Brittle laminated label for laser printing

Abstract

To provide a brittle laminated label for laser printing which has an alteration preventing function that the label is broken and cannot be reused when the label is peeled off after once stuck and is excellent in low-temperature flexibility.SOLUTION: A laser-printable brittle laminated label 100 includes (A) a colored layer 10 containing a first acrylic resin and a pigment, (B) a white layer 20 containing a second acrylic resin, a white pigment, and inorganic particles 21, and (C) an adhesive layer 30 laminated on the white layer (B), wherein the content of the inorganic particles 21 in the white layer 20 (B) is 7.5 to 25 parts by mass based on 100 parts by mass of the second acrylic resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser-markable brittle laminate label. More specifically, the present invention relates to a laser-markable brittle laminate label that has a tamper-proof function in that the label is destroyed and cannot be reused when peeled off after being attached, and also has excellent low-temperature flexibility. [Background technology]

[0002] Laser marking labels are labels made by laminating a resin film that is compatible with laser marking. Laser marking labels can be printed with any desired characters or designs, and are particularly suitable for recording variable information such as serial numbers. Therefore, laser marking labels are used for traceability and certification labels for machinery, automobiles, electronic components, etc.

[0003] Laser marking labels used on automobile parts, etc., are also required to have a tamper-proof function that causes the label to crack when peeled off, as a countermeasure against counterfeit products. For example, a laser-printable brittle laminate label with a tamper-proof function has been proposed as such a laser marking label (see, for example, Patent Document 1).

[0004] Specifically, Patent Document 1 describes: (A) coloring Patent Document 1 discloses a laser-markable brittle laminate label that comprises a (A) colored layer, (B) a support layer, a (C) destructible layer, a (D) adhesive layer, and (E) a release paper, and that becomes unreusable when peeled off after adhering to a substrate because the colored layer is destroyed. Hereinafter, the laser-markable brittle laminate label disclosed in Patent Document 1 will also be referred to simply as a "brittle laminate label." In the brittle laminate label disclosed in Patent Document 1, the (A) colored layer is made of a crosslinked acrylic resin and is the outermost layer when the laminate is attached to a substrate. The (B) support layer has a visible color difference from the (A) colored layer and is made of a crosslinked acrylic resin laminated on the (A) colored layer. The (C) destructible layer is laminated on the (B) support layer, the (D) adhesive layer is laminated on the (C) destructible layer, and the (E) release paper is laminated on the (D) adhesive layer. The brittle laminate label described in Patent Document 1 is said to have a crack angle of 85 degrees to 140 degrees at 10°C, and (E) a peel force of 150 mN / 25.4 mm or less when peeled from the release paper. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5091724 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the brittle laminated label described in Patent Document 1 has excellent anti-tampering capabilities, its high brittleness leaves room for improvement in terms of ease of handling. In particular, the brittle laminated label described in Patent Document 1 hardens and loses flexibility at low temperatures, which can lead to easy cracking (see, for example, Comparative Example 7 described below). Therefore, the brittle laminated label described in Patent Document 1 has the problem of being particularly difficult to handle in low-temperature environments, and can also crack during transportation to cold regions.

[0007] Therefore, the problem that the present invention aims to solve is to provide a brittle laminated label for laser printing that has a tamper-proof function in that the label is destroyed and cannot be reused when peeled off after being attached, and that also has excellent low-temperature flexibility and is easy to handle even in low-temperature environments. [Means for solving the problem]

[0008] In order to achieve the above object, the present inventors have investigated the causes of the above-mentioned problems. Specifically, first, in the laser-markable brittle laminate label described in Patent Document 1, an attempt was made to improve low-temperature flexibility by removing the (C) destructive layer, but it was discovered that the flexibility became too high and brittleness was insufficient (see, for example, Comparative Examples 1 and 8 described below). Therefore, in order to compensate for the insufficient brittleness, the inventors tried removing the (C) destructive layer and adding acrylic beads to the (B) support layer, but it was discovered that there was almost no improvement in brittleness (see, for example, Comparative Example 2 described below).

[0009] Based on the above findings, the inventors conducted extensive research to find a way to combine the contradictory properties of brittleness and low-temperature flexibility in a laser-markable brittle laminate label. As a result, they discovered that in a laser-markable brittle laminate label consisting of (A) a colored layer, (B) a white layer, and (C) an adhesive layer, by using inorganic particles instead of acrylic beads as the filler in (B) the white layer, it is possible to achieve both tamper resistance and low-temperature flexibility, and thus completed the present invention.

[0010] According to the present invention, there is provided a laser-markable brittle laminate label as shown below.

[0011] [1] A laser-markable brittle laminate label comprising: (A) a colored layer containing a first acrylic resin and a pigment; (B) a white layer containing a second acrylic resin, a white pigment, and inorganic particles; and (C) an adhesive layer laminated on the (B) white layer, wherein the content of the inorganic particles in the (B) white layer is 7.5 to 25 parts by mass per 100 parts by mass of the second acrylic resin.

[0012] [2] The laser-markable brittle laminate label according to [1] above, wherein the inorganic particles have an average particle size of 1 to 10 μm.

[0013] [3] The laser-markable brittle laminate label according to [1] or [2], wherein the inorganic particles are silica particles.

[0014] [4] The laser-markable brittle laminate label according to [1] or [2], wherein the thickness of the (B) white layer is 40 to 80 μm.

[0015] [5] The laser-markable brittle laminate label according to [1] or [2] above, wherein the total thickness of the (A) colored layer and the (B) white layer is 50 to 95 μm. [Effects of the Invention]

[0016] The laser-markable brittle laminate label of the present invention can achieve both tamper resistance and low-temperature flexibility. That is, the laser-markable brittle laminate label of the present invention has a tamper resistance function in which, once attached, the label is destroyed and cannot be reused when peeled off, and also has excellent low-temperature flexibility. Therefore, the laser-markable brittle laminate label of the present invention is easy to handle even in low-temperature environments and is less likely to be damaged during transportation to cold regions, etc. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view schematically showing a first embodiment of a laser-markable brittle laminate label of the present invention. [Figure 2] 1 is an electron microscope photograph of a cross section of the laser-markable brittle laminate label of Example 2. [Figure 3] 1 is an electron microscope photograph of a cross section of the laser-markable brittle laminate label of Comparative Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below with reference to preferred embodiments thereof. However, the present invention is not limited to the following embodiments and examples, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents.

[0019] In this specification, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this specification, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples.

[0020] In this specification, the term "acrylic resin" refers to a resin composed of a resin composition including an acrylic (co)polymer that contains structural units derived from (meth)acrylic monomers and in which the proportion of structural units derived from (meth)acrylic monomers is 50 mass % or more, and a crosslinking agent. In this specification, when simply written as "acrylic resin", it means both the first acrylic resin and the second acrylic resin, and when simply written as "acrylic resin", it means both the first crosslinking agent and the second crosslinking agent.

[0021] In this specification, the term "acrylic (co)polymer" refers to a (co)polymer obtained by polymerizing (meth)acrylic monomers such as (meth)acrylic acid and its derivatives using a polymerization initiator, and may be a homopolymer or a copolymer. In addition, in this specification, the term "first acrylic (co)polymer" refers to the acrylic (co)polymer that constitutes the first acrylic resin, and the term "second acrylic (co)polymer" refers to the acrylic (co)polymer that constitutes the second acrylic resin. Furthermore, in this specification, the term "first crosslinking agent" refers to a crosslinking agent that constitutes a first acrylic resin, and the term "second crosslinking agent" refers to a crosslinking agent that constitutes a second acrylic resin.

[0022] In this specification, "(meth)acrylic" means one or both of acrylic and methacrylic. In addition, in this specification, "(meth)acrylate" means either or both of acrylate and methacrylate. Furthermore, in this specification, "(meth)acryloyl" means one or both of acryloyl and methacryloyl. Furthermore, in this specification, the terms "(meth)acrylic monomer" and "(meth)acrylic monomer" refer to a monomer having a (meth)acryloyl group.

