Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-03-03
2001-10-09
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S177000, C525S184000
Reexamination Certificate
active
06300413
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crosslinkable hot-melt adhesive coating based on a powder mixture comprising a commercially customary, amine-terminated copolyamide or copolyester and a pulverized extrudate consisting of an atactic polyolefin and a pulverulent isocyanate or an epoxide, for producing a base dot as a barrier to strikeback in double dot coating. The upper dot consists of an amine- or acid-regulated copolyamide, in order to ensure good attachment to the lower dot. The invention relates in particular to a hot-melt adhesive composition for the dot coating of bondable interlinings for the clothing industry, especially outerwear, and technical laminates. Instead of the copolyamide, it is also possible to employ HO-terminated copolyesters.
2. Description of the Background
In order to solve the problems regarding the reduced resistance to laundering and dry cleaning and regarding the relatively weak adhesion, improved hot-melt adhesive compositions, but also improved coating technologies, have been developed. Duodot or double dot coatings are described, for example, in patents DE 22 14 236, DE 22 31 723, DE 25 36 911 and DE 32 30 579.
Coating supports have been improved by using finer yarns with low-denier individual fibers down to the microfiber range and also synthetic yarns, examples being high-bulk acrylic or polyester yarns. The wovens originally used have largely been replaced by stitch-bonded fabrics. These new combinations lead to very soft, but also very open constructions which place even greater requirements on the coating methods and hot-melt adhesive compositions, especially with regard to strikeback and strikethrough of the hot-melt adhesive composition.
Costs and quality reasons have led to a marked reduction in the amount of coating applied per m
2
on interlining material. Whereas formerly the amounts applied were commonly 18-25 g/m
2
, they are nowadays 7-15 g/m
2
.
Despite these small amounts, it is necessary to ensure sufficient adhesion and resistance properties for the hot-melt composition; in other words, the hot-melt adhesive must not strike away into the interlining, since then it would no longer be available for the actual bonding.
An object that had developed in the art was to find an effective strikeback barrier which exhibits high bond strength, good attachment of the upper dot to the base layer and good resistance to laundering and dry cleaning at reduced amounts of coating of the adhesive.
A range of strikeback barriers is known which are (i) crosslinking acrylate dispersions or polyurethane dispersions, to (ii) powder-filled pastes based on high-melting copolyamides or polyethylene to (iii) highly viscous thermoplastic polyurethane powders.
All systems have more or less severe disadvantages in terms of application, the attachment to the upper dot and/or resistance to laundering. In addition, the dispersions cannot be employed on coarse, hairy interlinings.
When self-crosslinking acrylate or polyurethane dispersions are coated on a fabric, partial crosslinking occurs, even in the course of coating, which leads to a deposit on the screens and thus to clogging of the stencil holes. Laborious cleaning of the unit is required. Great difficulties are experienced when there is production-induced standstill. A further problem is the attachment of the upper dot to the base layer. The highly viscous powder-filled systems based on polyamide, polyethylene and polyurethane do not achieve the required strikeback reliability.
It has so far not been possible to provide a stable crosslinkable system for the base dot. Either the isocyanates, which are employed preferably, can not be stabilized to water (the matrix for coating pastes), or the activation temperature for crosslinking (greater than 160° C.) is too high.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a crosslinkable hot-melt composition which exhibits improved adhesivity and improved laundering resistance.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a crosslinkable hot-melt composition comprising:
a reactive powder mixed with a crosslinking component of a crosslinking agent bound in a polyolefin matrix, wherewith the components of the composition do not react by crosslinking until the mixture is melted, said composition being useful for the coating and/or lamination of sheet-like structures.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has now surprisingly become possible to prepare a very reactive system having an activation temperature in the range from about 100-130° C., which is also water resistant. The crosslinkable hot-melt adhesive composition of the invention for the coating and/or lamination of sheetlike structures has the feature that the reactive components present in the hot-melt adhesive composition do not react, with crosslinking, until in the melt. In this case, the crosslinking component is incorporated by extrusion into a polyolefin in the melt.
In a preferred embodiment, a commercially customary copolyamide having terminal amine groups is mixed with a trimerized diisocyanate which has been passivated by extrusion with an atactic polyolefin, and the mixture is processed as an aqueous paste by rotary screen printing. Instead of the copolyamide, it is also possible to employ a copolyester. In the course of subsequent drying in the oven at about 120° C., crosslinking is initiated within a few seconds to give a crosslinked strikeback barrier for the double dot. In this way it is possible to avoid the customary problems of isocyanate-containing systems, which are, for example, that capped isocyanates (with caprolactam or oximes as capping agent or obtained by dimerization) require excessive activation temperatures. Furthermore, no extraneous substances should be released in the course of bonding. The other problem has been that unblocked isocyanates react with water while still in the paste.
The isocyanate had to be stabilized against water, and against diffusion of atmospheric moisture, in order to ensure its activatability at relatively low temperatures. This has surprisingly been possible by binding the isocyanate into a polyolefin polymer, preferably atactic polypropylene, by extrusion, said polymer not absorbing any water by diffusion and having a melting point of about 120° C. and being of such low viscosity that it is possible on pressing to obtain a reaction of the amine-regulated copolyamide with the isocyanate Suitable isocyanates are solid isocyanates having more than two free NCO groups and a melting range from 100-130° C. The polymer of the matrix must not react with the isocyanate. Other suitable crosslinking components are epoxides having a melting range from 90-130° C., preferably from 100-120° C., a molecular weight range from 2000-6000, preferably from 2500-3000, and more than two epoxide groups per molecule; an example which may be mentioned is bisphenol A.
As the polymer matrix it is preferred to employ atactic polypropylene. It should have a melt viscosity of from 8000-50,000 mPas at 190° C. and a softening range from 80-150° C., preferably a melt viscosity of from 8000-30,000 mPas at 190° C. and a softening range from 100-140° C. Examples of suitable commercial products are VESTOPLAST 408, 308, 508, 520, 703, 704, 708 and 750 from Huels AG. The polyolefin can also be an atactic &agr;-olefin copolymer or a terpolymer based on ethene, propene and 1-butene and having the characteristics described above. In order to achieve particularly good attachment of the upper dot to the base dot, it is advisable to employ an amine-regulated copolyamide as the upper dot material. Suitable products for the base dot and upper dot are low-melting grades of low viscosity. The melting point should range from 90-150° C., preferably from 115-130° C., with a solution viscosity eta rel in the range from 1.2-1.7, preferably from 1.25-1.4. By this means, the boundary layer reacts with the isocyan
Gurke Thorsten
Losensky Hans-Willi
Simon Ulrich
Degussa-Huels Aktiengesellschaft
Lipman Bernard
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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