Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
  • B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
  • B32B27/205—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents the fillers creating voids or cavities, e.g. by stretching
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
  • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
  • B32B27/306—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl acetate or vinyl alcohol (co)polymers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B27/00—Layered products comprising a layer of synthetic resin
  • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
  • B32B7/04—Interconnection of layers
  • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2250/00—Layers arrangement
  • B32B2250/24—All layers being polymeric
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/40—Properties of the layers or laminate having particular optical properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B2307/00—Properties of the layers or laminate
  • B32B2307/40—Properties of the layers or laminate having particular optical properties
  • B32B2307/402—Coloured

Definitions

• the present invention relates to an indicator comprising a color-changing layer which comprises a porous film having pores therein and a liquid retained in the pores of the porous film.
• Indicators that is, time indicators, which utilizes a phenomenon that color of a frosted glass plate or a paper sheet holding a liquid on its surface changes with the evaporation of the liquid, are known (cf. JP-A-57-158682 and JP-A-07-281603) .
• JP-A-57-158682 and JP-A-07-281603 do not uniformly change their color in use, and thus it is difficult to know a remaining validity time, or the color of indicators changes during long term storage.
• An object of the present invention is to provide an indicator which suffers from less color change during storage and uniformly changes its color at any portion of the indicator in use so that the remaining validity time can be definitely determined.
• the present invention provides an indicator comprising a color-changing layer (A) which comprises a porous film having pores therein and a liquid compound retained in the pores, and a substrate layer (B) having a barrier property, which are laminated with a first adhesive layer (D) , wherein the liquid compound has a vapor pressure of from 1 x 10 "6 to 5 x ICT 3 mmHg at 25°C, and the porous film comprises a polyolefin resin containing at least 10% by weight of polyolefin having a molecular chain length of at least 2850 ran.
• the color- changing layer (A) comprises a porous film having pores therein and a liquid compound retained in the pores.
• the color of the color-changing layer (A) changes with the evaporation of the liquid compound retained in the porous film to indicate the remaining validity time of the indicator.
• the "color-changing" is intended to mean the change of transparency of the porous film.
• the porous film constituting the color-changing layer (A) comprises a polyolefin resin containing 10% by weight of polyolefin having a molecular chain length of at least 2850 ran.
• a porous film made of such a specific polyolefin resin has better strength than conventionally used porous films and thus it has a large number of pores having a uniform size. Since the color-changing layer (A) comprises such a porous film, the color of the layer (A) changes uniformly at any portion thereof.
• the polyolefin having a molecular chain length of at least 2850 nm is one having a molecular chain length of at least 2850 nm measured by gel permeation chromatography (GPC) using polystyrene as a reference material.
• GPC gel permeation chromatography
• Specific examples of such polyolefin include a homopolymer of ethylene, a copolymer of ethylene and an ⁇ -olefin having 3 to 12 carbon atoms, a homopolymer of propylene, a copolymer of propylene and an ⁇ -olefin having 4 to 12 carbon atoms, each having such a molecular chain length.
• the polyolefin resin constituting the porous film of the color-changing layer (A) may contain polyolefin with good processability such as a polyolefin having a molecular chain length of less than 2850 nm, an olefin wax, etc. in an acceptable amount in view of the objects of the present invention.
• the porous film of the color-changing layer (A) may contain 90% by weight or less of polyolefin other than the polyolefin having a molecular chain length of at least 2850 nm.
• the porous film of the color-changing layer should contain 10% by weight or more of the polyolefin having a molecular chain length of at least 2850 nm.
• the olefin wax is polyolefin having a weight average molecular weight of from 700 to 6000, which is usually a solid material at 25°C.
• the olefin wax include ethylene resin waxes (e.g. low density polyethylene, linear polyethylene (ethylene- ⁇ -olefin copolymers) , high density polyethylene, etc.), propylene resin waxes (e.g. polypropylene, ethylene-propylene copolymer, etc.), waxes of poly (4-methylpentene-l) , poly (butene-1) and ethylene- vinyl acetate copolymers, and so on.
• ethylene resin waxes e.g. low density polyethylene, linear polyethylene (ethylene- ⁇ -olefin copolymers) , high density polyethylene, etc.
• propylene resin waxes e.g. polypropylene, ethylene-propylene copolymer, etc.
