Laser-markable resin laminates and containers

Abstract

To provide a resin laminate having a layer capable of laser marking and exhibiting clear laser marking characteristics without blurring of the printed characters, and to provide a resin laminate that does not exhibit blurring of the printed characters even when scraps of the resin laminate having a laser marking layer are added to layers other than the laser marking layer. [Solution] A resin laminate having at least one laser-markable layer, wherein the laser-markable layer is marked by laser irradiation, and the laser-markable resin laminate satisfies the following conditions (1) and (2). (1) The resin laminate has discolored areas that can be observed by cross-sectional observation in the thickness direction, and the total thickness of the discolored areas is 20 μm or more and 250 μm or less. (2) Of the discolored areas observed in (1), the outermost layer closest to the laser irradiation side is the most intensely discolored.

Description

Technical Field

[0001] The present invention relates to a resin laminate capable of laser marking and a container using the same.

Background Art

[0002] Conventionally, it has been common practice to print the manufacturing date, filling date, expiration date, lot number, etc. on the surface of a package filled with contents. For example, a laser marking method, an inkjet method, etc. are used, and the laser marking method is known as a method of performing colored marking by irradiating a resin composition with laser light. The laser marking method is a method of dispersing a laser marking agent that develops color by irradiating laser light in a resin composition and irradiating the resin composition with laser light to draw the desired characters or patterns (Patent Document 1). In the present invention, a layer on which the laser marking method can be performed is referred to as a laser marking layer.

[0003] On the other hand, it is known that many resin compositions for packaging contents such as foods and pharmaceuticals are composed of a resin laminate of two or more layers for various reasons such as barrier properties, content protection properties, heat resistance, and bag breakage resistance. For example, a bottle container filled with mayonnaise has a laminated structure such as a polyethylene layer / adhesive layer / ethylene-vinyl alcohol copolymer layer / adhesive layer / polyethylene layer as an example.

[0004] Attempts have been made to add a laser marking layer to resin laminates to print the manufacturing date, filling date, expiration date, lot number, etc. (Patent Document 2). However, if scraps generated during the resin laminate manufacturing process are reused and used again as raw materials for the resin laminate, the laser marking agent, which is a characteristic of the laser marking method, will also be contained in the scraps. If the scraps are used in layers other than the laser marking layer, the printing will occur in multiple layers, including the laser marking layer and the layer to which the scraps are added, resulting in a blurred appearance of the print. On the other hand, if the scraps are added only to the laser marking layer, the amount of scraps that can be used is limited, increasing manufacturing costs. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-144784 [Patent Document 2] Patent No. 6260265 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide a resin laminate having a layer that can be laser-marked and exhibiting clear laser marking characteristics without blurring of the printed characters, and to provide a resin laminate that does not blur the printed characters even when scraps of a resin laminate equipped with a laser marking layer are added to a layer other than the laser marking layer. [Means for solving the problem]

[0007] The present invention consists of the following configuration. [1] A resin laminate having at least one laser-markable layer, wherein the laser-markable layer is marked by laser irradiation and the following conditions (1) and (2) are met. (1) The resin laminate has discolored areas that can be observed by cross-sectional observation in the thickness direction, and the total thickness of the discolored areas is 20 μm or more and 250 μm or less. (2) Of the discolored areas observed in (1), the outermost layer closest to the laser irradiation side is the most intensely discolored. [2] The laser-markable resin laminate according to [1], characterized in that the thickness of one laser marking layer is 20 μm or more and 300 μm or less. [3] The laser-markable resin laminate according to [1] or [2], characterized by having at least two or more laser-markable layers. [4] 355nm of the resin laminate -1 A laser-markable resin laminate according to any one of [1] to [3], characterized in that its reflectance in light rays is 10% or more and 25% or less. [5] A laser-markable resin laminate according to any one of [1] to [4], characterized in that the color L* value of the marked area after laser irradiation is 10 or more and 60 or less. [6] A laser-markable resin laminate according to any one of [1] to [5], characterized in that the haze of the resin laminate is 5% or more and 90% or less. [7] A container comprising a laser-markable resin laminate as described in any of [1] to [6] above, wherein the resin laminate constitutes at least the wall portion of the container. [8] The container according to [7], characterized in that the container is formed by blow molding. [9] A resin laminate having a laser-marked portion, wherein the laser-markable resin laminate according to any one of [1] to [6] above is laser-marked.

