WO2023178636A1

WO2023178636A1 - Diaper core

Info

Publication number: WO2023178636A1
Application number: PCT/CN2022/082954
Authority: WO
Inventors: Miaoru LING; Lori-Ann S. Prioleau; Clinton G. WIENER; Daniel S. Mcdonald; Mahfuza Begum Ali
Original assignee: 3M Innovative Properties Company
Priority date: 2022-03-25
Filing date: 2022-03-25
Publication date: 2023-09-28

Abstract

A diaper core (10) comprises: a nonwoven base sheet (12) having a hydrophilic first side (16) and a hydrophobic opposing second side (20); the base sheet (12) having a first edge (30) in the longitudinal direction and a second opposing edge (32) in the longitudinal direction; a plurality of water-based adhesive spots (34) located on the first side (16) and a plurality of SAP particles (26) adhered to the first side (16) by the water-based adhesive spots (34); a longitudinal center channel (38) located in the middle one third of the width of the base sheet (12), the center channel (38) void of the plurality of water-based adhesive spots (34) and the plurality of SAP particles (26); a nonwoven cover sheet (46) positioned over the plurality of water-based adhesive spots (34) and the plurality of SAP particles (26); the nonwoven cover sheet (46) laminated to the base sheet (12) by a plurality of ultrasonic bonds (50) positioned along the longitudinal edges (30, 32) of the base sheet (12). The diaper core (10) can prevent gel blocking and have excellent uptake of human wastes.

Description

DIAPER CORE

BACKGROUND

Diapers are a common item used by parents of children prior to the child being toilet trained. In particular, disposable diapers are preferred for their convenience and superior absorbency.

SUMMARY

Modern disposable diapers have an impervious back sheet, a middle absorbent layer and a body facing intake layer. Generally, the entire diaper is made on a diaper manufacturing line where the various components are assembled to make the diaper. However, a simpler diaper manufacturing line is possible when using a pre-made diaper core that accommodates the uptake of human waste since all the pulp and/or superabsorbent handling machinery to place the fluid management components for the absorbent layer on the diaper line can be eliminated. A pre-made diaper core absorbent article has a back sheet, an absorbent core, and an intake layer formed into a premade pad.

Additionally, eliminating pulp or other fibrous absorbent materials from the diaper core can make it thinner and more comfortable for the baby. The challenge is to ensure the diaper core has good uptake of human waste if the pulp fibers are eliminated. Optimizing the placement and utilization of super absorbent polymer (SAP) particles when no absorbent fibrous materials are used can be challenging due to the propensity of gel blocking and insufficient absorbency.

The inventors have determined that by using a spot pattern of SAP particles, a center channel, specific classes of adhesives, and nonwoven materials to make the diaper core, excellent uptake of human wastes is possible even in a diaper core without any added pulp.

Hence, in one embodiment, the invention resides in a diaper core having a nonwoven base sheet having a first side and an opposing second side; the first side being hydrophilic and the second side being hydrophobic; the base sheet having a longitudinal length, a cross-web direction width, a first edge in the longitudinal direction and a second opposing edge in the longitudinal direction; a plurality of water-based adhesive spots located on the first side and a plurality of SAP particles adhered to the first side by the water-based adhesive spots; a longitudinal center channel located in the middle one third of the width of the base sheet, the center channel having a channel width between a first channel edge in the longitudinal direction and a second channel edge in the longitudinal direction; and the center channel void of the plurality of water-based adhesive spots and the plurality of SAP particles; a nonwoven cover sheet positioned over the plurality of water-based adhesive spots and the plurality of SAP particles; the nonwoven cover sheet laminated to the base sheet by a plurality of ultrasonic bonds positioned along the first edge, the second edge, and forming the first channel edge and the second channel edge of the diaper core.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the absorbent core showing the longitudinal channel, the sealed edges, and the hidden SAP spots.

FIG. 2 is an exploded view of the various layers in the diaper core.

FIG. 3 is a top view of the water based adhesive spots.

FIG. 4 is a cross section view of the SMS base sheet and the water based adhesive spots.

FIG. 5 is a top view of SAP particles adhered to the water based adhesive spots.

FIG. 6 is a side view of a longitudinal channel in the diaper core having three sealing lines.

FIG. 7 is a top view of the diaper core with the top sheet removed showing a hotmelt adhesive filament network over the SAP particles.

FIG. 8 is the print pattern for Example 16 in Table 3.

FIG. 9 is the print pattern for Example 17 in Table 3.

FIG. 10 is the print pattern for Example 18 in Table 3.

FIG. 11 is the print pattern for Example 19 in Table 3.

FIG. 12 is the print pattern for Example 20 in Table 3.

FIG. 13 is the print pattern for Example 21 in Table 3.

FIG. 14 is the print pattern for Example 22 in Table 3.

FIG. 15 is a schematic view of a manufacturing line to make the diaper core.

FIG. 16 is a schematic of a drop test fixture.

FIG. 17 is a schematic of a wicking fixture.

DETAILED DESCRIPTION

Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “about 0.1%to about 5%” or “about 0.1%to 5%” should be interpreted to include not just about 0.1%to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1%to 0.5%, 1.1%to 2.2%, 3.3%to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y, ” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z, ” unless indicated otherwise.

In this document, the terms “a, ” “an, ” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” or “at least one of A or B” has the same meaning as “A, B, or A and B. ” In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

The term “about” as used herein can allow for a degree of variability in a value or range. For example, within 10%, within 5%, or within 1%of a stated value or of a stated limit of a range and includes the exact stated value or range.

The term “substantially” as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999%or more, or 100%. The term “substantially free of” as used herein can mean having none or having a trivial amount of, such that the amount of material present does not affect the material properties of the composition including the material, such that the composition is about 0 wt%to about 5 wt%of the material, or about 0 wt%to about 1 wt%, or about 5 wt%or less, or less than or equal to about 4.5 wt%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt%or less.

