Composite article resistant to moisture-induced debonding

The articles of this invention have increased resistance to moisture induced delamination at a bond line comprising a substrate, a second layer an dan adhesive. The increased resistance to moisture and increase in bond strength between the adhesive, the substrate and the second layer is produced through a novel adhesive. The adhesive after spraying cools to below the softening point of the components but retains sufficient liquidity to fully wet or to penetrate the second layer causing the layers to be bonded to the film substrate through intimate adhesive bonds or by bonding through a physical entrapment. The physical entrapment of the nonwoven layer substantially prevents moisture-induced debonding or delamination.

FIELD OF THE INVENTION 
The invention relates to a disposable composite article made by joining its 
components with an adhesive. The invention more particularly relates to 
disposable articles made by adhesively bonding a film, a woven or nonwoven 
fabric, tissue or sheet to a substrate using a novel adhesive that can be 
sprayed on during construction. Still further, the invention relates to 
the manufacture of a disposable composite article having a covering 
envelope and an internal absorbent layer, held within the envelope. The 
envelope can be formed from a porous front sheet adhered to an impervious 
back sheet and can have further layers added made of a film or fabric. The 
absorbent layer can be made of tissue, absorbent fiber, or combinations of 
other absorbents and wrapping layers. Such layers are constructed using 
the adhesive of the invention to bind the absorbents in a mechanically 
stable form or to join the outer wrap to the absorbent. The sprayable hot 
melt adhesive composition typically contains a particular blend of 
thermoplastic block copolymer, a compatible tackifying resin, and a solid 
plasticizer. 
More particularly, the invention relates to disposable articles such as 
disposable infant and adult diapers and feminine pads that are resistant 
to moisture-induced debonding because of the unique qualities of the 
adhesives of the invention and to novel methods of article manufacture. 
BACKGROUND OF THE INVENTION 
Disposable articles and their manufacture from construction materials 
including fabrics, films, and adhesives are described in a variety of 
United States patents. Korpman, U.S. Pat. No. 4,028,292 teaches a 
thermoplastic composition which is resistant to heat deterioration at 
elevated temperatures comprising an oil-insoluble, heat reactive phenol 
formaldehyde resin and a suitable antioxidant of a metal dithiocarbamate. 
The only mention of plasticizers at all is in Column 4, lines 64-66, that 
states: "Plasticizers also may be used to supplement or partially replace 
the liquid portion of the resin." Collins et al., U.S. Pat. No. 4,136,699 
teaches a disposable article using a hot melt pressure sensitive adhesive 
as a positioning and construction material. Such adhesive, an improvement 
over Korpman but using a plasticizer oil, is typically extruded at high 
temperature onto the materials of construction during manufacture. 
Similarly, Chen et al., U.S. Pat. No. 4,460,364 teaches hot melt pressure 
sensitive adhesives used in the manufacture of sanitary products. Schmidt, 
Jr. et al., U.S. Pat. No. 4,526,577 teaches the use of 
styrene-butadiene-styrene block copolymers in the manufacture of 
disposable laminates using multiline extrusion adhesive application 
technology. Puletti et al., U.S. Pat. No. 4,627,847 also teaches the use 
of hot melt adhesives in disposable article construction. The adhesives 
disclosed in Collins et al., Chen et al., Schmidt, Jr. et al. and Puletti 
each use a plasticizing oil, and Puletti teaches that at column 4, lines 
1-24, the adhesive can be applied to articles with a variety of 
conventional methods, including spraying and extrusion. Boyce et al., U.S. 
Pat. No. 4,284,542 teach hot melt adhesive and sealant compositions based 
on alkali metal ionomers of random copolymers of ethylene, methyl 
acrylate, and one or more carboxylated monomers having improved high 
temperature viscosity stability when the composition contains 0.05-10 
parts of ammonium polyphosphate per each one hundred parts of ionomer or 
resin. Both liquid and solid plasticizers are useful in the compositions 
of Boyce et al. Only solid plasticizers are useful in the adhesives of the 
present invention. Tsukahara, U.S. Pat. No. 4,745,026 teaches thermal 
delayed tack sheets containing an aqueous based adhesive components 
including a polymer, a solid plasticizer and preferably a tackifier. In 
Column 1, line 45, the specification states: 
"The tackifier is an auxiliary component for increasing tackiness, when 
activated by heating, and it preferably blended but is not an essential 
ingredient." 
The tackifier of the present invention is an essential component since the 
tackifier and plasticizer interact to control the crystallization rate of 
the solid plasticizer, cold flow-open time and final onset of 
crystallization. An extensive list of solid plasticizers is taught in 
Tsukahara. However, the list does not include cyclohexane dimenthanol 
dibenzoate. 
In the conventional production of such articles, hot melt adhesives are 
typically extruded at elevated temperature directly onto a work piece. 
Additional layers of a nonwoven fabric or film can be adhered through the 
hot melt adhesive bonds. With extruded hot melt adhesives, disposable 
articles with mechanical bonding caused by entrapped layers of fabric or 
tissue can be made because the adhesive can be extruded at high 
temperature directly on the work piece. The hot extruded adhesive retains 
sufficient heat that the material remains liquid for a sufficient time 
such that the adhesive can soak into the fabric or tissue to form 
entrapping bonds. Additionally, atomized or misted typically aqueous based 
adhesives have been used in other end uses in which the adhesive is 
delivered in the form of a spray of finely divided droplets. However, such 
adhesives have had little or no success in disposable articles. 
In recent years, increasing attention has been directed to development of 
hot melt adhesives that can be sprayed onto the work piece or substrate in 
a manufacturing regimen. The use of spray-on adhesives have been found to 
increase productivity. Conventional spray-on adhesives are sprayed from a 
plurality of narrow orifices in the form of fibers, threads or filaments 
having a substantially circular cross-section with a diameter of about 
0.01 to 0.001 inches. The spray-on adhesive takes on the form of fibers 
that have substantial surface area in comparison to the mass of the fiber. 