[10] A container having a laser-marked portion in which the laser-markable resin laminate in the container described in [7] or [8] has been laser-marked. [Effects of the Invention]

[0008] The present invention provides a resin laminate having a layer capable of laser marking and exhibiting clear laser marking characteristics without blurring of the printed characters, and also provides a resin laminate that does not blur the printed characters even when scraps of a resin laminate with a laser marking layer are added to a layer other than the laser marking layer. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram showing an example of the structure of the resin laminate of the present invention. [Figure 2] A schematic diagram showing the resin laminate of the present invention when irradiated with laser light. [Figure 3] A schematic diagram showing the resin laminate of the present invention when irradiated with laser light (when the laser marking layer is thick). [Figure 4] A schematic diagram of the resin laminate of the present invention when irradiated with laser light (when the laser marking agent concentration in the laser marking layer is high). [Modes for carrying out the invention]

[0010] The resin laminate of the present invention will be described below. Figure 1 shows an example of the layer configuration in the cross-sectional direction of the resin laminate of the present invention. As shown in the figure, the resin laminate A of the present invention must have at least one laser marking layer M that can be laser-marked by laser irradiation. The laser marking layer M must contain a laser marking agent P that has a discoloration function upon laser irradiation. The resin laminate of the present invention must normally hardly react to laser light and therefore cannot be laser-marked by laser irradiation. The laser marking agent P is excited by the energy of the laser light, and the surrounding resin is carbonized, making laser marking or printing possible. In addition to the carbonization of the resin, some types of laser marking agent P change to black themselves. Laser marking or printing on the laser marking layer M is possible due to the individual or combined effect of this carbonization and the discoloration of the laser marking agent P. From the viewpoint of laser marking density and printing density, it is preferable to select a laser marking agent P that has both a resin carbonization function and its own discoloration function. In the following, the terms "laser marking" and "laser printing" are used synonymously unless otherwise noted.

[0011] On the other hand, an end material Q containing a laser marking agent P may be added to a layer other than the laser marking layer M, or the end material Q may be added to the laser marking layer M. The end material Q referred to here is a resin composition such as a molding burr generated when the resin laminate of the present invention is produced, a fragment generated by cutting a sheet-like resin laminate, or a pulverized product of a defective-shaped product, which cannot be used as a product. In the prior art (for example, Patent Document 2), when the end material Q is added to the laser marking layer M, there are problems such as double blurring of the printing after laser irradiation. Therefore, the layer to which the end material Q is added was limited to only the laser marking layer M, but doing so results in a problem that the upper limit of the amount of the end material Q that can be used (the raw material blending ratio of the end material Q in the entire laminate) becomes low, leading to an increase in the unit cost. As will be described later, the present inventors have found a surprising fact that blurring of the marking does not occur by making the discolored portion closest to the laser irradiation side the darkest, even without limiting the layer to which the end material Q is added. By this, the upper limit of the use of the end material Q was successfully expanded, and the unit cost of the container could be reduced. From the viewpoint of suppressing the manufacturing cost by using as much of the end material Q as possible, it is preferable to add the end material Q to both a layer other than the laser marking layer M and the laser marking layer M. FIG. 1 shows an example of a three-layer (layer 1 of the first layer, laser marking layer M, layer 2 of the second layer) laminate example, but the number of laminated layers is not particularly limited.

[0012] The laser marking agent that develops color by laser light may be not only particles composed of a single material, but also a mixture of various types of material particles, or may be in the form of molecules or elements dissolved in a solvent. Specific types of laser marking agents include bismuth, gadolinium, neodymium, molybdenum, niobium, titanium, antimony, tin, aluminum, calcium, and barium, either as elements or oxides, and mixtures thereof. They may also contain minerals such as mica. Among these, titanium dioxide, calcium carbonate, bismuth trioxide, antimony trioxide, and barium sulfate are preferred, and titanium dioxide, calcium carbonate, and bismuth trioxide are more preferred. Furthermore, the particle size of the laser marking agent is preferably 0.1 μm or more and 30 μm or less. If the particle size of the laser marking agent is less than 0.1 μm, the color change during laser irradiation may not be sufficient. On the other hand, if the particle size of the laser marking agent exceeds 30 μm, there is a concern that it may accelerate the clogging of filters in the resin melting process when manufacturing containers such as blow-molded bodies. The particle size of the laser marking agent is more preferably 1 μm or more and 20 μm or less, and even more preferably 5 μm or more and 15 μm or less.

