Target substance sensing sheet

Abstract

To provide a target substance sensing sheet with improved safety.SOLUTION: A target substance sensing sheet 20 has a first adhesive layer 5a containing an indicator that changes color in the presence of a target substance. The indicator is at least one selected from substances approved as food additives in Japan and substances extracted from food that are not approved as food additives. The indicator used may be at least one selected from the group including at least one polyphenol compound and at least one quinone dye.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a detection target substance sensing sheet with improved safety. [Background technology]

[0002] Nitrogen-containing foods such as meat and fish spoil relatively easily and often cause serious food poisoning. However, consumers who purchase these foods often store them in the refrigerator before cooking them. For this reason, there is a strong need to know the freshness of food without opening the package.

[0003] Japanese Patent Laid-Open Publication No. 2021-43067 (Patent Document 1) discloses a gas sensor (target substance sensing sheet) that includes an adhesive layer containing an indicator that changes color in the presence of a substance to be detected, and a first substrate provided on one side of the adhesive layer. This target substance sensing sheet changes color upon detecting gases such as ammonia, allowing the freshness of food to be visually confirmed without opening the package. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-43067 Summary of the Invention [Problem to be solved by the invention]

[0005] The gas sensor described in Patent Document 1 lists indicators that can be used, but some of these, such as bromocresol purple (BCP), are skin irritants. In this target substance sensing sheet, the adhesive layer containing the indicator is covered by the first substrate, so it is unlikely to come into direct contact with food. However, it is desirable that even the parts that do not come into contact with food be made of highly safe materials.

[0006] When using the target substance sensing sheet, there is a possibility that the adhesive layer containing the indicator may come into contact with the fingers. Although the target substance sensing sheet can be used for purposes other than sensing the freshness of food, there is a common problem of it coming into contact with the skin during use, and therefore, there is a demand for improving the safety of the constituent materials regardless of the purpose.

[0007] An object of the present invention is to provide a target substance sensing sheet with improved safety. [Means for solving the problem]

[0008] One example of a target substance sensing sheet disclosed in the present specification comprises an adhesive layer containing an indicator that changes color in the presence of a target substance, the indicator being at least one selected from substances approved as food additives in Japan and substances extracted from food that are not approved as food additives. [Effects of the Invention]

[0009] The target substance sensing sheet disclosed in this specification is provided with an adhesive layer containing at least one indicator selected from substances approved as food additives in Japan, making it safer than conventional target substance sensing sheets. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing a target substance sensing sheet according to a first embodiment disclosed in this specification. [Figure 2] FIG. 2 is a plan view of only the printed layer 15a of the target substance sensing sheet according to the first embodiment, as viewed from the outside of the packaging material 10. [Figure 3] FIG. 3 is a cross-sectional view showing a target substance sensing sheet according to the second embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing a target substance sensing sheet according to the third embodiment. [Figure 5]FIG. 5(a) is a cross-sectional view showing a target substance sensing sheet according to a fourth embodiment, and FIG. 5(b) is a diagram showing an example of how to use the target substance sensing sheet shown in (a). DETAILED DESCRIPTION OF THE INVENTION

[0011] (First embodiment) Fig. 1 is a cross-sectional view showing a target substance sensing sheet according to a first embodiment disclosed in this specification, and Fig. 2 is a plan view showing only the printed layer 15a of the target substance sensing sheet according to the first embodiment as viewed from the outside of the packaging material 10. Here, as an example of a target substance sensing sheet according to the present disclosure, a sheet (label) that senses the freshness of food through a color change caused by a substance to be detected will be described.

[0012] As shown in FIG. 1 , the target substance sensing sheet 20 of this embodiment comprises a first substrate 7a that is permeable to the target gas, a first adhesive layer 5a provided in contact with one side of the first substrate 7a, a sheet-like second substrate 3 provided on the side of the first adhesive layer 5a opposite the first substrate 7a, and a second adhesive layer 1 provided on the side of the second substrate 3 opposite the first adhesive layer 5a. Before use of the target substance sensing sheet 20, a resin film or paper release liner may be provided on the side of the second adhesive layer 1 opposite the second substrate 3. The second substrate 3 may be made of a transparent or translucent material so that the color of the first adhesive layer 5a can be visually recognized by consumers, and transparent materials are preferably used.

[0013] At least one surface of the second substrate 3 may be provided with a printed layer 15a, which includes a printed portion 16a made of color ink or the like and a window region 19a where the printed portion 16a is not provided. FIG. 1 illustrates an example in which the printed layer 15a is formed on the first adhesive layer 5a side of the second substrate 3. The printed layer 15a may also be provided on at least one surface of the first substrate 7a, as long as it does not prevent the gas to be detected from reaching the first adhesive layer 5a. The ink constituting the printed portion 16a may be any material that does not dissolve in water at least after hardening and drying. However, inks containing substances approved as food coloring additives or substances extracted from food as their main component are preferred. For example, the printed portion 16a made of edible ink can be easily formed using a commercially available food printer, such as the SO-KEN Food Printer FL200.

