JP6665425B2 - Multilayer laminated film for laser printing and printed body comprising the same - Google Patents

Description

  The present invention relates to a laser-printed multilayer laminated film that can be printed by a laser and a printed body made of the same.

2. Description of the Related Art Printing on a film by irradiating a YAG laser or a YVO ₄ laser or the like is conventionally known. As a multilayered film for laser printing that can be printed by these lasers, a film using a special ink that changes color by laser irradiation as an intermediate layer (color-forming layer) is known (Patent Document 1).
Since such a special ink is very expensive, the special ink layer is provided in advance only on a portion of the substrate to be printed. However, it is difficult to align the position even on the spot, and the print position cannot be easily changed. Further, there is a disadvantage that the printing line is thin and it is difficult to read.

Also, conventional ink also discolored slightly by irradiation of a YAG or YVO ₄ laser. Therefore, it is also known to use such a normal ink as an intermediate layer (color-forming layer) (Patent Document 2). However, in this method, a printed portion is formed by vaporizing the intermediate layer by irradiating a strong laser beam and deforming the substrate without breaking it.
That is, in order to obtain sufficient visibility, the laser output is applied until the intermediate layer in the laser-irradiated portion is completely evaporated over the entire thickness in the depth direction (the direction from one surface of the film to the other surface). It needs to be raised. Therefore, there is a problem that a film serving as a base is perforated by irradiation of a strong laser beam. In addition, since it is necessary to irradiate a strong laser beam, there is a problem that the printing speed is low.

JP 2007-55110A JP 2007-217048 A

  The present invention solves the above problems, is made of inexpensive materials, is easy to manufacture, easily changes the printing position, and has a low output that does not damage the base film. It is an object of the present invention to provide a laser-printed multilayer laminated film capable of obtaining a thick and easy-to-read print line by irradiating a laser, and a printed body using the same.

  The present inventors have conducted various studies and found that the lamination strength between the base layer and the printing layer on the viewing side was made smaller than the lamination strength between the printing layer and the sealant layer, so that the base layer and the printing layer were printed. A gap can be easily formed only between the layer and the layer by low-power laser irradiation input from the viewer side, and the carbonized ink composition spreads and diffuses on the surface of the gap, so that the line is thick and clear. It has been found for the first time that a laser printed image can be formed.

That is, at least, a base layer, a printing layer, and a multilayer laminated film for laser printing comprising a sealant layer, the base layer is a layer made of a resin film, the first layer adjacent to the base layer A print layer, at least two layers of a sealant layer and an adjacent second print layer, wherein the print layer is a layer made of an ink composition containing a metal oxide and a binder resin. It has been found that a multilayer laminated film for laser printing achieves the above object.
More preferably, the difference between the lamination strength between the base layer and the printing layer and the lamination strength between the printing layer and the sealant layer is 0.2 N / 15 mm or more. The invention is a film.

And this invention is characterized by the following points.
1. At least, a base layer, a printed layer, and a multilayer laminated film for laser printing including a sealant layer, wherein the base layer is a layer formed of a resin film, and the printed layer is formed of a metal oxide and a binder resin. A first printing layer adjacent to the base material layer, and at least two layers of a second printing layer adjacent to the sealant layer, wherein the second printing layer includes: The binder resin is a chlorinated polypropylene resin, and in the first printing layer, the binder resin is a resin other than the chlorinated polypropylene resin, and the sealant layer is a layer made of a polypropylene resin. The multilayer laminated film for laser printing described above.
2. The difference between the laminate strength between the base layer and the first print layer and the laminate strength between the second print layer and the sealant layer is 0.2 N / 15 mm or more. 2. The multilayer laminated film for laser printing according to 1 above.
3. 3. The multilayer laminated film for laser printing according to the above 1 or 2, wherein the ink composition is a resin composition obtained by diluting 70 to 90 parts by mass of a metal oxide and 10 to 30 parts by mass of a binder resin with a solvent. .
4. The multilayer film for laser printing according to any one of the above items 1 to 3, wherein the metal oxide in the ink composition is titanium oxide.
5. The total coating amount of the ink composition of the first and second printed layer, characterized in that a 0.5 to 6.0 g / m ² The coating amount after drying, any of the above 1 to 4 A multilayer printed film for laser marking according to the above item.
6. The resin film forming the base material layer is a stretched polypropylene film,
The multilayered film for laser printing according to any one of the above items 1 to 5, wherein the binder resin in the ink composition forming the first print layer is a urethane resin.
7. 7. A gap between the base layer and the first printing layer by irradiating the multilayered film for laser printing according to any one of the above 1 to 6 with a YAG or YVO ₄ laser from the base layer side. , And having a laser printed image.

