Organopolysiloxane resin compositions, curable compositions, coatings, and coated substrates thereof

Abstract

A resin composition, a curable composition, and a coated substrate are provided. The resin composition includes a branched organopolysiloxane, wherein the branched organopolysiloxane comprises the structure MmDnToQp, wherein m is selected such that all chain ends are terminated with M units, n is 1 to 10,000, o is 1 to 100, and p is 0 to 10. The branched organopolysiloxane has a structure of multiple chains, with each chain having acrylate groups. Also provided is a curable composition including the resin composition and an initiator, and a coated substrate wherein the resin composition is disposed with an initiator on the surface of a porous substrate.

Description

[0001] ORGANOPOLYSILOXANE RESIN COMPOSITIONS, CURABLE COMPOSITIONS, COATINGS, AND COATED SUBSTRATES THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to dual-curable resin compositions based on branched organopolysiloxanes. When cured, these resin compositions may be used as protective coatings that impart excellent stain and moisture resistance to architectural substrates such as wood, concrete, stone, brick, or stucco.

[0004] BACKGROUND

[0005] Protective coatings are essential for the preservation and long-term durability of architectural substrates. In interior applications, common substrates such as wood or concrete are exposed to moisture, chemicals, abrasion, and household chemicals causing staining and damage. In exterior applications, these substrates can be exposed to weathering, mechanical stresses caused by temperature and moisture fluctuations, and microbiological degradation. To offer longterm protection, a protective coating must balance weatherability, chemical resistance, and moisture resistance. To increase operational efficiency and minimize the down time, it is important for a coating to have short cure times. Existing coatings are unable to meet both requirements simultaneously, creating a need for a new high-performance rapid-cure coating.

[0006] Moreover, to provide long-term durability, protective coatings, particularly for outdoor applications, need to withstand prolonged weathering. Weathering describes the degradation of both the protective coating and the underlying substrate from exposure to UV radiation, moisture, and wind. Wood is particularly susceptible to UV degradation and the effects of water or moisture absorption. UV radiation promotes oxidation of the lignin, decreasing the cohesive strength of the cellulosic structure, and causing delamination. Moisture absorption from rain or standing water causes swelling, shrinking, cracking, and mechanical stresses within the substrates and any protective coatings applied. Freeze / thaw cycles may further accelerate the degradation of substrates which have absorbed moisture. Substrates may also be scoured by wind and wind-driven particles, contributing to uneven wear on different areas where dirt and mold can accumulate. In addition to weathering, the highly porous nature of many architectural substrates allows chemicals to easily penetrate the substrate, leaving a permanent discoloration through bleaching or staining.

[0007] The use of a curable composition as a protective coating can mitigate the aforementioned problems. A suitable protective coating seals the pores of substrates to prevent the ingress of moisture, dirt, or chemicals and forms a film on the surface of the substrate acting as an additional barrier. Polysiloxane-based curable coatings have been popular in the market due to their durability and protective properties, which results from the unique hydrophobicity of silicones and the strong silicone-oxygen bonds in the polysiloxane network. However, existing polysiloxane-based coatings use a slow moisture cure process. The moisture cure process may require up to several weeks depending on the use of a catalyst, the catalyst type, and catalyst concentration. During the curing process, coated substrates must be handled with care as the uncured polysiloxane-based curable compositions are easily damaged. Coated substrates also cannot be stacked or further processed without damaging the uncured coating which negatively affects the lead times. Further, the cure time of a moisture-cured polysiloxane-based curable composition is affected by relative humidity, which leads to seasonal variations in cure time and creates additional manufacturing challenges. As a result, existing polysiloxane-based curable compositions often sacrifice final properties (e.g., stain resistance) for a fast cure. Accordingly, an objective of the present invention is to provide a polysiloxane-based coating having high durability and protective properties with a rapid curing process. BRIEF SUMMARY OF THE INVENTION

[0008] A resin composition for use with an initiator is provided, including a branched organopolysiloxane. The branched organopolysiloxane may have a specified degree of branching characterized by the quantity of T units and Q units. The branched organopolysiloxane may also be selected to have a specific acrylate content of 4 to 15 acrylates per chain and a specific residual alkoxy content to achieve the satisfactory performance of the curable composition.

[0009] In some embodiments, the resin composition may be dual curable, with a first curing step radiation curing or thermal curing, followed by a second moisture curing step. The radiation curing step may include UV curing, electron beam (EB) curing, or LED curing.

[0010] In some embodiments, the resin composition may include additives such as viscosity modifiers, synergists, surface additives, rheological modifiers, UV stabilizers, pigments, fillers, or matting agents to achieve the desired coating performance.

[0011] In other embodiments, the resin composition may be disposed with an initiator to form a curable composition. In further embodiments, the curable composition may be applied to a porous substrate and cured to form a coating. A coated substrate includes a porous substrate with a coating covering one or more surfaces of the porous substrate.

[0012] BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0013] The above, as well as other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which:

[0014] FIG. 1 is a photograph illustrating shrinking and cracking of coating made from an existing resin composition. FIG. 2 is a photograph illustrating the results of a chemical resistance test.

[0015] DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the present invention will be described in detail. However, it should be understood that the present invention is not limited to the following embodiments, and that various elements may be variously modified or selectively mixed according to need. Accordingly, it is to be understood that the invention includes all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.

[0017] In addition, throughout this specification, when an element is referred to as "including" an element, it is understood that it may include other elements as well, not meaning excluding other elements unless specifically stated otherwise. The terms "about", "substantially", and the like used in the present specification are to be understood, when manufacturing and material tolerances inherent in the meanings mentioned are presented, as they mean "the numerical value" or "in close proximity to the numerical value", and not in a limiting sense.