[0014] The first adhesive layer 5a contains an indicator that changes color in the presence of a detection target substance. The detection target substance is not particularly limited as long as it is a substance that serves as an indicator of food freshness, but it may be, for example, one selected from ammonia and amines, hydrogen sulfide, and carbon dioxide, the concentration of which changes due to the proliferation of aerobic bacteria, or a mixture of two or more selected from these. These detection target substances are gaseous at room temperature and normal pressure. When at least one of ammonia and amines is used as the detection target substance, their aqueous solutions are weakly basic, so a pH indicator, as described below, can be used as the indicator. When the food 13 is a protein-based food such as meat or fish, a large amount of ammonia and amines is produced as the food spoils. Therefore, the color change range of the indicator used should be, for example, within a pH range of 3 to 10.

[0015] The target substance sensing sheet 20 of this embodiment uses as an indicator at least one selected from substances approved as food additives in Japan and substances extracted from food that are not approved as food additives. Food additives approved under the Food Sanitation Act include designated food additives designated by the Minister of Health, Labour and Welfare after safety evaluation, existing food additives approved for use based on a long history of use, and general food and beverage additives that are commonly consumed and used as additives. Among these food additives, substances that change color in the presence of the target substance are used in the target substance sensing sheet 20 of this embodiment.

[0016] Food additives that can be used as indicators include, for example, at least one selected from the group consisting of at least one polyphenol compound and at least one quinone dye. Examples of polyphenol compounds include anthocyanin dyes such as red cabbage dye, purple sweet potato dye, grape skin dye, grape juice dye, elderberry dye, purple corn dye, perilla dye, red radish dye, and butterfly pea dye, as well as extracts containing chlorogenic acid such as enzymatically hydrolyzed apple extract, green coffee bean extract, and sunflower seed extract, persimmon tannin, tannic acid, tea extract, and turmeric dye (curcumin). Examples of quinone dyes include cochineal dye (carminic acid) and lac dye.

[0017] Although the color tone varies slightly depending on the type, anthocyanin pigments tend to change color continuously over a pH range of at least 3 to 10, from red to reddish purple (near pH 3), purple (near pH 7), blue (near pH 9), and yellow-green (strong alkaline). This makes them ideal for detecting ammonia and amines, which exhibit weak alkaline properties in the presence of moisture. Anthocyanin pigments are water-soluble but also soluble in ethanol and methanol. By dissolving them in these alcohols and adding them to a solvent-based adhesive and stirring, they can be dispersed in the adhesive layer, similar to the case of emulsion adhesives. Among anthocyanin pigments, purple sweet potato pigments have relatively high stability in alkaline environments, enabling the creation of target substance-sensing sheets with excellent long-term stability.

[0018] Turmeric pigment is yellow in acidic conditions and turns reddish-brown in neutral to alkaline conditions. It is relatively stable to heat. Turmeric pigment also changes color within the pH range of 3 to 10, so it can be used to detect ammonia and amines to determine the freshness and spoilage of meat and fish. Adding turmeric pigment can also impart bacteriostatic properties to the adhesive layer.

[0019] Many food-derived pigments, such as anthocyanin pigments, used as food additives, are stable under acidic conditions (e.g., pH 3.5 or less), but their stability decreases under alkaline conditions. Therefore, when preparing the first adhesive layer 5a, using an alcoholic solution of an indicator adjusted to a weak acidity, for example, pH 3.0 to 5.0, can prevent discoloration due to light or heat. By preparing the first adhesive layer 5a to exhibit a weak acidity in the presence of moisture, a change in color tone can be reliably confirmed when detecting ammonia or the like. Furthermore, if an unused target substance-sensing sheet 20 is not stored in a sealed state, it may become weakly acidic in the presence of moisture due to carbon dioxide in the air. However, by preparing the first adhesive layer 5a from the beginning to be weakly acidic in the presence of moisture, discoloration during product storage can be reduced.

[0020] In addition to the food additive that serves as the indicator, the first adhesive layer 5a may contain additives that promote color development or stabilize the components. For example, when using green coffee bean extract containing chlorogenic acid as an indicator, glycine, which is approved as a food additive, may be used as an additive. In the presence of glycine, chlorogenic acid contained in green coffee bean extract becomes colorless at pH 2 to 6 and yellow-green at pH 7 to 9, and the color deepens as the pH increases. Therefore, green coffee bean extract can also be used to detect the freshness and spoilage of meat and fish. The turmeric pigment and green coffee extract described above can be dissolved in acetone as well as methanol and ethanol, and tannic acid can also be dissolved in methyl ethyl ketone (MEK), making them easy to mix and disperse with solvent-based adhesives. Turmeric pigment can also be dissolved in ethyl acetate and toluene.

