Patent Publication Number: US-2016244898-A1

Title: Producing a shaped article

Description:
The present invention provides a process for producing a shaped article from a sheetlike fibrous nonwoven web and an aqueous polymeric dispersion, which process comprises 
     a) incorporating an aqueous polymeric dispersion whose polymer particles comprise a polymer having a glass transition temperature Tg≧35 and ≦130° C. into a fibrous nonwoven web, then 
     b) drying the fibrous nonwoven web thus treated, 
     c) bringing the dried fibrous nonwoven web to a temperature T o  above the glass transition temperature of the polymer, and then 
     d) compressing the heated fibrous nonwoven web in a molding press whose contact faces have a temperature T u  below the glass transition temperature of the polymer to form the shaped article and effect cooling to a temperature &lt;Tg. 
     The present invention further provides the shaped articles obtainable by the present process and also for their use and a process for producing a shaped article precursor and the shaped article precursor itself. 
     Shaped articles formed from fibrous nonwoven webs and their methods of making are known (see for example Industrial Applications of Natural Fibres: Structure, Properties and Technical Applications, in particular section 19.4, 2010 John Wiley &amp; Sons, Ltd). In one common version of the process for producing shaped articles, fibrous nonwoven webs generally comprising 50 wt % of thermoplastic fibers, for example polypropylene, are heated in a first step to melt the thermoplastic fibers and then compressed in a second step to form the shaped article and cool down. 
     In a second common version of the process for producing shaped articles, the fibrous nonwoven webs, in particular fibrous nonwoven webs composed of fibers of natural origin, are drenched (impregnated) with a binder comprising an aqueous polymeric dispersion and a so-called crosslinker and the drenched fibrous nonwoven webs thus obtained are subsequently dried and brought into the desired shape by forming a thermoset binder. Aqueous binder systems comprising a polymeric dispersion and a crosslinker and also their use for producing fibrous nonwoven webs are known to the person skilled in the art, for example from EP-A 735061, EP-A 1005508, EP-A 1240205, EP-A 1234004, EP-A 1268936, EP-A 1340774, EP-A 1846524, EP-A 2072578, EP-A 2328972, WO 2011/29810 or WO 2012/117017. 
     Existing processes are disadvantageous in that, although the shaped articles of the first version are obtainable by a two-step process (1st heating, 2nd compressing), their thermal stability is not always entirely satisfactory. In the second version, shaped articles are not obtainable via a two-step process, since their binder components will have already cured in the heating step to produce a thermoset plastics material devoid of thermoformability. 
     The problem addressed by the present invention was therefore that of providing a two-step process for producing shaped articles which makes shaped articles having good thermal stability obtainable on proceeding from an aqueous polymeric dispersion. 
     The problem was solved by the process defined at the beginning. 
     For the purposes of the present invention, a fibrous nonwoven web is sheetlike fibrous layer of finite length, continuous-filament fibers or yarns of any type or origin that have been combined into a nonwoven web and bonded together in some way, in particular by mechanical consolidation or chemical bonding. 
     Fibrous nonwoven webs useful for the purposes of the present invention are obtained using natural fibers, such as vegetable, animal and mineral fibers, or manufactured fibers, in particular manufactured fibers composed of natural or synthetic polymers. Examples of vegetable fibers are cotton fibers, flax fibers, hemp fibers, kenaf fibers, jute fibers, wood fibers or sisal fibers. Examples of animal fibers are wool and other animal hairs, an example of mineral fibers is rockwool, an example of manufactured fibers of natural origin are viscose fibers and examples of manufactured fibers of synthetic origin are polyester fibers, such as polytrimethylene terephthalate, polyethylene naphthalate, polyethylene terephthalate or polybutylene terephthalate fibers and also the different polycarbonate fibers, polyolefin fibers, in particular polyethylene or polypropylene fibers, polyamide fibers, such as polycaprolactam fibers (nylon-6), polyamide fibers composed of hexamethylenediamine and adipic acid (nylon-6,6), polyamide fibers composed of hexamethylenediamine and terephthalic acid (nylon-6,T), polyamide fibers composed of para-phenylenediamine and terephthalic acid (aramid), and also mineral fibers, such as glass fibers, carbon fibers or basalt fibers. 