As a result, the sprayed adhesive fiber cools very rapidly upon contact 
with the ambient atmosphere. Typically, in the manufacture of disposable 
articles, after spraying the spray-on adhesives reach ambient temperatures 
before contacting the work piece or are cooled substantially upon 
immediate contact with the work piece. This is in sharp contrast to 
extruded hot melt adhesives that retain a significant amount of heat and 
can remain melted after application. By ambient temperature, we mean the 
temperature of the surrounding atmosphere and the temperature of the work 
piece. In these construction applications, the work piece and the 
temperature of the manufacturing locus are typically not substantially 
different. Conventional spray-on adhesives, after application to a work 
piece, typically take the form of a solid mesh or web which is the result 
of the combined application of a plurality of adhesive fibers creating a 
substantially overlapping pattern of threads or fibers of adhesive 
covering the area of application on the work piece. With conventional 
spray adhesive technology, the disposable articles are manufactured by 
contacting a substrate such as a film or woven or nonwoven fabric with the 
cooled adhesive web on a second substrate and forming a bond between the 
substrates or layers by pressure. Such conventional spray-on adhesives 
form typically a laminated surface-to-surface adhesive bond with the film 
substrates and the fabric layers. By surface-to-surface bonds we mean a 
physical bond between the adhesive surface and the surface of a sheet or 
fiber substrate, wherein mechanical entrapment of the substrate in the 
adhesive does not make a major contribution to bond strength. Conventional 
spray-on adhesives, when cooled, form adhesive webs with solid 
characteristics that have little or no cold flow. After cooling, 
conventional spray-on adhesives have insufficient liquidity to flow onto 
and wet the surface of the film or fabric or flow into the fabric to 
entrap or enmesh the fabric in the adhesive mass. Due to the solid nature 
of the cooled spray-on adhesive, the conventional adhesives rely upon 
limited surface bonding to obtain an acceptable level of adhesion. 
Such surface bonding can result in a disposable article subject to 
moisture-induced delamination or debonding. The laminated or composite 
disposable articles often come into contact with moisture from a variety 
of sources. Such moisture tends to associate with the fibers of the woven 
or nonwoven fabric or the surface of other substrates. Such moisture can 
penetrate limited surface-to-surface adhesive bond between the 
conventional spray-on adhesive and any substrate or porous layer, 
weakening the bond and resulting in substantial weakening or failure of 
the bond. These debonding phenomena can be made significantly worse by the 
hydrophilicity of the underlying substrate. Hydrophilic substrates are 
preferred since they promote absorbance of moisture in the disposable 
article. Additionally, in the manufacture of disposable articles, 
surfactants can be part of any one component or can be post-added to the 
composite article after manufacture. while such surfactants can improve 
water absorbance, such surfactants can also enhance moisture-induced 
delamination. further, if added to the disposable article after 
manufacture in the form of an aqueous dispersion or spray, the surfactant 
can directly enhance moisture-induced delamination. 
Such moisture-induced debonding or delamination can be a significant 
problem in the construction of or the use of disposable diapers, feminine 
pads, incontinent pads, mattress covers,or any other product in which the 
article components such as a fabric is joined to a sheet or film substrate 
through surface adhesive bonds. The physical integrity of the article can 
be compromised due to adhesive bond failure resulting in waste, 
inconvenience, embarrassment or discomfort. We believe that the weakness 
in the bonds between the fabric and the conventional hot melt adhesives 
results from the fact that, upon application, the conventional spray-on 
adhesive cools so rapidly that the adhesive forms only limited surface 
bond and cannot flow onto the surface or into the fabric to enmesh woven 
or nonwoven fibers to form a more secure mechanical bond. 
Accordingly, a substantial need exists in the manufacture of articles from 
woven or nonwoven fabrics for spray-on adhesive that retains flowability 
or liquidity and can resist the moisture-induced delamination or debonding 
of such articles made with a hot melt spray-on adhesive. 
BRIEF DISCUSSION OF THE INVENTION 
We have found a novel spray-on adhesive composition made from components 
that interact to produce a composition that, after cooling below the 
softening points of the components, retains sufficient liquidity, for a 
sufficient period of time, to permit the adhesive composition to flow onto 
the surface or to penetrate the constituent parts of a disposable 
composite article, such as a film, a tissue or a woven or nonwoven fabric, 
sufficiently to enmesh or entrap sufficient fibers and to create a strong 
mechanical bond that is not substantially weakened, debonded, or 
delaminated by moisture. In sharp contrast to the limited surface bonding 
of conventional spray-on adhesives, the spray-on adhesives of the 
invention do not merely bond to the limited areas of surface of the fibers 
in the fabric, but cause the adhesive to flow onto the surface to 
intimately bond or to enmesh or entrap the fibers of the nonwoven. We have 
found that the cyclohexane dimenthanol dibenzoate solid plasticizer in the 
adhesive formulations causes the delay in onset of the formation of strong 
bonds. The delay in onset, (i.e.) the crystallization rate of the adhesive 
is controlled by the degree of aromaticity of the resin. An aromatic resin 
is more compatible with the cyclohexane dimenthanol dibenzoate solid 
plasticizer in the formulation causing slow crystallization, whereas an 
aliphatic resin is less compatible causing the resulting composition to 
crystallize quickly. Aromatic and aliphatic resins are blended or a resin 
having both aromatic and aliphatic character is used to compound adhesives 
having intermediate rates of crystallization. As a result, bonds that 
involve the mechanical entrapment of the fibers, even in the presence of 
substantial quantities of moisture, resist weakening, debonding, or 
delamination. By reciting that the spray-on adhesive of this invention 
substantially reduces the onset of moisture-induced weakening or 
delamination, we mean that the adhesive bonds formed by the liquidity of 
the adhesive retain sufficient bond strength, to prevent failure of the 
adhesive and to maintain an intact article during use while wet. The 
intimate bonds formed by the spray-on adhesives of the invention are 
distinguished from the limited surface bonding resent in the prior art by 
the flowability of the adhesives of the invention. Since the adhesives of 
the invention retain substantial flowability, bonding is obtained by 
flowing and fully wetting the surfaces that are combined in the 
manufacturing processes. In the use of the prior art adhesives, since they 
become solidified before or immediately after application, they tend to 
have substantially less flowability and can only bond where applied with 
little or no cold flow.

