CA2099610A1

CA2099610A1 - Process for preparing moulded articles by compressing small particles or granules based on polyisocyanate polyaddition products

Info

Publication number: CA2099610A1
Application number: CA002099610A
Authority: CA
Inventors: Joachim Wagner; Werner Rasshofer; Thomas Elsner
Original assignee: Individual
Current assignee: Bayer AG
Priority date: 1990-12-07
Filing date: 1991-11-26
Publication date: 1992-06-08
Also published as: EP0560804A1; DE4039020A1; WO1992010350A1; JPH06503044A; KR930703131A

Abstract

The invention concerns the production of moulded articles by compressing small particles or granules of polyisocyanate polyaddition products in a press at pressures of up to 1,000 bar and temperatures of up to 230 ·C. The invention enables the strength of the moulded articles to be increased by virtue of the fact that, during compression, an additional shear stress is produced between the individual particles or granules.

Description

` ~099~0 A process for preparing moulded articles by compressing small particles or granules based o~ polyisocyanate polyaddition products _ _ _ _ The invention relates to a process for preparing moulded articles by compressing small particles or granules based on polyisocyanate polyaddition products in a compression mould at pressures of up ~o 1000 bar and temperatures of up to 230C.

It is known ~EP~A 3 310 896; EP-~ 2 348 760) that moulded articles may be prepared by the e~trusion of particles based on polyisocyanate polyaddition products under the e~ect of pressure a~d hea~, as described at the beginning.
~ere, the particles for this purpose may be obtained in corresponding ~i~es directly from a reaction mi~ture being moulded or by granulating the material, either as it is produced for this purpose or as it arises during recycli~g.
Depending on the desired physical properties of the moulded articles being made, granulating of the material takes place from coarse grains down to a powder. Particles of different sizes can also be mixed. If requiredl a moulding compound may be produced from the granulated material.

Compression (hot pressing, thenmoforming, thermopressing and in particular extrusion may be referred to) generally ~akes place in compression moulds made from steel and fitted ~th sealing vertical flash faces.
`- In order for the mollldsd articles being produced to be very homogeneous the material being compressed must be distributed as uniformly as possible in the mould cavity.
During compression the particles or granules are pressed isostatically against each other and thereby are brought into direct contact. The quality of this contact largely determines the properties which can be produced in the Le A 28 054 ~ ~' .': ~ ''' ' ' '' ,' ;

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' ' ' 2~99~i9 moulded article being made. For a given material, this ~uality may be af~ected by the choice of temperature, prassure and time of compression.

There is the object of improving the known processes to the effect that, for a given material, at a given temperature, a given pressure and/or a given time of compression, the particles or granules are held together better and thus the mechanical properties of the moulded article are greatly increased.

This object is achieved when an additional shear ætress is present between the individual particles or individual granuleæ during compression.
This shear stress is achieved via a characteristic relative movement of the particles. With normal compression of a layer of uniform dep~h, however, the particles are only subject to pressure.
- Preferably, the shear stress is caused by specifically accumulating the material being compressed in one place in the mould cavity.

Surprisingly, a consider~ble improvement in the mechanical properties of the moulded article being produced has been demonstrated by this simple measure. On closing the mould and during the compression process, the material spreads out in the mould cavity, wherein the relative motion between the particles is produced. It goes without saying that in the case of larger cavities the material being compressed may accumulate at several places. It is only important to ensure that ~he desired shear stress occurs by means of adequate flow paths and adequate relative motion of the particles.

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According to one variant of the new process the shear stress is produced by extruding the particles or granules through openings in the mould cavity.

That means, in the simplest case, that the mould cavity is open at the sides. However, it is expedient to provide specific openings in order to obtain the desired flow paths~ ~oulded articles produced in this way, though, ha~e to be trimmed.
Alternatively, the same e~fect may be achieved by producing the shear stress by extruding the partiales or granules out of the mould cavity into supplementary cavities.

According to one ~urther particular way of performing the new process, the shear stress is varied over the time of compression.

Using this measure it is possible to bestow locally ~O variable properties on the moulded article.

As polyisocyanate polyaddition products may be used e.g.
those which have been prepared in single- or multi-stage processes by the reaction of a) organic polyisocyanates, b) compounds with a molecular weight between 1800 and 12000, which have a statistical a~erage o~ ak least 3 0 2 0 5 groups which react with isocyanate groups, optionally c) polyamines with at least 2 primary and/or secondary aromatically bonded amino groups, in the molecular weight range of 108 to 400, .

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and optionally d) (cyclo)alkanepolyols or (cyclo)alkanepolyamines in the molecular weight range of 60 to 1799 which optionally possess ether groups, with a NC0 reactivity of at least 2, and optionally with the joint us~ of e) the auxiliary agents and additives which are ~nown per ~e from polyurethane chemi~try, while maintaining an isoayanate index o~ 60 to 140, and optionally in addition f) fillers and/or reinforcing matarials.