[0021] As described above, the first adhesive layer 5a contains at least one indicator selected from substances approved as food additives and substances extracted from food that are not approved as food additives, so that even if the indicator leaches into the food container, the possibility of it compromising food safety is reduced.

[0022] The adhesive for forming the first adhesive layer 5a may be an emulsion adhesive or a solvent-based adhesive, and these adhesives preferably comply with the positive list system of the Food Sanitation Act, which came into effect on June 1, 2020.

[0023] As the emulsion adhesive, a commercially available acrylic adhesive in which water and adhesive components are dispersed can be used. Since many food additives serving as indicators are easily soluble in water, adding an aqueous solution of the indicator to the emulsion adhesive makes it easier to disperse the indicator in the adhesive layer. As the solvent-based adhesive, for example, known rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, polyester-based adhesives, etc. can be used. The adhesive may be a heat-curable or ultraviolet (UV)-curable type. Since food 13 is often stored in a cold place such as a refrigerator, it is preferable that the adhesive used maintains adhesive strength after curing at least at 0°C to 10°C or below to a degree that prevents peeling from second substrate 3 on which printed layer 15a is provided.

[0024] Furthermore, the first pressure-sensitive adhesive layer 5a may contain 10% by mass or more of a plant-derived component as a countermeasure against environmental issues. If an acrylic pressure-sensitive adhesive is used, a plant-derived rosin-based or terpene-based tackifier may be included. If a urethane-based or polyester-based pressure-sensitive adhesive is used, the material to be polymerized may contain a plant-derived component, and if a rubber-based pressure-sensitive adhesive is used, it may contain natural rubber. The biomass content of the first pressure-sensitive adhesive layer 5a may be, for example, 10% or more.

[0025] The concentration of the indicator in the first pressure-sensitive adhesive layer 5a varies depending on the indicator used, but may be, for example, 2% by mass to 80% by mass, or 20% by mass to 60% by mass. If the indicator concentration is too low, the sensitivity to the detection target substance decreases, making detection difficult, while if the indicator concentration is too high, the indicator may easily bleed out from the first pressure-sensitive adhesive layer 5a, or the cohesive strength and adhesive strength of the first pressure-sensitive adhesive layer 5a may decrease.

[0026] The thickness of the first adhesive layer 5a is not particularly limited, but may be, for example, 1 μm to 100 μm, or 10 μm to 30 μm. If the first adhesive layer 5a is too thin, it is difficult to form the layer, and if the first adhesive layer 5a is too thick, it takes a long time to form the layer, increasing production costs. Furthermore, if the thickness of the first adhesive layer 5a is 10 μm or more, the color change is easily visible, making it easier to ensure sufficient sensitivity for practical use to the substance to be detected.

[0027] The above-mentioned first base material 7a is provided for the purpose of protecting the first adhesive layer 5a from direct contact with the food 13. If the first adhesive layer 5a comes into direct contact with the food 13 and the indicator migrates to the food 13, it will be difficult for consumers to distinguish the original color of the food 13. Therefore, when the target substance-sensing sheet 20 is used by being attached to the inside of the packaging material 10, it is preferable that the first base material 7a be provided.

[0028] The first substrate 7a is made of a material that exhibits excellent permeability to gaseous target substances. Examples of materials that can be used include resin films such as polyethylene (PE) film, polypropylene (PP) film, polyurethane (PU) film, and polystyrene (PS) film, as well as laminates thereof, nonwoven fabrics, and paper. Among these, PE film, PP film, PU film, and PS film allow permeation of gaseous target substances while substantially blocking the passage of liquids. Therefore, when used as the material for the first substrate 7a, the indicator in the first adhesive layer 5a can be prevented from leaching into the food container. The thickness of the first substrate 7a may be within a range that allows permeation of gaseous target substances and ensures waterproofing. However, the thinner the thickness, the easier it is for the target substances to pass through. For example, if the first base material 7a is made of PE, PP, or PU, a film thickness of 100 μm or less makes it easier to detect changes in food freshness, 50 μm or less makes it even easier to detect changes in food freshness, and 10 μm or less makes it easier to detect changes in food freshness more quickly and sensitively.

[0029] The first substrate 7a may be made of a material that complies with the positive list system of the Food Sanitation Act. With this configuration, it has been confirmed that harmful substances such as constituent monomers of resins do not leach out from the first substrate 7a, so when the target substance-sensing sheet 20 is attached to the inside of the packaging material 10, it is guaranteed that the food will not be contaminated with harmful substances.