     It is particularly advantageous to use fibrous nonwoven webs in the present invention which are constructed of lignocellulosic fibers, such as cotton fibers, flax fibers, hemp fibers, kenaf fibers, jute fibers, wood fibers and/or sisal fibers, or mixtures thereof with thermoplastic fibers, such as polyester or polyolefin fibers. It is especially advantageous to use fibrous nonwoven webs constructed exclusively of lignocellulosic fibers, in particular hemp, kenaf, flax and/or wood fibers. The fibrous nonwoven webs are advantageously constructed of hemp and/or kenaf. 
     Fibrous nonwoven webs useful for the purposes of the present invention generally have a basis weight of ≧100 and ≦3000 g/m 2 , advantageously of ≧600 and ≦2000 g/m 2  and more advantageously of ≧800 and ≦1400 g/m 2 . 
     It is further important that the fibrous nonwoven webs can be used in the present invention not only in the form of formatted single pieces but also in the form of continuous sheets of fibrous nonwoven web. 
     The present invention employs aqueous polymeric dispersions whose polymer particles comprise a polymer having a glass transition temperature Tg≧35 and ≦130° C. 
     Aqueous polymeric dispersions are common general knowledge. Aqueous polymeric dispersions are fluidic systems comprising polymer coils, consisting of a plurality of interentangled polymer chains and known as polymer particles, dispersely distributed as disperse phase in the aqueous dispersing medium. 
     Aqueous polymeric dispersions are obtainable in particular by free-radically initiated aqueous emulsion polymerization of ethylenically unsaturated monomers. This method has been extensively described and therefore is well known to a person skilled in the art [cf. for instance Encyclopedia of Polymer Science and Engineering, Vol. 8, pages 659 to 677, John Wiley &amp; Sons, Inc., 1987; D. C. Blackley, Emulsion Polymerisation, pages 155 to 465, Applied Science Publishers, Ltd., Essex, 1975; D. C. Blackley, Polymer Latices, 2nd Edition, Vol. 1, pages 33 to 415, Chapman &amp; Hall, 1997; H. Warson, The Applications of Synthetic Resin Emulsions, pages 49 to 244, Ernest Benn, Ltd., London, 1972; J. Piirma, Emulsion Polymerisation, pages 1 to 287, Academic Press, 1982; F. Holscher, Dispersionen synthetischer Hochpolymerer, pages 1 to 160, Springer-Verlag, Berlin, 1969 and the patent DE-A 40 03 422]. In a typical free-radically initiated aqueous emulsion polymerization, the ethylenically unsaturated monomers are dispersed in the aqueous medium, generally together with chain transfer agents and dispersing assistants, such as emulsifiers and/or protective colloids, and polymerized using at least one water-soluble free-radical polymerization initiator. In the aqueous polymeric dispersions obtained, the residual levels of unconverted ethylenically unsaturated monomers are frequently reduced by chemical and/or physical methods likewise known to a person skilled in the art [see for instance EP-A 771328, DE-A 19624299, DE-A 19621027, DE-A 19741184, DE-A 19741187, DE-A 19805122, DE-A 19828183, DE-A 19839199, DE-A 19840586 and 19847115], the polymer solids content is adjusted to a desired value by diluting or concentrating, or the aqueous polymeric dispersion is admixed with further customary added-substance materials, for example bactericidal or foam- or viscosity-modifying additives. 
     In addition to these so-called primary aqueous polymeric dispersions, a person skilled in the art is also aware of so-called secondary aqueous polymeric dispersions. Secondary aqueous polymeric dispersions are aqueous polymeric dispersions which are formed by producing the polymer outside the aqueous dispersing medium, for example in a solution in a suitable nonaqueous solvent. This solution is subsequently transferred into the aqueous dispersing medium and the solvent is removed, generally distillatively, under dispersal. 
     The aqueous polymeric dispersions used according to the present invention have polymer particles comprising a polymer having a glass transition temperature Tg≧35 and ≦130° C., in particular ≧60 and ≦120° C. and advantageously ≧70 and ≦110° C. Glass transition temperature refers to the limit which the glass transition temperature approaches with increasing molecular weight according to G. Kanig (Kolloid-Zeitschrift &amp; Zeitschrift fur Polymere, vol. 190, page 1, equation 1). For the purposes of the present invention, the glass transition temperature Tg is determined by the differential scanning calorimetry method of ASTM D 3418-12 (20 K/min, mid-point measurement). 