[0013] Examples of laser types (wavelengths) that can be used for laser printing on the resin laminate of the present invention include CO2 lasers (1060 nm), YAG lasers (1064 nm), YVO4 lasers (1064 nm), fiber lasers (1064, 1090 nm), green lasers (532 nm), and UV lasers (355 nm). Among these, the type of laser used for laser printing in the present invention is not particularly limited, but CO2 lasers are often used to burn through plastics and are often used for purposes other than printing, which is the essence of the present invention, so they are not preferred as a laser source. YAG lasers, YVO4 lasers, fiber lasers, green lasers, and UV lasers are preferred as laser sources, YAG lasers, fiber lasers, and UV lasers are more preferred, and UV lasers are particularly preferred because they cause less thermal damage. Commercially available laser printing equipment can be used, with representative examples including the Brother Industrial Printing LM-2550 (YAG laser), Omron MX-Z2000H-V1 (fiber laser), Trotec 8028 Trotec Speedy 100 flexx (fiber laser), Keyence MD-X1000 (YVO4 laser), and MD-U1000C (UV laser). Laser printing conditions vary depending on the equipment manufacturer and model, as well as the resin being printed on, so it is difficult to generalize. However, taking the Keyence MD-U1000C (UV laser, wavelength 355nm) as an example, the conditions are as follows.

[0014] The laser power is preferably 20% or more and 80% or less of the maximum 13 W of the device specification. If the output is less than 20%, the printing density will decrease and the visibility will decrease, which is not preferable. If the output is 80% or more, holes will occur in the display body, which is not preferable. More preferably, the output is 25% or more and 75% or less, and even more preferably 30% or more and 70% or less. The pulse frequency is preferably 10 kHz or more and 100 kHz or less. When the frequency is less than 10 kHz, the laser energy per irradiation becomes high and the thickness reduction rate of the printed portion tends to exceed 80 vol%, which is not preferable. On the contrary, when the frequency exceeds 100 kHz, the thickness reduction rate of the printed portion tends to be 80 vol% or less, but the color L* value of the printed portion tends to be 10 or less, which is not preferable. More preferably, it is 15 kHz or more and 95 kHz or less, and even more preferably 20 kHz or more and 90 kHz or less. The scan speed is preferably 10 mm / second or more and 3000 mm / second or less. If the scan speed is less than 10 mm / second, the printing speed will extremely decrease, so the production speed of the display body will be slow, which is not preferable. On the other hand, if the scan speed exceeds 3000 mm / second, the printing density will decrease and the color L* value will tend to be 10 or less, which is not preferable. More preferably, the scan speed is 100 mm / second or more and 2900 mm / second or less, and even more preferably 200 mm / second or more and 2800 mm / second or less.

[0015] After laser printing on the resin laminate of the present invention, in the discolored portion observed by cross-sectional observation in the thickness direction of the resin laminate, it is necessary that the discolored portion closest to the laser irradiation side is the darkest. It was newly discovered that even if the layer on the inner side, that is, the content side, is discolored, blurring does not occur when the discolored portion on the laser irradiation side, that is, the side visually visible, is the darkest. Presumably, the blurring of the printing is considered to be greatly affected by the discolored portion closest to the laser irradiation side, and the influence inside the discolored portion is small. On the other hand, when the discolored portion closest to the laser irradiation side is not the darkest, blurring of the printing occurs.

[0016] The thickness of each laser marking layer is preferably 20 μm to 300 μm. If the thickness of the laser marking layer is less than 20 μm, not only will the printing density due to laser irradiation be insufficient, but the density of the discolored areas will also be lighter, making blurring of the printing more likely, which is undesirable. On the other hand, if the thickness of the laser marking layer exceeds 300 μm, the printing density will be sufficient, but molding will be difficult, which is undesirable. The reason why the printing density becomes higher as the laser marking layer gets thicker is, although this is speculative, thought to be because the laser marking agent reflects the laser light more frequently, as schematically shown in Figures 1 and 2, resulting in a larger proportion of the discolored area. The thickness of the laser marking layer is more preferably 50 μm to 270 μm, even more preferably 80 μm to 240 μm, and particularly preferably 100 μm to 220 μm.