[0018] Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

[0019] Existing polysiloxane-based curable compositions are usually prepared through end-capping of a, co- silanol terminated organopolysiloxanes with different crosslinkers such as aminosilanes, alkoxysilanes, acetoxysilanes, and oximosilanes, which contain hydrolyzable groups attached to the silicone atom of thereof. Such curable compositions can be designed in one- and two- component formulations and are typically cured by moisture. The moisture curing mechanism is based on the hydrolysis of the hydrolyzable groups with moisture, followed by a condensation of the formed silanol groups to form polysiloxane networks. As discussed above, the process of moisture curing is slow and reduces manufacturing capacities of coated substrates. The use of a radiation (or dual radiation / moisture) curing mechanism can resolve the above-mentioned problem. Radiation-curing is a rapid crosslinking method based on radical polymerization that could be triggered by different sources of radiation such as Ultra-Violet (UV) and Electron-Beam (EB). Radiation and / or the combination of radiation with moisture curing can result in fast curing and short dry-to-touch times (in a matter of minutes), which will significantly reduce the lead times in the manufacturing sites. The existing radiation-curable organopolysiloxane-based curable compositions inlcude linear organopolysiloxanes prepared by hydrosilylating an ethylenically unsaturated compound such as acrylate monomers with a silane or polysiloxane bearing silicone-bonded hydrogen. This process is described in US11180680B2 and US2003 / 0064232A1 . However, when linear organopolysiloxanes are incorporated into resin compositions, the resulting coatings have a low crosslink density, contributing to poor thermal stability and high water uptake.

[0020] Further, the hydrosilylation process used for preparing these compositions, presents additional disadvantages. Both Si-H functional organosilicone compounds and noble metal hydrosilylation catalysts, such as platinum-based catalysts, are very expensive. Furthermore, if the hydrosilylation reaction is not complete, unreacted ethylenically unsaturated reactants must be removed, for example, by subjecting the product mixture to stripping or vacuum. The process of removing unreacted ethylenically unsaturated reactants requires further raising the temperature, which can cause undesirable acrylate homopolymerization. Moreover, if the final product contains unreacted Si-H groups, exposure to moisture can liberate explosive hydrogen gas.

[0021] Lastly, existing resin compositions based on linear polysiloxane backbones are elastic in nature and do not provide the necessary crosslink density to repel dirt and stains. Although this deficiency can be mitigated by adding reinforcing fillers, such reinforcing fillers block UV and hinder the curing process. Therefore, a resin composition and applications thereof that overcome the above-described issues is provided.

[0022] In an embodiment, the resin composition is provided for use with an initiator, which includes a branched organopolysiloxane and optional additives. The branched organopolysiloxane is selected to have a certain degree of branching, acrylate functionalities, and residual alkoxy content.

[0023] Branched Organopolysiloxane

[0024] It has been found that highly branched radiation-curable organopolysiloxanes offer superior protection when used in a resin composition. Such highly branched organopolysiloxanes can be prepared by hydrolysis reaction and subsequent dehydration condensation reaction of silicon- bonded detachable or hydrolysable groups of a silicone compound having a polymerizable ethylenically unsaturated group and a condensable hydroxyl or alkoxy group. A desirable characteristic of these reactive silicones is that they react exclusively through the intended reactive organic functionality, or in other words, have “defined reactivity.”

[0025] The structure of the highly branched organopolysiloxane may be understood as an arrangement of M units, D units, T units, and Q units, defined as follows:

[0026] R1aRb(OR2)cSiOi / 2 (M unit) where a, b, and c are each 0 to 3 and the sum of a+b+c is 3;

[0027] R1aRb(OR2)cSiO2 / 2 (D unit) where a, b, and c are each 0 to 2 and the sum of a+b+c is 2;

[0028] R1aRb(OR2)cSiO3 / 2(T unit) where a, b, and c are 0 or 1 and the sum of a+b+c is 1 ; and

[0029] SiO4 / 2(Q unit).

[0030] In the above formulae, R is a non-reactive group. R may be an organic group with little or no reactivity under expected preparation conditions, and subsequently under curing conditions. R groups include Si-C bonded, optionally substituted hydrocarbon groups, such as alkyl groups, alkenyl groups (when the reactive group is a group other than a (meth)acrylic group), aryl groups, aralkyl groups, and alkaryl groups, where the alkyl groups may be linear, branched, or cyclic. Non-reactive groups do not include Si-O bonded alkoxy groups, Si-N bonded nitrogencontaining groups, and silicon-bonded halogen.

[0031] Suitable R groups include linear alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl, decyl, dodecyl, octadecyl, etc., branched alkyl groups such as 2-butyl, and ethylhexyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, methylcyclohexyl, and cyclohexylmethyl; alkenyl groups such as vinyl, co-hexene, and allyl, preferably vinyl; aryl groups such as phenyl and napthyl; alkaryl groups such as tolyl and xylyl; and arylalkyl groups such as benzyl, and the a- and [3- phenylethyl groups. This list is non-limiting.

[0032] In other embodiments, suitable R groups include substituted non-reactive groups and halo- substituted hydrocarbon groups such as fluorinated and chlorinated hydrocarbon groups, for example, perfluoropropyl, chloropropyl, chloroethyl, o-, m-, and p-chlorophenyl, and the like, and hydrocarbon groups substituted with cyano groups, hydroxyl groups or alkoxy groups (including polyoxyalkylene groups).

