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
1998-11-13
2001-01-30
Sergent, Rabon (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...
C156S331400, C156S331700, C528S073000, C528S080000, C528S081000, C528S083000, C528S905000
Reexamination Certificate
active
06180744
ABSTRACT:
The present invention relates to compositions suitable for use as moisture curing hot melt adhesives.
The technology of hot melt adhesives and moisture curing hot melt adhesives is well known. Conventional hot melt adhesives are thermoplastic materials. They are applied molten at high temperatures and the adhesion comes entirely from the cooling of the material back to the solid state. Hot melt adhesives set immediately upon cooling from the liquid to the solid state, but may develop improved properties over minutes or days with crystallization. The two main drawbacks of this type of adhesive are the very high application temperatures, limiting the type of substrate, and the poor heat resistance of the final adhesive bond as reheating will again soften the material.
Moisture curing polyurethane hot melt adhesives have been developed to improve performance in these areas. These materials are polyester based and have terminal isocyanate groups which, after application, utilize the moisture in the air to cure (set) to produce a more heat resistant bond.
The molecular weight, and hence viscosity, of the polyurethanes used in moisture curing hot melt adhesives is significantly lower than that of the conventional thermoplastics used in conventional hot melt adhesives. This allows application of moisture curing hot melt adhesives at much lower temperatures, for example 120° C., compared to 160° C. for conventional hot melt adhesives, which causes much less damage to substrates. However, the lower molecular weight of the polyurethanes used in the moisture curing hot melt adhesives gives rise to other problems. Prior to any moisture curing taking place, moisture curing polyurethanes form an initial bond much more slowly than conventional hot melt adhesives, therefore the “green strength” (bond strength immediately after application) is lower.
The present invention seeks to overcome the problems of traditional moisture curing hot melt adhesives. The inventors have developed moisture curing hot melt adhesives with more rapid solidification and therefore greater “green strength” than other moisture curing hot melt adhesives on the market.
The present invention provides a composition, suitable for use as a moisture curing hot melt adhesive. The compositions of the present invention comprise at least one isocyanate terminated polyester obtainable by enzyme catalysed polyesterification of one or more monomers selected from dicarboxylic acids, diols or polyols and/or hydroxyacids in the presence or absence of an inert organic solvent and reacting the product with a diisocyanate and optionally at least one conventionally produced isocyanate terminated polyester. Preferably the diisocyanate is MDI (4,4′-diphenylmethane diisocyanate).
It is possible for isocyanate terminated polyesters used in the composition of the invention to be 100% polyester(s) obtained by enzyme catalysed polyesterification. However, it has been found that when up to 60% by weight of the polyester(s) are conventional polyester(s) the performance and physical properties of the composition are improved. Preferably at least 40% by weight, more preferably at least 50% by weight, more preferably at least 60% by weight, even more preferably at least 70% by weight, still more preferably at least 80% by weight and most preferably at least 90% by weight of the polyester(s) used are produced by enzyme catalysed polyesterification.
The composition may also contain additives conventionally present in moisture curing hot melt adhesives, for example antioxidants, oxazolidine, crosslinking agents and catalysts, in an amount of up to 5 parts per hundred (pph) of the overall composition per additive component.
The polyesters used in the composition of the invention may be produced by processes, such as those described in GB-A-2272904 and PCT/GB93/02461, involving an enzymatic polyesterification, either in the presence or absence of an organic solvent, which affords polyesters having high weight average molecular weight and low dispersity whilst also being extremely pure in terms of freedom from unwanted by-products. Polyesters produced by this process comprise as repeating units
(i) residues of at least one aliphatic hydroxycarboxylic acid, or derivative thereof; or
(ii) residues of (a) at least one aliphatic dicarboxylic acid or derivative thereof, (b) at least one aliphatic diol or polyol, and optionally (c) at least one aliphatic hydroxycarboxylic acid, or derivative thereof.
The process comprises reacting the components defined in (i) or the components defined in (ii) in the presence or absence of a solvent and in the presence of a lipase such that the molar ratio of acid groups to hydroxyl groups in the reactants is 1:1 to 1:1.1.
As used herein the term “polyester” is intended to encompass materials obtainable by this process from any suitable combination of the monomers defined herein.
Aliphatic hydroxycarboxylic acids suitable for use in this process include those of formula:
HOCH
2
—R
1
—CO
2
H
wherein R
1
is a bond or a divalent radical of a substituted or unsubstituted C
1
to C
12
alkyl group optionally having one or more carbon—carbon double bonds and optionally having one or more carbon—carbon triple bonds.
Suitable aliphatic dicarboxylic acids include those of formula:
HO
2
C—R
2
—CO
2
H
wherein R
2
is a bond or a divalent radical defined as for R
1
.
Suitable aliphatic diols include those of formula:
HOCH
2
—R
3
—CH
2
OH
wherein R
3
may be a bond or a divalent radical defined as for R
1
.
Suitable aliphatic polyols include those of formula:
HOCH
2
—R
4
—CH
2
OH
wherein R
4
is a divalent radical defined as for R
1
and bearing at least one hydroxyl substituent.
Each of the C
1
to C
12
alkyl groups mentioned above may be substituted or unsubstituted and may be cyclic, branched or straight chain, optionally having at least one carbon—carbon double bond, either in the cis- or trans-conformation and optionally having at least one carbon—carbon triple bond. When the C
1
to C
12
alkyl group has more than one double or triple carbon-carbon bond, these bonds may be conjugated or non-conjugated. The C
1
to C
12
alkyl group is optionally substituted with one or more substituents (which, when there are two or more substituents, may be the same or different) each selected from halogen atoms, for example, fluorine, chlorine or bromine, hydroxyl, —OR5 where R
5
is hydrogen or a C
1
to C
12
alkyl, carboxyl, and —CO
2
R
6
where R
6
is hydrogen or a C
1
to C
12
alkyl.
Preferably the diol has from 2 to 14 carbon atoms and is an &agr;,&ohgr;-diol, for example 1,4-butanediol, diethylene glycol, ethylene glycol, propylene glycol, pentanediol, hexane-1,6-diol or dodecane-1,12-diol, most preferably 1,4-butanediol.
Diethylene glycol has a lower activity than other suitable diols so that, when diethylene glycol is used as a monomer, it is necessary to carry out the reaction either at higher temperature, in which case the dispersity is relatively wide, or at low temperature for a long period.
Preferably the diacid has from 2 to 14 carbon atoms, for example, oxalic acid, succinic acid, fumaric acid, citric acid, malic acid, malonic acid, maleic acid or adipic acid. Most preferably the diacid is adipic acid.
The hydroxy acids must have a non-sterically hindered primary or secondary hydroxyl. Tertiary hydroxyl and sterically hindered primary and secondary hydroxyls are unlikely to react under the conditions of the enzyme catalysed process. Preferred hydroxy acids are hydroxy-straight chain aliphatic carboxylic acids,
At high dilution certain hydroxy carboxylic acids tend to form lactones and it is therefore preferred that, when such hydroxy acids are used in the enzyme catalysed process, they are used only in high concentration in order to avoid the unwanted lactonisation reaction.
Preferably the hydroxycarboxylic acid has from 2 to 14 carbon atoms, for example glycolic acid, lactic acid, 2-hydroxybutyric acid, 2-hydroxy isobutyric acid, 2-hydroxy caproic acid, 2-hydroxy isocaproic acid, citric acid or malic acid.
As used her
Taylor Alan
Thompson Julie Anne
Baxenden Chemicals Limited
Nixon & Vanderhye
Sergent Rabon
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