[0017] Preferably, the total thickness of the discolored areas observed by cross-sectional observation in the thickness direction of the resin laminate after laser printing is 20 μm or more and 250 μm or less. If the total thickness of the discolored areas is less than 20 μm, the printing density will not be sufficient, which is undesirable. On the other hand, if the total thickness of the discolored areas exceeds 250 μm, the printing density will be sufficient, but as a result the thickness of the resin laminate will increase, making molding difficult, which is undesirable. More preferably, the total thickness of the discolored areas is 50 μm or more and 220 μm or less, even more preferably 80 μm or more and 190 μm or less, and particularly preferably 100 μm or more and 170 μm or less.

[0018] The amount of laser marking agent added to the laser marking layer is preferably 0.01% by mass or more and 1.00% by mass or less. If the amount of laser marking agent added is less than 0.01% by mass, the printing density due to laser irradiation will not be sufficient, which is undesirable. On the other hand, if the amount of laser marking agent added exceeds 1.00% by mass, the printing density will be sufficient, but it will be more prone to punctures during laser irradiation, which is undesirable. The reason why the printing density becomes higher when the amount of laser marking agent added is speculatively thought to be because the laser marking agent reflects the laser light more frequently, as schematically shown in Figure 3, resulting in a larger proportion of discolored areas. The amount of laser marking agent added is more preferably 0.05% by mass or more and 0.96% by mass or less, even more preferably 0.10% by mass or more and 0.91% by mass or less, and particularly preferably 0.20% by mass or more and 0.81% by mass or less.

[0019] The laser marking agent can be added at any stage in the manufacturing process of the resin that will be the raw material for the laser marking layer, or the resin laminate that will be the laser marking agent layer. For example, in the stage of manufacturing the resin, methods include blending a slurry of particles dispersed in a solvent with the resin raw material using a vented kneading extruder, or blending dried particles with the resin using a kneading extruder (masterbatch formation). Among these methods, the method of using a masterbatch containing the laser marking agent as the raw material for the resin laminate is preferred. The amount of laser marking agent added to the masterbatch is preferably 0.1% by mass or more and 50% by mass or less. If the amount of laser marking agent added is less than 0.1% by mass, it becomes difficult to uniformly disperse the laser marking agent in the masterbatch, which is undesirable. On the other hand, if the amount of laser marking agent added exceeds 50% by mass, it becomes difficult not only to make the shape of the masterbatch uniform, but also to uniformly disperse the masterbatch when it is added to the resin laminate, which is undesirable. The amount of laser marking agent added is more preferably 1% by mass or more and 40% by mass or less, even more preferably 2% by mass to 30% by mass or less, and particularly preferably 3% by mass to 20% by mass or less. When using a masterbatch as a raw material for a resin laminate, there are no particular limitations on the method of adding it, but examples include mixing all the raw materials, including the masterbatch, beforehand and then adding them to the compounding extruder, or mixing all the raw materials, including the masterbatch, immediately before the compounding extruder. Among these, the method of mixing all the raw materials, including the masterbatch, immediately before the compounding extruder is preferred because it allows for uniform addition of the masterbatch to the resin laminate. On the other hand, if the raw materials, including the masterbatch, are not mixed before adding, the dispersion of the laser marking agent in the resin laminate may become uneven, resulting in blurring or deterioration of the laser printing density.

[0020] The value of "amount of laser marking agent added (ppm) × thickness of laser marking layer (μm) / 100" for the laser marking layer is preferably between 600 and 20000. A value of 600 or less is undesirable because the printing density due to laser irradiation will not be sufficient. On the other hand, a value exceeding 20000 will result in sufficient printing density, but it is undesirable because it will make it easier for holes to occur during laser irradiation. As described above, a larger amount of laser marking agent and a thicker laser marking layer increase the frequency of reflection of laser light by the laser marking agent, which is thought to result in a larger proportion of discolored areas, and therefore the printing density increases as this value increases. In addition, a larger amount of laser marking agent and a thicker laser marking layer increase the frequency of reflection within the laser marking layer, making it more difficult for laser light to reach layers deeper than the laser marking layer, and as a result, blurring of the printing is more easily suppressed. The value is more preferably between 1000 and 19600, even more preferably between 5000 and 15600, and particularly preferably between 8000 and 12600.