[0023] [Laser-printable brittle laminate label] A first embodiment of the laser-markable brittle laminate label of the present invention is a laser-markable brittle laminate label 100 as shown in FIG. 1. Here, FIG. 1 is a cross-sectional view schematically showing the first embodiment of the laser-markable brittle laminate label of the present invention. As shown in FIG. 1, the laser-markable brittle laminate label 100 includes (A) a colored layer 10 containing a first acrylic resin and a pigment, (B) a white layer 20 containing a second acrylic resin, a white pigment, and inorganic particles 21, and (C) a pressure-sensitive adhesive layer 30. Hereinafter, the colored layer 10 containing the (A) first acrylic resin and a pigment will also be simply referred to as the "(A) colored layer 10." Similarly, the white layer 20 containing the (B) second acrylic resin, a white pigment, and inorganic particles 21 will also be referred to as the "(B) white layer 20." In the laser-markable brittle laminate label 100 of this embodiment, the content of the inorganic particles 21 in the (B) white layer 20 is 7.5 to 25 parts by mass relative to 100 parts by mass of the second acrylic resin.

[0024] The laser-markable brittle laminate label 100 of this embodiment is a laser-markable brittle laminate label 100 that is produced by adjusting the output of laser light, concentrating the laser light, and irradiating it in a pattern such as characters onto a (A) colored layer 10 that has the ability to absorb laser light, causing the irradiated portions to heat, melt, and turn into mist, or heat, decompose, and incinerate, removing them in a pattern, and causing the removed portions to take on the color of a (B) white layer 20 (i.e., white), thereby revealing the desired printing or image. Hereinafter, the laser-markable brittle laminate label may be simply referred to as a "brittle laminate label" or "label."

[0025] The brittle laminated label 100 of this embodiment has a tamper-proof function in that once attached, the label is destroyed and cannot be reused if peeled off, and also has excellent low-temperature flexibility. Therefore, the brittle laminated label of this embodiment is easy to handle even in low-temperature environments such as -20 to 0°C, and is less likely to be damaged during transportation to cold regions.

[0026] More specifically, the brittle laminated label 100 of this embodiment has a (A) colored layer 10 on its surface as the uppermost layer of the label. By destroying and removing the (A) colored layer 10 into a desired shape by irradiating it with laser light, the color of the (B) white layer 20 becomes visible in the removed area, allowing desired printing or images to appear. Therefore, the brittle laminated label 100 of this embodiment can be said to be a laminate having the (A) colored layer 10 and the (B) white layer 20 of different colors.

[0027] The (B) white layer 20 is laminated on the (A) colored layer 10, and is colored white in the removed portion of the (A) colored layer 10 so as to be visually distinguishable from the (A) colored layer 10. The (B) white layer 20 also contains inorganic particles 21 as a component that imparts brittleness. By including the (B) white layer 20 configured in this manner, the brittle laminated label 100 of this embodiment breaks when attached to an adherend such as a substrate and then attempted to be peeled off by hand or with a tool. While there are various mechanisms for this breakage, it is presumed that in the brittle laminated label 100 of this embodiment, the inorganic particles 21 deposited in the (B) white layer 20 form a layer, and as a result, stress strain associated with peeling causes breakage at the interfaces of the inorganic particles 21, resulting in the development of brittleness.

[0028] Each component of the brittle laminate label of this embodiment will be described in more detail below.

[0029] [(A) Colored layer] The (A) colored layer contains a first acrylic resin and a pigment. The brittle laminate label of this embodiment is a label consisting of a laminate in which the (A) colored layer, the (B) white layer, and the (C) adhesive layer are laminated in that order, and the (A) colored layer is arranged so as to become the outermost layer of the label when the (C) adhesive layer is attached to an adherend.

[0030] The (A) colored layer is made of a resin composition containing a first acrylic resin and a pigment, and is a layer having the ability to absorb laser light. The (A) colored layer may be configured to be etched by irradiation with laser light.

[0031] The first acrylic resin contained in the (A) pigmented layer is preferably an acrylic resin obtained by crosslinking a first acrylic (co)polymer with an isocyanate crosslinking agent. Because acrylic resins are amorphous, they undergo thermal decomposition without melting. During thermal decomposition, (meth)acrylic monomers are released as gas mainly through cleavage of the main chain, making them less susceptible to discoloration due to heat. Therefore, by including the first acrylic resin in the (A) colored layer, printing with laser light becomes sharper, which is preferable.

[0032] The first acrylic resin contained in the (A) colored layer is not particularly limited, but is preferably an acrylic resin composed of a resin composition containing a first acrylic (co)polymer obtained by polymerizing at least one of a (meth)acrylic monomer having a hydroxyl group and (meth)acrylic acid, and a first crosslinking agent. This is because the hydroxyl groups and carboxyl groups of the first acrylic (co)polymer serve as reaction sites with the crosslinking agent, making it easy to control the pot life and tensile elongation at break after mixing with the first crosslinking agent.

[0033] The first acrylic (co)polymer is preferably an acrylic (co)polymer obtained by, for example, polymerizing a (meth)acrylic monomer having a hydroxyl group alone, or a mixture of a (meth)acrylic monomer having a hydroxyl group and another (meth)acrylic monomer (hereinafter also referred to as "another (meth)acrylic monomer"). Examples of polymerization methods include solution polymerization, bulk polymerization, and emulsion polymerization.

[0034] Examples of (meth)acrylic monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, 3-methyl-3-hydroxybutyl (meth)acrylate, 1,1-dimethyl-3-hydroxybutyl (meth)acrylate, 1,3-dimethyl 3-hydroxybutyl (meth)acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth)acrylate, 2-ethyl-3-hydroxyhexyl (meth)acrylate, N-hydroxyethyl (meth)acrylamide, glycerin mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, poly(ethylene glycol-propylene glycol) mono(meth)acrylate, pentaerythritol tetra(meth)acrylate, and pentaerythritol tri(meth)acrylate. The (meth)acrylic monomer having a hydroxyl group may be one or more kinds.

[0035] Examples of other (meth)acrylic monomers include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, i-octyl (meth)acrylate, n-nonyl (meth)acrylate, i-nonyl (meth)acrylate, n-decyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Monomers include (meth)acrylate monomers having an aromatic ring, such as phenyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate; alkoxyalkyl (meth)acrylate monomers, such as 2-methoxyethyl (meth)acrylate and 2-ethoxyethyl (meth)acrylate; (meth)acrylate monomers having a carboxy group, such as (meth)acrylic acid; (meth)acrylate monomers having an amino group, such as 2-dimethylaminoethyl (meth)acrylate, 2-diethylaminoethyl (meth)acrylate, 2-diisopropylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylamide; glycidyl (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate. The other (meth)acrylic monomer may be one or more kinds.

[0036] The first acrylic (co)polymer may also be an acrylic (co)polymer obtained by mixing and polymerizing a (meth)acrylic monomer having a hydroxyl group, another (meth)acrylic monomer, and further another polymerizable monomer. Further examples of the polymerizable monomer include polymerizable monomers having a carboxy group such as crotonic acid, maleic acid, fumaric acid, itaconic acid, glutaconic acid, and citraconic acid; polymerizable monomers derived from aromatic monovinyls such as styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, and vinyltoluene; polymerizable monomers derived from vinyl cyanides such as acrylonitrile and methacrylonitrile; and polymerizable monomers derived from vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, and vinyl versatate. Furthermore, one or more other polymerizable monomers may be used.

[0037] Considering the hardness of the first acrylic resin after crosslinking, the first acrylic (co)polymer is preferably a first acrylic (co)polymer obtained by polymerizing a mixture containing a (meth)acrylic monomer having a hydroxyl group and a methacrylic acid alkyl ester monomer, more preferably a first acrylic (co)polymer obtained by polymerizing a mixture containing a (meth)acrylic monomer having a hydroxyl group and methyl methacrylate (MMA), and even more preferably a first acrylic (co)polymer obtained by polymerizing a mixture containing 2-hydroxyethyl methacrylate and methyl methacrylate (MMA).

[0038] Examples of the first crosslinking agent include an isocyanate-based crosslinking agent, a melamine-based crosslinking agent, a benzoguanamine-based crosslinking agent, a urea-based crosslinking agent, and a metal chelate-based crosslinking agent. However, in consideration of the physical properties of the first acrylic resin, such as heat resistance and control of the tensile elongation at break after crosslinking, an isocyanate-based crosslinking agent is preferred.

