JP7465108B2 - Temperature-sensitive dye film - Google Patents

Description

The present invention belongs to the technical field of laminated resin films made of synthetic resins. The present invention relates to a laminated resin film, which is a thermosensitive dye film with a resin layer containing a thermosensitive color material sandwiched between the layers.

There are many inventions of laminated resin films that are mainly composed of polyethylene-based resins or polypropylene-based resins (for example, Patent Documents 1 and 2). These conventional laminated resin films are basically colorless and transparent, white, or colored from the beginning. Although they may become cloudy due to the influence of the contents, they do not develop color during use, and once a color has developed, it does not fade.

On the other hand, various thermosensitive color changing compositions that develop or lose color depending on temperature are known. For example, Patent Document 3 discloses a novel thermosensitive color changing composition (microcapsules) that contains a leuco dye, a color developing substance, and a specific color changing temperature regulator. The color changing temperature regulator is, for example, a composition that is at least one of the following compounds: a: 4-hydroxymethylbiphenyl decanoic acid ester, b: phenyl benzoate-n-decyl ether, c: 4-hydroxybenzophenone lauryl ether, d: 4-chloro-4'-hydroxybenzophenone lauric acid ester, and e: decyl ether of 4-hydroxymethylbiphenyl. The thermosensitive color changing composition is said to have a wide hysteresis width.

Patent Document 4 discloses a thermochromic sheet using a thermochromic composition that was publicly known prior to the filing of this patent application. This sheet has a base sheet, for example, a sheet made of plastic, synthetic paper, rubber, etc., on the lower layer of which is provided an adhesive heat-absorbing layer, and on the upper layer of which is provided a reversible thermochromic layer that reversibly changes color in the temperature range of 25 to 36° C. Since this sheet has a reversible thermochromic layer, the effectiveness of the heat-absorbing effect can be easily determined by visual inspection.

JP 2018-176690 A JP 2017-121707 A JP 2012-188648 A Japanese Patent Application Laid-Open No. 9-313520

The main objective of the present invention is to provide a thermosensitive dye film that is a laminated resin film mainly composed of synthetic resin, in which the coloring or decoloring (hereinafter also referred to as "discoloration") of the film can be confirmed at a certain temperature, and which can prevent peeling of the dye-containing portion due to rubbing, etc.

As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by sandwiching a resin layer containing a temperature-sensitive color material between laminated resin films, and have thus completed the present invention.
The present invention can include, for example, the following.

[1] A thermosensitive dye film, which is a laminated resin film having a base layer and a surface layer mainly composed of synthetic resin, characterized in that a resin layer (thermosensitive dye layer) containing a thermosensitive color material is sandwiched between the two layers.
[2] The temperature-sensitive dye film according to the above [1], wherein a laminated region having the temperature-sensitive dye layer and a laminated region not having the temperature-sensitive dye layer are mixed.
[3] The temperature-sensitive dye film according to the above [2], wherein in the laminated region having the temperature-sensitive dye layer, a portion having the temperature-sensitive dye layer and a portion not having the temperature-sensitive dye layer are mixed.
[4] The temperature-sensitive dye film according to the above [3], in which the portions having a temperature-sensitive dye layer and the portions not having a temperature-sensitive dye layer are formed in a linear manner and alternately parallel to the width direction of the film.
[5] The temperature-sensitive dye film according to any one of the above [1] to [4], wherein the temperature-sensitive dye layer changes color at a plurality of temperature points.
[6] The temperature-sensitive dye film according to any one of the above [1] to [5], wherein the coloring/decoloring of the temperature-sensitive dye layer is reversible.

According to the present invention, the color change of the film allows one to check at a glance that a certain temperature has been reached, making it possible to easily indicate the environmental condition, and also preventing peeling of the dye-containing portion due to rubbing, etc. In addition, in one embodiment, the content of other prints can be easily ascertained. In another embodiment, the visibility of the discolored portion can be improved.

