Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2000-07-19
2004-03-30
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S480000, C428S481000, C428S483000, C156S332000, C524S306000, C524S311000, C525S411000, C525S438000, C525S440030, C525S444000
Reexamination Certificate
active
06713184
ABSTRACT:
This invention relates to an adhesive and to its use, more particularly in the production of a composite material, for example for a composite material containing at least one nonwoven.
Adhesives are increasingly entering many areas of daily life because, in general, they represent a simple, permanent and safe method of fixing materials. In the production of composite materials in particular, adhesives have been successfully used in the creation of durable bonds. Whereas the bonding of materials with a relatively polar structure and hence generally with a relatively polar surface to one another generally presents no difficulties under normal circumstances, the bonding of materials with a substantially nonpolar surface is generally problematical. However, even greater difficulties can be involved in the bonding of substantially nonpolar materials to polar materials because the adhesive to be used is intended to show adhesion to both materials despite their different polarities.
Accordingly, problems in the production of composite materials can arise, for example, when at least one of the materials to be bonded is a polyolefin. Polyolefins generally show poor adhesion to many adhesives so that polyolefin materials are difficult and, in some cases, impossible to bond to one another or to other materials in composite materials.
Composite materials of the type used in particular in the field of personal hygiene are mostly materials with a limited useful life which, for example, are discarded after being used only once, more particularly disposable products. Accordingly, since the space available for waste disposal is decreasing, increasing interest is being shown in composite materials which have at least one at least substantially biodegradable constituent in order to preserve waste disposal space in the long term.
There is an increasing trend towards at least partly biodegradable systems, particularly in the case of such articles as packs, packaging foams, bonding materials, films, bags, medical articles, for example plasters or bandages, or hygiene articles, for example diapers, tampons and sanitary napkins. Since articles such as these are often composed of various materials and, generally, comprise at least one bond, it is desirable with a view to improving their biodegradability for the adhesive bond itself to be at least substantially biodegradable while, at the same time, enabling even different materials to be reliably bonded.
Thus, WO 97/04036 describes an adhesive containing polyhydroxy-alkanoates as biodegradable (co)polymers. The adhesive is suitable both for the production of nonwovens and for the production of absorbent materials of the type used, for example, in sanitary articles.
EP-A-0 705 895 relates to a starch-based hotmelt adhesive and to its use for bonding nonwovens to similar or different substrates. The adhesive contains 20 to 60% by weight of a starch ester with a medium or high degree of substitution. If the adhesive in the composite material is contacted with water at a certain temperature, the nonwoven can be separated from the substrate.
EP-A0 741 177 relates to biodegradable hotmelt adhesives of polylactides. This document makes particular mention of polyhydroxybutyrate/polyhydroxyvalerate polymers which contain sucrose benzoate as tackifier. The hotmelt adhesives are used for bonding packs, for example paperboard articles, in book binding and for the production of fabric-based composites or disposable sanitary articles.
EP-A-0 741 178 relates to biodegradable hotmelt adhesives of polyesters which contain at least one hydroxy group per recurring unit. The described polyesters are combined with such additives as tackifiers, plasticizers or stabilizers. The polyesters are prepared by reacting dicarboxylic acids with diglycidyl ethers.
Where they are used as adhesives, the biodegradable polymers known from the prior art have disadvantages which prevent or at least restrict their use in various fields, particularly when the adhesive is expected to meet stringent thermal or mechanical stability requirements. Thus, polyhydroxybutyrates, polyhydroxyvalerates and polylactides, for example, show poor mechanical and thermal stability by comparison with conventional hotmelt adhesives which makes them appear unsuitable for high-temperature applications and imposes exacting demands on processing in the melt. In addition, many biodegradable adhesives form bonds with inadequate strength at low temperatures.
Accordingly, a first problem addressed by the present invention was to provide an adhesive which would form a strong bond between materials of which at least one contains a polyolefin, even in cases where dermatologically compatible coatings are used in hygiene products.
Another problem addressed by the present inven,ion was to provide an adhesive for the production of composite materials which would be at least partly biodegradable, would satisfy stringent mechanical and thermal stability requirements, would establish a strong adhesive bond even at low temperatures and would lend itself to production from readily accessible, commercially available raw materials, for example in conventional polycondensation reactors.
These problems have been solved by an adhesive which contains components A and B, components A and B being polyesters with different properties and/or different compositions as described in more detail hereinafter.
Accordingly, the present invention relates to an adhesive containing components A and B in which
a) component A contains at least one polyester with a molecular weight (M
n
) of at least 8000 and has a total enthalpy of fusion of at most 20 mJ/mg and
b) component B contains at least one polyester with a molecular weight (M
n
) of less than 8000 and, more particularly, in the range from 1000 to 6500 and a glass transition temperature of at most 60° C. and, more particularly, in the range from −10 to 40° C.,
the adhesive having a melt viscosity of 500 to 25,000 mPas (Brookfield RVT DVII, 140° C., spindle 27) and a softening point of 70 to 100° C. (ASTM E28).
In the context of the present invention, a polyester is understood to be a polymer which can be obtained either by ring-opening polymerization of lactones or by polycondensation of hydroxycarboxylic acids or by polycondensation of polyols and polycarboxylic acids, preferably diols and dicarboxylic acids, optionally with a small percentage content of trifunctional or higher alcohols and/or carboxylic acids.
Terms used in the present specification are defined in the following.
The term “amorphous” applies to polymers which have only a very small percentage content, if any, of crystalline structures, i.e. are substantially isotropic. Accordingly, “amorphous” polymers are polymers which, in differential thermoanalysis (DTA, normally differential scanning calorimetry—DSC), show no melt transition or which have an enthalpy of fusion of less than 20 mJ/mg, preferably less than 15 mJ/mg and more preferably less than 10 mJ/mg. Accordingly, these polymers may have enthalpies of fusion of, for example, 18, 17, 16, 14, 13, 12, 11, 9 or 8 mJ/mg. However, the values measured for. the enthalpy of fusion of the particular polymer may even be lower, for example 5, 4, 3 or 2 mJ/mg or less. In one preferred embodiment, the enthalpy of fusion of such a polymer is around 0 mJ/mg. Another criterion which the expert may use to judge whether a polyester is amorphous is the diffraction of X-rays, electron beams or neutron beams at solids.
The term “partly crystalline” means that the corresponding polymer contains crystalline structures, i.e. is not completely isotropic. Typically, these polymers are polymers which, in differential thermoanalysis (DTA, normally differential scanning calorimetry—DSC), show a melt transition of which the enthalpy of fusion is greater than 20 mJ/mg.
The “glass transition temperature” is the term normally used in polymer chemistry for the temperature at which molecular movements of relatively large chain segments can be detected in a polymer. In general, the detectable lower
Eisenberger Heike
Ferencz Andreas
Fischer Herbert
Taal Eduard F.
Carmen Michael F.
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Short Patricia A.
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