[0030] When the strength of the first base material 7a is low, a protective material (not shown) may be provided to cover the surface of the first base material 7a opposite to the first pressure-sensitive adhesive layer 5a.

[0031] The color of the first substrate 7a is not particularly limited as long as it transmits the detection target substance and allows the color of the first adhesive layer 5a to be visible. For example, by making the first substrate 7a white, the color of the first adhesive layer 5a can be easily seen from the outside of the packaging material 10. For example, by adding white titanium oxide, which is approved as a food additive, to the first substrate 7a, the first substrate 7a can be made white while the target substance-sensing sheet 20 complies with the regulations of the Food Sanitation Act.

[0032] As described above, the second substrate 3 may be made of a transparent or translucent resin material or the like, as long as it is made of a material that allows the printing layer 15a to be formed on one side, and its thickness is not particularly limited. Like the first substrate 7a, the second substrate 3 is preferably made of a material that complies with the Positive List System of the Food Sanitation Act, as this reduces the possibility of food contamination. Examples of materials that can be used to make the second substrate 3 include polyester resins such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyurethane (PU).

[0033] 2, the printed layer 15a may display information such as a color sample 21 of the first adhesive layer 5a from before discoloration to after discoloration, and a food freshness assessment guide 23. The display of this information makes it easier for consumers to assess the freshness of food when purchasing it. The formation of the window region 19a described above in the printed layer 15a allows consumers to see the color of the first adhesive layer 5a even when the target substance-sensing sheet 20 is attached to the inside of the packaging material 10.

[0034] The second adhesive layer 1 is formed of, for example, a cured product of a known solvent-based adhesive or emulsion adhesive. Examples of solvent-based adhesives that can be used include known rubber-based adhesives, acrylic-based adhesives, silicone-based adhesives, urethane-based adhesives, and polyester-based adhesives. The adhesive may be a thermosetting type or an ultraviolet (UV)-curing type. The thickness of the second adhesive layer 1 is not particularly limited as long as it has sufficient adhesive strength to prevent the layer from falling off the packaging material 10.

[0035] As shown in Figure 1, the target substance sensing sheet 20 can be attached to the inside of a transparent packaging material 10 (such as plastic wrap) that encases a container containing food 13. With this configuration, the target substance sensing sheet 20 of this embodiment can visually detect, via the first adhesive layer 5a, gas that is generated from the food 13 as it spoils and that has permeated the first base material 7a. This allows consumers to visually check the freshness of the food without opening the packaging, eliminating the need to discard food that is close to its expiration date but is still edible.

[0036] The packaging material 10 may be formed of a transparent material, such as a wrap film made of polyvinyl chloride or polymethylpentene, or various laminated films, so long as the color of the first adhesive layer 5a can be seen from the outside. The target substance sensing sheet 20 can be used even if the packaging material 10 has high gas barrier properties. Therefore, for example, by combining it with a packaging material 10 that aims to extend the shelf life of food, the occurrence of food waste can be effectively reduced. The target substance sensing sheet 20 may be such that the color of the indicator reversibly changes in response to the presence of the detection target substance. In this case, the target substance sensing sheet 20 can be reused multiple times.

[0037] As described above, in the target substance sensing sheet 20 of this embodiment, at least one substance selected from substances approved as food additives or substances extracted from foods that are not approved as food additives is contained as an indicator in the first adhesive layer 5a, thereby improving safety compared to using an indicator that is corrosive or irritating to the skin. Therefore, the safety of the food 13 can be ensured even when the target substance sensing sheet 20 is attached to any position that may come into contact with the food.

[0038] Furthermore, when the first substrate 7a, the first adhesive layer 5a, the printed portion 16a, the second substrate 3 and the second adhesive layer 1 are each made of materials that comply with the positive list system of the Food Sanitation Act, the risk of harmful substances transferring to the food 13 can be extremely reduced even when the target substance sensing sheet 20 is attached to a location where it may come into contact with the food 13.

[0039] Furthermore, it is preferable that the target substance sensing sheet 20 as a whole conforms to the standards for foods, additives, etc. set forth in the Food Sanitation Act (Ministry of Health and Welfare Notification No. 370 of 1959, and Ministry of Health, Labour and Welfare Notification No. 381 of December 4, 2020, as amended).

