DE10115004A1 - Control of moisture induced curing of polyurethane foam with a pH indicator, useful for curing foamed assembly materials, adhesives, and jointing compounds ensures adequate curing by following the color change with increase in pH - Google Patents

Abstract

A moisture cured polyurethane resin (PR) cured with an excess of isocyanate groups obtained from; (A) compounds with at least two isocyanate groups; (B) compounds with at least two hydrogen atoms reactive to isocyanate groups; and (C) an amine compound, and containing a pH indicator, or this is added to the PR, which indicates the moisture curing of the PR by a sudden color change when the pH increases is new. An Independent claim is also included for curing of PR containing unreacted isocyanate groups with addition of a pH indicator for indicating alteration of the PR with rise in pH.

Description

The invention relates to moisture-curing polyurethane plastics, which contain an indicator of the progress of curing through color change displays. The invention further relates to a method for moisture removal curing and the use of the polyurethane plastics according to the invention as Assembly foams, adhesives and sealants.

Polymers with very different compositions are known as polyurethanes (PUR) tongue. Common to all PUR is that they are characteristic chains member have urethane groups. The percentage of urethane groups compared to others however, the groups linking the monomer units can be very small. Next the urethane bond can include urea, amide, biuret, acyl urine substance, urethonimine, isocyanurate and carbodiimide bonds through the reaction be formed. Link in many industrially important PUR plastics the urethane groups polyalkylene ether or polyester sequences, which in turn moles can have specific weights of 200 to 6000 g / mol.

The production of polyurethane foams by implementing higher moles kularen, preferably polyester and / or polyether polyols and optionally Chain extenders and / or crosslinking agents with organic and / or modes Organic polyisocyanates are known and are used in numerous patent and literature publications.

The variety of possible connections is not only due to the reactivity of the Isocyanate bond, but also due to the multitude of different ones the isocyanate group of reactive monomers. Furthermore, regarding their functionality different monomers simultaneously used side by side be set. The most common monomers besides the diisocyanates have Al alcohol, carboxylic acid and / or amine groups. In addition, the Re also plays action of the isocyanate group with water plays an important role.

The reactions of the NCO group are extremely sensitive to Various types of catalysts. Both Lewis bases and Lewis acids are effective catalysts. The most important Lewis bases are tertiary amines and different structure. The main catalytic Lewis acids are organotin metal compounds. The catalysts are often used as a system, i.e. H.  as a combination of several catalysts, such as a Lewis base with a Lewis Acid. The catalytic converter / the catalytic converter system accelerates of two sometimes three main reactions used simultaneously and often in Kon compete with each other.

One of these reactions (chain structure: first reaction type) is the chain extension de Isocyanate-hydroxyl reaction, in which a hydroxyl-containing molecule with a Isocyanate-containing molecule reacts to form a urethane. In this reaction a secondary nitrogen atom is generated in the urethane groups. Are next to the Hydroxyl groups also other reactive hydrogen groups, such as such as amine groups, also have other chemical linkages (e.g. Urea groups) for chain building. In addition, excess isocya nat groups also by means of dimerization, trimersization and carbodiimidisia reaction with each other (networking: second reaction type).

The third reaction is the isocyanate-water reaction, in which a molecule with iso cyanate end group is extended to form a urea group and Koh produces dioxide. The gas released acts as a blowing agent to close the foam to bloat or to aid the expansion of the foam. This reaction is called a propellant called reaction.

It is known that tertiary amines are the crosslinking reaction (second type of reaction) catalyze effectively. These are often referred to as gel catalysts. Some of the However, tertiary amines are also effective catalysts for the third reaction, the iso cyanate-water reaction and can therefore also be used as blow catalysts (blowing or Propellant catalysts).

The different reactions often run simultaneously and depending on the application with optimally coordinated speed, so that the desired structure tur of the PUR plastic is obtained.

The invention relates to both semi-rigid foams and adhesives and sealants.

In the construction sector, prepolymers are usually terminated with isocyanate for PUR foams polymers that can be cast or sprayed.  