Referring to FIGS. 1-5, the diaper core 10 has a nonwoven base sheet 12 having three layers; a spunbond layer 14 on a first side 16, a spunbond layer 18 on an opposing second side 20, and a middle layer 22 of a meltblown nonwoven. The first side 16 is hydrophilic and the second side 20 is hydrophobic. The base sheet 12 having a machine direction length 24, a cross machine direction width 26, a first edge 30 in the machine direction and a second opposing edge 32 in the machine direction. A plurality of water-based adhesive spots 34 is located on the first side 16 and a plurality of SAP particles 36 is adhered to the first side 16 by the water-based adhesive spots 34. A machine direction or longitudinal center channel 38 is located in the middle one third of the width of the base sheet and the center channel 38 having a channel width 40 between a first channel edge 42 in the longitudinal direction and a second channel edge 44 in the longitudinal direction. The center channel 38 is void of the plurality of water-based adhesive spots 34 and the plurality of SAP particles 36. A nonwoven cover sheet 46 is positioned over the plurality of water-based adhesive spots 34 and the plurality of SAP particles 36. In some embodiments, the nonwoven cover sheet 46 is laminated to the base sheet 12 by a layer of hotmelt adhesive filaments 48 applied over the plurality of SAP particles 36. A plurality of ultrasonic bonds 50 positioned along the first edge 30, the second edge 32, the first channel edge 42 and the second channel edge 44 of the diaper core 10 hold the base sheet 12 and cover sheet together 46 and form the center channel 38.

Base Sheet

The base sheet 12 in one embodiment has three layers: an 11 gsm spunbond layer 14 on a first side 16, an 11 gsm spunbond layer 18 on an opposing second side 20, and a 3 gsm middle layer 22 of a meltblown nonwoven. The first side 16 is hydrophilic and the second side 20 is hydrophobic. Preferably the middle melt blown layer 22 is also hydrophobic. Structuring the base sheet 12 in this manner keeps the water based adhesive spots 34 constrained to the hydrophilic spunbond layer 14 on the first side 16. This prevents bleed through of the water based adhesive and allows for less adhesive to be used since it does not penetrate all the way through the base sheet. A suitable base sheet can be manufactured as a 25 gsm SMS nonwoven by a nonwoven manufacturer such as 3M Company.

Other suitable one, two, three, or multi-layer base sheets with a first side 16 that is hydrophilic and a second side 20 that is hydrophobic can be used. The base sheet should be selected to have the water based adhesive spots penetrate the first side but not bleed through to the second side. For example, a two-layer spunbond -spunbond base sheet is possible. Alternatively, a five-layer base sheet of spunbond -spunbond -meltblown -meltblown -spunbond is possible. In various embodiments, suitable basis weights for the base sheet are from 20 to 40 gsm, or 25 to 35 gsm.

Water-Based Adhesive Spots

To prevent gel blocking and allow for wicking and capillary action within the absorbent layer of SAP, it was determined that the SAP should be applied as discrete spots or islands with surrounding areas free of SAP. To accomplish this, a pattern of water based adhesive spots was screen printed onto the hydrophilic spunbond layer 14.

It was determined in the Examples that a holt melt adhesive did not allow for enough SAP to be anchored in the adhesive islands. As such, capacity and the rate of liquid uptake was too low. Solvent based adhesives were tried and it was found that the adhesive encapsulated the SAP too much, preventing uptake of liquids and lower capacity when compared to the same weight of SAP adhered by water-based adhesives. As such, a water-based adhesive was found to be necessary. However, as shown in the Examples, certain water-based adhesives failed to adequately adhere the swollen SAP particles during Drop Testing and required the use of an optional hotmelt filament adhesive layer to secure the swollen SAP particles. Other water-based adhesives with specific chemistries were found to pass the Drop Testing without the optional hotmelt filament adhesive layer.

It was also determined that certain water-based adhesives are preferred for their ability to continue to adhere the gelled and swollen SAP after a saline insult without the hotmelt adhesive filament layer. Testing several classes of emulsion with non-reactive chemistries it was found that SBR (styrene-butadiene-copolymer rubbers) was the chemistry (non-reactive) that had the necessary attachment. Within that class, it was also found that certain requirements were also needed for good SAP adhesion to the SMS base sheet. First, the Tg should be low such as preferably below -20 degrees Celsius, or below -15 degrees Celsius. Second, the SBR should be listed as carboxylated, containing some carboxylation of some type introduced into the polymer to add some acid groups and polarity. Several samples were tested with Tg <-20 degrees Celsius and no carboxylation, and carboxylation and Tg >-20 degrees Celsius, and it was found in both materials, attachment of the SAP particles was poor. Therefore, desirable parameters of the water-based SAP adhesive are carboxylation of some degree, or carboxylation greater than >0.1%, or greater than >0.5%and Tg of less than <-20 degrees Celsius, or less than <-15 degrees Celsius.

Another embodiment with ability to lock the SAP particles in place is a cationic and silane containing emulsion polymer as disclosed in US patents 9, 828, 530 and US 10, 703, 927 both herein incorporated by reference in their entirety. In this case, the attachment of SAP particles was found to improve but not to the same degree as the above materials. The cationic containing monomer likely interacts with the acid groups of the SAP and the silane containing monomer will react to form a covalent bond with the acid groups in the SAP. In this embodiment, it is preferred that the emulsion polymer comprises at least 1%by weight silane containing monomer and at least 2%by weight of the cationic containing monomer.

