MXPA97005529A - Adhesive with hot fusion that has it - Google Patents

Abstract

The present invention relates to a hot melt adhesive having superior properties for the construction of soft waste articles and more specifically to disposable soft articles which may be exposed to moisture for prolonged periods of time, the adhesive composition includes approximately 10 percent to about 60 weight percent of a butene-1-ethylene copolymer, about 20% to about 80% by weight of a tackifying resin, about 5% to about 30% by weight of a plasticizer and about 0.1% to a about 3% by weight of an antioxidant, wherein the total of ingredients is 100% by weight, of the complementary composition

Description

HOT FUSION ADHESIVE THAT HAS IMPROVED WET RESISTANCE PROPERTIES BACKGROUND OF THE INVENTION The present invention relates to hot melt adhesives that exhibit improved open times and more specifically to hot melt adhesives having improved wet strength properties. , and that find utility in the manufacture of disposable woven garments. DESCRIPTION OF PREVIOUS TECHNIQUE The prior art is replete with numerous examples of hot melt adhesives that are employed for the construction of disposable soft articles. Specific applications for these prior art adhesives have included disposable diapers, sanitary napkins, surgical bandages, hospital cushions and adult incontinence products, to name a few. Still further, the prior art methods of applying these prior art adhesives have included but are not limited to wheel or spray and extrusion application systems (multiple strips or slots). Those skilled in the art will readily recognize that many different polymers have been employed in adhesives that are used in the construction of soft disposable articles. In this regard, typical hot melt adhesives have employed polymers that have included S-I-S (styrene-isoprene-styrene); SBS (styrene-butadiene-styrene); SEBS (styrene-ethylene-butylene-styrene); EVA (ethylene vinyl acetate); and APAO (amorphous poly olefin). While these polymers when properly mixed provide acceptable adhesion to most substrates employed in typical diaper construction and furthermore provide acceptable adhesion under dry conditions, they have several disadvantages that have diminished their usefulness. One of the most notable disadvantages of the adhesives of the prior art relates to the manner in which the adhesive reacts when exposed to liquids such as water, urine or the like. For example, when the adhesives of the prior art are applied to polyolefin substrates (such as polyethylene, polypropylene or nonwoven substrates, as the case may be), almost all adhesives will give good dry bonds and will normally maintain a bond strength. acceptable when wet. However, when substrates such as tissue or core core fluff are used, certain problems arise. For example, while many of the adhesives formulated with the polymers, noted above, will give excellent dry bond strengths, the same adhesive bonds appear to break easily when the substrates are exposed to water, urine or other discharges or water-based solutions. This detachment of attachment of the various substrates can cause the lint core to buckle, and also results in poor fit, problems of absorption and leakage of the garment, especially when the garment is of the type that includes disposable diapers or incontinence products. . More recently, manufacturers of disposable nonwoven garments such as diapers have been involved in generating products that are much thinner in their thickness and overall profile and that incorporate super absorbent materials instead of the fluff, which is normally in the core. In this regard, it will be understood that non-woven fibers comprise long fibers of wood pulp that are interwoven together to form a given mass. In contrast, super absorbent material includes small sphere-shaped particles that do not connect with each other to form a coherent mass such as nonwoven material. Therefore, core integrity becomes an even more important aspect with these thinner garments. Therefore, it has long been known that it would be desirable to have a hot melt adhesive that is useful for bonding to substrates that are typically used in the construction of non-woven garments, such as polyethylene; Polypropylene; nonwoven; tissue or fluff, and which also maintains an acceptable bond strength with the previously identified substrates following exposure thereof for prolonged periods of time to water, urine or similar materials, and which in addition is substantially not a blocker under normal conditions of storage and use .