So are usually used for the foaming of joints, door and window connections Sen prefers one-component foams curing with moisture by extrusion used from pressurized cans (so-called assembly foam). The prepo lymer is creamy when discharged by evaporation of the propellant then foams and hardens due to the moisture from the surrounding area exercise and the air, with a two to three-fold increase in volume. Two-component systems in refillable container systems are also for outdoors insulation known. Polyurethane plastics described above harden upon contact with the humidity, but have the disadvantage that it is not easy is known when the curing process is so far completed that the Hardening allows a load to be lifted.

Methods for the quantitative detection of free isocyanate are from laboratory analysis known groups. The so-called NCO value is determined by Um setting the residual isocyanate groups with a secondary aliphatic amine and acidimetric back titration of the excess amine against bromophenol blue. The used amine is titrated back by adding an acid - here hydrochloric acid. However, this method requires a complex sample preparation, as well as a analytical know-how of the user and suitable laboratory equipment and is therefore we which can still be used for assembly foams for adhesives.

The object of the present invention is the adequate curing of a moist action-hardening polyurethane plastic in the form of a color change to make adjustable.

The object is achieved according to the invention by a moisture-curing polyurethane plastic which, before moisture curing, has an excess of isocyanate groups, prepared from or containing:

• A) compounds with at least two isocyanate groups,
• B) polymer compounds which contain at least two isocyanate Groups have reactive hydrogen atoms, and
• C) an amine compound

characterized in that the polyurethane plastic

• A) contains a pH indicator or this to the polyurethane plastic is set and the indicator is the moisture curing of the polyurethane -Plastic indicates by color change, the color change  is brought about by increasing the pH, preferably by changes tion of the pH value from acid towards neutral.

Moisture-curing polyurethane plastics are polymer masses that over have closed isocyanate groups and under the influence of water as moisture hardening. Water is added either through atmospheric humidity, ambient damp (e.g. masonry) or by the targeted addition of water.

The object of the invention is further be by PUR plastics above Written type, which preferably the pH indicator in a concentration from 0.01 to 0.20 wt .-% based on the prepolymer. Larger amounts of The indicator leads to an intensification of the color change, but can often be reduced fig no longer completely dissolve in the PUR composition. This can lead to failure lungs, which may lead to blockages of valves through which the polymer mixtures spread, lead and moreover an uneven staining of the PUR Result in plastics.

Bromophenol blue is preferably used as the pH indicator. The polyurethane Plastic that has an excess of isocyanate groups before moisture curing has a yellow color before contact with moisture. With increasing hardening the color changes from yellow-green to blue-green. When the blue-green color is reached The PU plastic is sufficiently hardened and tack-free. More preferred Embodiments are the subject of the dependent claims.

The following can be used to produce the PUR plastics according to the invention Components are used, which he exemplifies in the following under (1) to (8) are refined.

(1) Organic and / or modified organic polyisocyanates

The known organic, z. B. aliphatic, cy cloaliphatic, arylaliphatic, cycloaliphatic-aromatic and preferably aromatic, di- and / or polyisocyanates.

Common representatives of aliphatic polyisocyanates are e.g. B. 1,6-diisocyanato hexane, 3,5,5-trimethyl-1-isocyanato-3-isocyanato-methyl-cyclohexane, 4,4'-diiso cyanato-dicyclohexylmethane, trimer hexane diisocyanate and 2,6-diisocyanatohexanoic acid methyl ester.  Common aromatic polyisocyanates are 2,4-diiso cyanato-toluene, 1,5-diisocyanato-naphthalene and 4,4'-diisocyanatodiphenylmethane.

Examples of aromatic polyisocyanates are: 4,4- and 2,4-Diphenylmethane diisocyanate (MDI), mixtures of MDI isomers and Po lyphenyl polymethylene polyisocyanates, 2,4- and 2,6-tolylene diisocyanate (TDI) as well as the corresponding commercial isomer mixtures.

So-called modified polyvalent isocyanates, ie. H. Products, by chemical reaction of organic compounds with polyisocyanates will hold. Examples include ester, urea, biuret, allophanate, Isocyanurate and preferably carbodiimide, uretonimine and / or urethane groups containing di- and / or polyisocyanates.

In particular, the following may be considered: Pre containing urethane groups polymers with an NCO content of 14 to 2.8 wt .-% or quasi-prepolymers, the are produced by reacting diols, oxalkylene glycols and / or Po lyoxyalkylene glycols with polyisocyanates.