Water Based Adhesive Patterns

The water-based adhesive spots can be circular, oval, square, rhombus, diamond, polygon, or other suitable shape. In some embodiments, a spot length 100, L, is longer in the longitudinal direction than a spot width 102, W, in the cross-web direction as shown in FIG. 8. In some embodiments, a spot length 100, L, is shorter in the longitudinal direction than a spot width 102, W, in the cross-web direction as shown in FIG. 11. In some embodiments, a spot length, L, is approximately the same in the longitudinal direction as a spot width, W, in the cross-web direction. In a preferred embodiment, the spot length, L, is 14.8 mm and is longer in the longitudinal direction than a spot width, W, of 6.9 mm. This locates the major axis of the adhesive spot along the longitudinal direction length of the diaper core and in Example 17, it was found this prevented high rewet, which is undesirable in a diaper core.

The water based adhesive spots in some embodiments can be arranged onto the base sheet in an ordered array versus a random placement. The adhesive spots in the array may be aligned in an XY array such that there are a plurality of microchannels 104 devoid of SAP particles between the adhesive spots as shown in FIGS. 10-11. Some of the microchannels are parallel to the longitudinal direction and some of the microchannels are parallel to the cross-web direction. Such a configuration may be less preferred since the fluid could easily follow a straight, shorter microchannel in the cross-web direction from the center channel 38 and travel easily to the edge forming a leak.

The water based adhesive spots in the array in some embodiments can be arranged in a staggered array such that adjacent adhesive spots in the columns of adhesive spots in the longitudinal direction overlap in the length direction and there are cross-hatched diagonal microchannels 104 (relative to the longitudinal direction) extending from the center channel to the edges that are devoid of SAP particles between the adhesive spots as shown in FIGS. 8, 9, and 12. Such a configuration may be preferred since the fluid path to the edge is longer from the center channel 38 helping to mitigate leaks from the edge.

It was determined that a plurality of microchannels and a center channel are useful to move fluid within the diaper core and utilize SAP particles more remote from the diaper core insult location. As such, the pattern percentage coverage for the adhesive spots should be less than 100%. However, too few adhesive spots results in insufficient SAP particle attachment and reduced capacity. Too much pattern percentage, even with microchannels, can lead to gel blocking and closing of the microchannels. Therefore, the adhesive spot pattern coverage in various embodiments can be from 20%to 95%, or from 30%to 90%, or from 40%to 85%, or from 60%to 80%. In the Examples, a pattern coverage of approximately 70%was found to provide preferred results. The uncoated longitudinal direction center channel 38 area is included in this calculation as an area devoid of adhesive spots.

Preferably there are more numerous and smaller adhesive spots present than fewer larger adhesive spots in the pattern for a given pattern percentage. This forms more microchannels in the structure. In some embodiments, there are at least 3 to 10 or 3 to 6 adhesive spots between the longitudinal direction center channel 38 and the first edge 30 at any particular cross-web location. This can help to prevent edge leaks. In some embodiments, for a base sheet sample size measuring 400 mm in the longitudinal direction and 105 mm in the cross-web direction there are preferably from 100 to 400, or 125 to 375, or 150 to 350 adhesive spots per 0.042 square meters. Or when converting to square meters, there are 2380 to 9524, or 2975 to 8925, or 3572 to 8330 adhesive spots per square meter.

SAP

After screen printing the plurality of water-based adhesive spots, SAP particles are drop coated onto the printed base sheet. The SAP particles then adhere to the plurality of water-based adhesive spots. Excess SAP is removed using vacuum or the web is run though a vertical section or inverted to allow gravity to remove excess particles and recycled to be reapplied.

Suitable super absorbent polymer particles are known to those of skill in the art of personal care articles. Suitable SAP particles can have a particle size range of 300 to 500 microns and a be applied at a rate of 100 to 400 gsm, or 150 to 350 gsm, or 200 to 250 gsm. Suitabel SAP particles are available from Nippon Shokubai Co. under the trade designation “QAX-1808” or “W2080” ; from BASF under the trade designation “HYSORB N7059” ; from Sumitomo Seika under the trade designation “AQUA KEEP” ; and from Sanwet under the trade designation “IM-930” .

Longitudinal Direction Center Channel

A longitudinal direction center channel 38 is located in the middle one third of the width of the base sheet and the center channel 38 has a channel width 40 between a first channel edge 42 in the machine direction and a second channel edge 44 in the machine direction. The center channel need not be perfectly centered in the base sheet in the longitudinal direction. The center channel 38 is void of the plurality of water-based adhesive spots 34 and the plurality of SAP particles 36.

The center channel allows for liquids to flow relatively unencumbered the length of the diaper core. It also acts as a “header” to feed liquid in the cross-web direction to the microchannels 104. The center channel width is preferably from 2 to 25 mm, or from 5 to 20 mm.

The center channel is formed by longitudinal direction ultrasonic bond line (s) 200. The lines may be continuous or intermittent (dashes) extending in the longitudinal direction. Areas within the center channel where there is a bond line 200 are hydrophobic while unsealed areas 210 in the center channel (between the bond lines) are hydrophilic as seen in FIG. 6. There may be one, to, three or more bond lines in the center channel and any combination of solid or intermittent can be used. If a single bond line is used, the first channel edge 42 and the second channel edge 44 are the outermost edges of the bond line. If multiple bond lines are used, the first channel edge 42 and the second channel edge 44 are the outermost edges of the outermost bond lines as there may be one or more interior bond lines too as shown in FIG. 6. In one embodiment, three bond lines that are solid having a width from 1-2 mm wide and spaced apart equally are used. The center channel comprises three longitudinal bond lines, a first bond line forming the first channel edge, a second bond line located at the channel middle, and a third bond line forming the second channel edge and unsealed hydrophilic areas are located between the bond lines as shown in FIG. 6.

