JP7825983B2 - Absorbent article and indicator composition - Google Patents

Description

The present disclosure relates to absorbent articles and indicator compositions.

Absorbent articles such as disposable diapers are known that are equipped with indicators that can detect the presence or absence of urination or changes in the wearer's health condition by changing color.

Indicators applied to absorbent articles can qualitatively display the specific gravity of the wearer's urine, as disclosed in Patent Document 1, for example.

In recent years, indicators for detecting urine made from thermoplastic solid materials have also been put to practical use. For example, Patent Document 2 discloses a thermoplastic indicator composition. According to this document, such an indicator composition can hold the wetness indicator in a desired position within the product, and can also contribute to reducing leaching of the colorant by forming intermolecular bonding forces.

JP 2009-18183 A Special table 2015-529151 publication

Absorbent articles equipped with an indicator that can detect changes in urine specific gravity require high visibility, i.e., ease of discrimination between the color differences corresponding to urine specific gravity, and high responsiveness, i.e., the speed with which the indicator changes color after the wearer urinates.

The present invention aims to provide an absorbent article equipped with an indicator that can detect changes in urine specific gravity with improved visibility and responsiveness.

One aspect of the present invention (Aspect 1) is
The device has a top sheet layer, an absorbent layer, an indicator layer, and a leak-proof layer in this order,
the absorbent layer has an absorbent core layer and a core wrap layer covering at least the leakproof layer side of the absorbent core layer,
The indicator layer comprises:
The outer color of the protective layer is adjusted to an alkaline color in an initial state before contact with urine, and is capable of changing color to a color corresponding to the specific gravity of urine upon contact with urine; and the protective layer is at least partially directly bonded to the core wrap layer and the leakproof layer and disposed therebetween.
It is an absorbent article.

In the absorbent article according to aspect 1, the indicator layer can change color in accordance with the specific gravity of urine. More specifically, unlike the color change for detecting the presence or absence of urination (i.e., a color change from an acidic color to an alkaline color), the indicator layer changes color from an alkaline appearance color in accordance with the specific gravity of urine (i.e., in accordance with the ion concentrations of sodium ions (Na ⁺ ), potassium ions (K ⁺ ), calcium ions (Ca ²⁺ ), magnesium ions (Mg ²⁺ ), etc. in the urine), so that when the indicator layer is applied to an absorbent article such as a disposable diaper, a wearer of the absorbent article or an assistant thereof can easily recognize the change in the specific gravity of urine.

Absorbent articles using such indicator layers require high visibility in order to more accurately confirm color changes. Furthermore, color changes according to urine specific gravity are useful for determining the wearer's physical condition, such as their growth rate or the presence or absence of dehydration, but it is desirable to determine such conditions as quickly as possible after the wearer has urinated.

In the absorbent article according to aspect 1, the indicator layer is directly bonded to and positioned between the core wrap layer and the leakproof layer.

When the indicator layer is directly bonded to the core wrap layer, urine held in the core wrap layer easily flows into the indicator layer through the bonded area. This causes the indicator layer to change color more quickly than when the indicator layer is not directly bonded to the core wrap layer. This improves responsiveness.

Furthermore, when the indicator layer is directly bonded to the leakproof layer, it is easier to see the indicator layer from the leakproof layer side compared to when the indicator layer is not directly bonded to the leakproof layer.

In other words, the absorbent article according to aspect 1 has high visibility and responsiveness.

In another aspect (Aspect 2) of the present invention, in the absorbent article described in Aspect 1, the indicator layer contains a thermoplastic component having a melting point or softening point within the range of 40°C to 120°C.

In the absorbent article of Aspect 2, the indicator layer contains a thermoplastic component having a melting point or softening point within the range of 40°C to 120°C. When the indicator layer contains a thermoplastic component having a melting point or softening point within this range, the absorbent article described in Aspect 1 can be easily formed, for example, by applying the indicator layer to the leakproof layer at the melting point or softening point during the manufacture of the absorbent article, and then placing the core wrap layer on the indicator layer before the indicator layer solidifies and optionally pressing.

Furthermore, absorbent articles are typically used at temperatures below 40°C, for example, around 36°C, which is the wearer's general body temperature. Therefore, the indicator layer is less likely to deform due to temperature during use, and the bond between the indicator layer and the core wrap layer and leakproof layer is less likely to be destroyed by, for example, the wearer's movements.

In other words, the absorbent article according to aspect 2 has high productivity and durability while achieving high visibility and responsiveness.

In yet another aspect (Aspect 3) of the present invention, in the absorbent article described in Aspect 1 or 2, the indicator layer further contains at least one of a hydrophilic polymer and an amine-based cationic surfactant.

In the absorbent article according to aspect 3, the indicator layer further contains at least one of a hydrophilic polymer and an amine-based cationic surfactant. Therefore, the indicator layer is highly responsive in changing color to changes in urine specific gravity when it comes into contact with urine, and can clearly change color even when the change in urine specific gravity is small.

In other words, the absorbent article according to aspect 3 has high responsiveness.

In yet another aspect (Aspect 4) of the present invention, in the absorbent article described in any one of Aspects 1 to 3, the indicator layer changes color to blue or green when it comes into contact with low-specific-gravity urine, and changes color to yellow or orange when it comes into contact with high-specific-gravity urine.

In the absorbent article of aspect 4, the indicator layer does not undergo a color change to detect the presence or absence of urination (i.e., a color change from the acidic side of the pH indicator in the indicator to the alkaline side), but rather changes color to blue or green when it comes into contact with low-specific-gravity urine and to yellow or orange when it comes into contact with high-specific-gravity urine. Therefore, when applied to absorbent articles such as disposable diapers, the wearer of the absorbent article or their assistant can easily recognize changes in urine specific gravity, and in particular, the color change from the initial color before contact with urine to yellow or orange when it comes into contact with high-specific-gravity urine is more easily visible.

In other words, the absorbent article according to aspect 4 can detect changes in urine specific gravity more accurately and easily.

In yet another aspect (Aspect 5) of the present invention, in the absorbent article described in any one of Aspects 1 to 4, the indicator layer contains a liquid component that is liquid at 36°C, and when the absorbent article is viewed in the stacking direction, the liquid component is impregnated into the leakproof layer in at least a portion of the area that overlaps with the indicator layer.

When the leakproof layer is impregnated with liquid components, the liquid components fill the gaps between the indicator layer and the leakproof layer, as well as the tiny spaces inside the leakproof layer. This reduces diffuse reflection in these areas, making the visible light transmittance higher than in other parts of the leakproof layer.

As a result, in the absorbent article according to aspect 5, when the absorbent article is viewed from the stacking direction, the visible light transmittance of at least a portion of the leakproof layer that overlaps with the indicator layer is high, making it easier to visually recognize discoloration of the indicator layer from the leakproof layer side.

In yet another aspect (Aspect 6) of the present invention, in the absorbent article described in any one of Aspects 1 to 5, the leakproof layer is a layer of hydrophobic nonwoven fabric, and the indicator layer has a leakproof layer impregnated portion that penetrates into the leakproof layer.

When the leak-barrier layer is a hydrophobic nonwoven fabric, it can prevent liquid in urine from leaking to the opposite side of the leak-barrier layer while allowing volatile components in urine, such as water vapor, to escape. However, such layers typically tend to have lower visible light transmittance than non-porous layers due to the difference in refractive index between the air in the voids in the nonwoven fabric and the material that makes up the leak-barrier layer.

The absorbent article according to aspect 6 has a leakproof layer impregnated portion in which the indicator layer is embedded in the leakproof layer.

When the indicator layer is embedded in the leakproof layer, when viewed from the stacking direction of the absorbent article, the thickness of the leakproof layer alone, where the indicator layer is not embedded, in the area overlapping the impregnated portion of the leakproof layer is thinner than the thickness of the leakproof layer alone in other areas where the indicator layer is not embedded. Therefore, when viewed from the stacking direction of the absorbent article, the indicator layer is more visible in the area overlapping the impregnated portion of the leakproof layer when viewed from the leakproof layer side.

In other words, in the absorbent article according to aspect 6, when the absorbent article is viewed from the stacking direction, the visible light transmittance of at least a portion of the leakproof layer that overlaps with the indicator layer is high, making it easier to visually recognize discoloration of the indicator layer from the leakproof layer side.

In yet another aspect (Aspect 7) of the present invention, the absorbent article described in any one of Aspects 1 to 6 further comprises a backsheet layer on the side of the leakproof layer opposite the side on which the indicator layer is disposed, and when the absorbent article is viewed in the stacking direction, the basis weight of at least a portion of the area of the backsheet layer that overlaps with the indicator layer is smaller than that of the remaining portions of the backsheet layer.

