WO1997030098A1

WO1997030098A1 - Process for binding cork

Info

Publication number: WO1997030098A1
Application number: PCT/EP1997/000355
Authority: WO
Inventors: Stefan Emiel Jozef Ghislain Priemen
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1996-02-19
Filing date: 1997-01-27
Publication date: 1997-08-21
Anticipated expiration: 1998-08-19
Also published as: ZA971288B; TNSN97038A1; ID15962A; AU1595497A; MA24086A1

Abstract

Process for binding cork comprising the steps of a) bringing cork material in contact with a polyisocyanate composition and b) subsequently allowing said cork material to bind, wherein said polyisocyanate composition comprises an isocyanate-containing prepolymer composition having an NCO content of from 2 to 25 % by weight as obtainable by reacting an isocyanate-reactive polymer composition having an average nominal functionality of from 1.8 to 6, and an average equivalent weight of from 500 to 7000 with a stoichiometric excess of a diphenylmethane diisocyanate composition.

Description

DESCRIPTION

PROCESS FOR BINDING CORK

This invention relates to a process for binding cork and in particular a process for binding cork using isocyanate-containing prepolymers as binders.

The use of organic polyisocyanates as binders for lignocellulosic material such as cork in the manufacture of sheets or moulded bodies such as cork panels or cork bottle stoppers is well known.

In a typical process the organic polyisocyanate, optionally in the form of a solution, dispersion or aqueous emulsion, is applied to the lignocellulosic material which is then subjected to heat and pressure.

As polyisocyanates aliphatic, cycloaliphatic and, preferably, aromatic polyisocyanates are used as are their partial reaction products with isocyanate-reactive compounds such as polyols (so-called prepolymers) .

We have now found that certain prepolymers based on diphenylmethane diisocyanate (MDI) are particularly suitable for binding cork.

Therefore the present invention provides a process for binding cork comprising the steps of a) bringing said cork in contact with a polyisocyanate composition and b) subsequently allowing said cork to bind, wherein the polyisocyanate composition comprises an isocyanate-containing prepolymer composition having an NCO content of from 2 to 25 % by weight, preferably 2 to 15 %, most preferably 2 to 7 % by weight as obtainable by reacting an isocyanate-reactive polymer composition having an average nominal functionality of from 1.8 to 6, preferably 2 to 4, and an average equivalent weight of from 500 to 7000 with a stoichiometric excess of a diphenylmethane diisocyanate (MDI) composition.

The term "nominal functionality" refers to the functionality, with respect to isocyanates, that an isocyanate-reactive polymer would be expected to have with regards to its monomeric components. Thus, for a polyether polyol, the average nominal functionality is the average functionality (number of active hydrogen atoms) of the initiator or initiators used in its preparation.

The diphenylmethane diisocyanate composition used to make the prepolymers can contain so-called polymeric MDI which is a mixture of diphenylmethane diisocyanates and higher functional oligomers thereof. Thus mixtures can be used containing pure MDI and so-called polymeric MDI. The average isocyanate functionality of the MDi composition is preferably from 2 to 2.3 although higher functionality MDI compositions can be used as well.

Preferably the MDI composition contains at least 60 %, preferably 100 % by weight of difunctional MDI's: 2,4*-, 2,2*- and 4,4'-isomers of diphenylmethane diisocyanate and mixtures thereof.

In a process where heat is used to bind the cork the MDi composition preferably contains at least 60 % , preferably at least 85 % and more preferably at least 95 % on a weight basis of diisocyanate components of

4,4'-diphenylmethane diisocyanate. Suitable isocyanates therefore include isomer mixtures containing not more than 40 %, preferably not more than

30 %, and more preferably not more than 20 % by weight of the 2, '-isomer and not more than 5 % by weight of the 2,2'-isomer.

In the case of moisture curing of the cork MDI compositions containing higher amounts of the 2,4'-isomer are preferred.

