NO301337B1 - Penetrating polyurethane-urea based blend for porous substrates and application of blend in stain and sealant - Google Patents

Description

Coatings (finishes) that are applicable to porous substrates, such as wood, concrete, cement, brick and the like, typically fall into two broad classes: Surface coatings and penetrating coatings. Surface coatings can have a high molecular weight, can be highly cross-linked, and are characterized by the fact that they form a continuous film over the substrate. Varnish and clear polyurethane coatings are typically classified as surface coatings.

Penetrating coatings, on the other hand, are formulated to protect a substrate, and usually change a substrate's color, while maintaining the substrate's natural structure. Penetrating, pigmented stains, non-pigmented wood preservatives and water sealers are typical examples of penetrating coatings. One important feature of penetrating coatings is that they are formulated so that they do not form a visible surface film or a visible coating on the wooden substrate. They typically have low molecular weight and very small particle size. They are durable, well-suited for structured, exposed surfaces, such as exterior cladding, decks, steps and the like, and can contain water-repellent agents, and they can be easily applied. The ability to penetrate the surface without leaving a significant or visible film on the surface virtually eliminates the peeling and cracking that can occur with varnishes and surface coatings.

Penetrating coatings can further be divided into subgroups such as clear systems or colored systems. The clear systems typically contain a water-repellent agent. When applied to a wooden substrate or to a porous substrate, these compositions serve to protect the substrate from moisture. In addition to the protective characteristics, the colored systems are formulated so that they change the color of the wood surface or the porous surface without covering the grain or structure of the substrate.

This invention is directed to penetrating finishes, particularly penetrating stains and waterproofing agents. In the past, commercial stains and waterproofing agents for buildings were formulated from oil-based mixtures. Many commercially available wood stains still use pure linseed oil. Oil-based mixtures are relatively inexpensive and provide good spreading characteristics. Such stain types, however, typically lack good abrasion resistance and good drying characteristics. They also typically have a very high content of volatile organic compounds (VOC = volatile organic compounds).

As new environmental laws and regulations were added that regulated the maximum amounts of VOCs allowed in paints, coatings, stains, sealants and the like, many attempts were made in the prior art to formulate penetrating stains that meet the requirements for VOCs.

For example, European patent application No. 0 314 3 78 Al describes a water-based alkyd topcoat stain containing a water-reducible alkyd resin with a medium long oil chain, solubilized in water using propylene glycol tertiary butyl ether as solvent. It is stated that the product has low VOC, good water resistance, abrasion resistance and the like.

Likewise, US Patent No. 4,276,329 describes a mixture for the treatment and protection of wooden surfaces, comprising a low molecular weight alkyd resin in a coalescing agent consisting of water and glycol ether.

US Patent No. 4,432,797 describes a water-based, thickened stain containing a film-forming resin, pigment, thickener and water. It is taught that the resin is either an alkyld polymer, an aqueous acrylic polymer, or an aqueous solution of a modified polysaccharide polymer.

GB Patent Application No. 2 215 732 A describes a water-based wood stain formulation comprising a water-soluble acrylic resin and a pigment.

GB Patent No. 1 589 605 describes a method for producing a penetrating wood stain from a suspension of finely divided solids in an oil-in-water emulsion.

The present invention relates to penetrating mixtures with low VOC for pickling and protection of porous surfaces, such as wood, concrete, cement, brick and the like. In particular, this invention relates to stable water dispersions of polyurethane-urea types with a small particle size, which can penetrate into the surface to be coated. The dispersions are particularly useful as an environmentally friendly penetrating stain and waterproofing agent.

The dispersions in the mixtures according to the present invention are stable dispersions with a small particle size and with a low content of VOC, of polyurethane-urea types in aqueous solution, and which are particularly suitable as penetrating stains and water sealing agents. The dispersions have excellent wear resistance, storage stability, penetration ability on porous surfaces and stability against UV light. These dispersions are particularly suitable for use, either alone or with additional components, such as pigments, waxes and the like, as penetrating stains and water sealing agents. The polyurethane-urea types are predominantly linear molecules with essentially no cross-linking, and they have a low molecular weight. The mixtures according to this invention differ from surface coatings and paints in that they do not form a visible film when applied to a porous substrate, such as wood, concrete, cement, brick and the like.