In the absorbent article according to aspect 7, when viewed in the stacking direction, the basis weight of at least a portion of the area of the backsheet layer that overlaps with the indicator layer is smaller than that of the remaining portions of the backsheet layer.

As a result, in the absorbent article according to aspect 7, the discoloration of the indicator layer is more easily visible from the backsheet layer side.

In yet another aspect (Aspect 8) of the present invention, in the absorbent article described in any one of Aspects 1 to 7, when the absorbent article is viewed in the stacking direction, the layers closer to the leakproof layer than the indicator layer have a visible light transmittance of 30.0% or more and 90.0% or less in the visible spectral range, at least in the region overlapping with the indicator layer.

In the absorbent article of aspect 8, the layers closer to the leakproof layer than the indicator layer have a visible light transmittance of 30.0% or more and 90.0% or less in the visible spectrum, at least in the region where they overlap with the indicator layer.

In the absorbent article according to aspect 8, the layer on the leakproof layer side has a predetermined visible light transmittance. Therefore, the color change of the indicator layer can be detected through the layer on the leakproof layer side of the indicator layer, while feces and urine cannot be seen through those layers.

Note that "layers closer to the leakproof layer than the indicator layer" refer to all layers located on the opposite side of the indicator layer from the side on which the absorbent layer is located, when viewed in the stacking direction. Therefore, for example, if an absorbent article is arranged in the order of top sheet layer/absorbent layer/indicator layer/leakproof layer/...other layers..., "layers closer to the leakproof layer than the indicator layer" refers to the leakproof layer and the above-mentioned "other layers."

In yet another aspect (Aspect 9) of the present invention, in the absorbent article described in any one of Aspects 1 to 8, the indicator layer has a core wrap layer impregnation portion that is embedded within the core wrap layer.

In the absorbent article according to Aspect 9, the indicator layer has a core wrap layer impregnated portion that penetrates into the core wrap layer. Within the core wrap layer, urine easily travels along the core wrap layer impregnated portion to the entire indicator layer. In other words, when the wearer urinates, the core wrap layer impregnated portion acts as a path for urine flowing from the absorbent core layer into the core wrap layer to pass through the core wrap layer and reach the entire indicator layer.

As a result, the absorbent article according to aspect 9 can achieve even higher responsiveness.

In yet another aspect (Aspect 10) of the present invention, in the absorbent article described in Aspect 9, when the absorbent article is viewed in the stacking direction, the area of the impregnated portion of the core wrap layer is 20.0% or more of the area of the indicator layer.

In the absorbent article of Aspect 10, assuming the configuration of the absorbent article of Aspect 9, when the absorbent article is viewed in the stacking direction, the area of the impregnated portion of the core wrap layer is larger than a predetermined percentage of the area of the indicator layer, making it particularly easy for urine to move through the impregnated portion of the core wrap layer and throughout the indicator layer within the core wrap layer.

This allows for even higher responsiveness.

In yet another aspect (Aspect 11) of the present invention, in the absorbent article described in Aspects 9 or 10, the impregnated portion of the core wrap layer partially extends to the surface of the core wrap layer facing the absorbent core layer and is in contact with the absorbent core layer.

In the absorbent article of aspect 11, this configuration allows urine absorbed by the absorbent core layer to come into direct contact with the indicator layer.

As a result, the absorbent article according to aspect 11 can achieve even higher responsiveness.

In yet another aspect (Aspect 12) of the present invention, in the absorbent article described in Aspect 11, when the absorbent article is viewed in the stacking direction, the area of the portion of the core wrap layer impregnated portion that reaches the surface on the absorbent core layer side is 50.0% or less of the area of the indicator layer.

In the absorbent article of Aspect 12, due to the above configuration, urine that travels from the absorbent core layer side of the core wrap layer through the core wrap layer impregnation portion and reaches the indicator layer is easily diffused in the planar direction by the core wrap layer near the portion of the indicator layer that is on the core wrap layer side, making it particularly easy for urine to move throughout the entire indicator layer. This makes it possible to achieve even higher responsiveness.

In yet another aspect (Aspect 13) of the present invention, in the absorbent article described in any one of Aspects 1 to 12, when the absorbent article is viewed in the stacking direction, the density of at least a portion of the area of the absorbent core layer that overlaps with the indicator layer is greater than that of other areas of the absorbent core layer.

In areas of the absorbent core layer that are denser than other areas, such as around embossed areas, urine moves faster in the thickness direction than in other areas. This is because urine moves more easily through the denser areas.

In the absorbent article according to aspect 13, when the absorbent article is viewed in the stacking direction, a portion of the absorbent core layer that is denser than other regions overlaps with at least a portion of the region that overlaps with the indicator layer. This makes it easier for urine to move to the indicator layer more quickly when the wearer urinates.

As a result, the absorbent article according to aspect 13 can achieve even higher responsiveness.

In yet another aspect (Aspect 14) of the present invention, in the absorbent article described in any one of Aspects 1 to 13, the indicator layer has a non-impregnated portion that is not impregnated into either the core wrap layer or the leakproof layer.

The non-impregnated portion of the indicator layer has a higher density of the components that make up the indicator layer compared to the portions that are impregnated in the core wrap layer and leakproof layer. As a result, the non-impregnated portion is more susceptible to discoloration by urine than the portions that are impregnated in the core wrap layer and leakproof layer.

As a result, the absorbent article according to aspect 14 can achieve higher visibility.

In yet another aspect (Aspect 15) of the present invention, the absorbent article described in any one of Aspects 1 to 14 is for use in toilet training.

Before toilet training can begin, a child's physical and mental development, including brain and urinary functions, must reach a certain level, but this level of development varies from person to person, making it difficult to determine.

In the absorbent article of aspect 15, the indicator layer responds to urine, and the toilet training indicator responds differently to urine depending on the infant's developmental stage, making it possible to determine when it is time to start toilet training for the infant.

Yet another aspect (Aspect 16) of the present invention is an indicator composition that, in its initial state before contact with urine, has an appearance color adjusted to the alkaline side, and upon contact with urine, changes color to a color corresponding to the urine specific gravity, and contains a thermoplastic component that has a melting point or softening point within the range of 40°C to 120°C.

The indicator composition according to aspect 16 is adjusted to have an appearance color on the alkaline side in an initial state before contact with urine, and is capable of changing color upon contact with urine to a color corresponding to the specific gravity of urine. More specifically, unlike the color change for detecting the presence or absence of urination (i.e., the color change from the acidic side of the pH indicator in the indicator to the alkaline side), the indicator composition changes color from the appearance color on the alkaline side in response to the specific gravity of urine (i.e., in response to the ion concentrations of sodium ions (Na ⁺ ), potassium ions (K ⁺ ), calcium ions (Ca ²⁺ ), magnesium ions (Mg ²⁺ ), etc. in the urine), so that when applied to absorbent articles such as disposable diapers, the wearer of the absorbent article or their assistant can easily recognize the change in the specific gravity of urine.

The indicator composition according to aspect 16 contains a thermoplastic component having a melting point or softening point within the range of 40°C to 120°C. Therefore, for example, when manufacturing an absorbent article, the indicator composition can be applied to the leakproof layer at the melting point or softening point, and then a core wrap layer can be placed on the indicator composition before the indicator composition solidifies, thereby easily forming the absorbent articles described in aspects 1 to 15.

This disclosure makes it possible to provide an absorbent article equipped with an indicator that can detect changes in urine specific gravity with improved visibility and responsiveness.

FIG. 1 is a schematic diagram of a disposable diaper 1 according to a first embodiment of the present invention. FIG. 2 is an enlarged end view of the cross section of the disposable diaper 1 taken along line II-II in FIG. FIG. 3 is an enlarged view of region X in FIG. FIG. 4 is an enlarged view of a region similar to region X in FIG. 2 of a disposable diaper 1 according to a second embodiment of the present invention. FIG. 5 is an enlarged view of a region similar to region X in FIG. 2 of a disposable diaper 1 according to a third embodiment of the present invention. FIG. 6 is an enlarged view of a region similar to region X in FIG. 2 of a disposable diaper 1 according to a fourth embodiment of the present invention. FIG. 7 is an enlarged view of a region similar to region X in FIG. 2 of a disposable diaper 1 according to a fifth embodiment of the present invention.

Embodiments of the present disclosure are described in detail below. The present disclosure is not limited to the following embodiments, and various modifications can be made within the spirit and scope of the disclosure. The absorbent article of the present invention will be described in detail below using an embodiment in which the absorbent article is applied to a disposable diaper, which is an example of an absorbent article. In this specification, unless otherwise specified, the "side that is closer to the wearer's skin when the absorbent article is worn" in the thickness direction of the absorbent article is referred to as the "skin-facing side," and the "side that is closer to the wearer's skin when the absorbent article is worn" is referred to as the "non-skin-facing side." Furthermore, in the present invention, the layering direction of the absorbent article refers to the direction in which the layers that make up the absorbent article are layered when the absorbent article is in its unfolded state.