Hot Melt Adhesive Filaments

The nonwoven cover sheet 40 is optionally adhered to the base sheet 12 by a layer of hotmelt adhesive filaments 48 applied over the top of the plurality of SAP particles 36 as seen in FIG. 7. It was determined in the Examples that the chemistry used for some of the water-based adhesive spots failed the Drop Test unless the optional hotmelt adhesive filaments were applied. Furthermore, it was determined that a water-based adhesive instead of the preferred hotmelt adhesive may not work to attach the cover sheet and help hold the SAP particles in place after being insulted by saline and subjected to the Drop Test. It was also determined that a solvent-based adhesive instead of the preferred hotmelt adhesive may not work to attach the cover sheet and help hold the SAP particles in place because the solvent-based adhesive encapsulated the SAP particles too much preventing the uptake of liquids and significantly reducing the liquid capacity of the diaper core.

Thus, the optional holt melt adhesive was unexpectantly found to work even though it is applied directly over the SAP particles and yet it does not encapsulate the SAP preventing fluid uptake. The hot melt adhesive is applied as filaments or strands as seen in FIG. 7. The filaments can hold the SAP particles together both before and after swelling helping to prevent SAP particle migration and gel blocking.

It was determined that the printed water-based adhesive spots with attached SAP particles can at a minimum swell two times in size such that the top layer of swollen SAP particles were no longer physically anchored to anything at that point with certain water-based adhesive chemistries such as Examples 4-7. This problem allowed for the “gelled” SAP particles to become mobile upon absorbent diaper core movement. A solution that was found to keep the “gelled” SAP particles contained during movement, was hot melt adhesive strands (filaments) that were sprayed on top of the SAP particles before fluid absorption, forming a network structure that kept the “gelled” SAP particles immobile and intact while not compromising fluid intake to the SAP particles. The hot melt adhesive was hydrophobic for resisting wash-away during the fluid insult process. Too high of a basis weight /tightly woven network of filament strands impeded too much fluid from getting to the SAP particles. This slowed down the Strike Through Time and absorption speed. The desired hot melt adhesive basis weight range for effective performance was 2 -15 gsm, preferably 3 -8 gsm, and most preferably 4 -5 gsm. The adhesive strand thickness range for effective performance was 10 -30 microns; preferably 12 -20 microns; and most preferably 12 - 15 microns. The improvement in utilizing a hot melt adhesive filament network in keeping the SAP “gel” in place was demonstrated by the Drop Test as specified in Test Method 1.

A non-contact spray coating technique was used for applying the hot melt adhesive by utilizing a hot die under air pressure as shown in FIG. 15. The hot melt adhesive was sprayed directly on top of the SAP particles as filaments to hold and retain the SAP particles. During testing, it was determined that if the hot melt adhesive was instead first applied to the nonwoven top sheet and then the top sheet laminated onto the SAP particles and base sheet, the SAP particles did not stay in place and failed the Drop Test. This confirmed the unexpected result of needing to apply the hot melt adhesive as filaments directly onto the SAP particles.

Suitable hot melt adhesives can include the following chemistries: styrenic polymer of styrene-butadiene polymer, rubber-based adhesives, and/or acrylic-based adhesives which can be obtained from Bostik, Henkel, and H. B. Fuller.

Nonwoven Cover Sheet

The nonwoven cover sheet helps to contain the SAP particles and is preferably highly permeable and soft to the touch. In some embodiments, the nonwovens are often referred to as air-through nonwovens having good air permeability. Another suitable cover sheet can include a two-layer spunbond-spunbond nonwoven. Suitable nonwovens can have a basis weight from 20 to 80 gsm, or from 30 to 50 gsm.

Edge Sealing

The first edge 30 and the second edge 32 are ultrasonically sealed to help prevent SAP particle leakage, liquid leakage, and to attach the cover sheet to the base sheet. In one embodiment, a 2 mm wide bond seal was placed 2 mm inboard from the outer edge was used. Other suitable seals can be employed and there can be more than one seal line used and the widths of the seal lines can be varied. The seal strength should be sufficient such that a soiled diaper core does not come apart at the seam.

Process of Making

Referring now to FIG. 15 a process for making the diaper core is illustrated. An SMS base sheet is unwound 50 and screen printed 52 with a plurality of water-based adhesive spots. SAP is drop coated 54 onto the adhesive spots forming SAP islands and excess SAP is removed by a vacuum system (not shown) . Hot melt adhesive is applied as filaments 56 to the SAP islands and a nonwoven cover sheet is unwound 58 and brought into contact with the hotmelt adhesive and the SAP islands. Thereafter, the laminated diaper core is ultrasonically welded 60 and has a plurality of ultrasonic bond lines 50 positioned along the first edge 30, the second edge 32, the first channel edge 42, and the second channel edge 44 of the diaper core 10. The finished diaper core is then wound into a roll 62 for shipping.

EXAMPLES

Table 1: Materials List

Test Methods:

For Test Methods 1-3, the Saline Solution described below was prepared and utilized.

Saline Solution (Artificial Urine) Preparation

A testing liquid consisting of a 9 g/l solution of sodium chloride in distilled water with a surface tension of (70 +/-2) mN/m was made. One liter (1000 grams) of distilled water was weighed and put into a container. Then 9.0 grams of sodium chloride and 0.1 grams of Sensient FD&C Blue No. 1 Powder were weighed and then added to the premeasured 1 liter of distilled water in container. A magnetic stirring bar was then added into the solution and the solution stirred on a magnetic stirrer for 15 minutes.