The preparations used are penetrating stain types and waterproofing agents that have a low VOC content, and are stable dispersions of polyurethane-urea types with a small particle size in an aqueous medium. As mentioned, the particle size of the polyurethane-urea molecules is less than 0.2 µm, and most preferably in the range from 0.01 to 0.1 µm. The polyurethane-urea types are predominantly linear molecules, and have a low molecular weight. Before the dispersion in water, the polyurethane-urea intermediates have a weight average molecular weight which is generally less than approx. 10,000. After dispersion in an aqueous medium, the polyurethane-urea types have a theoretical free isocyanate functionality of zero and a weight average molecular weight that is generally less than approx. 50,000. Due to the low molecular weight and the linear character of the molecules, the dispersions also have lower viscosities, and they can thus be formulated with higher solids levels using less solvents.

The present invention thus comprises a mixture which penetrates into porous substrates without forming a noticeable film on the substrate, characterized in that it comprises

a) a dispersion ion in an aqueous medium of a polyurethane-urea with a particle diameter of less than 0.2 µm, the polyurethane-urea comprising the reaction product, formed in the presence of between 0.01 and 0.06% by weight of a catalyst , off

i) at least one diol with

ii) at least one diisocyanate functional material;

where the ratio between i) and ii) is such that the ratio between isocyanate functionality and hydroxy functionality

is in the range between 1.01 : 1 and 1.5 : 1; where between 1 and 10% by weight of the total polymer solids are made up of diols with the ability to contribute ionic or hydrophilic groups to the polyurethane-urea, the reaction product of i) and ii) being neutralized to at least 80% with a weak base

before dispersing in the aqueous medium, and

b) a surface tension modifying agent selected from 2,2,4-trimethylalkyldiol monoisobutyrate solvents;

glycols; glycol ethers; alcohols, and mixtures thereof in an amount between 0.25 and 5.0% by volume, based on the total volume of the mixture, as stated in crawl.

The diol in this mixture is selected from the group stated in claim 2.

The invention also relates to the use of the mixtures, as well as at least one dye in the case of stain, and at least one paraffin or wax in the case of the waterproofing mixture, in a water-based penetrating stain or waterproofing agent, as stated in claim 5.

The mixtures according to this invention are prepared by first reacting at least one diol, preferably selected from the group consisting of diols such as

1) polyester diols formed by the reaction of saturated and unsaturated polyhydric alcohols, such as ethylene glycol, propylene glycol, neopentyl glycol, 1,4-butanediol, 1,4-butenediol, 1,6-hexanediol, furandimethanol and cyclohexanedimethanol, with saturated and unsaturated polycarboxylic acids and derivatives of these, such as maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, adipic acid, isophthalic acid, terephthalic acid, phthalic anhydride, dimethyl terephthalate, dimeric acids and the like; 2) polyesters formed by reaction of lactones, such as caprolactone, with a diol; 3) polyetherdiols, such as the products of the polymerization of a cyclic oxide, such as ethylene oxide, propylene oxide or tetrahydrofuran; 4) polyetherdiols formed by adding one or more cyclic oxides to water, ethylene glycol, propylene glycol, diethylene glycol, cyclohexanedimethanol, glycerol or bisphenol A; 5) polycarbonate diols, such as the reaction product of 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol or tetraethylene glycol with diaryl carbonates, such as diphenyl carbonate or phosgene; 6) polyacetal diols, such as the reaction product of a glycol, such as diethylene glycol, triethylene glycol or hexanediol with a formaldehyde; 7) low molecular weight diols, such as dihydroxyalkanoic acids,

including dimethylpropionic acid;

and mixtures thereof, with at least one aromatic, cycloaliphatic or aliphatic diisocyanate functional component, preferably selected from the group consisting of tetramethylene diisocyanate, hexamethylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, isophorone diisocyanates, Desmodur W<®> (a 4,4'-dicyclohexylmethane diisocyanate available from Mobay), benzene-1,3-bis(1-isocyanate-1-methyl-ethyl)[m-TMXDI], and mixtures thereof.

Present during the reaction is up to 0.06%, preferably between 0.01% and 0.04%, (wt% based on total amount of solid diol and diisocyanate) of a catalyst, such as dibutyl tin dilaurate, tin octoate and the like.

The preferred ratio between diol and diisocyanate should be such that there is an excess of isocyanate functionality in relation to hydroxy functionality. As mentioned, the equivalent ratio between NCO and OH is between 1.01:1 to 1.5:1; preferably between 1.01:1 and 1.3:1.

To be sure that the polyurethane-urea intermediate is dispersible in an aqueous medium, it is important that a percentage of the total weight of the polymeric solids, as mentioned between 1% and 10%, is made up of diols, which have the ability to contribute ionic or hydrophilic groups to the polyurethane-urea, - e.g. diols containing carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, ammonium salts, phosphonium salts or sulfonium salts.