(2) polymer compounds with at least two reactive hydrogen atoms

In addition to polyether and high-molecular-weight compounds, there are also Polyester polyols also polythioether polyols, polyester amides, hydroxyl groups term polyacetals and hydroxyl-containing aliphatic polycarbonates or Mi at least two of the compounds mentioned. As a poly mer compounds with at least two reactive hydrogen atoms are proposed preferably compounds with a molecular weight of greater than 300 g / mol hen.

The most important are polyether polyols, such as polypropylene oxide or Po polyethylene oxide or its copolymers. These can e.g. B. with the help of di- or polyfunctional alcohols have been produced as starter molecules. The poly ether component preferably has a molecular weight between 800 g / mol and 2000 g / mol and a functionality of 1.5 to 3.

To produce the polyesters used according to the invention, di- and tri-radio tional polyols polycondensed with dicarboxylic acids or their anhydrides. Geeig Nete polyols are e.g. B. ethylene glycol, 2-propanediol, 1,4-butanediol, 1,6-hexanediol,  Glycerin, trimethylolpropane, pentaerythritol, glycerin and hexanetriol. Suitable Di carboxylic acids or anhydrides are succinic acid, adipic acid, phthalic acid and Isophthalic. The polyesters preferably have a molecular weight between 300 and 3000 and a relatively high hydroxyl number at a ratio moderately low acid number.

Mixtures of polyether polyols and polyether polyamines are also suitable. Suitable polyester polyols can, for example, from organic dicarboxylic acids with 2 to 12 carbon atoms and polyhydric alcohols with 2 to 12 carbons atoms of matter, are produced.

The polyester amides that can be used include, for. B. from polyvalent, saturated and / or unsaturated carboxylic acids or their anhydrides and polyvalent ge saturated and / or unsaturated amino alcohols or mixtures of polyvalent gene alcohols and amino alcohols and / or polyamines, predominantly linear condensates.

Urea groups can be found in the polyurethanes produced according to the invention by using water or diamines. Ethylenediamine, 1,2- Propylenediamine, diaminocyclohexane or piparazine act e.g. B. as chain extensions rer or crosslinking agent. Are polyurethane prepolymers with amine end groups more reactive than those with a hydroxyl group, so that these polyurethanes harden faster Compounds with polymercapto groups can also be used.

(3) low molecular chain extenders and / or crosslinking agents (optional)

Such agents include polyfunctional, especially di- and trifunctional, Compounds with molecular weights from 18 to about 400 g / mol, preferably from 62 to about 300 g / mol. For example, di- and / or trialkanolamines, such as. B. diethanolamine and triethanolamine, aliphatic Diols and / or triols with 2 to 6 carbon atoms in the alkylene radical, such as. B. ethane, 1,4-butane, 1,5-pentane, 1,6-hexanediol, glycerin and / or trimethylolpropane, what water and low molecular ethoxylation and / or propoxylation products, herge represents from the aforementioned dialkanolamines, trialkanolamines, diols and / or Triplets and aliphatic and / or aromatic diamines.  

Dialkanolamines, diols and / or triols and in particular are preferably used special ethanediol, 1,4-butanediol, 1,6-hexanediol, diethanolamine, trimethylolpropane, Pentaerythritol, glycerol or hexanetriol or mixtures of at least two of the aforementioned connections.

(4) blowing agent

Physically active blowing agents are used in the area of the assembly foams puts. Substances which are suitable compared to the organic, if appropriate modified polyisocyanates are inert and boiling points below 0 ° C, preferably below -15 ° C, at atmospheric pressure, so that during discharge evaporate suddenly. Examples of such, preferably usable substances are low-boiling hydrocarbons, such as propane, n / i-butane, Ethers such as dimethyl ether and halogenated hydrocarbons such. B. R 134a and R152a.

To blowing agents used in the production of polyurethane foams moisture (water) preferably include humidity associated with Isocyanate groups reacted to form carbon dioxide as a propellant.

(5) Flame retardant (optional)

To increase the flame resistance while reducing the flue gas Densities in the event of fire are, for example, halogenated, or ganic compounds preferably phosphoric acid esters in effective amounts used. Halogenated, mostly bro come as flame retardants mated, aromatic or aliphatic polyester polyols, starch, phosphorus compounds conditions such. B. tricresyl phosphate, and inorganic salts and preferably modifi decorated or unmodified ammonium polyphosphates.