• the molecular chain length is measured by gel permeation chromatography (GPC) using polystyrene as a reference material according to the following procedures:
• GPC gel permeation chromatography
• a solvent which allows an unknown material to be analyzed and reference polystyrene samples having known molecular weights to dissolve therein is used as a mobile phase used in GPC.
• the Q factor of polystyrene is 41.3.
• the molecular chain length of each reference polystyrene sample is calculated and further a retention time corresponding to the molecular chain length of each reference polystyrene sample is determined.
• an unknown sample (a polyolefin resin) is subjected to the GPC analysis to obtain a retention time- eluted component amount curve.
• a molecular chain length of a reference polystyrene sample having a retention time T in the GPC analysis is L
• a molecular chain length of an unknown sample having the retention time T is considered to be L.
• a molecular chain length-eluted component amount curve showing the molecular chain length distribution of the unknown sample is derived from the above retention time-eluted component amount curve for the unknown sample.
• the content of polyolefin having a molecular chain length of at least 2850 nm is obtained as a percentage of an integrated value of an area corresponding to the molecular chain length of 2850 nm or more in the molecular chain length-eluted component amount curve for the unknown sample, based on an integrated value of a whole area in the molecular chain length-eluted component amount curve.
• the porous film used in the present invention preferably has an average pore size of from 0.06 to 0.1 ⁇ m, which is measured in accordance with JIS K1150 using a porosimeter.
• the porous film preferably has a Gurley value (gas permeability) of from 100 to 250 sec/100 cc, and a thickness of from 5 to 20 ⁇ m.
• Gurley value gas permeability
• the indicator having a color-changing layer comprising such a porous film has good uniformity in color change so that the remaining validity time is easily determined, and also it has excellent storage stability.
• a Gurley value of a porous film is measured in accordance with JIS P8117 using a B-type densometer.
• the porous film has a Gurley value of 150 sec/100 cc, it has a pore volume of about 50% by volume.
• the Gurley value of the porous film is too large, the average pore size is too large.
• the Gurley value depends on the thickness of the porous film.
• the indicator having a color-changing layer comprising a porous film with a Gurley value and a thickness in the above ranges is excellent in the uniformity of color change.
• the substrate layer of the indicator should be visible through the color- changing layer for the entire valid period of the indicator, From these points of view, the porous film constituting the color-changing layer (A) preferably has a thickness of 20 ⁇ m or less, more preferably 15 ⁇ m or less.
• the porous film used in the present invention may be produced as follows: A polyolefin resin containing 10.5% by weight or more of polyolefin having a molecular chain length of 2850 nm or more, 5 to 100 parts by weight of an olefin wax based on 100 parts by weight of the polyolefin resin, and 100 to 400 parts by weight of a water-soluble filler based on 100 parts by weight of the total amount of the polyolefin resin and the olefin wax are mixed to obtain a polyolefin resin composition, and then the polyolefin resin composition is molded in the form of a sheet by a sheet-forming method such as tubular processing, calendering, T-die extrusion, a Scaif process, etc.
• a sheet-forming method such as tubular processing, calendering, T-die extrusion, a Scaif process, etc.
• the water-soluble filler is leached out from the sheet with an aqueous solvent, and the filler-free sheet is dried.
• the dried sheet is stretched under conditions such that the pores formed by the removal of the filler are not collapsed. Thereby, a porous film, which can be used in the present invention, is obtained.
• a stretching machine such as a tenter may be used.
• the liquid compound used in the present invention is in a liquid state at 25 0 C, and has a vapor pressure of from 1 x 10 "6 to 5 x ICT 3 mmHg at 25°C, which is measured by the method reported by Stephen F. Donovan in New Method for Estimating Vapor Pressure by the Use of Gas Chromatography, Journal of Chromatography A. 749, 1996, 121-129.
• the liquid compound in the color-changing layer has a vapor pressure lower than 1 x 10 ⁇ 6 mmHg, the start of the color change is delayed under usual environment conditions, and the color of the indicator may not uniformly change.
• the color of the indicator changes in a very short period of time under usual environment conditions.
• a compound having such a high vapor pressure cannot be used in the present invention, since the indicator is used at least for several days.
