WO2013017508A1 - Paper structures impregnated with polyurea, and a process for production thereof - Google Patents

Abstract

The invention relates to pressure-resistant and flexurally stiff paper structures impregnated with urethane-modified polyurea, and to a process for production thereof.

Description

 Polyurea impregnated paper structures and a process for their preparation

The invention relates to pressure-resistant and rigid paper structures impregnated with urethane-modified polyurea, and to a process for their preparation.

To save weight in the construction of load-bearing structures, such. In the

Vehicle construction, sandwich elements used. These are constructed from a light core layer and adherent solid cover layers on both sides. As easy core situations come

Rigid foams of polystyrene, polyurethane, Kunststoffgewirke or paper structures, such. Paper honeycomb, for use. As cover layers, inter alia plywood, glass fiber reinforced plastics or metal foils are used. The task of such material composites is to achieve maximum carrying capacity with the lowest possible weight. When using cheap paper honeycomb is the

Moisture sensitivity, however, a hurdle. In order to increase the load capacity of paper honeycombs under humid conditions, they are often soaked with synthetic resins and thereby reinforced. Correspondingly suitable synthetic resins may be formaldehyde condensates (US Pat. No. 6,372,322) and polyester resins. Synthetic resins based on isocyanates are also described. Also, the combination of alkyd resins with isocyanates is known (US-A 2744042).

W.J. McKillip et al. describe that toluene diisocyanates are superior to aliphatic isocyanates. Methylene diphenyl diisocyanate, in turn, is superior to tolylene diisocyanate in its reactivity according to these authors. In US-A 5008359 it is shown that polymeric diphenylmethane diisocyanate (MDI) is suitable. Catalysts are explicitly omitted here.

US-A-5292391 and US-A-5332458 also use the inexpensive, unmodified, polymeric diphenylmethane diisocyanate (MDI). The polymeric MDI used in US Pat. No. 5,580,243 has a content of 40-60% of monomeric 4,4'-diphenylmethane diisocyanate and has a wide range of functionalities and viscosities.

It is disclosed in US-A 5140086 that a dilution of the polymeric diphenylmethanediisocyanate with organic solvents, in particular with propylene glycol, represents an improvement of the reaction rate. Triacetin and triethyl citrate (US Pat. No. 5,580,922) and phosphoric acid esters (US Pat. No. 5,580,243) are likewise used as solvents and

Flame retardant described and used accordingly. "

 - 2-

The sandwich elements described in DE-A 102006016943, DE-A 102008033559 and DE-A 102008051436 are produced from a core material of isocyanate-finished paper honeycombs having improved compressive strength.

The object of the present invention was therefore to provide a paper structure which a) contains no solvent or can be prepared without the use of solvents and thus can be used indoors, b) can be produced without difficulty and within a short time to form a supporting element and c) for curing with moisture, a sufficiently hydrophilic synthetic resin is used. The paper structure thus obtained should have a significantly improved bending or compressive rigidity.

Surprisingly, the object could be achieved by a polyurea-impregnated paper structure, wherein the isocyanate used for the impregnation was chemically modified with long-chain ethylene oxide-containing polyethers. In this case, the hardness of the paper structure could be increased, although the content of isocyanate groups in the isocyanate used, which is essential for the crosslinking of the paper structure and the polyurea, is significantly reduced by the modification with the polyethers per unit mass. In addition, it was surprising that the introduction of soft segments (from the modification of the isocyanate with the ethylene oxide-containing polyethers) in the polyurea leads to an improvement in the hardness and the bending stiffness.

