Shrink label

Abstract

Provided is a shrink label capable of suppressing the occurrence of failure of attachment onto a container while suppressing the occurrence of ink cracking.　A shrink label 10 comprises an outer layer 3b which is an aqueous acrylic ink layer on a heat-shrinkable substrate 1, said aqueous acrylic ink layer containing a hardening agent and an acrylic resin. The dynamic friction coefficient of the outer layer 3b with respect to a polyester surface having 0.1 mL of water droplets thereon is 1.0 or less, and the dynamic friction coefficient of the outer layer 3b with respect to a polyester surface having 0.01 mL of water droplets thereon is 2.5 or less.

Description

[[Technical Field]]

[0001] The present disclosure relates to shrink labels. [[Background Art]]

[0002] In recent years, plastic containers such as polyethylene terephthalate bottles (PET bottles) have been used for a wide variety of products. It has also become common for a shrink label including a printed layer for displaying product information and the like to be attached to the body of a plastic container.

[0003] For example, Patent Document 1 describes a heat-shrinkable tubular film attached to the outer circumference of the body of a container, which is improved to prevent abnormal attachment by providing a dynamic friction coefficient adjusting film for adjusting the dynamic friction coefficient on the inner surface on the outer circumference side of the container body.

[0004] Conventionally, as plastic labels, an ink layer has been formed by applying oil-based ink to the surface of a plastic film. However, from the perspective of increasing environmental awareness in recent years and suppressing the generation of VOC (volatile organic compounds), it has been desired to use water-based inks that use an aqueous solvent instead of oil-based inks that use organic solvents. [[Prior Art Documents]] [[Patent Documents]]

[0005] [[Patent Document 1]] Japanese Unexamined Patent Publication No. 2019-014157 [[Summary of the Invention]] [[Problems to be Solved by the Invention]]

[0006] However, when a water-based ink layer was formed on the innermost surface of a shrink label made of a heat-shrinkable tubular film, as described in Patent Document 1, ink cracking of the water-based ink layer and poor attachment to the container sometimes occurred, so improvement was needed. [Means for solving the problem]

[0007] According to the embodiments disclosed herein, a shrink label can be provided comprising a heat-shrinkable substrate and an outer layer which is an aqueous acrylic ink layer on the substrate, wherein the outer layer comprises an acrylic resin and a curing agent, and the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.1 mL (milliliter) water droplet is 1.0 or less, and the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.01 mL water droplet is 2.5 or less. [Effects of the Invention]

[0008] According to the embodiments disclosed herein, it is possible to provide a shrink label that can suppress the occurrence of ink cracking while also suppressing the occurrence of improper attachment to the container. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of an example of a shrink label according to an embodiment. [Figure 2] This is a schematic plan view of a test specimen used to measure the static and dynamic friction coefficients of a shrink label according to the embodiment. [Figure 3] This is a schematic plan view of the mating material used to measure the static and dynamic friction coefficients of the shrink label in the embodiment. [Figure 4] This is a schematic side view of a tensile testing machine used to measure the static and dynamic friction coefficients of shrink labels in an embodiment. [Figure 5] This is a schematic plan view illustrating the method for measuring the static and dynamic friction coefficients of a shrink label according to an embodiment. [Figure 6]This is a schematic cross-sectional view of the shrink label from Experimental Example 7. [Figure 7] This is a schematic side view of the shrink labels for cylindrical experimental examples 1-7. [Figure 8] This is a schematic perspective view illustrating the ink cracking evaluation method for shrink labels in Experimental Examples 1-7. [Figure 9] This is a photograph of an example of a shrink label from Experimental Examples 1-7 that was evaluated as having ink peeling due to ink cracking. [Figure 10] This is a schematic plan view of an example of a test specimen, with all four sides secured with tape, used to evaluate the blocking resistance of shrink labels in Experimental Examples 1-7. [Figure 11] This is a schematic perspective view of an example of how test specimens were placed on the base used to evaluate the blocking resistance of shrink labels in Experimental Examples 1-7. [Modes for carrying out the invention]

[0010] The embodiments will be described below. In the drawings used to describe the embodiments, the same reference numerals represent the same part or a corresponding part.

[0011] <Shrink label> Figure 1 shows a schematic cross-sectional view of an example of a shrink label according to the embodiment. The shrink label 10 shown in Figure 1 comprises a base material 1 and an outer layer 3b which is an aqueous acrylic ink layer on the base material 1. Between the base material 1 and the outer layer 3b are a color ink layer 2 on the base material 1 and an inner layer 3a on the color ink layer 2.

[0012] <Heat-shrinkable base material> The heat-shrinkable base material 1 (hereinafter referred to as "base material 1") contains a resin capable of supporting at least the outer layer 3b and capable of shrinking when heated. When base material 1 is immersed in 90°C hot water for 10 seconds, the heat shrinkage rate of base material 1 in the main shrinkage direction is, for example, 30% or more, preferably 50% or more.

