CA2171542C

CA2171542C - Polystyrene-ethylene/butylene-polystyrene hot melt adhesive

Info

Publication number: CA2171542C
Application number: CA002171542A
Authority: CA
Inventors: Carolyn Marie Anderson; Eugene R. Simmons
Original assignee: HB Fuller Licensing and Financing Inc
Current assignee: HB Fuller Licensing and Financing Inc
Priority date: 1993-10-12
Filing date: 1994-09-29
Publication date: 1999-09-14
Anticipated expiration: 2014-09-29
Also published as: DE69415040T2; WO1995010576A1; US5459193A; JPH09505840A; MXPA94007873A; CA2171542A1; EP0723571B1; EP0723571A1; DE69415040D1

Abstract

An improved hot melt adhesive with low self-adhesion. The adhesive is useful for disposable articles and employs a S-EB-S block copolymer. The adhesive does not require a release liner and has superior stay-in-place properties.

Description

WO 95110576 21 715 ~ 2 _ . -. PCTlUS9ali 1024 POL!fSTYRENE-ETHYLENE/BUTYLENE-POLYSTYREN'F
HOT MELT ADH .STVE
Fteld of the Invent~~n This invention relates to hot melt adhesives comprising a high molecular weight polystyrene ,' ethylene/but:ylene-polystyrene block copolymer and articles constructed therefrom. This invention particularly ., relates to certain improved positioning adhesive formulation:: for disposable articles such as sanitary napkins, in~:ontinent pads, bed pads, and feminine pads, where an adhesive layer is used to attach the article to a woven fabric substrate, such as an undergarment or bed sheet.
Backcround of the Invention Block copolymers have been used in the hot melt adhesive industry for a variety of applications. Block copolymers <sre often the preferred polymer base due to their good heat stability, high cohesive strength, and compatibility with a wide range of tackifiers and plasticizers.

Rratone G-1651, a high molecular weight S-EB-S linear A-B-A block copolymer, having a molecular weight of about 240,000, ha;s been used in the past by the injection molding industry for shoe soles. Due to its high molecular wE3ight, it is believed that it has not been previously used by the hot melt adhesive industry.

The u~te of hot melt adhesives comprised of conventional molecular weight block copolymers for purposes of adhering an absorbent article, such as a sanitary napkin, to an undergarment is known. Raykovitz et al., U.S. Patent No. 4,704,110 teaches an absorbent article utilizing an adhesive with a S-B-S multi-block A-B-A-B-A-B copolymer. Nelson et al. EP 0,525,251, teaches an improved ;positioning adhesive including a S-I-S linear A-B-A block copolymer containing at least 25 parts styrene. C:ollins et al., U.S. Patent No. 4,136,699 teaches a conventional molecular weight S-EB-S linear A-B-WO 95/10576 21 715 ~ 2 PCT/US94/11024 A block copolymer based construction and positioning adhesive fo=' absorbent articles. The prior art, to date, has not shown the use of a high molecular weight S-EB-S in hot melt adr~esives .
A positioning adhesive is commonly applied to a release linE:r and transfer coated to the garment facing surface of .an article such as a sanitary napkin. Upon removal of the release liner, it is common for the adhesive to accidently come in contact with itself prior to placement on the undergarment. This~is particularly a problem with winged products. When the positioning adhesives' composition is in accordance with the teachings of Raykovitz, Nelson, or Collins, the positioning adhesive is of such high self adhesion (in excess of the strength of the garment facing surface) that the adhesive layers are separable only at the expensive of destroying the article. Thus there is a need for an adhesive which adheres adequately to an undergarment, yet can be separated from itself.
Another problem associated with prior art positioning,adhesives concerns "stay in place" properties.
Under conditions of low pressure, the positioning adhesive tends to lose adhesion to the undergarment. In many instances this loss of adhesion causes the sanitary napkin to shift from its original position or become unattached from the undergarment entirely.
,~ummarv of the Invention It is therefore an object of this invention to provide an .improved positioning adhesive with low self adhesion, thereby being able to be removed from itself without destroying the article. Further; another object of this invention is to provide a pressure sensitive adhesive that may be used with or without release paper on articles that traditionally incorporate such release paper. The present adhesive also has superior stay-in-place properties.