DETAILED DESCRIPTION OF THE INVENTION 
Briefly, the nonwoven articles of the invention obtain their substantial 
resistance to moisture-induced delamination or debonding because a 
substrate layer is joined with a separate layer through an adhesive that 
is sprayed on. The adhesives typically comprise a thermoplastic block 
copolymer such as an A-B-A block copolymer, an A-(B-A).sub.n -B-A, 
multiblock or tapered block copolymer, wherein n is an integer of about 1 
or more, or a radial block copolymer. In the block copolymer, each A 
comprises a polystyrene block and each B comprises a rubbery block. In 
addition to the block copolymer, the adhesive contains a tackifying resin 
which is a rosin acid or rosin ester or is aliphatic or mixed 
aliphatic-aromatic in character. The adhesive additionally comprises a 
plasticizer compound that has a softening point that is greater than 
disposable article manufacturing ambient temperature (typically 
25.degree.-35.degree. C.). 
We have found that these components cooperate to form an adhesive having 
improved article assembly properties (low viscosity at application 
temperatures), but additionally, after spraying and cooling to ambient 
temperatures, retains a liquid character for a substantial period of time 
which is sufficient to either fully wet the surface or to penetrate the 
porous layers. As a result the adhesive retains an extended open time, 
exhibits a good viscosity profile, and excellent dry and wet bond 
strength. The adhesive components can be formulated to retain liquid 
characteristics for a substantial period of time. The adhesive during this 
liquid period can flow onto the surfaces of the article component to fully 
wet out the surface creating enhanced bonding resistant to moisture. 
Additionally, the adhesive during this period of liquidity can flow into, 
surround and mechanically entrap or enmesh the fibers of a woven or 
nonwoven fabric or layer. While solidification is delayed, the adhesive, 
after solidification occurs, has enhanced cohesive strength because of the 
nature of the components. The use of the phrase sufficient liquidity for 
sufficient time to form moisture resistant bonds indicates that the 
adhesive remains liquid (with a viscosity less than 5,000 cP, preferably 
less than 2,000 cP, most preferably less than 1,000 cP, at 350.degree. F.) 
with little or no peel strength (less than 50 grams, preferably less than 
30 grams) until solidification occurs over a period typically greater than 
5 minutes, greater than 10 minutes or greater than 60 minutes, depending 
on the adhesive used. Since the adhesive remains liquid and does not 
solidify, it has little peel strength until it solidifies. After 
solidification the cohesive strength of the adhesive generally exceeds the 
strength of the materials used in the disposable article. 
THE BLOCK COPOLYMER 
Thermoplastic block copolymers that can be used in the novel adhesives of 
the invention in manufacturing disposable articles are thermoplastic 
rubbers that terminate in hard, glassy end blocks which are 
thermodynamically incompatible with the rubbery midblocks. such polymers 
consequently consist of two phases in a solid state, a continuous rubber 
phase and a substantially discontinuous hard, glassy or plastic phase 
which locks the rubber molecules in place. The end blocks produce physical 
crosslinking because the end blocks of a plurality of molecules are joined 
by physical van der Waals' attraction in a single domain or crosslinked 
site. Such an interaction forms domains which are stable. The literature 
describes numerous molecular variations of the thermoplastic rubber 
copolymers, including the A-B-A structure, an A-B-C structure, a branched 
or radial configuration and a multiblock or tapered block structure with 
repeating segments A-(B-A).sub.n -B-A, and so forth, wherein n is an 
integer of at least 1 to 15. 
The A blocks are typically homopolymeric polystyrene. However, other vinyl 
arene monomers can be used in preparing either a homo or copolymeric 
plastic or glassy end or A block. the B blocks typically comprise rubbery 
polymers derived from diene monomers including isoprene and butadiene. The 
midblocks can be post treated to improve their heat stability through 
hydrogenation or other treatment. We believe the size and amount of the A 
or end blocks in conjunction with the time to reform the end block domains 
is important to the important properties of the invention. As the A blocks 
increase in size the rate and tendency of the adhesive to solidify 
increases. We believe this is due to the interaction between the A blocks, 
the tackifier and primarily the solid plasticizer. Large A blocks or 
insufficiently plasticized A blocks can rapidly solidify after cooling, 
can be free of the delayed solidification effect and can have reduced 
moisture resistance. While the total styrene content of the polymers can 
be as much as 51 wt-% of the polymer, and since the polymers can have more 
tan two A blocks for optional performance, the largest A block should be 
less than or equal to about 15 wt-% of the polymer, and most preferably is 
less than or equal to 10 wt-% of the polymer. In an S-B-S 
(styrene-butadiene-styrene) copolymer the preferred molecular weight is 
about 50,000 to 120,000 and the preferred styrene content is about 20 to 
35 wt-%. In an S-I-S (styrene-isoprene-styrene) copolymer the preferred 
molecular weight is about 100,000 to 150,000 and the preferred styrene 
content is about 14-30 wt-%. Hydrogenating the butadiene midblocks 
produces rubbery midblocks that are typically considered to be 
ethylene-butylene midblocks. 
Such block copolymers are available from Shell Chemical Company, Enichem 
and Fina. Multiblock or tapered block copolymers (the A-(B-A).sub.n -B-A 
type) are available from Firestone under the STEREON 840A and 845 
trademarks. 
TACKIFYING RESIN 
The adhesives of the invention contain a tackifying resin in combination 
with a thermoplastic block copolymer and the plasticizer. Tackifying 
resins useful in the adhesives of the invention comprise rosin derivatives 
including wood rosin, tall oil tall oil derivatives, rosin ester resins, 
natural and synthetic terpenes and aliphatic or mixed aromatic-aliphatic 
tackifying resins. 
Aromatic monomers useful in forming the aliphatic-aromatic adhesive 
compositions of the invention can be prepared from any monomer containing 
substantial aromatic qualities and a polymerizable unsaturated group. 
Typical examples of such aromatic monomers including the styrenic monomers 
styrene, alphamethylstyrene, vinyl toluene, methoxystyrene, 
t-butylstyrene, chlorostyrene, etc., indene monomers including indene, 
methyl indene and others. Aliphatic monomers are typically natural and 
synthetic terpenes which contain C.sub.5 and C.sub.6 cyclohexyl or 
cyclopenyl saturated groups that can additionally contain a variety of 
substantially aliphatic ring substituents. Aliphatic tackifying resins can 
be made by polymerizing a feed stream containing sufficient aliphatic 
monomer such that the resulting resin exhibits aliphatic characteristics. 