     According to Fox (T. G. Fox, Bull. Am. Phys. Soc. 1956 [Ser. II] 1, page 123 and as per Ullmann&#39;s Encyclopädie der technischen Chemie, vol. 19, page 18, 4th edition, Verlag Chemie, Weinheim, 1980), the glass transition temperature of at most lightly crosslinked copolymers is given to good approximation by: 
       1/ Tg=x 1/ Tg 1+ x 2/ Tg 2+ . . .  xn/Tgn,    
     where x1, x2, . . . xn are the mass fractions of monomers 1, 2, . . . n and Tg1, Tg2, . . . Tgn are the glass transition temperatures in degrees kelvin of the polymers each constructed of just one of the monomers 1, 2, . . . n. The Tg values of the homopolymers of most monomers are known and are given for example in Ullmann&#39;s Encyclopedia of Industrial Chemistry, 5th edition, vol. A21, page 169, Verlag Chemie, Weinheim, 1992; further sources of glass transition temperaratures of homopolymers are for example J. Brandrup, E. H. Immergut, Polymer Handbook, 1st Ed., J. Wiley, New York, 1966; 2nd Ed. J.Wiley, New York, 1975 and 3rd Ed. J. Wiley, New York, 1989. 
     Therefore, a person skilled in the art, who will be aware of the aforementioned relationships, will find it a very simple matter to prepare or select aqueous polymeric dispersions whose polymer particles comprise an appropriate polymer having a glass transition temperature Tg in the range ≧35 and ≦130° C. 
     It is advantageous for the purposes of the present invention to use in particular aqueous polymeric dispersions whose polymer particles comprise 
     50 to 99.9 wt % of esters of acrylic and/or methacrylic acid with alkanols of 1 to 12 carbon atoms and/or styrene, or 
     50 to 99.9 wt % of styrene and/or butadiene, or 
     50 to 99.9 wt % of vinyl chloride and/or vinylidene chloride, or 
     40 to 99.9 wt % of vinyl acetate, vinyl propionate, vinyl esters of Versatic acid, vinyl esters of long-chain fatty acids and/or ethylene 
     in polymerized form and which have a glass transition temperature Tg in the range of the present invention. 
     It is particularly advantageous for the purposes of the present invention to use polymeric dispersions whose polymer particles comprise
         0.1 to 5 wt % of at least one α,β-monoethylenically unsaturated mono- and/or dicarboxylic acid of 3 to 6 carbon atoms and/or the amide thereof, and   50 to 99.9 wt % of at least one ester of acrylic and/or methacrylic acid with alkanols of 1 to 12 carbon atoms and/or styrene, or   0.1 to 5 wt % of at least one α,β-monoethylenically unsaturated mono- and/or dicarboxylic acid of 3 to 6 carbon atoms and/or the amide thereof, and   50 to 99.9 wt % of styrene and/or butadiene, or   0.1 to 5 wt % of at least one α,β-monoethylenically unsaturated mono- and/or dicarboxylic acid of 3 to 6 carbon atoms and/or the amide thereof, and   50 to 99.9 wt % of vinyl chloride and/or vinylidene chloride, or   0.1 to 5 wt % of at least one α,β-monoethylenically unsaturated mono- and/or dicarboxylic acid of 3 to 6 carbon atoms and/or the amide thereof, and   40 to 99.9 wt % of vinyl acetate, vinyl propionate, vinyl esters of Versatic acid, vinyl esters of long-chain fatty acids and/or ethylene       

     in polymerized form and which have a glass transition temperature Tg in the range of the present invention. 
     The weight-average diameter of the polymer particles present in aqueous polymeric dispersions useful in the present invention is generally in the range ≧10 and ≦1000 nm, often ≧50 and ≦500 nm or ≧80 and ≦300 nm. The solids contents of aqueous polymeric dispersions useful in the present invention are further generally ≧10 and ≦70 wt %, advantageously ≧30 and ≦70 wt % and more advantageously ≧40 and ≦60 wt %. 