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved hot melt adhesive which is useful for the manufacture of soft disposable articles. A further object of the present invention is to provide a hot melt adhesive which can be used as a construction adhesive, and which can also be applied by employing extrusion or spray techniques at least to a polyolefin, or a non-woven substrate and less polyethylene, polypropylene, non-woven, tissue or fluff. Another object of the present invention is to provide a hot melt adhesive having the following preferred composition: about 25% by weight, of a butene-1-ethylene copolymer; about 50% by weight of a resin imparting tackiness; about 25% by weight of a plasticizer; and about 0.1 to about 3% by weight of a hindered phenolic antioxidant, and wherein the hot melt adhesive composition exhibits improved flow properties at room temperature and open time, and furthermore has a viscosity from about 2,000 cP to 162.8. ° C (325 ° F) and a melting point of approximately 76.7 ° C (170 ° F) and approximately 93.3 ° C (200 ° F). Another object of the present invention is to provide an adhesive composition that when applied to a tissue laminate in an amount equal to about 3 milligrams per 6.45 cm 2 (square inch) and at a temperature of about 148.9 ° C (300 ° F) and in addition with an open time of approximately 1 second, it produces a peel strength when measured by using a dry Instron roughness evaluation of approximately 100 grams. Another object of the present invention is to provide a hot melt adhesive composition and wherein the adhesive composition is substantially non-blocking under normal storage conditions, and furthermore when applied to a non-woven substrate and tissue in an amount that is equal to approximately 2 milligrams per 6.45 cm2 (square inch) and at a temperature of 148.9 ° C (300 ° F) forms a joint that has average peel strength of approximately 50 grams after exposure to water for at least one hour duration. Another object of the present invention is to provide a hot melt adhesive composition utilizing a butene-1-ethylene copolymer, and wherein the adhesive composition possesses an excellent balance of high specific adhesive, high temperature strength, and acceptable viscosity. during normal application temperatures. Additional objects and advantages of the present invention are to provide a hot melt adhesive composition for the purposes described and which is durable, easy to apply, using conventional manufacturing techniques; and furthermore does not have the numerous disadvantages attributable to the prior art adhesives employed for substantially identical purposes to date. DESCRIPTION OF THE PREFERRED MODALITY The preferred adhesive composition of the present invention includes: about 10% to about 60% by weight of a buten-1-ethylene copolymer; about 20% to about 80% by weight of a resin imparting tack; about 5% to about 30% by weight of a plasticizer; and about 0.1% to about 3% by weight of an antioxidant and wherein the hot melt adhesive composition has a viscosity of about 1,000 a. approximately 50,000 cP at 167.8 ° C (325 ° F) and a melting point of approximately 76.7 ° C - 93.3 ° C (170 ° F-200 ° F).