1 is a schematic diagram showing one embodiment of the temperature-sensitive dye film according to the present invention, in which a temperature-sensitive color material (temperature-sensitive dye layer) is colored. The upper figure shows a plan view, and the lower figure shows a cross-sectional view of the upper figure cut horizontally. 1 is a schematic diagram showing one embodiment of the temperature-sensitive dye film according to the present invention, in which a temperature-sensitive color material (temperature-sensitive dye layer) is colored, where part A shows a laminated region having a temperature-sensitive dye layer, and part B shows a laminated region not having a temperature-sensitive dye layer. 1 is a photograph showing one embodiment of a temperature-sensitive dye film according to the present invention, in which a temperature-sensitive color material (temperature-sensitive dye layer) has developed color.

1. About the Temperature-Sensitive Dye Film of the Present Invention The temperature-sensitive dye film of the present invention (hereinafter referred to as "the film of the present invention") is a laminated resin film having a base layer and a surface layer mainly composed of synthetic resin, characterized in that a resin layer (temperature-sensitive dye layer) containing a temperature-sensitive color material is sandwiched between the two layers (see the lower diagram of Figure 1). In the film of the present invention, the temperature-sensitive dye layer containing a temperature-sensitive color material is sandwiched between the base layer and the surface layer, and the dye-containing portion is not exposed to the outside, so that it is less susceptible to deterioration due to external forces, etc.
The base layer and surface layer according to the present invention are preferably transparent or semi-transparent, but may be milky white or colored.

The substrate layer, surface layer, and temperature-sensitive dye layer in the film of the present invention may each be a single layer or a multilayer of two or more layers. The substrate layer may also have heat sealability. When the substrate layer has heat sealability, the substrate layers can be bonded together to form a bag-shaped film of the present invention.

The film of the present invention may have a mixture of laminated regions having a temperature-sensitive dye layer and laminated regions not having a temperature-sensitive dye layer. For example, the film of the present invention may have a mixture of a region (region A in FIG. 2) consisting of three layers, i.e., a base layer/temperature-sensitive dye layer/surface layer, and a region (region B in FIG. 2) consisting of two layers, i.e., a base layer/surface layer, not having a temperature-sensitive dye layer. When a color-developing portion and other printed matter are present, if the film develops color, it may be difficult to see the contents of the printed matter. As shown in region B in FIG. 2 and the upper part of FIG. 3, the film of the present invention has a portion that does not develop color due to temperature, so that the contents of the other printed matter can be seen from there, thereby solving such a problem.
In the film of the present invention, the laminated region having a temperature-sensitive dye layer (region A) and the laminated region not having a temperature-sensitive dye layer (region B) may be present in one location per unit, or may be present independently in two or more locations.

In the film of the present invention, the laminated region (region A) having the temperature-sensitive dye layer may also have a mixture of parts having the temperature-sensitive dye layer and parts not having the temperature-sensitive dye layer. As a preferred embodiment, for example, as shown in each figure, both parts are formed in straight lines or stripes alternately and parallel to the width direction of the film. The discontinuous parallel existence of parts not having the temperature-sensitive dye layer between the regions creates a color contrast, which can improve the visibility of the discolored parts. When the temperature-sensitive dye layer is arranged in stripes as shown in each figure, the width and spacing of each temperature-sensitive dye layer are appropriately set depending on the application.

1.1 Synthetic resin constituting the film of the present invention The base layer and surface layer of the film of the present invention are mainly composed of synthetic resin. The temperature-sensitive dye layer of the film of the present invention is also mainly composed of synthetic resin, except for the temperature-sensitive color material. Examples of such synthetic resins include polyethylene-based resins and polypropylene-based resins.
Here, "mainly composed of synthetic resin" generally means that the material is composed of 50% by weight or more of synthetic resin, preferably 70% by weight or more of synthetic resin, and more preferably 90% by weight or more of synthetic resin.
The resins constituting the base layer, the surface layer and the temperature-sensitive dye layer may be the same or different. Examples of the polyethylene-based resin and the polypropylene-based resin include the following.