Test Method 1: Drop Test

Sample Insult Procedure

To insult the absorbent core test sample, the test sample was placed onto a flat surface and the insult cylinder test apparatus (77 mm tall, 50 mm circumference, weighing 80 grams and constructed from PVC pipe) was gently placed on the center of the dried adhesive/SAP test sample. 75 grams of Saline Solution was weighed into a beaker and then poured into the opening of the test apparatus in a swift motion (trying to dispense in under 3 seconds) . The test apparatus was then removed once all the Saline Solution was absorbed by the test sample. The test sample was then left undisturbed to sit for 40 minutes before testing.

Drop Test Apparatus

The drop test apparatus 300 as shown in FIG. 16 was used to drop the absorbent core a known distance while attached to a rod. The apparatus was approximately 53 cm high and suspended a drop rod on two horizontal support arms at a height of 52.4 cm from a horizontal surface. The support arms were spaced apart approximately 38.7 cm from outside edge to outside edge. Beneath the support arms where a pair of longer impact arms spaced apart approximately 38.7 cm that would catch and hold the drop rod after being released. The impact arms were spaced lower 13.0 cm vertically (top of support arm to top of impact arm) from the support arms. The drop bar was 1 cm in diameter, 41.5 cm in length, weighed 149.5 grams and was made from aluminum. One method to build the test apparatus is to use 80/20 T-slot available from Aluminum Building System (Grainger, Bloomington, MN) . The diaper core test samples were attached to the drop rod with two binder clips measuring 5 cm wide and weighing about 25.2 grams that clipped the diaper core to the drop bar.

Test Procedure

The drop rod was rested on the upper support arms of the drop test equipment. Using the two binder clips, one end of diaper core test sample was wound around the drop rod such that the free end touched or almost touched the body of the diaper core and was clipped to the drop rod by placing the two binder clips to hold in place as shown. The diaper core should be clipped to the drop rod such that the center channel is vertical. The test sample on the drop rod was slightly lifted off the support arms (no more than 13 mm) , moved forward, and then released while approximately horizontal such that it fell and struck both of the lower impact arms of the test apparatus (total drop height of 13 cm) and came to a rest on the impact arms. No additional force was introduced to the test sample as it was dropped. This action counted as 1 drop. The action was repeated until diaper core failure or until the diaper core passed 10 drops onto the support arms.

Definition of Success Criteria

Test samples were dropped up to ten times or until observed failure. Failure was defined as 50%or more of the “gelled” SAP falling off of the base adhesive/nonwoven layer prior to 10 drops. Success was defined as 51%or more of the “gelled” SAP or more adhering to the base adhesive/nonwoven layer after 10 drops.

Test Method 2: Strike Through and Rewet Tests

Test Sample Area:

Strike Through Test:

The absorbent core test sample was placed on a flat surface. The center of the test sample from the ends and sides was measured and marked with a small center dot. The insult cylinder test apparatus as used in Test Method 1 was placed in the center of the test diaper core concentric with the center dot. The Saline Solution was weighed out into a beaker in an amount based on test sample area and poured into the opening of the test apparatus in a swift motion (trying to dispense entire liquid amount in under 3 seconds) . A stopwatch was started as soon as pouring began. The stopwatch was stopped as soon as all of the Saline Solution was observed absorbed through the top sheet of test sample. The 1 ^st Strike Through time was recorded. The stopwatch was started immediately to allow for total liquid and after 10 minutes the insult cylinder test apparatus was then removed. The distance the fluid traveled was measured in the length and width direction of absorbent test sample from the center dot without disturbing test sample. The distance was recorded in mm. After 10 minutes, the insult cylinder test apparatus was again placed concentric with the center dot on the previous insult location. The Saline Solution amount was weighed out into a beaker based on test sample area and poured into the opening of the test apparatus in a swift motion (trying to dispense entire liquid amount in under 3 seconds) . The stopwatch was started as soon as pouring began. The stopwatch was stopped as soon as all of the Saline Solution was absorbed through the top sheet of test sample. The 2 ^nd Strike Through time was recorded. The stopwatch was started immediately and kept running for 5 minutes. The insult cylinder test apparatus was removed. The distance the fluid traveled was measured in the length and width direction from the center dot without disturbing test sample after the 5 minutes. Distance in mm was recorded.

Rewet Test:

At the 10-minute mark for the 1 ^st Strike Through time or 5-minute mark after the 2 ^nd Strike Through time, a set of 20 pieces of pre-weighed filter paper (Fisher Brand Q5; 9.0 cm diameter) was placed on the “insult spot” or center dot. A 5 kg weight was then placed onto the top of the filter paper. The stopwatch was started. After 5 minutes, the 5 kg weight was removed, and the 20 pieces of filter paper weighed. Rewet was calculated for each test sample using the following method: Rewet = weight of wet filter paper –weight of dry filter paper. Rewet sample measurements were made in triplicate with the mean value reported.

Test Method 3: Strike Through and Fluid Traveled Tests Using a U-Shaped Test Apparatus

The test apparatus 400 for the U-shape Strike Through and Fluid Travel Tests is shown in FIG. 17. Plexiglass (3 mm thick) was shaped in the form of a U with the legs of the U spaced about 305 mm apart and the depth of the U about 225 mm and the width of the U about 210 mm and having a top cover. Fastener hook strips (25 mm by 152 mm) , obtained from 3M Company, St. Paul, MN, under the trade designation "3M HOOK CHK-00732" , were adhered to the U to hold the ends of the diaper core and to hold the edges of the diaper core near the middle where they would tend to wrap the legs of a wearer to anchor diaper core to the test apparatus. A 25.4 mm hole was placed 27 cm from one edge of apparatus (approximate center) into the top cover for fluid to “insult” diaper core. Standard 19.1 mm inside diameter tubing was threaded through the hole and sealed with Multipurpose RTV Silicon Sealant, obtained from Grainger, Bloomington, MN. The tubing was 23 cm in length and reached from the bottom of the U to the top hole and slightly through opening in the top plate for sealing purpose. A standard high-density polyethylene funnel, obtained from Cole-Palmer, under the name EW-06122, was inserted into the hole to ensure easy pouring of Saline Solution.