Surprisingly, there are number of further advantages in addition to the better adh~sion of the particles or granules to each other associated with the process according to the invention, ~hese being improved moulded-part surfaces, especially the degree of shine, and improved mechanical characteristics with better maintenance of properties as compared wit~ the properties o~ the ungranulaked starting products.

The optional auxiliary agents and additives e~ which are used when preparing the polyisocyanate polyaddition products are for example internal mould release agents, catalysts for the polyisocyanate polyaddition reaction, lu~ricants, surface active additives, cell regulators, pigments, dyes, flame retardants, stabilisers, plasticisers or fungistatically or bacteriostatically active substances, such as are described by way of example, for instance, in EP-B 0 081 701, column 6, line 40 to column 9, line 31.

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Among the preferred auxiliary agents and additives which are optionally used are included the per se known fillers and/or reinfor~ing materials such as, for example, barium sulphate, kieselguhr, slurried calcium carbonate, mica, cellulose fibres, lignocellulose fibres, also granulated natural or synthetic rubbers, synthetic ~ibres, especially polyamide ~ibres, LC fibres, aramide fibres, inorganic fibres, especially glass fibres, glas~ flakes, glass beads, or carbon fibres, carbides, metal fibr6s, metal mats made from aluminium, steel or copper, wherein these fillers and/or rein~orciny material~ may be used in amounts o~ up to 80% by w~ight, preferably up to 50% by weight, based on the total weight of the filled or reinforced polyisocyanate polyaddition products.
The fibrous fillers may also be present in the form of woven ~abrics, mats, knitted fabrics, non-woven fabrics, gratings, grids, meshes or interlocked fabrics etc.

The fillers and reinforcing materials e) which may be used when preparing the polyisocyanate polyaddition products are also the additional fillers and reinforcing materials f) which may be incorporated in the process according to the invention. When incorporating fillers and reinforcing materials f) in accordance with the process according to the invention, it is completely irrelevant whether fillers and reinforcing materials are already present in the granulated polyisocyanate polyaddition products or not.

Crushing or granulating the polyisocyanate polyaddition products takes place in equipment which is suitable for producing small and very small parts from larger moulded articles. Suitable methods for granulating are e.g. cutting processes, tearing, chopping or granulating processes, such as are well-known to the specialist. Suitable equipment for granulating is available commercially.

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Very suitable are, for example, granulators with rotating knives and subsequent screening. Such devices are obtainable e.g. from ~he Weiss company, D 6340, Dillenburg, Germany.

Implementation of the process according to the invention, i.e. the processing of the milled ox granulated polyisocyanate addi~ion products by the action of pressure and temperature, may take place using any equipment which is suitable for this æuch as e.g. compression moulds, SMC
clamps, RIM clamps, calenders or thermoforming compression moulds. When performing the process according to the invention, however, the material does not melt, as is known to happen in the strict sense of ~thermoplastic~ plastics;
a liquid macroscopic phase of relatively low viscosity does not appear at any time.

The moulding tools to be used in the process according to the invention preferably have a vertical flash face, which facilitates a build up of pressure in the material, and cavities or open places which allow material ~o escape from the actual area of the moulded article after closing the moulding tool and applying pressure and in this way facilitates a shearing action after the actual build up of pressure.

The process according to the invention allows the preparation of moulded articles in the form of hollow bodies for inserts~ cartons, containers of various dimensions and volumes; as covers for dashboards, control panels, steering column covers; as linings for wheel guards, for plane motor vehicle body parts such as door panels, side parts, mudguards, engine compartment bonnets or boot lids; as well as for the produc~ion of hub caps, seats or seat backs. In sheet form, the products of the process according to the invention are also suitable as desk pads, display boards wi~h magnetic supports, adhesi~e -- - -6- ~ -.~ , 2~9~ ~

labels, protective sheeting and coverings for a very wide range of purposes. The products of the process according to the invention may also be used in the form of seats, seat backs, cushions, suitcases and similar con~ainers, structural parts for car bodies, chassis, reinforcement elements, sections such as e.g. frames, supports, rigid e~ternal parts of car bodies, such as mud guards or bonnets or boot lids, hub caps, reinforcement elements for screens, motor vehicle internal door cladding, doors, tail-gates, roofs and similar articles. rhey may also be compressed with wood and similar materials and then be used in car interiors. ~hey are also suitable for articles in the leisure area.

In addition, the products of the process according to the invention may be used in the form of small moulded articles as keyboard elements, rigid-elastic seals and collars, recessed grips and handles, small damping elements or plain or spacing washers, or also as reinforced and non-reinforced sections for cable ducts and sealing lips or asany other small, sturdy item.

