Polymers with low molecular weight moieties and high glass transition temperature moieties for early blocking resistance

Abstract

Polymers, including single-stage and multi-stage polymers, are disclosed that combine the structural integrity of polymers having a high glass transition temperature (Tg) with the properties of softer, lower molecular weight polymers that quickly coalesce and have flexibility to maintain scrub resistance. The external stages of the single-stage or multi-stage polymer contain both a crosslinking monomer and a chain transfer agent at different portions of the stage. Building compositions containing these film-forming polymers exhibit resistance to obstructions within one hour after application to a substrate.

Description

[0001] Cross-reference to related patent applications

[0002] This patent application is a partial continuation application of U.S. Patent Application Serial No. 16 / 921,059 under 35 U.S.C. § 120, which was filed on July 6, 2020. This application is hereby incorporated by reference in its entirety. Field of the Invention

[0003] The present invention relates to a polymer that combines the structural integrity of a polymer having a high glass transition temperature (Tg) with the properties of a softer, lower molecular weight polymer that rapidly coalesces and has flexibility to maintain scrub resistance. Background of the invention

[0005] One problem with painting building structures such as residential and commercial buildings is that when two freshly painted surfaces come into contact with each other, these surfaces adhere to each other. Thus, windows and window frames or doors and door frames stick to each other. When a window or door is forced open, the paint film peels off from the painted surface, leaving an unsightly pattern on the surface. This is known as blocking in the painting industry. A common method of measuring blocking, for example, ASTM D4946 - 89, is to rate the painted surface after 24 hours of drying or after 7 days, as discussed in, for example, U.S. Patent Nos. 9,611,393, 10,301,501, and 10,273,378.

[0006] Soft polymers, i.e., low Tg polymers, exhibit higher blocking when incorporated into paints and dyes. Paints with high gloss or sheen also exhibit more blocking than low - gloss paints due to a higher resin content. Tackiness is a similar phenomenon that describes the tendency of dry paint on a surface to stick to or adhere to a person or object pressed against the painted surface, especially in high - humidity environments.

[0007] U.S. Patent Publication No. US2005 / 0107527 discloses a block - resistant core - shell polymer that requires weak acid monomers, strong acid monomers, and keto - containing monomers in the core and shell phases. US2005 / 0107527 discloses varying the various components in the core - shell structure, which substantially maintains the block resistance. However, US2005 / 0107527 conducted its block - resistance test 1 day after the paint film was dried, which is much longer than the actual paint application time. Co - owned U.S. Patent Publication No. US 2014 / 0235752 discloses a core - shell - skin self - coalescing polymer that utilizes a chain transfer agent added in the last 10% of the shell monomer mixture during emulsion polymerization to form a thin skin with a lower molecular weight.

[0008] However, it is not practical to place the painted surface for one day or seven days after painting to determine the blocking level, and it cannot approximate the actual situation. Therefore, there is still a need for aqueous building compositions such as paints or coatings that exhibit good blocking resistance when the composition dries or shortly after application to a surface. SUMMARY OF THE INVENTION

[0009] Accordingly, a preferred embodiment of the present invention relates to a building composition comprising a paint and a dye composition that exhibits blocking resistance when the composition dries or shortly after application to a surface or substrate, preferably within one hour after application to a surface or substrate.

[0010] As used herein, a stage of latex particles in a multi-stage latex particle is defined as having the same film-forming monomer mixture, excluding any crosslinking monomers, any wet adhesion monomers, any monomers having a weight percentage of less than about 1.5% for which Tg information is not available, and any chain transfer agents. A portion of one stage of a multi-stage latex particle or a single-stage latex particle is a portion of the stage in which a crosslinking monomer is added, a CTA is added, or neither a crosslinking monomer nor a CTA is added.

[0011] One embodiment of the present invention relates to copolymer latex particles comprising at least one stage. The at least one stage is formed from a first monomer mixture of one or more film-forming monomers, and the at least one stage is copolymerized with at least one crosslinking monomer to form an inner portion of the at least one stage. The outer portion of the at least one stage is copolymerized in the presence of a chain transfer agent (CTA). The at least one crosslinking monomer accounts for about 1 wt% to about 8 wt%, preferably about 2 wt% to about 7 wt%, and more preferably about 3 wt% to about 5 wt% of the total monomers in the entire polymer of the latex particles. The CTA accounts for about 0.2 wt% to about 1 wt%, preferably about 0.25 wt% to about 0.90 wt%, and more preferably about 0.30 wt% to about 0.80 wt% of the total monomers in the entire polymer of the latex particles.

