JPH0484960A - Absorptive articles - Google Patents

Abstract

PURPOSE:To lessen the penetration of a softener, etc., to the rear side by providing a moisture permeable sheet which is coated with the adhesive consisting essentially of a styrenic block polymer, a tackiness imparting resin and the softener and having a two-phase block structure of styrene and rubber and has a prescribed moisture permeation rate. CONSTITUTION:The moisture permeable sheet having 0.7 to 2.8g/100cm<2>.h moisture permeation is used and the adhesive which consists essentially of the styrenic block polymer (styrene/ethylene/styrene block copolymer), the tackiness imparting resin (C9 peteroleum resin) and the softener (naththenic process oil) and has the two-phase block structure of the styrene phase 1 and the rubber phase 2 is used. The softener, etc., which are the compsn. component of the adhesive are held into the adhesive in this way even if the molecular motion is increased by a temp. rise. The degree at which the 'penetration to the rear side' to bleed out the softener, etc., to the surface of the moisture permeable sheet is lessened from the results of comparative tests.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to absorbent articles, and more specifically, in disposable disposable diapers and the like using a moisture-permeable sheet, a softening agent, etc., which is a component of an adhesive, seeps out. , so-called “back-cutting is a phenomenon°′
The present invention relates to an absorbent article in which the degree of occurrence of this phenomenon is small.

[Conventional technology]

A typical disposable diaper is constructed by interposing an absorbent body between a liquid-permeable sheet on the side that contacts the skin and a liquid-impermeable sheet on the clothing side, and fixing them at predetermined portions with adhesive.

Therefore, in order to improve the adhesion of the diaper constituent materials and its coating suitability, the above adhesive is formulated with a reduced proportion of the base elastomer and an increased proportion of the tackifier and softener. Depending on the composition, the mainstream is a low-viscosity type by destroying the block structure of the base elastomer.

Further, as the liquid-impermeable sheet, a moisture-permeable sheet is usually used in order to prevent stuffiness during use of the diaper.

[Problem to be solved by the invention]

However, when a low-viscosity adhesive is used for disposable diapers made with moisture-permeable sheets, the softener, which is one of the adhesive's components, is not retained in the adhesive and is susceptible to heat. This causes the so-called "bleed-out phenomenon" in which the moisture seeps out onto the surface of the moisture-permeable sheet.

If such a "lining-out phenomenon" occurs, the surface of the moisture-permeable sheet may feel sticky, the diaper's cord properties may be adversely affected, the diapers may block against each other when holding the pack, or the adhesive composition may There were various disadvantages such as changes in adhesive properties over time.

Therefore, the object of the present invention is to prevent the seeping components such as softeners, which are compositional components in the adhesive, from seeping out onto the surface of the moisture permeable sheet.
The object of the present invention is to provide an absorbent article in which the "back-out phenomenon" occurs to a small degree.

[Means to solve the problem]

As a result of intensive research to achieve the above purpose, the present inventors have found that
As an adhesive for absorbent articles using moisture-permeable sheets, we use an adhesive whose main components are a styrene block polymer, a tackifier resin, and a softener, and which maintains a two-phase block structure of a styrene phase and a rubber phase. As a result, it was found that while maintaining adhesion and coatability, the degree of occurrence of the "bleed-out phenomenon" in which the softening agent, etc., which is a component of the adhesive, seeps onto the surface of the moisture permeable sheet is small.

The present invention has been made based on the above findings, and provides an absorbent article including a moisture permeable sheet coated with an adhesive, wherein the moisture permeable sheet has a moisture permeability of 0.7 g/100 crJ.
h ~2.8 g/100 cd・h moisture permeable sheet,
The absorbent article is characterized in that the adhesive contains a styrene block polymer tackifier resin and a softener as main components and maintains a two-phase block structure of a styrene phase and a rubber phase. This is what we provide.

The absorbent article of the present invention will be described in detail below.

The moisture permeable sheet used in the present invention has a moisture permeability of 0.7
g/100ci-h~2.8 g/100ca-h
belongs to. When such a moisture-permeable sheet is used as a liquid-impermeable sheet of a disposable diaper, it is possible to prevent stuffiness during use of the diaper.

