Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1996-09-12
2002-10-01
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S094000, C521S040500, C524S564000, C525S328200, C525S330200, C528S489000
Reexamination Certificate
active
06458230
ABSTRACT:
This invention relates to a process for preparing recyclable fiber composites by bonding the fibers together by means of a polymeric bonding agent.
A significant obstacle to the universal recycling of industrial goods is the nonunitary nature of their materials of construction. Moldings or composites coated with paint or plastic where the components are difficult to separate present a particular problem. Frequently, these materials are difficult or impossible to recycle and therefore have to be disposed of in a costly manner. The material re-use of post-use goods or off-cuts from the manufacture of consumer goods is very attractive for processors. Consequently, the substantial conversion of post-use parts with various compositions into new parts of the same type has not only appreciable economic but also environmental significance.
To enhance their resistance to mechanical stress, fibrous structures are consolidated with bonding agents to form fiber composites. These bonding agents, also known as bonders or binders, may take the form of, for example, dispersions and be used in that form. The enhanced strength results from the bonding-together of the fibers by the filming (film-forming) polymers which adhere to the fiber and thus reinforce the fibrous structure. In numerous applications, this polymer film has to be sufficiently stable to contact with water in order that the gross fiber-bonder assembly or composite may have adequate mechanical strength in the wet state, too.
Of interest from a recycling point of view are for example the stamping or cutting wastes from the formating of bonder-consolidated nonwoven articles, the fiber and also bonder fraction of which are lost for the further production process. Examples are wastes from the manufacture of interlinings for textile applications, diapers or sanitary protection articles. Products of this kind are soft and flexible. A further concern is the recycling of consumer goods such as the interior trim of motor vehicles, wheel arch trim, parcel shelves and other, comparable parts comprising loadbearing articles comprising binder-containing, pressed materials. Products of this kind are rigid, molded, inflexible and generally thermoplastically (de)formable. A further concern is the recycling and also re-use of textile floor coverings, carpet materials or fitted carpets and carpet tiles. These sheetlike materials usually consist of needled or bonder-consolidated fibrous materials with a foam backing containing a high proportion of filler-containing foamed latex. Products of this kind are less flexible, but not rigid.
The parts in question here are fiber composites in which the fibers are bonded with thermosetting or thermoplastic binders and densified and consolidated by means of pressure and heat. The mechanical separation of such a fiber composite would inescapably lead to a destruction of the fiber itself or of the bonding agent polymer, so that the recovered material could not be used to fabricate a new part having equivalent production and structural component properties.
Such fiber composites are in particular nonwovens (see Ullmann's Enc. d. techn. Chem.), in particular in the form of thermoformable needle-felt carpets, as used for example in the automotive industry. It is known to recycle such nonwovens by dissolving the polymeric binder out of the nonwoven and recovering the fiber web obtained (DE-A-43 15 875). The disadvantage of this process is the disposing of the binder solution. EP-A-0 576 128 discloses dispersion mixtures in particular for adhesives which are suitable for repulping without tackiness. These mixtures can also be used for adhering nonwoven textiles. When used for impregnating nonwovens, the latter lack wet strength and disintegrate on contact with neutral water. EP-A-0 538 625 discloses textile floorcoverings produced by needling a backing layer onto a raw state material and impregnating the backing layer with a latex dispersion. This dispersion can be dissolved out of the floor covering with the aid of a solvent. However, industrially practical recycling of the floor coverings is not possible as a result. U.S. Pat. No. 3,843,321 describes a process for recovering fibers from nonwovens by treating the latter with an aqueous solution of an alkali metal hydroxide and an organic solvent at elevated temperature. It is true that the fibers are hardly damaged, but the bonding agent polymer is completely destroyed. EP-B-0 518 004 discloses a recycling process for glass matt reinforced thermoplastics wherein the material is comminuted and pulverized. The powder is used in mixture with a resin as hardener as bonding agent for textile fibers or textile web. EP-A-0 547 533 discloses using recyclable components in the manufacture of a textile floor covering. Possible recycling operations mentioned are comminuting, melting and renewed extrusion or depolymerization. Finally, EP-A-0 316 676 discloses a dissoluble adhesive film where the dissolved copolymer is obtained by acidification in small lumps or clumps which are separated from the aqueous system by a simple mechanical separating operation.
It is an object of the present invention to provide bonding agents which meet the otherwise required properties, but are easily and completely removable from the fibers and thereafter re-usable, so that not only the fibers but also the bonding agents themselves can be recycled into the original production process.
We have found that this object is achieved according to this invention on using a bonding agent comprising an aqueous addition polymer dispersion comprising, in a state of dispersion, an addition polymer fraction which films at use temperature with the proviso that the total amount of the addition polymer fraction of the aqueous addition polymer dispersion which films at use temperature and is present in the aqueous addition polymer dispersion in a state of dispersion is converted into an aqueous addition polymer solution when the pH of the aqueous dispersing medium is changed. In an embodiment of the process of this invention, the aqueous addition polymer dispersion's addition polymer fraction which films ad use temperature has protic acid groups and its state of dispersion in the aqueous medium is converted into an aqueous addition polymer solution by raising the pH of the aqueous medium. In another embodiment of the process of this invention, the aqueous addition polymer dispersion's addition polymer fraction which films at use temperature has (basic groups, in particular amino groups, and its state of dispersion in the aqueous medium is converted into an aqueous addition polymer solution by lowering the pH of the aqueous medium. In a specific embodiment of this invention, the fraction which films at use temperature is free-radically polymerized from the following:
A) from 50 to 99% by weight of one or more monomers A selected from the group comprising (meth)acrylic esters, vinyl esters, aromatic vinyl compounds, vinyl ethers, ethylenically unsaturated nitrites, olefinic hydrocarbons; and
B) from 1 to 50% by weight of one or more water-soluble monomers B selected from the group comprising ethylenically unsaturated carboxylic acids, organic ethylenically unsaturated sulfonic acids, organic ethylenically unsaturated carboxamides, N-methylol compounds of ethylenically unsaturated carboxamides and hydroxyalkyl (meth)acrylates.
The filming addition polymer fraction is prepared in the presence of from 0.01 to 10% by weight, based on A+B, of a substance which regulates the free-radical polymerization reaction.
This invention accordingly employs as bonding agents aqueous addition polymer dispersions whose films are soluble either in an alkaline aqueous medium (in the case of dispersion addition polymers containing protic acids as copolymerized units) or in an acidic aqueous medium (in the case of dispersion addition polymers containing basic compounds, for ex ample amines, as copolymerized units) and make it possible to regenerate the bonding agent dispersion by reversing the adjustment of the pH of
Kirchner Werner
Morrison Bradley Ronald
Offner Roland
Rupaner Robert
Schumacher Karl-Heinz
BASF - Aktiengesellschaft
Gallagher John J.
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