[0021] The thickness of the resin laminate of the present invention is preferably 20 μm or more and 5000 μm or less. If the thickness of the resin laminate is less than 20 μm, a sufficient thickness for the laser marking layer cannot be secured, and the printing density by laser irradiation will be insufficient. On the other hand, if the thickness of the resin laminate exceeds 5000 μm, molding becomes difficult. The thickness of the resin laminate is more preferably 100 μm or more and 4000 μm or less, even more preferably 200 μm or more and 3000 μm or less, and particularly preferably 300 μm or more and 2000 μm or less.

[0022] 355nm of the resin laminate of the present invention -1 The reflectance to light rays is preferably between 10% and 25%. If the reflectance is less than 10%, the print density will not be sufficient, which is undesirable. On the other hand, if the reflectance exceeds 25%, the print density will be sufficient, but holes are more likely to occur when the laser is irradiated, which is undesirable. When the reflectance is high, the laser marking agent reflects the laser light more frequently, resulting in a higher proportion of discolored areas and thus a higher print density. The reflectance is more preferably between 12% and 23%, even more preferably between 14% and 21%, and particularly preferably between 16% and 19%.

[0023] The color L* value of the printed area after laser printing on the resin laminate of the present invention is preferably 10 or more and 60 or less. If the color L* value of the printed area is less than 10, the print density will not be sufficient and will be undesirable. On the other hand, if the color L* value of the printed area exceeds 60, the print density will be sufficient, but holes will be more likely to occur during laser irradiation, which is undesirable. The color L* value of the printed area is more preferably 15 or more and 55 or less, even more preferably 20 or more and 50 or less, and particularly preferably 25 or more and 45 or less.

[0024] The haze of the resin laminate of the present invention is preferably 5% to 90%. If the haze is less than 5%, the transparency is excellent, but as a result the print density becomes insufficient, which is undesirable. On the other hand, if the haze exceeds 90%, the transparency deteriorates, which is undesirable. The haze is more preferably 10% to 85%, even more preferably 15% to 80%, and particularly preferably 20% to 75%.

[0025] The resin used in the laser marking layer is not particularly limited, but examples include polyethylene, polyolefins such as polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polymethacrylate, polyacrylonitrile, polycarbonate and copolymers thereof, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides, and polyacetals, which may be used individually or in combination of several types.

[0026] Examples of polyolefins include polypropylene (PP) and polyethylene (PE). When using polypropylene, the stereoregularity is not particularly limited and may be isotactic, syndiotactic, or atactic, and each may be present in any proportion. When using polyethylene, its density (degree of branching) is not particularly limited and may be high density (HDPE), linear low density (LLDPE), or low density (LDPE). In addition to the homopolymers mentioned above, raw materials obtained by copolymerizing two or more different monomers may also be used. Examples of monomers used in copolymerization include ethylene and α-olefins. Examples of α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 4-methyl-1-pentene, 4-methyl-1-hexene, ethylene vinyl alcohol, maleic acid, itaconic acid, and fumaric acid. The copolymerization can be random copolymerization or block copolymerization. Furthermore, in addition to the raw materials listed above, polyolefin elastomers and ionomers may also be used.

[0027] The thickness of each layer other than the laser marking layer varies depending on the function of that layer (protective film, support layer, adhesive layer, barrier layer, etc.), so it cannot be determined in general and should be set to the appropriate thickness for the product.

[0028] The form of the resin composition laminate of the present invention is not particularly limited, but examples include planar forms such as sheet-like film products and panel-like products, as well as three-dimensional forms, and can be appropriately selected depending on the application.

[0029] Examples of products with a three-dimensional form include bag-shaped resin products formed using film-like materials, resin products obtained by molding processes, and products obtained by various molding methods such as blow molding. Examples of resin products obtained by blow molding include containers such as multilayer resin containers. In such containers, it is preferable that at least the walls of the container are made of the resin laminate of the present invention.

[0030] An example of a multilayer resin container having a laser-markable layer is a bottle container for storing mayonnaise. From the viewpoint of extending the shelf life of the contents, a mayonnaise container is preferably constructed by laminating a barrier layer (oxygen barrier resin layer). Furthermore, a configuration including an innermost layer and an outer layer is more preferable, and it is even more preferable to provide an adhesive layer between the oxygen barrier resin layer and the other layers. The lamination configuration of the resin composition of the present invention is not particularly limited, but examples include an innermost layer, an inner layer, an adhesive layer, an oxygen barrier resin layer, an adhesive layer, an outer layer, and a laser-marking layer (outermost layer) in order from the inside to the outside of the container. However, the positional relationship of each layer is not limited to this.