Absorbent Articles
The absorbent article of the present invention comprises a top sheet layer, an absorbent layer, an indicator layer, and a leakproof layer in this order, and the absorbent layer comprises an absorbent core layer and a core wrap layer covering at least the leakproof layer side of the absorbent core layer. The indicator layer is initially adjusted to have an appearance color on the alkaline side before contact with urine, and is capable of changing color to a color corresponding to the specific gravity of urine upon contact with urine, and is at least partially directly bonded to and disposed between the core wrap layer and the leakproof layer.

Here, "directly bonded" means that the indicator layer and the leakproof layer, and the indicator layer and the core wrap layer, are bonded in direct physical contact with each other without any other layer, such as an adhesive layer, in between.

Furthermore, when the indicator layer is "disposed between" the leakproof layer and the core wrap layer, it means that the absorbent article has a configuration in which the core wrap layer, indicator layer, and leakproof layer are arranged in that order when viewed from the stacking direction. Therefore, a portion of the indicator layer may penetrate into the core wrap layer and/or the leakproof layer. Here, even if a portion of the indicator layer that penetrates into the core wrap layer and/or the leakproof layer reaches the opposite side of the core wrap layer and/or the leakproof layer (the skin-facing side of the core wrap layer and/or the non-skin-facing side of the leakproof layer), the indicator layer is considered to be disposed between the core wrap layer and the leakproof layer.

In the absorbent article of the present invention, the indicator layer can change color in response to the specific gravity of urine. More specifically, unlike the color change for detecting the presence or absence of urination (i.e., a color change from the acidic side color of the pH indicator in the indicator to the alkaline side color), the indicator layer changes color from the alkaline side appearance color in response to the specific gravity of urine (i.e., in response to the ion concentrations of sodium ions (Na ⁺ ), potassium ions (K ⁺ ), calcium ions (Ca ²⁺ ), magnesium ions (Mg ²⁺ ), etc. in the urine), so that when applied to an absorbent article such as a disposable diaper, a wearer of the absorbent article or an assistant thereof can easily recognize the change in the specific gravity of urine.

Absorbent articles using such indicator layers require high visibility in order to more accurately confirm color changes. Furthermore, color changes according to urine specific gravity are useful for determining the wearer's physical condition, such as their growth rate or the presence or absence of dehydration, but it is desirable to determine such conditions as quickly as possible after the wearer has urinated.

In the absorbent article of the present invention, the indicator layer is directly bonded to and positioned between the core wrap layer and the leakproof layer.

When the indicator layer is directly bonded to the core wrap layer, urine held in the core wrap layer easily flows into the indicator layer through the bonded area. This causes the indicator layer to change color more quickly than when the indicator layer is not directly bonded to the core wrap layer. This improves responsiveness.

Furthermore, when the indicator layer is directly bonded to the leakproof layer, it is easier to see the indicator layer from the leakproof layer side compared to when the indicator layer is not directly bonded to the leakproof layer.

In other words, the absorbent article of the present invention has high visibility and responsiveness.

Figure 1 is a schematic diagram of a disposable diaper 1 according to a first embodiment of the present invention. Figure 2 is an enlarged end view of a cross section of the disposable diaper 1 taken along line II-II in Figure 1. Note that Figures 1 and 2 are not intended to limit the absorbent article of the present invention.

As shown in FIG. 1, disposable diaper 1 has a front portion that is positioned around the wearer's lower abdomen when worn, a rear portion that is positioned around the wearer's buttocks when worn, and an intermediate portion that is positioned between the front and rear portions and is positioned around the wearer's crotch when worn. Disposable diaper 1 has a pants-type outer shape, with both left and right ends of the front portion and both left and right ends of the rear portion joined together, forming a waist opening formed by the upper end of the front portion and the upper end of the rear portion, and a pair of leg openings formed on both left and right sides of the intermediate portion. In other words, disposable diaper 1 is a so-called pants-type disposable diaper.

As shown in Figure 2, the disposable diaper 1, like conventional disposable diapers, comprises, in this order from the skin-facing side to the non-skin-facing side, a top sheet layer 2, an absorbent layer 4, an indicator layer 5, and a leakproof layer 3. The absorbent layer 4 comprises an absorbent core layer 4a and a core wrap layer 4b covering at least the leakproof layer 3 side of the absorbent core layer 4a (in Figure 2, it covers the entire layer). The indicator layer 5 is initially adjusted to an alkaline appearance color before contact with urine, and upon contact with urine, can change color to a color corresponding to the specific gravity of urine. The indicator layer 5 is at least partially directly bonded to and disposed between the core wrap layer 4b and the leakproof layer 3.

The absorbent article of the present invention is not particularly limited as long as it is an absorbent article that is intended to absorb at least urine, and can be applied to a variety of absorbent articles, including pants-type disposable diapers, tape-type disposable diapers, incontinence pads, and the like.

For example, if the indicator of the present invention is applied to a disposable diaper for toilet training an infant, it has the advantage of being able to appropriately visualize the change in the specific gravity of the urine excreted from the infant, thereby making it possible to estimate whether the infant's body is ready for toilet training. In other words, the absorbent article of the present invention is preferably for use in toilet training.

Furthermore, when the indicator of the present invention is applied to adult disposable diapers, it has the advantage of being able to detect signs of dehydration by appropriately visualizing changes in the specific gravity of urine excreted by an adult wearer, such as a care recipient.

In addition, the absorbent article of the present invention may have a colored portion that serves as a color sample of the color change in urine specific gravity, in order to make it easier to determine the color change in the indicator layer depending on the urine specific gravity.

The colored portion is preferably located on the non-skin-facing side of the leakproof layer, i.e., on the side of the leakproof layer opposite the side on which the indicator layer is located when the absorbent article is viewed in the stacking direction. This allows the color of the colored portion to closely match the color change of the indicator layer, making it possible to more accurately observe the color change of the indicator layer in response to the specific gravity of urine.

It is also preferable that the colored portion be spaced apart from the indicator layer in the planar direction when the absorbent article is in its unfolded state. This allows the color change of the indicator layer and the colored portion to be clearly distinguished.

The degree of discoloration of the indicator layer may be determined with the naked eye, or may be determined by optically measuring reflectance, etc. When determining the degree of discoloration with the naked eye, for example, it can be determined by visually comparing the color tone of the indicator with the color tone of a pre-created standard color chart (i.e., color sample). When determining the degree of discoloration with optical measurement, for example, it can be determined by processing an image of the indicator taken with a photographing device such as a digital camera or smartphone using an image processing program installed on a computer, smartphone, etc.

Top sheet layer
The top sheet layer is disposed at a position on the skin-facing side in the thickness direction of the absorbent article, and forms the contact surface that can come into contact with the wearer's skin, i.e., the skin-facing surface of the absorbent article, and is formed from a liquid-permeable sheet-like material such as a nonwoven fabric. The outer shape, various dimensions, basis weight, etc. of the top sheet layer are not particularly limited as long as they can be used as the top sheet layer of an absorbent article, and any outer shape, various dimensions, basis weight, etc. can be adopted depending on the desired liquid permeability, feel to the skin, flexibility, strength, etc.

<Absorbent layer>
The absorbent layer has an absorbent core layer and a core wrap layer covering at least the leakproof layer side of the absorbent core layer.

The outer shape, various dimensions, basis weight, etc. of the absorbent layer are not particularly limited as long as they can be used as an absorbent layer in an absorbent article, and any outer shape, various dimensions, basis weight, etc. can be adopted depending on the desired absorbency, flexibility, strength, etc.

(Absorbent core layer)
The absorbent core layer can be made of an absorbent material containing at least one of absorbent fibers and superabsorbent polymers. Examples of absorbent fibers include pulp fibers (e.g., ground pulp), cotton, rayon, acetate, and other cellulosic fibers. Examples of superabsorbent polymers include starch-based superabsorbent polymers and granular synthetic polymer-based superabsorbent polymers (so-called "SAP") such as sodium acrylate copolymers.

When the absorbent article is viewed in the stacking direction, it is preferable that the density of at least a portion of the area of the absorbent core layer that overlaps with the indicator layer is greater than that of other areas of the absorbent core layer.

The portion of the absorbent core layer that has a higher density than other areas of the absorbent core layer may be, for example, an embossed portion applied to the absorbent core layer.

Urine moves more easily around the high-density regions of the absorbent core layer through the high-density areas, and therefore moves faster in the thickness direction than in other parts of the absorbent core layer. Therefore, when the wearer urinates, urine tends to move to the indicator layer more quickly when the absorbent core layer has a high-density region compared to when the absorbent core layer does not have a high-density region.