[0013] As the resin contained in the base material 1, for example, a thermoplastic resin can be used. As the resin contained in the base material 1, for example, polyester (PET)-based resin, polypropylene-based resin, polystyrene (PS)-based resin, or polyethylene-based resin can be used. The base material 1 may, for example, be composed of a single layer containing one or more of the above-mentioned resins, or may be composed of a plurality of layers obtained by laminating a plurality of such single layers.

[0014] <Color ink layer> The color ink layer 2 is a layer formed by drying color ink printed on the base material 1. The color ink layer 2 may, for example, contain different color pigments. By containing different color pigments, a plurality of color ink layers 2 having different colors can be provided in predetermined regions of the base material 1. Accordingly, regions of a single-layer color ink layer 2 and regions of a multi-layer color ink layer 2 formed by overlapping color ink layers 2 can be provided to form a predetermined design or characters. As the one or more color inks printed on the base material 1 and used for forming the color ink layer 2, for example, water-based color inks containing an aqueous solvent such as water or an aqueous alcohol solution (which may be an aqueous dispersion medium in the case of an emulsion, the same applies hereinafter), a resin such as a urethane-based resin, additives, color pigments and the like can be used. From the viewpoints of conformability to heat shrinkage and the effect of preventing ink cracking, the one or more color inks used for forming the color ink layer 2 preferably contain a thermoplastic resin as a resin component, and more preferably contain a urethane-based thermoplastic resin. As the urethane-based resin contained in the one or more color inks used for forming the color ink layer 2, for example, the same urethane-based resin as the urethane-based resin described later that is used for forming the inner layer 3a described later can be used.

[0015] <Inner layer> The inner layer 3a is a layer formed by drying the ink on the color ink layer 2. As the ink used for forming the inner layer 3a, for example, an aqueous ink containing an aqueous solvent such as water or an aqueous alcohol solution, a resin, and a curing agent can be used.

[0016] Examples of resins contained in the ink used for forming the inner layer 3a include acrylic resins, urethane resins, polyester resins, polyamide resins, cellulose resins, vinyl chloride resins, vinyl acetate resins, polyolefin resins (for example, polyethylene resins, polybutadiene resins, etc.), isocyanate resins, rosin resins, polyvinyl alcohol resins (PVA resins), and imine resins. Among these, acrylic resins or urethane resins are preferably used. Further, as the resin contained in the ink used for forming the inner layer 3a, for example, a thermoplastic resin can be used. As the acrylic resin contained in the ink used for forming the inner layer 3a, for example, the same acrylic resin as the acrylic resin described later that is used for forming the outer layer 3b described later can be used.

[0017] As the urethane resin contained in the ink used for forming the inner layer 3a, for example, a resin obtained by reacting a polyisocyanate compound with a polyol compound (that is, a copolymer of a polyisocyanate compound and a polyol compound) can be used.

[0018] As the polyisocyanate compound, for example, one or a mixture of two or more known aromatic, aliphatic, and alicyclic diisocyanates can be used. Examples of the diisocyanates include tolylene diisocyanate, 4,4-diphenylmethane diisocyanate, 1,3-phenylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, 1,5-naphthalene diisocyanate, and isophorone diisocyanate.

[0019] Examples of polyol compounds that can be used include low molecular weight glycols such as ethylene glycol, diethylene glycol, 1,3-propanediol, propylene glycol (1,2-propanediol), butanediol (1,3-butanediol, 1,4-butanediol, etc.), 1,6-hexanediol, and cyclohexanedimethanol; polyether diols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and polytetramethylene glycol-polycaprolactone copolymers; polyester diols obtained from diols such as propylene glycol, butanediol, and hexanediol with dibasic acids such as adipic acid, sebacic acid, azelaic acid, isophthalic acid, terephthalic acid, and fumaric acid; and lactone diols such as polycaprolactone diol, polyvalerolactone diol, and lactone block copolymer diol.

[0020] As the curing agent contained in the ink used to form the inner layer 3a, for example, a curing agent corresponding to the resin contained in the inner layer 3a can be used. For example, if the resin contained in the inner layer 3a has a hydroxyl group or an amino group, an isocyanate-based curing agent can be used. Also, for example, if the resin contained in the inner layer 3a has an amino group or a carbonyl group, an epoxy-based curing agent can be used. Also, for example, if the resin contained in the inner layer 3a has a carbonyl group, a carbodiimide-based curing agent, an aziridine-based curing agent, or a hydrazide-based curing agent can be used. The content ratio of the curing agent can be, for example, 1.5% by weight or more and 15% by weight or less of the total inner layer 3a.