Unmodified forms of MDI can be used as well as modified forms that is to say MDI modified in known manner by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine or isocyanurate residues. These so- called MDI variants particularly include uretonirmne-modified MDI having NCO contents of at least 25 % by weight and polyether-based prepolymers having NCO contents of at least 20 % by weight.

Still further diphenylmethane diisocyanate compositions which may be used n preparing the prepolymer include mixtures of the above described MDI types and up to 20 % by weight of another polyisocyanate or mixture of polyisocyanates. Other polyisocyanates which may be used in admixture with the MDI include aliphatic, cycloaliphatic and araliphatic polyisocyanates, especially dusocyanates, for example hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-1,4-dιιsocyanate, 4,4'-dicyclohexylmethane dusocyanates and m- and p-tetramethylxylene dusocyanates and, especially, aromatic polyisocyanates such as tolylene dusocyanates and phenylene dusocyanates.

The average nominal functionality of the isocyanate-reactive polymer is preferably 2 to 4, more preferably 2 to 3. Preferred average equivalent weights lie in the range from 1000 to 5000.

Mixtures of two or more isocyanate-reactive polymers varying in functionality, equivalent weight and/or chemical constitution (end groups or backbone) may be used provided such mixtures conform to the average functionality and average equivalent weight criteria specified herein.

Also some isocyanate-reactive polymers having functionalities and equivalent weights net within the specified ranges can be used.

Thus, for example, isocyanate-reactive polymers known for use in the manufacture of rigid polyurethane foams having functionalities of 2 to 8 and equivalent weights of 10 to 750 can be used provided the total isocyanate- reactive composition conforms to the average functionality and average equivalent weight criteria specified herein.

Isocyanate-reactive groups which may be present m the isocyanate-reactive polymer include primary amine, secondary amine, thiol, carboxy, enamino and, especially, hydroxyl groups.

Particularly important isocyanate-reactive polymers include polymeric polyols. Suitable polyols and methods for their preparation have been fully described in the prior art and, as examples of such polyols, there may be mentioned polyesters, polyesteramides, polythioethers, polycarbonates, polyacetals, polyolefms, polysiloxanes"and, especially, polyethers.

Polyether polyols which may be used include products obtained by the polymerisation of a cyclic oxide, for example ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran in the presence, where necessary, of polyfunctional initiators. Suitable initiator compounds contain a plurality of active hydrogen atoms and include water and polyols, for example ethylene glycol, propylene glycol, diethylene glycol, cyclohexane dimethanol, resorcmol, bisphenol A, glycerol, tnmethylolpropane, 1,2,6- hexanetπol or pentaerythritol. Mixtures of initiators and/or cyclic oxides may be used.

Especially useful polyether polyols include polyoxypropylene diols and triols and poly(oxyethylene-oxypropylene) diols and triols obtained by the simultaneous or sequential addition of ethylene and propylene oxides to di- or trifunctional initiators as fully described in the prior art. Random copolymers having oxyethylene contents of 10 to 80 S, block copolymers having oxyethylene contents of from 2 to 30 ϊ, preferably from 5 to 25 % and random/block copolymers having oxyethylene contents of up to 50 %, based on the total weight of oxyalkylene units may be mentioned. Mixtures of the said diols and triols can be particularly useful. Other particularly useful polyether polyols include polytetramethylene glycols obtained by the polymerisation of tetrahydrofuran. Particularly useful are also mixtures of polypropylene-polyethylene oxide polyols with up to 5 ^■ of another polyol, for example a polyalkylene oxide, a polyester polyol, a polycarbonate polyol, a polyacetal polyol or a polytetramethylene glycol.