Figure 3 is an enlarged view of area X in Figure 2. Note that Figure 3 is not intended to limit the absorbent article of the present invention.

As shown in FIG. 3, the absorbent core layer 4a of the disposable diaper 1 according to the first embodiment of the present invention has a portion having a higher density than other regions of the absorbent core layer 4a, i.e., a high-density region 41. When viewed in the stacking direction, the high-density region 41 overlaps with at least a portion of the region overlapping with the indicator layer 5.

(Core wrap layer)
The core wrap layer is a hydrophilic layer that covers at least the leakbarrier side of the absorbent core layer. The core wrap layer can be formed, for example, from an SMS nonwoven fabric, an SB nonwoven fabric, a spunlace nonwoven fabric, or a tissue sheet (pulp fiber). The core wrap layer needs to cover at least the leakbarrier side of the absorbent core layer, but it may also cover the entire surface of the absorbent core layer, for example.

<Indicator layer>
The indicator layer is adjusted to have an appearance color on the alkaline side in its initial state before coming into contact with urine, and is capable of changing color to a color corresponding to the specific gravity of urine upon contact with urine, and is at least partially directly bonded to the core wrap layer and the leakproof layer and disposed between them.

The indicator layer may contain a thermoplastic component with a melting or softening point within the range of 40°C to 120°C. Here, "softening point" and "melting point" refer to the "endothermic onset temperature" and "peak top temperature," respectively, when measuring the endothermic behavior of the solid-to-liquid transition at a heating rate of 10°C/min using a differential scanning calorimeter. Specific components are described below in the "Indicator Composition" section.

When the indicator layer contains a thermoplastic component having a melting point or softening point within this range, the absorbent article described in Aspect 1 can be easily formed, for example, by applying the indicator layer to the leakproof layer at the melting point or softening point during the manufacture of the absorbent article, and then placing the core wrap layer on the indicator layer before the indicator layer solidifies and optionally pressing them together.

Furthermore, absorbent articles are typically used at temperatures below 40°C, for example, around 36°C, which is the wearer's general body temperature. Therefore, the indicator layer is less likely to deform due to temperature during use, and the bond between the indicator layer and the core wrap layer and leakproof layer is less likely to be destroyed by, for example, the wearer's movements.

This allows for high visibility and responsiveness while also achieving high productivity and durability.

The indicator layer may further contain at least one of a hydrophilic polymer and an amine-based cationic surfactant. Specific hydrophilic polymers and amine-based cationic surfactants are described below in the "Indicator Composition" section.

When the indicator layer further contains at least one of a hydrophilic polymer and an amine-based cationic surfactant, the color change is highly responsive to changes in urine specific gravity when the indicator layer comes into contact with urine, and a clear color change can occur even when the change in urine specific gravity is small.

The indicator layer may also contain a liquid component that is liquid at 36°C. Specific components are described below in the "Indicator Composition" section.

The indicator layer can also change color to blue or green when it comes into contact with low-specific-gravity urine, and to yellow or orange when it comes into contact with high-specific-gravity urine. The composition for achieving this color change is also described below in the "Indicator Composition" section.

If the indicator layer is different from the color change required to detect the presence or absence of urination (i.e., a color change from an acidic to an alkaline color), and instead changes color to blue or green when it comes into contact with low-specific-gravity urine and yellow or orange when it comes into contact with high-specific-gravity urine, when applied to absorbent articles such as disposable diapers, the wearer of the absorbent article or their assistant can easily recognize the change in urine specific gravity, and in particular, the color change from the initial color before contact with urine to yellow or orange when it comes into contact with high-specific-gravity urine is more easily visible. This allows for more accurate and easier detection of changes in urine specific gravity.

The following descriptions of "indicator compositions" are merely examples of materials that can be used to form the indicator layer of the absorbent article of the present invention, and the materials that can form the indicator layer of the absorbent article of the present invention are not limited to these.

(Core wrap layer impregnation part)
The indicator layer preferably has a core wrap layer impregnation portion that penetrates into the core wrap layer.

When the indicator layer has a core wrap layer impregnated portion, urine easily migrates through the core wrap layer impregnated portion within the core wrap layer to the entire indicator layer. In other words, when the wearer urinates, the core wrap layer impregnated portion acts as a path for urine flowing from the absorbent core layer into the core wrap layer through the core wrap layer to reach the entire indicator layer. This makes it easy for urine to migrate through the core wrap layer impregnated portion within the core wrap layer to the entire indicator layer.

Here, the indicator layer "penetrating" into the core wrap layer means that solid components of the indicator composition that makes up the indicator layer, such as the thermoplastic components described below in "Indicator Composition," are present within the core wrap layer. The impregnated portion of the core wrap layer is continuous with the other portions of the indicator layer.

The presence or absence of the core wrap layer impregnated portion can be determined, for example, by observing a cross section of the absorbent article in the stacking direction using an electron microscope.

When the absorbent article is viewed in the stacking direction, it is preferable that the area of the impregnated portion of the core wrap layer be 20.0% or more of the area of the indicator layer.

When the area of the impregnated portion of the core wrap layer is 20.0% or more of the area of the indicator layer, urine is particularly likely to migrate through the impregnated portion of the core wrap layer and throughout the entire indicator layer. This allows for even higher responsiveness.

Furthermore, when the absorbent article is viewed in the stacking direction, the area of the impregnated portion of the core wrap layer may be 30.0% or more and 95.0% or less of the area of the indicator layer. This percentage may be 20.0% or more, 30.0% or more, 40.0% or more, or 50.0% or more, and may be 95.0% or less, 75.0% or less, or 65.0% or less.

Figure 4 is an enlarged view of a region similar to region X in Figure 2 of a disposable diaper 1 according to a second embodiment of the present invention. Note that Figure 4 is not intended to limit the absorbent article of the present invention.

As shown in FIG. 4, in a disposable diaper 1 according to the second embodiment of the present invention, the indicator layer 5 has a core wrap layer impregnated portion 52 that extends into the core wrap layer 4b.

It is also preferable that the impregnated portion of the core wrap layer partially reaches the surface of the core wrap layer facing the absorbent core layer and is in contact with the absorbent core layer.

This configuration allows urine absorbed by the absorbent core layer to come into direct contact with the indicator layer. This allows urine absorbed by the absorbent core layer to diffuse more quickly throughout the indicator layer, achieving even faster responsiveness.

The ratio of the area of the impregnated portion of the core wrap layer, as viewed from the stacking direction of the absorbent article, to the area of the indicator layer can be measured, for example, by the following methods (1) to (5):
(1) A sample in which the core wrap layer, indicator layer, and leakproof layer are integrated is removed from the absorbent article, and the area where the indicator layer is present is identified (for example, for a sample in which the indicator layer is applied to an area 6 mm wide x 100 mm long, a 6 mm wide x 50 mm long area in the longitudinal center). This area is the area to be measured.
(2) Peeling the core wrap layer from the absorbent article. The peeled core wrap layer is also peeled from both the absorbent core layer and the indicator layer.
(3) Place the core wrap layer with the indicator layer side facing up on the standard white plate, and take an image including the area to be measured with a digital camera. * Take the image under normal indoor lighting conditions, taking care to avoid shadows or reflected light.
(4) For the captured image, adjust the white balance in the captured area, and set the H (hue) value in the HSV color space of the material constituting the core wrap layer (the area that does not overlap with the indicator layer) to be within the range of 40 to 70.
(5) Next, measure the area of the portion in the measurement area where the H (color layer) value is 100 or more, and divide the area by the area of the entire measurement area to obtain the ratio of the area of the impregnated portion of the core wrap layer when viewed from the stacking direction of the absorbent article to the area of the indicator layer.

When the absorbent article is viewed in the stacking direction, it is preferable that the area of the portion of the core wrap layer impregnated portion that reaches the surface on the absorbent core layer side be 50.0% or less of the area of the indicator layer.

When the area of the portion of the core wrap layer impregnated portion that reaches the surface facing the absorbent core layer is within the above-mentioned range, urine that travels from the absorbent core layer side of the core wrap layer through the core wrap layer impregnated portion and reaches the indicator layer is easily diffused in the planar direction by the core wrap layer near the portion of the indicator layer facing the core wrap layer, making it particularly easy for urine to move throughout the entire indicator layer.

This allows for even higher responsiveness.

When the absorbent article is viewed in the stacking direction, it is particularly preferable that the area of the portion of the impregnated portion of the core wrap layer that reaches the surface on the absorbent core layer side be 50.0% or less and 0.2% or more of the area of the indicator layer.