[0040] The planar size of the target substance sensing sheet 20 is not particularly limited, but it should be about 1 / 100 to 2 / 3 of the area of ​​the container package in which the food 13 is sealed by the packaging material 10 (i.e., the area where the food can be seen by the consumer) and should not exceed 1 cm. 2 If the area of ​​the target substance sensing sheet 20 is within this range, the color change of the first adhesive layer 5a will be easily visible, and the consumer will be able to easily check the condition and color of the food 13 itself. When a window region 19a is formed in the printing layer 15a, the area of ​​the window region 19a is not particularly limited, but may be, for example, 0.5 cm 2 If this is the case, the color change of the first pressure-sensitive adhesive layer 5a can be easily recognized visually.

[0041] Anthocyanin pigments have the property of absorbing ultraviolet rays, which is one of the causes of food deterioration. Therefore, when anthocyanin pigments are used as indicators, the deterioration of the food 13 due to ultraviolet rays can be reduced by making the area of ​​the target substance sensing sheet 20 as large as possible.

[0042] -Method of manufacturing target substance sensing sheet- First, a coating solution is prepared by adding a solution of an indicator dissolved in a solvent such as water or ethanol to a pressure-sensitive adhesive composition containing a pressure-sensitive adhesive and a curing agent, and mixing the resulting solution. This coating solution is applied to the release surface of a known release liner (not shown) using a known comma-type coater or similar to a predetermined thickness, and then dried and cured to form a first pressure-sensitive adhesive layer 5a. Next, a transparent first substrate 7a made of PE, PU, ​​or similar is bonded to the first pressure-sensitive adhesive layer 5a on the release liner, producing a gas-sensing laminate sheet 18 (see FIG. 1) comprising the first pressure-sensitive adhesive layer 5a and the first substrate 7a.

[0043] Next, a coating liquid prepared by mixing an adhesive and a curing agent is applied to the release surface of a known release liner using a known comma-type coater or the like to a predetermined film thickness, and then dried and cured to produce second adhesive layer 1. Next, a second substrate 3 having a printing layer 15a printed on one surface is bonded to the second adhesive layer 1 to produce a label body 22 having the second substrate 3 and the second adhesive layer 1. The printing layer 15a may be formed using a known food printer.

[0044] Next, the surface of the label body 22 opposite the second adhesive layer 1 is bonded to the first adhesive layer 5a of the gas-sensing laminate sheet 18 to produce a roll-shaped target substance sensing sheet 20. The target substance sensing sheet 20 is then slit and cut, and punched as necessary to form a sheet of a predetermined size and shape.

[0045] The method for manufacturing the target substance sensing sheet 20 is not limited to the above-mentioned method. For example, instead of the above-mentioned method, a substrate-less target substance sensing sheet having, from the bottom, a first release liner, a first adhesive layer 5a containing an indicator, and a second release liner may be formed, and then this sheet may be bonded to the first substrate 7a to form the gas-sensing laminate sheet 18. Alternatively, the production of the gas-sensing laminate sheet 18 and the bonding of the label body 22 may be carried out continuously on the same line.

[0046] (Second embodiment) FIG. 3 is a cross-sectional view showing a target substance sensing sheet according to a second embodiment disclosed herein. As shown in the figure, a target substance sensing sheet 30 according to this embodiment includes a first substrate 7b and a first adhesive layer 5b provided in contact with one surface of the first substrate 7b. A printed layer 15b including a printed section 16b made of color ink or the like and having a window region 19b may be provided on at least one surface of the first substrate 7b. Like the first adhesive layer 5a of the target substance sensing sheet 20 according to the first embodiment, the first adhesive layer 5b is formed from a cured product of a solvent-based adhesive composition or an emulsion adhesive composition, and contains at least one substance selected from substances approved as food additives and substances extracted from foods that are not approved as food additives.

[0047] The target substance sensing sheet 30 of this embodiment differs from the target substance sensing sheet 20 of the first embodiment in that it does not have a second substrate 3 and a second adhesive layer 1, but rather has a first adhesive layer 5b containing an indicator attached directly to the inside (food 13 side) of the packaging material 10. The constituent materials and film thicknesses of the first adhesive layer 5b, first substrate 7b, and printed portion 16b are the same as those of the target substance sensing sheet 20 of the first embodiment.

[0048] According to the target substance sensing sheet 30 of this embodiment, the film structure is simpler than that of the target substance sensing sheet 20 of the first embodiment, and the first adhesive layer 5b containing the indicator can be directly attached to the packaging material 10, making it possible to further reduce manufacturing costs.

[0049] The concentration of the indicator in the first adhesive layer 5b varies depending on the indicator used, but may be, for example, 2% by mass to 80% by mass, or 20% by mass to 60% by mass. By setting the indicator concentration within this range, it is possible to reduce bleed-out of the indicator while ensuring sufficient sensitivity to the detection target substance, and to maintain cohesive strength and adhesive strength within appropriate ranges. Here, the upper limit of the indicator concentration contained in the first adhesive layer 5b is slightly lower than that of the first adhesive layer 5b in the target substance-sensing sheet 20 according to the first embodiment, in order to prevent it from falling off from the packaging material 10.

