper has a resin layer (thermoplastic resin layer or protective layer) in addition to the paper base material, the material, thickness, density, etc. of the resin layer were specified by a known method and the following procedure, and then the basis weight of the paper base material was calculated. Specifically, the mass (total mass) of the Clupak paper having the thermoplastic resin layer and protective layer cut to a specified size was measured, and then the Clupak paper having the thermoplastic resin layer and protective layer was impregnated with an aqueous enzyme solution such as cellulase to confirm that the paper base material was completely dissolved, and the mass of only the thermoplastic resin layer and protective layer (resin layer mass) was measured, and the mass of only the paper base material was calculated by subtracting the resin layer mass from the total mass, and the basis weight of the paper base material was measured. In addition, when a printing layer is present, it can also be removed using a grinding device (manufactured by Sagawa Seisakusho Co., Ltd., grinding wheel dimensions φ50.8×12.7 mm) and measured.

<Thickness>
The thickness of the paper base material (paper thickness) was measured in accordance with JIS P 8118: 2014. When the Clupak paper has a printed layer, a resin layer, and a protective layer in addition to the paper base material, the thicknesses of the paper base layer, the printed layer, the thermoplastic resin layer, and the protective layer are measured from an observation image of a cross section of the Clupak paper taken with a scanning electron microscope (SEM).

<Density>
The density of the paper base material is calculated from the thickness and basis weight obtained by the above-mentioned measuring method.

<Bag flexibility evaluation>
The obtained Clupak paper or paper base material was cut out to obtain a sheet 1 having a length of 200 mm and a width of 150 mm. The width of the sheet 1 was in the paper-making direction (MD). A double-sided tape 2 having a width of 10 mm (type: Scotch super strong double-sided tape Premier Gold Super Multipurpose PPS-10, manufactured by 3M) was attached to the sheet 1 as shown in Figure 1, and the sheet was folded in half at the center in the longitudinal direction (MD) (position 100 mm from the end) and fixed so that no gaps were formed, to obtain a bag 3.
The bag 3 was filled with water, and the amount of water filled until the water spilled out was evaluated. The larger the value, the better the bag flexibility. The bag was made so that the side with the printed layer was on the outside of the bag.
4: Water filling volume is 150mL or more.
3: The amount of water filled is greater than or equal to 100 mL and less than 150 mL.
2: The amount of water filled is greater than or equal to 50 mL and less than 100 mL.
1: The water filling volume is less than 50 mL.

<Drop impact resistance evaluation>
From the obtained Clupak paper or paper base material, a bag similar to the bag 3 produced in the above <Evaluation of bag flexibility> was produced. The bag was produced so that the side on which the printed layer was provided was on the outside of the bag.
A 50 g disk-shaped weight (product number: 201900401, manufactured by Murakami Scale Manufacturing Co., Ltd.) was filled into bag 3 and sealed with the 10 mm wide double-sided tape used in <Bag Flexibility Evaluation> to prepare a bag filled with the weight. The bag filled with the weight was left to stand for one day in an environment of 23±5°C and 50±10% as a temperature and humidity adjustment treatment.
The bags after the temperature and humidity conditioning treatment were dropped from a height of 30 cm onto a SUS plate with the top surface 4 (filling port) of the bag facing up. The dropped bags were then dropped in the same manner with the bottom surface 5 facing up. The above drop test (2 drops per bag) was performed a total of 5 tests per level using newly produced bags to evaluate the drop impact resistance. A higher value indicates better drop impact resistance.
4: In all five tests, the bag was not torn or dented.
3: In all five tests, the bags were not torn, but some were dented.
2: In tests 1 to 4, the bag broke.
In all 1:5 tests, the bag broke.