The Saline Solution amount was weighed into a beaker based on test sample area and poured into the opening of the funnel in a swift motion (trying to dispense entire liquid amount in under 3 seconds) . A stopwatch was started and watched as the insult liquid entered the absorbent core. The stopwatch was stopped after all liquid entered the core and the time recorded (in seconds) for the Saline Solution to be completely absorbed. The 1 ^st Strike Through time was recorded. After 5 minutes, the distance that the fluid traveled as the diaper core was held by the U-shaped support against the force of gravity was measured with a tape measure. Distance was recorded in mm. The stopwatch was kept running for 10 minutes. Repeat above procedure when testing a 2 ^nd, strike through time.

Test Method 4: Basis Weight

ASTM D3776 Standard Test Method was used for measuring Mass Per Unit Area (Weight) of Fabric to determine basis weight.

Adhesive Example Number 6 with a Tackifier:

100 grams of BASF ACRONAL A220NA was measured into a jar and then 20 grams of LAWTER’s SNOWTACK SE724G was added to the same jar. This solution was then stirred under 300 rpm with a 3-blade mixer for 5 minutes before use. The solution was then used for coating and testing in Example 6.

Examples:

Examples 1-16 (Base Adhesive Samples)

A one-inch-wide masking tape, obtained under the trade designation “SCOTCH 232” , from 3M Company, St. Paul, MN, was used to secure the top and bottom of the base SMS nonwoven down onto a flat surface so the test sample did not move during Mayer Drawdown coating. With a number 4 Mayer Drawdown Rod (BYK-Gardner, Columbia, MD) about 6 mL of the adhesive, as received from manufacturer or as made per described method above, was placed to the top middle portion of the SMS nonwoven using a 3 mL disposable pipette. The Meyer Rod was then pulled across the nonwoven at a constant speed to coat the nonwoven. The Meyer Rod was then placed in a container of water for cleaning. Within 30 seconds of coating the adhesive, about 30 grams of SAP was applied onto the entire sample of wet adhesive trying to cover the entire coated sample evenly. The sample was air dried for 30 seconds and excess SAP particles were removed by holding the sample in a vertical position and gently shaking by moving hands back and forth horizontally about 2.54 cm while gripping the sample until no more SAP particles fell off. The sample was then placed on a flat surface and the sample allowed to dry for at least 8 hours before testing. For Example 17, the diaper core was produced on a machine having the process steps as shown in Figure 15.

Table 2: Base Adhesive Samples (Examples 1-17)

Examples 18-25 (Print Design Samples)

A sample of SMS nonwoven was cut 150 mm wide by 450 mm long. The top and bottom of the nonwoven was taped down onto the flat surface such that the sample did not move during adhesive screen coating. The printing screen was then placed on the top of the nonwoven, with the center of the screen overlapping with the center of the bottom nonwoven. The screen (500 mm in width, 910 mm in length and 10 mm in thickness) , obtained from XunDa Printing Equipment Company, Shenzhen, China, was used for the adhesive coating of the corresponding printing patterns shown in Table 3. The patterned section of the screen had a mesh size of 40 while the rest of the screen had no such mesh to direct the adhesive to penetrate through the areas with the mesh. A metal/rubber hybrid plate (metal part on the top: 55 mm in height, 35 mm in width and 300 mm in length; rubber part on the bottom in contact with the screen during adhesive coating: 60 mm in height, 10 mm in width and 300 mm in length) was used to apply manual pressure of approximately 0.05 MPa by pushing around 10 g of BASF Acronal 220na adhesive on the top of the screen to penetrate through the mesh and deposit onto the hydrophilic side of the SMS nonwoven. During manual pressure application, the metal plate was pulled in the longitudinal direction of the screen at a constant speed to print the adhesive on the SMS nonwoven. Within 30 seconds of coating the adhesive, about 30 grams of SAP was applied onto the entire sample of wet adhesive in such a way that the entire sample was coated evenly. The sample was then allowed to sit for 2 minutes, and excess SAP particles were removed by holding the sample in a vertical position and gently shaking by moving hands back and forth horizontally about 2.54 cm while gripping the sample until no more SAP particles fell off. The air-through nonwoven was placed on the top of the SAP layer to cover the SAP particles and then the sample was cut to 400 mm in length which covered the whole SAP patterned area of the nonwoven. MD tunnels (if any) and edge lines were drawn on the top of the air-through nonwoven and then the lines welded with an ultrasonic welder at power level of 10 (US-004 Sewfree Ultrasonic Multi-Purpose Welder, H&H, Hong Kong) . The edges of the welded sample were cut, and an absorbent sample (400 mm in length and 105 mm in width) was laid on a flat surface and the sample allowed to dry for at least 8 hours before testing. The Strike Through Time and Rewet tests were conducted for samples 18-26 following the procedure of Test Method 1 and results are shown in Table 8.