[0033] In a preferred embodiment, R1is an acrylate group or a methacrylate group Si-O bonded to silicon and OR2is an Si-O bonded alkoxy group, wherein R2is a non-reactive organic group selected from the same list as R. Therefore, the structure of the branched organopolysiloxane can be characterized as:

[0034] MmDnToQp where M units represent a termination point of the structure, D units represent linear portions of the structure, and T units and Q units represent branching points of the branched organopolysiloxane. Thus, the degree of branching can be characterized by the relative amounts of T units and Q units in the branched organopolysiloxane.

[0035] In an embodiment of the present invention, m is selected such that all chain ends are terminated with M groups, n may be 1 to 10,000, preferably 2 to 1000, more preferably 2 to 100, o is 0 to 100, preferably 15 to 85, more preferably 20 to 40, p is 0 to 10, preferably 0 to 5, more preferably 0. It is preferable to limit p, corresponding to the number of Q units, to only those present as an unavoidable consequence of the hydrolytic condensation. In the most preferred embodiment, the branched organopolysiloxane contains no Q units, thus p may be 0.

[0036] The number of T units of the branched organopolysiloxane may be selected to improve the performance of the resin composition. If the organopolysiloxane contains insufficient T units, the structure and properties resemble a linear organopolysiloxane which makes the resulting coating susceptible to dirt and mold pickup. It may also be desirable to limit the number of T units because over crosslinking can result in undesirable brittleness and cracking in the coating. In the most preferred embodiments, the branched organopolysiloxane contains zero Q units because Q units reduce reactivity, chain growth, and therefore molecular weight of the final oligomer.

[0037] In an embodiment, preferred organopolysiloxanes are liquids, with a viscosity of 50 cps to 5000 cps, preferably 75 to 3000 cps, more preferably 100 cps to 2000 cps at 23°C , using the standard rotational viscometers. In an embodiment of the present invention, the branched organopolysiloxane contains a defined quantity of acrylate functionalities and / or a defined residual alkoxy content. The branched organopolysiloxane has 4 to 15 acrylate functionalities per chain, preferably 6 to 14 acrylate functionalities, more preferably 8 to 13 acrylate functionalities. The quantity of acrylate functionalities may be selected to control the crosslink density, which in turn, significantly improves the stain resistance and water uptake of the cured coating. The resin composition requires a sufficient crosslink density to prevent the diffusion of chemicals or reagents into the network and improve stain resistance. Further, increased crosslink density also reduces water uptake. However, excess crosslink density limits the segmental motions in the polymeric network, resulting in brittleness and undesirable cracking in the resulting coating.

[0038] The branched organopolysiloxane has a residual alkoxy content of 0.2 to 3.0 wt%, preferably 0.3 to 2.0 wt%, more preferably 0.5 to 1.5 wt%, based on a total weight of the branched organopolysiloxane. It may be desirable to limit the proportion of residual alkoxy groups, as residual alkoxy groups further crosslink in the presence of moisture. As a result, curable compositions with an excess residual alkoxy content demonstrate cracking, shrinkage, and voids from the outgassing of condensation reaction alcohol. The outgassing and resulting coating damage may occur as early as the initial cure.

[0039] Moreover, unreacted alkoxy groups are water-sensitive and decrease the mobility of growing polymer chains during the radiation curing process. Further, a higher residual alkoxy content increases the concentration of volatile organic compounds (VOCs) due to the evolution of alcohol during condensation. VOCs are particularly undesirable in coating and sealing applications due to harmful health effects.

[0040] The reactive organopolysiloxanes are prepared via direct condensation reaction of silicon- bonded detachable or hydrolyzable groups of a silicone compound, preferably alkoxy groups, with hydroxy-bearing reagents that also bear polymerizable ethylenically unsaturated groups. The condensation takes place generally with the aid of an acidic or basic condensation catalyst such as an alkali metal hydroxide. Methods and conditions of condensation of silanes are well known in the art. Liberated alcohol is removed, for example as an overhead, and the amount of alcohol collected, e.g., in a cooled condenser, may be used to assess the progress of condensation.

[0041] Examples of the hydroxy- and ethylenically unsaturated-bearing reagents include but are not limited to linear or branched c1-c12 alkyl esters of (meth)acrylic acid such as 2-hydroxyethyl, 2- or 3-hydroxy-propyl or 2-, 3- or 4-hydroxybutyl (meth)acrylates. Also suitable are the monohydric alcohols containing acroyloyl groups and reaction products substantially containing monohydric alcohols monohydric alcohols which are obtained by the esterification of n-hydric alcohols such as glycerol and / or pentaerythritol with (meth)acrylic acid, wherein “n” preferably represents a whole number, or a fractional number ranging from greater than 2 to 4, preferably 3, and wherein (n-0.8) to (n-1.2), preferably (n-1) moles of (meth)acrylic acid are used per mole of alcohols.

[0042] Examples of such compounds include but are not limited to, glycerol mono-, and di- (meth)acrylate, glycerol 1 ,3-diglycerolate di(meth)acrylate, and Pentaerythritol di-, tri-, or tetra- (meth)acrylate. Other suitable examples could be the reaction product of (meth)acrylic acid with epoxy-functional components, such as 2-Hydroxy-3-phenoxy propyl acrylate and bisphenol A glycidyl dimethacrylate. The epoxy-functional component could be optionally selected from biorenewable based materials such as epoxidized plant oils. Examples of such products include acrylated epoxidized- soybean oil, caster oil, palm oil, linseed oil, and canola oil.

[0043] The resin composition may contain 60 to 100 wt% of the branched organopolysiloxane, preferably 90 to 97 wt%, more preferably 80 to 95% by weight of the total composition.