1.1.1 Polyethylene Resin In the present invention, preferred examples of the polyethylene resin include ethylene homopolymers, copolymers of ethylene and alkyl methacrylate esters, copolymers of ethylene and other α-olefins, copolymers of ethylene and vinyl acetate, and mixtures thereof.

An example of an ethylene homopolymer is branched low-density polyethylene, which has low density and contains long-chain branches as well as short-chain branches such as ethyl groups. This is produced by the high-pressure method, i.e., the radical polymerization method of ethylene under high pressure of 1000 atmospheres or more.

Examples of the alkyl methacrylate ester, which is the raw material monomer in the copolymer of ethylene and alkyl methacrylate ester, include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and cyclohexyl methacrylate. The most preferred is a copolymer of ethylene and methyl methacrylate.

In the copolymer of ethylene and another α-olefin, the other α-olefin than ethylene may be, for example, an α-olefin having 3 to 20 carbon atoms, specifically, for example, propylene, 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, etc. Among these, those having 3 to 8 carbon atoms, such as 1-hexene, 4-methyl-1-pentene, and 1-octene, are preferred. These other α-olefins than ethylene may be used alone or in combination of two or more kinds.

The content ratio of ethylene and the other α-olefin in the copolymer of ethylene and the other α-olefin is usually 75 to 99.5% by weight of ethylene and 0.5 to 25% by weight of the other α-olefin, preferably 85 to 99% by weight of ethylene and 1 to 15% by weight of the other α-olefin, and more preferably 90 to 98% by weight of ethylene and 2 to 10% by weight of the other α-olefin.
An example of a copolymer of ethylene and another α-olefin is linear low density polyethylene (LLDPE).

For copolymers of ethylene and vinyl acetate, the vinyl acetate content is 4 to 20% by weight, preferably 6 to 15% by weight.

Among these polyethylene resins, those having a melt flow rate (MFR) value measured in accordance with ISO 1133 (1997) at 190°C under a load of 21.18 N (2.16 kg) within the range of 0.5 to 30 g/10 min are preferred, and those having a melt flow rate value within the range of 2 to 10 g/10 min are more preferred.
Furthermore, among the polyethylene resins, those having a density measured in accordance with JIS K 7112 within the range of 0.85 to 0.94 g/cm ³ are preferred, and those having a density within the range of 0.86 to 0.934 g/cm ³ are more preferred.

Among polyethylene resins, branched low-density polyethylene, ethylene-methyl methacrylate copolymer, linear low-density polyethylene, and ethylene-vinyl acetate copolymer are preferred because they have high melt tension when molten, resulting in good thickness accuracy during processing such as extrusion molding.

1.1.2 Polypropylene-based resin In the present invention, examples of the polypropylene-based resin include propylene homopolymers and copolymers of propylene and other α-olefins. Examples of the α-olefins other than propylene include α-olefins having 2 to 10 carbon atoms other than propylene, specifically, α-olefins such as ethylene, 1-butene, 1-pentene, and 1-hexene. Among these, α-olefins having 2 to 4 carbon atoms, such as ethylene and 1-butene, are preferred, and ethylene is more preferred. These α-olefins other than propylene may be used alone or in combination of two or more. The content of the α-olefins other than propylene is suitably 1.3% by weight or less, and preferably 0.5% by weight or less.

Among polypropylene-based resins, it is preferable that the melt flow rate (MFR) value, measured in accordance with ISO1133 (1997) at 230°C and a load of 21.18N (2.16kg), is within the range of 0.5 to 20g/10min. Also, crystalline polypropylene-based resins with a melting point of 155°C to 165°C and a melt flow rate value within the range of 2 to 4g/10min are more preferable. The melt flow rate (MFR) value of the polymer can be adjusted as appropriate depending on the type and content of α-olefins other than propylene, the molecular weight of the polymer, and the degree of polymerization.