[0031] The inner layer, outer layer, and laser marking layer, as examples of the above-mentioned laminated structure, are all resin layers that contribute to the container shape and mechanical properties. A polyolefin resin composition is preferred as the resin constituting these layers. Furthermore, examples of resins that constitute the oxygen barrier resin layer include ethylene-vinyl alcohol copolymer (EVOH) or metaxylenediamine nylon, from the standpoint of oxygen barrier properties and safety. Resins to prevent correlation delamination may be added to EVOH.

[0032] Examples of resins constituting the adhesive layer include polyolefins such as polyethylene that have been graft-modified with carboxylic acids such as maleic acid, itaconic acid, and fumaric acid, or their anhydrides, amides, or esters. Polyethylene graft-modified with maleic acid or maleic anhydride is also a preferred option. [Examples]

[0033] Next, the present invention will be specifically described using examples and comparative examples. However, the present invention is not limited in any way to the embodiments of these examples, and can be modified as appropriate without departing from the spirit of the invention.

[0034] [Thickness] Five points were measured using a micrometer (Millitron 1254D, manufactured by Feinpluf), and the average value was calculated.

[0035] [Hayes] The haze of the resin laminate was measured in accordance with JIS K7136 using a haze meter "500A" (manufactured by Nippon Denshoku Industries Co., Ltd.). Two measurements were taken, and the average value was used as the haze value.

[0036] [355nm -1 [Reflectance in light rays] 355nm -1 The reflectance in the light ray was determined by diffuse reflectance measurement using a spectrophotometer (Shimadzu Corporation, UV-3600Plus spectrophotometer with large sample chamber unit MPC-603A). Measurement conditions were: scan speed 200 nm / sec, slit width 20 nm, sample pitch 2.0 nm, and barium sulfate was used as the standard white plate. Wavelength 220 nm -1 ~500nm -1Of the reflectance, 355nm -1 The reflectance was used as the representative value.

[0037] [Thickness of each layer] The total thickness, measured with a micrometer, was calculated from the ratio of resin extrusion in each layer.

[0038] [Laser printing evaluation] The letter "B" was printed onto a resin laminate by irradiating it with a laser. A 355nm ultraviolet (UV) laser marker (MD-U1000, manufactured by Keyence Corporation) was used as the printing machine, and the laser was irradiated under the following conditions: laser power 40%, scan speed 1000 mm / sec, pulse frequency 40 kHz, and spot variable -20. The letter "B" was 4 mm wide and 5 mm high.

[0039] [Color L* value] To evaluate the color L* value, a spectrophotometer (ZE-6000, manufactured by Nippon Denshoku Co., Ltd.) was used, and the L* value of the laser-printed area, which was printed using the laser printing evaluation method described above, was measured by reflection. The sample used for measurement was a flat section. The measurement method for the printed area was specifically as follows: A 6φ sample stage (with an opening approximately 1 cm in diameter where the measurement light hits) and a 6φ eyepiece were used as the measurement light source for the colorimeter. A black cardboard cutout with a diameter of 5 mm was prepared so that only the letter "B" could fit into the opening of the sample stage. The letter "B" was placed over the cutout circle and set on the sample stage, and the measurement light was adjusted so that it passed only through the letter "B".

[0040] [Observation of discolored areas in the cross-section] Based on the laser printing evaluation described above, a sample cut to 15 mm x 10 mm was fixed in the sample holder of a microtome (Daiwa Koki Co., Ltd., RX-860) so that the laser-printed area would be included, and a thin cross-sectional film parallel to the long side of the sample was prepared. The cross-section of the prepared thin cross-sectional film was observed using a differential interference microscope (Nikon Corporation, ECLIPSE LV150N). The thickness of the discolored area was defined as the thickness of the area where discoloration was visually confirmed.

[0041] [Shading of discolored areas in the cross-section] Based on the images obtained from the observation of the discolored areas described above, the degree of discoloration was visually evaluated on a 5-point scale. 1 represents the lightest discoloration, and 5 represents the darkest.

[0042] [Print blurring] In the laser printing evaluation, the laser-printed resin laminate was placed on a white cardboard base and visually inspected from a distance of 70 cm. If the characters appeared blurry, it was rated as ×; if they were clearly visible, it was rated as ○.