Such feed streams can contain other aliphatic unsaturated monomers such as 
1,3-butadiene, cis-1,3-pentadiene, trans-1,3-pentadiene, 
2-methyl-1,3-butadiene, 2-methyl-2-butene, cyclopentadiene, 
dicyclopentadiene, terpene monomers and others. Mixed aliphatic-aromatic 
resins contain sufficient aromatic monomers and sufficient aliphatic 
monomers and optionally other C.sub.3 -C.sub.8 unsaturated monomers to 
produce a resin having both aliphatic and aromatic character. 
The adhesive compositions of the invention can contain rosin and rosin 
derivatives as a tackifying agent. Rosin is a solid material that occurs 
naturally in the oleo resin of pine trees and typically is derived from 
the oleo resinous extrudate of the living tree, from aged stumps and from 
tall oil produced as a by-product of kraft paper manufacture. After it is 
obtained, rosin can be treated by hydrogenation, dehydrogenation, 
polymerization, esterification and others. Rosin is typically classed as a 
gum rosin, a wood rosin, and as a tall oil rosin. The materials can be 
used unmodified and additionally can be used in the form of esters of 
polyhydric alcohols and can be polymerized through the inherent 
unsaturation of the molecules. The materials are commercially available 
and can be blended into the adhesive compositions using standard blending 
techniques. 
Representative examples of such rosin derivative tackifying resins include 
the pentaerythritol esters of tall oil, gum rosin, wood rosin or mixtures 
thereof. 
Representative examples of such aliphatic resins include hydrogenated 
synthetic C.sub.9 resins, synthetic branched and unbranched C.sub.5 resins 
and mixtures thereof. 
Representative examples of such aromatic aliphatic tackifying resins 
include styrenated terpene resins, styrenated C.sub.5 resins or mixtures 
thereof. 
The selection of tackifying resins is based on the nature of the B or 
midblock of the block copolymer. Rosin derivatives are best for 
S-I-S/S-B-S blends and can be used with S-I-S or S-B-S along. Hydrogenated 
C.sub.9 or straight aliphatic resins are preferred for S-I-S copolymers. 
For S-B-S copolymers styrenated terpenes are preferred. 
PLASTICIZER 
A plasticizer is broadly defined as a typically organic composition that 
can be added to rubbers and other resins to improve extrudability, 
flexibility, workability or stretchability. Typical plasticizers in 
adhesives are plasticizing oils that are liquid at typical ambient 
temperature. The plasticizer used in the spray-on adhesives of the 
invention is typically a solid composition having a softening point of at 
least 45.degree. C. Preferably, the plasticizer composition has a 
softening point of at least 60.degree. C. Increased softening points 
(60.degree.-130.degree. C.) can aid in improving heat resistance or 
preventing bond failure at high temperatures. The selection of plasticizer 
and the use of small amounts of oil can aid in the control over the time 
from spraying to solidification. The preferred plasticizers of the 
invention have some substantial aromatic character. Such aromatic 
character enables the solid plasticizers to interact with the tackifying 
resins and the end or A blocks of the thermoplastic copolymer which 
results in the unique property of the adhesive composition that it retains 
substantial liquidity for a substantial period of time after cooling below 
the softening points of the components. The solid plasticizer of the 
invention retains plasticizing properties during the time it remains in a 
liquid state prior to adhesive solidification. After solidification the 
plasticizers can associate with the A or end blocks due to plasticizer 
aromaticity or can phase out and can no longer interact with an plasticize 
the polymer units. Once phased out, the plasticizer becomes generally 
inactive with respect to adhesive properties. After the plasticizer 
solidifies, the adhesive retains adhesive and cohesive strength through 
the polymer and tackifying resin regardless of the physical state of the 
plasticizer. However, the plasticizer, if it does not phase out, can 
increase cohesive strength of the adhesive after solidification if it 
associates in the A block phase. 
A second class of useful plasticizer comprises an aromatic carboxylic acid 
ester of a polyfunctional alcohol having 1 to 10 hydroxyl groups. 
Polyfunctional alcohols that can be used in the compositions of this class 
of plasticizers include compounds having at least two hydroxyl groups and 
at least two carbon atoms in the molecule. Specific examples of preferred 
hydroxy compounds include ethylene glycol, propylene glycol, 1,2-butylene 
glycol, 1,4-butylene glycol, glycerine, glucose, fructose, sucrose, 
mannitol, trimethylol ethane, 1,4-cyclohexane dimethanol, pentaerythritol, 
2,2-dimethyl-1,3-propane diols, 2-hydroxy methyl-2-methyl-1,3-propane 
diol, neopentyl glycol, and other useful polyfunctional hydroxyl 
compounds. Aromatic acids that can be used with the polyfunctional 
alcohols to form this class ester plasticizer compounds of the invention 
include aromatic carboxylic acids, typically having at least one aromatic 
group and at least one carboxyl function. Representative acids include 
benzoic acid, naphthanoic acid and 4-methyl benzoic acid. Preferred 
plasticizer comprises 1,4-cyclohexane dimethanol dibenzoate. 
In the manufacture of disposable articles, materials or components that are 
not sufficiently hydrophilic can be treated with surfactants or wetting 
agents to increase or enhance the wettability or hydrophilicity of the 
components. Since the disposable articles are designed to absorb and 
sequester water from the skin of the user of the disposable article, the 
articles are typically manufactured from hydrophilic materials that absorb 
and remove water from the surface of the user's skin. However, in certain 
disposable articles materials that are not sufficiently hydrophilic are 
used. Such materials include polyolefins, elastics, nonwovens, films, etc. 
Such materials with measurable hydrophobicity which are not sufficiently 
hydrophilic can be treated with wetting agents to increase their 
hydrophilicity. Very often the hydrophobic materials are covers or 
covering sheets over the hydrophilic materials. To enhance passage of the 
moisture from the user to the hydrophilic internal layers the hydrophobic 
cover sheets are made hydrophilic using surfactant or wetting agent 
materials. Preferred surfactant or wetting materials for use in the 
invention comprise nonionic surfactants typically manufactured by the 
oligomerization or polymerization of ethylene oxide or propylene oxide. 