• liquid compound which can be used according to the present invention examples include isopropyl myristate (vapor pressure: 5.54 x 10 ⁇ 5 mmHg), methyl laurate (vapor pressure: 1.57 x 10 "3 mmHg), ethyl laurate (vapor pressure: 6.85 x 10 "4 mmHg), isopropyl palmitate (vapor pressure: 8.14 x 10 "6 mmHg), dibutyl sebacate (vapor pressure: 2.70 x 10 "6 mmHg), dioctyl maleate (vapor pressure: 3.13 x 10 "5 mmHg), triethyl acetylcitrate (vapor pressure: 1.46 x 10 ⁇ 4 mmHg), tributyl acetylcitrate (vapor pressure: 1.27 x 10 ⁇ 6 mmHg) , etc.
• the vapor pressures indicated in the brackets are those at 25°C.
• the liquid compound preferably has a refractive index in a range of (a refractive index of a porous film) ⁇ 0.1, from the viewpoint of the transparency of the color-changing layer comprising the porous film and the liquid compound.
• the liquid compound may be retained in the porous film by any method.
• a conventional dry laminator or a printing machine such as a gravure printer can be used.
• the porous film is dipped in the liquid compound contained in a container, or the liquid compound is dropped on the porous film.
• the substrate layer (B) is a layer having a barrier property, which is laminated onto the color-changing layer (A) with a first adhesive layer (D) .
• the barrier property of the layer (B) means a property for preventing the diffusion of the liquid compound from the color-changing layer (A) to the layer (B) .
• the substrate layer has an oxygen permeability of 40 cc/m 2 . day .atom or less, which is measured in accordance with ASTM D3985 at a temperature of
• the color-changing layer (A) of the indicator of the present invention is transparent so that the substrate layer (B) can be seen through the color-changing layer (A) , when a sufficient amount of the liquid compound is retained in the color-changing layer (A) . As the liquid compound evaporates, the color-changing layer (A) is gradually opacified.
• the valid period of the indicator expires. That is, a period in which the substrate layer (B) is seen through the color-changing layer (A) is a valid period of the indicator of the present invention.
• Examples of a material having a barrier property used to form the substrate layer (B) include an unstretched, uniaxially stretched or biaxially stretched film of a polymer having a good barrier property such as an ethylene- vinyl alcohol copolymer (EVOH) , polyethylene naphthalate, polyacrylonitrile, polyvinyl chloride, etc./ a laminate film comprising a support film such as an unstretched, uniaxially stretched or biaxially stretched film of the above polymer having a good barrier property or a polymer having a low barrier property such as polyolefin (e.g.
• a polymer having a good barrier property such as an ethylene- vinyl alcohol copolymer (EVOH) , polyethylene naphthalate, polyacrylonitrile, polyvinyl chloride, etc./ a laminate film comprising a support film such as an unstretched, uniaxially stretched or biaxially stretched film of the above polymer having a good barrier property or a polymer having
• an "inorganic layered compound” is an inorganic compound having a layered structure of piled-up unit crystal layers.
• the inorganic layered compound examples include kaolinite, montmorillonite, mica, talc, vermiculite, etc.
• the substrate layer preferably comprises a film of a resin colored with a pigment, etc., or a film having monochrome or polychrome characters, images, designs, etc. printed on the surface thereof on which the color-changing layer (A) is provided.
• the barrier layer and the color-changing layer (A) are preferably adhered with the first adhesive layer (D) , since the diffusion of the liquid compound from the color- changing layer (A) to the substrate layer (B) is effectively suppressed.
• the color-changing layer (A) and the substrate layer (B) are laminated with the first adhesive layer (D) .
• the first adhesive constituting the layer (D) may be an adhesive for dry lamination which is commonly used in a packaging material.
• Specific examples of such an adhesive include two-component adhesives such as two-component aliphatic or aromatic polyether adhesives, two-component aliphatic or aromatic polyester adhesives, etc.; and one- component adhesives such as polyethylene imine adhesives, polybutadiene adhesives, etc. Since the liquid compound may diffuse from the color-changing layer (A) to the adhesive layer (D) , the adhesive strength between the layers (A) and (B) may decrease.
• a two- component adhesive having a high initial adhesive strength such as a two-component aliphatic or aromatic polyester adhesive is preferably used, in particular, an adhesive having high resistance to organic solvents is preferably used.
• the adhesive layer having a smaller thickness is more preferable.