Butene-1-homopolymers and copolymers which are useful in the present invention, are primarily straight-chain molecules with regular and spatially ordered structures of ethyl side groups. These side groups are the result when butene-1 is polymerized through the double bond 1, 2, carbon and on a main structure of ethylene chain. This is described in more detail in U.S. Pat. No. 3,362,940. When cooled from a melt, the ethyl side groups initially line up in a tetragonal spatial montage. Over time, the tetragonal crystalline phase shape is transferred to a stable hexagonal spatial structure, with a subsequent development of improved physical properties. A more complete discussion of the polymer used herein can be found in the reference to Mostert, U.S. Pat. No. 4,937,138, the contents of which are hereby incorporated by reference. As will be seen from the above description, the present polymer is useful in amounts of about 10% to about 60% by weight. A commercially available butene-1-ethylene copolymer can be secured from the Shell Chemical Company of Houston, Texas under the trade name Duraflex 8910 PC. As noted above, resins imparting useful tackiness within the scope of the present invention have an approximate weight of 20% to about 80% by weight. The tackifying resins can be selected from any of the non-polar types, which are commercially available. An example of a commercially available tackifying resin that is useful for the present invention includes the resin which is commercially identified by the commercial designation Escorez 1310 LC and which is manufactured by Exxon Chemical Company. Typically, non-polar tackifying resins which are useful with the present invention include resins having partially or completely hydrogenated C9 or C5 hydrocarbon resins, with softening points that is in a range of about 70 ° C to about 125 ° C. . Sticky imparting resins which are useful for the present invention can probably include polar tackifying resins, however the selection of polar tack imparting resins available is limited in view of the fact that many of the polar resins seem only partially compatible with the butene-1-homopolymer and copolymers. As noted above, the resin imparting select tackiness that is useful with the present invention will be about 20% to about 80% by weight of the entire adhesive composition and more preferably about 50%. The plasticizer which finds utility in the present invention can be any number of different plasticizers but the inventors have discovered that a plasticizer which includes a mono-olefin polymer such as is commercially available under the trade designation Indopol H-100 and which is manufactured by Amoco, is particularly useful in the present invention. As will be appreciated, plasticizers have typically been employed to reduce the viscosity of the total adhesive composition without substantially decreasing the adhesive strength and / or the service temperature of the adhesive. As noted above, the present adhesive composition has a viscosity of about 2,000 cP a. about 50,000 cP at 162.8 ° C (325 ° F) and a melting point of about 76.7 ° C to about 93.3 ° C (about 170 ° F to about 200 ° F). In view of the unexpectedly favorable viscosities, the adhesive composition of the present invention has improved spray characteristics when employed with conventional manufacturing equipment. As discussed previously, the hot melt adhesive composition of the present invention includes from about 0.1% to about 3% by weight, of an antioxidant. As a general matter, it is understood that antioxidants and stabilizers are important to protect the otherwise vulnerable copolymer and thus the adhesive composition from the deleterious effects of oxidative and thermal degradation which is frequently experienced during the manufacture and application of adhesive compounds as well as in ordinary use of final product. It will be understood that this degradation is usually manifested by the deterioration of the adhesive composition in appearance, physical properties and performance. Among the most useful stabilizers are hindered high molecular weight phenols, and mutilfunctional phenols, such as sulfur and phosphorus-containing phenols. In this regard, hindered phenols are well known to those skilled in the art, and can be characterized as phenolic compounds that also contain sterically bulky radicals in immediate proximity to the phenolic hydroxyl group. In particular, tertiary butyl groups are generally substituted on the benzene ring in at least one of the ortho positions with respect to the phenolic hydroxyl groups. The presence of sterically bulky substituted radicals in the vicinity of the hydroxyl group is considered to retard its drawing frequency and correspondingly its reactivity. This steric hindrance is considered to provide the phenolic compounds with their stabilizing properties. A suitable antioxidant for use with the present invention is commercially available from CIBA-GEIGY Company under the trade name Igranox 1010. The performance of these stabilizers is well known in the art and can further be improved by using synergists such as, for example, thiodipropionate esters and phosphites; and metal chelating and deactivating agents, such as for example ethylenediamine tetraacetic acid, its salts and disalicylpropylenedimide.

The hot melt adhesive composition of the present invention can be formulated using any of the techniques known in the art. A representative example of the prior art process involves placing all the plasticizer and stabilizer in a jacketed mixing kettle, and preferably in a heavy duty blender type Ba er-Perkins or ay mixer, which is equipped with rotors and subsequently raised the temperature of this mixture to a range of about 121.1 ° C to about 176.7 ° C (about 250 ° F to about 350 ° F). It will be understood that the precise temperature to be used in this step will depend on the melting point of the particular ingredients. When the initial mixture, previously noted, has been heated, the mixture is covered with a layer of carbon dioxide at a slow flow rate, and the above-described resin is added slowly. When the resin melts, and the desired temperature is reached, the copolymer is added to the mixture. The resulting adhesive composition mixture is then stirred until the copolymer is completely dissolved. Then vacuum is applied to the mixture to remove any trapped air. Optional additives may be incorporated into the hot melt construction adhesive compositions in order to modify particular physical properties. These additives may include dyes, such as titanium dioxide and fillers such as talc and clay. However, these additional additives do not include nucleating agents such as those described in U.S. Pat. No. 4,937,138 to Mostert, in view of the undesirable effects imparted to the adhesive composition when these nucleating agents are added thereto. The invention is further illustrated by way of examples noted below. In that aspect, an adhesive composition according to the teachings of the present invention is made by the general procedure described above. This adhesive composition has the following constituent elements: about 25% by weight, of a butene-1-ethylene copolymer; about 50% by weight of a resin imparting tackiness; about 25% by weight of a plasticizer; and about 0.1 to about 3% by weight of a hindered phenolic antioxidant, and wherein the hot melt adhesive composition after application exhibits improved flow properties at room temperature and open time, and furthermore has a viscosity of about 2,000. cP at 162.8 ° C (325 ° F) and a melting point of approximately 76.7 ° C (170 ° F).

