Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
1999-10-14
2001-03-27
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C525S123000, C525S125000
Reexamination Certificate
active
06207785
ABSTRACT:
The present invention relates to hot-melt adhesive compositions based on hydroxylated polydiene and more particularly to hot-melt adhesive (HMA) compositions which are provided in the form of a polymer containing free isocyanate functional groups, the said polymer resulting from the reaction of a polyisocyanate (A), of a polydienepolyol (B) and of a copolymer (C) of ethylene containing hydroxyl functional groups.
According to a specific form of the invention, the polydienepolyol is a hydroxytelechelic polybutadiene and the copolymer (C) is either an ethylene/vinyl acetate/hydroxyethyl (meth)acrylate copolymer or an ethylene/alkyl (meth)acrylate/hydroxyethyl (meth)acrylate copolymer.
This composition, generally used in combination with an adhesive (tackifying) resin, makes it possible to produce bondings which are resistant to high temperature after crosslinking of the free NCO functional groups, generally under the effect of atmospheric moisture.
For some years, there has been an increasing search to present adhesive compositions in the solid form. In this case, they are hot-melt adhesives (HMA) having, as base, a thermoplastic resin which is solid at room temperature. These adhesives become fluid when heated, the bonding of the surfaces to be joined being ensured when the adhesive again becomes stiff on cooling. These hot-melt adhesives generally result from the combination of three base constituents: a thermoplastic resin, an adhesive (tackifying) resin and a wax, with which may be combined additives such as stabilizer, filler, plasticizers and others. The most well known base thermoplastic resins are polyamides, atactic polypropylene, ethylene/vinyl acetate (EVA) copolymers and ethylene/alkyl (meth)acrylate copolymers. In the present state, these hot-melt adhesives have good adhesive properties but have the disadvantage of exhibiting poor heat resistance, a resistance which barely exceeds 60 to 80° C.
To overcome this disadvantage, a new generation of crosslinkable hot-melt products: polyurethane hot-melt adhesives, is developed. These products are prepared conventionally by reaction of polyisocyanate with polyols of polyester type, at least one of which is solid at ambient temperature. These adhesives are applied at high temperature as a melt phase. They have the disadvantage of being incompatible with the adhesive (tackifying) resins, which greatly restricts the formulation possibilities. This is then reflected by a limited ability to bond to certain well defined substrates. In addition, these products have assembly times of the order of a few minutes, which is too long for some high-output-rate applications. The assembly time of a hot-melt adhesive is the time available for performing the bonding, between the instant when the adhesive is applied in the molten state to the first substrate to be bonded and the instant when the hot-melt adhesive is no longer sufficiently fluid to allow the second substrate to be assembled correctly.
Another type of crosslinkable hot-melt adhesive has been developed from hydroxylated ethylene/vinyl acetate copolymers reacting with a blocked polyisocyanate in stoichiometric amount, as described in European Patent EP 294,271. These hot-melt adhesives, which are compatible with the adhesive (tackifying) resins, have good adhesive properties but have the disadvantage of requiring subsequent heat treatments at temperatures of at least 140° C. for several minutes, to ensure their good crosslinking. Such bonding conditions are not acceptable in the case of some thermally sensitive substrates.
EP 380,379 describes crosslinkable hot-melt adhesive compositions which are provided in the form of a prepolymer containing free isocyanate functional groups, the said prepolymer resulting from the reaction of a copolymer of ethylene and of vinyl acetate containing hydroxyl functional groups with a polyisocyanate. This prior art describes the copolymers obtained by direct copolymerization of ethylene, of vinyl acetate and of hydroxyethyl acrylate, as well as the ethylene/vinyl acetate/vinyl alcohol copolymers obtained by partial hydrolysis of ethylene/vinyl acetate copolymers.
EP 600,767 is similar to the above but a primary alcohol (dodcanol) is added to the ethylene/vinyl acetate/hydroxyethyl acrylate copolymer.
The essential difference in composition between these prior arts and the present invention is thus the joint use of polydienepolyol and of a hydroxylated copolymer (C) for reacting with the polyisocyanate, instead of EVA/HEA (ethylene/vinyl acetate/hydroxyethyl acrylate copolymer) alone or instead of EVA/HEA and dodecanol.
This makes it possible:
to reduce the viscosity of the prepolymer during the preparation, all the more so since the EVA/HEAs have low MFI values, and thus to facilitate the synthesis of the HMA. The flow index is denoted by MI (Melt Index) or MFI (Melt Flow Index),
after preparation, to give an HMA which has a lower viscosity, especially if the starting material is an EVA/HEA with a low MFI value, and thus to make it possible to employ the HMA at a lower temperature (110-140° C.),
to improve the low-temperature performance, by virtue of the addition of a compound with a very low Tg,
to improve the applicative performance of the HMA, in particular in terms of resistance to hydrolysis and mechanical, adhesive and cohesive properties.
It is also possible to add, to the compositions of the invention, a speciality monoalcohol (hydroxylated tackifying resins).
EP 293,602 describes hot-melt adhesive compositions comprising (i) the reaction product of a polyisocyanate with a polyol and (ii) a thermoplastic polymer, such as an EVA (ethylene/vinyl acetate copolymer) or an SEBS (styrene-ethylene/butene-styrene block copolymer). The thermoplastic polymer (ii) is not functionalized and it is therefore not bonded to the polyurethane network formed during the crosslinking, whereas, in the present invention, the copolymer (C) is bonded to the polyurethane network. Thus, the compositions of the invention have the following advantages:
1. Improvement in the mechanical, peel and cohesion properties of an HMA adhesive seal in temperature by crosslinking with atmospheric moisture.
2. Possibility of applying the hot-melt adhesive at “low temperature” (110-140° C.).
3. Improvement in the low-temperature adhesive performance.
4. Improvement in the applicative performance of the hot-melt adhesive.
Resistance to hydrolysis
Adhesion
Mechanical strength
Cohesion.
The polyisocyanate (A) is generally chosen from aliphatic, cycloaliphatic or aromatic polyisocyanates well known to a person skilled in the art, as well as mixtures of these compounds.
Mention may be made, as examples of aliphatic polyisocyanates, of hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (HMDI), ethylene diisocyanate, ethylidene diisocyanate, propylene diisocyanate, butylene diisocyanate, dichlorohexamethylene diisocyanate, furfurylidene diisocyanate and the mixtures as well as the derivatives (dimer, trimer, biuret or allophanate) of these compounds.
Mention may be made, as examples of cycloaliphatic polyisocyanates, of isophorone diisocyanate (IPDI), 1,3-cyclopentylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene diisocyanate and the mixtures and derivatives (dimer, trimer, biuret or allophanate) of these compounds.
Mention may be made, as examples of aromatic polyisocyanates, of 4,4′-diphenylmethane diisocyanate (MDI) and its isomers, in particular 2,4′- and 2,2′-diphenylmethane diisocyanate, toluene diisocyanate (TDI) and its isomers, in particular 2,4- and 2,6-toluene diisocyanate, 2,2-diphenylpropane 4,4′-diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, xylene diisocyanate, 1,4-naphthalene diisocyanate, 1,5-naphthalene diisocyanate, azobenzene 4,4′-diisocyanate, diphenyl sulphone 4,4′-diisocyanate, 1-chlorobenzene 2,4-diisocyanate, 4,4′,4″-triisocyanatotriphenylmethane, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane 2,2′,5,5&prime
Flat Jean-Jacques
Lebez Jean
Pierrot Jean-Michel
Atofina
Gorr Rachel
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