Among polypropylene-based resins, those having an isotactic pentad fraction (IP) of 94.0% to 96.0% as determined by ¹³ C nuclear magnetic resonance spectroscopy are preferred.

1.2 Temperature-sensitive dye layer The temperature-sensitive dye layer is a resin layer containing a temperature-sensitive color material. As described above, the temperature-sensitive dye layer is sandwiched between the base layer and the surface layer, or the temperature-sensitive color material is contained between the base layer and the surface layer, and is not exposed to the outside as in the sheet described in Patent Document 4. Therefore, the temperature-sensitive dye layer is not easily peeled off due to rubbing or the like.
In the lower diagram of FIG. 1 showing the cross-sectional shape of the temperature-sensitive dye layer, the cross-section of the temperature-sensitive dye layer is shown as a square, but this is a conceptual diagram, and in reality, the cross-section is often a rounded shape such as an ellipse.

1.2.1 Temperature-sensitive color material There are no particular limitations on the temperature-sensitive color material, so long as it has the property of at least developing color at a specific temperature point and can be blended with a synthetic resin. A temperature-sensitive color material is usually a composition in which a plurality of compounds are combined to exhibit the property. Known temperature-sensitive color materials can be used, and it is preferable that the material exhibits reversible temperature-sensitive color change, which allows color development and decolorization to be repeated. For example, the following can be mentioned.

<A> A thermosensitive color-changing composition described in Patent Document 3. Specifically, in a thermosensitive color-changing composition containing a leuco dye (color former), a color-developing substance (electron-accepting compound), and a color-changing temperature regulator, the color-changing temperature regulator is one or more of the following compounds a to e, or a microcapsule encapsulating this composition.

<B> A warm-sensitive color material containing three components: an electron-donating color-forming organic compound, an electron-accepting compound, and an organic compound medium that reversibly induces a color reaction (see, for example, JP-B-51-35414, JP-B-51-44706, JP-B-1-17154, etc.). Specifically,
(1) A thermosensitive color material having three essential components: (a) an electron-donating color-forming organic compound, (b) a compound having a phenolic hydroxyl group, and (c) a chain aliphatic monohydric alcohol.
(2) A warm-color material having three essential components: (a) an electron-donating color-forming organic compound, (b) a compound having a phenolic hydroxyl group, and (c) a compound selected from esters obtained from aliphatic monohydric alcohols and aliphatic monocarboxylic acids.
(3) A thermosensitive color material having three essential components, namely (a) an electron-donating color-forming organic compound, (b) a compound having a phenolic hydroxyl group, and (c) a compound selected from either a higher aliphatic monohydric alcohol or an ester obtained from an aliphatic monocarboxylic acid and a chain aliphatic monohydric alcohol, and encapsulated in microcapsules.

(4) A warm-color material comprising three essential components, namely, (a) an electron-donating organic color-forming compound, (b) a compound having a phenolic hydroxyl group, and (c) a compound selected from a higher aliphatic monohydric alcohol and an ester obtained from an aliphatic monocarboxylic acid and a chain aliphatic monohydric alcohol, dissolved or dispersed in a vehicle. Alternatively, a warm-color material comprising a compatible solution comprising three essential components, namely, (a) an electron-donating organic color-forming compound selected from pyridines, quinazolines, and bisquinazolines, which, as described in JP-A-7-186546, exhibits a highly colored and bright color such as fluorescent yellow, yellow-orange, orange, red-orange, or red when colored, and exhibits no color residue when decolorized, (b) a compound that is electron-accepting to the electron-donating organic color-forming compound, and (c) a compound that is a reaction medium that reversibly causes an electron transfer reaction between the components (a) and (b) in a specific temperature range. A highly sensitive temperature-sensitive color material having a hysteresis width of 3° C. or less in the color density-temperature curve according to temperature change, as described in JP-B-1-29398.
(5) In addition, a thermosensitive color-changing color-memory thermosensitive color material that changes color with a large hysteresis characteristic is described in JP-B-4-17154. Also, a thermosensitive color material described in JP-A-6-135144, which is obtained by dispersing in the form of fine particles in a vinyl chloride-vinyl acetate copolymer resin or the like a homogeneous compatible solution of an electron-donating color-forming organic compound, a compound having a phenolic hydroxyl group, and a reaction medium that determines the temperature at which the color-forming reaction between the two occurs.