[0044] Curable Compositions and Initiator The resin composition may be used with a variety of initiators known in the art to form a curable composition. Such initiators include photoinitiators for UV curing, accelerators for high-energy radiation curing, and peroxides or azo compounds for thermal curing.

[0045] In an embodiment, the initiator is a photoinitiator known in the art. Suitable photoinitators include Norrish type I photoinitiators, such as acetophenones and their derivatives, including hydroxy acetophenone and aminoacetophenones. Other suitable photoinitiators include phosphine oxides that are excited into a triplet state upon irradiation with UV light and subsequently undergo a-cleavage, forming two radical fragments capable of initiating a polymerization reaction. The polymerization reaction may be initiated by either one of the radical fragments or both fragments. Examples of such photoinitiators include 2-hydroxy-2-methyl-1- phenylpropanone, 1 -hydroxycyclohexyl phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2- hydroxy-2-methyl-1-propane-1-one, 2,2-dimethoxy-2-phenylacetophenone, 2-methyl-1-[4- (methylthio)phenyl]2-morpholinopropan-1-one, and 2-benzyl-2-dimethylamino-4- morpholinobutyrophenone. Norrish type I photoinitiators are commercially available, such as SpeedCure 2022, a trade name of Arkema Inc.

[0046] Also suitable are Norrish type II photoinitiators, which upon UV irradiation, abstract a hydrogen atom from a co-initiator, also known as a synergist, forming two radicals. Examples of suitable Norrish type II photoinitiators include benzophenones, thioxanthones, and benzoylformates, such as benzophenone, 4-methylbenzophenone, Methyl-2-benzoylbenzoate, 4,4’ bis(diethylamino)benzophenone, 4-benzoyl-4’-methyldiphenyl sulfide, 4-phenylbenzophenone, 2- isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, 2,4-diethylthioxanthone, and Methylbenzoylformate.

[0047] Norrish type II photoinitiators may be used in combination with synergists. Commonly used synergists include amine synergists which act as hydrogen donors. Examples of suitable amine synergists include tertiary amines and aminobenzoates such as 2-(dimethylamino) ethyl benzoate, 2-Ethylhexyl-4-(dimethylamino)benzoate, and 2-butoxy ethyl-4- (dimethylamino)benzoate. Preferable amine synergists include polymeric amine synergists having an aminobenzene modified with a polyether chain connecting to the aminobenzene through an ether linkage, and acrylate functional oligomeric amine resins. More preferable amine synergists include acrylate functional oligomeric amine resins that can become a part of the polymeric network upon exposure to UV radiation. Amine synergists that can become a part of the polymeric network provide low odor and low migration.

[0048] Amine synergists provide the additional benefit of mitigating oxygen inhibition, which is caused by the undesired reaction of radical intermediates with molecular oxygen, thereby decreasing the efficiency of the curing process. Amine synergists produce a-aminoalkyl radicals, which rapidly scavenge oxygen present in the formulation, thereby allowing the desired polymerization process to proceed (European Patent No. EP2550250A2). Polymerizable amine synergists are commercially available, such as Ebecryl 7100, a trade name of Arkema Inc. In some embodiments, a polymerizable amine synergist may be added at a concentration of 1 to 3 wt%, based on the total mass of the curable composition, to help mitigate oxygen inhibition.

[0049] According to an embodiment, at least one photoinitiator may be included in the curable composition in an amount sufficient to obtain the desired cure response. The selection of photoinitiators and the concentrations thereof vary based on factors including the types of UV cure equipment, the UV spectral output range of the UV bulb, cure rate, depth of cure, and durability desired. In preferred formulations of the curable composition, a blend of at least two photoinitiators, and more preferably three photoinitiators are included in a concentration of 0.25 to 15 wt% based on the total weight of the curable composition. In a preferred embodiment, the blend includes 2-hydroxy-2-methyl-1-phenylpropanone in a concentration of 2.4 to 3.6 wt%, Phenyl bis(2,4,6-trimethyl benzoyl)-phosphine oxide in a concentration of 0.4 to 1.2 wt%, and Ethyl (2,4,6-trimethyl benzoyl) phenyl phosphinate in a concentration of 0.2 to 0.4 wt%. Additives

[0050] In certain embodiments, the curable composition may optionally include various additives to improve the appearance or performance of the cured coatings. Suitable additives include viscosity modifiers, surface additives, rheological modifiers, UV stabilizers, pigments, fillers, matting agents, and mixtures thereof.

[0051] In an embodiment, particularly for outdoor applications, the curable composition may include a stabilizer package containing UV stabilizers such as benzotriazole or benzotriazine derivatives, in combination with hindered amine light stabilizers (HALS) to maximize the weathering resistance and exterior durability. Preferably, the UV stabilizer is from the hydroxyphenyl benzotriazole class, provided in amount between 0.1 to 2%, more preferably about 1.5 to 2% by weight of binder solids and / or a blend of hindered amines such as Bis(1 , 2,2,6, 6-pentamethyl-4- piperidyl)sebacate, and methyl(1 ,2,2,6,6-penta-4-piperidyl)sebacate in a range of 0.5-2%, preferably, 0.5-1% by weight of the total binder solids. Suitable hydroxyphenyl benzotriazole stabilizers are commercially available, such as SpeedBlock 1130 sold by Arkema. Suitable hindered amine light stabilizers are also commercially available, such as SpeedBlock UV-92 sold by Arkema. The disclosed concentrations of stabilizers are optimized to avoid negatively affecting the cure response, and therefore, film properties.

[0052] In other embodiments, the curable composition may optionally include flow agents to improve flow characteristics. Suitable flow agents include reactive and non-reactive acrylic or silicone- based flow agents. Preferred flow agents include polymerizable flow agents that can become part of the polymer network. Such flow agents are commercially available, for example those sold under the tradename BYK-UV 3535 by BYK USA Inc.