[0039] The term "isocyanate-based crosslinking agent" refers to a compound having two or more isocyanate groups in one molecule. Examples of the isocyanate-based crosslinking agent include aliphatic polyisocyanate-based compounds, alicyclic polyisocyanate-based compounds, and aromatic polyisocyanate-based compounds.

[0040] Examples of the aliphatic polyisocyanate compound include an aliphatic polyisocyanate compound, a polymer of an aliphatic polyisocyanate compound, an adduct of an aliphatic polyisocyanate compound and a polyol compound (for example, trimethylolpropane (hereinafter also referred to as "TMP")), and a biuret of an aliphatic polyisocyanate compound. Specific examples of the aliphatic polyisocyanate compound include hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI), tetramethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate.

[0041] Examples of the alicyclic polyisocyanate compound include an alicyclic polyisocyanate compound, a polymer of an alicyclic polyisocyanate compound, an adduct of an alicyclic polyisocyanate compound and a polyol compound, and a biuret of an alicyclic polyisocyanate compound. Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated 4,4'-diphenylmethane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0042] Examples of the aromatic polyisocyanate compound include an aromatic polyisocyanate compound, a polymer of an aromatic polyisocyanate compound, an adduct of an aromatic polyisocyanate compound and a polyol compound, and a biuret of an aromatic polyisocyanate compound. Specific examples of aromatic polyisocyanate compounds include tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), and 4,4'-diphenylmethane diisocyanate.

[0043] As the first crosslinking agent, an alicyclic polyisocyanate compound is preferred, and an isophorone diisocyanate compound is more preferred. Examples of the isophorone diisocyanate compound include IPDI, a biuret of IPDI, an IPDI polymer (for example, an isocyanurate), and an adduct of IPDI and a polyol compound. As the isophorone diisocyanate compound, an adduct of IPDI is preferred, and an adduct of IPDI and TMP is more preferred.

[0044] As the isocyanate-based crosslinking agent, currently or previously available commercially available products can be used. Examples of commercially available isocyanate crosslinking agents include "Coronate (registered trademark) HX", "HK", "HL", "HL-S", "L", "L-45E", "2031", "2037", "2234", "2770", "2785", "2793", "Aquanate (registered trademark) 200" and "210" (all manufactured by Tosoh Corporation), "Sumidur (registered trademark) N75", "N3300", "Desmodur (registered trademark) N75" Examples of such compounds include "MPA / X", "N100", "N3200" and "N3400" (all manufactured by Sumika Covestro Urethane Co., Ltd.), "Duranate (registered trademark) D201", "E405-70B", "E405-80T", "AE700-100", "24A-100", "TSE-100" and "TMA-100" (all manufactured by Asahi Kasei Corporation), and "Takenate (registered trademark) D-110N", "D-101E", "D-120N", "D-140N", "D-160N", "D-172N", "M-631N", "MT-Olestar (registered trademark) NP1200" and "Stabio (registered trademark) XD-340N" (all manufactured by Mitsui Chemicals, Inc.).

[0045] The first crosslinking agent may be a single isocyanate crosslinking agent, or may be a combination of two or more isocyanate crosslinking agents.

[0046] The amount of the first crosslinking agent used can be adjusted appropriately depending on the type of the first acrylic (co)polymer, the type of the first crosslinking agent, the physical properties required for the (A) colored layer, etc. For example, the first crosslinking agent is used in an amount such that the molar ratio of the crosslinkable functional group in the first crosslinking agent to the reactive functional group in the first acrylic (co)polymer is preferably 0.5 to 1.5, more preferably 0.8 to 1.2. Here, the reactive functional group varies depending on the crosslinkable functional group. For example, when the crosslinkable functional group is an isocyanate group, the reactive functional group is a hydroxyl group, a carboxyl group, an amino group, etc., and can be determined based on the technical common sense of a person skilled in the art.

[0047] The (A) colored layer contains a pigment as a colorant. The pigment contained in the (A) colored layer is preferably a pigment that can be removed by laser light irradiation and has weather resistance and durability that allows for long-term use. There are no particular limitations on the pigment, but it can be selected from known colorants, for example.

[0048] The pigment contained in the (A) colored layer is not particularly limited as long as it has a visible color difference from the (B) white layer. That is, the pigment contained in the (A) colored layer may be any color tone, such as yellow, orange, red, purple, blue, green, brown, or black, as long as it is a color different from the white pigment contained in the (B) white layer (in other words, a pigment other than a white pigment). For example, a black pigment can be suitably used as the pigment contained in the (A) colored layer.

[0049] Black pigments include organic pigments and inorganic pigments, and preferred organic pigments include aniline black, perylene black, etc. Preferred inorganic pigments include carbon black, iron black, cobalt oxide pigments, etc.

[0050] Among the above-mentioned pigments, carbon black and the like are more preferably used. The average particle size of the carbon black is preferably 10 to 500 nm, more preferably 15 to 120 nm. As such carbon black, for example, various commercially available types of carbon black with a fine average particle size can be used.

[0051] The content of the pigment in the (A) colored layer is not particularly limited. For example, the amount of pigment in the (A) colored layer may be sufficient to provide sufficient hiding power for the (B) white layer while being removable by laser light irradiation. For example, the content of the pigment in the (A) colored layer is preferably 1 to 300 parts by mass, more preferably 5 to 200 parts by mass, per 100 parts by mass of the first acrylic resin. If the content is less than 1 part by mass per 100 parts by mass of the first acrylic resin, the hiding power is generally low, and it may be difficult to achieve a contrast with the back surface. On the other hand, if the content exceeds 300 parts by mass per 100 parts by mass of the first acrylic resin, the (A) colored layer becomes too brittle, and cracks may occur in the (A) colored layer, for example, when the label is attached to a curved surface.

[0052] In addition to the pigments described above, the (A) colored layer may contain curing catalysts, leveling agents, stabilizers, flame retardants, antioxidants, antistatic agents, mildew inhibitors, lubricants, fillers, matting agents, etc., to the extent that the physical properties are not affected.

[0053] When carbon black is used as the pigment, the pigment itself can be the compound that converts laser light into heat. On the other hand, if the pigment used does not have sufficient absorption of laser light, the (A) colored layer may further contain a compound for converting laser light into heat. For example, the (A) colored layer may contain a mixture of two or more pigments, or may contain a mixture of one or more pigments and one or more compounds that can convert laser light into heat.

[0054] Examples of compounds for converting laser light into heat include carbon black and infrared absorbing agents such as cyanine and phthalocyanine.

[0055] The thickness of the (A) colored layer is not particularly limited, but is preferably 10 to 30 μm, and more preferably 10 to 20 μm. If the (A) colored layer is 10 μm or thicker, it can have sufficient hiding power, and if it is 30 μm or thicker, the irradiated area can be easily removed by laser light irradiation.

[0056] The total thickness of the (A) colored layer and the (B) white layer is preferably 50 to 95 μm, and more preferably 60 to 85 μm. A total thickness of 50 μm or more is preferred in terms of suitability for laser printing, and a total thickness of 95 μm or less is preferred in terms of low-temperature flexibility and handleability.

[0057] [(B) White layer] The (B) white layer contains a second acrylic resin, a white pigment, and inorganic particles. The (B) white layer has a visible color difference from the (A) colored layer, and when laminated with the (A) colored layer, it imparts low-temperature flexibility and functions as a layer that imparts brittleness when the label is broken. Because the (B) white layer has a visible color difference from the (A) colored layer, desired printing or images can be produced in a color (white) different from that of the (A) colored layer in the area where the (A) colored layer is removed by laser light irradiation. The (B) white layer also contains inorganic particles as a component that imparts brittleness, and has the function of actively inducing label breakage when the label attached to the adherend is peeled off. Furthermore, the (B) white layer contains the inorganic particles described above, making it possible to achieve both the contradictory properties of brittleness and low-temperature flexibility for a brittle laminate label.