<Printing method>
The printing papers of the examples and comparative examples were printed with an ultraviolet laser under the following conditions.
A 30 mm square was marked using an ultraviolet laser (product number: MD-U1020C, manufactured by Keyence Corporation). The printed layer was irradiated with the ultraviolet laser.
The irradiation conditions were as follows:
Wavelength: 355 nm
Output: 80% (2.5W at 100% output)
Frequency: 40kHz
Focal length: 300 mm (focusing is performed using the height correction included with the device)
・Spot diameter = 40 μm (when focused)
Fill interval: 0.04 mm
Scan speed: 3000 mm/sec
・Spot variable: 100
<Evaluation method>
The above-printed Clupak paper was made into a bag using a horizontal pillow packaging machine (product number: FW3410/B, manufactured by Fujikikai Co., Ltd.), the heat-sealed portion on the top surface was opened, a disk-shaped weight having a mass of 50 g (product number: 201900401, manufactured by Murakami Scale Manufacturing Co., Ltd.) was filled, and the filling port was sealed with double-sided tape (model: Scotch Super Strong Double-sided Tape Premier Gold Super Multi-Purpose PPS-10, manufactured by 3M Co., Ltd.). The bag was made so that the printed surface was on the outside of the bag. In accordance with JIS P 8113:2006 (Testing Method for Tensile Properties of Paper and Paperboard), the bag was left to stand for one day or more under an environment of 23±5°C and 50±10%, and the same bag was dropped once each onto a floor covered with a SUS plate from a height of 30 cm so that the ultraviolet laser printed portion fell onto the floor without accelerating, and the state of the printed portion after the test was observed.
In addition, similar evaluations were performed four times each using newly prepared bags, for a total of five evaluations.
The evaluation criteria are as follows:
A: The bag was not torn, dented or wrinkled after being made into a bag or dropped, the 30 mm square print was not distorted and visibility was good.
B: One or more of the bags after being made and dropped had tears or wrinkles, the 30 mm square print was distorted, and visibility was reduced.

The physical properties and evaluation results of Examples 1 to 15 and Comparative Examples 1 to 6 are shown in Table 1.

As shown in Table 1, the Clupak paper for ultraviolet laser printing of the examples has drop impact resistance and excellent flexibility, and furthermore, it is possible to print with an ultraviolet laser. Even when a drop test was performed after printing, a print with excellent visibility was obtained.
On the other hand, sufficient drop impact resistance was not obtained in Comparative Examples 1, 2, 4, and 5, in which the puncture strength was less than 7.5 N. Furthermore, sufficient flexibility was not obtained in Comparative Example 3, in which the stiffness in the vertical direction exceeded 0.70 mNm.

1: Sheet, 2: Double-sided tape, 3: Bag, 4: Top of bag, 5: Bottom of bag

Claims (12)

A printing layer containing an inorganic compound that changes color when irradiated with an ultraviolet laser is provided on a paper base material containing pulp,
The stiffness in the longitudinal direction, measured in accordance with ISO2493-1:2010, is 0.05 mNm or more and 0.70 mNm or less, and the stiffness in the lateral direction is 0.05 mNm or more and 0.45 mNm or less;
Clupak paper for ultraviolet laser printing, having a puncture strength of 7.50 N or more and 18.00 N or less , and a specific puncture strength of 0.05 N·m ² /g or more and 0.30 N·m ² /g or less , measured in accordance with JIS Z 1707:2019. Clupak paper for ultraviolet laser printing according to claim 1, wherein the stiffness in the longitudinal direction is 0.05 mNm or more and 0.55 mNm or less, and the stiffness in the transverse direction is 0.05 mNm or more and 0.35 mNm or less. Clupak paper for ultraviolet laser printing according to claim 1, wherein the puncture strength is 12.50 N or more. Clupak paper for ultraviolet laser printing according to claim 1, wherein the length-weighted average fiber length of the pulp is 1.2 mm or more and 1.9 mm or less. 2. The Clupak paper for ultraviolet laser printing according to claim 1, wherein the basis weight of the paper base is 30 g/m2 or ^more and 120 g/m2 ^{or less} . The Clupak paper for ultraviolet laser printing according to claim 1, having a specific puncture strength of 0.13 N·m ² /g or more. The Clupak paper for ultraviolet laser printing according to claim 1, further comprising at least one layer selected from a protective layer and a thermoplastic resin layer in addition to the paper base material. Clupak paper for ultraviolet laser printing according to claim 1, wherein the inorganic compound that changes color when irradiated with an ultraviolet laser is at least one selected from the group consisting of titanium oxide and zinc oxide. A printed matter obtained from the Clupak paper for ultraviolet laser printing according to any one of claims 1 to 8,
The printed layer has a printed area containing the inorganic compound, which has been discolored by irradiation with an ultraviolet laser, at least in a part thereof.
Printed matter. A processed product made using Clupak paper for ultraviolet laser printing according to any one of claims 1 to 8. A processed product made using the printed matter described in claim 9. A step of irradiating the UV laser printing Clupak paper according to any one of claims 1 to 8 with a UV laser to discolor the irradiated area, thereby printing.
A method for producing printed matter.

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