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209~`3 a E~nple 1 Plates were prepared from the following components:

NC0 reactive component:

83.3 parts of a po~yethertriol wi~h a~ 0~l number oE
28, prepared by blockwise add~ion o~ ~irst 83%
by wt. of propylene oxide and then 17~ by wt. of ethylene oxide to krimethylolpropane with largely primary hydro~yl groups 4 parts of a mixture of 1 part of carbon black and 4 parts of a polyether with an OX number of 35, prepared by blockwise addition of first 87% by wt. of propylene oxide and then 13% by wt. of ethylene oxide to trimethylolpropane 12 parts of a mixture of 80% of 1-methyl=2,4-diamino-3,5-diethylbenzPne and 20% of 1-methyl-2,6-diamino-3,5-diethylbenzene 0.1 part of Dabco~ 33 LV, an amine catalyst from Air Products, USA
0.1 part of Fomrez~ UL 28, a tin catalyst from Witco, USA

~C0 component:

PU 0743, a commercial product from Bayer AG, D-5090 Leverkusen, Germany, based on a urethane-modified MDI with - 23% NCo and a density of 1.22 g/cm'.
The ~C0 reactive component and the NCo component were used r in the ra$io of 100:39.

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-- - - - - - -. ., 209n~10 TQ prepare the PUR granules, the plates prepared as above were granulated in a cutting granulator from Pallmann, D-S660 Zweibrucken, Type PS-4--5, with a 4 mm sc~eening insert. Impact grinders, which grind the material to a powder of c 2 mm, or even hammer mills could also be used for granulating.

The granulated material was preheated in a heating cabinet set at 180C for a period of 15 minutes and then immediately placed in a vertical flash face sheet mould.
The mould was closed and ~hen ~he pressure wa~ increased to 200 bar using a hydraulic pre~s (model 200 T from Schwabenthan, D-1000 Berlin, Germany).

The actual compression process lasted for 3 minutes at 180C. Then the plates were removed from the still warm mould. The surface of the plates showed the typical granular structure and was very smooth. An ASTM tensile specimen was taken from these plates and the tensile ~0 strength was determined as being 4.2 MPa and the elongation at breaking point was determined as being 88%, according to DIN 53 504.

The test was repeatsd using the same conditions of compression, but between compression plates which were open at the sides. In this way the particles were stressed by a shearing force. The plate-like moulded article produced in this way showed clearly visible flow lines and was only half as thick for the same amount of material. The tensile test on an ASTM tensile specimen from these plates resulted in a tensile stren~th of 8.8 MPa ~nd an elongation at breaking point of 310%.

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Pl~tes were prepared fxom the followîng componen~s:

NCO reactive component:

83~3 parts of a polyethertriol with an OH number of 35, prepared by blockwise addition o~ first 87% by wt. o~
propylene oxide and then 13% by wt. of ethylene oxide to trimethylolpropane with largely primary OH groups 4 parts of a mixture of 1 part of carbon black and 4 parts of a polyether with an OH number of 35, prepared by bloc~wise addition of first 87% by wt. of propylene o~ide and then 13% by wt~ of ethylene oxide to trimethylolpropane 12.5 parts of a mi~ture o~ 65% of 1-methyl-2,4-diamino-3,5-diethylbenzene and 35% of 1 me~hyl-2,6-diamino-3,5-diethylbenzene O.1 parts of Dabco~ 33 LY, an amine catalyst from Air Products, USA

0.1 parts of Fomrez~ UL 28, a tin catalyst from Witco, USA

NCO component:

PU 0743, a commercial product from Bayer AG, D-5090 Leverkusen, Cermany, based on urethane-modified MDI with 23% NCO and a density of lq22 g/cm3.

The NCO reactive component and the ~CO component were used in the ratio of 100:39.
Granulating and preparation for the compressioIl process and _~, 10 - . .

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the compression process itself took place as described in example 1.

The sample from moulded articles prepared using the S vertical ~lash face mould gave a tensile stxength of 13.3 MPa with an elongation at breaking point of 390%. A sample from the moulded article prepared between two compression plates which were open at the sides had a tensile strength of 16.3 MPa with an elongation at breaking point of 440%.

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Claims

Patent Claims

1. A process for preparing moulded articles by.
compressing small particles or granules based on polyisocyanate polyaddition products in a compression mould under the action of pressures up to 1000 bar and temperatures up to 230°C, characterised in that an additional shear stress occurs between the individual particles or the individual granules during compression.

2. A process according to Claim 1, characterised in that the shear stress is caused by specific accumulation of the material to be compressed at a place in the mould cavity.

3. A process according to Claim 1, characterised in that the shear stress is produced by extruding particles or granules through openings in the mould cavity.

4. A process according to Claim 1, characterised in that the shear stress is produced by extruding particles or granules out of the mould cavity into supplementary cavities.

5. A process according to one of Claims 1 to 4, characterised in that the shear stress is varied over the time of compression.