[0058] The reason why the (B) white layer contains inorganic particles that enable both the contradictory properties of brittleness and low-temperature flexibility is not clear, but is speculated as follows. First, when the (B) white layer contains organic particles such as acrylic particles, they are highly compatible with the second acrylic resin, which is the resin component that makes up the (B) white layer, and it is thought that the acrylic particles are uniformly mixed in the second acrylic resin layer. Therefore, even if acrylic particles are used as a component that imparts brittleness to the (B) white layer, it is speculated that the second acrylic resin layer acts as a stress relief function, making it difficult to ensure brittleness.

[0059] On the other hand, when inorganic particles are used, their compatibility with the second acrylic resin decreases, so they remain undissolved in the layer of the second acrylic resin, which is thought to cause uneven distribution (accumulation) of the inorganic particles during the manufacturing process. It is presumed that the uneven distribution of the inorganic particles in a relatively dense state contributes to brittleness, and that low-temperature flexibility can be ensured by forming a layer of the second acrylic resin in which the inorganic particles are relatively dispersed, thereby achieving both brittleness and low-temperature flexibility.

[0060] The (B) white layer contains a second acrylic resin. The second acrylic resin contained in the (B) white layer is the same as the first acrylic resin contained in the (A) colored layer described above, but because the (B) white layer also requires a certain degree of flexibility, the second crosslinking agent and additives that are preferably used are partially different from those used in the (A) colored layer. The first acrylic (co)polymer and the second acrylic (co)polymer may be the same or different.

[0061] Examples of the second crosslinking agent include isocyanate-based crosslinking agents, melamine-based crosslinking agents, benzoguanamine-based crosslinking agents, urea-based crosslinking agents, and metal chelate-based crosslinking agents, with isocyanate-based crosslinking agents being preferred.

[0062] Examples of the isocyanate-based crosslinking agent include the isocyanate-based crosslinking agents exemplified as the first crosslinking agent. As the second crosslinking agent, in consideration of flexibility after crosslinking, an aliphatic polyisocyanate compound is preferred, and a hexamethylene diisocyanate compound is more preferred. Examples of hexamethylene diisocyanate compounds include HDI, biuret of HDI, polymers of HDI (for example, isocyanurate), and adducts of HDI and polyol compounds. As the hexamethylene diisocyanate-based compound, a polymer of HDI is preferred, and an isocyanurate of HDI is more preferred.

[0063] The amount of the second crosslinking agent used can be appropriately adjusted depending on the type of second acrylic (co)polymer, the type of second crosslinking agent, the physical properties required for the (B) white layer, etc. For example, the second crosslinking agent is used in an amount such that the molar ratio of the crosslinkable functional groups in the second crosslinking agent to the reactive functional groups in the second acrylic (co)polymer is preferably 0.1 to 1.3, more preferably 0.2 to 1.0. If the amount of the second crosslinking agent is too large, the flexibility of the second acrylic resin may be impaired, and if it is too small, the heat resistance and durability of the second acrylic resin may be impaired.

[0064] The white layer (B) contains a white pigment and is colored to a color that is visible from the colored layer (A). The white pigment is preferably an inorganic pigment, such as zinc oxide, zinc sulfide, titanium dioxide, calcium carbonate, clay, barium sulfate, alumina white, silica, muscovite, and talc.

[0065] Titanium oxide is more preferably used as the white pigment contained in the (B) white layer. The average particle size of such titanium oxide is preferably 10 to 500 nm, more preferably 20 to 100 nm. For example, various commercially available titanium oxides with fine average particle sizes can be used as the titanium oxide.

[0066] The content of the white pigment in the (B) white layer is not particularly limited. For example, the content of the white pigment in the (B) white layer is preferably 10 to 400 parts by mass, and more preferably 30 to 300 parts by mass, per 100 parts by mass of the second acrylic resin. For example, if the content is less than 10 parts by mass per 100 parts by mass of the second acrylic resin, the contrast difference between the laser-printed and non-printed areas will be small, which is undesirable because the printed lines may become unclear. On the other hand, if the content exceeds 400 parts by mass per 100 parts by mass of the second acrylic resin, the white layer will become excessively brittle, which may make it difficult to achieve good low-temperature flexibility, which is undesirable.

[0067] The (B) white layer contains inorganic particles as a component that imparts brittleness. Examples of inorganic particles include silica particles, glass beads, calcium carbonate particles, alumina particles, and aluminum powder. From the viewpoint of dispersibility during blending, silica particles having a relatively low specific gravity are preferred, and porous silica particles are more preferred.

[0068] There are no particular restrictions on the average particle size of the inorganic particles, as long as it is equal to or less than the thickness of the (B) white layer. The average particle size of the inorganic particles is preferably 1 to 10 μm, and more preferably 1 to 5 μm. If the average particle size of the inorganic particles is within the above-mentioned numerical range, it is possible to impart brittleness to the brittle laminated label and also to make the brittle laminated label less susceptible to unwanted cracks during application, etc. For example, if the average particle size of the inorganic particles is less than 1 μm, it is undesirable because it may result in insufficient brittleness. On the other hand, if the average particle size of the inorganic particles exceeds 10 μm, it will have a significant impact on brittleness, making the label excessively brittle and preventing good low-temperature flexibility. The average particle size of inorganic particles is a value measured using a laser diffraction / scattering particle size distribution analyzer. More specifically, the average particle size of inorganic particles can be measured by the following method. First, inorganic particles are dispersed in distilled water, and the concentration is adjusted so that the transmittance of a semiconductor laser (wavelength 650 nm) is 80 to 90%. The aqueous solution with the adjusted concentration is used as a measurement sample, and the average particle size of the inorganic particles is measured using a laser diffraction / scattering particle size distribution analyzer. For example, although not particularly limited, the laser diffraction / scattering particle size distribution analyzer may be the "Partica LA-960 (product name)" manufactured by Horiba, Ltd.

[0069] The content of inorganic particles in the (B) white layer is 7.5 to 25 parts by mass, preferably 10 to 20 parts by mass, per 100 parts by mass of the second acrylic resin. If the content of inorganic particles is less than 7.5 parts by mass per 100 parts by mass of the second acrylic resin, the brittle laminated label will be insufficient, and will not break easily when peeled off from an adherend. On the other hand, if the content of inorganic particles is more than 25 parts by mass per 100 parts by mass of the second acrylic resin, good low-temperature flexibility will not be obtained.

[0070] In addition to the above-mentioned white pigment and inorganic particles, the (B) white layer may contain, to the extent that the physical properties are not affected, a curing catalyst, a leveling agent, a stabilizer, a flame retardant, an antioxidant, an antistatic agent, an antifungal agent, a lubricant, a filler, a flexibility imparting agent, a matting agent, etc. Among these, it is preferable that the (B) white layer further contains a flexibility imparting agent in order to maintain its flexibility.

[0071] Examples of softening agents include glycol compounds. The glycol compound refers to a condensation compound of a diol, and examples thereof include ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, polyethylene glycol, polytetramethylene ether glycol, tetrahydrofuran-neopentyl glycol copolymer, etc. As the glycol compound serving as a softening agent, polymer-type glycol compounds are preferred in terms of the volatility of the glycol itself, the degree of softening imparted per added amount, and water resistance, and polytetramethylene ether glycol is particularly preferred in terms of availability, price, etc.

[0072] The content of the glycol compound is not particularly limited, but is preferably 5 to 40 parts by mass, and more preferably 5 to 20 parts by mass, per 100 parts by mass of the second acrylic resin. If the content of the glycol compound is 5 parts by mass or more, the brittle laminated label is less likely to crack or break even if it is bent slightly during application, making it easier to handle. On the other hand, if the content of the glycol compound is less than 40 parts by mass, the brittle laminated label does not have excessive flexibility, and once applied and peeled off, the label is destroyed and becomes unreusable, improving tamper resistance.

[0073] The thickness of the (B) white layer is not particularly limited, but is preferably 40 to 80 μm, and more preferably 50 to 70 μm. A thickness of 40 μm or more is preferred because it broadens the range of optimal laser printing conditions. A thickness of 80 μm or less is also preferred because it provides good low-temperature flexibility.