A particularly interesting category of polyol components consists of polyether polyols having an average oxyethylene content of from 10 to 25 _* by weight of total oxyalkylene residues due to the presence therein of at least one polyoxyalkylene polyol containing oxyethylene (ethylene oxide) residues. Preferred polyol components comprise at least one poly(oxyethylene-oxypropylene) polyol each having an oxyethylene content in the range from 10 to 25 % on a weight basis of total oxyalkylene residues. Other useful polyol components in this category contain a mixture of polyols including polyols, for example poly(oxyethylene-oxypropylene) polyols, polyoxypropylene polyols and/or polyoxyethylene polyols, having oxyethylene contents outside the 10 to 25 % range provided the overall oxyethylene content of the component is within the specified range. Such mixtures may optionally contain one or more poly(oxyethylene-oxypropylene) polyol having an oxyethylene content in the 10 to 25 % range. In addition to the possibility of using mixtures of polyols varying in oxyethylene content, mixtures of two or more polyols varying in functionality, equivalent weight and/or polymer backbone may be used provided such mixtures conform to the average functionality and average equivalent weight criteria specified herein.

Polyester polyols which may be used include hydroxyl-terminated reaction products of polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1, -butanediol, neopentyl glycol, 1, 6-hexanediol, cyclohexane dimethanol, bis (hydroxylethyl) terephthalate, glycerol, trimethylolpropane, pentaerythritol or polyether polyols or mixtures of such polyhydric alcohols, and polycarboxylic acids, especially dicarboxylic acids or their ester-forming derivatives, for example succinic, glutaric and adipic acids or their dimethyl esters, sebacic acids, phthalic anhydride, tetrachlorophthalic anhydride or dimethyl terephthalate or mixtures thereof. Polyesteramides may be obtained by the inclusion of aminoalcohols such as ethanolamine in polyesterification mixtures. Polyesters obtained by the polymerisation of lactones, for example caprolactone, in conjunction with a polyol, or of hydroxy carboxylic acids such as hydroxy caproic acid, may also be used.

Polythioether polyols which may be used include products obtained by condensing thioglycol either alone or with other glycols, alkylene oxides, dicarboxylic acids, formaldehyde, amino-alcohols or aminocarboxylic acids.

Polycarbonate polyols which may be used include products obtained by reacting diols such as 1, 3-propanediol, 1, -butanediol, 1,6-hexanediol, diethylene glycol or tetraethylene glycol with diaryl carbonates, for example diphenyl carbonate, or with phosgene.

Polyacetal polyols which may be used include those prepared by reacting glycols such as diethylene glycol, triethylene glycol or hexanediol with formaldehyde. Suitable polyacetals may also be prepared by polymerising cyclic acetals.

Suitable polyolefin polyols include hydroxy-terminated butadiene homo- and copolymers and suitable polysiloxane polyols include polydimethylsiloxane diols and triols.

Other useful isocyanate-reactive polymers for preparing the prepolymers include polymeric polyamines, especially diamines and triamines, corresponding to the above described polymeric polyols. Suitable polyamines of polyether polyols as described, for example, in US-P-3654370 or may be obtained by cyanoethylation of polyols followed by hydrogenation. Polyoxypropylene diamines and triamines and mixtures thereof are preferred. Also useful are polymers containing both amino and hydroxyl groups obtained by the partial amination of polyols.

Further isocyanate-reactive polymers which may be used in preparing the prepolymers include imino-functional polymers. Such polymers have been described in US-P-4794129 together with methods for their preparation and include polymers terminating in imine, oxazoline, imidazoline, N-alkyl imidazoline, oxazine, diazine, imino-ester, amidine, imidine, isourea and guanidine groups. The preferred imino-functional polymers are imine- terminated polyethers such as may be obtained, for example by reacting a polyether polyamine, especially a polyoxypropylene diamine or triamine, with an aldehyde or ketone.

Enamine functional polymers may be prepared either from secondary amine terminated resins (i.e. polyethers) by reaction with ketones/aldehydes having one or more alpha hydrogens, or by reacting ketone/aldehyde terminated resins (bearing alpha hydrogens) with secondary amines, providing for removal of the water formed in the reactions. Secondary amine terminated resins can be obtained, for example by catalytic hydrogenation of the imino-functional polymers described hereinabove. Ketone/aldehyde terminated resins may be obtained, in general, by oxidation of the corresponding secondary or primary hydroxyl terminated resin. More highly enamine functional polymers can be prepared by oxidising a primary hydroxy functional resin to the corresponding polycarboxylic acid, conversion of the said groups to orthoesters, end treatment of the latter, with an excess of a secondary amine. Each orthoester must contain at least one alpha hydrogen atom.

