Compositions useful as binders for the production of composite materials

Compositions made up of an aromatic polyisocyanate and a polyester having an average molecular weight of from about 600 to about 5000, obtainable by self-condensation of ricinoleic acid, optionally with co-utilization of a C.sub.2 -C.sub.20 starter polyol and optional additives. These compositions are useful as binders for the production of composite materials.

BACKGROUND OF THE INVENTION
 The present invention relates to new isocyanate-based compositions useful
 as binders for the production of composite materials.
 Composite materials (also called compression-molded materials) such as
 chipboards, composite boards or other molded bodies are produced by hot
 molding an inorganic or organic raw material such as a mass of wood chips,
 wood fibers, or other lignocellulose-containing material, with a binder
 such as an aqueous dispersion of a urea/formaldehyde resin or a
 phenol/formaldehyde resin. Isocyanates or isocyanate solutions may be used
 instead of formaldehyde resins as binders for hardboards (See, e.g.,
 German Auslegeschrift 1,271,984; and German Offenlegungschriften
 1,492,507; 1,653,177; and 2,109,686). The use of polyisocyanates as
 binders improves the stability and moisture characteristics of the
 composite materials and increases their mechanical strength.
 Polyisocyanates also have far-reaching process engineering advantages when
 used as binders. These advantages are discussed in German
 Offenlegungschrift 2,109,688.
 The large-scale, industrial production of composite materials bonded with
 polyisocyanates (particularly lignocellulose-containing materials such as
 chipboards, fiberboards and plywood) is, however, impeded by the high
 adhesiveness of the polyisocyanate. This adhesiveness causes the molded
 composite to adhere strongly to all metal parts (especially pressing
 plates made of steel or aluminum) after the hot molding and makes mold
 release difficult.
 Previously proposed methods for solving this release problem each have
 their disadvantages. Some of those disadvantages are greater than others.
 Release agents developed especially for use with isocyanates frequently
 have a good release action but they are unreliable in large-scale
 application, uneconomical and can also cause defective gluing or coating
 difficulties in the further processing of boards made with the release
 agent
 German Offenlegungschrift 1,653,178 discloses the production of boards or
 molded bodies by hot molding mixtures of lignocellulose-containing
 material and polyisocyanates. In the disclosed process, the pressing
 plates or molds may be treated with polyhydroxylic compounds (e.g..
 glycerol, ethylene glycol, polyester polyols or polyether polyols) before
 compression molding. The fact that a separate operation is necessary for
 the application of the release agent and that part of the polyisocyanate
 is consumed by reaction with the release agent makes this process
 disadvantageous.
 Another approach to improving the release behavior of molded bodies is
 disclosed in German Offenlegungschrift 2,325,926. In this disclosure,
 release agents which catalyze the formation of isocyanurate in the
 isocyanate are used. The disadvantage of this process is that the catalyst
 has a destabilizing effect on the isocyanate which effectively prevents
 production of an isocyanate binder which will satisfy a specification.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to provide a composition which is
 useful as a binder for the production of composite materials.
 It is also an object of the present invention to provide a binder
 composition which may be used for the production of composite materials
 which does not adversely affect the removability of a composite article
 from a mold.
 It is a further object of the present invention to provide a binder
 composition which is storage stable.
 It is another object of the present invention to provide a process for the
 production of composite materials in which the composite material may be
 readily removed from a mold.
 These and other objects which will be apparent to those skilled in the art
 are accomplished by using a composition made up of (a) an aromatic
 polyisocyanate in combination with (b) a polyester obtained by
 self-condensation of ricinoleic acid, optionally with the use of a starter
 polyol.
 DETAILED DESCRIPTION OF THE PRESENT INVENTION
 The present invention provides a composition made up of (a) an aromatic
 polyisocyanate and (b) a polyester having an average molecular weight of
 from about 600 to about 5000 which polyester is obtainable by
 self-condensation of ricinoleic acid, optionally using a C.sub.2 -C.sub.20
 starter polyol, and optional additives.