(6) stabilizers

To avoid collapses and to build up a fine, uniform cell structure, foam stabilizers are used. This is surface Chenactive substances, mainly polyether-modified polysiloxanes, which serve and support the homogenization of the starting materials if also suitable to regulate the cell structure of the foams. Called examples include siloxane-oxyalkylene copolymers and other organopolysi loxanes, ethoxylated alkylphenols and ethoxylated fatty alcohols.  

(7) catalysts

To speed up the implementation between the connections with at least two reactive hydrogen atoms, hydroxyl-containing chain extension and / or crosslinking agents and moisture as blowing agents and the organic and / or modified organic polyisocyanates are polyurethane catalysts ren admitted.

Suitable catalysts are: Lewis bases, i. H. Electro pair donors e.g. B. aromati cal and / or aliphatic amines and Lewis acids, d. H. electron pair, z. B. metal salts and / or organometallic compounds.

Catalysts are particularly preferred over the NCO prepolymers are indifferent, but significantly activate the isocyanate-water reaction and that do not or not negatively affect the storage stability of the one-component system influence. Catalysts of bis (alkylamino) alkyl ether compounds such as Dimorpholinodiethylether (DMDEE), as well as such bis (alkylamino) alkylether Compounds that are described in DE 197 42 720.

Tin salts, e.g. B. Dialkyltin Dicar bonic acid esters and especially dibutyltin carboxylate, tin dioctoate, tin diethylhexoate, Dibutyltin laurate, dibutyltin dilaurate, dibutyltin mercaptide and dibutyltin bis called dodecyl mercaptite.

(8) Other auxiliaries and / or additives (optional)

The reaction mixture can optionally also contain other auxiliaries and / or additives are incorporated. Surfaces are mentioned, for example active substances, stabilizers, hydrolysis protection agents, pore regulators, fungistatic and Bacteriostatic substances, dyes, pigments and fillers, soft makers, drying agents, fillers, latent hardeners, adhesion improvers, foam stabilizers, also known as silicone oils or emulsifiers. These are e.g. B. Polysiloxane-polyether copolymers of various structures. More possible additives are hydrolysis stabilizers, oxidation stabilizers, UV Stabilizers, flame retardants or dyes, preferably in the form of Color pastes.  

In the context of the invention, the polyurethanes can be of different manufacturers be produced. Polyurethanes are made using the one-shot process preferably in the absence of solvents in the presence of all reactions on components manufactured. The procedure sets an approximately comparable Re Action speed of the various H-active components and the Polyiso cyanate ahead.

One differentiates from this the prepolymer process. Polyurethane prepolymers are intermediate stages of isocyanate polyaddition. One differentiates between NCO Prepolymers with terminal NCO groups and hydroxy prepolymers. The NCO prepolymers have a special meaning because they are used with a variety of active hydrogen-containing compounds can be cured. she are by reacting di- or polyhydroxy compounds with a mola Ren excess di- or polyisocyanate obtained. These mixtures can still contain a substantial percentage of the monomeric isocyanate.

The indicators to be used according to the invention are preferably used in prepolymer Mixtures used. The PUR prepolymer preferably has a functionality from about 2 to 4 and preferably a molar mass of greater than 3000 g / mol.

One-component systems or two-component systems can be used to manufacture polyurethanes component systems are used. A distinction is made between physically drying ones component systems and drying by exposure to atmospheric moisture component systems.

The latter preferably contain relatively low molecular weight prepolymers (2000 -2000 g / mol) with terminal NCO groups. Here is the curing speed depending on the ambient humidity and the temperature. On Storage stability is an important requirement of such one-component systems. The Indicators to be used according to the invention are preferably in / for moist keitshärenden one-component systems used, it u. a. a credit to Indicators to be used according to the invention is part of the single component systems not to negatively influence their storage stability.

One-component systems are excess PUs containing isocyanate groups Compounds, possibly further polyol compounds and foam stabilizers gates, plasticizers, and other auxiliaries may contain. These are common  stored in pressure containers in the presence of propellants, relax when Discharge under evaporation of the blowing agent and crosslink under the influence of the order moisture to firm PUR foams.