  The multilayered film for laser marking of the present invention does not require the use of a special ink for laser marking. For example, a white ink commonly used as a base for printing a packaging film can be used as an ink composition for forming a print layer in the present invention. Therefore, it can be manufactured from an inexpensive material, and there is no need to provide an additional layer for laser printing in the film manufacturing process.

Further, by irradiating the laser-printed multilayer laminated film of the present invention with a YAG or YVO ₄ laser from the substrate layer side, the ink composition forming the print layer is gasified. This gas then accumulates at the interface between the substrate layer and the printed layer that are laminated at a particular lamination strength, forming voids therein.
As a result, the ink composition carbonized by the laser irradiation spreads at the boundary between the base material and the printing layer and has a low output, that is, without increasing the laser output until the printing layer is completely evaporated over the entire thickness. A laser-printed image with excellent visibility from the material layer side can be clearly formed.

  Further, in the printed body of the present invention, a laser-printed image is provided not on the film surface but on the inside, that is, between the base material layer and the printing layer. Therefore, the image is excellent in abrasion resistance, so that it can be effectively prevented from disappearing due to rubbing or the like, and falsification can be effectively prevented.

  From these advantages, the laser-printed multilayer laminated film of the present invention is suitably used as a packaging material for foodstuffs, etc. Information can be recorded as a laser-printed image.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing which shows an example about the layer structure of the multilayer laminated film for laser printing of this invention. FIG. 2 is a schematic cross-sectional view illustrating an example of a layer configuration of a printed body of the present invention.

The present invention will be described in detail below.
<I> Layer Configuration of Laser-Printed Multilayer Laminated Film and Printed Body of the Present Invention FIG. 1 is a schematic cross-sectional view showing an example of the layered structure of the laser-printed multilayer laminated film of the present invention.
As shown in FIG. 1, the multilayer laminated film for laser printing of the present invention is basically composed of a base layer 1, a printed layer 2 and a sealant layer 3.

Further, in order to adjust the lamination strength of the printing layer and the sealant layer, any surface may be subjected to a desired surface treatment before lamination, if necessary.
As the surface treatment, for example, a pretreatment such as a corona discharge treatment, an ozone treatment, a low-temperature plasma treatment using an oxygen gas or a nitrogen gas, a glow discharge treatment, an oxidation treatment using a chemical, or the like can be performed. .

Further, for example, a primer coating agent layer, an undercoating agent layer, an anchor coating agent layer, and the like may be provided between the printing layer and the sealant layer.
As shown in FIG. 2, the printed body of the present invention is manufactured by irradiating the multilayered film for laser printing of the present invention with a YAG or YVO ₄ laser from the substrate layer side. The surface of the layer has a printed portion where the carbonized ink composition spreads.

<II> Substrate layer In the present invention, a resin film is used for the substrate layer in accordance with the purpose of use, application and the like. More preferably, an arbitrary resin film having a laminate strength with the print layer of 0.1 to 2.0 N / 15 mm when the print layer is laminated can be used.

  Specifically, it becomes a basic material, and further, after printing, constitutes a surface protective layer, and because it can see through a laser printed image, etc., it is excellent in mechanical, physical, chemical, etc. A resin film having strength, excellent piercing resistance, and the like, and excellent heat resistance, moisture resistance, transparency, and the like can be used.

In the present invention, such a resin film is selected from, for example, various resin films such as polyethylene resin, polypropylene resin, cyclic polyolefin resin, fluorine resin, polystyrene resin, polyester resin, polyamide resin, urethane resin, and cellulose resin. be able to.
As the resin film, any one of an unstretched film and a stretched film stretched in a uniaxial or biaxial direction can be used.

Further, in the present invention, the thickness of the resin film, strength, piercing resistance, etc., as long as it is a thickness that can be held to the minimum necessary, too thick, there is also a disadvantage of increasing the cost, conversely On the other hand, if it is too thin, the strength, piercing resistance and the like are undesirably reduced.
In the present invention, for the above reasons, about 3 to 100 μm, preferably about 5 to 50 μm is most desirable.