     The step of incorporating the aqueous polymeric dispersion into the fibrous nonwoven web is familiar to a person skilled in the art and is effected in particular by uniform spraying with or dipping of the fibrous nonwoven web into the aqueous polymeric dispersion, or preferably by mangling a polymer dispersion foam into the fibrous nonwoven web. The amount of aqueous polymeric dispersion in the incorporating step is chosen such that from 1 to 100 g, advantageously from 10 to 50 g and more advantageously from 20 to 30 g of polymer (solids) become incorporated into the fibrous nonwoven web per 100 g of fibrous nonwoven web used (dry; moisture content &lt;10 wt %). The step of incorporating the aqueous polymeric dispersion into the fibrous nonwoven web is advantageously effected such that the distribution of the aqueous polymeric dispersion in the fibrous nonwoven web is homogeneous. 
     After the aqueous polymeric dispersion has been incorporated into the fibrous nonwoven web as per process step a), the treated fibrous nonwoven web is dried in process step b). The treated fibrous nonwoven web is dried therein by customary continuous or batch processes familiar to a person skilled in the art, as for example by heating at atmospheric pressure (1.013 bar absolute solute≡1 atm) or under a negative pressure (&lt;1.013 bar absolute), with or without passage therethrough or thereover of a dry gas stream in, for example, brine ovens, belt dryers, air-flotation dryers, drum dryers or drying cabinets. The drying temperature is generally in the range ≧50 and ≦220° C., advantageously in the range ≧90 and ≦200° C. and more advantageously in the range ≧140 and ≦180° C. at atmospheric pressure. This temperature can in principle be below, equal to or above the glass transition temperature of the polymer of the polymer particles. It is essential, however, that drying be continued until the residual moisture content of the fibrous nonwoven web obtained as per process step b) is ≦20 wt %, advantageously ≦15 wt % and more advantageously ≦10 wt %. For the purposes of the present invention, the residual moisture content shall be determined by determining the moisture content of the untreated fibrous nonwoven web in a first step by drying a sample of the untreated fibrous nonwoven web in an IR radiator (for example of the Sartorius MA 100 type) at 120° C. to constant weight. The difference in the weight of the untreated fibrous nonwoven web before and after drying is used to calculate the moisture content of the untreated fibrous nonwoven web. In a second step, then, the fibrous nonwoven web to be treated is weighed before the actual incorporation of the aqueous polymeric dispersion and the moisture content is subtracted to calculate the dry weight of the fibrous nonwoven web [F ut ]. Thereafter the aqueous polymeric dispersion, the total solids content of which and the polymer solids content of which are known, is incorporated into the fibrous nonwoven web in such an amount that the desired polymer quantity to be incorporated (and hence also the desired solids quantity [M F ]) are obtained. This is followed by drying the treated fibrous nonwoven web sufficiently in terms of intensity and duration until the weight of the dried treated fibrous nonwoven web [F bt ] at room temperature (about 20 to 25° C.) minus the sum formed by adding together the dry weight of the untreated fibrous nonwoven web [F ut ] and the total amount of solids incorporated into the fibrous nonwoven web [M F ], divided by the sum formed by adding together the dry weight of the untreated fibrous nonwoven web [F ut ] and the total amount of solids incorporated into the fibrous nonwoven web [M F ], multiplied by 100 {corresponding to (F bt −F ut −M F )/(F ut +M F )×100} is equal to a value ≦20 wt %, advantageously ≦ 15  wt % and more advantageously ≦10 wt %. 
     The dried treated fibrous nonwoven webs obtained after process step b) can be further processed directly. However, they may also be cooled down to a temperature below the glass transition temperature Tg of the polymer and be kept, parked and/or shipped to further processors—and not subjected to process steps c) and d) until later—in the form of shaped article precursors, for example formatted single pieces (shaped article blanks) or rolled-up continuous fibrous nonwoven web sheets. 
     The present invention accordingly likewise discloses a process for producing a shaped article precursor from a sheetlike fibrous nonwoven web and an aqueous polymer dispersion, which process comprises 
     a) incorporating an aqueous polymeric dispersion whose polymer has a glass transition temperature Tg≧35 and ≦130° C. into a fibrous nonwoven web, and then 
     b) drying the fibrous nonwoven web thus treated to a residual moisture content ≦20 wt %. 