[0012] Preferably, the inner portion and the outer portion of the at least one stage do not overlap. The inner portion and the outer portion are preferably separated by an intermediate portion that does not contain the at least one crosslinking monomer and the CTA. The outer portion accounts for about 10 wt% to about 60 wt% of the at least one stage, preferably about 15 wt% to about 35 wt% of the at least one stage, and more preferably about 20 wt% ± 1.5 wt%.

[0013] The copolymer latex particles can further comprise at least one internal phase formed from an internal monomer mixture of one or more film-forming monomers (which is different from the first monomer mixture), wherein the calculated glass transition temperature (Tgc) of the at least one internal phase ranges from about 25 °C to about 100 °C, preferably from about 30 °C to about 85 °C and preferably from about 35 °C to about 75 °C. The internal monomer mixture can further comprise at least one crosslinking monomer. The Tgc of the at least one internal phase is about 20 °C to about 90 °C higher than the Tgc of the at least one phase, preferably about 50 °C to about 80 °C higher, and preferably about 55 °C to about 75 °C higher.

[0014] The copolymer latex particles can further comprise an innermost phase located inside the at least one internal phase or a second internal phase located outside the at least one internal phase.

[0015] The total weight average molecular weight of the at least one phase ranges from about 30,000 Daltons to about 120,000 Daltons, and preferably from about 40,000 Daltons to about 110,000 Daltons, or preferably from about 50,000 Daltons to about 100,000 Daltons.

[0016] The weight average molecular weight of the at least one internal phase ranges from about 150,000 Daltons to about 260,000 Daltons, preferably from about 160,000 Daltons to about 250,000 Daltons, and more preferably from about 170,000 Daltons to about 240,000 Daltons.

[0017] The weight average molecular weight of the aggregate of the copolymer latex particles including all phases ranges from about 100,000 Daltons to about 200,000 Daltons, preferably from about 110,000 Daltons to about 190,000 Daltons, and more preferably from about 120,000 Daltons to about 180,000 Daltons.

[0018] Another embodiment of the present invention relates to an aqueous latex architectural composition comprising the two-phase or three-phase latex particles of the present invention discussed herein, an optional opacifying pigment, and a hydrazine or hydrazone compound crosslinked with the at least one crosslinking monomer.

[0019] Another embodiment relates to copolymer latex particles comprising at least a core stage and a shell stage. The core stage is formed from a core monomer mixture of one or more film-forming monomers, and the calculated glass transition temperature (Tgc) of the core stage ranges from about 25 °C to about 100 °C. The shell stage is formed from a shell monomer mixture of one or more film-forming monomers (which is different from the core monomer mixture), wherein the shell monomer mixture includes at least one crosslinking monomer, and wherein the outer portion of the shell stage undergoes copolymerization in the presence of a chain transfer agent (CTA). The at least one crosslinking monomer ranges from 1 wt% to about 8 wt% of the entire polymer of the total monomers in the latex particles, and the CTA ranges from about 0.2 wt% to about 1 wt% of the entire polymer of the total monomers in the latex particles. The outer portion of the shell stage with CTA accounts for about 15 wt% to about 90 wt% of the outer stage, preferably about 15 wt% to about 70 wt%, about 15 wt% to about 35 wt% of the outer stage, more preferably about 20 wt% ± 1.5 wt%. In this embodiment, the crosslinking monomer is distributed throughout the shell stage.

[0020] Detailed description of the preferred embodiments

[0021] The present invention relates to a latex resin for use in aqueous architectural compositions such as paints and stains that forms a paint film with good antiblocking properties when the paint dries or shortly after drying (preferably within one hour after paint application). The latex resin can be a preferred multi-stage polymer or a less preferred single-stage polymer. Advantageously, the consumer can be confident that the paint or stain is antiblocking shortly after application of the paint or stain.

[0022] The polymeric latex resin of the present invention improves the antiblocking properties of the paint film without the addition of antiblocking additives. Commonly used antiblocking additives include silicone-based materials, fluorosurfactants commercially available as the Capstone TM FS family of surfactants, and waxes. During film formulation, these additives migrate to the surface of the film to form a release layer that reduces the mixing of the contacting resin film, as described in "Fluoroadditives: Antiblock Characteristics in Architectural Paint Systems" PCIPaint & Coating Industry Magazine, October 1, 2003. As shown in the following examples, the polymeric latex resin of the present invention improves the antiblocking properties of the paint film without the addition of antiblocking additives. It is foreseen that antiblocking additives will be used in combination with the polymeric latex resin of the present invention to maximize the antiblocking properties of the paint film.