[0050] In the target substance sensing sheet 30 of this embodiment, when a printed layer 15b is formed on at least one surface of the first base material 7b, if the window region 19b is too small, the printed portion 16b will make it difficult for the detection target substance to reach the first adhesive layer 5b. Therefore, the area of ​​the window region 19b should be at least ¼ of the entire area of ​​the target substance sensing sheet 30 and no larger than 0.5 cm. 2 It is preferable that this is equal to or greater than this.

[0051] (Third embodiment) FIG. 4 is a cross-sectional view showing a target substance sensing sheet according to a third embodiment disclosed herein. As shown in the figure, a target substance sensing sheet 40 of this embodiment includes a sheet-like first substrate 7c and a first adhesive layer 5c provided in contact with one surface of the first substrate 7c. A printed layer 15c including a printed section 16c made of color ink or the like and having a window region 19c formed therein may be provided on at least one surface of the first substrate 7c. Like the first adhesive layer 5a of the target substance sensing sheet 20 according to the first embodiment, the first adhesive layer 5c is formed from a cured product of a solvent-based adhesive composition or an emulsion adhesive composition, and contains at least one substance selected from substances approved as food additives and substances extracted from foods that are not approved as food additives.

[0052] The target substance sensing sheet 40 of this embodiment is similar to the target substance sensing sheet 30 of the second embodiment in that it does not have a second substrate 3 and a second adhesive layer 1, but differs in that it is used by being attached to the outside of the packaging material 10 and that the constituent material of the first substrate 7c is not limited to a gas-permeable material.

[0053] The target substance sensing sheet 40 of this embodiment detects a gaseous target substance that has permeated the packaging material 10 by detecting a color change in the first adhesive layer 5c. Therefore, the first substrate 7c does not need to be made of a gas-permeable material; it may be made of a known transparent or translucent resin material so that the first adhesive layer 5c is visible to consumers. Examples of materials that can be used for the first substrate 7c include polyester resins such as PET, PE, PP, PS, and PU. Although the first substrate 7c is attached to the outside of the packaging material 10, safety can be further enhanced by making the first substrate 7c from a material that complies with the Positive List System of the Food Sanitation Act. The thickness of the first substrate 7c is not particularly limited, but may be, for example, 100 μm or less to reduce manufacturing costs.

[0054] The planar size of the target substance sensing sheet 40 is not particularly limited, but like the target substance sensing sheet 20 according to the first embodiment, it may be approximately 1 / 10 to 2 / 3 of the area in which the food 13 is sealed by the packaging material 10. When the printed layer 15c is formed, the area of ​​the window region 19c is not particularly limited, but may be, for example, 1 cm 2 It may be more than that.

[0055] Other than the above-mentioned differences, the configuration is the same as that of the target substance sensing sheet 20 according to the second embodiment, and therefore a description thereof will be omitted.

[0056] (Fourth embodiment) In the above embodiment, an example has been described in which the target substance sensing sheet is used to detect the freshness of food, but the use of the target substance sensing sheet disclosed in this specification is not limited to this.

[0057] FIG. 5(a) is a cross-sectional view showing a target substance sensing sheet according to a fourth embodiment, and FIG. 5(b) is a diagram showing an example of how to use the target substance sensing sheet shown in (a). As shown in FIG. 5(a), the target substance sensing sheet 50 of this embodiment includes a sheet-like first substrate 7d and a first adhesive layer 5d provided in contact with one surface of the first substrate 7d. At least one surface of the first substrate 7d may be provided with a printed layer 15d including a printed section 16d made of color ink or the like and having a window region 19d formed therein. The printed layer 15d may include a color sample 21 and a color judgment guide 23 (see FIG. 2), as in the target substance sensing sheets according to the first to third embodiments.

[0058] The first adhesive layer 5d, like the first adhesive layer 5a of the target substance sensing sheet 20 according to the first embodiment, is formed from a cured product of a solvent-based adhesive composition or an emulsion adhesive composition, and contains at least one substance selected from substances approved as food additives and substances extracted from food that are not approved as food additives.

[0059] The target substance sensing sheet 50 of this embodiment has the same configuration as the target substance sensing sheet 40 of the third embodiment, but differs from the target substance sensing sheet 40 in that it is used as a skin pH sensor that is attached to human skin. In other words, the target substance sensing sheet 50 detects the skin itself or sweat (a mixture of salt, lactic acid, urea, etc.) released from the skin.