WO 95/10576 ~t 1 715 4 2 PCT/US9.t11102J

The present invention is a hot melt adhesive comprising ~s S-EB-S block copolymer having a molecular weight greater than about.200,000 as measured by Gel Permeation Chromatography, with values reported relative to polystyrene standards.
In the present invention, it has been found that a high molecular weight S-EB-S block copolymer provides surprising ~~roperties in a hot melt adhesive. The high molecular wE~ight S-EB-S polymer can be. used in place of conventional, molecular weight S-EH-S block copolymers at lower concentrations in a variety of applications where high cohesive strength is an important parameter.
Brief Description of the Drawings Figure 1 is a perspective view of a disposable article such as a panty liner folded upon itself.
Figure 2 is the panty liner of figure 1 unfolded.
Figure 3 is theology data of the prior art and the present invesntion.
p~tailed Description of the Invention Typically, disposable articles such as sanitary napkins, incontinent pads, bed pads, or feminine pads utilize an adhesive Which attaches the article to a woven fabric substrate, such as an undergarment or bedsheet.
Prior to this invention, the adhesive would be covered with a release liner, which was typically a silicon coated paper or sonae type of low surface energy polymeric film.
When the user would remove the article from its packaging, the release liner would be peeled away and the article would be positioned on a target surface, typically an undergarment: or bedpad. The requirement of release paper is undesirable both from a cost standpoint and an . environmental standpoint. The release paper, after being peeled away from the article, serves no purpose and thus must be discarded.
The adhes~.ve of the present invention avoids the ";