 In a preferred embodiment of the present invention, polyisocyanate (a) is a
 polyisocyanate based on (i) diphenylmethane diisocyanate or (ii) a mixture
 of diphenylmethane diisocyanates and polyphenylpolymethylene
 polyisocyanates in which the proportion of diphenylmethane diisocyanates
 in the polyisocyanate mixture is preferably between 35 and 75 wt %. It is
 also preferred that polyester (b) have an average molecular weight of from
 about 620 to about 3000. Where a starter polyol is used in the production
 of polyester (b), it is preferred that the polyol be 1,6-hexanediol. It is
 also preferred that components (a) and (b) have been caused to react
 together completely or partially, optionally not until during application
 of the composition to the material from which a composite material is to
 be made.
 The present invention is also directed to the use of the above-described
 composition, optionally in combination with known polyhydroxylic compounds
 having a molecular weight of from about 400 to about 10,000, as a binder
 for the production of composite materials.
 It is also preferred that the binder of the present invention be used to
 produce composite materials which are based on cellulose-containing and/or
 lignocellulose-containing materials. In another preferred embodiment of
 the invention, ground scrap plastics (most preferably isocyanate-based
 scrap plastics) are used together with cellulose-containing and/or
 lignocellulose-containing materials to produce composite materials.
 In the compositions of the present invention, the weight ratio of component
 (a) to component (b) is usually between 100:1 and 100:200, preferably
 between 100:5 and 100:30.
 Polyesters (b) which are preferably used in the compositions of the present
 invention are the polyesters obtained by self-condensation of ricinoleic
 acid on a C.sub.2 -C.sub.20 starter polyol. The polyesters obtained are
 hydroxyfunctional polyesters. It is also possible, however, to use
 polyesters that are obtained by self-condensation of ricinoleic acid as
 component (b). These self-condensation polyesters have one more carboxyl
 group per molecule than the polyesters produced using a starter polyol.
 Any of the known polyols having a functionality of from 2 to 6 and a
 molecular weight of from about 62 to about 399 may be used as the C.sub.2
 -C.sub.20 starter polyol for the production of the polyester to be used in
 the practice of the present invention. Specific examples of suitable
 starter polyols include: ethylene glycol; 1,2- and 1,3-propanediol; 1,4-
 and 2,3-butanediol; 1,6- and 2,5-hexanediol; 2-ethylhexanediol;
 1,12-octadecanediol; 3-methyl-1,5-pentanediol; 1,8-octanediol; neopentyl
 glycol; 1,4-bis (hydroxymethyl) cyclohexane; 2-methyl-1,3-propanediol;
 glycerol; trimethylolpropane; 1,2,6-hexanetriol; 1,2,4-butanetriol;
 trimethylolethane; pentaerythritol; quinitol; mannitol; sorbitol;
 formitol; 1,4,3,6-dianhydosorbitol; methylglycoside; diethylene glycol;
 triethylene glycol; tetraethylene glycol and higher polyethylene glycols;
 dipropylene glycol and higher polypropylene glycols; and dibutylene glycol
 and higher polybutylene glycols.
 In the production of composite materials (compression-molded materials) by
 hot molding using the compositions of the present invention as binders,
 other additives may optionally be used. Such additives include those known
 in the ad, e.g., polyether polyols having molecular weights of from about
 400 to about 10,000 and/or alkylene carbonates (EP-0 352,558).
 When the compositions of the present invention are used as binders, they
 make it possible to produce compression-molded materials (e.g.,
 chipboards) by hot molding, optionally after a single conditioning of the
 mold by application of a release agent. Repeated application of a mold
 release agent is not necessary. A noticeable reduction of the molding time
 is also repeatedly observed.
 The compositions of the present invention to be used as binders can be
 produced by mixing components (a) and (b) and optionally (c) at
 temperatures of from about 0.degree. C. to about 300.degree. C.,
 preferably from about 10.degree. C. to about 100.degree. C. The components
 may even be mixed just before use or while being applied to the material
 from which the composite is to be produced.
 Any aromatic polyisocyanate may be used as component (a) to produce the
 compositions of the present invention. Such isocyanates are described, for
 example, by W. Siefken in Justus Liebigs Annalen der Chemie 562, pp
 75-136. Aromatic polyisocyanates which are liquid at room temperature are
 particularly preferred. Examples of suitable polyisocyanates include those
 represented by the formula
EQU Q(NCO).sub.n
 in which
 n represents a number of from 2 to 4, preferably 2 to 3, and
 Q represents an aromatic hydrocarbon group having from 6 to 15 (preferably
 from 8 to 13) carbon atoms.