More specifically, butene-1-ethylene copolymer commercially insured from Shell Chemical Company is commercially obtained from Duraflex 8910-Pc; the resin imparting pegajosid d is commercially purchased from Exxon Chemical Company under the trade name Escorez 1310 LC; the plasticizer is purchased commercially from Arnaco Chemical Company under the trade designation Indopol H-100; and the antioxidant is commercially purchased under the commercial designation of Irganox 1010 from CIBA-GEIGY. The resulting hot melt adhesive composition upon testing is found useful for a multi-strip construction or multiple lines of non-woven garments. In addition, various substrates are sprayed and extruded and is generally acceptable for all intended purposes. The specific performance characteristics of this preferred formulation and the examples that follow are discussed in more detail below. A second example of the adhesive composition is formulated and had the following characteristics: about 40% by weight of a butene-1-ethylene copolymer; about 40% by weight of a resin imparting tackiness; about 20% by weight of a plasticizer, and about 1% by weight of a hindered phenolic antioxidant, and wherein the adhesive composition has a viscosity of about 4000 cP at a temperature of about 162 ° C (325 ° F) and a melting point of approximately 82.2 ° C (18? 'F). A third example of the adhesive composition is formulated and had the following characteristics: about 50% by weight of a butene-1-ethylene copolymer; about 30% by weight of a resin imparting tackiness; about 20% by weight of a plasticizer, and about 1% by weight of a hindered phenolic antioxidant, and wherein the adhesive composition has a viscosity of about 5500 cP at a temperature of about 1 2 ° C (325 ° F) and a melting point of approximately 86.7 ° C (188 ° F). A fourth example of the adhesive composition is formulated and had the following characteristics: about 25% by weight of a butene-1-ethylene copolymer; about 65% by weight of a resin imparting tackiness; about 10% by weight of a plasticizer, and about 1% by weight of a hindered phenolic antioxidant, and wherein the adhesive composition has a viscosity of about 1500 cP at a temperature of about 162 ° C (325 ° F) and a melting point of approximately 78.3 ° C (173 ° F). In each of the examples noted above, it was found that adhesives formulated according to these examples are useful for building soft non-woven disposable articles. As previously noted, traditional hot melt adhesives that have been formulated using SIS, SBS, SEBS and APAO are prone when exposed to water for prolonged periods of time to lose their bond strengths, with the result that laminations prepared with these Adhesives will fail when exposed to water for extended periods of time. As will be understood, these detachments of a non-woven garment, such as a diaper or the like, can cause the core integrity of the garment to fail with resulting undesirable effects such as leakage or efficient fit. In order to demonstrate the novel and unexpected results achieved by the present invention, the inventors compared and contrasted the adhesive compositions of the present invention with the prior art adhesive compositions which have been commercially available for some time and which also utilize the polymers such as SIS, SBS, SEBS and APAO as noted above. For example, the prior art adhesive compositions were applied in an amount equal to about 3 milligrams per 6.45 cm (square inch) and a temperature of 148.9 ° C (300 ° F) and in addition with an open time of about 0.5 second. to form a tissue laminate. It was discovered that the adhesive present when measured by an evaluation of Instron dry stripping resistance, under similar coating conditions, produces a bond strength of approximately 100 grams, this bond strength is comparable with more traditional adhesive compositions. However, when the same adhesive composition is compared to more traditional adhesives after one hour of soaking in tap water, it was discovered that traditional adhesives, as noted above, produce bond strengths in the range of about 5 to about 25 grams. In contrast, adhesives manufactured in accordance with the teaching of the present invention produce bond strength exceeding 50 grams, thereby making a very attractive adhesive for use in building a non-woven garment and more specifically a diaper that can be exposed to water by prolonged periods of time.

The present composition is further tested by applying it to a tissue and non-woven substrate to form a laminate. The adhesive is applied in an amount equal to approximately 2 milligrams per 6.45 cm2 (square inch) and at a temperature of 148.9 ° C (300 ° F) and also with an open time of approximately 1.0 second. After laminate formation, it is immersed in water for about 1 hour. After submersion, the adhesive release resistance is tested in a manner similar to that discussed above. The test results showed that the lamination had an average peel strength of approximately 50 grams after water exposure for 1 hour. Traditional adhesive compositions exhibit greatly reduced bond strengths over the ranges noted above. What is surprising, however, was the percentage of binding strength retained. For example, a standard adhesive such as H2120-01 and available from Findley Adhesives had a bond strength after soaking for 1 hour of approximately 5.7 grams, which represents approximately 2% of its dry bond strength. In contrast, the adhesive of the present invention after one hour of soaking retained a bond strength of approximately 56.6 grams representing approximately 36% of its dry bond strength.