When the area of the core wrap layer impregnated portion that reaches the surface facing the absorbent core layer is 50% or less, urine that travels from the absorbent core layer side of the core wrap layer through the core wrap layer impregnated portion to reach the indicator layer is diffused in the surface direction by the core wrap layer to a particularly large extent near the portion of the indicator layer on the core wrap layer side. On the other hand, when the area of the core wrap layer impregnated portion that reaches the surface facing the absorbent core layer is 0.2% or more, a sufficient path is formed for urine to travel from the absorbent core layer side of the core wrap layer through the core wrap layer impregnated portion to reach the indicator layer.

The area of the portion of the core wrap layer impregnated portion that reaches the surface on the absorbent core layer side may be 50.0% or less, 20.0% or less, or 5.0% or less of the area of the indicator layer, and may be 0.2% or more, 0.5% or more, or 1.0% or more.

The ratio of the area of the portion of the impregnated portion of the core wrap layer that reaches the surface on the absorbent core layer side to the area of the indicator layer can be measured, for example, by the following methods (1) to (5):
(1) A sample in which the core wrap layer, indicator layer, and leakproof layer are integrated is removed from the absorbent article, and the area where the indicator layer is present is identified (for example, for a sample in which the indicator layer is applied to an area 6 mm wide x 100 mm long, a 6 mm wide x 50 mm long area in the longitudinal center). This area is the area to be measured.
(2) Peeling the core wrap layer from the absorbent article. The peeled core wrap layer is also peeled from both the absorbent core layer and the indicator layer.
(3) Place the core wrap layer with the absorbing core layer side facing up on the standard white board, and take an image including the area to be measured with a digital camera. * Take the image under normal indoor lighting conditions, taking care to avoid shadows or reflected light.
(4) For the captured image, adjust the white balance in the captured area, and set the H (hue) value in the HSV color space of the material constituting the core wrap layer (the area that does not overlap with the indicator layer) to be within the range of 40 to 70.
(5) Next, measure the area of the portion in the measurement area where the H (color layer) value is 100 or more, and divide the area by the area of the entire measurement area to obtain the ratio of the area of the impregnated portion of the core wrap layer when viewed from the stacking direction of the absorbent article to the area of the indicator layer.

Figure 5 is an enlarged view of a region similar to region X in Figure 2 of a disposable diaper 1 according to a third embodiment of the present invention. Note that Figure 5 is not intended to limit the absorbent article of the present invention.

As shown in Figure 5, in a disposable diaper 1 according to the third embodiment of the present invention, the core wrap layer impregnated portion 52 partially extends to the surface of the core wrap layer 4b facing the absorbent core layer 4a and is in contact with the absorbent core layer 4a.

(Leakproof layer impregnated part)
When the leak-barrier layer is a layer of hydrophobic nonwoven fabric, the indicator layer preferably has a leak-barrier layer impregnated portion that penetrates into the leak-barrier layer.

When the leakproof layer is a hydrophobic nonwoven fabric layer, it can prevent liquid in urine from leaking to the opposite side of the leakproof layer while allowing volatile components in urine, such as water vapor, to escape. However, hydrophobic nonwoven fabric layers typically tend to have lower visible light transmittance than non-porous layers due to the difference in refractive index between the air in the voids in the nonwoven fabric and the material that forms the leakproof layer. If the indicator layer is embedded in the leakproof layer, the thickness of only the leakproof layer without the indicator layer is reduced when viewed from the non-skin-facing side of the absorbent article, thereby improving the visibility of the indicator layer.

Here, the phrase "the indicator layer penetrates" into the leakproof layer means that solid components of the indicator composition that makes up the indicator layer, such as the thermoplastic components described below in "Indicator Composition," are present within the leakproof layer. The impregnated portion of the leakproof layer is continuous with the other parts of the indicator layer.

The presence or absence of the leakproof layer impregnated portion can be determined, for example, by observing a cross section of the absorbent article in the layering direction using an electron microscope.

Figure 6 is an enlarged view of a region similar to region X in Figure 2 of a disposable diaper 1 according to a fourth embodiment of the present invention. Note that Figure 6 is not intended to limit the absorbent article of the present invention.

As shown in Figure 6, in a disposable diaper 1 according to the fourth embodiment of the present invention, the indicator layer 5 has a leak-proof layer impregnated portion 53 that penetrates into the leak-proof layer 3.

(Non-impregnated area)
The indicator layer preferably has a non-impregnated portion that is not impregnated in either the core wrap layer or the leakproof layer.

As mentioned above, the non-impregnated portion of the indicator layer has a high density of the components that make up the indicator layer. Therefore, the non-impregnated portion is more susceptible to discoloration by urine than the portions impregnated in the core wrap layer and leakproof layer.

The non-impregnated portion does not presuppose the presence of a portion where the indicator layer is impregnated into the core wrap layer and the leakproof layer, i.e., a core wrap layer-impregnated portion and/or a leakproof layer-impregnated portion. In other words, the indicator layer may be composed of only a non-impregnated portion. Note that if the indicator layer has a core wrap layer-impregnated portion and/or a leakproof layer-impregnated portion, the non-impregnated portion is continuous with these portions.

From the perspective of improving reactivity, if the indicator layer has an impregnated portion in the core wrap layer and/or an impregnated portion in the leakproof layer, it is preferable that the non-impregnated portion be thicker than these layers in the stacking direction of the absorbent article.

The presence or absence of non-impregnated portions can be determined, for example, by observing a cross section of the absorbent article in the stacking direction using an electron microscope. Furthermore, the thicknesses of the non-impregnated portions, the impregnated portions of the core wrap layer, and the impregnated portions of the leakproof layer can also be compared, for example, by observing a cross section of the absorbent article in the stacking direction using an electron microscope.

The non-impregnated portion is arranged between the core wrap layer and the leakproof layer, for example, in a manner as shown in Figures 3 to 7.

<Leak proof layer>
The leak-proof layer is disposed on the non-skin-facing side of the absorbent article in the thickness direction, forming the non-skin-facing surface of the absorbent article, and is made of a liquid-impermeable sheet-like member such as a resin film or a hydrophobic nonwoven fabric, which can prevent excrement such as urine excreted by the wearer of the absorbent article from leaking out of the absorbent article.

In the absorbent article of the present invention, if the indicator layer contains a liquid component that is liquid at 36°C, it is preferable that, when the absorbent article is viewed in the stacking direction, the liquid component is impregnated into the leakproof layer in at least a portion of the area that overlaps with the indicator layer.

When the leakproof layer is impregnated with a liquid component, the liquid component fills the gap between the indicator layer and the leakproof layer, as well as the minute spaces within the leakproof layer. This reduces diffuse reflection in these areas, making the visible light transmittance higher than in other areas of the leakproof layer. This makes it easier to see the discoloration of the indicator layer from the leakproof layer side, i.e., the side of the absorbent article that does not face the skin.

The manner in which the liquid component is impregnated into the leakproof layer is not particularly limited. For example, if the leakproof layer is a moisture-permeable film with fine pores or a hydrophobic nonwoven fabric, the liquid component can be impregnated into the leakproof layer by filling the pores in the leakproof layer or the voids in the nonwoven fabric. Also, if the leakproof layer is a film without pores, the liquid component can be impregnated into the film by penetrating into it.

Figure 7 is an enlarged view of an area similar to area X in Figure 2 of a disposable diaper 1 according to a fifth embodiment of the present invention.

As shown in Figure 7, in a disposable diaper 1 according to the fifth embodiment of the present invention, the leakproof layer 3 is impregnated with a liquid component 51 in at least a portion of the area of the leakproof layer 3 that overlaps with the indicator layer 5.

In order to improve the visibility of discoloration of the indicator layer according to the specific gravity of urine from the non-skin-facing side of the absorbent article while suppressing the visibility of feces and urine from the same side, it is preferable that, when the absorbent article is viewed in the stacking direction, the layers closer to the leakproof layer than the indicator layer have a visible light transmittance of 30.0% or more and 90.0% or less in the visible spectrum, at least in the region overlapping with the indicator layer.

Note that "a layer closer to the leakproof layer than the indicator layer" is synonymous with a layer of the absorbent article closer to the non-skin-facing side of the indicator layer, and refers to, for example, the leakproof layer. If the absorbent article of the present invention has another layer in addition to the leakproof layer closer to the non-skin-facing side of the indicator layer, "a layer closer to the leakproof layer than the indicator layer" refers to the combination of the leakproof layer and that layer.

The visible light transmittance in the visible spectral range can be determined by peeling off the layer closer to the leakproof layer than the indicator layer from the absorbent article and measuring the visible light transmittance in the thickness direction using a transmittance meter (a cross-illumination type color difference meter A300/ZE-2000 manufactured by Nippon Denshoku Industries Co., Ltd.).