The isocyanate-terminated prepolymer may be prepared by reacting the diphenylmethane diisocyanate composition with the isocyanate-reactive polymer under conditions that have been fully described in the prior art for the preparation of prepolymers. To achieve a final NCO content within the specified range, an initial ratio of isocyanate to isocyanate-reactive groups (for example NCO/OH) would typically be within the range from 3:1 to 20:1. Preferred prepolymers are made by reacting the starting materials at initial ratio of isocyanate to isocyanate-reactive groups in the range 3.5:1 to 15:1, especially 4:1 to 10:1, to give prepolymers having NCO contents of 4 to 12 S.

The viscosity of the prepolymer for use in the present process is preferably between 1500 and 8000 cP but can be higher as well.

In US 4692292 an isocyanate prepolymer containing 4.5 % NCO groups is used to produce a cork panel; no further characteristics of the isocyanate prepolymer are given.

The lower volatility of MDI relative to TDI is an advantage to the use of MDI prepolymers in the present process from the industrial hygiene point of view. In terms of resilience and flexibility similar properties as with TDI prepolymers are obtained.

The moulded cork bodies are prepared by bringing the cork into contact with the polyisocyanate composition like by means of mixing, spraying and/or spreading the composition with/onto the cork parts and by pressing the combination of the polyisocyanate composition and the cork parts, preferably by hot-pressing although curing at room temperature is possible as well. Such binding processes are commonly known in the art.

Granulated cork material is fed into a mixer, e.g., a horizontal helicoidal mixer, mixing extruder or conventional mixing equipment for production of composites. A well defined quantity of polyisocyanate adhesive is slowly poured over the granulates or fed into the extruder, while continuing mixing or blending, in order to obtain a homogeneous distribution of the binder and to obtain a uniform mixture. Mixing time can range from a few seconds to 20 minutes. Some water or hydrophobic waxes may be added. Depending on the shape of the final body, moulds are filled by extrusion or by pouring the treated cork material into them and cured under pressure. Temperature and moisture level determine the cure time.

Moisture level may vary between 2 and 20 i . Temperature may vary between 20 and 150°C.

The polyisocyanate composition for use in the present process may contain conventional additives such as release agents.

External release agents applied to the mould before filling can be used as well. The polyisocyanate compositions may be applied in such amounts to give a weight ratio of polyisocyanate/cork material in the range of 0.1:99.9 to

30:70 and preferably in the range of 0.5:99.5 to 10:90.

Density of the obtained cork bodies is usually in the range 250 to 750 kg/m³.

The cork bodies can be in the form of blocs which are cut into panels for use e.g. as floor tiles or in the form of stoppers for bottles.

More detailed descriptions of methods of manufacturing moulded bodies based on cork are available in the prior art. The techniques and equipment conventionally used can be adapted for use with the polyisocyanate compositions of the present invention.

The invention is illustrated but not limited by the following examples.

EXAMPLE 1

MDI prepolymers were made from pure 4, '-MDI and various polyols at different NCO values. The polyols used and the NCO value of the obtained prepolymers are given in Table 1.

Polyol 1 is a polyoxyalkylene polyol of molecular weight 6000 and average functionality 2.3, initiated with a triol; oxyethylene content is 15 % . Polyol 2 is a polyoxyalkylene polyol of molecular weight 3740 and average functionality 1.8, initiated with a diol; oxyethylene content is 15 %. Polyol 3 has a molecular weight of 2000 and average functionality 2; Arcol 1020 available from ARCO Chem Corp.

Table 1

Prepolymer No. Polyol No. NCO value (%)

1 3 5

2 1 5

3 2 5

4 2 4

5 2 6

6 2 7

The MDI-prepolymers were mixed with cork at a loading of 25 % on cork weight basis. An ANCHOR mixer was used to distribute the prepolymer on the cork. The prepolymer was added while the cork was stirred in a bucket.