[0021] The inner layer 3a may be a white ink layer, for example, by including a white pigment in the ink used to form the inner layer 3a, or it may be a transparent ink layer (medium) by not including a colored pigment in the ink used to form the inner layer 3a.

[0022] <Outer layer> The outer layer 3b is a layer formed by the drying of the aqueous acrylic ink on the inner layer 3a. As the aqueous acrylic ink used to form the outer layer 3b, for example, an aqueous acrylic ink containing an aqueous solvent, an acrylic resin, and a curing agent can be used, and it is preferable to use an aqueous acrylic emulsion ink in which the acrylic resin is dispersed in the aqueous solvent.

[0023] The acrylic resin contained in the aqueous acrylic ink used to form the outer layer 3b can be, for example, a polymer composed of at least acrylic monomers as monomer components, and it is preferable to use an acrylic thermoplastic resin. The monomer components constituting the above acrylic resin may also include monomer components other than acrylic monomers.

[0024] Examples of acrylic monomers include alkyl esters of (meth)acrylates having linear or branched alkyl groups, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate [preferably C (meth)acrylate]. 1-12 Alkyl esters, etc.; (meth)acrylic acid; carboxyl group-containing (meth)acrylic acid esters such as carboxyethyl acrylate; hydroxyl group-containing (meth)acrylic acid esters such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, diethylene glycol mono(meth)acrylate, dipropylene glycol mono(meth)acrylate [preferably hydroxy C (meth)acrylate] 1-8Examples include monomers having a (meth)acryloyl group (monomers having at least an acryloyl group or a methacryloyl group), such as alkyl esters, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and other cycloalkyl (meth)acrylate esters; (meth)acrylamide derivatives such as N-methylol (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, and N,N-diethyl (meth)acrylamide; and dialkylaminoalkyl (meth)acrylate esters such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dipropylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and dipropylaminopropyl (meth)acrylate. The acrylic monomer may be used alone or in combination of two or more.

[0025] Examples of monomer components constituting acrylic resins other than acrylic monomers include carboxyl group-containing polymerizable unsaturated compounds or their anhydrides such as crotonic acid, itaconic acid, fumaric acid, and maleic acid; styrene compounds such as styrene, vinyltoluene, and α-methylstyrene; vinyl esters such as vinyl acetate and vinyl propionate; vinyl halides such as vinyl chloride; vinyl ethers such as methyl vinyl ether; cyano group-containing vinyl compounds such as (meth)acrylonitrile; ethylene or propylene, etc.

[0026] As the curing agent contained in the water-based acrylic ink used to form the outer layer 3b, the curing agent contained in the ink used to form the inner layer 3a can be used, for example, an epoxy-based curing agent can be used. When a curing agent is contained in the water-based acrylic ink used to form the outer layer 3b, it tends to suppress the occurrence of ink cracking in the outer layer 3b. The content ratio of the curing agent contained in the water-based acrylic ink used to form the outer layer 3b can be set to 1% to 10% by weight of the total outer layer 3b, for example, from the viewpoint of suppressing the occurrence of ink cracking while also suppressing the occurrence of improper attachment to the container.

[0027] The outer layer 3b may be a white ink layer, for example, by including a white pigment in the water-based acrylic ink used to form the outer layer 3b, or it may be a transparent ink layer (medium) by not including a coloring pigment in the water-based acrylic ink used to form the outer layer 3b.

[0028] <Percentage of hardening agent content> It is preferable that the curing agent content of the outer layer 3b be lower than that of the inner layer 3a. This is because, as a result of diligent research by the inventors, it has been found that by making the curing agent content of the outer layer 3b lower than that of the inner layer 3a, it is possible to provide a shrink label 10 that can ensure appropriate water resistance and suppress the occurrence of blocking, even while using water-based acrylic ink in the outer layer 3b. Blocking refers to the phenomenon in which, when shrink labels 10 are wound onto a label roll, the water-based acrylic ink constituting the outer layer 3b of the shrink label 10 is transferred to the base material 1 of another shrink label 10 located directly above or below the shrink label 10, causing the shrink labels 10 located above and below each other to stick together, making it difficult to unwind the shrink labels 10 from the label roll.

[0029] Furthermore, from the viewpoint of suppressing the occurrence of this blocking (blocking prevention), the inventors diligently investigated and found that by making the content ratio of the curing agent in the outer layer 3b lower than that of the curing agent in the inner layer 3a, it was possible to improve the blocking prevention and successfully develop a shrink label 10 with excellent water resistance. The reason for this is not clear, but it is presumed that at least the following 1) and 2) are involved.