WO 95/10576 21 715 4~ 2 PCT/US94/11024 requirement of release paper, in that it has low self adhes ion . I;n other words , the adhes ive may be folded over upon itself and thereafter be peeled apart successfully.
The adhesive has the strength to secure the article to its target surface, but has self-adhesion properties which do not exceed the tear strength of the article. The ability of the adhesive to fold upon itself defeats the need for release paper. When the user thereafter prepares to place the article on the target surface, the article is unfolded such that the adhesive is not folded upon itself.
Thereafter, the article is placed on the target surface.
Prior adhesives could not be successfully folded over to achieve such an article. The prior adhesives were so tacky from a practical standpoint, they could not be peeled apart without destroying the article. Prior to the present invention, if the adhesive was made such that it was not tacky, the adhesive characteristics diminished to such a point: that it could not effectively be used to adhere the article to the target surface. In other words, the adhesive was not tacky enough to provide the required adhesion between the target surface and the article.
Figure 1 illustrates one of the embodiments of the product of this invention. Panty liner 10 has two transverse edges 25 and two longitudinal edges 27. Panty liner 10 also has one or more areas of attachment 30 which serve to naaintain panty liner 10 in the folded configuration prior to use.
Figure 2 illustrates the embodiment depicted in figure 1 after it has been opened: In this view, the actual areas in which attachment means 30 are located can be seen. Choosing the patterns of attachment means 30 on the garment facing side 20 of the panty liner so that they would contacts each other when the article is folded eliminates t;he need for release paper on the garment facing side of panty liner 10. The adhesion areas 30 should completely cover one another. Thus, as shown in figure l, each attachment means 30 is placed in an r-p -- WO 95/10576 ~ ~ ~ ~ ~ ~ ~ pCI,NS9.~,1 IUZ.i alternating pattern with another attachment means.
Attachment cneans 30 comprises the adhesive of the present invention. The adhesive may be on a supported~adhesive strip or applied directly to a permeable back sheet or a 5 surface modj.fied polyolefin.
Figure 3 illustrates the present invention's advantage over the prior art. Example 1 is compared to comparative Examples A, B, and C. The prior art illustrates a balance of tack and shear strength that requires a high modulus at room temperature in order to maintain enough cohesive strength. (G', G" crossover 80°C
to 100°C). In contrast, the present invention allows for lower G' at room temperature and therefore better tack properties while maintaining a higher than normal crossover paint (110°C and above). In other words, the present invention has high tack and high cohesive strength rather than having to sacrifice one for the othe=.
The Adhesive The major component of the adhesive of this invention, present in the amount of about 5 to 20% by weight, preferably in an amount of about 5 to 15% by weight for superior positioning properties, and most preferably in an amount of about 8 to 12% by weight for superior loW self adhesion, comprises a S-EB-S linear AB-A block copolymer having a molecular weight in excess of about 200,000. Polymers of this type, such as Rratonm 6-1651, commercially available from Shell Corporation, are not intended. for the hot melt adhesive industry, but rather direcaed at the injection molding industry.
Therefore, typical technical information relating to adhesive peri:ormance properties is unknown.
As described above, the present invention results in a superior adhesive with at least two beneficial properties. The adhesive has superior positioning properties, which result in excellent stay-in-place properties. When the article is positioned on the target ~ 1 715 4~ 2 p~'~us9an iota surface, it will stay in position much better than prior adhesives. Further, the present invention also is a low self adhesion adhesive, as described above.
We have found the above S-EB-S block copolymer may also have added thereto, a compatible A-B-A block copolymer, A-B-A-B-A-B' multiblock copolymer or radial block copolymer thermoplastic resins. Such A-H-A block copolymers are disclosed in Collina, U.S. Patent No.
4,136,699. In the present invention, an A-B-A block copolymer available under the tradename Rraton 6-1654, commerciall~r available from Shell Corporation is preferred. In a preferred composition, 0-15 weight percent of an A-B-A block copolymer is useful, a more preferred composition of 0-10 weight percent and a most preferred c~~mposition of 0-6 weight percent is useful.
The additional block copolymer is preferred, but not necessary.
Tacki ~y_i n_,~ Resin The adt;~esives of the invention preferably contain a tackifying resin. Tackifying resins may be present in an amount from 0 to 60 percent by weight. Preferably the resin is present in an amount of 30 to 60 weight percent.
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 terpenea and aliphatic aromatic or mixed aliphatic-aromatic tackifying resins. Aromatic monomers useful in forming the aromatic containing resin compositions of this invention can be prepared from any monomer containing substantial aromatic qualities and a polymerizabl~~ unsaturated group. Typical examples of such aromatic monomers include styrenic monomers, styrene, alphamethyl styrene, vinyl toluene, methoxy styrene, tertiary butyl styrene,. chlorostyrene, etc., indene monomers including indene, methyl indene and others.
Aliphatic monomers are typically natural and synthetic a WO 95/10576 21 715 4 2 Prrius9amo2a terpenes which contain C6 and CS cyclohexyl or cyclopentyl saturated groups that can additionally contain a variety of substantial aromatic ring substituents. Aliphatic tackifying resins can be made by polymerizing a feed stream containing sufficient aliphatic monomers such that . the result:Lng 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-11,3-butadiene, 2-methyl-2 butane, c,yclopentadiene, dicyclopentadiene, terpene monomer, t~erpene phenolic resins and others. Mixed aliphatic ~sromatic resins contain sufficient aromatic monomers and sufficient aliphatic monomers to produce a resin having both aliphatic and aromatic character. The preferred tackifying agent is a hydrogenated C~ resin.
Representative examples of useful aliphatic resins include hydrogenated synthetic C9 resins, synthetic branched and unbranched C5 resins and mixtures thereof.
Representatj.ve examples of aromatic tackifying resins include styrenated terpene resins, styrenated C5 resins or mixtures thereof.
The adthesive 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 rosin of pine trees and typically is derived from the oleo resinous exudate 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 other post treatment processes. Rosin is typically classed as a gum rosin, a wood rosin, or as a tall oil rosin which indicates its source. The materials can be used unmodified, in the form of esters of polyhydric a~lcohols, and can be polymerized through the inherent unfcaturation of the molecules. Materials are -~ WO 95/10576 2 ~ ~ ~ 5 ~ 2 pC?/U$9.1111014 commercially available and can be blended into the adhesive compositions using standard blending techniques.
Representative examples of such rosin derivatives include pentaerythrit:ol esters of tall oil, gum rosin,~wood rosin, or mixtures thereof .
Specific: examples 'of useful tackifying resins that can be compatible with the adhesives of the invention include materials such as natural and modified rosins, glycerol, and pentaerythritol esters of natural and modified rosins, copolymers and terpolymers of natural terpenes, po:lyterpene resins having a softening point as determined by ASTM method E28-58 T, of from about 80°C to 150°C, pheno:Lic modified terpene resins and hydrogenated derivatives thereof; aliphatic petroleum hydrocarbon resins having a ring and ball softening point of from about 70°C to 135°C, aromatic petroleum hydrocarbon resins and hydrogenated derivatives thereof and alicyclic petroleum hydrocarbon resins and the hydrogenated derivatives thereof. Liquid resins are also envisioned, thus the softening points are irrelevant for liquids.
Plaaticizers A plasticizes is broadly defined as a typically organic composition that can be added to thermoplastics, rubbers and other resins to improve extrudability, flexibility, workability, or stretchability.
Plasticizing oils are used in the adhesive of the invention. Preferably, the plasticizing agent is a liquid at ambient temperature, such as hydrocarbon oils or polybutene, and is present in an amount of about 20 to 95%
by weight of the adhesive. More preferably, the plasticizes :is in an amount of 30 to 50 weight percent.
Such oils are primarily hydrocarbon oils low in aromatic content and are paraffinic or naphathenic in character.
The oils are preferably low in volatility, are clear and have as little color and odor as possible. The use of a plasticizing oil in this invention also contemplates the 21 715 ~ 2 PCT/US9'/11024 use of olefin oligomers, polybutene low molecular weight polymers, vegetable oils and their derivatives and similar plasticizing liquids.
As is known in the art, various other components can be added to modify the, tack, color, odor, etc., of a hot melt adhesive. It is generally preferred that the other components or ingredients should be relatively inert and have negligible effects upon the properties contributed by the block copolymer, tackifying agent, and plasticizing oil. Antioxidants and other stabilizing ingredients can also be added to protect the adhesive from various heat and light induced degradation, but are not essential to the composilaons of this invention.