The reaction is typically carried out by adding the diol together with the catalyst to a reaction vessel, heating the contents to a temperature between 70°C and 100°C, and adding the diisocyanate-functional materials, either continuously or stepwise over a time period, preferably between 1/2 hour and approx. 4 hours. Optionally, a solvent may be present, such as n-methylpyrrolidinone, dimethylformamide, methyl ethyl ketone, toluene and mixtures thereof in an amount which may be up to 20% by weight based on the total weight of the materials present in the reaction vessel. After complete addition of the diisocyanate materials, the temperature in the reaction vessel is maintained between 80°C and 100°C for as long as necessary to bring the residual percentage of isocyanate (percentage based on the total weight of solids in the polymer) below approx. . 3.0%, preferably in a range between approx. 1.6% and approx. 2.4%. This takes approximately 2-4 hours. Residual isocyanate percentage can be measured by any technique known in the field. The contents are then cooled to below approx. 7 0°C, and the ionic groups present in the product of the above reaction are then neutralized by the addition of a weak base, such as triethylamine, trimethylamine, triisopropylamine, tributylamine, triethylenediamine (e.g. DABCO®, commercially available from Air Products Co.), N,N-dimethylcyclohexylamine, N,N-dimethylstearylamine, N,N-dimethylaniline, N-methylmorpholine, N-ethylmorpholine, N-methylpiperazine, N-methylpyrrolidine, N-methylpiperidine, N,N-dimethyl-ethanolamine, N,N-diethyl-ethanol-amine, triethanolamine, N-methyl-diethanolamine, dimethylamino-propanol, 2-methoxyethyl-dimethylamine, N-hydroxyethyl-piperazine, 2-(2-dimethylaminethoxy)- ethanol and 5-diethylamine-2-petanone and mixtures thereof. The most preferred neutralizing agents are the tertiary amines because they are not reactive with the free isocyanate groups. The amount of weak base added is sufficient to neutralize at least 80% of the ionic groups present in the solution. Preferably, the weak base is added in an amount sufficient to neutralize 100% of the ionic groups. The weak base can be added in excess, i.e. in an amount that is greater than the amount necessary to neutralize the ionic groups.

The intermediate product at this stage has a weight average molecular weight of less than 10,000, and due to the difunctional nature of both the diols and the diisocyanates, has predominantly linear molecules.

The intermediate is then dispersed in water or in a water-based solvent. The percentage of solids in the water or in the aqueous solvent can be between 20% by weight and 60% by weight, preferably between 30 and 50% by weight.

A difunctional amine compound, such as ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, cyclohexylenediamine, piperazine, hydrazine, mixtures thereof, equivalents thereof and the like, in an amount sufficient to react with up to 80% of the theoretical amount of residual NCO functionality can optionally be included in the dispersing medium for chain extension of the polyurethane. Amounts of chain extenders higher than this tend to give dispersions with molecular weights that are unacceptably high for use as penetrating stains and waterproofing agents on porous substrates. Chain extenders with a functionality greater than 2 should not be included in significant amounts because they - tend to cause unacceptably high levels of branching so that the mixture acts as a film-forming polymer rather than a penetrating mixture when applied to wood or another porous substrate.

Preferably, all hydroxy functional components are exclusively difunctional. A negligible amount of the total number of OH equivalents may originate from higher functionality alcohols; however, a significant amount of such alcohols is not desired because this results in an intermediate product and thus in a final polymer that exhibits high molecular weight and strong branching. The most preferred hydroxy functional starting materials are a combination of 1) the polyester diols formed by the reaction of saturated and unsaturated dihydric alcohols, such as ethylene glycol, propylene glycol, neopentyl glycol, 1,4-butanediol, 1,4-butenediol, 1,6- hexanediol, furandimethanol, and cyclohexanedimethanol, with saturated and unsaturated polycarboxylic acids, such as maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, adipic acid, isophthalic acid, terephthalic acid, phthalic anhydride, dimethyl terephthalate, dimeric acids and the like; and 2) a diol containing hydrophilic groups. One such preferred polyester diol is Rucoflex<®> 1015-120 (a mixture of polyester diols based on neopentyl glycol, hexanediol and adipic acid, commercially available from Ruco Polymer Corporation). A particularly preferred diol containing hydrophilic groups is dimethylolpropionic acid. When used, these two diols are preferably present in such large amounts that the Rucoflex nvaterial contributes between 40% and 70% of the total material's H function.