[0060] The indicator contained in the first adhesive layer 5d can be one that changes color within a pH range of 4.5 to 6.0 in order to accurately detect the condition of the skin or sweat. Among polyphenol compounds, anthocyanin pigments are preferably used as indicators because they change color continuously within a pH range of 4.5 to 6.0.

[0061] As shown in Figure 5(b), by attaching the target substance sensing sheet 50 to the skin 27 at any location with little body hair, such as the inside of the arm, the palm of the hand, or the nape of the neck, and waiting for a predetermined time, the color of the first adhesive layer 5d changes due to the moisture or sweat released from the skin 27, making it possible to visually check the pH of the skin 27 or sweat.

[0062] The pH of skin is generally said to be about 4.5 to 6.0, and the pH of sweat is said to be about 4.0 to 6.8. Therefore, the pH of the skin or sweat released from the skin can be confirmed by the color of the first pressure-sensitive adhesive layer 5d, which contains an indicator that changes color at least within the pH range of 4.5 to 6.0.

[0063] While healthy skin exhibits a weak acidity, dryness and roughness of the skin tend to increase the skin's pH. Therefore, there is a strong consumer need to be able to check the condition of their skin. The target substance sensing sheet 50 of this embodiment makes it possible to visually convey the pH of the skin or sweat to the user in a simple manner.

[0064] The indicators used in the target substance sensing sheet 50 are basically water-soluble, so they are unlikely to be absorbed by the skin, and even if they are absorbed, it is thought that the possibility of them causing harm to the human body is extremely low. Furthermore, it is thought that anthocyanin pigments and the like are extremely unlikely to cause allergic reactions compared to pigments derived from non-plants.

[0065] When the first adhesive layer 5d is formed from a cured product of a solvent-based adhesive, it is more preferable that the target substance-sensing sheet 50 pass a known skin allergy test. Alternatively, safety may be ensured by having an adhesive sheet with an adhesive layer made of the same components as the first adhesive layer 5d but not containing an indicator pass the skin allergy test.

[0066] If the first base material 7d is transparent or translucent, the color of the first adhesive layer 5d can be confirmed while the base material is attached to the skin 27. If the first base material 7d is white, the color can be easily confirmed from the side of the first adhesive layer 5d after the base material is peeled off from the skin 27.

[0067] Furthermore, the printed layer 15d does not necessarily have to be provided, and color samples, instructions describing a guide for determining skin pH, and the like may be separately attached to the product package.

[0068] -Other embodiments- The target substance sensing sheets 20, 30, 40, and 50 according to the first to fourth embodiments are examples of the target substance sensing sheets disclosed herein, and the thickness, material, shape, and type and concentration of the indicator of each component can be appropriately modified without departing from the spirit of the present invention. For example, a target substance sensing sheet need only have an adhesive layer composed of a cured product of an adhesive containing at least an indicator, and does not necessarily require a substrate. For example, even a target substance sensing sheet comprising an adhesive layer that changes color in the presence of a substance to be detected and a first release liner and a second release liner sandwiching this adhesive layer can be attached to a packaging material for use.

[0069] In the example shown in Figure 3, a gas-permeable first base material 7b and a printed layer 15b are formed in this order on the first adhesive layer 5b. However, the gas-permeable first base material 7b may be made of edible ink by forming a gas-permeable printed portion on the entire surface of the first adhesive layer 5b using a food printer or the like. In this case, the indicator in the first adhesive layer 5b can be prevented from coming into contact with the food 13 with a simple configuration. In this case, the thickness of the printed portion may be any thickness, for example, from 1 µm to 10 µm.

[0070] Furthermore, the target substance sensing sheet described above is not limited to applications such as sensing the freshness of food or as a skin pH sensor, but can be used to detect any target substance. For example, if the gaseous substance to be detected is specified in advance, the target substance sensing sheet 30 shown in Fig. 3 can be attached to a pipe joint where gas leakage is a concern, or the target substance sensing sheet 20 shown in Fig. 1 can be attached to the wall surface of a room, thereby making it possible to use it as a gas leak detection sensor. [Example]

[0071] <Preparation of target substance sensing sheet> Powdered purple sweet potato pigment, which is approved as a food additive (Nichino Color R-M100P manufactured by Nihon Noh Chemical Industry Co., Ltd.; (containing 50.0% by mass of purple sweet potato pigment, 48.8% by mass of reduced dextrin, and 1.2% by mass of citric acid)), was dissolved in water and then added to an emulsion-based acrylic adhesive to a predetermined concentration. A coating liquid was prepared by mixing the solution with an isocyanate-based curing agent.