[0043] [Print density] In the laser printing evaluation, the laser-printed resin laminate was placed on a white cardboard base and visually inspected from a distance of 70 cm. A "○" was given if the characters were clearly visible, and a "×" if the characters were not visible.

[0044] [Specifications of the mayonnaise bottle] The resin materials that make up the mayonnaise bottle we created are as follows: Low-density polyethylene (LDPE) Laser marking MB: 2% by mass of laser marking agent was added to 98% by mass of LDPE. The laser marking agent used was a mica pigment coated with antimony-doped tin oxide (MERCK Iriotec(R) 8825; particle size distribution 5-25 μm, color light gray). Modified polyethylene: Ethylene-vinyl alcohol copolymer resin (EVOH) Scrap material: Mayonnaise bottles prepared in Example 1 were crushed and used.

[0045] (Example 1) The laminated structure consisted of outer layer 1 (LDPE: laser marking MB = 98% by mass), outer layer 2 (LDPE = 100%), adhesive layer 3 (modified polyethylene = 100%), oxygen barrier resin layer 4 (EVOH = 100%), adhesive layer 5 (modified polyethylene = 100%), inner layer 6 (LDPE = 100%), and inner layer 7 (LDPE = 100%), which were then molded into a bottle shape by blow molding. The inner layer side is the side that contains the contents. The total thickness of the layers was 80 / 80 / 5 / 8 / 5 / 80 / 80 μm for outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7, totaling 338 μm. The laminated structure and evaluation results are shown in the table. There were no practical problems with either blurring or print density.

[0046] (Example 2) Except for changing the resin composition of outer layer 1 to LDPE: laser marking MB: scrap material = 48.2:1.8:50.0 mass%, the bottle shape was formed in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0047] (Example 3) Except for changing the resin composition of outer layer 1 to LDPE:laser marking MB:scrap material = 48.2:1.8:50.0 mass%, and the resin composition of outer layer 2 to LDPE:scrap material = 50:50 mass%, the bottle shape was molded in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0048] (Example 4) Except for changing the resin composition of outer layer 1 to LDPE:laser marking MB:scrap material = 48.2:1.8:50.0 mass%, and the resin composition of inner layer 6 to LDPE:scrap material = 50:50 mass%, the product was molded into a bottle shape in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0049] (Example 5) Except for changing the resin composition of outer layer 1 to LDPE:laser marking MB:scrap material = 47.2:2.8:50.0 mass%, and the resin composition of inner layer 6 to LDPE:scrap material = 50:50 mass%, the bottle shape was molded in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0050] (Example 6) Except for changing the resin composition of outer layer 1 to LDPE:laser marking MB:scrap material = 49.2:0.8:50.0 mass%, and the resin composition of inner layer 6 to LDPE:scrap material = 50:50 mass%, the product was molded into a bottle shape in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0051] (Example 7) Except for changing the resin composition of outer layer 1 to LDPE:laser marking MB:scrap material = 48.2:1.8:50.0 mass%, and the resin composition of outer layer 2 to LDPE:scrap material = 10:90 mass%, the product was molded into a bottle shape in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0052] (Example 8) Except for changing the resin composition of outer layer 1 to LDPE:laser marking MB:scrap material = 48.2:1.8:50.0 mass%, and the resin composition of inner layer 6 to LDPE:scrap material = 10:90 mass%, the bottle shape was molded in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0053] (Example 9) Except for changing the resin composition of outer layer 1 to LDPE: laser marking MB: scrap material = 48.2:1.8:50.0 mass%, and changing the thickness of outer layer 1, the bottle shape was formed in the same manner as in Example 1. The total thickness of outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 was 300 / 80 / 5 / 8 / 5 / 80 / 80 μm, for a total of 558 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0054] (Example 10) Except for changing the resin composition of outer layer 1 to LDPE: laser marking MB: scrap material = 48.2:1.8:50.0 mass%, and the thickness of outer layer 1, the bottle shape was molded in the same manner as in Example 1. The total thickness of outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 was 20 / 80 / 5 / 8 / 5 / 80 / 80 μm, for a total of 278 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0055] (Example 11) The bottle shape was formed in the same manner as in Example 1, except that the resin composition of outer layer 1 was LDPE: laser marking MB: scrap material = 47.2:2.8:50.0 mass%, the resin composition of inner layer 6 was LDPE: scrap material = 10:90 mass%, and the thickness of outer layer 1 was changed. The total thickness of the layers was 300 / 80 / 5 / 8 / 5 / 80 / 80 μm for outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7, totaling 558 μm. The lamination structure and evaluation results are shown in the table. There were no practical problems with either blurring or density of the printing.