[0023] Without being limited to any particular theory, the inventors of the present invention believe that for a multi-stage polymer, the core should be hard or have a high Tg or MFFT to provide good anti-blocking properties. Preferably, one or more monomers having crosslinking ability (such as diacetone acrylamide (DAAM)) are added to the monomer mixture for the core to provide scrub resistance. The crosslinking monomer is preferably crosslinked with a hydrazine or hydrazone compound present in the aqueous phase of the architectural coating. The inventors of the present invention also believe that the crosslinking monomer increases the structural integrity of the resin, thereby enhancing or maintaining the scrub resistance of the paint film. In addition, omitting the crosslinking monomer from the outer stage can prevent the outer stage from reducing the cleaning ability of the paint film. The outer stage or shell should have a low molecular weight, preferably achieved by adding CTA in the polymerization of the outer stage, and the outer stage preferably has a lower Tg or MFFT to provide good film coalescence and film formation. The lower molecular weight monomer chains have better fluidity and help the latex particles to coalesce faster to provide early anti-blocking properties.

[0024] Without being limited to any particular theory, the inventors of the present invention believe that, as shown in the following examples and samples, adding a chain transfer agent to reduce the molecular weight of the shell or outer stage, combined with a relatively large shell (preferably greater than about 65% by weight, preferably greater than 70% or 75% by weight of all monomers in the latex polymer), can enable the latex of the present invention to exhibit anti-blocking ability one hour after application to a substrate.

[0025] When the multi-stage polymer has a third stage or more, it is preferably the innermost stage and softer than the hardest stage. The hardest stage is preferably smaller in size and weight and is preferably sandwiched between a softer inner stage and a softer shell. Preferably, a crosslinking monomer is added to the monomer mixture for the innermost and / or intermediate stages to improve scrub resistance. The resulting polymer has good anti-blocking properties, scrub resistance, and good cleaning ability. Preferably, the Tg of each stage of the multi-stage polymer will be different from each other.

[0026] Without being limited to any particular theory, the inventors of the present invention believe that for a single-stage polymer in which the Tg is substantially the same throughout the polymer or the Tg only gradually changes inside the polymer, the hardness of the polymer changes from hard in the innermost region and becomes softer in the outermost region. Adding CTA in the later stage of polymerization will reduce the molecular weight of the polymer. This will mimic the structure and properties of the multi-stage polymer of the present invention.

[0027] The MFFT of the polymer of the present invention should be low enough to achieve LTC, that is, preferably less than about 15 °C or about 10 °C, preferably less than about 5 °C or about 0 °C. For a multi-stage polymer, in the innermost region, the monomer mixture should have a certain amount of crosslinking monomer to increase hardness, and in the outermost region, CTA is added to reduce the molecular weight (MW) to achieve coalescence.

[0028] As described below, the Tg can be easily calculated by Fox's equation, which sums the weight fraction of each monomer and the Tg of the monomer polymer made entirely of that monomer. As calculated, the Tg generally does not include the hardness caused by crosslinking of the polymer chains. When a crosslinking monomer is added to the monomer mixture, it is typically used in a relatively low amount, e.g., less than about 10 wt%, as discussed below. Preferably, the calculated Tg includes the film-forming monomers. Crosslinking monomers and any monomers that contribute less than about 1.5 wt% to the polymer and whose Tg is not widely available (such as wet adhesion monomers) are omitted from the Tg calculation. CTA is also omitted from the Tg calculation.

[0029] The overall Tg of the copolymer calculated by Fox's equation includes the individual Tgs of the various monomers being copolymerized, as shown below:

[0030] 1 / Tg agg = Wf1 / Tg1 + Wf2 / Tg2 + Wf x / Tg x ,

[0031] where,

[0032] Tg agg is the overall Tg of the copolymer,

[0033] Wf x is the weight fraction of each monomer x,

[0034] Tg x is the Tg of the polymer made of a single monomer x,

[0035] x is the number of monomers in the copolymer.