• the thickness of the adhesive layer is usually 0.5 to 4 ⁇ m, preferably 0.7 to 2 ⁇ m.
• the color-changing layer (A) and the layer (B) is laminated with the layer (D) preferably by dry lamination, which comprises the steps of coating one surface of the substrate with the first adhesive diluted with a solvent, evaporating off the solvent, and then laminating the color- changing layer (A) on the resulting layer of the first adhesive.
• the laminate may optionally be aged.
• the indicator of the present invention is preferably stored in a period from the production of the indicator until the start of use (i.e. the start of displaying a valid term) with avoiding the evaporation of the liquid compound retained in the porous film of the color-changing layer.
• a layer (C) having a barrier property is preferably laminated on the color-changing layer (A) with a second adhesive layer (E) .
• the second adhesive may be a pressure-sensitive adhesive.
• a material constituting the layer (C) having a barrier property may be the same as the material of the substrate constituting the layer (B) .
• the layer (C) is preferably a laminate comprising a support film and a layer of a composition containing a resin and an inorganic layered compound dispersed therein.
• the layer (C) consists of such a laminate, preferably the layer of the resin composition of the laminate is adhered to the color- changing layer (A) with the adhesive layer (E) .
• the second adhesive layer (E) and the layer (C) are both peeled from the indicator when the indicator is used, that is, when the display of the valid period starts. Therefore, as the second adhesive, preferably a pressure-sensitive adhesive which leaves no adhesive deposit, that is, which does not leave a part or whole of the layer (E) on the color-changing layer (A) after peeling off of the layers (C) and (E) , is used.
• Examples of the pressure-sensitive adhesive constituting the layer (E) include general solvent-based acrylic pressure-sensitive adhesives and general aqueous emulsion acrylic pressure-sensitive adhesives.
• a pressure-sensitive adhesive having resistance to the liquid compound contained in the color-changing layer (A) is used.
• a pressure-sensitive adhesive having low resistance to the liquid compound is used, it is dissolved in or swelled with the liquid compound so that it may migrate into the pores of the porous film together with the liquid compound. In such a case, the function of the indicator to display a valid term may be deteriorated.
• the pressure-sensitive adhesive having resistance to the liquid compound is an acrylic pressure-sensitive adhesive having a number average molecular weight Mn of at least 50,000, more preferably at least 100,000, which is measured by GPC using polystyrene as a reference material.
• the acrylic pressure-sensitive adhesive may be a pressure-sensitive adhesive comprising a polymer of an acrylic monomer such as 2-ethylhexyl acrylate, n-butyl acrylate, etc.
• the aqueous emulsion pressure-sensitive adhesive is more preferable than the solvent-based pressure-sensitive adhesive from the viewpoint of the resistance to the liquid compound.
• the aqueous emulsion pressure-sensitive adhesive may be an emulsion containing a resin which comprises an acrylic monomer such as 2- ethylhexyl acrylate, n-butyl acrylate, etc. dispersed in water and having a solid content of about 50%.
• the thickness of the layer (E) is preferably 1 to 20 ⁇ m.
• the color-changing layer (A) and the layer (C) may be laminated with the layer (E) by dry lamination. Specific dry lamination method includes the following steps:
• a laminate film of a porous film and a substrate adhered with the first adhesive layer (D) is supplied from a supplier of a dry laminator/
• step (3) a film made of a barrier material supplied from another supplier of the dry laminator is press bonded to the color- changing layer (A) of the laminate formed in step (2) with providing a pressure-sensitive adhesive between them.
• the pressure-sensitive adhesive is usually coated on one surface of the film made of the barrier material before the press bonding to the laminate.
• the porous film impregnated with the liquid compound may optionally be dried in an oven.
• the valid term of the indicator of the present invention can be adjusted by selecting the kind and amount of the liquid compound retained in the color-changing layer (A) and/or the thickness of the porous film of the color- changing layer (A) .
• a release paper may be laminated on the surface of the layer (B) having no layer (D) with an pressure-sensitive adhesive layer. In such a case, the release paper is removed and then the indicator is adhered to a desired part of a product using the pressure-sensitive adhesive layer.
• the shape of the indicator of the present invention may not be limited.
• the layer (C) of the barrier material the layer (C) can be easily peeled off when it has a larger area than other layers.
• a stripping tape may be provided on the layer (C) .