[0030] 1) The curing agent in the inner layer 3a improves the water resistance of the outer layer 3b itself, and also penetrates into the color ink layer 2, thereby improving the water resistance of the color ink layer 2. As a result, the water resistance of the entire printed layer, including the color ink layer 2, inner layer 3a, and outer layer 3b, can be improved.

[0031] 2) Because the amount of hardener in the outer layer 3b is not excessive, the blocking prevention properties can be improved.

[0032] The shrink label 10 may be cylindrical. If the shrink label 10 is cylindrical, for example, it can be made cylindrical such that the outer layer 3b is on the inside of the cylinder.

[0033] <How to manufacture labels> The shrink label 10 can be manufactured, for example, as follows. First, a step is taken to form a color ink layer 2 on the substrate 1. This step can be performed, for example, by printing the color ink used to form the color ink layer 2 onto the surface of the substrate 1 using flexographic printing or gravure printing, and then drying the color ink.

[0034] Next, a step is performed to form an inner layer 3a on the color ink layer 2. This step can be performed, for example, by printing the ink used to form the inner layer 3a onto the surface of the color ink layer 2 using flexographic printing or gravure printing, and then drying the ink.

[0035] Next, a step is performed to form the outer layer 3b on the inner layer 3a. This step can be performed, for example, by printing an aqueous acrylic ink used to form the outer layer 3b onto the surface of the inner layer 3a using flexographic printing or gravure printing, and then drying the aqueous acrylic ink. Through the above steps, it is possible to manufacture the shrink label 10.

[0036] <Coefficient of dynamic friction of the outer layer against a polyester surface with 0.1 mL and 0.01 mL water droplets> The coefficient of dynamic friction of the outer layer 3b with respect to the polyester surface of the shrink label 10 with a 0.1 mL water droplet is set to 1.0 or less, and the coefficient of dynamic friction of the outer layer 3b with respect to the polyester surface with a 0.01 mL water droplet is set to 2.5 or less. Generally, the innermost surface of a shrink label that is attached to a container is often provided with an aqueous urethane ink layer, which is made by printing and drying an aqueous urethane ink containing urethane resin and a curing agent in an aqueous solvent. However, when a shrink label with such an aqueous urethane ink layer on its innermost surface is used, poor attachment of the shrink label to the container sometimes occurs.

[0037] As a result of diligent research by the inventors, it was discovered that the occurrence of ink cracking in the shrink label 10 while suppressing the occurrence of improper attachment to the container can be suppressed by making the outer layer 3b constituting the innermost surface on the container attachment side of the shrink label 10 an aqueous acrylic ink layer formed using an aqueous acrylic ink containing an acrylic resin and a curing agent, and by setting the values ​​of the dynamic friction coefficients of the outer layer 3b of the shrink label 10 with respect to a polyester surface with 0.1 mL of water droplets and the dynamic friction coefficients of the outer layer 3b of the shrink label 10 with respect to a polyester surface with 0.01 mL of water droplets, measured using a special measurement method, to 1.0 or less and 2.5 or less, respectively, thereby completing the present invention.

[0038] From the viewpoint of suppressing the occurrence of ink cracking in the shrink label 10 and preventing improper attachment to the container, the coefficient of dynamic friction of the outer layer 3b of the shrink label 10 with respect to a polyester surface having 0.1 mL of water droplets is preferably 0.6 or less, and more preferably 0.1 or more and 0.5 or less.

[0039] From the viewpoint of suppressing the occurrence of ink cracking in the shrink label 10 and preventing improper attachment to the container, the coefficient of dynamic friction of the outer layer 3b of the shrink label 10 with respect to a polyester surface having 0.01 mL of water droplets is preferably 2.5 or less, more preferably 2.0 or less, and even more preferably 0.1 to 1.5.

[0040] <Static friction coefficient of the outer layer against a polyester surface with 0.1 mL and 0.01 mL water droplets>

[0041] From the viewpoint of suppressing the occurrence of ink cracking in the shrink label 10 and suppressing the occurrence of poor mounting to a container, it is preferable that the static friction coefficient of the shrink label 10 at the outer layer 3b against a polyester surface having a 0.1 mL water droplet is 0.6 or less, and more preferably 0.1 or more and 0.5 or less. From the viewpoint of suppressing the occurrence of ink cracking in the shrink label 10 and suppressing the occurrence of poor mounting to a container, it is preferable that the static friction coefficient of the shrink label 10 at the outer layer 3b against a polyester surface having a 0.01 mL water droplet is 0.6 or less, and more preferably 0.1 or more and 0.5 or less.

[0042] <Dynamic friction coefficient of the outer layer against a polyester surface in a dry state with no water droplets (hereinafter referred to as "in DRY condition")> From the viewpoint of suppressing the occurrence of ink cracking in the shrink label 10 and suppressing the occurrence of poor mounting to a container, it is preferable that the dynamic friction coefficient of the shrink label 10 at the outer layer 3b against a polyester surface in DRY condition is 0.6 or less, and more preferably 0.1 or more and 0.5 or less.