  In the present invention, a stretched polypropylene film can be particularly preferably used as the resin film forming the base layer. The stretched polypropylene film is excellent in stability, processability, cost, heat resistance, chemical resistance, and the like, particularly in use as a packaging material, and is also preferably used as a printing layer described below. When laminating objects, a preferable lamination strength with the printing layer can be obtained.

<III> Printing Layer In the present invention, the printing layer is a layer provided by laminating an ink composition containing a metal oxide and a binder resin on a base layer by printing, coating, or the like.

  In the present invention, as a metal oxide constituting the ink composition, titanium oxide, magnesium oxide, zinc oxide, aluminum oxide, silicon oxide, or the like can be used. In particular, titanium oxide, which is frequently used as a white pigment in a white ink used as a printing base of a packaging film, is preferably used.

  The binder resin constituting the ink composition for forming the first print layer is a conventionally known binder resin, and preferably has a laminate strength with the base layer when laminated on the base layer. Can be used. Any binder resin having a particle size of 0.1 to 2.0 N / 15 mm can be used.

Specifically, a urethane resin, a polyester resin, an acrylic resin, a cellulosic resin, and the like can be given. These resins are used alone or in combination of two or more. Particularly, in a white ink used as a printing base, a urethane resin frequently used as a binder resin is preferably used.
The urethane resin also provides a favorable lamination strength with the substrate layer when laminated on a stretched polypropylene film suitably used as the above-mentioned substrate layer.
As the binder resin of the second print layer of the present invention, a polypropylene-based resin is preferable in consideration of adhesiveness with the sealant layer and print reproducibility, and further, in consideration of strong adhesiveness with the sealant layer such as a polypropylene resin. Particularly, a polypropylene resin having a polar group, for example, a chlorinated polypropylene resin is suitable.

As the ink composition of the present invention, any white ink conventionally used as a printing base can be suitably used. As the composition, the content of the metal oxide is particularly preferably 70 to 90 mass%. Part, more preferably 75 to 85 parts by mass, and the content of the binder resin is 10 to 30 parts by mass, more preferably 15 to 25 parts by mass.
These may be diluted with a conventional solvent as needed, and printed or coated on the base material layer to form a printed layer. When the amount of the metal oxide is larger than the above range, the film is easily damaged by laser irradiation. Conversely, if the amount of the metal oxide is less than the above range, the printed image tends to be unclear.

In order to adjust the lamination strength between the base layer and the printing layer to a desired range, an optional additive may be added to the ink composition as needed. As an example of this, for example, addition of an antiblocking agent, a curing agent and the like in order to lower the lamination strength can be mentioned.
In addition, additives such as a pigment dispersant, an antifoaming agent, a leveling agent, a wax, a silane coupling agent, a preservative, a rust inhibitor, a plasticizer, a flame retardant, and a color developer may be added. These additives are used particularly for the purpose of improving printability, printing effect, and the like, and the type and amount of the additives can be appropriately selected depending on the printing method, printing substrate, and printing conditions.

  Further, the lamination strength may be adjusted by subjecting the lamination surface of the base material layer to a surface treatment such as corona treatment, or by laminating a printing layer on an untreated surface.

Further, in the present invention, the print layer may have a configuration in which two or more print layers made of the same or different ink compositions are laminated. Here, the ink composition for forming the printing layer on the side in contact with the base material layer has a lamination strength between the base material layer and the base material layer. The kind, content, lamination method and the like of the binder resin are selected so as to be in the range of 0.1 to 2.0 N / 15 mm.
Further, the ink composition forming the printing layer on the side in contact with the sealant layer has a laminate strength between the sealant layer and the sealant layer, and the difference is preferably 0.2 N / 15 mm or more. Adjust in the same way. With this configuration, at the time of laser irradiation, a gap is reliably formed at the boundary between the base material layer and the print layer, and delamination between the print layer and the sealant layer can be prevented.

The total thickness of the printed layer, be the coating amount of the ink composition, 1.5~6.0g / m ² The coating amount after drying, more preferably 2.0~4.0g / m ² preferable. If the print layer is thicker than this, the film is more likely to be damaged by laser irradiation. Conversely, if it is thinner than this, the printed image tends to be unclear.