• a laminate having the same structure as the indicator of the present invention except that no liquid compound is retained in the porous film is placed for comparing the color together with the indicator so that a user can certainly identify the remaining validity time.
• the indicator of the present invention is attached to an insect-proof device comprising a bug-proof repellent, an insecticide, an insect repellent, etc., and used as an indicator indicating a remaining validity time of insect- proofing effects.
• an insect-proof device comprising a bug-proof repellent, an insecticide, an insect repellent, etc.
• the indicator of the present invention may be used in any application that requires the display of a remaining validity time.
• a Gurley value (sec/100 cc) of a porous film is measured in accordance with JIS P8117 using a B-type densometer (manufactured by Toyo Seiki Seisaku-Sho, Ltd.). Gurley values are measured at ten arbitrary points of the porous film and averaged. The averaged value is used as the Gurley value of the porous film.
• (2) Measurement of average pore size of porous film An average pore size of a porous film is measured by a mercury-pouring method in accordance with JIS K1150 using a porosimeter (manufactured by Shimadzu Corporation) . Pore sizes are measured at five arbitrary points of the porous film and averaged. The averaged value is used as the average pore size of the porous film.
• GPC Gel Chromatograph Alliance GPC 2000 (manufactured by Waters Corporation) .
• the conditions of GPC measurement are as follows: Columns: TSKgel GMHHR-H(S) HT (30 cm x 2) and TSKgel GMH6- HTL (30 cm x 2) (both available from Tosoh Corporation)
• Mobile phase o-Dichlorobenzene Detector: Differential refractometer Flow rate: 1.0 mL/min. Column temperature: 140 0 C Injection amount: 500 ⁇ L
• a sample (30 mg) is completely dissolved in o- chlorobenzene (20 mL) at 145°C, and the solution is filtrated through a sintered filter having a pore size of 0.45 ⁇ m. The filtrate is used as a liquid to be supplied.
• a calibration curve is obtained using 16 reference polystyrene samples having known molecular weights. Polystyrene has a Q factor of 41.3.
• Ten indicators each having the layer (C) of a barrier material are stored at 4O 0 C for 10 days. Then, the layer (C) is peeled off from each indicator and the indicators are kept standing at room temperature. The number of days until the color changes is counted, and a deviation (unit: days) from an average number of days is calculated.
• porous film (1) With 100 parts by weight of a polyethylene powder (HI- ZEX MILLION 340 M manufactured by Mitsui Chemicals, Inc.; weight average molecular chain length: 17,000 nin; weight average molecular weight: 3, 000, 000; melting point: 136 0 C), 43 parts by weight of olefin-base wax powder (HI-WAX HOP manufactured by Mitsui Chemicals, Inc.; weight average molecular weight: 1,000; melting point: 110 0 C) and 150 parts by weight of calcium carbonate (Vigot 10 manufactured by Shiraishi Calcium Kaisha, Ltd.; average particle size:
• Composition (1) 0.15 ⁇ m (measured with SEM) were mixed, and the mixture was kneaded with a twin-screw kneader to obtain Composition (1) .
• Composition (1) was rolled with calender rolls kept at 150°C to obtain Sheet (1) having a thickness of about 70 ⁇ m.
• Sheet (1) was dipped in an aqueous solution of hydrochloric acid to leach out calcium carbonate and then washed with aqueous sodium hydroxide and further with water, followed by drying to obtain a resin sheet.
• the resin sheet was stretched at a draw ratio of 5 in a transverse direction at a stretching temperature of 100°C to obtain Porous film (1), which was wound in a roll form.
• the resin component of Porous film (1) contained 28% by weight of polyethylene having a molecular chain length of 2850 ⁇ m or more.
• SEVIX YPET-G2 inorganic layered compound manufactured by Nihon Ecowrap Co., Ltd.; thickness: 12 ⁇ m
• the roll of the substrate was loaded on a supplier (the first supplier) of a dry laminator, and unwound at a rate of 5 m/min. Then, an aliphatic polyester adhesive was coated on the coated surface of the substrate with a gravure roll, and an organic solvent in the adhesive was removed in an oven kept at 80 0 C to form the adhesive layer (D) having a thickness of 2 ⁇ m.
• the substrate having the adhesive layer (D) was press bonded to Porous film (1) which was being unwound from another supplier (the second supplier) of the dry laminator, and the laminate was aged at 40 0 C for 2 days to obtain Laminate (1) consisting of the substrate layer (B) and Porous film (1) which were adhered with the adhesive layer (D) .