[0074] [(C) Adhesive layer] The brittle laminate label of this embodiment includes a (C) adhesive layer laminated on a (B) white layer. The (C) adhesive layer is a layer whose main function is to increase the adhesiveness of the brittle laminate label to an adherend. That is, the (C) adhesive layer is a layer for attaching the brittle laminate label to an adherend, and is disposed on the surface of the brittle laminate label opposite the surface on which the (A) colored layer is disposed (i.e., the surface serving as the uppermost layer). In particular, it is preferred that the (C) adhesive layer is laminated on the (B) white layer, and the brittle laminate label is composed of a laminate in which the (A) colored layer, (B) white layer, and (C) adhesive layer are laminated in this order.

[0075] The pressure-sensitive adhesive layer (C) is formed from a pressure-sensitive adhesive composition (hereinafter also simply referred to as "pressure-sensitive adhesive"), and is a so-called cured product of the pressure-sensitive adhesive.

[0076] The adhesive for forming the adhesive layer (C) is not particularly limited. Examples of the adhesive include acrylic adhesives, urethane adhesives, silicone adhesives, and rubber adhesives. Among these, acrylic adhesives are preferred.

[0077] The acrylic pressure-sensitive adhesive for forming the pressure-sensitive adhesive layer (C) may contain additives such as a tackifier, an ultraviolet absorber, a light stabilizer, and an antioxidant, if necessary.

[0078] The thickness of the (C) pressure-sensitive adhesive layer is not particularly limited, but is preferably 15 to 100 μm, more preferably 20 to 70 μm, and particularly preferably 25 to 45 μm. A thickness of 15 μm or more is preferable in that adhesion to the adherend can be ensured. Furthermore, a thickness of less than 100 μm provides good adhesion and is cost-effective.

[0079] There are no particular restrictions on the adhesive strength of the (C) pressure-sensitive adhesive layer, but for example, it is preferable that the measured value in a 180° fold-peel test using a tensile tester after being applied as a 25.4 mm wide tape to an adherend and left for 24 hours is 5 N / 25.4 mm or more. If the above-mentioned measured value (i.e., the adhesive strength of the (C) pressure-sensitive adhesive layer) is less than 5 N / 25.4 mm, problems such as the edge of the brittle laminate label lifting up may occur when the brittle laminate label is attached to an uneven curved surface.

[0080] [Physical properties and usage of laser-printable brittle laminate labels] The brittle laminated label of this embodiment preferably has a tensile elongation of 3 to 15%, more preferably 5 to 13%, in an environment of 23°C and 55% RH. If the tensile elongation is less than 3%, the label tends to be too brittle and not be able to achieve good low-temperature flexibility. On the other hand, if the tensile elongation is more than 15%, the label tends to be too brittle and not be able to achieve good tamper resistance. Here, the tensile elongation (%) can be measured by the following method. First, a laser-markable brittle laminate label is cut to 25 mm x 150 mm to prepare a test piece. Then, a tensile test is performed on the prepared test piece under conditions of a gripping width of 25 mm, a chuck distance of 100 mm, and a tensile speed of 200 mm / min, and the tensile elongation (%) of the test piece is measured. The tensile test can be performed using a universal testing machine, Tensilon "RTG-1310 (trade name)" (manufactured by A&D Co., Ltd.).

[0081] Furthermore, the brittle laminated label of this embodiment preferably has a tensile modulus of 1000 to 1800 MPa, more preferably 1200 to 1700 MPa, in an environment of 23°C and 55% RH. If the tensile modulus is less than 1000 MPa, the label tends to be too brittle and not have good low-temperature flexibility. On the other hand, if the tensile modulus exceeds 1800 MPa, the label tends to be too insufficient in brittleness and not have good tamper resistance. Here, the tensile modulus (MPa) can be determined by conducting a tensile test in the same manner as in the above-mentioned tensile elongation (%) and measuring the tensile modulus (MPa) of the test piece.

[0082] The brittle laminated label of this embodiment breaks when an attempt is made to peel it off by hand or with a tool after it has been attached to an adherend. There are various mechanisms for this breakdown, but it is presumed that in the brittle laminated label of this embodiment, the inorganic particles deposited in the (B) white layer form a layer, and as a result, the stress strain associated with peeling causes breakage at the interfaces of the inorganic particles 21, resulting in the label becoming brittle.

[0083] 1, the brittle laminate label of the embodiment has a (B) white layer 20 laminated on a (C) adhesive layer 30, and a (A) colored layer 10 that can be removed by laser light irradiation laminated on top of that. When laser light is irradiated onto the brittle laminate label 100, the (A) colored layer 10 is removed in the shape of the laser light irradiation, exposing the (B) white layer 20, and a desired printed image or the like is formed by the color contrast between the (A) colored layer 10 and the (B) white layer 20.

[0084] There are no particular limitations on the laser that can be used for irradiation, and examples include CO2 laser, Nd:YAG laser, excimer laser, semiconductor laser, semiconductor-pumped solid-state laser, Ar laser, N2 / Dye laser, HeCd laser, etc. Among these, it is preferable to use a CO2 laser, Nd:YAG laser, etc., which generally require inexpensive equipment and are relatively easy to handle.

[0085] The brittle laminate label of this embodiment is one or more labels arranged on a release paper, which may be a release paper that has been subjected to a known release treatment.

[0086] The brittle laminated label can be formed as a sheet in which tens to hundreds of brittle laminated labels are arranged in succession by printing a serial number or the like using a laser printing device and then providing cuts or the like so that the label can be easily divided into labels of a predetermined size or shape.The brittle laminated labels can then be peeled off one by one from the sheet in which the brittle laminated labels are arranged in succession on a release paper, and the peeled brittle laminated labels can be attached one by one to an adherend such as a part or a substrate for use.

[0087] The brittle laminated label of this embodiment can be individually printed differently using a laser printing device depending on the purpose, and can be used to print serial numbers, dates, etc. for product management and quality assurance purposes, and to display individual information such as the manufacturing date and expiration date. The brittle laminated label of this embodiment has a tamper-proof function in that the label is destroyed and cannot be reused when peeled off after being attached, and it also has excellent low-temperature flexibility. Therefore, the brittle laminated label is easy to handle even in low-temperature environments and is less likely to be damaged when transported to cold regions, etc.

[0088] [Method for manufacturing laser-printable brittle laminate labels] There are no particular limitations on the method for producing the laser-markable brittle laminate label of this embodiment, and it can be produced in accordance with known laminate label production methods. An example of a method for producing a laser-markable brittle laminate label will be described below, although the method for producing a laser-markable brittle laminate label of this embodiment is not limited to the following method.

[0089] First, as a resin solution for forming the (A) colored layer, a resin solution for the colored layer is prepared by appropriately mixing the first acrylic resin and pigment described above. Then, the prepared resin solution for the colored layer is applied to a processing film and dried to form the (A) colored layer. For example, a release-treated PET film can be used as the processing film.

[0090] Next, the second acrylic resin, white pigment, inorganic particles, etc. described above are mixed appropriately to prepare a resin solution for forming the (B) white layer. The prepared resin solution for the white layer is then applied to the (A) colored layer formed on the processing film and dried to form the (B) white layer. In this way, a laminate film is obtained in which the (A) colored layer and the (B) white layer are laminated on the processing film.

[0091] Separately, a pressure-sensitive adhesive composition solution containing the pressure-sensitive adhesive composition described above is prepared as a resin solution for forming the (C) pressure-sensitive adhesive layer. The prepared pressure-sensitive adhesive composition solution is then applied, for example, to a release paper and dried to form the (C) pressure-sensitive adhesive layer. Next, a laminate film having the previously prepared (A) colored layer and (B) white layer laminated thereon is attached to the (C) pressure-sensitive adhesive layer formed on the release paper, with the surface of the (B) white layer in contact with the (C) pressure-sensitive adhesive layer. The process film provided on the (A) colored layer side is then peeled off to produce a laser-markable brittle laminate label. [Example]

[0092] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "%" and "parts" are by mass unless otherwise specified.

[0093] (Preparation of acrylic resins (1) to (3)) The acrylic resins (1) to (3) used in the present examples and comparative examples were prepared as follows: Details of the acrylic resins (1) to (3) are shown in Table 1 below.