[0056] (Comparative Example 1) Except for changing the resin composition of outer layer 1 to LDPE:laser marking MB:scrap material = 49.9:0.1:50.0 mass%, and the resin composition of inner layer 6 to LDPE:scrap material = 50:50 mass%, the bottle shape was molded in the same manner as in Example 1. The total thickness of the layers was 338 μm, with outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 being 80 / 80 / 5 / 8 / 5 / 80 / 80 μm. The lamination structure and evaluation results are shown in the table. The discolored area on the laser irradiation side showed not only faint contrast and blurred printing, but also faint print density.

[0057] (Comparative Example 2) The bottle shape was molded in the same manner as in Example 1, except that the resin composition of outer layer 1 was LDPE: laser marking MB: scrap = 47.2:2.8:50.0 mass%, the resin composition of inner layer 6 was LDPE: scrap = 50:50 mass%, and the thickness of outer layer 1 was changed. The total thickness of outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 was 350 / 80 / 5 / 8 / 5 / 80 / 80 μm, for a total of 608 μm. The lamination structure and evaluation results are shown in the table. The discolored area was thick and the transparency was poor.

[0058] (Comparative Example 3) Except for changing the resin composition of outer layer 1 to LDPE: laser marking MB: scrap material = 48.2:1.8:50.0 mass%, and the thickness of outer layer 1, the bottle shape was formed in the same manner as in Example 1. The total thickness of outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 was 12 / 80 / 5 / 8 / 5 / 80 / 80 μm, totaling 270 μm. The lamination structure and evaluation results are shown in the table. The result was that the thickness of the discolored area was small and the print density was light.

[0059] (Comparative Example 4) Except for changing the thickness of outer layer 1, the bottle shape was molded in the same manner as in Example 1. The total thickness of outer layer 1 / outer layer 2 / adhesive layer 3 / oxygen barrier resin layer / adhesive layer 5 / inner layer 6 / inner layer 7 was 12 / 80 / 5 / 8 / 5 / 80 / 80 μm, for a total of 270 μm. The lamination structure and evaluation results are shown in the table. The discolored area was thin and the print density was light.

[0060] [Table 1A]

[0061] [Table 1B] [Industrial applicability]

[0062] The present invention provides a laser-markable resin laminate that does not exhibit blurring of the markings even when scraps of a resin laminate equipped with a laser-marking layer are added to layers other than the laser-marking layer, making it industrially useful. [Explanation of Symbols]

[0063] 1. The first layer 2. Second layer A laser-markable resin laminate M Laser Marking Layer P Laser Marking Agent Q: Scrap material

Claims

1. A resin laminate having at least one laser-markable layer, wherein the laser-markable layer is marked by laser irradiation, and the laser-markable resin laminate satisfies the following conditions (1) and (2). (1) The resin laminate has discolored areas that can be observed by cross-sectional observation in the thickness direction, and the total thickness of the discolored areas is 20 μm or more and 250 μm or less. (2) Of the discolored areas observed in (1), the outermost layer closest to the laser irradiation side is the most intensely discolored.

2. The laser-markable resin laminate according to claim 1, characterized in that the thickness of one laser marking layer is 20 μm or more and 300 μm or less.

3. The laser-markable resin laminate according to claim 1, characterized in that it has at least two or more layers that can be laser-marked.

4. 355 nm of the resin laminate －１ A laser-markable resin laminate according to claim 1, characterized in that its reflectance in light rays is 10% or more and 25% or less.

5. The laser-markable resin laminate according to claim 1, characterized in that the color L* value of the marked area after laser irradiation is 10 or more and 60 or less.

6. The laser-markable resin laminate according to claim 1, characterized in that the haze of the resin laminate is 5% or more and 90% or less.

7. A container comprising a laser-markable resin laminate as described in any one of claims 1 to 6, wherein the resin laminate constitutes at least the wall portion of the container.

8. The container according to claim 7, characterized in that the container is formed by blow molding.

9. A resin laminate that is laser-markable according to any one of claims 1 to 6, having a laser-marked portion.

10. A container having a laser-marked portion, wherein the laser-markable resin laminate in the container according to claim 7 or 8 is laser-marked.

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