Such materials typically take the form of polyethylene glycol, 
polypropylene glycol, ethoxylated or propoxylated alcohols, ethoxylated or 
propoxylated phenols or other related molecules having as a major polymer 
backbone polyethylene oxide, polypropylene oxide, or mixtures thereof. 
The adhesive compositions of the invention can contain other compatible 
polymers, fillers, pigments, dyes, catalysts, inhibitors, antioxidants, UV 
absorbers, waxes, and other conventional additives. 
The following Table A sets forth useful proportions of the components of 
the invention. 
TABLE A 
______________________________________ 
Most 
Useful Preferred 
Preferred 
______________________________________ 
Block 10-40 12-28 15-25 
copolymer 
Tackifying 
30-80 45-75 50-65 
resin 
Plasticizer 
5-40 10-30 15-25 
______________________________________ 
The articles of the invention at a minimum comprise a film layer or a 
permeable layer adhesively joined with a substrate. 
The permeable layer can comprise a cellulosic tissue, a woven or nonwoven 
fabric or other thin, flexible, porous or wettable sheet-like material. 
The tissue layer is a well known, typically loosely formed cellulosic 
sheet of high porosity or permeability. The fabric layer consists of a 
fluid permeable flexible material that can be made of either hydrophilic 
or hydrophobic fiber components. Woven and nonwoven webs comprising the 
fabric can comprise natural or synthetic fibers or mixtures thereof. Woven 
and nonwoven materials are well known and their construction methods have 
been practiced for many years. Woven fabrics are typically manufactured in 
weaving machines forming an interlocking mesh of fibers forming the layer. 
Nonwoven fabrics can be made through a dry-laid or wet-laid method in 
carding processes, air laying processes or spun bond processes to produce 
a web that is mechanically, chemically or thermally formed. The fabric 
layers for use in the compounds and articles of this invention typically 
have a basis weight in the range of about 10 to 25, preferably 14 to 18 
grams per square yard, a minimum dry tensile strength of at least 800 
grams per centimeter.sup.2 squared in the machine direction, and at least 
200 grams per centimeter.sup.2 in a cross machine direction. Synthetic 
materials commonly used in forming the fabric top sheets include rayon, 
polyester, polypropylene, polyethylene, nylon and others. 
The substrate materials that can be used in the manufacture of the 
disposable articles of the invention, in combination with the tissue or 
woven or nonwoven fabric, comprises any typical substrate used in the 
manufacture of disposable articles including films, sheets, elastics, 
absorbents, cellulosic fluffs or fill, other tissue, woven or nonwoven 
fabrics, etc. 
Absorbent layers can be adhered to other substrates using the adhesives of 
the invention. Such absorbent layers can comprise cellulosic pulp or 
fluff. Such fluff layers are often formed and wrapped in tissue to provide 
mechanical integrity to the fluff which has little inherent integrity. 
Fluff is typically manufactured through formation of cellulosic fibers. 
However, other materials can be utilized to form high absorbent fluff or 
pulp layers. 
Elastic bands or elements can be used in the manufacture of the disposable 
articles of this invention. 
The film or sheet-like layer used in the invention comprises a flexible 
sheet-like or film substrate. Such films are typically manufactured from 
thermoplastic resins and take the form of a thin layer having a thickness 
of about 0.5 to 2.0 mils. Such films comprise polyethylene, polypropylene, 
ethylene-propylene copolymers, ethylene acrylate copolymers, ethylene 
vinyl acetate copolymers, polyvinyl chloride polymers, polyvinylidene 
chloride polymers, polyester polymers and others. Such films can be 
perforate or imperforate. In addition to the above materials used in the 
composite articles of the invention, a variety of other materials can be 
used, including other wrapping materials, deodorants, perfumes, dyes, and 
decorative appliques, which provide further absorbency, instructional 
legends, and pleasing appearance or smells. 
In somewhat greater detail, the adhesives of the invention can be used in 
the manufacture of disposable articles including disposable diapers, 
incontinent devices or diapers, feminine pads, and disposable bed pads by 
adhering a porous layer to a substrate. The assembly operations that 
deserve note include adhering a porous nonwoven layer to a back sheet and 
adhering a tissue layer to an absorbent core. 
In the manufacture of absorbents for disposables, it is common to wrap 
loosely assembled fluff or batts of absorbent material within a tissue 
overwrap. In such manufacture, the tissue surrounds the absorbent material 
in an overlapping fashion such that the spray-on adhesive can be applied 
to the overlap area, causing the adhesive to penetrate the overlap to 
contact the underlying fluff or batt. The spray-on adhesive in contact 
with the tissue and absorbent material forms a strong mechanical bond 
which maintains the tissue wrap and provides mechanical support and 
integrity to the underlying fluff or absorbent batt material. As a result 
of using the manufacturing techniques of the invention, the tissue-covered 
absorbent material obtains substantial mechanical integrity from the 
adhesive and tissue structure. During use, the tissue and adhesive 
maintains the fluff or batt in place and prevents movement of the 
absorbent material resulting in an inappropriate segregation of absorbent 
material in a small portion of the absorbent article. Such mechanical 
integrity insures that the absorbent material stays in place to provide 
absorbency and protection. 
In the manufacture of composite articles, the fluid permeable fabric top 
sheet is adhered to a film back sheet. An absorbent layer can be 
introduced into the space between the fabric layer and the back sheet. 
Typically a fluid in contact with the fabric layer passes through the 
fabric layer and is absorbed and held within the absorbent layer. The 
absorbent core typically comprises a highly porous, highly absorbent 
loosely contacted fluff, wrapped or encased within a tissue cover. The 
absorbent fluff typically has little mechanical integrity. The tissue wrap 
or cover, once adhered to the fluff, provides the absorbent layer with 
substantial dimensional integrity preventing the absorbent material from 
migrating or collecting in an inappropriate portion of the diaper. The 
tissue wrap ensures that the absorbent material remains evenly distributed 
within the envelope created by the back sheet and the fabric layer. The 
manufactured diaper or the components of the diaper can have elastic bands 
or segments adhesively attached to provide security for the wearer. such 
elastic bands create a snug fit at the waist and the leg apertures of the 
disposable articles. The adhesive compositions of the invention can be 
used to form bonds between the surfaces of the film materials between 
apertured films and nonapertured films, between tissue and nonwoven or 
woven fabric layers, between absorbent fluff and tissue overwraps, and 
between elastic bands or elements and any structural component of the 
disposable diaper. 