 Specific examples of such polyisocyanates are disclosed in German
 Offenlegungschrift 2,832,253 at pages 10 and 11.
 Aromatic polyisocyanates which are readily available are generally
 preferred. Examples of commercially available polyisocyanates include: the
 2,4- and 2,6-tolylene diisocyanates and mixtures of these isomers ("TDI");
 polyphenylpolymethylene polyisocyanates such as those which are produced
 by aniline-formaldehyde condensation and subsequent phosgenation ("crude
 MDI"); and aromatic polyisocyanates having carbodiimide groups, urethane
 groups, allophanate groups, isocyanurate groups, urea groups or biuret
 groups ("modified polyisocyanates"). Modified polyisocyanates derived from
 2,4- and/or 2,6-tolylene diisocyanate or from 4,4'- and/or
 2,4'-diphenylmethane diisocyanate are most preferred.
 Suitable lignocellulose-containing raw materials which can be bonded with
 the compositions of the present invention include: wood, bark, cork,
 bagasse, straw, flax, bamboo, alfalfa grass, rice husks, sisal fibers and
 coconut fibers. Composite materials may also be produced from other
 organic raw materials (e.g., plastics wastes of all kinds) and/or
 inorganic raw materials (e.g., expanded mica or silicate spheres) when the
 compositions of the present invention are used as binders. The material to
 be bonded can be used in the form of granules, chips, fibers, spheres or
 flour, and have a moisture content of from about 0 to about 35 wt %.
 It is possible to apply the two components of the composition of the
 present invention (i.e., polyisocyanate (a) and polyricinoleic acid
 polyester (b)) separately to the material to be bonded, the components
 optionally being dissolved in an inert organic solvent (as an additive).
 It is preferred, however, that the polyisocyanate (a) and the
 polyricinoleic acid polyester (b) be caused to react together completely
 or partially, optionally together with additives such as polyethers having
 hydroxyl groups and/or alkylene carbonates and/or solvents, in a separate
 operation prior to being applied to the material to be bonded.
 When polyisocyanate (a) is caused to react with polyester (b) in an
 operation separate from the bonding operation, from about 1 to about 200
 parts by weight, preferably from about 5 to about 30 parts by weight, of
 polyricinoleic acid polyester (b) per 100 parts by weight of isocyanate
 (a) are generally used. Components (a) and (b) may be combined at a
 temperature of from about 0.degree. to about 300.degree. C., preferably
 from about 10.degree. to about 100.degree. C. These components need not be
 combined until shortly before or during application to the material to be
 bonded. Polyisocyanate (a) and polyester (b) may optionally be combined in
 the presence of an inert organic solvent such as hydrocarbon fractions.
 The self-releasing, binder combinations obtained are stable in storage and
 can be used at any time in accordance with the present invention.
 From about 0.5 to about 20 wt %, preferably from about 2 to about 12 wt %,
 of the binder, based on the total weight of the molded body, is added to
 the organic and/or inorganic material to be bonded. The resultant mixture
 is then molded, generally under pressure and heat (e.g., from about 1 to
 about 150 bar and from about 70 to about 250.degree. C.) to produce boards
 or three-dimensional molded bodies.
 Multilayer boards or molded parts can be produced analogously from veneers,
 papers or fabrics by treating the layers, as described above, with the
 binder of the present invention and then molding them, usually at elevated
 temperature and elevated pressure. Temperatures are preferably maintained
 at from about 100 to about 250.degree. C., most preferably from about 130
 to about 200.degree. C. The initial molding pressure is preferably between
 5 and 150 bar. The pressure usually drops in the course of the molding
 operation to almost zero.