  The method for laminating the print layer is not particularly limited, but a method such as inkjet, dipping, spin coating, or printing can be used. In the present invention, a method of laminating by printing is preferable. In particular, the printing process can be simplified by solid printing on the entire surface or a part of the printing base.

<IV> Sealant layer In the present invention, the sealant layer is a layer made of a conventional thermoplastic resin or a layer made of a film of the resin as the sealant layer.

Specific examples of the thermoplastic resin include polypropylene, polyethylene, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, and ethylene-methacrylic acid copolymer. Resins such as coalescing can be used alone or in combination of two or more.
In the thermoplastic resin forming the sealant layer, lubricants, fillers, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents are used for various purposes such as adjusting the lamination strength with the print layer. Various additives such as a flame retardant and a colorant can be added.

In applications as a packaging material, a polyolefin such as polyethylene and polypropylene is preferably used because the innermost layer is in contact with the contents.
When the base material layer is made of a stretched polypropylene film and a urethane resin is used as a binder resin in the ink composition, polypropylene is used as a resin for forming a sealant layer, and the polypropylene is used on the print layer. By laminating the layers by extrusion coating, suitable lamination strength with the print layer is obtained, and a clear printed image is obtained by laser irradiation.
When a chlorinated polypropylene resin is used as the binder resin in the ink composition, polypropylene is used as a resin for forming the sealant layer, and by laminating the same, Suitable lamination strength is obtained, and a clear printed image is obtained by laser irradiation.

The thickness of the sealant layer can be appropriately set according to the application of the multilayer film for laser printing, but is preferably 3 to 100 μm, and more preferably 5 to 50 μm.
In order to adjust the lamination strength between the printing layer and the sealant layer, any surface can be subjected to a desired surface treatment before lamination, if necessary. As the surface treatment, for example, a pretreatment such as a corona discharge treatment, an ozone treatment, a low-temperature plasma treatment using an oxygen gas or a nitrogen gas, a glow discharge treatment, an oxidation treatment using a chemical, or the like can be performed. .

Further, between the printing layer and the sealant layer, for example, a primer coating agent layer, an undercoating agent layer, an anchor coating agent layer, and the like may be provided.
The method of laminating the sealant layer is not particularly limited, but the laminating can be performed by extrusion coating the thermoplastic resin forming the sealant layer on the printing layer. Further, a film made of the thermoplastic resin may be laminated by a dry lamination or a sandwich lamination method.

  As the adhesive for dry lamination, a urethane adhesive, a vinyl adhesive, an acrylic adhesive, an epoxy adhesive, or the like can be used. As the adhesive resin for sandwich lamination, any thermoplastic resin can be used.

In the present invention, depending on the application of the multilayer laminated film for laser printing, between the printing layer and the sealant layer, any functional layer, for example, a gas barrier film, and any laminating method such as stretched polyamide resin film, For example, it may be provided by a dry lamination method or the like.
In any case, a combination of resin types, a laminating method, an adhesive type, a surface treatment method, and the like are selected so that the laminating strength with the print layer is appropriate.

<V> Laminating strength In the multilayer laminated film for laser printing of the present invention, the difference between the laminating strength between the base layer and the printing layer and the laminating strength between the printing layer and the sealant layer is preferably 0.1. It is 2 N / 15 mm or more, more preferably 0.5 N / 15 mm or more. Laser printing is optimally performed by a configuration having a laminate strength in this range.
If the difference in the lamination strength between the substrate layer and the printing layer, or between the printing layer and the sealant, is less than 0.2 N / 15 mm, delamination occurs between layers other than the substrate and the printing layer, and a gap is generated between the substrate and the printing layer. And the printed image becomes unclear.
If the difference between the lamination strength between the base layer and the printing layer and the lamination strength between the printing layer and the sealant layer is smaller than 0.2 N / 15 mm, voids are generated even in areas other than the base layer and the printing layer, so that the printing layer can be formed reliably Is spoiled.

  In the present invention, the lamination strength is a value measured by a T-type peel adhesion strength test performed at a moving speed of 50 mm / min, the width of a measurement sample is 15 mm, and other conditions are based on JIS K6854.