     The aqueous polymeric dispersion is incorporated into the fibrous nonwoven web and the treated fibrous nonwoven web is dried as described above for process steps a) and b). The shaped article precursors obtained are cooled down to room temperature. 
     The shaped article precursors (shaped article blanks or rolled-up fibrous nonwoven web sheets) obtained by the aforementioned process are stored in individual or bundled/stacked form, advantageously in an atmosphere having a relative humidity ≦20 wt %, or sealed in gas and/or moisture tight with a protective foil. Shaped article precursors thus sealed in have an unlimited shelf-life or are easy to ship to further processors in that form. 
     The shaped article precursor obtained by the aforementioned process is used in particular for producing shaped articles by subjecting the shaped article precursor additionally to process steps c) and d). 
     However, the dried treated fibrous nonwoven webs obtained after process step b) can also be further processed directly. When the treated fibrous nonwoven web is dried at a temperature below the glass transition temperature Tg and/or the shaped article precursor has a temperature below the glass transition temperature Tg, process step c) comprises heating the dried fibrous nonwoven web to a temperature T o  above the glass transition temperature Tg of the polymer. In the event that the treated fibrous nonwoven web is dried in process step b) at a temperature above the glass transition temperature Tg of the polymer, process step c) may coincide with process step b) when the fibrous nonwoven web post drying step b) has a temperature that corresponds to the further processing temperature T o . When, by contrast, the treated fibrous nonwoven web post drying step b) has a temperature above the further processing temperature T o , the dried treated fibrous nonwoven web is cooled down to the further processing temperature T o . 
     In process step c), the dried fibrous nonwoven web is brought to a temperature T o , where T o  (in ° C.) is generally a value Tg+≧10° C., in particular Tg+≧20° C. and in particular Tg+≧50° C. It is particularly advantageous for the temperature T o  to have a value in the range Tg≦+(≧80 and ≦140)° C. 
     In one preferred embodiment, the fibrous nonwoven web is additionally precompressed to a thickness D c  in process step c), where the thickness D c  corresponds to D d +≦0.3 D d , advantageously D d +≦0.2 D d  and more advantageously D d +≦0.1 D d , where D d  is the shaped article thickness obtained on completion of process step d). In other words, the thickness D c  on cornpletion of process step c) corresponds to the final thickness D d  of the shaped article on completion of process step d) plus ≦30%, advantageously plus ≦20% and more advantageously plus ≦10% of the final thickness D d . Good thermal input (heating) is the technical benefit of precompressing. 
     Following process step c), the heated fibrous nonwoven web is transferred in process step d) into a molding press whose contact faces have a temperature T u  below the glass transition temperature Tg of the polymer, and compressed therein to form the shaped article and cooled down to a temperature below the glass transition temperature Tg. 
     The contact faces of the molding press have a temperature T u  (in ° C.) which is generally in the region Tg−(≧10)° C., advantageously Tg−(≧20)° C. and more advantageously Tg−(≧ 50 )° C. It is particularly advantageous for the temperature T u  to be in the range ≧60 and ≧100° C. below the glass transition temperature Tg. 
     The thickness D d  of the shaped article on completion of process step d) is (without decorative material) generally ≧0.5 and ≦10 mm, advantageously ≧1 and ≦7 mm and more advantageously ≧1.5 and ≦4 mm. 
     In one advantageous embodiment, the process according to the present invention further comprises a step c1) of applying a sheetlike decorative material ≦10 mm in thickness atop either and/or both of the surfaces of the heated fibrous nonwoven web after step c) and before step d). 
     Decorative material useful in the present invention comprises advantageously a textile sheet material, for example a fibrous nonwoven web fabric, a woven fabric or a knitted fabric composed of natural or synthetic fibers, a polymeric foil, for example a thermoplastic polyvinyl chloride, polyolefin or polyester foil, a foamed sheet material, for example a sheet material composed of a polyolefin foam or a polyurethane foam, or a foamed sheet material in turn coated (laminated) with a textile sheet material, a polymeric foil or a further foamed sheet material on the surface which does not come into contact with the heated fibrous nonwoven web. 