 The compositions of the present invention may also be used as binders in
 combination with any of the polyhydroxylic compounds having a molecular
 weight of from about 400 to about 10,000 known in the art of polyurethane
 chemistry as an optional additive (c). Examples of such polyhydroxylic
 compounds include polyesters and polyethers. These polyhydroxylic acid
 compounds used as additives (c) are included in quantities such that
 NCO/OH ratio of binder to polyhydroxylic compound is between 1.2:1 and
 10:1, preferably from 1.5:1 to 1:1. It is possible to charge the aromatic
 polyisocyanate component (a), the polyester (b) and the optional additives
 (c) as separate components or preferably as a reactive mixture. Such
 compositions have practical importance as binders in, for example, the
 bonding of cork meal. It is also possible to add any of the known blowing
 agents (on an amount of from about 0.5 to 30 wt %, relative to the total
 composition), and/or other additives influencing foaming or chemical
 reaction between polyisocyanates, lignocellulose-containing material and
 optionally polyhydroxylic compounds, such as stabilizers, catalysts and
 activators. The additives, if used, are generally included in an amount of
 from about 0.05 to about 10 wt %, based on the weight of the binder or
 impregnating agent
 The compositions to be used as binders in accordance with the present
 invention may also be combined with aqueous solutions of condensation
 products of formaldehyde with urea and/or melamine and/or phenol which
 have predominantly been used in the wood materials industry. The binders
 of the present invention may also be used with other less common binders
 and impregnating agents such as those based on latices of polyvinyl
 acetate or other plastics, spent sulfite liquor or tannin. In such
 combinations, the mixing ratio of the composition of the present invention
 to additional binder(s) should generally be maintained between 1:20 and
 20:1, preferably between 1:5 and 5:1, parts by weight. The polyisocyanate
 composition of the present invention and the additional binder(s) can be
 charged to the material to be bonded either separately or as a mixture.
 Such combinations of binders are particularly advantageous in the
 production of multilayer boards having special properties. The outer
 layers can, for example, be treated with the compositions of the present
 invention (alone or together with conventional binders and/or adhesives)
 and one or more inner layers may be treated with conventional adhesives
 (alone or together with the compositions of the present invention) and
 subsequently molded together.
 The outstanding mechanical properties and advantageous behavior during
 moisture fluctuation of the boards and molded parts based on
 lignocellulose-containing raw materials produced in accordance with the
 present invention make them suitable for use in construction. In order to
 provide the boards or molded parts with the resistance to fungal attack,
 insect damage or the effect of fire usually required of them, any of the
 commercially available organic or inorganic preventive agents can be
 added, in pure form or as a solution, to the binder compositions of the
 present invention. Such preventive agents may be included in the
 compositions of the present invention in an amount of from about 0.05 to
 about 30 wt %, preferably from about 0.5 to about 20 wt %, based on the
 weight of the lignocellulose-containing raw materials.
 Solvents which may be used in the binder compositions of the present
 invention include water and organic solvents such as residual oils from
 petroleum processing, chlorinated hydrocarbons etc. The gluing quality is
 usually not impaired by use of such solvents.
 In contrast to boards glued with phenol-formaldehyde resin, neither salt
 blooming nor "color bleeding" occurs in composite materials produced in
 accordance with the present invention.
 Considerable improvements in the production of chipboards, with regard both
 to mechanical properties and to process engineering, are achieved when the
 compositions of the present invention are used instead of the conventional
 binders based on phenol/formaldehyde resins or urea/formaldehyde resins.
 In the case of wood chipboards, when the binder of the present invention
 is used in the same quantity as the known phenol/formaldehyde or
 urea/formaldehyde resins, the bonding strength may be increased by up to
 50% in addition to improvement in other mechanical properties). When the
 compositions of the present invention are used in a concentration which is
 25 to 70% less than at which known phenol/formaldehyde resins or
 urea/formaldehyde resins are used, the composite material produced has a
 mechanical property profile which is substantially the same as that of
 composites made with the known resins. Optimum material properties are
 achieved when a composition of the present invention which is based on a
 mixture of diphenylmethane diisocyanates and polyphenylpolymethylene
 polyisocyanates is used as the binder.
 Optimum properties are obtained whether or not the polyisocyanate is
 produced by distilling off 2,4'- and/or 4,4'-diisocyanatodiphenylmethane
 from crude diphenylmethane diisocyanate or from polyarylamines or by
 separating pure diaminodiphenylmethane from crude diaminodiphenylmethane
 by distillation and subsequently phosgenating the undistilled bottoms
 fraction so obtained.
 The polyisocyanate mixture used in the compositions of the present
 invention preferably contains between 35 and 75 wt % of
 diisocyanatodiphenylmethane.