The most preferred isocyanate functional materials are exclusively diisocyanates selected from the group consisting of Desmodur W<®> (4,4'-dicyclohexylmethane diisocyanate), m-TMXDI (benzene-1,3(1-isocyanate-l- methylethyl), IPDI (isophorone diisocyanates) and mixtures thereof. Most preferred is a combination of Desmodur W<®> and m-TMXDI.

As is the case with the alcohols, a small proportion of the diisocyanate functional materials may have a functionality greater than 2; for the same reasons, however, a significant percentage of such diisocyanate constituents is not acceptable because of the effect on molecular weight and chain branching for both the intermediate and the final product. If a mixture of 2 or more diisocyanates is used, the ratio between NCO equivalents supplied by the individual isocyanates is not critical.

The dispersion medium is preferably water. Water with a low percentage of diamine present or added for chain extension with the remaining NCO is preferred. The amount of dispersing medium should be between 40 and 80% by weight of the total reaction components. More preferably, the percentage of dispersing medium is between 50 and 80% by weight. If a chain extender is used, it should preferably be present or added in an amount sufficient to react with up to 80% of the remaining NCO functionality. The final chain-extended dispersion should have a weight average molecular weight less than 50,000.

Immediately after the dispersion in the dispersing medium, the mixture can be modified with other standard ingredients that are usually used for the formulation of penetrating stains, wood preservatives and water sealants. The dispersions can e.g. combined with other ingredients, such as pigments, dyes, paraffins, waxes, UV light stabilizers, rheology modifiers, anti-mould agents, biocides, fungicides and other conventional additives, to form excellent penetrating stains, preservatives and/or sealants for wood , concrete, cement, brick and other porous building surfaces. Dyes and pigment dispersions are typically added, if used, in amounts up to 15% by volume of the total mixture. Paraffin and ethylene waxes used to provide water resistance to penetrating finishes are typically used, if used, in amounts up to about 2 - 3% by weight, of the total mixture.

As mentioned, a surface tension-modifying component is added to the mixture to reduce the carrier's surface tension. It has been found that adding such a surface tension modifying ingredient results in the formulation being more easily able to penetrate into the porous substrate where it is applied. Suitable solvents for use as surface tension modifying agents include 2,2,4-trimethylalkyldiol monoisobutyrate solvents available from Eastman Chemial and marketed under the trade name Texanol™, glycols such as ethylene glycol, propylene glycol, di-propylene glycol, and the like, glycol ethers such such as 2-butoxy-ethanol (Butyl Cellosolve<®>), , diethylene glycol monobutyl ether (Butyl Carbitol<®>), and the like, and alcohols, such as methanol, ethanol, propanol and the like; and mixtures thereof. In general, the surface tension modifier should be added in an amount sufficient to reduce the carrier's surface tension to a level where the formulation achieves the desired penetration into the porous substrate. The amount of surface tension modifier required is between 0.25 and 5.0% by volume, based on the total volume of the formulation. It should be understood, however, that many additives for standard stains and sealants are commercially available in a medium that imparts some surface tension-modifying effect. One should especially be aware that many commercially available rheology modifiers are sold in glycol and glycol ether media. The media can contribute some surface tension-modifying properties. The Rheolate™ materials are e.g. commercially available in a butyl carbitol medium. In addition, some mold poisons and fungicides are commercially available in petroleum distillate media. These media can also contribute with some surface tension-modifying characteristics. In general, media which can be expected to impart a surface tension-modifying effect, and which are present in significant quantities, should be included when the total percentage content of surface tension-modifying agents is calculated.

The following examples show the methods for producing the penetrating finishes according to this invention. The examples are intended to be representative of the formulations that can be prepared.

Example I - Preparation<g> of the dispersion

112.2 g n-methylpyrrolidinone, 591.96 g Rucoflex 1015-120 (1.3 equivalents OH), 69.74 g dimethylolpropionic acid (1.04 equivalents OH) and 1.6 g dibutyltin dilaurate (10% solution in n-methylpyrrolidinone ) is added to a reaction vessel equipped with a nitrogen blanket. Stirring begins and the temperature is increased to approx. 80°C. An addition over 2 hours of 161.6 g of Desmodur W (1.23 equivalents of NCO) and 188.03 g of m-TMXDI (1.54 equivalents of NCO) is begun. After addition of all isocyanate functional materials, the reaction is held at 80°C for approximately 3 hours. 63.02 g of triethylamine is added to neutralize the ionic groups, and the reaction is allowed to continue for another half hour. The resulting material is dispersed in 1,500 g of water, and 10.4 g of ethylenediamine is added.