The above-mentioned thermosensitive color materials are effective when used as is, but it is preferable to use them by encapsulating them in microcapsules. This is because the reversible thermochromic material maintains the same composition under various conditions of use and can achieve the same effect. By encapsulating them in microcapsules, a chemically and physically stable pigment can be formed, and a particle size of 0.1 to 100 μm, preferably 3 to 30 μm, is practical. Microencapsulation can be performed by known methods such as interfacial polymerization, in situ polymerization, liquid curing coating, phase separation from an aqueous solution, phase separation from an organic solvent, melt dispersion cooling, air suspension coating, and spray drying, and is appropriately selected depending on the application. Furthermore, a secondary resin film can be provided on the surface of the microcapsules depending on the purpose to impart durability or modify the surface properties for practical use.

The thermal color material is preferably microencapsulated from the viewpoint of ease of handling, etc. A more specific example of the thermal color material is "TC Color" manufactured by Sakura Cray-Pas Corporation.
The temperature-sensitive color material may be used alone or in combination of two or more kinds.

The content of the temperature-sensitive color material in the temperature-sensitive dye layer is not particularly limited as long as the color development at a specified temperature point can be confirmed, and varies depending on the type of temperature-sensitive color material and synthetic resin used, but is usually in the range of 0.001 to 40% by weight, preferably in the range of 0.1 to 10% by weight, and more preferably in the range of 1 to 20% by weight. If the content of the temperature-sensitive color material is in this range, it is preferable because the color change is easily confirmed.

1.2.2 Mode of Temperature-Sensitive Dye Layer The color change of the temperature-sensitive dye layer according to the present invention may occur at one temperature point or at two or more temperature points. When the color change occurs at multiple temperature points, the color change at each temperature point may be the same or different, but when two color change temperature points are close to each other, it is preferable that the two colors at the temperature points are distinguishable by the naked eye.
Color changes at multiple temperature points can be realized by including multiple temperature-sensitive color materials that change color at different temperature points in a single temperature-sensitive dye layer. It can also be realized by having two or more temperature-sensitive dye layers, each of which contains a temperature-sensitive color material that changes color at a different temperature point. When the temperature-sensitive dye layer has three or more layers, some of the layers may contain the same temperature-sensitive color material.

It is preferable that the color change (coloring/decoloring) of the temperature-sensitive dye layer is reversible and can be repeated. The film of the present invention having such a temperature-sensitive dye layer can be reused. For this purpose, a temperature-sensitive color material having the reversibility is usually used.

1.3 Others The film of the present invention may contain an antiblocking agent, a lubricant, an antifogging agent, etc., within the scope of not impairing the effects of the present invention. Examples of such antiblocking agents include commonly used inorganic silica, kaolin, zeolite, etc., or organic crosslinked acrylic beads, etc. Examples of lubricants include calcium stearate, etc. Examples of antifogging agents include three types of agents: alkyldiethanolamine, alkyldiethanolamine fatty acid ester, and glycerin fatty acid ester. The antiblocking agent, lubricant, and antifogging agent may each be used alone or in combination of two or more types.
The amounts of the antiblocking agent, lubricant, antifogging agent, etc. added can be appropriately adjusted depending on the type of resin, etc., within a range that does not impair the effects of the present invention.

The film of the present invention can further contain various additives in appropriate amounts, provided that the effects of the present invention are not impaired. Examples of such additives include nucleating agents, antioxidants, flame retardants, antistatic agents, fillers, pigments, etc.