Two-component systems usually consist of a polyhydroxy component - the if necessary, even through a diisocyanate to a prepolymer with terminal OH Groups can be extended - as the main component and an isocyanate adduct as a crosslinker. The PUR foams can be made using the one-shot process Mixing two components can be made. So the two of them Components only intensively before the production of flexible polyurethane foams be mixed. The reaction mixtures can be in open or closed Molds as well as foams are foamed.

The indicator is preferably used in PUR plastics, their gelling craze tion is largely completed before curing by the isocyanate Water reaction starts.

The indicator can be the PUR plastic in the manufacture of the polyol component or added to the stabilizer component (silicone compound).

It has surprisingly been found that moisture curing increases with increasing correlates with free amine groups and these cause a pH change that can be visualized by adding the pH indicator.

example

Using a formulation for a commercially available one-component Can foam made of polyol mixture, polymeric MDI and blowing agent were tested cans made. The polyol blend consisted of the polyols, flame retardant medium, silicone stabilizer, catalyst and bromophenol blue together as an indicator.

The indicator turned the polyol mixture deep blue (pH greater than 4.6). After adding the calculated amounts of MDI and blowing agent, the prepoly showed a yellow color (pH value) after the completion of the prepolymer formation reaction less than 3.9), obviously caused by the NCO / OH reaction (urethane formation) during prepolymer formation.  

The NCO / H ₂ O (CO ₂ development, amine and urea formation) which sets in due to the action of atmospheric humidity gradually increases the pH, so that a change in color of freshly discharged foam to blue was again observed, apparently caused by the initially essentially intermediate Formation of primary amine groups, whereby - as an explanation attempt - the content of NCO groups continued to decrease as the reaction progressed, so that less and less urea groups were formed and more and more primary (basic) amine groups remained in the PUR plastic.

The foam fully hardened with the addition of the bromphenol blue indicator had a blue-green color. The colored foam could be, for example, by adding of mineral acid, no longer change color. The bleed of the non-tacky yet fully reacted foam showed a radial gradient starting in Core with yellow over yellow-green to blue-green to the edge. Thus, the curing could can be visually tracked inside the foam.

Claims (10)

1. Moisture-curing polyurethane plastic which has an excess of isocyanate groups before moisture-curing, made from or containing:

• A) compounds with at least two isocyanate groups,
• B) compounds which have at least two hydrogen atoms which are reactive toward isocyanate groups, and
• C) an amine compound

characterized in that the polyurethane plastic

• A) contains a pH indicator or this is added to the polyurethane plastic and the indicator indicates the moisture curing of the polyurethane plastic by color change, the color change being brought about by increasing the pH.

2. Polyurethane plastic according to claim 1, characterized in that the indicator in a concentration of 0.01 to 0.2 wt .-%, preferably 0.02 to 0.1 wt .-%, based on the prepolymer is used. 3. Polyurethane plastic according to one of the preceding claims, since characterized in that the pH indicator has a color change point in the pH-Be ranges from 2.5 to 7, preferably 3 to 6 and particularly preferably 3 to 4.6. 4. Polyurethane plastic according to one of the preceding claims, since characterized in that the pH indicator bromophenol blue, bromocresol green, Is bromocresol purple or bromotymol blue. 5. Polyurethane plastic according to one of the preceding claims, since characterized in that the amine compound (C) at least partly from a Amine catalyst for the water-isocyanate reaction. 6. Polyurethane plastic according to claim 5, characterized in that the Amine catalyst for the water isocyanate reaction a bisalkylamine (Mono / poly) alkyl ether compound.   7. Polyurethane plastic according to one of the preceding claims, since characterized in that the polyurethane plastic as a 1-component system is used. 8. Use of the polyurethane plastics according to one of the preceding Requirements as assembly foams, adhesives and sealing compounds. 9. Process for curing polyurethane plastics not containing set isocyanate groups, characterized in that the polyurethane A pH indicator is added to plastic before moisture curing and the pH Indicator of a change in the pH value of the polyurethane plastic by increasing the pH value. 10. A method for curing polyurethane plastics according to claim 9 characterized in that the moisture curing by air humidity he follows.