 Having thus described our invention, the following examples are given as
 being illustrative thereof. All parts and percentages given in these
 examples are parts by weight and percentages by weight unless otherwise
 indicated.

EXAMPLES
 The following polyisocyanates were used to make binder compositions (% data
 in wt %):
 POLYISOCYANATE A 1: Diisocyanatodiphenylmethane which was distilled off
 from the crude phosgenation product of an aniline/formaldehyde condensate
 in an amount such that the distillation residue had a viscosity of 100 cP
 at 25.degree. C. (binuclear content=59.7%; trinuclear content=21.3%;
 higher-nuclear polyisocyanates content=19.0%).
 POLYISOCYANATE A 2: Diisocyanatodiphenylmethane having a viscosity of 200
 cP at 25.degree. C. (binuclear content=44.3%; trinuclear content=23.5%;
 higher-nuclear polyisocyanates content=32.2%).
 POLYISOCYANATE A 3: Diisocyanatodiphenylmethane having a viscosity of 400
 cP at 25.degree. C. (binuclear content=45.1%; trinuclear content=22.3%;
 higher-nuclear polyisocyanates content=32.6%).
 POLYISOCYANATE A 4: Diisocyanatodiphenylmethane having a viscosity of 300
 cP at 25.degree. C. (binuclear content=56.8%; trinuclear content=27.6%;
 higher-nuclear polyisocyanates content=15.6%).
 POLYISOCYANATE A 5: An isocyanate mixture made up of 80%
 4,4'-diisocyanatodiphenylmethane, 10% 2,4'-diisocyanatodiphenylmethane and
 10% higher-nuclear polyisocyanate.
 POLYISOCYANATE A 6: An isocyanate mixture with a content of approximately
 45% 4,4'- and 55% 2,4'-diphenylmethane diisocyanate.
 POLYISOCYANATE A 7: Pure monomeric 4,4'-diphenylmethane diisocyanate.
 POLYISOCYANATE A 8: A semiprepolymer having an NCO content of approximately
 23%, obtained by reaction of POLYISOCYANATE A 7 with technical
 tripropylene glycol.
 POLYISOCYANATE A 9: An isocyanate mixture made up of approximately 80%
 tolylene 2,4-diisocyanate and 20% tolylene 2,6-diisocyanate.
 The polyricinoleic acid polyesters used to produce compositions in
 accordance with the present invention were prepared by a conventional
 ester condensation procedure (See, e.g., EP-180,749) at elevated
 temperatures and with simultaneous removal of water, optionally with use
 of conventional catalysts.
 The following polyesters were made:
 POLYESTER B 1: Reaction product of 1 mole of 1,6-dihydroxyethane and 7
 moles of ricinoleic acid (commercially available under the name Nouracid
 CS 80 from Akzo GmbH). OH number=approximately 35; viscosity (25.degree.
 C.)=920 mPa.multidot.s.
 POLYESTER B 2: Self-condensation product of 4 moles of ricinoleic acid. OH
 number=approximately 51; viscosity (25.degree. C.)=820 mPa.multidot.s.
 POLYESTER B 3: Condensation product of 1 mole of 1,6-hexanediol and 2 moles
 of ricinoleic acid. OH number=147; viscosity (25.degree. C.)=300
 mPa.multidot.s.
 POLYESTER B 4: Condensation product of 1 mole of 1,6-hexanediol and 14
 moles of ricinoleic acid. OH number=approximately 27.7; viscosity
 (25.degree. C.)=1480 mPa.multidot.s.
 POLYESTER B 5: Condensation product of 1 mole of ethylene glycol and 7
 moles of ricinoleic acid. OH number=approximately 39; viscosity
 (25.degree. C.)=1000 mPa.multidot.s.
 POLYESTER B 6: Condensation product of 1 mole of 1,12-octanediol and 7
 moles of ricinoleic acid. OH number=approximately 28; viscosity
 (25.degree. C.)=900 mPa.multidot.s.
 POLYESTER B 7: Condensation product of 1 mole of diethylene glycol and 6.75
 moles of ricinoleic acid. OH number=approximately 34; viscosity
 (25.degree. C.)=920 mPa.multidot.s.
 POLYESTER B 8: Reaction product of 1 mole of trimethylolpropane and 10.5
 moles of ricinoleic acid. OH number=approximately 44; viscosity
 (25.degree. C.)=1560 mPa.multidot.s.