The thickness of the base layer in the film of the present invention is usually within the range of 2 to 200 μm, preferably within the range of 10 to 125 μm, and more preferably within the range of 20 to 50 μm. The thickness of the surface layer in the film of the present invention is usually within the range of 2 to 200 μm, preferably within the range of 10 to 125 μm, and more preferably within the range of 20 to 50 μm. The thickness of the temperature-sensitive dye layer in the film of the present invention is usually within the range of 10 to 380 μm, preferably within the range of 20 to 300 μm, and more preferably within the range of 30 to 200 μm.
The total thickness of the film of the present invention is usually within the range of 10 to 400 μm, preferably within the range of 15 to 250 μm, and more preferably within the range of 20 to 100 μm.

The thickness ratio of the base layer to the total thickness of the film of the present invention is usually within the range of 10 to 95%, preferably within the range of 30 to 90%, and more preferably within the range of 50 to 90%. When the thickness ratio of the base layer to the total thickness of the film of the present invention is within this range, the color change can be easily confirmed visually, which is preferable.

2. Method for Producing the Film of the Present Invention The method for producing the film of the present invention is not particularly limited, and any method known in the art for laminated resin films can be used. However, taking into consideration the productivity and physical properties of the finished film, it is preferable to produce the film by extrusion molding of a flat sheet.

More specifically, the resin that constitutes the base layer, the resin that constitutes the temperature-sensitive dye layer, and the resin that constitutes the surface layer are each fed into three extruders set to the appropriate temperature, and after the resin is melted and kneaded in the extruders, it is extruded into a sheet from a T-die at 180°C to 250°C. In this case, either the feed block method or the multi-manifold method may be used to form the three-layer laminate structure. The extruded sheet (film) is cooled and solidified by a take-up roll at 25°C to 70°C. After being cooled and fixed, it is wound up by a winder to become a film roll.

In the production of the film of the present invention, known surface treatments such as corona discharge treatment, flame treatment, and ultraviolet irradiation treatment can be performed before winding up with a winding machine. In particular, corona discharge treatment is preferable from the viewpoint of simplicity. By performing the surface treatment, it is possible to impart wetting tension to the surface of the film and enhance the anti-fogging effect, and also to enhance the adhesion to printing ink when printing is performed on the film surface. This corona discharge treatment may be performed on both the surface layer surface and the sealing layer surface, or on either one of the surface layer surface or the sealing layer surface. The strength of the corona discharge treatment is preferably within the range of 1.8×10 ² to 9.0×10 ² J/m ² , and when both sides are treated, both sides may have the same strength or different strengths.

3. Uses of the Film of the Present Invention The film of the present invention can be used for any natural or artificial object to which the film of the present invention can be applied, and since at least a portion of the film develops color when a predetermined temperature is reached, the film of the present invention can be used for any natural or artificial object to which it is desired to visually identify that a certain predetermined temperature has been reached, without any particular limitation.

The present invention will be explained in more detail below with reference to examples and test examples, but the present invention is not limited to these examples in any way.

[Example] Production of the film of the present invention (1) The raw materials used are as follows.
PE-1: Linear low-density polyethylene (density: 0.92 g/cm ³ MFR: 2.0 g/10 min)
CL-1: TC color (Sakura Cray-Pas Corporation, blue, discoloration point: -5°C)
CL-2: TC Color (Sakura Cray-Pas Corporation, red, discoloration point: 20°C)

(2) PE-1 was used as the resin constituting the base layer and the surface layer. 98% by weight of PE-1 was used as the resin constituting the temperature-sensitive dye layer, and 1% by weight each of CL-1 and CL-2, which are temperature-sensitive color materials, was added.
Each of the above resins was fed into an extruder with a barrel temperature of 180 to 200°C, extruded into a sheet from a multilayer die at 205°C, and cooled and solidified by a take-up roll at 40°C to obtain a film. The obtained film is shown in Figure 3. As shown in the lower diagram (cross-sectional view) of Figure 1, the film has a temperature-sensitive dye layer sandwiched between a base layer and a surface layer, and has a multilayer structure region consisting of a laminate region having a temperature-sensitive dye layer (region A) and a laminate region not having a temperature-sensitive dye layer (region B), and in region A, the temperature-sensitive dye layer is formed in strips at regular intervals in the width direction of the film.
The resulting film had a total thickness of 50 μm.