[0094] The synthesis method for acrylic resins (1) to (3) is described below. Each acrylic resin was synthesized by solution polymerization. More specifically, an azo-based polymerization initiator was added to a predetermined amount of monomer mixture using an ester-based solvent under reflux temperature conditions. Next, the remaining monomer mixture was successively added dropwise over a predetermined time period, and the polymerization reaction was continued for another predetermined time period. Thereafter, the solution was diluted with a reaction solvent to a predetermined solids concentration, thereby obtaining solutions of each of acrylic resins (1) to (3).

[0095] In Table 1 below, the column "Monomer composition (parts by mass)" indicates the type and amount of monomer used in synthesizing the acrylic resins (1) to (3).

[0096] In Table 1 below, the column "Tg (°C)" indicates the glass transition temperature (°C) of the acrylic resins (1) to (3). The glass transition temperature (°C) was measured using a differential scanning calorimeter (DSC) in a nitrogen gas flow, with 10 mg of the measurement sample (i.e., homopolymer) at a heating rate of 10°C / min. The inflection point of the obtained DSC curve was taken as the glass transition temperature of the acrylic resins (1) to (3). The differential scanning calorimeter used was a differential scanning calorimeter manufactured by TA Instruments Japan (trade name: Discovery DSC 2500).

[0097] In addition, in the following Table 1, the column "Mw (10,000)" indicates the weight average molecular weight (10,000) of the acrylic resins (1) to (3), and the column "Solid content (mass%)" indicates the solid content concentration (mass%) of the acrylic resins (1) to (3). The term "solid content concentration (mass%)" used herein refers to the mass proportion of each acrylic resin in the solution obtained by synthesizing each acrylic resin. The weight-average molecular weight (10,000) of each of the acrylic resins (1) to (3) is a value measured by the following method. (1) After applying the acrylic resin solution to a release paper, it is dried at 100°C for 1 minute to obtain a film of the acrylic resin. (2) Using the film-like acrylic resin obtained in (1) above and tetrahydrofuran, a sample solution with a solids concentration of 0.2% by mass is obtained. Note that the "solids concentration" here refers to the mass proportion of the acrylic resin in the sample solution. (3) After filtering the sample solution obtained in (2) above through a filter (pore size: 0.25 μm), the weight-average molecular weight of the acrylic resin is determined as a standard polystyrene equivalent value by gel permeation chromatography (GPC) under the following conditions.

[0098] ~Conditions~ Measurement equipment: High-speed GPC [Model number: HLC-8420 GPC, manufactured by Tosoh Corporation] Detector: Differential refractometer (RI) [built into HLC-8420, manufactured by Tosoh Corporation] Column: TSKgel GMH XLTwo [Tosoh] Column temperature: 40℃ Eluent: tetrahydrofuran Sample solution injection volume: 100 μL Flow rate: 0.8mL / min

[0099] [Table 1]

[0100] The abbreviations in Table 1 above and the glass transition temperatures (Tg) of the corresponding homopolymers are shown below. EA: Ethyl acrylate (Tg: -22°C). nBA: n-butyl acrylate (Tg: -54°C). MMA: Methyl methacrylate (Tg: 105°C). nBMA: n-butyl methacrylate (Tg: 20°C). 2HEMA: 2-hydroxyethyl methacrylate (Tg: 85°C). ·AA: acrylic acid (Tg: 106°C).

[0101] (Preparation of Black Resin Solutions (1) and (2) for Colored Layer) The black resin solutions (1) and (2) for colored layers used in the examples and comparative examples were prepared as follows: The components of the black resin solutions (1) and (2) for colored layers are listed in Table 2 below.

[0102] (Preparation of black resin solution (1) for colored layer) A black resin solution (1) for the colored layer was prepared by mixing 50 parts by mass of acrylic resin (1), 46 parts by mass of acrylic resin (2), 26 parts by mass of an isocyanate crosslinking agent "Takenate D140N (60)" (manufactured by Mitsui Chemicals, Inc.), 1 part by mass of a curing catalyst "Nacem (registered trademark) Zirconium" (manufactured by Nippon Chemical Industry Co., Ltd., 1% by mass solution in acetylacetone), 25 parts by mass of black pigment "NBK-968" (manufactured by Nichiko Bix Co., Ltd.), and 23 parts by mass of methyl isobutyl ketone (MIBK).

[0103] (Preparation of black resin solution (2) for colored layer) A black resin solution (2) for the colored layer was prepared by mixing 50 parts by mass of acrylic resin (1), 46 parts by mass of acrylic resin (2), 18 parts by mass of melamine crosslinking agent "MS-11" (manufactured by Sanwa Chemical Co., Ltd.), 5 parts by mass of curing catalyst "CT-5" (manufactured by Sanwa Chemical Co., Ltd.), 15 parts by mass of black pigment "NX-591" (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and 23 parts by mass of methyl isobutyl ketone (MIBK).

[0104] [Table 2]

[0105] (Preparation of White Resin Solutions (1) to (9) for White Layer) The white resin solutions (1) to (9) for the white layer used in the examples and comparative examples were prepared as follows: The components of the white resin solutions (1) to (9) for the white layer are listed in Table 3 below.

[0106] (Preparation of White Resin Solution (1) for White Layer) 50 parts by mass of acrylic resin (1), 46 parts by mass of acrylic resin (2), 11 parts by mass of isocyanate crosslinking agent “Coronate HK” (manufactured by Nippon Polyurethane Industry Co., Ltd.), 1 part by mass of curing catalyst “Nacem (registered trademark) Zirconium” (manufactured by Nippon Chemical Industry Co., Ltd., acetylacetone 1% by mass solution), 240 parts by mass of white pigment “NBK-967” (manufactured by Nikko Bix Co., Ltd.), 10 parts by mass of flexibility imparting agent “PTMG-1000M” (manufactured by Sanyo Chemical Industries, Ltd.) as an additive, and 9 parts by mass of methyl isobutyl ketone (MIBK) were mixed to prepare a white resin solution (1) for the white layer.

[0107] (Preparation of white resin solution (2) for white layer) White resin solution (2) for the white layer was prepared in the same manner as white resin solution (1) for the white layer, except that 10 parts by mass of acrylic particles "Art Pearl J-4P" (manufactured by Negami Chemical Industrial Co., Ltd., average particle size 2.6 μm) was further mixed and methyl isobutyl ketone (MIBK) was changed to 15 parts by mass.

[0108] (Preparation of white resin solution (3) for white layer) White resin solution (3) for the white layer was prepared in the same manner as white resin solution (1) for the white layer, except that 2.5 parts by mass of silica particles "Sylysia 445" (manufactured by Fuji Silysia Chemical Ltd., average particle size 6.6 μm) was further mixed and the amount of methyl isobutyl ketone (MIBK) was changed to 10 parts by mass.

[0109] (Preparation of white resin solution (4) for white layer) White resin solution (4) for the white layer was prepared in the same manner as white resin solution (1) for the white layer, except that 5 parts by mass of silica particles "Sylysia 445" (manufactured by Fuji Silysia Chemical Ltd., average particle size 6.6 μm) were further mixed and the amount of methyl isobutyl ketone (MIBK) was changed to 12 parts by mass.

[0110] (Preparation of white resin solution (5) for white layer) White resin solution (5) for the white layer was prepared in the same manner as white resin solution (1) for the white layer, except that 10 parts by mass of silica particles "Sylysia 445" (manufactured by Fuji Silysia Chemical Ltd., average particle size 6.6 μm) were further mixed and the amount of methyl isobutyl ketone (MIBK) was changed to 15 parts by mass.

[0111] (Preparation of white resin solution (6) for white layer) White resin solution (6) for the white layer was prepared in the same manner as white resin solution (1) for the white layer, except that 20 parts by mass of silica particles "Sylysia 445" (manufactured by Fuji Silysia Chemical Ltd., average particle size 6.6 μm) was further mixed and the amount of methyl isobutyl ketone (MIBK) was changed to 21 parts by mass.

[0112] (Preparation of white resin solution (7) for white layer) White resin solution (7) for the white layer was prepared in the same manner as white resin solution (1) for the white layer, except that 30 parts by mass of silica particles "Sylysia 445" (manufactured by Fuji Silysia Chemical Ltd., average particle size 6.6 μm) was further mixed and the amount of methyl isobutyl ketone (MIBK) was changed to 27 parts by mass.