Table 3: Print Design Samples (Examples 18-25)

Examples	EX	18	EX 19	EX 20	EX 21	EX 22	EX 23	EX 24	EX 25
Pattern	Oval	Oval	Oval	Oval	Diamond		100%	100%+ Channel	Diamond
Single unit width B (mm)	6.1	6.9	6.1	14.2	7.6	0	0	14.1
Single unit length C (mm)	14.8	14.4	14.8	6.0	14.8	0	0	14.1
Total width F (mm)	105	105	105	105	105	105	105	105
Total length G (mm)	400	400	400	400	400	400	400	400
Center Channel Width (mm)	12	12	12	12	12	0	14	10
Edge Seal Widtha (mm)	5	5	5	5	5	5	5	5
Pattern qty in CD	12	12	12	6	14	0	0	6
Pattern qty in MD	24	26	24	50	24	0	0	26
Total Pattern Spot qty	288	312	288	300	336	0	0	156
Single unit area (Sqmm)	70.5	78.4	70.5	67.2	56.4	0	0	99.4
Total area (Sqmm)	20296	24457	20296	20161	18939	42000	32400	15506
Pattern %	48%	58%	48%	48%	45%	100%	87%	74%
Mesh
	40	40	40	40	40	120	90	40

Examples 26-28 (Center Channel Samples)

The center channel was centered in the top nonwoven layer and created by using heat bonding or ultrasonic welding. The base sheet nonwoven used was a blend of layers (hydrophilic on top and hydrophobic on bottom) . When creating the center channel with heat bonding or ultrasonic welding, the layers were melted together to create a hydrophobic weld line. In some embodiments as seen in FIG. 6 and discussed above, center channel welded area had hydrophobic and hydrophilic regions alternating alternately across the width of the center channel, depending on how many weld lines were used and how they were spaced in the cross-web direction. These alternating constructions allowed for “corrugations” , which helped the fluid move more longitudinally in the diaper core. These weld line (s) propelled the fluid (insult) down its’ length, increasing fluid distribution down the length of the absorbent article. Additionally, the diaper core edges under the heat bonding or ultrasonic bonding were changed from hydrophilic to hydrophobic, which prevented side leakage of the diaper core in the presence of excessive liquid.

For Examples 1 to 16, the diaper core was made by hand and followed the procedure under examples 1-16. For Example 17, the diaper core was produced on a machine having the process steps as shown in Figure 15. The diaper core material in endless form was ultrasonically welded with an ultrasonic welder machine (obtained from Emerson, St. Louise, MO, under the trade designation “BRANSON 900 SERIES” ) . The ultrasonic welder machine was a 20 Khz ultrasonic welder machine equipped with an 11.4 cm x 15.2 cm (4.5” x 6” ) aluminum block horn and booster of 1: 1.5. The weld method was Energy with a weld value of 700 J, at a pressure of 1379 kPa (200 psi) for a 7.62 cm (3 inch) circle with fabricated weld lines. Amplitude was set to 50%, line speed set at 12 feet per minute.

MD Tunnel Evaluation Using Test Method 3:

The absorbent core samples were cut to the size of 115 mm by 400 mm and then the insulted side of absorbent article was placed onto reclosable fastener hooks, obtained from 3M Company, St. Paul, MN, under the trade designation "3M HOOK CHK-00732" , following the shape of the U. The sample was then placed securely tight up against the plexiglass.

Table 4: MD Tunnel configuration

Comparative 1 was the inner diaper core removed from a Care Daily diaper size L (baby weight of 9-14 kg) . Care Daily (Shenzhen) Technology Development, Shenzhen, Guangdong Province, China.

Center Channel Evaluation Using Test Method 2:

The sample preparation of the flat-sample test was very similar to that of the U-shape test above. The major difference was that the flat-sample test did not use the U-shape test apparatus. Instead, all the liquid was insulted with the sample laid flat on a table. Samples with one longitudinal bond line and three longitudinal bond lines were compared with a sample without any center channel. From the test results below, the introduction of the center channel demonstrated its utility of directing the liquid flow, resulting in shorter Strike Through Time and longer liquid travel length.

Table 5: MD Tunnel Configuration

	Ex. 29	Ex. 30	Ex. 31
1st Strike Thru (sec)	20	19	12
2nd Strike Thru (sec)	10	9	7
Distance traveled length (mm)	255	300	300
Weld Width (mm)	0	0.5	0.5
Spacing Between Weld Lines (mm)	0	0	2.5

Examples 32-35 (Hot Melt Adhesive Samples)

It was determined that the printed spots with SAP particles at a minimum swell to 2X in their size and the top layer of swollen SAP particles were not physically anchored to anything. This problem allowed for the “gelled” SAP to become mobile upon absorbent core movement. A solution that was found that to keep the “gelled” SAP particles stationary during movement, was hot melt adhesive strands (filaments) that were sprayed on top of the SAP particles before fluid absorption, forming a network structure that kept the “gelled” SAP immobile and intact while not compromising fluid intake to the SAP. The hot melt adhesive was hydrophobic for resisting wash-away during the fluid insult process. Too high of a basis weight /tightly woven network of strands impeded fluid from getting to the SAP particles. This slowed down the Strike Through Time and absorption speed. The desired adhesive basis weight range was 2-15 gsm; preferably in the range of 3-8 gsm; and most preferably in the range of 4-5 gsm. Adhesive strand thickness range was 10-30 microns; preferably in the range of 12-20 microns; most preferably in the range of 12-15 microns. The improvement of the hot melt adhesive network keeping the SAP “gel” in place was demonstrated by the Drop Test specified in Test Method 1.

A non-contact spray coating technique was used for applying the hot melt adhesive by utilizing a hot die under air pressure as shown in FIG. 15. The hot melt adhesive was sprayed directly on top of the SAP particles as filaments to hold and retain the swelled SAP particles. The hot melt adhesive is sprayed in filaments or thin strands that form a network or web-like structure on the nonwoven top sheet layer.

Table 6: Hot Melt Adhesive Basis Weight

RESULTS:

Insult and Drop Test results were conducted following the procedure of Test Method 1 for Examples 1-17, with results shown in Table 7. Table 7 shows that selection of the correct water-based adhesive is important to passing the Drop Test if the hot melt adhesive is eliminated (Examples 9, 10, 13-16) and to the selection of a water-based adhesive that can be utilized by adding a layer of hot melt filaments over the SAP particles to pass the test (Example 17) .