<Backsheet layer>
The absorbent article of the present invention may further include a backsheet layer on the side of the leakproof layer opposite to the side where the indicator layer is located, i.e., on the non-skin-facing side. In this case, the backsheet layer forms the non-skin-facing surface of the absorbent article instead of the leakproof layer. The backsheet layer has a visible light transmittance that allows the color change of the indicator layer to be visually recognized when the absorbent article is viewed from the non-skin-facing side.

From the perspective of improving the visibility of the indicator layer, it is preferable that, when the absorbent article is viewed in the stacking direction, the basis weight of at least a portion of the area of the backsheet layer that overlaps with the indicator layer be smaller than that of the remaining portions of the backsheet layer.

Indicator Composition
The indicator composition of the present invention is an indicator composition that is adjusted to have an appearance color on the alkaline side in its initial state before contact with urine, and that can change color upon contact with urine to a color corresponding to the specific gravity of the urine, and that contains a thermoplastic component that has a melting point or softening point within the range of 40°C to 120°C.

As described above, the indicator composition of the present invention can be used to easily form the absorbent article of the present invention.

The indicator composition of the present disclosure is initially adjusted to have an appearance color on the alkaline side before coming into contact with urine, and upon contact with urine, can change color to a color corresponding to the urine's specific gravity. The indicator composition of the present invention can contain, for example, a pH indicator, 20% by mass or more of an aliphatic alcohol that is solid at room temperature, and at least one of 10% by mass or more of a hydrophilic polymer and 10% by mass or more of an amine-based cationic surfactant.

The indicator composition is initially adjusted to have an alkaline appearance color before coming into contact with urine, but when it comes into contact with urine excreted by a wearer of the absorbent article, it changes color to an acidic appearance color. At this time, the indicator composition changes color to a different color tone depending on the specific gravity of the urine.

Regarding the color tone of the indicator composition, the external colors of the alkaline and acidic sides are determined by the relative pH relationship before and after color change due to contact with urine, and the hue of each external color varies depending on the type of pH indicator contained in the indicator composition. For example, when bromothymol blue is used as the pH indicator, the external color of the alkaline side is purple, blue, or blue-green, and the external color of the acidic side is yellow-green, yellow, or orange. Unlike conventional color changes used to detect the presence or absence of urination (i.e., a color change from the acidic side color of the pH indicator in the indicator composition to the alkaline side color), the indicator composition of the present invention changes color from the alkaline side color to the acidic side color in response to urine specific gravity. Therefore, when applied to absorbent articles such as disposable diapers, the wearer of the absorbent article or their assistant can easily recognize changes in urine specific gravity.

The indicator composition of the present invention preferably changes color to blue or green upon contact with low-specific-gravity urine and to yellow or orange upon contact with high-specific-gravity urine. Unlike the color change required to detect the presence or absence of urination, i.e., the change from the acidic side of the pH indicator in the indicator composition to the alkaline side, such indicator compositions change color to blue or green upon contact with low-specific-gravity urine and to yellow or orange upon contact with high-specific-gravity urine. Therefore, when applied to absorbent articles, the wearer of the absorbent article or their assistant can easily recognize changes in urine specific gravity. In particular, the color change from the initial color before contact with urine to yellow or orange upon contact with high-specific-gravity urine is more easily visible. This allows such indicator compositions to more accurately and easily detect changes in urine specific gravity.

The means for adjusting the initial color of the indicator composition before contact with urine to an alkaline color is not particularly limited, but examples include adding an alkalizing agent (e.g., some pH adjusters such as bases, salts, and buffers) that causes the pH indicator contained in the indicator composition to change color to an alkaline color tone.

<pH indicator>
The indicator composition of the present invention may contain a pH indicator. The pH indicator is not particularly limited as long as it can be used in indicator compositions for absorbent articles, but a pH indicator whose dissociation is promoted by an increase in ionic strength is preferred. Specific examples of such pH indicators include bromothymol blue (BTB), gentian violet, bromocresol purple, malachite green, thymol blue, methyl yellow, bromophenol blue, Congo red, methyl orange, litmus, phenol red, chlorophenol red, neutral red, bromocresol green, methyl red, naphtholphthalein, cresol red, cresolphthalein, phenolphthalein, thymolphthalein, and alizarin yellow R. These pH indicators may be used alone or in combination.

Preferred pH indicators include bromothymol blue (BTB), bromocresol purple, thymol blue, phenol red, chlorophenol red, bromocresol green, and methyl red. These pH indicators are preferred because their dissociation is promoted by increasing the ionic strength.

The indicator composition of the present invention preferably contains two or more types of pH indicators. Using a combination of two or more types of pH indicators allows for a clear color change even in urine with a smaller difference in specific gravity, making it possible to detect changes in urine specific gravity more accurately and reliably. Furthermore, combining two or more types of pH indicators with different color change ranges can broaden the detection range for urine specific gravity and increase the degree of color change due to changes in urine specific gravity, making it easier to see.

When two or more pH indicators are used in combination, a combination of bromothymol blue with another pH indicator is preferred. Using such a combination as a pH indicator has the advantage of not only increasing the color change during color development, but also expanding the color change range. Other pH indicators that can be used in combination with bromothymol blue include, for example, thymol blue, phenol red, and methyl red. Among these pH indicators, methyl red is preferred. The combination of bromothymol blue and methyl red can achieve a stable and wide color change (color reaction).

The content of the pH indicator contained in the indicator composition is not particularly limited and can be set appropriately taking into consideration the responsiveness and visibility of the color reaction. Such a content is, for example, 0.01% to 10.0% by mass, preferably 0.01% to 5.0% by mass, and more preferably 0.05% to 4.0% by mass, relative to the total mass (100% by mass) of the composition for the indicator composition. When the content of the pH indicator is within this range, good visibility of the response (coloration) of the indicator composition can be ensured.

<Thermoplastic component>
The indicator composition of the present invention contains a thermoplastic component having a melting or softening point in the range of 40° C. to 120° C. The thermoplastic component may be, for example, an aliphatic alcohol.

(Fatty alcohol)
The indicator composition of the present invention may contain an aliphatic alcohol that is solid at room temperature (20° C.) in an amount of 20% by mass or more relative to the total mass (100% by mass) of the indicator composition. By containing such a specific aliphatic alcohol, the indicator composition is less likely to dissolve in moisture such as urine or humidity.

The fatty alcohols that can be used in the indicator composition of the present invention are not particularly limited as long as they are solid at room temperature and can be used in indicator compositions for absorbent articles, and examples include fatty alcohols having 8 to 34 carbon atoms (C8 to C34). One type of fatty alcohol may be used alone, or two or more types of fatty alcohols may be used in combination.

Preferred aliphatic alcohols include those having a melting point or softening point greater than 40°C and less than 120°C. Specific examples include 1-hexadecanol, 1-octadecanol, 1-eicosanol, 1-docosanol, 1-tetracosanol, 1-hexacosanol, and 1-octacosanol. When the aliphatic alcohol contained in the indicator composition has such a specific melting point or softening point, the indicator composition can be applied in a molten state to a substrate such as a nonwoven fabric or film, and then cooled and solidified, resulting in the indicator composition being uniformly formed at a precise position on the substrate. This allows indicator compositions containing the specific aliphatic alcohols to quickly change color upon contact with sodium ions (Na ⁺ ), potassium ions (K ⁺ ), calcium ions (Ca ²⁺ ), and magnesium ions (Mg ²⁺ ) in urine. Furthermore, even if the color change is small, the color change is easily visible, allowing for more accurate and reliable detection of changes in urine specific gravity.

The content of the aliphatic alcohol contained in the indicator composition is not particularly limited as long as it is 20% by mass or more relative to the total mass (100% by mass) of the indicator composition, and can be set appropriately taking into consideration factors such as the resistance to solubility in water such as urine or moisture, and visibility. Such a content is, for example, 20% to 80% by mass, and preferably 30% to 60% by mass, relative to the total mass (100% by mass) of the composition for the indicator composition.

<Hydrophilic polymer>
The indicator composition of the present invention may contain at least one of 10% by mass or more of a hydrophilic polymer and 10% by mass or more of an amine-based cationic surfactant. By containing a predetermined amount of such a component, the indicator composition becomes more responsive to color change in response to changes in urine specific gravity when contacted with urine, and can clearly change color even when the change in urine specific gravity is small.

Hydrophilic polymers that can be used in the indicator composition of the present invention are not particularly limited as long as they are hydrophilic, and examples include polyamides, cellulose-based polymers (e.g., cellulose, cellulose derivatives, etc.), acrylic polymers (e.g., polyacrylic acid, polyacrylamide, maleic anhydride polymers, etc.), polyols (e.g., polyethylene glycol, etc.), polyvinylpyrrolidone, polyvinyl alcohol, polyallylamine, polyethyleneimine, oxazoline-based polymers (e.g., poly(2-oxazoline), poly(2-ethyl-2-oxazoline), poly(2-methyl-2-oxazoline), etc.). One type of hydrophilic polymer may be used alone, or two or more types of hydrophilic polymers may be used in combination.