[Test Example 1] Confirmation of discoloration due to temperature The film of the present invention prepared in the above example was placed on a white paper. The temperature was gradually lowered from 20°C or higher, and the color change was measured by applying a spectrophotometer CM-600d (manufactured by Konica Minolta Sensing Co., Ltd.) from directly above, in a mode that includes regular reflection light, with an observation field of view of 10° and an observation light source of standard illuminant D65 for colorimetry, in the L*a*b* color system.

The measurement was performed on an undamaged portion of the film of the present invention. The low temperature was set to −5° C., and the high temperature was set to 20° C. The film was left in the set temperature environment for a sufficient period until the film temperature matched the set temperature, and then the measurement was performed.
Then, the color difference (ΔE) between the low temperature (−5° C.) and the high temperature (20° C.) was calculated using the following formula.

If ΔE is 1.0 or less, the color difference cannot be visually discerned.
When ΔE exceeds 1.0, a color change can be recognized, and when ΔE is 3.0 or more, a color change can be clearly recognized.

The results are shown in Table 1. Color evaluation (color coordinates) was based on Japanese Industrial Standards (JIS) Z8730. In the table, an increase in the a* value indicates a stronger red color, and a decrease in the b* value indicates a stronger blue color.

As shown in Table 1, the values of a* and b* changed significantly only in the dye-containing portion (temperature-sensitive dye layer) of the film of the present invention, indicating an increase in red and blue, and supporting the fact that the color changed to purple. In the dye-free portion (non-temperature-sensitive dye layer) of the film of the present invention, almost no change in the values of a* and b* due to temperature was observed.
In the dye-containing portion (temperature-sensitive dye layer) of the film of the present invention, the color difference between the low temperature (-5°C) and the high temperature (20°C) showed a large value, while in the dye-free portion (non-temperature-sensitive dye layer) of the film of the present invention, only a small value was shown.

The film of the present invention changes color, developing or fading, at a certain temperature, and is therefore useful as a film material for items for which it is desired to confirm at a glance that a certain temperature has been reached.

1 Surface layer 2 Temperature-sensitive dye layer 3 Base layer A Laminated region having a temperature-sensitive dye layer B Laminated region not having a temperature-sensitive dye layer

Claims (6)

A laminated resin film having a base layer and a surface layer,
The laminated resin film is a co-extruded film,
Each of the base layer and the surface layer contains 50% by weight or more of a synthetic resin,
A temperature-sensitive dye film, characterized in that a resin layer containing a temperature-sensitive color material (temperature-sensitive dye layer) is sandwiched between the base layer and the surface layer . The temperature-sensitive dye film according to claim 1, which has a mixture of laminated regions that have the temperature-sensitive dye layer and laminated regions that do not. The temperature-sensitive dye film according to claim 2, in which the laminated region having the temperature-sensitive dye layer includes a mixture of parts having the temperature-sensitive dye layer and parts not having the temperature-sensitive dye layer. The temperature-sensitive dye film according to claim 3, in which the laminated parts having a temperature-sensitive dye layer and the laminated parts not having a temperature-sensitive dye layer are formed in a straight line, alternately parallel to the width direction of the film. The temperature-sensitive dye film according to any one of claims 1 to 4, in which the temperature-sensitive dye layer changes color at multiple temperature points. The temperature-sensitive dye film according to any one of claims 1 to 5, wherein the coloring/decoloring of the temperature-sensitive dye layer is reversible.

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