[0113] (Preparation of white resin solution (8) for white layer) White resin solution (8) for the white layer was prepared in the same manner as white resin solution (1) for the white layer, except that 40 parts by mass of silica particles "Sylysia 445" (manufactured by Fuji Silysia Chemical Ltd., average particle size 6.6 μm) was further mixed and the amount of methyl isobutyl ketone (MIBK) was changed to 33 parts by mass.

[0114] (Preparation of white resin solution (9) for white layer) A white resin solution (9) for the white layer was prepared by mixing 92 parts by mass of acrylic resin (2), 200 parts by mass of white pigment “NX-501” (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), 32 parts by mass of isocyanate crosslinking agent “Coronate HK” (manufactured by Nippon Polyurethane Industry Co., Ltd.), 10 parts by mass of flexibility imparting agent “PTMG-1000M” (manufactured by Sanyo Chemical Industries, Ltd.) as an additive, and 8 parts by mass of methyl isobutyl ketone (MIBK).

[0115] [Table 3]

[0116] (Preparation of white resin solution for destruction layer) 92 parts by weight of acrylic resin (2), 200 parts by weight of white pigment "NX-501" (manufactured by Dainichiseika Color & Chemicals Co., Ltd.), 32 parts by weight of isocyanate crosslinking agent "Coronate HK" (manufactured by Nippon Polyurethane Industry Co., Ltd.), 10 parts by weight of flexibility imparting agent "PTMG-1000M" (manufactured by Sanyo Chemical Industries, Ltd.), 9 parts by weight of methyl isobutyl ketone (MIBK), and 8 parts by weight of acrylic particles "Art Pearl GR-300" (manufactured by Negami Industrial Co., Ltd., average particle size 25.6 μm) were mixed to prepare a white resin solution for the destructible layer. The components of the white resin solution for the destructible layer are shown in Table 4 below.

[0117] [Table 4]

[0118] [Average particle size (μm)] The method for measuring the average particle size of each particle used in preparing the white resin solutions (2) to (8) for the white layer and the white resin solution for the destructible layer is as follows. First, each particle was dispersed in distilled water, and the concentration was adjusted so that the transmittance of a semiconductor laser (wavelength 650 nm) was 80% to 90%. The aqueous solution with the adjusted concentration was used as a measurement sample, and the average particle size of each particle was measured using a laser diffraction / scattering particle size distribution analyzer "Partica LA-960" (manufactured by Horiba, Ltd.).

[0119] (Preparation of Pressure-Sensitive Adhesive Composition Solutions (1) and (2)) The pressure-sensitive adhesive composition solutions (1) and (2) used in the examples and comparative examples were prepared as follows: The components of the pressure-sensitive adhesive composition solutions (1) and (2) are listed in Table 5 below.

[0120] (Preparation of Pressure-Sensitive Adhesive Composition Solution (1)) A pressure-sensitive adhesive composition solution (1) was prepared by mixing 100 parts by mass of acrylic resin (3), 6 parts by mass of aluminum chelate crosslinking agent "Nissetsu CK-405" (manufactured by Nippon Carbide Industries Co., Ltd.), and 37 parts by mass of ethyl acetate.

[0121] (Preparation of Pressure-Sensitive Adhesive Composition Solution (2)) A pressure-sensitive adhesive composition solution (2) was prepared by mixing 85 parts by mass of acrylic resin (3), 2 parts by mass of aluminum chelate crosslinking agent "Nissetsu CK-401" (manufactured by Nippon Carbide Industries Co., Ltd.), 2 parts by mass of fluorescent brightener "Kayalite B" (manufactured by Nippon Shokubai Co., Ltd.), and 31 parts by mass of ethyl acetate.

[0122] [Table 5]

[0123] (Comparative Example 1) First, the black resin solution (1) for the colored layer was applied to a release-treated PET film ("P75 6505", manufactured by Lintec Corporation), dried at 70°C for 1.5 minutes, and then further dried at 140°C for 1.5 minutes to form a colored layer (thickness: 15 μm). Next, the white resin solution (1) for the white layer was applied to the formed colored layer so that the thickness after drying would be 60 μm, and then dried at 70°C for 3 minutes, and then further dried at 140°C for 3 minutes to produce a film (1) in which the colored layer and the white layer were laminated.

[0124] Furthermore, the adhesive composition solution (1) was applied to a single-sided release paper ("SLK-70AWP" (manufactured by Sumika Kakoshi Co., Ltd.) and dried at 100°C for 1.5 minutes to form an adhesive layer (thickness: 30 μm). The above-mentioned laminated film (1) was attached to the adhesive layer thus formed so that the surface of the white layer was in contact with the adhesive layer, and then the release-treated PET film on the colored layer side was peeled off, thereby producing the laser-markable brittle laminate label of Comparative Example 1.

[0125] (Comparative Examples 2 to 6 and Examples 1 to 2) Laser-markable brittle laminate labels of Comparative Examples 2 to 6 and Examples 1 and 2 were prepared in the same manner as Comparative Example (1), except that white resin solutions (2) to (8) for the white layer were used instead of white resin solution (1) for the white layer.

[0126] (Comparative Example 7) The black resin solution for the colored layer (2) was applied to a release-treated PET film ("P75 6505", manufactured by Lintec Corporation), dried at 70 ° C for 1.5 minutes, and then further dried at 140 ° C for 1.5 minutes to form a colored layer (thickness: 15 μm). Next, the white resin solution for the white layer (9) was applied to the formed colored layer so that the thickness after drying was 40 μm, and then dried at 70 ° C for 3 minutes, and then further dried at 140 ° C for 3 minutes to laminate the colored layer and white layer. Next, the white resin solution for the destructible layer was applied to the white layer so that the thickness after drying was 60 μm, and then dried at 70 ° C for 3 minutes, and then further dried at 140 ° C for 3 minutes to produce a film (9) in which the colored layer, white layer, and destructible layer were laminated.

[0127] Furthermore, the adhesive composition solution (2) was applied to a single-sided release paper ("SLK-70AWP" (manufactured by Sumika Kakoshi Co., Ltd.) and dried at 100°C for 1.5 minutes to form an adhesive layer (thickness: 30 μm). The above-mentioned laminated film (9) was attached to the adhesive layer thus formed so that the surface of the destructible layer was in contact with the adhesive layer, and the release-treated PET film on the colored layer side was peeled off to produce the laser-markable brittle laminate label of Comparative Example 7. The laser-markable brittle laminate label of Comparative Example 7 corresponds to the laser-markable brittle laminate label disclosed in the examples of Japanese Patent No. 5091724.

[0128] (Comparative Example 8) The black resin solution for the colored layer (2) was applied to a release-treated PET film ("P75 6505", manufactured by Lintec Corporation), dried at 70°C for 1.5 minutes, and then further dried at 140°C for 1.5 minutes to form a colored layer (thickness: 15 μm). Next, the white resin solution for the white layer (9) was applied to the formed colored layer so that the thickness after drying would be 60 μm, and then dried at 70°C for 3 minutes, followed by further drying at 140°C for 3 minutes to produce a film (10) in which the colored layer and white layer were laminated.

[0129] Furthermore, the adhesive composition solution (1) was applied to a single-sided release paper ("SLK-70AWP" (manufactured by Sumika Kakoshi Co., Ltd.) and dried at 100°C for 1.5 minutes to form an adhesive layer (thickness: 30 μm). The above-mentioned laminated film (10) was attached to the adhesive layer thus formed so that the surface of the white layer was in contact with the adhesive layer, and the release-treated PET film on the colored layer side was peeled off, thereby producing a laser-markable brittle laminate label of Comparative Example 8.

[0130] The layer structures of the laser-markable brittle laminate labels of Examples 1 and 2 and Comparative Examples 1 to 8 are shown in Table 6 below. The following tests and evaluations were carried out on the laser-markable brittle laminate labels of Examples 1 and 2 and Comparative Examples 1 to 8. The results are shown in Table 6 below.