In this specification, to distinguish between hydrophilic polymers and the sugar alcohol polymers of the sugar alcohol component described below, the term "hydrophilic polymer" excludes sugar alcohol polymers.

The indicator composition of the present invention preferably contains a polyamide as the hydrophilic polymer. When the indicator composition contains a polyamide as the hydrophilic polymer, it affects the morphological change of the pH indicator, widening the range of color change in urine specific gravity, and also enhancing the dissolving effect and speeding up the response. As a result, an indicator composition containing a polyamide as the hydrophilic polymer can accurately detect a wide range of changes in urine specific gravity. It is preferable that the polyamide have a softening point of 140°C or less.

The content of the hydrophilic polymer contained in the indicator composition is not particularly limited as long as it is 10% by mass or more relative to the total mass (100% by mass) of the indicator composition, and can be set appropriately taking into consideration factors such as the responsiveness and visibility of the color reaction. Such a content is, for example, 10% to 40% by mass, and preferably 15% to 30% by mass, relative to the total mass (100% by mass) of the composition for the indicator composition.

<Amine-based cationic surfactants>
The amine-based cationic surfactant that can be used in the indicator composition of the present invention is not particularly limited as long as it is an amine-based surfactant having a cationic hydrophilic group, and examples thereof include quaternary ammonium salt-type cationic surfactants, alkylamine salt-type surfactants, and cationic surfactants having a pyridine ring.

Specific examples of quaternary ammonium salt-type cationic surfactants include tetramethylammonium chloride, tetramethylammonium hydroxide, tetrabutylammonium chloride, dodecyldimethylbenzylammonium chloride, alkyltrimethylammonium chloride, octyltrimethylammonium chloride, decyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, alkyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, benzalkonium chloride, benzalkonium bromide, benzethonium chloride, dialkyldimethylammonium chloride, didecyldimethylammonium chloride, and distearyldimethylammonium chloride.

Specific examples of alkylamine salt-type cationic surfactants include monomethylamine hydrochloride, dimethylamine hydrochloride, and trimethylamine hydrochloride.

Specific examples of cationic surfactants having a pyridine ring include butylpyridinium chloride, dodecylpyridinium chloride, and cetylpyridinium chloride.

The above cationic surfactants may be used alone or in combination of two or more types.

The indicator composition of the present invention preferably contains a quaternary ammonium salt as the amine-based cationic surfactant. When the amine-based cationic surfactant contains a quaternary ammonium salt, the surfactant has high surfactant activity, and the indicator composition changes color more quickly when it comes into contact with urine. As a result, an indicator composition containing a quaternary ammonium salt as a cationic surfactant can more accurately detect changes in urine specific gravity.

The content of the cationic surfactant contained in the indicator composition is not particularly limited as long as it is 10% by mass or more relative to the total mass (100% by mass) of the indicator composition, and can be set appropriately taking into consideration factors such as the responsiveness and visibility of the color reaction. Such a content is, for example, 10% to 40% by mass, and preferably 15% to 30% by mass, relative to the total mass (100% by mass) of the composition for the indicator composition.

<Sugar alcohol ingredients>
The indicator composition of the present invention may further contain a sugar alcohol component as an optional component. Preferably, the indicator composition of the present invention further contains at least one component selected from the group consisting of a sugar alcohol and a sugar alcohol polymer, in a blending ratio of 2.5% by mass or more as the sugar alcohol component. When the indicator composition of the present invention contains such a sugar alcohol component, the hydrophilicity of the indicator composition is enhanced, and the rate of color change upon contact with urine can be increased.

Sugar alcohol components that can be used in the indicator composition of the present invention include sugar alcohols and their polymers. Specific examples include sugar alcohols such as glycerin, erythritol, D-threitol, L-threitol, D-arabinitol, L-arabinitol, xylitol, ribitol, D-iditol, galactitol, mannitol, volemitol, and perseitol, as well as polymers of these sugar alcohols. A preferred sugar alcohol component is, for example, glycerin. These sugar alcohol components may be used alone or in combination of two or more.

The content of the sugar alcohol component contained in the indicator composition is not particularly limited as long as it is 2.5% by mass or more relative to the total mass (100% by mass) of the indicator composition, and can be set appropriately taking into consideration the responsiveness and visibility of the color reaction. Such a content is, for example, 2.5% to 20% by mass, and preferably 3.0% to 15.0% by mass, relative to the total mass (100% by mass) of the composition for the indicator composition.

<Liquid ingredients>
The indicator composition of the present invention may contain a liquid component that is liquid at 36°C. Examples of such liquid components include wax and oil. The liquid component may be contained in the indicator composition as a plasticizer or tackifier. The indicator composition of the present invention preferably further contains at least one of wax and oil as a liquid component. When the indicator composition of the present invention contains such a liquid component, the indicator composition adheres better to a substrate, such as a nonwoven fabric or film, when the indicator composition is applied to the substrate, allowing the indicator composition to be accurately formed at a predetermined position on the substrate. This allows an indicator composition containing such a hydrophobic component to detect changes in urine specific gravity more accurately and reliably. The liquid component may be a hydrophobic liquid component. Alternatively, the liquid component may be a hydrophilic liquid component.

Waxes that can be used in the indicator composition of the present invention are not particularly limited as long as they can act as a plasticizer, and examples include well-known natural waxes and synthetic waxes. Specific examples of natural waxes include petroleum-derived waxes such as paraffin and microcrystalline wax; animal-derived waxes such as beeswax and spermaceti; plant-derived waxes such as carnauba wax; and mineral-derived waxes such as montan wax and ozokerite. Specific examples of synthetic waxes include polyethylene wax, Fischer-Tropsch wax, and fatty acid amides. Preferred waxes include petroleum-derived waxes such as paraffin and microcrystalline wax.

The oil that can be used in the indicator composition of the present invention is not particularly limited as long as it can act as a plasticizer, and examples include known paraffinic oils, naphthenic oils, and aromatic oils. Preferred oils include naphthenic oils.

Note that one type of liquid component may be used alone, or two or more types of liquid components may be used in combination.

The content of the liquid component contained in the indicator composition is not particularly limited as long as it does not impair the effects of the present invention, but it is, for example, 0.1% to 30.0% by mass, and preferably 1.0% to 20.0% by mass, relative to the total mass (100% by mass) of the indicator composition.

<Tackifying resin>
The indicator composition of the present invention may contain a tackifier resin. The tackifier resin is not particularly limited as long as it can act as a tackifier, and examples thereof include known natural resins and petroleum-based resins. Specific examples of natural resins include plant-derived resins such as rosin and rosin derivatives, terpene and modified terpene, etc. Specific examples of petroleum-based resins include C5 to C9 aliphatic or aromatic resins, and C5 to C9 aliphatic and aromatic copolymer resins.

<Alkalizing agent>
The indicator composition of the present invention may further contain an alkalizing agent. By containing such an alkalizing agent, the indicator composition is less likely to exhibit uneven color tone before and after color change due to contact with urine, making the color change more visible.

In addition, in indicator compositions, the alkalinizing agent is also used as a means of adjusting the initial appearance color of the indicator composition before contact with urine to the alkaline side.

The alkalizing agent that can be used in the indicator composition of the present invention is not particularly limited, but examples thereof include known sodium carbonate (Na ₂ CO ₃ ), sodium hydroxide (NaOH), potassium carbonate (K ₂ CO ₃ ), and the like.

The indicator composition of the present invention preferably further contains sodium carbonate as an alkalizing agent. Compared to other alkalizing agents such as sodium hydroxide and potassium carbonate, sodium carbonate mixes more uniformly with other components in the indicator composition, making uneven or abnormal color change less likely to occur, and even when the color change is small, the color change is easier to see. As a result, an indicator composition containing sodium carbonate as an alkalizing agent can more accurately and reliably detect changes in urine specific gravity.

<Other added ingredients>
The indicator composition of the present invention may further contain any additive component that can be used in indicator compositions for absorbent articles, including, but not limited to, antioxidants, light stabilizers, antibacterial agents, fragrances, etc.

The indicator composition consisting of the above components can be produced by mixing them using any suitable heat-melting method, although there are no particular limitations.

Examples 1 to 6 and Comparative Example 1
Example 1
An indicator composition was obtained by mixing 1-docosanol as a thermoplastic component, a quaternary ammonium salt as an amine-based cationic surfactant, a polyamide having a softening point of approximately 120°C as a hydrophilic polymer, methyl red and BTB as pH indicators, sodium carbonate as an alkalizing agent, glycerin as a sugar alcohol component, and naphthenic oil as a liquid component.