Cork mats of 14 x 14 x 0.5 cm and density 450 kg/m³ were made using a pressure of 100 bar, a temperature of 125°C and a press time of 3 minutes.

Tensile strength of the obtained cork mats was measured according to standard DIN 53571.

Results are presented in Table 2.

Table 2

Prepolymer No. Tensile strength (MPa)

4 0.839

3 0.832

5 1.125

1 0.632

2 1.635

These results show that the tensile strength of the cork bodies varies with the NCO content of the MDI prepolymer (prepolymer 4, 3 and 5) , an NCO content of 6 % giving the highest strength and varies with the functionality of the polyol used to make the prepolymer (prepolymer 1,3 and 2), the highest functionality leading to the strongest bodies.

EXAMPLE 2

Prepolymers as listed in Table 3 were made using the following procedure:

- the polyisocyanate was melted out at 80-85°C for 1 hour and stored in an oven at 40°C;

- the polyol was preheated to 40-45°C;

- the polyisocyanate was weighed in a reaction vessel and heated to 60°C under constant stirring;

- the polyol component was added to the polyisocyanate over a 30 min period gradually heating the reaction mixture up to 85^βC;

- the reaction mixture was heated and stirred for a further two hours to let reaction take place;

- the reaction mixture was cooled down to 60^CC and poured into a storage container.

The products used were:

As polyisocyanate: SUPRASEC MPR (NCO_v=33.4) which is an MDI diisocyanate containing at least 97.5 wt% 4,4'-MDI; available from Imperial Chemical

Industries; As polyols: Polyol 1, Polyol 2 and Polyol 3 as described in Example 1 above.

The prepolymers were mixed with the cork granules on a 25 % weight ratio to the cork weight. Cork granules were stirred with an anchor mixer in a bucket while dripping in the isocyanate prepolymer.

After mixing a pre-mat was formed having following dimensions 140 x 140 x

20 mm³, which was then compressed to a thickness of 5 mm. Pressing conditions: see Table 3.

As release agent Pural IMR (available from Air Products) was used sprayed on an aluminium-foil which separates press plates from cork mat.

The cork mats were tested by means of a tensile test performed on a dumb¬ bell shaped sample (standard DIN 53571) . Three samples were tested from each mat. The results are presented in Table 3.

Table 3

Polyol Ratio NCO Viscosity Tensile Pressing Conditions Polyol/Isocyanate (dumb-bell) Temp. Time

(pbw/pbw) (%) (cPs) (MPa) (°C) (min. )

Polyol 3 243.6/756.4 5 6780 0.632 125 3

Polyol 2 204.9/795.1 5 5200 0.832 125 3

Polyol 1 199.0/801.0 5 8760 1.635 125 3

Polyol 2 177.0/823.0 4 0.839 125 3

Polyol 2 232.7/767.3 6 1.125 125 3

Polyol 2 204.9/795.1 5 5200 0.299 100 2 0.512 100 3 0.519 100 4

Polyol 2 204.9/795.1 5 5200 0.561 125 2 0.832 125 3 0.780 125 4

Polyol 2 204.9/795.1 5 5200 0.572 150 2 0.549 150 3 0.578 150 4 EXAMPLE 3

Prepolymers were made using the procedure described above in Example 2.

Base products used:

Industries.

As polyols:

- Polyol 1 as described in Example 1;

- Polyol 4 being a polyoxyalkylene polyol of molecular weight 5250 and average functionality 2.4, initiated with glycerol;

- Polyol 5 being a polyoxyalkylene polyol of molecular weight 2158 and average functionality 1.9, initiated with diethyleneglycol;

- Polyol 6 being a polyoxyalkylene polyol of molecular weight 300 and average functionality 2.9, initiated with sorbitol.

The prepolymers were mixed with the cork granules on a 12 % weight ratio to the cork weight. Mixing was done by dripping the prepolymer into the granules under constant stirring.