In construction methods for the preparation of the disposable articles of 
the invention, the adhesives are typically applied from spray heads that 
deliver the adhesive at elevated temperatures (typically above about 
250.degree. F. and typically in the range of 275.degree.-400.degree. F.). 
The spray heads have apertures that range from about 0.01 to about 0.04 
inches. Under the operating conditions of typical adhesive spray machines, 
the diameter of the sprayed adhesive fiber can range from the size of the 
aperture to as little as about 0.001 inches depending on operating 
conditions. Depending on the end use and final bond strength desired, the 
adhesive can be used at application amounts that range from 0.5 milligrams 
per square inch to as much as 10 milligrams per square inch. preferably, 
because of the unique properties of the adhesives of this invention, the 
adhesives can be used at an application amount of from about 0.5 
milligrams per square inch to 5 milligrams per square inch. Conventional 
spray-on adhesives are typically used at high add-on rates within a range 
of 6 to 7 milligrams per square inch because of their tendency to debond 
or delaminate in the presence of moisture. The conventional add-on rate 
appears to be excessive because bonding characteristics of the adhesives 
are poor. Most preferably, in disposable diaper construction the adhesive 
of the invention is used at an application rate of about 1 to about 4 
milligrams per square inch. 
During the manufacture of disposable articles using the adhesives of the 
invention, two modes of application are preferred. One mode of operation 
involves spraying the adhesive upon a fabric, such as a tissue, a woven or 
nonwoven web, or other material having permeability to the adhesive. Such 
sprayed-on adhesive can penetrate the permeable tissue, nonwoven or woven 
fiber, to cause the sheet to be embedded in the adhesive and adhered to 
the substrate such as an absorbent layer, back layer, or film. 
Alternatively, the adhesives of the invention can be directly applied to 
back sheet or film and the tissue, woven or nonwoven fabric, or other 
material can be applied to the adhesive on the film. The adhesive retains 
sufficient liquidity that it can penetrate pores or apertures in the 
fabric to form a mechanical bond. In the manufacture of tissue fluff 
absorbent cores, the fluff is typically wrapped by tissue. the tissue 
layer can be wrapped around the fluff and can overlap. Adhesive can then 
be sprayed on the overlapping portion of tissue outerwrap, can penetrate 
the wrappings and adhere the tissue to the fluff ensuring that the fluff 
obtains dimensional stability from adherence to the outer wrap. 
In somewhat greater detail, the sprayable, hot melt adhesive compositions 
of the invention typically comprise an effective amount of a thermoplastic 
block copolymer base and an effective amount of a tackifying agent and 
sufficient solid plasticizers to form an effective adhesive that has the 
unique property that after spraying and cooling retains sufficient 
liquidity to penetrate a porous layer. 
The hot melt adhesives of the invention are made in common hot melt 
manufacturing equipment. In the manufacture of the hot melt adhesives of 
the invention, the thermoplastic block copolymers typically added to a 
melt comprising either the tackifier or the plasticizer material or 
mixtures thereof. Such additions facilitate the blending of the block 
copolymer into a smooth, uniform mixture. In such a manufacturing regimen, 
either the tackifier or the plasticizer or a portion thereof is added to 
the manufacturing equipment under inert atmosphere and is heated and 
agitated until melted. The thermoplastic block copolymer is then added to 
the melt at a rate such that the mixture forms a uniform smooth blend 
within a reasonable period. Antioxidant materials used in the manufacture 
of the adhesive can be added to the melt prior to, with, or after the 
addition of the block copolymer. Once a smooth blend of the copolymer in 
conjunction with an adhesive component is formed, the balance of the 
components of the hot melt adhesives can be added at a convenient rate. 
Once the uniform blend of all the adhesive ingredients is formed, the 
adhesive can be drawn off and packaged in a convenient form including in 
drums, blocks, pillows, pellets, granules, etc. 
The following examples provide additional information with respect to the 
manufacture of the adhesives of the invention and include the best mode. 
Following the standard laboratory blending procedures the following 
compositions were blended into a hot melt adhesive: 
EXAMPLE I 
Into a sigma blade mixer having a nitrogen atmosphere and heated to a 
temperature of 350.degree. F. was added about 100 grams of 500 processing 
oil (PENZOIL) and 5 grams of an antioxidant (IRGANOX 1010). The mixer was 
operated until the antioxidant was fully blended with the oil. Into the 
oil was added 200 grams of a styrene-isoprene-styrene block copolymer 
having 25 wt-% styrene (EUROPRENE SOL T193B, Enichem). After the copolymer 
had been fully added to the resin and a uniform melt resulted, 445 grams 
of the tackifying resin (ECR 177, Exxon) was slowly added to the mixer 
followed by 250 grams of a cyclohexane dibenzoate plasticizer (BENZOFLEX 
352, Velsicol). The single blade mixer was continued until the contents 
were a smooth melt blend and the material was withdrawn and packaged. 