[0043] <Static friction coefficient of the outer layer against a polyester surface in DRY condition> From the viewpoint of suppressing the occurrence of ink cracking in the shrink label 10 and suppressing the occurrence of poor mounting to a container, it is preferable that the static friction coefficient of the shrink label 10 at the outer layer 3b against a polyester surface in DRY condition is 0.6 or less, and more preferably 0.1 or more and 0.5 or less.

[0044] <Measurement of static friction coefficient and dynamic friction coefficient> The methods for measuring the static friction coefficient and dynamic friction coefficient of the outer layer against a polyester surface having a 0.1 mL water droplet, and the methods for measuring the static friction coefficient and dynamic friction coefficient of the outer layer against a polyester surface having a 0.01 mL water droplet are as follows.

[0045] First, prepare a rectangular shrink label 10 as shown in the schematic plan view of Figure 2. The width of the rectangular shrink label 10 shown in Figure 2 is 100 mm in the MD (Machine Direction) direction, and the width is 80 mm in the TD (Transverse Direction) direction.

[0046] Furthermore, a polyester film (Toyobo Co., Ltd.'s "E5100", 100 μm thick) having a rectangular untreated polyester surface 11 as shown in the schematic plan view of Figure 3 is prepared. The width of the rectangular polyester film shown in Figure 3 is 300 mm in the MD direction and 100 mm in the TD direction.

[0047] Next, a tensile testing machine 15 is prepared as shown in the schematic side view of Figure 4. The tensile testing machine 15 is a tensile testing machine (AGS-50G) manufactured by Shimadzu Corporation or a similar tensile testing machine capable of similar measurements. The tensile testing machine 15 is equipped with a wire 12, a load cell 13, a horizontally installed test stand 14, and a pulley 16 located above the test stand 14. The test stand 14 is made of a non-magnetic metal to prevent the effects of static electricity. The pulley 16 can rotate smoothly and is installed at a height and position where the wire 12 and the surface of the test stand 14 are parallel.

[0048] Next, as shown in Figure 4, the polyester film is placed on the test stand 14 so that the polyester surface 11 faces upwards and is wrinkle-free. Subsequently, a drop of 0.1 mL or 0.01 mL of tap water is dropped onto the polyester surface 11. Here, the drop is dropped at one location on the polyester surface 11 that corresponds to the center of the shrink label 10 placed on the polyester surface 11.

[0049] Next, a weight 17 is prepared, having a square base measuring 63 mm x 63 mm and a mass of 200 g ± 2 g (1.96 N ± 0.02 N). Then, the top surface of the base material 1 of the shrink label 10 is attached to the base surface of the weight 17 so as not to cause wrinkles in the shrink label 10. Here, the shrink label 10 is attached so that the center of the base surface of the weight 17 is located in the center of the top surface of the base material 1 of the shrink label 10.

[0050] Next, a shrink label 10 is attached to one end of the wire 12 connected to the load cell 13. The wire 12 is not kept taut but with a little slack.

[0051] Next, the shrink label 10 attached to the bottom surface of the weight 17 is gently placed so that the water droplets on the polyester surface 11 are in contact with the center of the surface of the outer layer 3b of the shrink label 10, and the surface of the outer layer 3b is parallel to the surface of the test stand 14.

[0052] Next, as shown in Figure 5, the load cell 13 pulls the wire 12 via the pulley 16 in the direction of arrow 18, parallel to the surface of the test stand 14, at a speed of 100 mm / min over a distance of 85 mm, thereby measuring the static and dynamic friction forces of the outer layer against a polyester surface with a 0.1 mL or 0.01 mL water droplet. Here, the dynamic friction force of the outer layer against a polyester surface with a 0.1 mL or 0.01 mL water droplet is taken as the average value over a distance of 10 mm to 85 mm. Then, the static friction coefficient and dynamic friction coefficient of the outer layer against a polyester surface with a 0.1 mL or 0.01 mL water droplet are calculated from the measured static and dynamic friction forces, respectively. The measurement conditions for the static and dynamic friction forces are based on JIS K 7125:1999. The measurement temperature and humidity for the static and dynamic friction forces are based on JIS K 7100 standard temperature conditions, class 2 (temperature: 23 ± 2°C, relative humidity: 50 ± 10%).