After mixing the cork was compressed in a mould to a density of 500 kg/m³ and cured in an oven at 100°C for 1 hour. Samples were demoulded the day after.

The samples were subjected to a tensile and compression/recovery test according to standard ISO 7322. The results are presented in Table 4.

Table 4

Polyisocyanate Polyol Ratio NCO Viscosity Compressibility Recovery Tensile

Polyol/Polyisocyanate

/Polyol

(pbw/pbw) (%) (cPs) ⁽%) (%) (MPa)

SUPRASEC MPR Polyol 1 143.6/856.4 3 23000 13.9 79.6 2.14

SUPRASEC MPR Polyol 1 199.0/801.0 5.03 7800 15.1 77.8 2.38

SUPRASEC MPR Polyol 1 256.3/743.7 7 4880 16.1 76.3 2.48

SUPRASEC MPR Polyol 1 340.8/659.2 10 2550 16.4 70.3 2.61

SUPRASEC MPR Polyol 4 206.6/793.4 5 10200 17 81.5 2.38

SUPRASEC MPR Polyol 5 238.5/761.5 5 19800 17.5 77.8 2.37

SUPRASEC MPR Polyol 1 + 19.9/80.1/5 3.78 — 16.5 87.4 2.092 Polyol 6

SUPRASEC MPR polyol 1 + 34.1/65.92/5 7.15 17.7 82.9 2.286 Polyol 6

Claims

1. Process for binding cork comprising the steps of a) bringing cork material in contact with a polyisocyanate composition and b) subsequently allowing said cork material to bind, characterised in that said polyisocyanate composition comprises an isocyanate-containing prepolymer composition having an NCO content of from 2 to 25 % by weight as obtainable by reacting an isocyanate- reactive polymer composition having an average nominal functionality of from 1.8 to 6, and an average equivalent weight of from 500 to 7000 with a stoichiometric excess of a diphenylmethane diisocyanate composition.

2. Process according to claim 1 wherein the NCO content of the prepolymer composition is in the range 2 to 15 % by weight.

3. Process according to claim 2 wherein the NCO content of the prepolymer composition is in the range 2 to 7 % by weight.

4. Process according to any one of the preceding claims wherein the average isocyanate functionality of the diphenylmethane diisocyanate composition is from 2 to 2.3.

5. Process according to any one of the preceding claims wherein the diphenylmethane diisocyanate composition contains at least 60 % by weight of difunctional diphenylmethane dusocyanates.

6. Process according to claim 5 wherein the diphenylmethane diisocyanate composition contains only difunctional diphenylmethane dusocyanates.

7. Process according to any one of the preceding claims wherein the diphenylmethane diisocyanate composition contains at least 60 % on a weight basis of diisocyanate components of 4, '-diphenylmethane diisocyanate.

Process according to claim 7 wherein the diphenylmethane diisocyanate composition contains at least 95 % on a weight basis of diisocyanate components of 4, '-diphenylmethane diisocyanate.

9. Process according to any one of the preceding claims wherein the average nominal functionality of the isocyanate-reactive polymer composition is between 2 and 4.

10. Process according to any one of the preceding claims wherein the average equivalent weight of the isocyanate-reactive polymer composition is between 1000 and 5000.

11. Process according to any one of the preceding claims wherein the isocyanate-reactive polymer composition contains a polyoxypropylene diol or triol or a poly(oxyethylene-oxypropylene) diol or triol.

12. Process according to any one of the preceding claims wherein the isocyanate-reactive polymer comprises a polyoxyalkylene polyol having an oxyethylene content of between 10 and 25 % on a weight basis of total oxyalkylene residues.

13. Process according to any one of the preceding claims wherein the viscosity of the isocyanate-containing prepolymer composition is between 1500 and 8000 cP.

14. Process according to any one of the preceding claims wherein step b) involves hot-pressing the combination of cork material and polyisocyanate composition.

15. Process according to any one of the preceding claims wherein the weight ratio polyisocyanate/cork material is in the range 0.1:99.9 to 30:70.