[0131] [Table 6]

[0132] [Tensile test] First, the prepared laser-markable brittle laminate label was cut into 25mm x 150mm test pieces. A tensile test was performed using a universal testing machine, Tensilon RTG-1310 (manufactured by A&D Corporation), at room temperature of 23°C and 55% RH, with a gripping width of 25mm, a chuck distance of 100mm, and a tensile speed of 200mm / min, to measure the tensile elongation (%) and tensile modulus (MPa). The measurement results are shown in Table 6 above.

[0133] [Tamper-proof evaluation] First, a design intended for actual use was printed on the prepared laser-markable brittle laminate label using a CO2 laser marker "ML-Z9510" (manufactured by Keyence Corporation). The printed laser-markable brittle laminate label was then cut into 40 mm x 60 mm pieces to prepare five test pieces. The five test pieces were then attached to a urethane-coated plate as an adherend and left to stand for 24 hours at room temperature of 23°C and 50% RH. Each test piece was then peeled from the adherend using a cutter. The number of cracks that occurred on each of the five test pieces was counted and evaluated as follows. In the tamper-resistance evaluation, a rating of A or B below was considered a pass. The number in parentheses in Table 6 indicates the number of test pieces with cracks. A: The number of cracked test pieces is 4 to 5. B: The number of cracked test pieces is 2 to 3. C: The number of test pieces in which cracks occurred is 0 to 1.

[0134] [Low temperature flexibility test] First, a design intended for actual use was printed on the prepared laser-markable brittle laminate label using a CO2 laser marker "ML-Z9510" (manufactured by Keyence Corporation). The printed laser-markable brittle laminate label was then cut into 40 mm x 60 mm pieces to prepare three test specimens. The three test specimens, with the release paper still attached, were placed in a low-temperature thermostatic chamber at -20°C for 48 hours, after which a wrapping test using an 8 mm diameter metal rod (made of SUS303) was performed once for each. The number of test specimens that did not crack was counted and evaluated as follows. In the low-temperature flexibility test, a rating of A or B below was considered a pass. The number in parentheses in Table 6 indicates the number of test specimens that did not crack. A: The number of test pieces in which no cracks occurred is 3. B: The number of test pieces in which no cracks occurred was two. C: The number of test pieces in which no cracks occurred is 0 to 1.

[0135] (result) The laser-markable brittle laminate labels of Examples 1 and 2 contained a predetermined amount of inorganic particles in the white layer, and were found to achieve good results in both the tamper-proofing evaluation and the low-temperature flexibility test. Therefore, it was found that in a laser-markable brittle laminate label consisting of a laminate in which a colored layer, a white layer, and an adhesive layer are laminated in this order, the inclusion of a predetermined amount of inorganic particles in the white layer can achieve both brittleness and low-temperature flexibility.

[0136] The laser-markable brittle laminate label of Comparative Example 1 did not contain inorganic particles in the white layer, and therefore, in the tamper-proofing evaluation, the number of test pieces that developed cracks was zero, indicating that the tamper-proofing properties were significantly poor.

[0137] The laser-markable brittle laminate label of Comparative Example 2 contained acrylic particles in the white layer, but in the tamper-proofing evaluation, only one test piece had cracks, indicating poor tamper-proofing. The reason for the poor tamper-proofing of the laser-markable brittle laminate label of Comparative Example 2 is presumed to be as follows. When acrylic particles were used as a brittleness-imparting component in the white layer as in Comparative Example 2, the acrylic particles were uniformly mixed in the acrylic resin layer due to the good compatibility between the acrylic particles and the acrylic resin. Therefore, even when acrylic particles were used as a brittleness-imparting component, the acrylic resin layer constituting the white layer acted as a stress relaxation layer, making it difficult to ensure brittleness.

[0138] Furthermore, even when inorganic particles were used as a brittleness-imparting component in the white layer, as in Comparative Examples 3 and 4, when the amount of inorganic particles was small, only one test piece developed cracks, and the tamper-proofing properties were poor.

[0139] On the other hand, when 10 to 20 parts by mass of inorganic particles were used as the brittleness-imparting component as in Examples 1 and 2, the number of test pieces in which cracks occurred was 2 to 4, and improvement in tamper-proofing was observed. FIG. 2 is an electron microscope photograph of a cross section of the laser-markable brittle laminate label of Example 2. The electron microscope photograph shown in FIG. 2 reveals that inorganic particles 21 are unevenly distributed on one side of the acrylic resin layer in the white layer 20. As described above, the inorganic particles 21 remain undissolved due to reduced compatibility with the acrylic resin, and it is presumed that uneven distribution (accumulation) of the inorganic particles 21 occurred during the manufacturing process. In the laser-markable brittle laminate labels of Examples 1 and 2, the unevenly distributed inorganic particles contribute to brittleness, and the formation of an acrylic resin layer with a small amount of inorganic particles ensures low-temperature flexibility, presumably achieving both brittleness and low-temperature flexibility. In FIG. 2, reference numeral 10 denotes a colored layer, reference numeral 30 denotes an adhesive layer, and reference numeral 40 denotes a release paper attached to the adhesive layer 30.

[0140] In the laser-markable brittle laminate labels of Comparative Examples 5 and 6, even when inorganic particles were used as a brittleness-imparting component in the white layer, the amount of inorganic particles was too high, so although the labels had excellent tamper-proofing properties, there were few areas where inorganic particles were not present, making it difficult to ensure low-temperature flexibility.

[0141] The laser-markable brittle laminate label of Comparative Example 7 did not contain inorganic particles in the white layer, and a destructible layer was further laminated below the white layer. The laser-markable brittle laminate label of Comparative Example 7 configured in this manner had excellent tamper-proofing properties, but because it contained a large amount of crosslinking agent, it hardened at low temperatures and had poor low-temperature flexibility. Here, Fig. 3 is an electron microscope photograph of a cross section of the laser-markable brittle laminate label of Comparative Example 7. The electron microscope photograph shown in Fig. 3 shows a cross section of a laser-markable brittle laminate label in which a colored layer 110, a white layer 120, a destructible layer 150, and an adhesive layer 130 are laminated in this order. The electron microscope photograph shown in Fig. 3 shows that the acrylic particles 121 contained in the destructible layer 150 are dispersed relatively evenly in the acrylic resin layer. In Fig. 3, reference numeral 140 denotes a release paper attached to the adhesive layer 130.

[0142] The laser-markable brittle laminate label of Comparative Example 8 did not contain inorganic particles in the white layer, and therefore in the tamper-proof evaluation, the number of test pieces that developed cracks was zero, indicating that the tamper-proof properties were significantly poor. [Industrial Applicability]

[0143] The laser-markable brittle laminated label of the present invention can be individually printed differently depending on the purpose using a laser printing device, and can be used to print serial numbers, dates, etc. for the purpose of product management and quality assurance, and to display individual information such as the manufacturing date, expiration date, etc. In particular, the brittle laminated label of the present invention has a tamper-proof function in that, once attached, if it is peeled off, the label is destroyed and cannot be reused, and it also has excellent low-temperature flexibility. [Explanation of symbols]

[0144] 10...Colored layer 20...white layer 21...Inorganic particles 30 Adhesive layer 40 ···Release paper 110...Colored layer 120...white layer 121 Acrylic particles 130 Adhesive layer 140 ···Release paper 150 Destruction layer 100 ···Laser-printable brittle laminate label

Claims

1. (A) a colored layer containing a first acrylic resin and a pigment; (B) a white layer containing a second acrylic resin, a white pigment, and inorganic particles; (C) a pressure-sensitive adhesive layer laminated on the (B) white layer, a content of the inorganic particles in the (B) white layer being 7.5 to 25 parts by mass per 100 parts by mass of the second acrylic resin;

2. 2. The laser-markable brittle laminate label according to claim 1, wherein the inorganic particles have an average particle size of 1 to 10 μm.

3. 3. The laser-markable brittle laminate label according to claim 1, wherein the inorganic particles are silica particles.

4. 3. The laser-markable brittle laminate label according to claim 1, wherein the thickness of the white layer (B) is 40 to 80 μm.

5. 3. The laser-markable brittle laminate label according to claim 1, wherein the total thickness of the colored layer (A) and the white layer (B) is 50 to 95 μm.

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