Therefore, in the present invention, the adhesive used is one that contains a styrene block polymer, a tackifier resin, and a softener as main components and maintains a two-phase block structure of a styrene phase and a rubber phase. .

Examples of the styrene block polymer of the adhesive include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-isoprene-styrene block copolymer (SI S), styrene-butadiene-
Styrene block copolymer (SBS), styrene-ethylene-propylene-styrene block copolymer (SEP)
S) etc. These styrenic block polymers are block copolymers in which the styrene portion has a molecular weight of 7,000 to 20,000 and the rubber portion has a molecular weight of 35,000 to 70,000.

The tackifying resin may include C1 petroleum resins, C1 petroleum resins, Cs/Cq petroleum resins, α-pinene, β-pinene, or dipentene, which have a softening point of 80°C or higher and a molecular weight of 400 to 2000. There are polymers such as polyterpene resins, rosin resins, and hydrogenated products thereof.In addition, the softening agents include process oils with a softening point of 10°C or less and an average molecular weight of 200 to 700, and various plasticizers. , polybutene, liquid resin, etc.

A preferable adhesive for maintaining the above two-phase block structure or a structure similar to it contains 150 to 20 parts by weight of tackifier resin per 100 parts by weight of the styrenic block polymer.
0 parts by weight, preferably 160 to 180 parts by weight, and the softener is set to 30 to 100 parts by weight, preferably 40 to 70 parts by weight. In an adhesive having such a composition, the proportion of the softening agent is approximately 10% to 25%.

Here, if the tackifier resin is less than 150 parts by weight and the softener is less than 30 parts by weight (the proportion of the softener is less than 10%), the tackiness and adhesive strength will decrease. Moreover, the increase in viscosity deteriorates the coating properties, which is not preferable.

Furthermore, if the tackifying resin exceeds 200 parts by weight and the softener exceeds 100 parts by weight (if the proportion of the softener exceeds 25%), the two-phase block structure may be destroyed. There is.

In addition to the styrenic block polymer tackifier resin and softener, an antioxidant is preferably added to the adhesive. In this case, the antioxidant is preferably added in an amount of 1 to 3 parts by weight per 100 parts by weight of the styrene block polymer. As the antioxidant, for example, Irganox 1°10 (trade name, manufactured by Ciba Gaigi Co., Ltd.), Irganox 1076 (trade name, manufactured by Ciba Gaigi Co., Ltd.), or Sumilizer GM (trade name, manufactured by Susumu Kagaku 2), etc. can be used.

The above adhesive can also be applied by hot melting at a temperature of 180° C. or lower, and is therefore suitable for producing absorbent articles such as disposable diapers.

The absorbent article of the present invention has the above-mentioned moisture permeability of 0.7 g/1
00c+fl-h~2.8 g/100c+Il-h
(7) A moisture-permeable sheet is used, and the adhesive described above is used as the adhesive applied to the moisture-permeable sheet, and can be used, for example, in disposable diapers, household goods, etc.

In the absorbent article of the present invention, the degree of occurrence of the "bleed-out phenomenon" is reduced by using the above-mentioned adhesive. Although the detailed reason is not clear, it is thought to be as follows.

The structure of the adhesive used in the present invention, which maintains a two-phase block structure of a styrene phase and a rubber phase, can be explained diagrammatically as shown in the conceptual diagram of FIG. As shown in the graph of FIG. 2, it is recognized that there are two peaks: a styrene phase relaxation peak and a rubber phase relaxation peak.

FIG. 2 shows the behavior of the dynamic viscoelasticity of the adhesive measured by the dynamic viscoelasticity measurement method, and the loss modulus E' and tan δ (tan δ - loss modulus E''/storage elasticity The graph shows the temperature (°C) on the horizontal axis.
), and the vertical axis represents tan δ.

Therefore, in the above adhesive, the movement of the rubber phase is restrained by the styrene domain, and as a result, the entanglement of the rubber phase molecular chains resides, and the seeping component is present in the entanglement of the rubber phase molecular chains. It is thought that the softener, low molecular weight polymer components, etc. are trapped, and the "bleed-out phenomenon" is prevented.