• the laminate was wound in a roll form.
• the roll of the same PET film as one used in the preparation of a substrate above (SEVIX YPET-G2) was loaded on a supplier of a dry laminator.
• An aqueous acrylic emulsion pressure-sensitive adhesive (manufactured by GANZ Chemical Co., Ltd.) was applied at a thickness of 20 ⁇ m to the coated surface of the PET film to form the adhesive layer (E) .
• the barrier film having the adhesive layer (E) was wound in a roll form. Production of indicator sheet
• the roll of Laminate (1) was loaded on a supplier (the first supplier) of a dry laminator. Then, isopropyl myristate (vapor pressure at 25°C: 5.54 x 10 "5 mmHg; liquid at room temperature) was applied to the surface of Porous film (1) of Laminate (1) while unwinding Laminate (1) from the roll. The applied isopropyl myristate was retained in the pores of Porous film (1) and formed the color-changing layer (A) . Thereby, Laminate (2) consisting of the color- changing layer (A) and the substrate layer (B) which were adhered with the adhesive layer (D) was obtained. The roll of the barrier film having the adhesive layer (E) was loaded on another supplier (the second supplier) of the dry laminator.
• Laminate (3) consisting of the barrier film (C) , the adhesive layer (E) , the color-changing layer (A) , the adhesive layer (D) and the substrate (B) , which were laminated in this order, was obtained.
• Laminate (3) was stamped out in the form of a disc having a diameter of 10 mm to obtain an indicator. This indicator was subjected to various evaluation tests descried above. The results are shown in Table 1.
• Example 2
• Example 3 An indicator was produced in the same manner as in Example 1 except that a solvent-based acrylic pressure- sensitive adhesive was used in place of the aqueous emulsion acrylic pressure-sensitive adhesive. The results of the evaluation tests of this indicator are also shown in Table 1.
• Example 3 An indicator was produced in the same manner as in Example 1 except that a solvent-based acrylic pressure- sensitive adhesive was used in place of the aqueous emulsion acrylic pressure-sensitive adhesive. The results of the evaluation tests of this indicator are also shown in Table 1. Example 3
• Example 1 except that a commercially sold laminate film consisting of a PET film (thickness: 12 ⁇ m) and an ethylene-vinyl alcohol copolymer film (thickness: 20 ⁇ m; ethylene content: 44% by mole) was used in place of the PET film coated with the inorganic layered compound as the layer (C) , and the adhesive layer (E) was formed on the layer of the ethylene-vinyl alcohol copolymer film.
• the results of the evaluation tests of this indicator are also shown in Table 1.
• Example 1 An indicator was produced in the same manner as in Example 1 except that an ethylene-vinyl alcohol copolymer film (thickness: 20 ⁇ m; ethylene content: 44% by mole) was used in place of the PET film coated with the inorganic layered compound as the layer (C) .
• the results of the evaluation tests of this indicator are also shown in Table 1. Comparative Example 1
• Polyethylene pellets 100 parts by weight (SUMIKATHENE-L, FS240 manufactured by Sumitomo Chemical Co., Ltd.) and calcium carbonate (300 parts by weight) were mixed with a Henschel mixer and further kneaded with a twin-screw extruder to obtain Composition (2) .
• Sheet (2) having a thickness of about 65 ⁇ m was produced in the same manner as in Example 1 except that Composition (2) was used in place of Composition (1) . Then, calcium carbonate was leached out from Sheet (2) in the same manner as in Example 1, and then stretched at a draw ratio of 5 in a transverse direction at a stretching temperature of 9O 0 C to obtain Porous film (2) .
• the resin component of Porous film (2) contained 1% by weight or less of polyethylene having a molecular chain length of 2850 ⁇ m or more.
• An indicator was produced in the same manner as in Example 1 except that a commercially sold porous polyethylene film (3) (thickness: 24 ⁇ m; average pore size: 0.04 ⁇ m; Gurley value: 420 sec/100 cc) was used in place of Porous film (1) .
• the resin component of Porous film (3) contained 8% by weight of polyethylene having a molecular chain length of 2850 ⁇ m or more. The results of the evaluation tests of this indicator are shown in Table 2.

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