The invention relates to a process for the production of pressure-resistant and rigid paper structures by impregnation with isocyanate and subsequent reaction with water, water vapor and / or atmospheric moisture, characterized in that i) the paper structure having at least one or more urethane groups

 having NCO prepolymers having an NCO content of 18 to 27 wt .-%, wherein the prepolymer is a reaction product of

A) diphenylmethane diisocyanate isomers and optionally higher homologs thereof and optionally modified diphenylmethane diisocyanates having at least 50 wt .-%, preferably 60 to 90 wt .-%, monomeric diphenyl methane diisocyanate and

B) polymeric polyalkylene oxides having from 1.8 to 8, preferably 2 to 6, particularly preferably 3 to 6, isocyanate-reactive groups per molecule (number-average functionality) and having at least 5 to 100 wt .-%, preferably at least 13 to 90 wt. -%, particularly preferably at least 17 to 90 wt .-%, most preferably at least 25 to 85% by weight, based on Polyalkylene oxide, ethylene oxide units and / or polymeric polycarbonate polyols having molecular weights of 1000 to 15000 is, optionally in admixture with modified diphenylmethane diisocyanates, impregnated and ii) the at least one or more NCO prepolymers are reacted with water, water vapor and / or atmospheric moisture.

The polyalkylene oxides preferably have molecular weights of from 1,000 to 15,000, more preferably from 3,000 to 13,000, and may be partially or wholly replaced by polycarbonate polyols having molecular weights of from 1,000 to 15,000. Preferably, the prepolymer catalysts in an amount of 0.05 to 1 wt.%, Based on the sum of components A) and B) added. As preferred catalysts metal-containing catalysts are used.

In a preferred process variant, catalysts are added to the water, as are normally used in polyurethane chemistry. These include e.g. Carboxylates, phenates, amine oxides and particularly preferably tertiary amine catalysts in an amount of

0.05 to 40 wt.%, Based on the water used for curing, preferably containing 2 to 4 hydroxyl groups per molecule. Examples of preferred amine catalysts are: alkoxylated ethylenediamine having 3 to 8 molecules of propylene oxide per ethylenediamine, alkoxylated triethanolamine and other alkoxylated amines, optionally in admixture with triethylenediamine and / or pentamethyldiethylenetriamine, dimethylbenzylamine or other tertiary amines known from the prior art.

The weight ratio of 4,4'-diphenylmethane diisocyanate to 2,4'-diphenylmethane diisocyanate is preferably between 5 to 1 and 1 to 2.

Also, modified diphenylmethane diisocyanates, such as uretonimines, carbodiimides or isocyanurates can be used as isocyanate component for the preparation of NCO prepolymers.

To improve the fire resistance of the reinforced paper structures, it is particularly advantageous to give the NCO prepolymer of one of the known from the prior art liquid or _Λ

 4-flame retardant (e.g., organic and / or inorganic phosphates or phosphites, expandable graphite).

Another object of the invention are pressure-resistant and rigid paper structures, which are impregnated with at least one urethane polyurea, said urethane polyurea having the urethane groups is obtainable from a) one or more urethane containing NCO prepolymers having an NCO content of 18 to 27 wt. -% available

A) diphenylmethane diisocyanate isomers and optionally higher

 Homologues thereof and optionally modified diphenylmethane diisocyanates having at least 50% by weight, preferably 60 to 90% by weight, of monomeric diphenylmethane diisocyanate and

B) polymeric polyalkylene oxides having from 1.8 to 8, preferably 2 to 6, particularly preferably 3 to 6, isocyanate-reactive groups per molecule (number-average functionality) and having at least 5 to 100 wt .-%, preferably at least 13 to 90 wt. -%, particularly preferably at least 17 to 90 wt .-%, most preferably at least 25 to 85 wt .-%, based on polyalkylene oxide, ethylene oxide units and / or polymeric polycarbonate polyols having molecular weights of 1000 to 15000, a '), optionally in admixture with modified diphenylmethane diisocyanates, and b) water, water vapor and / or atmospheric moisture.

A further subject of the invention are sandwich elements, which are characterized in that they comprise i) a core of the paper structure according to the invention and ii) at least one layer of fiber-reinforced polyurea and / or polyurethane located on at least one of the two sides of the core. The paper structure is impregnated, for example, by dipping the paper structure in the prepolymer or by applying the prepolymer to the paper structure or by spraying the paper structure with the prepolymer.