[0053] In other embodiments, the curable composition may optionally include matting agents to reduce gloss and maintain the natural appearance of wood or cementitious substrates. Optionally, pigments and / or fillers may be used to formulate a resin composition that can function as a wood stain or an opaque paint for wood and cementitious substrates. When pigments or fillers are used, the type and concentration of photoinitiators may be adjusted based on desired pigment volume concentration, dry film thickness, and rate of cure to achieve a suitable cure response. When using pigments or fillers, a preferred embodiment includes a blend of long- and shortwave absorbing photoinitiators, such as a liquid solution of 25 wt% bis-(2,6-dimethoxybenzoyl)- 2,4,4-trimethylpentyl phosphine oxide (i.e. , long-wave absorbing component) and 75 wt% 2- hydroxy-2-methyl-1-phenyl-propane-1-one (i.e., short-wave absorbing component), based on a total weight of the photoinitiators. The preferred concentrations of photoinitiators, when coupled with pigments and / or fillers, results in both surface- and through-cure. Other embodiments may optionally include condensation catalysts, rheological modifiers, adhesion promoters, hydrophobing agents such as waxes, silicone oils, fluorine-containing compounds, and other additives known in the art.

[0054] In certain embodiments, the additives may further include 5 to 30 wt%, preferably 5 to 20 wt%, more preferably 5 to 10 wt% of multifunctional acrylate monomers, methacrylate monomers, or a combination thereof, based on a total weight of the curable composition. The acrylate monomers and / or methacrylate monomers preferably contain at least two polymerizable unsaturated groups per molecule. Examples of suitable acrylate monomers and methacrylate monomers include di- or tri-propylene glycol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, 1 ,4-butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate and their ethoxylated and propoxylated derivatives, pentaerythritol tri- and tetra-(meth)acrylate, dipentaerythritol penta- and hexa- (meth)acrylate, and mixtures thereof. Such additives can be used to adjust the viscosity and crosslink density of the resin composition.

[0055] Curing In certain embodiments, the curable composition is dual-curable, with a primary curing step of radiation curing, thermal curing, or a combination thereof, and a second curing step of moisture curing. The primary curing step is completed quickly, in a matter of seconds or minutes, and allows the curable composition to be handled, stored, or worked. The second curing step occurs over a period of days or weeks and allows the resulting coating to achieve maximum resilience and durability.

[0056] In certain embodiments including a photoinitiator, the first curing step may include UV curing. Suitable UV light sources include low-, medium-, high-, and extra high- pressure mercury lamps, UV LED lamps, metal halide lamps, carbon arc lamps, xenon lamps, and other UV lamps known in the art. A suitable UV exposure dose is 100 to 5000 mJ / cm2, preferably 700 to 2000 mJ / cm2. The UV exposure dose may be adjusting by varying the distance between the lamp and the substrate and the exposure time. In a preferred embodiment, the curable composition may be exposed to UV on a continuous conveyer belt, to allow for rapid production of coated substrates.

[0057] In other embodiments including an accelerator, the first curing step may include exposure to high-energy radiation, such as electron beam radiation or cobalt 60 radiation. Procedures for electron beam curing are well-known in the art. A suitable radiation exposure dose is about 2 to 20 megarads. The radiation exposure dose will vary depending on the specific equipment used to deliver the electron beam. A dose calibration model may be defined based on the specific equipment used. Such radiation curing may be done without initiators, but accelerators may be added. Suitable accelerators include trialylcyanurate isocyanurate.

[0058] In yet other embodiments including a peroxide, the first curing step may include thermal curing. In a thermal curing process, the addition of free-radical-forming peroxides or azo compounds (CE) is preferred. Preferable peroxides and azo compounds include lauroyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxides, azobisisobutyronitrile, hydroperoxides such as tertbutyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-dihydroperoxyhexane, 2,5-dimethyl-2,5-dihydroperoxy-3- hexyne, and pinene hydroperoxide; dialkyl peroxides such as diisobutyl peroxide, di-tert-buty I peroxide, di-tert-amyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5- di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne, alpha, alpha'-bis(tert- butylperoxy)-di(iso butylperoxy)benzene, 1 ,1-bis(tertbutylperoxy)-3,3,5-trimethylcyclohexane, n- butyl 4,4'-bis(tertbutylperoxy)valerate, 2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane, 2,2- bis(tert-butylperoxy)butane, and 1 ,1-di(tert-butylperoxy)cyclohexane; diacyl peroxides such as decanoyl peroxide, lauroyl peroxide, stearoyl peroxide, succinyl peroxide, benzoyl peroxide, p- chlorobenzoyl peroxide, o-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and octanoyl peroxide; peroxy esters such as tert-butyl peroxyacetate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxylaurate, tert-butyl peroxybenzoate, di-tert-butyl diperoxyphthalate, 2,5-dimethyl- 2,5-di(benzoylperoxy)hexane, tert-butylperoxymaleic acid, tert-butylperoxyisopropyl carbonate, tert-butylperoxypivalate, and tert-butylperoxy neodecanoate; peroxy dicarbonates such as diisopropyl peroxydicarbonate and di-2-ethylhexyl peroxydicarbonate; and ketone peroxide.

[0059] Thermal curing with peroxides may be carried out at a temperature of -70°C to 220°C, preferably from -60°C to 200°C, more preferably -40°C to 150°C, and at the pressure of the surrounding atmosphere, i.e., from 900 hPa to 1100 hPa. The surrounding atmosphere may be air, nitrogen, xenon or another protective gas. The concentration of the organic peroxide added to the inventive composition as an initiator is usually in the range from 0.1 to 5 parts by weight per 100 parts by weight of the organopolysiloxane.