Table 7: Drop Test Results

Base SAP Adhesive:

First, testing several classes of emulsion with non-reactive chemistries it was found that SBR (styrene-butadiene-copolymer rubbers) was the only chemistry (non-reactive) that had improved attachment. Within that class it was also found that some key requirements were also needed for good SAP adhesion to the SMS base sheet. First, the Tg should be low-preferably below -20 degrees Celsius, or below -15 degrees Celsius. Second, the SBR should be listed as carboxylated, containing some carboxylation of some type introduced into the polymer to add some acid groups and polarity. Several samples were tested with Tg <-20 degrees Celsius and no carboxylation, and carboxylation and Tg >-20 degrees Celsius and it was found in both materials, attachment of the SAP was poor. Therefore, desirable parameters of the water-based SAP adhesive are carboxylation of some degree, or carboxylation greater than >0.1%, or greater than >0.5%and Tg of less than <-20 degrees Celsius, or less than <-15 degrees Celsius.

In other embodiments with a potential to lock the SAP in place, a cationic and Silane containing emulsion was used. In this case, the attachment of SAP was found to improve, not to the same degree as the above materials. The cationic group likely interacts with the acid groups of the SAP and the silane containing group will react to form a covalent bond with the acid groups in the SAP. In this embodiment, it is preferred to be using at least greater than >1%silane and at least greater than >2%cationic group.

Print Pattern:

Table 8: Print Pattern Results

Table 9: Center Channel U Shape Test Results

Sample #	Ex. 26	Ex. 27	Ex. 28	Comparative 1
1st Strike Thru (sec) -100 mL	21	17	12	16
Distance traveled after 1 ^st insult (mm)	205	280	230	180
2nd Strike Thru (sec) -100 mL	17	19	15	21
Distance traveled after 2 ^nd insult (mm)	290	340	270	185

The U shape test apparatus shows that the center channel provides some upward fluid flow when compared to no “open middle” area (ex. 28) or no middle area at all (comparative 1) .

Table 10: Center Channel Strike Through Results

The center channel number of lines shows an increase in fluid flow in the longitudinal direction.

Table 11: Hot Melt Adhesive Results

The addition of hot melt adhesive strands to the top of the SAP particles shows a significant improvement in overall diaper core integrity.

Claims

A diaper core comprising:

a nonwoven base sheet having a first side and an opposing second side; the first side being hydrophilic and the second side being hydrophobic; the base sheet having a longitudinal length, a cross-web direction width, a first edge in the longitudinal direction and a second opposing edge in the longitudinal direction;

a plurality of water-based adhesive spots located on the first side and a plurality of SAP particles adhered to the first side by the water-based adhesive spots;

a longitudinal center channel located in the middle one third of the width of the base sheet, the center channel having a channel width between a first channel edge in the longitudinal direction and a second channel edge in the longitudinal direction; and the center channel void of the plurality of water-based adhesive spots and the plurality of SAP particles.

a nonwoven cover sheet positioned over the plurality of water-based adhesive spots and the plurality of SAP particles; the nonwoven cover sheet laminated to the base sheet by a plurality of ultrasonic bonds positioned along the first edge, the second edge, and forming the first channel edge and the second channel edge of the diaper core.
The diaper core of claim 1 wherein the plurality of adhesive spots forms an XY array having a plurality of microchannels between adhesive spots parallel to the longitudinal direction and a plurality of microchannels between adhesive spots parallel to the cross-web direction.
The diaper core of claim 1 wherein the plurality of adhesive spots forms a staggered array having a plurality of microchannels between adhesive spots orientated diagonally to the longitudinal direction.
The diaper core of claims 1, 2, or 3 wherein the nonwoven base sheet is an SMS base sheet having three layers; a spunbond layer on the first side, a spunbond layer on the opposing second side, and a middle layer of a meltblown nonwoven.
The diaper core of claims 1, 2, 3, or 4 wherein a center channel width is from 2 to 25 mm.
The diaper core of claims 1, 2, 3, 4, or 5 wherein the center channel comprises three longitudinal bond lines, a first bond line at the first channel edge, a second bond line at a channel middle, and a third bond line at the second channel edge and unsealed hydrophilic areas are located between the bond lines.
The diaper core of claims 1, 2, 3, 4, 5, or 6 wherein an adhesive spot length, L, in the longitudinal direction is greater than an adhesive spot width, W, in the cross-web direction.
The diaper core of claims 1, 2, 3, 4, 5, 6, or 7 wherein an adhesive spot pattern coverage is from 20%to 95%.
The diaper core of claims 1, 2, 3, 4, 5, 6, 7, or 8 wherein there are 100 to 400 adhesive spots per 0.042 square meters.
The diaper core of claims 1, 2, 3, 4, 5, 6, 7, 8, or 9 wherein the layer of hotmelt adhesive filaments has a basis weight from 2 to 15 gsm.
The diaper core of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wherein the layer of hot melt adhesive filaments has a stand thickness from 10 to 30 microns.
The diaper core of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 wherein the water-based adhesive comprises a styrene-butadiene-copolymer rubber.
The diaper core of claim 12 wherein a glass transition temperature of the styrene-butadiene-copolymer rubber is less than -15 degrees Celsius.
The diaper core of claims 12 or 13 wherein the styrene-butadiene-copolymer rubber is carboxylated.
The diaper core of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 wherein the water-based adhesive comprises an emulsion polymer having a cationic containing monomer and a silane containing monomer, and wherein the emulsion polymer comprises at least 2%by weight of the cationic containing monomer and at least 1%by weight of the silane containing monomer.
The diaper core of claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 wherein a layer of hotmelt adhesive filaments is applied directly over the plurality of SAP particles to secure the SAP particles when swollen.