 POLYESTER B 9: Reaction product of 1 mole of diethylene glycol and 2 moles
 of ricinoleic acid. OH number=149; viscosity (25.degree. C.)=260
 mPa.multidot.s.
 POLYESTER B 10: Reaction product of 1 mole of tetraethylene glycol and 2
 moles of ricinoleic acid. OH number=139; viscosity (25.degree. C.)=240
 mPa.multidot.s.
 Binder compositions were prepared from the above-listed POLYISOCYANATES AND
 POLYESTERS by stirring a POLYISOCYANATE and a POLYESTER at elevated
 temperature in accordance with known techniques. Acidic additives
 (optional additives (c)) were used, if necessary, for stabilization. It is
 also possible to mix the components A and B shortly before, or not until
 during, application to the material to be bonded. The binder compositions
 made were as follows:
 COMPOSITION C 1 (according to the invention): 881.2 kg of POLYISOCYANATE A1
 were caused to react with 128.8 kg of POLYESTER B1 for 2 hours at
 80.degree. C. NCO content=27.1%; viscosity (25.degree. C.)=350
 mPa.multidot.s.
 COMPOSITION C 2 (according to the invention): POLYISOCYANATE A1 and
 POLYESTER B4 were mixed shortly before application in a ratio of 6.8:1 and
 used immediately.
 COMPOSITION C 3 (according to the invention): POLYISOCYANATE A1 and
 POLYESTER B5 were mixed shortly before application in a ratio of 6.8:1 and
 used immediately.
 COMPOSITION C 4 (according to the invention): POLYISOCYANATE A1 and
 POLYESTER B6 were mixed shortly before application in a ratio of 6.8:1 and
 used immediately.
 COMPOSITION C 5 (according to the invention): 8.47 kg of POLYISOCYANATE A1
 were mixed with 1.23 kg of POLYESTER B2 for 2 hours at 80.degree. C. NCO
 content=26.7%; viscosity (25.degree. C.)=610 mPa.multidot.s.
 COMPOSITION C 6 (according to the invention): 5 kg of POLYISOCYANATE A1
 were mixed with 5 kg of POLYESTER B1 for 2 hours at 80.degree. C. NCO
 content=14.2%; viscosity (25.degree. C.)=3120 mPa.multidot.s.
 COMPOSITION C 7 (according to the invention): 2.25 kg of POLYISOCYANATE A1
 were mixed with 4.5 kg of POLYESTER B1 for 2 hours at 80.degree. C. NCO
 content=8.2%; viscosity (25.degree. C.)=9600 mPa.multidot.s.
 COMPOSITION C 8 (according to the invention): 9 kg of POLYISOCYANATE A5
 were mixed with 1 kg of POLYESTER B1 for 2 hours at 80.degree. C. NCO
 content=28.7%; viscosity (25.degree. C.)=45 mPa.multidot.s.
 COMPOSITION C 9 (comparison): 4.5 kg of POLYISOCYANATE A1 were stirred with
 0.66 kg oleic acid for 2 hours at 80.degree. C. and 1 hour at 100.degree.
 C. NCO content=26.1%; viscosity (25.degree. C.)=560 mPa.multidot.s.
 COMPOSITION C 10 (comparison): 4.5 kg of POLYISOCYANATE A1 were stirred
 with 0.66 kg tall oil for 2 hours at 80.degree. C. and 1 hour at
 100.degree. C. NCO content=26.2%; viscosity (25.degree. C.)=535
 mPa.multidot.s.
 COMPOSITION C 11 (according to the invention): 9 kg of POLYISOCYANATE A 9
 were stirred with 1 kg of POLYESTER B1 at 80.degree. C. NCO content=42.8%;
 viscosity (25.degree. C.)=6.1 mPa.multidot.s.
 EXAMPLES OF APPLICATION
 Example 1 According to the Invention
 4060 g of industrially produced outer-layer softwood chips with a moisture
 content of 15% were mixed with 282 g of each of the COMPOSITIONS
 identified in Table 1 in a laboratory gluing machine. A briquette was
 formed from the glued chips on a steel cover plate, then provided with
 another steel cover plate on the top, and molded for 1.6 min. in a hot
 press at a hot-plate temperature of 180.degree. C. and an initial pressure
 of 25 bar.