  To achieve the above lamination strength, the range is determined by the combination of the type of the resin film forming the base layer, the type of the binder resin in the ink composition forming the printing layer, and the type of the resin forming the sealant layer. It is preferable to find a combination that can obtain the strength of (1). However, in order to intentionally lower the lamination strength, a printed layer may be laminated on the surface not subjected to corona treatment, or a material for preventing adhesion to the ink composition, for example, an anti-blocking agent may be added.

<VI> Printing In the present invention, printing is performed using a YAG (yttrium (Y) / aluminum (A) / garnet (G)) laser beam (wavelength = 1.064 μm) or a YVO ₄ (yttrium / vanadate) laser beam (wavelength = 1.064 μm).
These lasers have a property of transmitting through a transparent body, and by utilizing the property, furthermore, generation of smoke or the like at the time of printing is suppressed, and it is possible to adjust the influence on the color density and the film. . As a result, even when a laser-printed image is formed, an extremely clear laser-printed image without holes or the like can be formed.

By irradiating these lasers from the substrate layer side, at a low output, while minimizing damage to the film, the ink composition of the printing layer is gasified and carbonized, and the substrate layer and the printing layer To form a laser-printed image on the surface of the print layer efficiently.
And, since the laser-printed image is formed on the surface of the print layer, the visibility from the base material layer side is excellent.

In the present invention, the pulse condition for such printing, for example, the average output 0.8~5W at YVO ₄ laser machine (Keyence MD-V9600), more preferably 1.2～2W, Q-switching frequency 10 Pulse conditions of 〜30 KHz, scan speed of 300-4000 mm / s, more preferably 1500-4000 mm / s are used.
By performing printing under these conditions, high-speed printing is possible without forming a hole in the multilayer laminated film for laser printing, and a clear printed image is obtained.

<VII> Printed body In the printing step on the multilayer laminated film for laser printing of the present invention, even if the average output of the laser is set low or the scan speed is set high, a clear printed image, for example, Clear characters can be printed.

  In the printed body of the present invention, the diameter of the void formed between the base material layer and the printing layer by laser spot irradiation is preferably from 40 μm to 1 mm, more preferably from 400 to 700 μm. The carbonized ink composition spreads in these voids, and a clear printed image is obtained. If the diameter of the gap is smaller than this, loss of the printed image and narrowing of the line width occur, resulting in a lack of visibility. On the other hand, if it is larger than this, the image is undesirably destroyed.

In the present invention, the laser-printed image includes, but is not limited to, letters, numbers, symbols, patterns, and the like.
Moreover, the printed body obtained by printing on the multilayer laminated film for laser printing of the present invention can be applied to various packaging materials, labels, cards and the like.

  In the multilayer laminated film for laser printing of the present invention, the printing layer may be composed of a white ink that functions as a printing base. Therefore, a desired color printing layer can be provided in a portion where laser printing is not performed, using the printing layer as a base.

Hereinafter, the present invention will be described specifically with reference to examples, but these examples do not limit the present invention.
[Example 1]
On a corona-treated surface of a polypropylene film (P-2261, manufactured by Toyobo Co., Ltd., thickness: 20 μm), using a gravure printer, an ink composition having the following composition was applied at a coating amount of 0.8 g / m ^2.
(At the time of drying) to provide a first printed layer.
Ink composition Titanium oxide: 40 parts by mass Urethane resin: 15 parts by mass Mixed solvent: 50 parts by mass * Mixed solvent methyl ethyl ketone: n-propyl acetate: isopropyl alcohol = 3: 5: 2 (mass ratio)
Next, an ink composition having the following composition was applied onto the first printing layer using a gravure printing machine so as to have a coating amount of 0.8 / m ² (when dried). A printing layer was provided.
Ink composition Titanium oxide: 35 parts by mass Chlorinated polypropylene resin: 10 parts by mass Mixed solvent: 50 parts by mass * Mixed solvent: toluene: methyl ethyl ketone: ethyl acetate: isopropyl alcohol = 4: 3: 2: 1 (mass ratio)
Next, a polypropylene resin was laminated on the printed surface by an extrusion coating method so as to have a thickness of 13 μm, and a sealant layer was provided. Thereby, the multilayer laminated film for laser printing of the present invention was obtained. In this film, the difference between the lamination strength between the base layer and the first printing layer and the lamination strength between the second printing layer and the sealant layer was 0.5 N / 15 mm width.