[0060] Coated Substrates

[0061] The disclosed curable compositions can be applied to at least one surface of a porous substrate and cured to form a coating, resulting in a coated substrate. Suitable porous substates include wood, wood products and wood composites such as, plywood, fiberboards, particleboards, laminated veneer lumber, oriented strand lumber, cross-laminated timber, stone and synthetic stone products, tile, brick, cementitious materials such as concrete, stucco, tile, brick, pavers, and other non-metallic porous substrates such as ceramic and ceramic products, and plastic products such as fiber glass. The curable composition may be applied according to any coating method or combination of coating methods known in the art, including conventional spraying, air spraying, airless spraying, HVLP (high volume low pressure) spraying, brushing, doctor blade coating, dipping, curtain coating, and roll coating. Wood and wood-based substrates may optionally be sanded prior to application of the curable composition.

[0062] In an embodiment, the coating may include one or more coats applied to the porous substrate. Preferably a thin first coat is applied to seal the pores and provide a smooth, even surface. A suitable dry film thickness of the first coat is about 5 microns to about 40 microns, preferably about 10 microns to about 25 microns. Once applied, the first coat is cured according to one of the disclosed curing methods. Particularly for wood, it can be beneficial to sand the cured first coat to smooth the uneven surface, remove protrusions and bubbles, and improve the adhesion of the next layer. Then, a second coat may be applied on top of the first coat. A suitable dry film thickness of the second coat is about 15 to 60 microns, preferably about 25 microns to 50 microns. The second coat is then cured according to one of the disclosed curing methods. Additional coats may be applied with further curing steps in between each coat. The additional coats may optionally be sanded after curing and prior to the application of the subsequent coat. It may be desirable to apply the curable composition in multiple thinner coats to achieve the desired final thickness, as thinner applications decrease runs and bubbles in the curable composition.

[0063] EXAMPLES

[0064] The following examples are presented solely for the purpose of further illustrating and disclosing embodiments of the branched organopolysiloxane, the resin composition, curable compositions, coatings, and coated substrates thereof. Examples of the branched organopolysiloxane used in the invention include Samples S1 to S4. Examples of curable compositions include Examples 1- 5, which are described below. Comparative Examples 1-3, which are not part of the invention, are also described below.

[0065] Unless indicated otherwise, the following compositions are provided in weight percentages and the synthesis and testing are both carried out at the pressure of the surrounding atmosphere, i.e. , at about 1000 hPa, and at room temperature, i.e. , at about 20°C, or at a temperature which is established on combining the reactants at room temperature without additional heating or cooling.

[0066] Samples S1 to S5

[0067] Samples S1 to S4 are resin compositions prepared from an alkoxy-functional organopolysiloxane, one or more ethylenically unsaturated hydroxy- and acrylate-bearing reagents, and a catalyst. The ethylenically unsaturated hyrdoxy- and acrylate-bearing reagents were 2-hydroxyethylacrylate, 2-hydroxyethylmethacrylate, Pentaerythritol triacrylate, and combinations thereof. The reagents were charged to a 500 ml reaction flask and blanketed with nitrogen gas. To begin hydrolytic condensation, the condensation catalyst was slowly added. The contents were stirred without heating for 15 minutes. The temperature was then increased to 55°C. The reaction mixture was refluxed under partial vacuum at 55°C until the appropriate amount of alcohol was collected in a cooled trap. The charges and product properties are reported in Table 1.

[0068] Sample S5 is a resin composition prepared from a known organopolysiloxane used in existing curable compositions, but not suitable for the inventive curable compositions. Sample S5 was used to prepare the curable composition of Comparative Example 1 , which is not part of the present invention. Sample S5 was prepared according to the formula designated in Table 1 , using the same process as Samples S1 to S4. Table 1 : Samples of the prepared organopolysiloxanes

[0069] 1SILRES® IC232 is a methoxy-functional methyl / phenyl organopolysiloxane containing about 20 weight percent alkoxy groups, available from Wacker Chemical Corp., Adrian, Michigan.

[0070] 2SILRES® IC 368 is a methoxy-functional methyl-phenyl organopolysiloxane containing about 15 weight percent alkoxy groups, available from Wacker Chemical Corp., Adrian, Michigan.

[0071] 3SILRES® MSE100 is a methoxy-functional methyl organopolysiloxane containing about 30 weight percent alkoxy groups, available from Wacker Chemical Corp., Adrian, Michigan.

[0072] 4AII the organopolysiloxanes showed Newtonian behavior.

[0073] Examples 1-5 were prepared from the sample organopolysiloxanes S1 to S4, according to the compositions disclosed in Table 2, by mixing the organopolysiloxane with additives. Comparative Example 1 was prepared from the sample organopolysiloxane S5, according to the composition disclosed in Table 2. Comparative Example 1 represents a known UV-curable organopolysiloxane-based curable composition. Comparative Example 2 was prepared from a commercial non-silicone urethane acylate oligomer. Comparative Example 3 was prepared from a commercial non-silicone polyester acrylate oligomer. The compositions of Comparative Examples 2 and 3 are provided in Table 2. Comparative Examples 2 and 3 represent existing non-silicone UV-curable compositions known to have good stain resistance.

[0074] Table 2: Curable compositions

[0075] 1A commercial liquid polyester-modified acrylic resin for the formulation of EB or UV-curable coatings for wood.

[0076] 2A commercial liquid aliphatic urethane triacrylate oligomer for the formulation of EB or UV- curable coatings for wood.