 A chipboard which was satisfactorily separated from the cover plates was
 obtained. After the fourth repetition, the composite had "outstanding"
 release properties (i.e. there was no resistance to demolding).
 Example 1a Comparison
 Production of a chipboard with an unmodified isocyanate (PMDI) by the
 process described in Example 1 was attempted. In contrast to Example 1,
 the cover plates adhered so strongly to the chipboard that the cover
 plates could not be removed without destruction of the chipboards. (Table
 1, Experiment No. 5).
 Example 1b Comparison
 Products with "release properties" described in the patent literature were
 examined analogously to Comparative Example 1a (Table 1, Experiment Nos. 6
 and 7). The results were the same as those of Example 1a.
 Example 2 According to the Invention
 2990 g wheat straw chips with a moisture content of 15% produced under
 laboratory conditions were processed with 208 g of COMPOSITION C1 by the
 same procedure which was used in Example 1. Straw chipboard which could be
 satisfactorily separated from the mold initially and after the fourth
 repetition outstandingly was produced.
 Example 3 According to the Invention
 The steel cover plates of the mold were provided before molding with a
 cured separating film by application of a mold coating agent Examples 1
 and 2 were then repeated. Outstanding mold-release behavior was achieved
 from the start onwards. The outstanding mold-release behavior of the
 products of the present invention continued to be achieved even after
 disappearance of the releasing film.
 Example 4 According to the Invention
 Examples 1, 1a, 2 and 3 were repeated using a mold made with aluminum cover
 plates instead of steel. The results were the same as those obtained when
 steel plates were used.
 Example 5
 Three-ply 16 mm wood chipboards were made from industrially produced
 outer-ply and middle-ply chips and COMPOSITION C1 (according to the
 invention; Table 2) in combination with a mold coating agent as release
 agent for comparison, chipboards were produced from outer-ply and
 middle-ply chips and an unmodified isocyanate (PMDI) in combination with a
 mold coating agent as release agent. The properties of the resulting
 chipboards were determined in accordance with DIN 68 763. The board bonded
 with COMPOSITION C 1 had mechanical properties that were fully equivalent
 to those of the comparative board (Table 2).
 Example 6
 Example 5 was repeated using wheat straw outer-ply and middle-ply chips
 which had been produced under laboratory conditions instead of wood chips.
 The results are reported in Table 2.
 TABLE 1
 NUMBER COMPOSITION SEATION BEHAVIOR
 1 C1 Satisfactory for first 3 pressings;
 outstanding from 4th pressing on
 2 C2 Satisfactory for first 3 pressings;
 outstanding from 4th pressing on
 3 C3 Satisfactory for first 3 pressings;
 outstanding from 4th pressing on
 4 C4 Satisfactory for first 3 pressings;
 outstanding from 4th pressing on
 5 (Example 1a) Polyisocyanate Very strong adhesion; chipboard could not be
 removed without
 A1 destruction
 6 (Example 1b) C9 Very strong adhesion; chipboard could not be
 removed without
 destruction
 7 (Example 1b) C10 Very strong adhesion; chipboard could not be
 removed without
 destruction
 TABLE 2
 Transver. Transver.
 Amount of Molding Molding Tensile Tensile
 Material Binder Temp. Time Strength*** Strength
 to be bonded Binder (% adc)** (.degree. C.) (min.) (MPa) V 20
 (MPa) V 100
 wood chips COMP. C1 5 180 2.4 0.76 0.16
 wood chips unmod. 5 180 2.4 0.74 0.16
 PMDI A1*
 wheat straw COMP. C1 5 180 6.5 0.36 0.06
 chips
 wheat straw unmod. 5 180 6.5 0.30 0.05
 chips PMDI A1*
 *unmodified PMDI A1 = POLYISOCYANATE A1
 **% adc = approximate wt % (based on the weight of absolutely dry chips)
 ***apparent density of the board was approximately 620 kg/m.sup.3
 Although the invention has been described in detail in the foregoing for
 the purpose of illustration, it is to be understood that such detail is
 solely for that purpose and that variations can be made therein by those
 skilled in the art without departing from the spirit and scope of the
 invention except as it may be limited by the claims.