[Example 2]
On the first printing layer of Example 1, an ink having the same composition as that of the first ink layer was applied so as to have a coating amount of 2.0 g / m ² (when dried) to form a second layer. A printing layer was prepared in the same manner as in Example 1 except that the ink having the same composition as that of the second layer in Example 1 was applied so as to have a coating amount of 2.0 g / m ² (when dried).
In this film, the difference between the lamination strength between the base layer and the first printing layer and the lamination strength between the third printing layer and the sealant layer was 1.0 N / 15 mm width.

[Comparative Example 1]
Multilayer lamination for laser printing in the same manner as in Example 1 except that the second printing layer was not provided and the coating amount of the ink composition of the first printing layer was changed to 0.3 g / m ²⁾ (at the time of drying). A film was obtained. In this film, the lamination strength between the base layer and the first printing layer was 0.3 N / 15 mm width, and the lamination strength between the first printing layer and the sealant layer was 0.3 N / 15 mm width.

[Comparative Example 2]
Example 1 was prepared in the same manner as in Example 1 except that the first printed layer and the second printed layer were reversed. The difference between the lamination strength of the material layer and the first printing layer and the lamination strength of the second printing layer and the sealant layer was -0.2 N / 15 mm width.

[Laser marking method]
The laser-printed multilayer laminated films of Examples 1 and 2 and Comparative Example 1 were irradiated with a YVO ₄ laser from the substrate layer side under the following conditions to form a laser-printed image to obtain a printed body.
Laser irradiation conditions Average output 5 W, printing pulse 20 μm, scan speed 9000 mm / s, curve setting: 10, weight setting: 5, using a YVO ₄ laser machine (LP-Z250, manufactured by Panasonic SUNX)

Evaluation Result The obtained laser-printed image was evaluated for its line width, visibility and contrast. The results are shown in Table 1 below.

In the multilayer films for laser printing of Examples 1 and 2, the visibility of characters was good with a thick line width, and the contrast between the white printed portion and the printed portion was clear.
On the other hand, in the case of Comparative Example 1, the characters could be visually recognized, but the line width was narrow, and the contrast between the white printed portion and the printed portion was unclear. In Comparative Example 2, the entire character was blurred. As compared with Examples 1 and 2, the visibility was poor.

1. 1. Base material layer Printing layer 2a. First printed layer 2b. 2. second printing layer 3. sealant layer Printing section A. Void diameter

Claims (5)

At least, YAG or YVO ₄ laser base layer arranged on a side to be irradiated, the printing layer, and a multilayer laminated film for laser printing comprising a sealant layer,
The substrate layer is a layer made of a stretched polypropylene film ,
The printing layer is a layer made of an ink composition containing a metal oxide and a binder resin, and is at least two layers of a first printing layer adjacent to the base material layer and a second printing layer adjacent to the sealant layer. Consists of layers,
In the second print layer, the binder resin is a chlorinated polypropylene-based resin, and in the first print layer, the binder resin in the ink composition forming the print layer is a urethane resin;
The sealant layer is a layer made of a polypropylene resin,
The laminate strength between the substrate layer and the first printing layer is 0.1 to 2.0 N / 15 mm;
The lamination strength between the second printing layer and the sealant layer is larger than the lamination strength between the base layer and the first printing layer, and the difference is 0.2 to 0.5 N / 15 mm. The multilayer printed film for laser printing as described above,   The multilayer film for laser printing according to claim 1, wherein the ink composition is a resin composition obtained by diluting 70 to 90 parts by mass of a metal oxide and 10 to 30 parts by mass of a binder resin with a solvent.   The multilayered film for laser printing according to claim 1, wherein the metal oxide in the ink composition is titanium oxide. 4. The coating composition according to claim 1, wherein the total coating amount of the ink composition of the first and second printing layers is 0.5 to 6.0 g / m < ² > as a coating amount after drying. The multilayer laminated film for laser printing according to any one of claims 1 to 7. A multilayer laminated film for laser printing as claimed in any one of claims 1 to 4, YAG or YVO ₄ laser is irradiated from the base layer side, the base of the ink composition of the printed layer gasification and carbonized A printing method for forming a gap between a material layer and the first printing layer to form a laser-printed image on the surface of the printing layer.

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