Incidentally, if the amount of the softener is increased to more than 100 parts by weight, for example, if the proportion of the softener in the adhesive is about 30%, a peak with properties intermediate between the two peaks shown in FIG. 2 will be produced. 3 relaxation peak becomes visible. In such products (those with a three-phase structure), the styrene domains are reduced, and as a result, the entanglement of the rubber phase molecular chains is reduced, and the plasticized styrene domains are compatible with the rubber phase, and the intermediate It is thought that a phase exhibiting properties is formed, and as a result, the ability to trap and retain exuded components is reduced, resulting in the "bleed-out phenomenon."

Furthermore, when the amount of the softener is further increased, for example, the proportion of the softener in the adhesive becomes about 40%, the domain structure becomes completely compatible with the rubber phase, and the two relaxation peaks become 1.
It is thought that there will be two. In this case, the ability to trap and retain the exuding components is almost completely lost, and this results in “
It is thought that the phenomenon of "back-cutting" is further promoted.

Further, when the apparent activation energies of the styrene phase and the rubber phase, which constitute the two-phase block structure, are determined by frequency dispersion, the apparent activation energy of the styrene phase is 50 Kcal/ mo
1 or more, and the apparent activated fuel of the rubber phase is 35 Kcal/mol or more.

In this way, an adhesive in which the styrene phase has a large apparent activation energy of 50 Kcal/n+o1 or more, and the rubber phase has a large apparent activation energy of 35 Kcal/mol or more, has a large amount of energy required to cause molecular movement. Since the adhesive requires a lot of energy, even if heat is applied from the outside, the seeping components can be retained in the adhesive, which is thought to reduce the phenomenon of lining-out.

In addition, the above-mentioned "bleed-out" phenomenon occurs when adhesive is applied to a moisture-permeable sheet, and components such as softeners wet the surface of the moisture-permeable sheet and bleed through (bleed through). This is a phenomenon that occurs when frosted glass is wetted with water, allowing light to pass through it.
This is the same phenomenon as being able to see outside through frosted glass.

The present inventors attempted to quantify the above-mentioned "back-out phenomenon" by utilizing such a phenomenon. That is, as shown in FIG. 3, a black plate 4 is placed on the back side of a sample 3 made of a moisture-permeable sheet coated with adhesive, a transparent glass plate 5 is placed on the surface of the sample 3, and the sample 3 An attempt was made to quantify the degree of strike-through (extent of seepage) by measuring the reflectance of the reflected light from Sample 3 while irradiating blue incident light with a wavelength of 459 nm from the surface side of the sample.

According to this method, when the degree of bleed through is large (the degree of seepage is large), the incident blue light passes through the sample 3 and reaches the black plate 4, and is absorbed by the black plate 4. If the reflectance of the reflected light from the sample 3 decreases, and if the degree of bleed-through is small (the degree of seepage is small), the incident blue light will be less likely to pass through the sample 3 and reach the black plate 4. The light is reflected by the sample 3 without being absorbed by the black plate 4, and the reflectance of the light reflected from the sample 3 increases.

[Effect]

According to the absorbent article of the present invention, the moisture permeability is 0.7 g/100
A moisture-permeable sheet with a weight of c+fl-h to 2.8 g/100 cIil-h is used, and the adhesive applied to this moisture-permeable sheet contains a styrene block polymer, a tackifier resin, and a softener as main components, and the styrene phase and Since we used a material that maintains a two-phase block structure with the rubber phase, even if molecular motion increases due to temperature rise, the softener, etc., which is a component of the adhesive, can be retained in the adhesive. This eliminates the ``bleed-out phenomenon'' that occurs on the surface of the moisture-permeable sheet.

For this reason, the surface of the moisture permeable sheet may feel sticky,
There is no adverse effect on the diaper strap properties, there is no blocking between the diapers during pack storage, there is no problem such as sluggishness due to changes in the adhesive properties over time due to changes in the adhesive composition.

〔Example〕

The present invention will be explained in detail below.