[0072] Next, this coating solution was applied to a first release liner using a comma coater, dried, and cured. After that, a second release liner was attached and the sheet was cut to a specified size to produce a substrate-less target substance sensing sheet. For testing, one of the release liners was peeled off and the sheet was attached to an appropriate adherend. Furthermore, an acrylic adhesive with relatively high moisture permeability after curing was used to ensure rapid detection of the target substance.

[0073] <Test Method> -Test 1- Using the method described above, we prepared substrateless target substance sensing sheets with an adhesive layer containing purple sweet potato pigment at a concentration of 10% by weight based on the adhesive solids content. The adhesive layer was 10 μm thick. One release liner of the target substance sensing sheet was peeled off, and the adhesive layer was attached to a piece of white PET film as the substrate. The other release liner was then peeled off to expose the adhesive layer. With the adhesive layer exposed, each sample was sealed in a sealed container to which 0.05 g of ammonia water with a concentration of 0.28% by weight or 0.028% by weight had been dropped. The color of the adhesive layer was visually observed before the test began, after 10 minutes, and after 24 hours.

[0074] <Test Results> The results of Test 1 are shown in Table 1.

[0075] [Table 1] As shown in Table 1, when ammonia (the substance to be detected) was added to a sealed container, the color of the adhesive layer changed from dark reddish purple to purple and then to blue-purple, confirming that ammonia could be detected. Furthermore, there was no significant difference in the speed of the color change between when the ammonia concentration was 0.028% by mass and when it was 0.28% by mass.

[0076] From the above results, it was confirmed that the target substance sensing sheet can detect at least the presence of ammonia by the color change of the adhesive layer containing the indicator. [Industrial Applicability]

[0077] The target substance sensing sheet disclosed in this specification can be used as a label indicating the freshness of food, a skin pH sensor, an adhesive film-type gas sensor, etc. [Explanation of symbols]

[0078] 1 Second adhesive layer 3 Second substrate 5a, 5b, 5c, 5d First adhesive layer 7a, 7b, 7c, 7d First base material 10 Packaging materials 13 Food 15a, 15b, 15c, 15d printing layer 16a, 16b, 16c, 16d Printing section 18 Gas-sensing laminate sheet 19a, 19b, 19c, 19d Window area 20, 30, 40, 50 Target substance sensing sheet 21 color samples 22 Label body

Claims

1. a first adhesive layer containing an indicator that changes color in the presence of a substance to be detected; The target substance sensing sheet, wherein the indicator is at least one selected from substances approved as food additives in Japan and substances extracted from food that are not approved as food additives.

2. The target substance sensing sheet according to claim 1, The target substance sensing sheet, wherein the indicator is at least one selected from the group including at least one kind of polyphenol compound and at least one kind of quinone dye.

3. The target substance sensing sheet according to claim 2, the polyphenol compound is an anthocyanin pigment, The target substance sensing sheet, wherein the first adhesive layer is formed from a cured product of a solvent-based adhesive or an emulsion adhesive.

4. The target substance sensing sheet according to claim 1, the indicator is at least one polyphenol compound soluble in ethyl acetate, acetone, toluene, or methyl ethyl ketone; The target substance sensing sheet, wherein the first adhesive layer is formed from a cured product of a solvent-based adhesive.

5. The target substance sensing sheet according to claim 1, the detection target substance is a gaseous substance, A target substance sensing sheet further comprising a first substrate provided on one surface of the first adhesive layer and permeable to the target substance to be detected.

6. The target substance sensing sheet according to claim 5, the first adhesive layer detects a change in freshness of food through a color change caused by the detection target substance, The indicator changes color within a pH range of 3 to 10, The first substrate is a target substance sensing sheet made of a material that complies with the positive list system of the Food Sanitation Act or edible ink.

7. The target substance sensing sheet according to claim 6, a sheet-like second substrate provided on a surface of the first pressure-sensitive adhesive layer opposite to a surface on which the first substrate is provided; a second pressure-sensitive adhesive layer provided on a surface of the second substrate opposite to the first pressure-sensitive adhesive layer; The target substance sensing sheet further comprises:

8. The target substance sensing sheet according to claim 7, A target substance sensing sheet, wherein a window area is formed on at least one surface of the second substrate or the first substrate, and further comprising a printed layer including a color sample.

9. The target substance sensing sheet according to claim 8, The target substance sensing sheet, wherein the printed layer has a printed portion made of edible ink.

10. The target substance sensing sheet according to any one of claims 1 to 9, A target substance sensing sheet in which the color of the indicator reversibly changes in response to the presence of a target substance.

11. The target substance sensing sheet according to claim 1, The device further includes a first base material made of resin provided on one surface of the first pressure-sensitive adhesive layer, the first adhesive layer is attached to the skin during use and changes color in response to the pH of the skin; The indicator changes color within a pH range of 4.5 to 6.0.

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