______________________________________ 
Ingredient Trade Name PHA.sup.1 
______________________________________ 
S-I-S block copolymer 
Europrene 20 
193B 
Antioxidant IRGANOX 1010 0.5 
Hydrogenated C.sub.10 
ECR 177 44.5 
Tackifying resin 
500 Processing Oil 10 
cyclohexane dimethanol 
BENZOFLEX 352 
25 
dibenzoate 
______________________________________ 
.sup.1 PHA = parts by weight per each one hundred parts of adhesive 
EXAMPLE II 
Following the procedure of Example I the following compositions were 
blended into a hot melt adhesive: 
______________________________________ 
Ingredient Trade Name PHA.sup.2 
______________________________________ 
S-I-S block copolymer 
Europrene 20 
193B 
Antioxidant IRGANOX 1010 0.5 
Rosin Ester Tackifying 
Unitac H-100 22.25 
Resin 
Hydrogenated C.sub.10 
ECR 177 22.25 
Tackifying resin 
500 Processing Oil 10 
cyclohexane dimethanol 
BENZOFLEX 352 
25 
dibenzoate 
______________________________________ 
.sup.2 PHA = parts by weight per each hundred parts of adhesive 
EXAMPLE III 
Following the procedure of Example I the following compositions were 
blended into a hot melt adhesive: 
______________________________________ 
Ingredient Trade Name PHA.sup.3 
______________________________________ 
S-I-S block copolymer 
Europrene 20 
193B 
Antioxidant IRGANOX 1010 0.5 
Rosin Ester Tackifying 
Unitac H-100 33.375 
Resin 
Hydrogenated C.sub.10 
ECR 177 11.125 
Tackifying resin 
500 Processing Oil 10 
cyclohexane dimethanol 
BENZOFLEX 352 
25 
dibenzoate 
______________________________________ 
.sup.3 PHA = parts by weight per each one hundred parts of adheive 
EXAMPLE IV 
______________________________________ 
Ingredient Trade Name Grams 
______________________________________ 
S-I-S block copolymer 
KRATON-1117 20.0 
Tackifier PERMALYN 305 59.8 
1,4-cyclohexane BENZOFLEX 352 
20.0 
dimethanol dibenzoate 
Antioxidant IRGANOX 1010 0.2 
______________________________________ 
COMATIVE EXAMPLE A 
Following the procedure of Example I, 155 grams of a hydrogenated Cg 
tackifying resin (ESCOREZ 5320) and 25.5 grams of a 50--50 blend of 
antioxidants (IRGANOX 1010 and IRGANOX 1076) was blended in the sigma 
mixer followed by 127.5 grams of a styrene-ethylene-butylene-styrene block 
copolymer having 30 wt-% styrene (KRATON G 1652, Shell Chemical Co.). 
309.95 grams of the tackifying resin was then blended into the melt 
followed by 255 grams of a naphthenic oil (SHELLFLEX 371). 
COMATIVE EXAMPLE B 
Following the procedure of Comparative Example A the following compositions 
were blended into an adhesive: 
______________________________________ 
Ingredient Trade Name Grams 
______________________________________ 
Atactic poly B3A15 425 
alpha olefin 
Dicyclohexylphthalate 
DCHP 85 
plasticizer 
Tackifying resin 
WINGTACK 318.75 
EXTRA 
Antioxidant IRGANOX 1010 
4.25 
& IRGANOX 
1076 
Polyethylene EPOLENE C10 17.0 
______________________________________ 
COMATIVE EXAMPLE C 
Same as Comparative Example A except Shellflex oil was omitted and 549.95 
grams of tackifying resin and 170 grams of DCHP were used. 
COMATIVE EXAMPLE D 
Same as Example V except DCHP was omitted and an equal amount of a 
plasticizing oil (1200 ACS) was used. 
COMATIVE EXAMPLE E 
(Column 15, Example 5, Tsukahara et al., U.S. Pat. No. 4,745,026) 
______________________________________ 
Ingredient Trade Name Grams 
______________________________________ 
Resin EVA 28-400 33.0 
Dicyclohexylphthalate 
MORFLEX 150 49.5 
plasticizer 
Rosin ester UNITAC 17.0 
tackifying resin 
H-100 
Antioxidant IRGANOX 1010 
0.5 
______________________________________ 
Detailed Discussion of the Drawings 
FIG. 1 
FIG. 1 shows a Penetration Comparison in which both the Comparative 
Examples D and E change very little in penetration as a function of time. 
Such adhesives become viscous and reach their maximum hardness soon after 
reaching room temperature. In contrast, adhesives of the present invention 
remain fluid for a controlled period of time and later crystallize, 
reaching their maximum strength once fully crystallized. 
Determining the Needle Penetration of Hot Melt Adhesives 
Scope: 
The needle penetration test is used as a measure of consistency. Higher 
values indicate softer consistency and lower values indicate harder 
consistency. 
Reference: 
ASTM D5 
Material and Equipment: 
1. Standard ASTM Needle Penetrometer 
2. Automatic Dwell Timer or stop watch 
3. Environmental Chamber 
Sample Preparation: 
Sample must be of sufficient depth so that the needle, when fully 
penetrated, is only touching sample and not the substrate beneath the 
sample. 
Procedure: 
1. Sample was melted at 300.degree. F. and poured into an appropriately 
sized mold. 
2. Load penetrometer with 100 g (shaft and needle weight inclusive). 
3. Position needle lightly on the sample surface. 
4. Release shaft for 5.+-.0.1 seconds. 
5. Clean shaft, repeat steps 3 and 4, etc. 
Report: 
The penetration is the average of 3 or 5 readings and is reported in tenths 
of a millimeter, noting the temperature. 
FIG. 2 
FIG. 2 shows Rheology Curves. Comparative Example E maintains a relatively 
constant strength as a function of time, whereas adhesives of the present 
invention gain strength until such adhesives have fully crystallized. 
The increase in shear modulus as a result of crystallization is shown in 
FIG. 2. The ratio of the complex shear modulus, G.sup.* to its maximum 
value is plotted versus time. G.sup.*.10.sup.-7 is shown in FIG. 2. The 
fast crystallizing melt, Example 1, approached its maximum stiffness in 
approximately 45 minutes. The medium crystallizing melt, Example 2, 
approached its maximum level in approximately an hour. The modulus of the 
amorphous Example E does not change. (G.sub.norm is G.sup.* 
/G.sub.initial) 
Testing: 
A two step dynamic time sweep on the Rheometrics RDS 7700 was used to 
obtain the data. The sample was loaded between 25 mm diameter parallel 
plates and heated to 120.degree. C. until the sample completely lost any 
white coloration due presumably to crystallinity. The temperature was then 
lowered to 90.degree. C. and the loaded sample was allowed to equilibrate 
for 5 minutes. The test at a frequency of 10 radians/sec was then started. 
The first stage of the test lasted 5 minutes. The temperature of the 
liquid nitrogen controlled oven was lowered from 90.degree. C. to 
23.degree. C. (The temperature of the plates was note forced to reach 
23.degree. C. by lowering the oven set temperature below 23.degree. 
C.--this would have resulted in faster recrystallization due to the 
removal of latent heat.) The final stage of the test lasted either one or 
two hours. The temperature control was deactivated for this segment of the 
test so that any additional cooling of the sample would occur only due to 
natural convection with the ambient air. The sample was strained 
dynamically constantly throughout the test. The gap between the plates 
occupied by the sample was periodically reduced to compensate for sample 
shrinkage. 