_ Wo ~s~~o5~6 21 715 4 2 P~~S9a,> »~a to TEST METHQ~
This test method describes how to measure the removal force of an adhesive surface bonded to itself.
Material and Equipment:, 1. Mechanical roll-down device with 4 1/2 lb. roller.
Available through:, Engineering Service Glenview, IL 60025 2. Slip Peel Tester Available through: Instrumentors, Inc.
P.O. Box 36056 Cleveland, OH 44136 Telephones (216) 238-3430 The first step is to prepare hot melt coated adhesive films on Myla~~'(TMHIr!-156) or polyethylene (TMFai-156P) film using an Acumeter or Meltex coater at an appropriate application t'~smperature. The coat weight is checked as in TMHI~I-008 with a target coat weight of 50 g/m2 +/- 3 g/m2.
The adhesive coated Mylai is cut into two dimensions:
1 inch x 4 ins=hes in machine direction and 1 1/2 inches x 4 inches in machine direction. At one end of each strip, fold 1/4" of the strip onto itself length-wise to create a grip. Remove the release paper and place the adhesive surface of one 1" wide strip onto the adhesive surface of one 1 1/2" wide strip with the grips at the same end.
Place the composite on the mechanical roll-down device, and allow the roller two passes over the sample, one forward and one back. A timer is activated~and the sample is placed into the jaws of the slip-peel tester. The 1"
wide strip ifc placed into the jaw that moves and the 1 1/2" wide strip is placed into the jaw which is stationary. .No more than one minute after the sample has been removed from the roll-down device, the sample is peeled at la ipm, averaging over 10. seconds. The procedure is repeated five times, recording the average T-peel value and noting any legging or adhesive transfer.
The t-peel values are reported in grams per lineal inch.
The above test method is modified to measure the removal force of an adhesive surface that has been laminated to itself for a period of time under conditions WO 95/10576 PC'TNS94/11024 of elevated temperature and humidity. The test is repeated, hut the sample is placed in an envelope and incubated a,t 120°F and 50$ RIi for one week. The samples are thereafter tested as above, with the results reported below as laminates.
. In the disposable article industry, it is preferred to have an initial t-peel to cotton in the range of about 100-500, most preferred about 200-500 grams per lineal inch. The :stressed t-peel should be egual to or less than the initial t-peel. In order to achieve preferred stay-in-place properties, the initial t-peel value should be as close as possible to the delayed t-peel value. This indicates there is no loss of adhesion over time.
With regard to self peel, it is preferred to have a value of less than about 200, most preferably lees than about 100 grams per lineal inch. values greater than 200 grams per lineal inch often result in substrate or backing failure of ithe article.
The following examples were made to demonstrate the superior properties of the present invention. Three comparative examples were made, according to the teachings of the prio;c art. These are shown in Table 1. Table 2 illustrates three examples made with Example 1 and 3 being made accord:Lng to the preferred teachings of the present invention.
Table ?t illustrates the comparison between the prior art and the present invention.