The height of the paper weight, the quality of the paper (defined according to the fiber structure) and the honeycomb size have mutual effects on the (pressure) strength of the honeycomb.

After applying the coating material (NCO prepolymer) to the paper structures (preferably paper honeycombs), this should preferably penetrate into the fibers of the paper structures. Therefore, paper grades are preferably used which, on the one hand, have good absorbent properties and, on the other hand, do not over-swell during impregnation and consequently lose their structure and strength.

To optimize the use of material (NCO prepolymer) is after impregnation of the

Paper structures preferably excess coating material (NCO prepolymer) of the structures removed, for example by tapping, blotting or by means of dry compressed air or other dry compressed gases. By subsequent addition of water, for example via a spray, by dipping or pouring, the NCO prepolymer reacts with elimination of carbon dioxide and forms a foam which can also fill the interior of the paper structure (for example the honeycombs).

The impregnation of the paper structures according to the invention makes them waterproof, resistant to chemicals and considerably stiffer than untreated paper structures. They are also suitable for outdoor use.

The reinforced paper structures can be used as spacers for the production of

Sandwich elements are used.

The invention will be explained in more detail with reference to the following examples. Examples:

Starting Compounds:

Isocyanate A is a NCO prepolymer based on diphenylmethane diisocyanate having an NCO content of 23 wt .-% and a viscosity of 405 mPa · s at 25 ° C. It contains 25% by weight of polymeric polyalkylene oxide based on glycerol having a weight-average molecular weight of 4500 and an ethylene oxide content of 73% by weight. The MDI used consists of 83% by weight of monomeric MDI with a weight ratio of 4,4'-MDI to 2,4'-MDI of 2.9: 1 and 6% by weight of uretonimine.

Isocyanate B is a NCO prepolymer based on diphenylmethane diisocyanate having an NCO content of 21.3 wt .-% and a viscosity of 680 mPa · s at 25 ° C. It contains 31% by weight of polymeric polyalkylene oxide based on propylene glycol and glycerol with a weight average

Molecular weight of 3830 and an ethylene oxide content of 61 wt .-%. The MDI used consists of 72% by weight of monomeric MDI with a weight ratio of 4,4'-MDI to 2,4'-MDI of 2.2: 1. Isocyanate C is an NCO prepolymer based on diphenylmethane diisocyanate with an NCO-

Content of 22 wt .-% and a viscosity of 750 mPa-s at 25 ° C. It contains 24.7% by weight of polymeric polyalkylene oxide based on propylene glycol and glycerol having a weight-average molecular weight of 4840 and an ethylene oxide content of 17% by weight. The MDI used consists of 60% by weight of monomeric MDI with a weight ratio of 4,4'-MDI to 2,4'-MDI of 2.9: 1.

Isocyanate D is an NCO prepolymer based on diphenylmethane diisocyanate having an NCO content of 23.5% by weight and a viscosity of 534 mPa · s at 25 ° C. It contains 24.7% by weight of polymeric polyalkylene oxide having a weight-average molecular weight of 6000 based on glycerol and an ethylene oxide content of 17% by weight. The MDI used consists of 53% by weight of monomeric MDI with a weight ratio of 4,4 '-MDI to 2,4' -MDI of 2.4: 1 and a uretonimine content of about 2% by weight.

Isocyanate E is a propylene carbonate diluted, unmodified, polymeric

Diphenylmethane diisocyanate having a viscosity of 63 mPa · s at 25 ° C and an NCO content of about 24 wt .-%. The paper honeycomb used has a honeycomb diameter of 5 mm, a height of 6.5 mm and a basis weight of 430 g / m ² . Carrying out the experiments:

The paper was dipped in the corresponding isocyanate at room temperature, and after

 Dabbing the excess isocyanate with pulp, the isocyanate was cured with water without the addition of catalysts at 80 ° C for a period of 24 hours.

5 According to DIN ISO 826, the compressive strength and in

 Based on DIN EN ISO 178 the bending strength is determined. The results are in the

 given in the following table.