First, 5EBS (styrene-ethylene-butylene-styrene plotter copolymer) was used as the styrene block polymer, C1 petroleum resin was used as the tackifying resin, naphthene process oil was used as the softener, and Ciba-Geigi's 5EBS (styrene-ethylene-butylene-styrene plotter copolymer) was used as the styrene block polymer. Using Irganox 1010r pentaerythrityl-tetrakis (3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), it was kneaded in a kneader at a temperature of 160°C for 1 hour and 40 minutes. Adhesives having various weight ratios shown in Table 1 below were prepared.

The amount of antioxidant added was the same for all adhesives, and was 3% by weight based on 5EBS.

Next, the above adhesive was applied by hot melting at a temperature of 160°C onto a release paper to a thickness of 40±5μ, and then formed into a moisture permeable sheet with a moisture permeability of 1.7 g/100c+ll・h. Transfer coating was performed, and a disposable diaper was manufactured using this moisture permeable sheet. After storing the above disposable diaper at a temperature of 60''C for 10 days, the presence or absence of seepage was visually observed, and the results shown in Table 1 below were obtained.

In Table 1, the symbol ◯ indicates that almost no oozing occurred, the symbol Δ indicates that the oozing has changed to some extent, and the symbol × indicates that oozing occurred to a large extent.

In addition, in order to quantitatively measure the degree of seepage, a measurement sample was prepared by pasting the same moisture-permeable sheet as that used in the disposable diaper on a mount corresponding to the black panel 4 shown in FIG. 3. Then, the reflectance was measured after storing the measurement sample at a temperature of 60° C. for 10 days, and the reduction rate was calculated based on this reflectance, and these are also listed in Table-1.

Note that the reflectance was measured using a color difference meter (manufactured by NEC Corporation). Further, the rate of decrease in reflectance was calculated using the following formula.

Reduction rate of reflectance = (a-b)/a 1-(a/b) (%) a Reflectance of blank b; Reflectance after 10 days Furthermore, present invention products NO, 1, 2, comparison The phase structure and apparent activation energy of the adhesive used in Product No. 1.2 are also listed in Table 1.

Here, the phase structure was determined by dynamic viscoelasticity measurement. That is, first, the above adhesive is melted, the wire diameter is 0.5, and the winding diameter is 5M.
, a length of 6ffI [11] coil springs (manufactured by Seisou Hatsujo Seisakusho) were each impregnated with the solution. Next, using Reopybron (Toyo Baldwin DDV-II-BP),
At a frequency of 3.5 Hz, the storage elastic modulus E'', loss elastic modulus E'', and loss tangent tan δ (ta
nδ-E''/E゛) was measured. At this time, the temperature range was -200°C to +120°C. Also, the heating rate was 3
”I: /win, and liquid nitrogen was used as the refrigerant.

In addition, the apparent activation energy is determined by changing the frequency to 3.5 Hz, 11 Hz, and 35 Hz in the above dynamic viscoelasticity measurement.
, 110Hz. That is, first, each jan δ dispersion peak temperature corresponding to the styrene phase, rubber phase, and homogeneous phase at each frequency is measured, and then, based on the measurement results, using the Arrhenius equation shown below, lnf and -1/ A graph representing the relationship with T was obtained, and then, the apparent activation energy of the styrene phase, rubber phase, and homogeneous phase was obtained from the slope of the straight line shown in the graph.

Arrhenius formula % formula % E; apparent activation energy (cal/mol) R; gas constant T; dispersion peak temperature (K) In Table 1, St is the apparent activation energy of the styrene phase, and G is the apparent activation energy of the styrene phase. Apparent activity ratio table of rubber phase-1 As is clear from Table-1 above, inventive product No. 1 shows almost no staining when visually observed, and has a reflectance that quantifies the degree of staining. The rate of decrease in reflectance was as high as 66%, confirming that almost no phenomenon occurred during back-extraction.Also, the rate of decrease in reflectance was as low as 8%, confirming that almost no change over time occurred.

Furthermore, it was confirmed that the phase structure of the adhesive used was a two-phase block structure. Further, the apparent activation energy of the styrene phase was 75.9 cal/mol, and the apparent activation energy of the rubber phase was 39.0 cal/mol.