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t 1 1 I 1 V U

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t t h t t O O tf) N If1 VD O O n d 0t M u'1 O C1 w .-1 r-1 yr N fr1 ~ N rl ro H

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+ + + + p ~ o o , s o m m n u~ !rl N . . . , un n ca !~ o n '1' N 11 F1 n .1 s s N 01 .1 O d' > 1f1 er1 ~~ If1 N M N W

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+ + i f t * Ir1 u1 0 n n d 10 N 10 01 !~'1 R1 e1 O

E N N O !r1 N . w w w O tl) It1 Q7 n tl1 N n rl rl rl C) d N Gl G! C1~ C4 CL G1 CL I r-1 1 d I 1 I H d H

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W W

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WO 95/10576 ~ 1 715 4 2 PC'f/US94111024 * The laminate T-peel was not tested on the comparative sample because their self T-peel values are greater than 200g.
This table illustrates the utility and uniqueness of incorporating high molecular weight S-E8-S polymers, such as Kraton~G-1651, in positioning ndhesive formulations. Example 2 is the identical formula as ,Example 1 with the exception of substituting Rraton~ G-1654, having a molecular weight of 180,000, in place of Kratonm G-1654. Although the self T-peel values are very similar to Example 1, the laminate T-peel values are extremely high.
Example 3 represents the advantage of blending RratonmG
1651 in order to reduce the viscosity. Examples 1 i 3 are both preferred formulations due to their low self T-peel and low laminate T-peel values.
The present invention is not limited to the examples and embodiments set forth above. As will be understood by those of ordinary skill in the art, alternate embodiments, variations and modifications of the present invention are envisioned.

Claims

WE CLAIM

1. A hot melt adhesive composition comprising:
(a) about 5 to 20 percent by weight of a S-EB-S block copolymer having a molecular weight greater than about 200,000;
(b) about 20 to 95 weight percent of a plasticizes; and (c) up to about 60 weight percent by weight of a solid tackifying agent.

2. The hot melt adhesive of claim 1 wherein said S-EB-S block copolymer is present in an amount of about 5 to 15 percent by weight.

3. The hot melt adhesive of claim 1 wherein said S-EB-S block copolymer is present in an amount of about 8 to 12 percent by weight.

4. The hot melt adhesive of claim 3 exhibiting low self adhesion, with self t-peel values of less than about 200 grams per lineal inch.

5. The hot melt adhesive of claim 1 wherein said plasticizes is selected from the group consisting of liquid C5 resins, hydrogenated C5 resins, styrenated C5 resins, styrenated terpene resins, hydrogenated C9 resins, rosin derivatives, napthenic oil, paraffinic oil, polybutene and mixtures thereof.

6. The hot smelt adhesive of claim 1 wherein said tackifying agent is selected from the group consisting of C5 resins, hydrogenated C5 resins, styrenated C5 resins, styrenated terpene resins, hydrogenated C9 resins, rosin derivatives and mixtures thereof.

7. The hot melt adhesive of claim 1 further comprising a compatible block copolymer.

8. The hot melt adhesive of claim 7 wherein said block copolymer is an A-B-A block copolymer.

9. A hot melt positioning adhesive comprising:
(a) 5 - 15 percent by weight of a S-EB-S block copolymer having a molecular Weight of greater than 200,000;
(b) 30 to 95 percent of a compatible plasticizer selected from the group consisting of liquid C5 resins, hydrogenated C5 resins, styrenated C5 resins, styrenated terpene resins, hydrogenated C9 resins, rosin derivatives, napthenic oil, paraffinic oil, polybutene and mixtures thereof; and (c) up to about 60 percent by weight of a solid tackifying agent selected from the group consisting of C5 resins, hydrogenated C5 resins, styrenated C5 resins, styrenated terpene resins, hydrogenated C9 resins, rosin derivatives and mixtures thereof.

10. A hot melt pressure sensitive adhesive comprising:
(a) about 8 to 12 percent by weight of a S-EB-S block copolymer having a molecular weight greater than 200,000;
(b) about 30 - 50 percent by weight of a plasticizer selected from the group consisting of napthenic plasticizing oil, paraffinic plasticizing oil or mixtures thereof;
(c) about: 30 - 60 percent by weight of a tackifying agent selected form the group consisting of C5 resins, hydrogenated C5 resins, hydrogenated C9 resins and mixtures thereof;
said adhesive exhibiting a self t-peel of less than about 200 grams per lineal inch.