FIG. 3 
FIG. 3 are Crystallization Curves that demonstrate the ability to control 
the rate at which the adhesive crystallizes. The adhesives of the present 
invention are very fluid and transparent at first. As the cyclohexane 
dibenzoate plasticizer crystallizes the adhesive becomes opaque. The rate 
of crystallization is controlled by the selection of tackifying resin. An 
aromatic resin, such as Unitac H-100 is very compatible with the 
dibenzoate plasticizer slowing down the crystallization rate, whereas an 
aliphatic resin is less compatible allowing the dibenzoate plasticizer to 
crystallize relatively quickly. All formulations remain fluid and cold 
flow for a controlled period of time and reach their maximum strength upon 
crystallization. 
Measurement of Crystallization Time Using Percent Reflectance 
This test method describes how to measure crystallization time of a hot 
melt as measured by the Hunter Colorimeter to detect changes in 
reflectance of the hot melt as it cools, crystallizes and becomes opaque. 
We find that the opaque character is proportional to degree of 
crystallinity. 
Material and Equipment 
1. Hunter Colorimeter, Model D25A, with reduced area illumination 
2. Black color tile 
3. Y of the XYZ scale 
4. Half-pint metal can 
5. 300.degree. F. vacuum oven capable of a minimum of 20 inches of Hg 
6. Mylar film 
7. Can opener 
8. Ruler and graph paper 
9. Scale 
10. Half-pint glass jar 
11. 60-minute timer 
12. Stop watch 
Procedure 
1. Warm up Hunter Colorimeter for 15 minutes. 
2. Standardize the Colorimeter using the method described in the Hunter 
manual. 
3. Place between 50-70 grams of hot melt in a half-pint glass jar and put 
the jar in a 300.degree. F. oven for 60 minutes under 20-30 inches of Hg. 
4. Cut out two 5.times.5 in Mylar squares. 
5. Use a can opener to remove the top ring of a quarter-pint can. 
6. Place one of the Mylar squares on a scale, put the ring from the 
half-pint can on top of the Mylar square. 
7. Remove the jar of hot melt from the oven and start the stopwatch. Pour 
11 grams of hot melt into the can ring and place the second Mylar square 
on top of the hot melt. 
8. Place the sample over the specimen port of the Colorimeter. 
9. Place the black tile over the sample. 
10. Press the XYZ button and then read button of Colorimeter. 
11. Record the Y value and the time every five minutes until the reading 
stabilizes, which should be somewhere between 40 and 50. 
12. Graph the Y value vs. time and use triangulation to determine 
crystallization point. 
Moisture Resistance Test for Spray Applied Hot Melt Adhesives 
The test method is intended to assist in determining the differences in wet 
and dry bond strengths of spray applied hot melt adhesives. 
Equipment 
1. High quality hot melt spray equipment intended for the nonwoven 
industry. Preferred equipment manufacturers are Nordson, Acumeter, 
Slautterback, and Mercer. 
2. Tensile tester or T-peel tester with a load range of 1,000 grams and 
capable of a grip separation rate of 6 inches/minute. 
3. Cutting board of 1".times.6" cutting template. 
4. Suitable substrates. 
5. Purified water. 
Sample Preparation 
1. Spray apply the adhesive to one substrate at the rate of 4 mg./sq. in. 
Quickly nip the second substrate to the adhesive using a nip pressure of 
1.4 (20 psi). If the bond is expected to give substrate failure, slip in 
5-10 pieces of 2" wide release paper across the bond line. 
Make sure the spray pattern is as even as possible since small variations 
in coat weight can cause unexpectedly large variations in peel values. 
2. Cut a 1".times.6" sample out of the laminated area in the machine 
direction. If release paper was used, cut it in half in the cross 
direction and then cut 6" strips in the machine direction. Peel back 1" 
(or use the 1" release paper edge) and apply staples to both substrates to 
assist gripping. Make ten samples. 
3. Condition the samples at room temperature and 50.+-.10% RH for at least 
16 hours, but not more than 30 hours. 
Test Procedure 
1. Set the peel tester to the gram scale 6 inches/minute, 25 seconds. 
2. Dry delamination--clamp the substrates into the peel tester. Generally, 
the weaker substrate will be clamped to the moving grips. Set the position 
so that there is tension on the adhesive. Turn the peel tester on. Peel a 
total of five samples. 
Wet Delamination--place the 6" sample vertically into five inches of water. 
Leave in water for 30 seconds (longer if the substrates do not readily 
absorb water). Pat dry with paper towels. Attach the substrates to the 
clamps as described above. Set the position so that there is tension on 
the adhesive. Turn the peel tester on. Peel a total of five samples. 
Report 
Average peel strength of the dry and wet samples. Note the type of failure 
that occurred. also, report coat weight, application temperature, 
substrates used, and spray equipment used. Also note if water soak was 
longer than specified, or if more time was necessary after application to 
allow the adhesive to recrystallize completely. 
Test Results Comparative Examples 
Example A: Dry: good pull; some fiber tear. 
Wet: adhesive failure. 
Example B: Dry: weak bond. 
Wet: no bond. 
Example C: Dry: no bond to substrate. 
Wet: no bond to substrate. 
Example D: Dry: substrate failure. 
Wet: 34 grams. 
Test Results Examples of the Invention 
Example IV: Dry: cohesive failure if pulled slowly--tissue failure if 
pulled fast; 
Wet: excellent bond tissue failure--wet with nonionic surfactant weaker 
bonds but tissue failure if pulled fast. 
The Examples and data shown above indicate that the use of a solid 
plasticizer such as cyclohexane dimenthanol dibenzoate in combination with 
a particular selection of block copolymer and tackifying resin can produce 
an adhesive having both dry and wet bond strength to both film and porous 
substrate. The comparative Examples indicate that polymers that are not 
block copolymers and adhesives containing plasticizers other than those 
similar in properties to cyclohexane dimenthanol dibenzoate do not possess 
significant wet strength, and in some cases have poor dry strength. 
Additionally we have found that a blend of S-I-S and S-B-S copolymers can, 
in certain formulae, provide enhanced wet and dry bonding properties. 
Since many embodiments of the invention set forth above can be made without 
departing from the spirit and scope of the invention, the above 
specification, Examples and data are non-limiting and the invention 
resides in the claims hereinafter appended.