     The sheetlike decorative material is generally ≦10 mm in thickness. When the sheetlike decorative material comprises a textile sheet material or a polymeric foil, the thickness thereof is generally ≦3 mm, often advantageously ≦2 mm and often more advantageously ≦1 mm. When, however, the sheetlike decorative material comprises a foamed sheet material or a coated (laminated) foamed sheet material, the thickness thereof is frequently ≦8 mm, often ≦5 mm and particularly often ≦3 mm. 
     The process of the present invention can be carried out in a continuous or batchwise manner in steps a) to d). In one embodiment, process steps a) and b) for producing a shaped article precursor are carried out in a continuous manner. Thereafter, the process of the present invention can be interrupted. The subsequent process steps c) and d), optionally with inclusion of a process step c1, are advantageously coupled together and therefore are carried out in a continuous manner. In another embodiment, process steps a) to d), optionally with inclusion of a process step c1), are carried out in a continuous manner, i.e., the sequence of process steps a) to d) is not interrupted. 
     Following process step d), the shaped article obtained is further optionally fully cooled down to room temperature. 
     The shaped articles obtainable by the process of the present invention are very advantageously useful as structural element in vehicle construction, for example as door insert, door trim support, knee guard, glove compartment, parcel shelf, sun visor, center console, trunk lining or seat back lining, built structures, for example as room divider, dividing wall or ceiling panel, and furniture such as, for example, as sitting or backrest surface. 
     The process of the present invention will now be elucidated by the nonlimiting example which follows. 
    
    
     EXAMPLE 
     Needlepunched natural fibrous nonwoven webs consisting of 50 wt % each of hemp and kenaf fibers and having a basis weight of 1050 g/m 2  and a size of 34×28 cm were used. 
     The aqueous polymeric dispersion used was Acronal® S 940 from BASF SE, an aqueous polymeric dispersion based on styrene, n-butyl acrylate and methyl methacrylate and having a glass transition temperature Tg of 79° C. and a solids content of 50 wt %. 
     The aqueous polymeric dispersion was frothed at room temperature with a Major type Kenwood mixer into a stable foam having a density of 450 g per liter. Thereafter the polymer dispersion foam obtained was incorporated into the natural fibrous nonwoven web such that the binder quantity was 25 wt %, based on the dry weight of the fibrous nonwoven webs (solids/solids) via a horizontally operated HVF type roll stand from Mathis wherein the natural fibrous nonwoven webs passed downwardly between the rotating rolls. Thereafter the fibrous nonwoven webs obtained were dried in a circulating air drying cabinet at 90° C. to a residual moisture content of 8 wt %. 
     The fibrous nonwoven webs obtained after drying were then heated for 50 seconds in a pre-heated LaboPress P400S type press from Vogt at 180° C. and at the same time precompressed to a thickness of 2 mm. The shaped articles thus heated up and precompressed were removed from the pre-press and directly transferred into a WK P 600/3.5 type molding press from Wickert whose contact faces were at room temperature (20 to 25° C.) and compressed directly within 30 seconds into the final shaped articles which were 1.7 mm thick in their planar areas. 
     The shaped planar articles obtained (panels) were stored at 23° C. and 50% relative humidity for 24 hours and then subjected to a determination of the following parameters: density 0.86 g/cm 3− ; thickness: 1.7 mm, impact strength (as per Charpy ISO 179-1/FU, 05/2006): 16 kJ/m 2 ; modulus of elasticity (as per DIN 14125-VA, W2, 06/1998): 5150 N/mm 2 ; water absorption (as per DIN 52364, 04/1965): 45 wt %, swelling (as per DIN 52364, 04/1965): 26%. cm  1 : A method for producing a shaped article from a fibrous nonwoven web and an aqueous polymeric dispersion, the method comprising
         a) incorporating the aqueous polymeric dispersion whose polymer particles comprise a polymer having a glass transition temperature Tg≧35 and ≦130° C. into the fibrous nonwoven web,   b) subsequently drying the fibrous nonwoven web to obtain a dried fibrous nonwoven web,   c) bringing the dried fibrous nonwoven web to a temperature T o  above the glass transition temperature of the polymer to obtain a heated fibrous nonwoven web, and   d) subsequently compressing the heated fibrous nonwoven web in a molding press whose contact faces have a temperature T u  below the glass transition temperature of the polymer to form the shaped article and effect cooling to a temperature &lt;Tg.