[0077] 3DPGDA is dipropyleneglycol diacrylate and is available from BASF.

[0078] 4Speedcure 2022 is a formulated blend of type I photoinitiators available from Arkema.

[0079] 5SpeedBlock UV-92 is a blend of hindered amines including Bis( 1 ,2,2,6,6-pentamethyl-4-piperidyl)sebacate, and Methyl(1 ,2,2,6, 6-penta-4-piperidyl)sebacate available from Arkema.

[0080] 6SpeedBlock 1130 is a UV stabilizer from hydroxyphenyl benzotriazole class available from Arkema.

[0081] 7BYK-UV 3535 is a crosslinkable surface additive for radiation-curable systems for improving leveling and recoatability, available from BYK. The curable compositions of Examples 1-5 and Comparative Examples 1-3 were applied to concrete and wood substrates. The curable compositions were applied to concrete panels using foam brushes to achieve a dry film thickness of about 2 mils (50 pm). The curable composition was then cured with 3 passes under UV radiation. A UV-mercury system (LC6B Benchtop Conveyor by Heraeus Noblelight FUSION UV Systems, Inc.) with a D-bulb was used to cure the curable composition. The conveyor belt speed was set at 15 ft / min (4.5 m / min), which provided an energy density of ~838 mJ / cm2per pass.

[0082] For wood substrates, a first thin layer of the curable composition was brush-applied to the panels to seal the pores in the wood. The first thin layer was cured using the same process as the concrete panels, forming a first coat. Next, the first coat was sanded using 400-grit sandpaper. A second thin layer was then brush-applied to achieve a dry film thickness of about 2 mils (50 pm) and cured to form a second coat.

[0083] Following the initial application and UV curing process, the coatings were allowed to cure for one week to ensure complete moisture curing. The coatings were then subjected to an initial screening. Comparative Example 1 , using the organopolysiloxane of sample S5 exhibited significant macro and micro-cracks immediately after UV-curing. The cracking was likely due to the hard nature of methyl silicones, and the high alkoxy content of alkoxy in the curable composition, resulting in over-crosslinking and brittleness. The cracking is illustrated in FIG. 1. The coatings are clear and non-pigmented, but a blue dye has been applied to penetrate the cracks for visibility. All other coatings passed the initial screening.

[0084] Thermal Stability Test

[0085] The thermal stability of the coatings was investigated by thermogravimetric analysis under an air atmosphere in the temperature range of 0 to 1000 °C, at a heating rate of 10 °C / min. The results of the thermal analysis are summarized in Table 3. Table 3: Thermal properties of cured coatings

[0086] According to the results, the organopolysiloxane-based coatings (Examples 2-4 and Comparative Example 1) have significantly higher mass residues and 50% decomposition temperatures compared to acrylate-based control coatings (Comparative Examples 2-3). Therefore, the organosiloxane-based coatings demonstrate outstanding thermal stability compared to existing acrylate-based UV-curable curable compositions. The results also show that by increasing the organic content of the coatings (e.g., the addition of DPGDA monomer), the thermal stability reduces. This is due to the higher energy of Si-O bond (about 452 kJ / mol) backbone than the C-O bond (358.0 kJ / mol) and the C-C bond (347.0 kJ / mol).

[0087] Stain Resistance Test

[0088] The coatings were evaluated for stain resistance against common household and industrial chemicals. The test chemicals were applied to a wood sample coated with the sample curable compositions. The curable compositions were exposed to the test chemicals for 2 hours and 24 hours at room temperature. Following the exposure period, the test chemicals were removed by rinsing under tap water and rubbing with a soft sponge. The curable compositions were then visually examined for graying, whitening, spotting, softening, discoloration, and other film deteriorations. The stain resistance of the curable compositions was assigned a rating from 0-5, as described below. 5 - No Failure

[0089] 4 - Only visible with close inspection

[0090] 3 - Slight failure visible at an arm-length (1 .5 ft or 45 cm)

[0091] 2 - Moderate failure, wrinkled, severely softened 1 - Severe failure, film compromised.

[0092] 0 - Absolute, total failure.

[0093] The results of the stain resistance test are disclosed in Table 4.

[0094] Table 4: Stain resistance of the coatings

[0095] This test was selected because acrylate-based coatings, particularly UV-cured acrylate-based coatings, are known in the art to possess excellent stain resistance due to their high crosslink density, which prevents the diffusion of the chemicals / reagents into the network. However, the stain resistance test demonstrated that the inventive organosiloxane-based coatings have excellent stain resistance matching or exceeding acrylate-based coatings. The inventive organopolysiloxane-based coatings also outperform acrylate-based coatings in solvent resistance, demonstrated by the tests using wood cleaner and methyl ethyl ketone. The improved performance of the organosiloxane-based coatings is likely due to a combination of sufficient crosslink density together with the low surface energy of the silicones, which hinders the spreading and wetting of the stains. A photograph of a representative test samples after the 24 hour test is depicted in FIG. 2 wherein the samples correspond as follows: a) Comparative Example 2 b) Comparative Example 3 c) Comparative Example 1 d) Example 1 e) Example 2

[0096] Water Uptake Test

[0097] The coatings were further evaluated for their water absorption. The coatings prepared in the examples and the comparative examples were applied to the bottom and sides of a rectangular 3 inch by 6 inch (7.5 cm by 15 cm) concrete panel. The coated concrete panel was placed on a sponge that is submerged in a water bath. The level of the water bath was set at the top of the sponge to ensure that only the coated surfaces of the concrete panel were exposed to water.