When tested for the construction of multiple strips, and where the polyethylene and polypropylene are bonded together to form a lamination, the adhesive composition present when applied to the selected substrates, as discussed above, in an amount equal to about 1.5 milligrams per 6.45 cm2 (square inch) of adhesive at 148.9 ° C (300 ° F) and 0.5 second open time produces a bond equal to approximately 855 grams. In contrast, when compared to prior art adhesive compositions, the average peel strength under the same coating conditions resulted in bond strengths of approximately 661 grams. When comparing further against traditional adhesive compositions which are employed to form polyethylene and polypropylene laminations and wherein the adhesive composition of the present invention is applied to the selected substrates in an amount equal to about 3 milligrams per 6.45 cm 2 (square inch) and At a temperature of 148.9 ° C (300 ° F), the present formulation produces bond strengths, as reflected by average shear strength as measured by an Instron tensile tester, which is comparable to that produced by hot melt adhesives conventional Still further, when laminations were formed under the same conditions and that include a polyethylene substrate that is bonded to a non-woven material, the average peel strength of the present adhesive is significantly and quite unexpectedly improved relative to that produced by a composition. conventional hot melt adhesive. For example, under conditions noted above, the average peel strength for a lamination that is composed of a polyethylene and a nonwoven substrate, and wherein the adhesive composition of the present invention is applied in an amount equal to about 3 milligrams per 6.45. cm2 (square inch) and at a temperature of about 148.9 ° C (300 ° F) to about 339 grams, compared to traditional hot melt adhesive compositions that can be purchased commercially from Findley Adhesive Inc., under the trade designation H2275- 02 and which produces an average peel strength of approximately 208 grams. As noted previously, the adhesive composition of the present invention is substantially nonblocking under normal storage conditions. For example, the inventors prepared a polyethylene laminate which is combined with a nonwoven material to form a laminate. The adhesive of the present invention is applied to form the laminate in an amount equal to about 1.5 milligrams per 6.45 cm 2 (square inch) and at a temperature of about 148.9 ° C (300 ° F). The adhesive is applied with approximately 0.5 second of open time. In addition, a laminate is prepared under identical coating conditions by using a traditional hot melt adhesive composition such as commercially available from Findley Adhesives Inc., of Wauwatosa, Wisconsin and which is purchased under the trade designation H2275-02. When identical blocking samples were prepared and aged in an oven for 48 hours and at a temperature of 60 ° C (140 ° F), the traditional hot melt adhesive such as formulation H2275-02, exhibited an average release resistance of approximately 35 grams. In comparison, the adhesive composition of the present invention exhibits an average peel strength of about 8.5 grams. These results were surprising in view of the fact that the adhesive blocking values present were significantly lower than the state-of-the-art adhesive which is considered an excellent non-blocking adhesive for a non-woven garment structure. These results are significant in view of the conditions under which most non-woven garments are used. It is important to understand that it is very beneficial for an adhesive composition to flow for a while, thus allowing the non-woven fibers to penetrate, thereby establishing a mechanical bond therewith. Once the flow has occurred, however, it is important that the hot melt adhesive sets and hardens relatively and is not sticky (not blocking). This of course decreases the potential for blocking (sticking) to a. Substrate or attached surface such as may be the case when diapers are tied in a box and shipped at elevated temperatures; or worse, the possibility that the adhesive under certain conditions, such as elevated temperature, will adhere to the skin of a minor, or during storage, flow, completely outside the interface of the joint. As will be expected, an adhesive that remains tacky under these circumstances can make an associated non-woven article extremely uncomfortable to use, as would be the case when such adhesives are employed in garments such as incontinence garments, and feminine care items. or similar, which can be placed in an orientation where it is exposed to body hair. All of these tests noted above, the peel strength were measured at a rate of 30.48 cm2 (12 inches) per minute. In addition, five samples were tested in each case. Additionally, the blocking test was used to simulate compact packing. More specifically, the laminations employed in the blocking test were placed on non-woven garments such as a diaper or the like with the non-woven portion of laminate placed in contact with the non-woven substrate of the diaper. Then, samples weighing 200 grams per square centimeter were compressed for a period of 48 hours and at a temperature of 60 ° C (140 ° F). Then the samples were allowed to cool to room temperature. The samples were then tested for their peel strength in an Instron tensile tester at a rate of 30.48 cm (12 inches) per minute. A review of the above information will reveal that the adhesives of the present invention give similar peel strength compared to more traditional hot melt adhesives such as Findley Adhesives H2275-02, and furthermore showed improved binding strengths when exposed to water. In addition, the present adhesive composition does not appear to exhibit noticeable blocking characteristics, thus suggesting that the adhesive will be very useful for assembling nonwoven articles that will be packaged in a compact form. In addition to the above, the adhesive composition of the. present invention has low viscosity, and melting point, which makes this a very convenient adhesive for use with more traditional application methods. Therefore, it will be seen that the hot melt adhesive of the present invention provides a totally reliable and practical means for adhesively assembling a disposable soft article such as a disposable diaper, a feminine towel or the like, and furthermore avoid the detriments associated with prior art practices, including, among other things, employing various different adhesive compositions for assembling a disposable soft article. In addition to the foregoing, the improved hot melt adhesive of the present invention surprisingly and unusually exhibits convenient manufacturing viscosities when compared to the prior art, and in addition has peel strengths, after exposure to water which are greatly improved in relative comparison with the previous technique. It will be apparent to those skilled in the art that the above example has been developed for the purpose of illustration and that various variations may be practiced in the proportions, procedures and material without departing from the scope of the present invention. Therefore, it will be understood that this invention is not limited except by the claims that follow:

Claims (8)

1. CLAIMS 1. A hot melt adhesive composition having improved wet strength characteristics, characterized in that it comprises a formulation having the following ingredients: 10% to 60% by weight of a butene-1-ethylene copolymer; 20% to 80% by weight of a resin imparting tackiness; 5% to 30% by weight of a low molecular weight plasticizer having a molecular weight less than about 2000; and 0.1% to 3% by weight of an antioxidant, wherein the total of ingredients is 100% by weight based on the weight of the entire adhesive composition, wherein the hot melt adhesive composition has a viscosity of 1,000 to 50,000 cP at 162.8 ° C (325 ^) and a melting point of 76.7 to 93.3 ° C (170 to 200 ° F) and in addition where the adhesive composition, when a substrate of a laminate fabric is applied, the laminate of fabric composed of a first substrate and a second tissue substrate, in an amount of about 3.0 mg / 6.45 cm2 (square inch), at a temperature of 148.9 ° C (300 ° F) and with an open time between application of the adhesive composition to the substrate and contact with the other substrate of about 0.5 second, which produces an average peel strength of between at least about 50 grams and even failure of either the first substrate or the second tissue substrate following exposure to water for a period approximate 1 hour.
2. 2. A hot melt adhesive composition as described in claim 1, characterized in that the resin imparting tack is at least partially compatible with the butene-1-ethylene copolymer and the antioxidant is a hindered phenolic antioxidant.
3. 3. A hot melt adhesive composition as described in claim 1, characterized in that the plasticizer includes a mono-olefin polymer.
4. 4. A hot melt adhesive composition as described in claim 1, characterized in that the formulation comprises about 25% by weight of the butene-1-ethylene copolymer at about 49% by weight of the tackifying resin, approximately 25% by weight of the low molecular weight plasticizer and about 1% by weight of the antioxidant.
5. A hot melt adhesive composition as described in claim 1, characterized in that the adhesive composition when applied to a tissue laminate in an amount of about 3.0 mg / 6.45 cm2 (square inch) and at a temperature of 148.9 ° C (300 ° F) and with an open time of about 1 second, produces a peel strength of about 100 grams.
6. 6. A hot melt adhesive composition as described in claim 1, characterized in that the adhesive composition is non-blocking.
7. 7. A hot melt adhesive composition as described in claim 1, characterized in that the resin imparting tackiness at least partially compatible with the butene-1-ethylene copolymer and the plasticizer includes mono-olefin polymers.
8. 8. A hot melt adhesive composition as described in claim 1, characterized in that the low molecular weight plasticizer is polybutene.