[0053] Furthermore, the static and dynamic friction coefficients of the shrink label 10 of the outer layer 3b with respect to the polyester surface in the dry state were determined in the same manner as described above, except that no water droplets were dropped onto the polyester surface 11. [Examples]

[0054] <Preparation of shrink labels in Experimental Example 1> For Experimental Example 1, a shrink label 10 having the cross-sectional configuration shown in Figure 1 was prepared. First, a color ink layer 2 (0.6 μm thick) was formed by printing a water-based flexographic ink (Hydric FCF series) containing a urethane thermoplastic resin manufactured by Dainichi Seika containing a colored pigment onto one surface of a substrate 1 made of a 40 μm thick multilayer shrink film (surface layer: PET resin / core layer: PS resin / back layer: PET resin, manufactured by Gunze Corporation), and then drying it twice.

[0055] Next, an inner layer 3a consisting of a white aqueous urethane ink layer was formed by printing an aqueous urethane ink containing an aqueous solvent, a urethane resin, an isocyanate-based curing agent, and a white coloring pigment onto the color ink layer 2, and then drying it. In Experimental Example 1, the content of the isocyanate-based curing agent used to form the inner layer 3a was 5% by weight of the total inner layer 3a after drying of the aqueous urethane ink for forming the inner layer 3a.

[0056] Next, an aqueous urethane ink for forming the outer layer 3b, containing an aqueous solvent, a urethane resin, an isocyanate-based curing agent, and a white coloring pigment, was printed onto the inner layer 3a and then dried to form the outer layer 3b, which consists of a white aqueous urethane ink layer. In Experimental Example 1, the content of the isocyanate-based curing agent used to form the outer layer 3b was 2% by weight of the total outer layer 3b after drying of the aqueous urethane ink for forming the outer layer 3b. Through the above steps, the shrink label 10 of Experimental Example 1 was produced.

[0057] <Preparation of shrink labels in Experimental Example 2> The shrink label 10 of Experimental Example 2 was prepared using the same method and conditions as in Experimental Example 1, except that an outer layer 3b consisting of a white aqueous acrylic ink layer was formed by printing and then drying an aqueous acrylic ink containing an aqueous solvent, an acrylic resin, an epoxy curing agent, and a white coloring pigment. In Experimental Example 2, the content of the epoxy curing agent used to form the outer layer 3b was 2% by weight of the total outer layer 3b after drying of the aqueous acrylic ink used to form the outer layer 3b.

[0058] <Preparation of shrink labels in Experimental Example 3> The shrink label 10 of Experimental Example 3 was prepared using the same method and conditions as in Experimental Example 2, except that an inner layer 3a consisting of a white aqueous acrylic ink layer was formed by printing and then drying an aqueous acrylic ink containing an aqueous solvent, an acrylic resin, an epoxy curing agent, and a white coloring pigment. In Experimental Example 3, the content of the epoxy curing agent used to form the inner layer 3a was 3% by weight of the total inner layer 3a after drying of the aqueous acrylic ink used to form the inner layer 3a.

[0059] <Preparation of shrink labels in Experimental Example 4> The shrink label 10 of Experimental Example 4 was prepared using the same method and conditions as in Experimental Example 3, except that the epoxy-based curing agent used to form the inner layer 3a was set to 2% by weight of the total inner layer 3a after drying of the aqueous acrylic ink used to form the inner layer 3a, and the epoxy-based curing agent used to form the outer layer 3b was set to 3% by weight of the total outer layer 3b after drying of the aqueous acrylic ink used to form the outer layer 3b.

[0060] <Preparation of shrink labels in Experimental Example 5> The shrink label 10 of Experimental Example 5 was prepared using the same method and conditions as in Experimental Example 4, except that neither the water-based acrylic ink for forming the inner layer 3a nor the water-based acrylic ink for forming the outer layer 3b contained a curing agent.

[0061] <Preparation of shrink labels in Experimental Example 6> The shrink label 10 of Experimental Example 6 was prepared using the same method and conditions as in Experimental Example 1, except that the water-based urethane ink for forming the inner layer 3a did not contain a curing agent or a white coloring pigment, and an water-based acrylic ink containing a water-based solvent, an acrylic resin, and an epoxy curing agent was printed and then dried to form an outer layer 3b consisting of a transparent water-based acrylic ink layer, and the content of the epoxy curing agent used to form the outer layer 3b was set to 6% by weight of the total outer layer 3b after drying of the water-based acrylic ink for forming the outer layer 3b.

[0062] <Preparation of shrink labels in Experimental Example 7> The shrink label 10 of Experimental Example 7, having the cross-sectional configuration shown in Figure 6, was fabricated using the same method and under the same conditions as Experimental Example 6, except that the inner layer 3a was not formed. Note that the shrink labels 10 of Experimental Examples 2-4 and 6-7 are examples, while the shrink labels 10 of Experimental Examples 1 and 5 are comparative examples.