Dispersions prepared as described above generally have the following characteristics:

Example II - Wood stain

The following composition represents a typical penetrating stain formulation using the polyurethane-urea dispersion of Example I to which commercially available standard colorants and pigment dispersions can be added.

Example III - Waterproofing agent

The following formulation represents a typical non-pigmented water seal formulation in which the polyurethane-urea dispersion from Example I is used.

When producing this sealant, it is highly preferred to inactivate metal ions which may be present in the water, and which will tend to fall out of the solution when the surface tension modifier is added.

Claims (5)

1. Mixture which penetrates into porous substrates without forming a noticeable film on the substrate, characterized in that it comprises a) a dispersion in an aqueous medium of a polyurethane-urea with a particle diameter of less than 0.2 µm, the polyurethane being -the urea comprises the reaction product, formed in the presence of between 0.01 and 0.06% by weight of a catalyst, of i) at least one diol with ii) at least one diisocyanate functional material; where the ratio between i) and ii) is such that the ratio between isocyanate functionality and hydroxy functionality is in the range between 1.01:1 and 1.5:1; where between 1 and 10% by weight of the total polymer solids are made up of diols with the ability to contribute ionic or hydrophilic groups to the polyurethane-urea, the reaction product of i) and ii) being neutralized to at least 80% with a weak base before dispersing in the aqueous medium, and b) a surface tension modifying agent selected from the group consisting of 2,2,4-trimethylalkyldiol monoisobutyrate solvents; glycols; glycol ethers; alcohols, and mixtures thereof in an amount between 0.25 and 5.0% by volume, based on the total volume of the mixture, as well as optionally c) a diamine chain extender in an amount sufficient to react with up to 80% of the theoretical amount of rest-NCO- f unk's joiality. 2. Mixture according to claim 1, characterized in that the diol is selected from the group consisting of a) polyester diols formed by the reaction of saturated and unsaturated dihydric alcohols with saturated and unsaturated polycarboxylic acids and derivatives thereof; b) polyesters formed by the reaction of lactones with a diol; c) polyetherdiols resulting from the polymerization of a cyclic oxide; d) polyetherdiols formed by the addition of one or more cyclic oxides to water, ethylene glycol, propylene glycol, diethylene glycol, cyclohexanedimethanol, glycerol or bisphenol A; e) polycarbonate diols resulting from the reaction of 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol or tetraethylene glycol with diaryl carbonates; f) polyacetal diols resulting from the reaction of a glycol with formaldehyde; g) low molecular weight dihydroxyalkanoic acids; and mixtures thereof. 3. Mixture according to claim 1 or 2, characterized in that the diisocyanate-functional material is selected from the group consisting of tetramethylene diisocyanate, hexamethylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, isophorone diisocyanates, 4 ,4'-dicyclohexylmethane diisocyanate, benzene-1,3-bis(1-isocyanate-1-methylethyl), and mixtures thereof. 4. Mixture according to claim 1, characterized in that the diols which have the ability to contribute ionic or hydrophilic groups contain carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, ammonium salts, phosphonium salts or sulfonium salts. 5. Use of a mixture comprising a) a dispersion in an aqueous medium of a polyurethane-urea with a particle diameter of less than 0.2 µm, the polyurethane-urea comprising the reaction product, formed in the presence of between 0.01 and 0 .06% by weight of a catalyst, of i) at least one diol with ii) at least one diisocyanate-functional material; where the ratio between i) and ii) is such that the ratio between isocyanate functionality and hydroxy functionality is in the range between 1.01:1 and 1.5:1; where between 1 and 10% by weight of the total polymer solids are made up of diols with the ability to contribute ionic or hydrophilic groups to the polyurethane-urea, the reaction product of i) and ii) being neutralized to at least 80% with a weak base before dispersing in the aqueous medium, and b) at least one dye in the case of stain, and at least one paraffin or wax in the case of waterproofing agent, and c) a surface tension modifying agent selected from 2,2,4-trimethylalkyldiol monoisobutyrate solvents; glycols; glycol ethers; alcohols, and mixtures thereof in an amount between 0.25 and 5.0% by volume, based on the total volume of the mixture, in a water-based, penetrating stain or waterproofing agent, so that when applied to a porous building material, the stain/waterproofing agent penetrates into the substrate and does not form a visible film on the substrate.