In addition, almost the same results as the invention product No. 1 (reflectance 65%, reflectance reduction rate 10%) were obtained for the invention product No. 2.

Furthermore, it was confirmed that the phase structure of the adhesive used was a two-phase block structure. Further, the apparent activation energy of the styrene phase was 51.2 cal/mol, and the apparent activation energy of the rubber phase was 36.5 cal/mol.

On the other hand, the comparison product Grade 1 showed some bleeding when visually observed, and the reflectance, which quantifies the degree of bleeding, was as low as 57%, resulting in the "bleed-through phenomenon." Further, the rate of decrease in reflectance was as high as 21%, and there was a large change over time.

Further, the phase structure of the adhesive used was a three-phase structure. Also, the apparent activation energy of the styrene phase is 45.0
cal/+mol, lower than 50.0 cal/mol, and the apparent activation energy of the rubber phase is 31°5
cal/mol, which was lower than 35.0 cal/sol.

In addition, the comparison product Nα2 has a large amount of seepage when visually observed, and the reflectance, which is used to quantify the degree of seepage, is 52.
%, and the "bleed-out phenomenon" occurred significantly. Also,
The rate of decrease in reflectance was even higher at 28%, and a large change over time occurred.

Furthermore, the phase structure of the adhesive was such that the styrene domain was completely compatible with the rubber phase, resulting in a homogeneous phase. In addition, the apparent activation energy is 30.0 cal/mol, and the above sample Nα
It was even lower than in case 3.

In addition, the adhesives used for the inventive product Nα1.2 and the comparative product Nα1.2 were applied by hot melting at a temperature of 160° onto release paper at 5 g/ml in a spiral coating and at 0.07 g/piece/m in a bead coating. I worked on it. Then, the above-mentioned release paper was pasted onto a mount to prepare a sample for visually determining the change in stain over time. After this sample was stored at a temperature of 60° for 10 days, the change in exudation over time was visually judged, and the results shown in Table 2 below were obtained.

In Table 2, the symbol O indicates that almost no bleeding occurred, Δ indicates that some bleeding occurred, and × indicates that a large amount of bleeding occurred.

As is clear from Table 2 above, with the adhesive of the present invention Nα1.2, it has been confirmed that the "back-out phenomenon" hardly occurs in both spiral coating and bead coating. Ta.

On the other hand, with the comparative adhesive No. 3, when spiral coating and bead coating are applied, "° back-out is a phenomenon" in both cases.
occurred to some extent. In addition, with the comparative adhesive No. 2, when spiral coating and bead coating were applied, the "bleed-out phenomenon" occurred significantly in both cases.

〔Effect of the invention〕

In the absorbent article of the present invention, the "bleed-out phenomenon" in which seeping components such as softeners, which are constituents in the adhesive, seep out onto the surface of the moisture permeable sheet is small.

[Brief explanation of the drawings] Figure 1 is a conceptual diagram conceptually representing the phase structure of adhesives;
The figure is a graph obtained by measuring the behavior of dynamic viscoelasticity of an adhesive using a dynamic viscoelasticity measurement method, and shows tanδ (tanδ=loss modulus E''/storage modulus E) with respect to temperature dispersion.
Figure 3 is an explanatory diagram of the measurement principle showing the degree of "bleeding out is a phenomenon". l; Styrene phase 2; Rubber phase 3; Sample 4; Black plate 5; Transparent glass plate

Claims (2)

[Claims] (1) In an absorbent article equipped with a moisture permeable sheet coated with an adhesive, the moisture permeable sheet has a moisture permeability of 0.7 g/100 cm^2.
h~2.8g/100cm^2・h moisture permeable sheet, the adhesive has a styrene block polymer, tackifier resin, and softener as main components, and has a two-phase block structure of a styrene phase and a rubber phase. An absorbent article characterized by being an adhesive that retains. (2) The apparent activation energy of the above styrene phase is 5
0 Kcal/mol or more, and the absorbent article according to claim 1, wherein the apparent activation energy of the rubber phase is 35 Kcal/mol or more.