[0063] <Measurement of static and kinetic friction coefficients of shrink labels in Experimental Examples 1-7> The static and dynamic friction coefficients of the outer layer of the shrink labels in Experimental Examples 1-7 were measured against a polyester surface with a 0.1 mL water droplet, and against a polyester surface with a 0.01 mL water droplet, using the method described in the section "<Measurement of Static and Dynamic Friction Coefficients>" above. The results are shown in Table 1. In addition, the static and dynamic friction coefficients of the shrink labels in Experimental Examples 1-7 in their dry state were measured using the same method and conditions as described in the section "<Measurement of Static and Dynamic Friction Coefficients>" above, except that no water droplet was added. The results are shown in Table 1.

[0064] <Method for evaluating ink cracking of shrink labels in experimental examples 1-7> First, each of the shrink labels 10 from Experimental Examples 1 to 7 was cut to a length of 90 mm or more, and then wound up so that the outer layer 3b of the shrink label 10 was on the inside of the tube, as shown in the schematic side view of Figure 7. Next, using a bonding base, one end of each of the cut shrink labels 10 from Experimental Examples 1 to 7 was bonded together at the bonding portion 21 so that a predetermined length of inner waste portion 23 protruded, thereby forming each of the shrink labels 10 from Experimental Examples 1 to 7 into a tube with a folded diameter of 100 mm.

[0065] Next, a 225 mL bottle container 30 with no surface scratches and a strip-shaped spacer 31 were prepared, as shown in the schematic perspective view of Figure 8. The strip-shaped spacer 31 was a film with the same configuration as the shrink labels 10 of Experimental Examples 1 to 7, except that it was transparent without the use of coloring pigments. Three strips of film with no burrs on the cut ends were prepared for each of Experimental Examples 1 to 7, with a width of 8 mm in the TD direction and a width of 90 mm or more in the MD direction.

[0066] Next, as shown in Figure 8, for each test of the shrink label 10 in Experimental Examples 1 to 7, three spacers 31 corresponding to the test were attached to the outer surface of the bottle container 30 at predetermined intervals from each other. Subsequently, as shown in Figure 8, each of the cylindrical shrink labels 10 of Experimental Examples 1 to 7, prepared as described above, was placed over the outer surface of the bottle container 30 so as to cover the three spacers 31, and then immersed in 90°C hot water. The spacers 31 were attached at positions that were equally spaced from each other, avoiding the adhesive joints 21 of each of the cylindrical shrink labels 10 in Experimental Examples 1 to 7.

[0067] Next, hot water was poured into the bottle container 30, and it was then immersed in the hot water for another 20 seconds, followed by immersion in cold water for 5 seconds, before the bottle container 30 was removed. The bottle container 30 was then left to cool to room temperature, and after it had dried, the ink cracking was evaluated according to the following criteria. The results are shown in Table 1.

[0068] <Ink cracking evaluation criteria> A... No ink peeling occurred as shown in Figure 9. B...Ink peeling occurred as shown in Figure 9.

[0069] When the ink cracking evaluation criterion was A or higher, it was evaluated that the occurrence of ink cracking in the outer layer 2b of the shrink label was suppressed.

[0070] <Method for evaluating the blocking prevention properties of shrink labels in Experimental Examples 1-7> First, each of the shrink labels from Experimental Examples 1 to 7 was cut into a square measuring 50 mm in length and 50 mm in width to create test specimens of each of the shrink labels from Experimental Examples 1 to 7 (hereinafter referred to as "test specimens from Experimental Examples 1 to 7"). Next, each of the test specimens from Experimental Examples 1 to 7 was stacked in the order of paper-(test specimen-test specimen)-paper-(test specimen-test specimen)-paper-(test specimen-test specimen)-paper... Here, the stacking of (test specimen-test specimen) was done by stacking them in the order of (front / back (front surface of outer layer 3b)) and (back / back), so that these surfaces were in contact with each other, and this was repeated three times.

[0071] Next, as shown in the schematic plan view of Figure 10, the four sides of the stacked test specimens 41 were secured with tape 40 to prevent any shifting of the stacked state as described above. Here, the tape 40 was placed in a position where it would not be stepped on by the weight that would be placed on the test specimen 41, as described later. Next, as shown in the schematic perspective view of Figure 11, a base 51 having a convex part (cylindrical shape with a diameter of 35 mm) was prepared, and the test specimen 41 was placed on the convex part of the base 51. Next, a pressure of 20 kg was applied to the test specimen 41, and it was left for 24 hours in an environment with a temperature of 25°C and a humidity of 92%. After that, the blocking prevention performance of each test specimen from Experimental Examples 1 to 7 was evaluated according to the following criteria. The results are shown in Table 1.

[0072] <Evaluation Criteria for Blocking Prevention> A: No contact between test specimens B: There is some adhesion between the test pieces (resistance is felt when separating the test pieces, or a peeling sound is heard). C: The test specimens are in complete contact with each other. Ink peeling (transfer) is present.