[0098] The coatings were continuously exposed to water for 24 hours. After 24 hours, the panels were removed, and any excess water was wiped from the surface and sides of the panels using a damp sponge. The coated concrete panels were then weighed to determine the water uptake. The % water uptake was calculated according to the equation: 100 where G is the percent water uptake, W1 is the weight of uncoated concrete panel after 24 hours, and W2is the weight of the coated concrete panels after 24 hours. Samples were run in duplicates and the average weights were used to calculate the water uptake. The results of the water uptake test are displayed in Table 5 below:

[0099] Table 5: Percent Water Uptake of Concrete Panels After 24 Hours

[0100] Organopolysiloxane-based coatings showed significantly lower water uptake compared to acrylate-based coatings. The decreased water uptake is likely due to the hydrophobic nature of the polysiloxanes. When applied in architectural and construction applications, the decreased water uptake leads to a decrease in staining and can mitigate damage caused by moisture or freeze / thaw expansion.

[0101] From the foregoing detailed description, it will be apparent that various modifications, additions, and other alternative embodiments are possible without departing from the true scope and spirit. The embodiments and examples discussed herein were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to use the invention in various embodiments and with various modifications as are suited to the particular use contemplated. As should be appreciated, all such modifications and variations are within the scope of the invention.

Claims

CLAIMS1. A resin composition, comprising a branched organopolysiloxane, wherein the branched organopolysiloxane comprises the structure MmDnToQp, wherein the structure MmDnToQp comprises M units, D units, T units, and Q units, said M units, D units, T units, and Q units defined asR1aRb(OR2)cSiOi / 2 (M unit) wherein a, b, and c are each 0 to 3 and the sum of a+b+c is 3;R1aRb(OR2)cSiO2 / 2 (D unit) wherein a, b, and c are each 0 to 2 and the sum of a+b+c is 2;R1aRb(OR2)cSiO3 / 2 (T unit) wherein a, b, and c are 0 or 1 and the sum of a+b+c is 1 ; andSiO4 / 2(Q unit) wherein R is a non-reactive organic group, R1is an acrylate group or a methacrylate group, and OR2is an Si-O bonded alkoxy group, wherein R2is a non-reactive organic group, wherein m is selected such that all chain ends are terminated with M units, n is 1 to 10,000, o is 1 to 100, p is 0 to 10, wherein the branched organopolysiloxane has a branched structure comprising a plurality of chains, wherein the plurality of chains each have an acrylate content of 4 to 15 acrylates per chain, wherein the branched organopolysiloxane is disposed in the resin composition in a concentration of 60 to 100 wt%, based on a total weight of the resin composition.

2. The resin composition of claim 1 , wherein n is 2 to 1000, o is 15 to 85, p is 0 to 5.

3. The resin composition of claim 2, wherein n is 2 to 100, o is 20 to 40, p is 0 to 3.

4. The resin composition of claim 1 , wherein the resin composition is curable by a first curing method and a second curing method, wherein the first curing method comprises thermal curing or radiation curing, and the second curing method is moisture curing.

5. The resin composition of claim 4, wherein the first curing method is a radiation curing method.

6. The resin composition of claim 5, wherein the radiation curing method comprises UV curing, electron beam (EB) curing, UV-LED curing, or a combination thereof.

7. A curable composition comprising a resin composition according to claim 1 , and an initiator.

8. The curable composition of claim 7, wherein the initiator comprises a photoinitiator, and said photoinitiator comprises a Norrish type I initiator, a Norrish type II initiator, or a combination thereof.

9. The curable composition of claim 7, wherein the initiator comprises a thermal initiator, wherein said thermal initiator comprises a peroxide or an azo compound.

10. The curable composition of claim 7, wherein the composition additionally comprises an additive selected from the group consisting of viscosity modifiers, amine synergists, surface additives, rheological modifiers, UV stabilizers, pigments, fillers, matting agents, acrylate monomers, methacrylate monomers, and mixtures thereof.11 . The curable composition of claim 10, wherein the additive comprises a UV stabilizer, wherein said UV stabilizer comprises a derivative of benzotriazole or benzotriazine.

12. The curable composition of claim 10, wherein the additive comprises an acrylate monomer, a methacrylate monomer, or a mixture thereof.

13. The curable composition of claim 10, wherein the additive comprises an amine synergist.

14. The curable composition of claim 13, wherein the amine synergist is a polymeric acrylated synergist.

15. The curable composition of claim 7, wherein the resin composition is curable by a first curing method and a second curing method, wherein the first curing method comprises thermal curing or radiation curing, and the second curing method is moisture curing.

16. The curable composition substrate of claim 7, wherein the first curing method is a radiation curing method, said radiation curing method comprising UV curing, electron beam (EB) curing, and UV-LED curing.

17. A coated substrate, comprising a coating disposed on at least one surface of a porous substrate, wherein the coating comprises a resin composition according to claim 1 and an initiator.

18. The coated substrate of claim 17, wherein the porous substrate is selected from the group consisting of wood, wood products, wood composites, plywood, fiberboard, particleboard, laminated veneer lumber, oriented strand lumber, cross-laminated timber, stone, synthetic stone products, cementitious materials, concrete, stucco, tile, brick, pavers, ceramic, ceramic products, fiber glass, non-metallic porous substrates, plastic products, and combinations thereof.

19. The coated substrate of claim 17, wherein the initiator comprises a photoinitiator, wherein said photoinitiator comprises a Norrish type I initiator, a Norrish type II initiator, or a combination thereof.

20. The coated substrate of claim 17, wherein the coating comprises an additive selected from the group consisting of viscosity modifiers, synergists, surface additives, rheological modifiers, UV stabilizers, pigments, fillers, matting agents, acrylate monomers, methacrylate monomers, and mixtures thereof.

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