Table:

Example 1 Example 2 Example 3 Example 4 Example 5 Example ι

 comparison

 Isocyanate A B C D E -

NCO content

 Weight% 23.27 21.47 22.02 23.71 25.12 over

 NCO content

 Weight% 22.98 21.04 21.68 23.30 24.09 - is

 isocyanate

 2.3 2.4 2.3 2.6 2.9 - functionality

 relationship

 1: 2.9 1: 2.2 1: 2.9 1: 2.4 1: 11 - 2.4'MDI: 4.4 'MDI

 2-core MDI wt% 83.0 72.8 78.0 62.0 40.0 -

3-core MDI wt% 6.3 10.5 8.4 14.4 22.8 -

4-core MDI% by weight 2.1 3.4 2.8 2.8 7.6 -

EO in PET wt% 73.0 61.5 16.0 17.7 0.0 -

Viscosity at 25 ° C mPas 405.0 680.0 743.0 534.0 63.00

paper honeycomb

Wall thickness mm 6.8 6.9 6.8 6.9 6.7 g PUR / g Honeycomb% 65% 74% 79% 78% 43% 0 ⁽ "

 * according to DIN ISO 845

The flexural strength was determined at a constant span of 80 mm.

The table shows that the use of the NCO prepolymers A, B, C and D compared to the use of polymeric MDI (isocyanate E) paper structures with improved flexural and / or 5 provides compressive strength.

Claims

claims: 1. A process for the production of pressure-resistant and rigid paper structures by  Impregnation with isocyanate and subsequent reaction with water, water vapor and / or atmospheric moisture, characterized in that i) the paper structure with at least one or more urethane containing NCO prepolymers having an NCO content of 18 to 27 wt .-%, wherein the prepolymer a reaction product A) diphenylmethane diisocyanate isomers and optionally higher homologues thereof and optionally modified diphenylmethane diisocyanates having at least 50% by weight of monomeric diphenylmethane diisocyanate and B) polymeric polyalkylene oxides having from 1.8 to 8 isocyanate-reactive groups per molecule and at least 5 to 100 wt .-%, based on polyalkylene oxide, ethylene oxide units and / or polymeric polycarbonate polyols having molecular weights of 1000 to 15,000, optionally in admixture with modified Diphenylmethandiisocyanaten, is impregnated and ii) the at least one or more NCO prepolymers are reacted with water, water vapor and / or atmospheric moisture. 2. The method according to claim 1, characterized in that the NCO prepolymer  Catalysts in an amount of 0.05 to 1 wt .-%, based on the NCO prepolymer added. 3. The method according to claim 1, characterized in that the tertiary water  Amine catalysts in an amount of 0.05 to 40 wt .-%, based on the water used, containing 2 to 4 hydroxyl groups per molecule. 4. The method according to claim 1, characterized in that the weight ratio of 4,4 '-Diphenylmethandiisocyanat to 2,4'- diphenylmethane diisocyanate between 5 to 1 and 1 to 2. 5. Pressure-resistant and rigid paper structures impregnated with at least one urethane-containing polyurea, the urethane-containing polyurea obtainable from a) one or more urethane-containing NCO prepolymers having an NCO content of 18 to 27% by weight obtainable from A) diphenylmethane diisocyanate isomers and optionally higher  Homologues thereof and optionally modified diphenylmethane diisocyanates with at least 50% by weight of monomeric diphenylmethane diisocyanate and B) polymeric polyalkylene oxides having 1.8 to 8 isocyanate-reactive groups per molecule and at least 5 to 100 wt .-%, based on polyalkylene oxide, ethylene oxide units and / or polymeric polycarbonate polyols having molecular weights of 1000 to 15000, a ') optionally in admixture with modified diphenylmethane diisocyanates, and b) water, water vapor and / or atmospheric moisture. Sandwich elements, characterized in that they comprise i) a core of the paper structure according to claim 5 and ii) at least one layer of fiber-reinforced polyurea and / or polyurethane located on at least one of the two sides of the core.