Next, this indicator composition was melted at 90°C and applied to the surface of a polyethylene film serving as a leakproof layer for a disposable diaper. Then, before the indicator composition was cooled, the absorbent layer of the disposable diaper (absorbent core layer: superabsorbent polymer and pulp fiber, core wrap layer: hydrophilically treated SMS nonwoven fabric) was layered on top of the indicator composition and pressed at a predetermined pressure. Finally, the indicator composition was cooled and solidified to produce the disposable diaper of Example 1, in which the indicator layer was positioned between the leakproof layer and the core wrap layer and directly bonded to those layers.

Examples 2 to 6
Disposable diapers of Examples 1 to 6 were produced in the same manner as in Example 1, except that the melting temperatures of the indicator compositions and the pressing pressures were varied. The melting temperatures of the indicator compositions and the pressing pressures are as shown in Table 1.

Comparative Example 1
The disposable diaper of Comparative Example 1 was produced in the same manner as in Example 1, except that the indicator composition was cooled and solidified before laminating the absorbent layer on top of the indicator composition, and pressing was not performed. In the disposable diaper of Comparative Example 1, the indicator composition was cooled and solidified to form the indicator layer, and then the core wrap layer was laminated on top of the indicator layer, so the indicator layer and the absorbent layer were not bonded. The melting temperatures of the indicator compositions are as shown in Table 1.

<Evaluation of discoloration>
Urine with a specific gravity ranging from 1.000 to 1.040 was prepared, and after contacting the urine with each specific gravity with the indicator composition used in the production of each example, the discernible color change of the indicator was evaluated by comparing it with a color sample. Color changes corresponding to the urine specific gravity were confirmed for urine with all specific gravities.

Observation of the permeability of the leak-proof layer
In the disposable diapers of Examples 1 to 6, when viewed in the stacking direction, the transparency of the portion of the leakproof layer overlapping with the indicator layer was higher than that of the disposable diaper of Comparative Example 1. This was because naphthenic oil, which was a liquid component contained in the indicator layer, was impregnated into the polyethylene film serving as the leakproof layer.

<Evaluation of discoloration speed>
Urine was dropped onto the absorbent layer side of the disposable diaper and brought into contact with the indicator layer to be evaluated. The color of the indicator layer after 3 minutes (the color after discoloration due to urine), the color of the indicator after 5 minutes, and the color of the indicator after 10 minutes were compared using a color sample from the leak-proof layer side to evaluate the identity of the two colors.

If the color of the entire indicator layer changed to the same color as the color sample, it was marked with a "◎", if only part of the indicator layer changed to the same color as the color sample, it was marked with a "〇", if the color changed to the same color as the color sample to a degree that was at least discernible, it was marked with a "△", and if no change was observed or if there was a change but it was difficult to determine whether it was the same color as the color sample, it was marked with an "X".

The results are shown in Table 1 below.

<Area ratio measurement>
For each disposable diaper example, the areas of the colored portions of the material constituting the indicator layer on the non-skin-facing side and the skin-facing side of the core wrap layer were measured by the following method.
(1) A sample in which the core wrap layer, indicator layer, and leakproof layer are integrated is removed from the absorbent article, and the area where the indicator layer is present is identified (for example, for a sample in which the indicator layer is applied to an area 6 mm wide x 100 mm long, a 6 mm wide x 50 mm long area in the longitudinal center). This area is the area to be measured.
(2) Peeling the core wrap layer from the absorbent article. The peeled core wrap layer is also peeled from both the absorbent core layer and the indicator layer.
(3) Place the core wrap layer with the absorbing core layer side facing up on the standard white plate, and take an image including the area to be measured with a digital camera. Similarly, place the core wrap layer with the indicator layer side facing up on the standard white plate, and take an image including the area to be measured with a digital camera. *Photographs should be taken under normal indoor lighting conditions, taking care to avoid shadows and reflected light.
(4) For the captured image, adjust the white balance in the captured area, and set the H (hue) value in the HSV color space of the material constituting the core wrap layer (the area that does not overlap with the indicator layer) to be within the range of 40 to 70.
(5) Next, measure the area of the portion in the measurement area where the H (color layer) value is 100 or more, and divide the area by the area of the entire measurement area to obtain the ratio of the area of the impregnated portion of the core wrap layer when viewed from the stacking direction of the absorbent article to the area of the indicator layer.

The ratio of the area of the impregnated portion of the core wrap layer when viewed from the stacking direction of the absorbent article to the area of the indicator layer was determined by dividing the area of the colored portion of the material composing the indicator layer on the non-skin-facing side of the core wrap layer by the area of the indicator layer. Similarly, the ratio of the area of the impregnated portion of the core wrap layer that reaches the surface on the absorbent core layer side to the area of the indicator layer was determined by dividing the area of the colored portion of the material composing the indicator layer on the skin-facing side of the core wrap layer by the area of the indicator layer.

The results are shown in Table 1 below.

REFERENCE SIGNS LIST 1 Disposable diaper 2 Top sheet layer 3 Leakage barrier layer 31 Low basis weight region 4 Absorbent layer 4a Absorbent core layer 4b Core wrap layer 41 High density region 5 Indicator layer 51 Liquid component 52 Core wrap impregnated portion 53 Leakage barrier layer impregnated portion

Claims (16)

The device has a top sheet layer, an absorbent layer, an indicator layer, and a leak-proof layer in this order,
the absorbent layer has an absorbent core layer and a core wrap layer covering at least the leakproof layer side of the absorbent core layer,
The indicator layer comprises:
The outer color of the protective layer is adjusted to an alkaline color in an initial state before contact with urine, and is capable of changing color to a color corresponding to the specific gravity of urine upon contact with urine; and the protective layer is at least partially directly bonded to the core wrap layer and the leakproof layer and disposed therebetween.
Absorbent articles. The absorbent article according to claim 1, wherein the indicator layer contains a thermoplastic component having a melting point or softening point within the range of 40°C to 120°C. The absorbent article according to claim 1 or 2, wherein the indicator layer further contains at least one of a hydrophilic polymer and an amine-based cationic surfactant. The absorbent article according to any one of claims 1 to 3, wherein the indicator layer changes color to blue or green when it comes into contact with low-specific-gravity urine, and changes color to yellow or orange when it comes into contact with high-specific-gravity urine. the indicator layer contains a liquid component that is liquid at 36°C;
When the absorbent article is viewed from the stacking direction, the liquid component is impregnated into the leakproof layer in at least a part of the portion of the leakproof layer that overlaps with the indicator layer.
The absorbent article according to any one of claims 1 to 4. the leak-proof layer is a layer of hydrophobic nonwoven fabric,
the indicator layer has a leak-proof layer-impregnated portion that penetrates into the leak-proof layer;
The absorbent article according to any one of claims 1 to 5. The device further includes a backsheet layer on the leakproof layer opposite to the side on which the indicator layer is disposed,
The absorbent article according to any one of claims 1 to 6, wherein, when the absorbent article is viewed from the stacking direction, the basis weight of at least a portion of the area of the backsheet layer that overlaps with the indicator layer is smaller than that of other portions of the backsheet layer. The absorbent article according to any one of claims 1 to 7, wherein, when the absorbent article is viewed in the stacking direction, the layers closer to the leakproof layer than the indicator layer have a visible light transmittance of 30.0% or more and 90.0% or less in the visible spectrum range, collectively, at least in the region overlapping with the indicator layer. The absorbent article described in any one of claims 1 to 8, wherein the indicator layer has a core wrap layer impregnation portion that penetrates into the core wrap layer. The absorbent article of claim 9, wherein, when the absorbent article is viewed in the stacking direction, the area of the impregnated portion of the core wrap layer is 20.0% or more of the area of the indicator layer. the core wrap layer impregnated portion partially reaches the surface of the core wrap layer facing the absorbent core layer and is in contact with the absorbent core layer;
The absorbent article according to claim 9 or 10. When the absorbent article is viewed from the stacking direction, the area of the portion of the core wrap layer impregnated portion that reaches the surface on the absorbent core layer side is 50.0% or less of the area of the indicator layer.
The absorbent article of claim 11. The absorbent article according to any one of claims 1 to 12, wherein, when the absorbent article is viewed in the stacking direction, the density of at least a portion of the absorbent core layer overlapping with the indicator layer is higher than that of other regions of the absorbent core layer. The absorbent article described in any one of claims 1 to 13, wherein the indicator layer has a non-impregnated portion that is not impregnated into either the core wrap layer or the leakproof layer. The absorbent article according to any one of claims 1 to 14, which is for toilet training. The absorbent article of claim 3 , wherein the indicator layer comprises a polyamide as a response enhancer.