[0073] A shrink label was evaluated as being able to suppress the occurrence of blocking if its blocking prevention performance was rated B or higher.

[0074] <Evaluation method for label application suitability of shrink labels in experimental examples 1-7> The label application suitability of each shrink label 10 in Experimental Example 1 was evaluated using the LSA9000 series labeling machine manufactured by FujiaStec Co., Ltd., according to the following evaluation criteria. The results are shown in Table 1. The label application suitability was evaluated by continuously applying labels to 500 PET containers, and the surface of the PET containers was moistened with water droplets during application.

[0075] <Evaluation Criteria for Label Application Suitability> A: Label misalignment defect rate is 1.5% or less. B: Label misalignment defect rate: 1.6%~3.0% C: Label misalignment / attachment defect rate of 3.1% or more

[0076] When the label application suitability evaluation criterion was B or higher, it was evaluated that the occurrence of improper application of shrink labels to containers was suppressed.

[0077] [Table 1]

[0078] As shown in Table 1, the shrink labels 10 of Experimental Examples 2-4 and 6-7, which are examples that have an outer layer 3b which is an aqueous acrylic ink layer containing an acrylic resin and a curing agent on a substrate 1, were able to suppress the occurrence of ink cracking of the outer layer 3b. However, the shrink label 10 of Experimental Example 5, which is a comparative example in which the outer layer 3b does not contain a curing agent, was not able to suppress the occurrence of ink cracking of the outer layer 3b.

[0079] Furthermore, as shown in Table 1, the shrink labels of Experimental Examples 2-4 and 6-7, which are examples equipped with an outer layer 3b that is an aqueous acrylic ink layer containing an acrylic resin and a curing agent on a base material 1, were able to suppress the occurrence of improper attachment to the container. However, the shrink label of Comparative Example 1, which is a comparative example equipped with an outer layer 3b that is an aqueous urethane ink layer containing a urethane resin and a curing agent on a base material 1, was unable to suppress the occurrence of improper attachment to the container.

[0080] Furthermore, as shown in Table 1, the shrink label of Experimental Example 2, which has an inner layer 3a consisting of an aqueous urethane ink layer on a substrate 1 and an outer layer 3b consisting of an aqueous acrylic ink layer on the inner layer 3a, was able to suppress the occurrence of blocking more effectively than the shrink labels of Experimental Examples 3 and 4, in which the inner layer 3a consists of an aqueous acrylic ink layer.

[0081] As described above, the embodiments and experimental examples have been explained, but it was also planned from the outset that the configurations of each of the embodiments and experimental examples described above could be combined as appropriate.

[0082] The embodiments and experimental examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0083] 1 Substrate, 2 Color ink layer, 3a Inner layer, 3b Outer layer, 10 Shrink label, 11 Polyester surface, 12 Wire, 13 Load cell, 14 Test stand, 15 Tensile testing machine, 16 Pulley, 17, 52, 53 Weights, 18 Arrow, 21 Bonding section, 23 Inner waste section, 30 Bottle container, 31 Spacer, 40 Tape, 41 Test specimen, 51 Base.

Claims

1. A heat-shrinkable base material, The substrate comprises an outer layer which is an aqueous acrylic ink layer, The outer layer comprises an acrylic resin and a curing agent. A shrink label wherein the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.1 mL water droplet is 1.0 or less, and the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.01 mL water droplet is 2.5 or less, The shrink label further includes a color ink layer between the substrate and the outer layer, The aforementioned color ink layer is a shrink label containing a urethane-based resin.

2. A heat-shrinkable base material, The substrate comprises an outer layer which is an aqueous acrylic ink layer, The outer layer comprises an acrylic resin and a curing agent. A shrink label wherein the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.1 mL water droplet is 1.0 or less, and the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.01 mL water droplet is 2.5 or less, The shrink label further includes an inner layer between the substrate and the outer layer, The inner layer comprises a resin and a curing agent. A shrink label in which the resin of the inner layer is an acrylic resin or a urethane resin.

3. A heat-shrinkable base material, The substrate comprises an outer layer which is an aqueous acrylic ink layer, The outer layer comprises an acrylic resin and a curing agent. A shrink label wherein the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.1 mL water droplet is 1.0 or less, and the coefficient of dynamic friction of the outer layer against a polyester surface with a 0.01 mL water droplet is 2.5 or less, The shrink label further includes an inner layer and a color ink layer between the substrate and the outer layer. The inner layer comprises a resin and a curing agent. The resin of the inner layer is an acrylic resin or a urethane resin. The aforementioned color ink layer is a shrink label containing a urethane-based resin.

4. The shrink label according to claim 2 or 3, wherein the content ratio of the curing agent in the outer layer is smaller than the content ratio of the curing agent in the inner layer.

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