[0036] Differential scanning calorimetry (DSC) is a technique commonly used in experimental measurements of the response of polymers to heating. DSC can be used to study the melting or glass transition of crystalline polymers to measure Tg. DSC can measure the hardness caused by crosslinking of polymers (resulting in an increase in Tg), as well as the hardness of uncrosslinked polymers. A DSC apparatus typically includes a measurement chamber that holds two shallow pans and a computer for controlling the heating of the pans. The sample pan contains the material being studied. The second pan (which can be empty) is used as a reference. The computer is used to monitor the temperature and regulate the rate of change of the pan temperature. A typical heating rate is about 10 °C / min. For a given amount of heat, the rate of temperature change of the two pans is different. This difference depends on the composition of the pan contents and physical changes such as phase transitions. For heat flux, the system typically varies the heat supplied to one of the pans to keep the temperatures of the two pans the same. The difference in the heat output of the two heaters is recorded. If a polymer in its solid state is heated, it will reach its Tg at some point. At this time, due to the change in chain mobility, the mechanical properties of the polymer change from those of a brittle material to those of an elastic material. The heat capacity of the polymer is different before and after Tg. The heat capacity Cp of the polymer is typically higher above Tg. Importantly, it is noted that this transition does not occur suddenly at a specific temperature but occurs over a temperature range. The temperature in the middle of the inclined region is taken as Tg. Due to the change in heat capacity, the glass transition results in a kink in the plot of heat against temperature. In the plot of heat flow against temperature, it is a gradual transition that occurs over a temperature range. The glass transition temperature is taken as the middle of the inclined region. See generally polymerscience.physik.hu-berlin.de / docs / manuals / DSC.

[0037] The Tg values obtained by DSC reported herein were measured using solid samples of the polymer that do not contain any crosslinking compounds (such as hydrazine or hydrazone) that would crosslink with monomers such as DAAM in the aqueous phase of the paint or dye. Thus, the reported Tg (DSC) is the Tg of the uncrosslinked polymer.

[0038] The Tg values of common film-forming monomers and DAAM are shown below.

[0039] Monomer Tg (°C) BA -54 2-EHA -50 EA -24 MMA 105 MAA 228 Styrene 100 VA 30 DAAM 85

[0040] The minimum film-forming temperature (MFFT) is preferably measured by ISO 2115 (April 2001). Tg and MFFT are reported in degrees Celsius. Unless otherwise indicated, the Tg values reported herein were calculated by Fox's equation. Unless otherwise indicated, the molecular weight is the weight-average molecular weight (MW w)。All percentages are by weight (wt%). The particle size or particle diameter (if present) is the volume average particle size (D v ).

[0041] Suitable emulsion latex particles include, but are not limited to, acrylic, vinyl, vinyl-acrylic, or styrene-acrylic polymers or copolymers. The latex particles coalesce and / or crosslink to form a paint film on a substrate. For the present invention, latexes made primarily from acrylic monomers are preferred, as illustrated in the examples below. Exemplary, non-limiting monomers suitable for forming the emulsion latex particles of the present invention are described below.

[0042] Any (meth)acrylic monomer can be used in the present invention. Suitable (meth)acrylic monomers include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isooctyl (meth)acrylate, lauryl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, alkyl (meth)acrylic acids, such as methyl (meth)acrylic acid, (meth)acrylic acid, wet adhesion monomers, such as N-(2-methacryloyloxyethyl)ethyleneurea, and multifunctional monomers, such as divinylbenzene, diacrylates (for crosslinking functions, etc.), acrylic acid, ionic acrylate salts, alkylacrylic acids, ionic alkylacrylate salts, haloacrylic acids, ionic haloacrylate salts, acrylamide, alkylacrylamide, monoalkylacrylamide, monoalkylalkylacrylamide, acrylic acid alkyl esters, alkylacrylic acid alkyl esters, acrylonitrile, alkylacrylonitrile, dialkylacrylamide, dialkylalkylacrylamide, acrylic acid hydroxyalkyl esters, alkylacrylic acid hydroxyalkyl esters, acrylate esters that are only partially esterified with alkylene glycols, acrylate esters that are only partially esterified with non-polymeric polyhydroxy compounds such as glycerol, acrylate esters that are only partially esterified with polymeric polyhydroxy compounds, itaconic acid, itaconic acid mono- and diesters, and combinations thereof. The preferred (meth)acrylic acid alkyl ester monomers are methyl methacrylate and butyl acrylate.

[0043] Preferred monomers containing aromatic groups are styrene and α-methylstyrene. Other suitable monomers containing aromatic groups include, but are not limited to, 2,4-diphenyl-4-methyl-1-pentene, 2,4-dimethylstyrene, 2,4,6-trimethylstyrene, 2,3,4,5,6-pentafluorostyrene, (vinylbenzyl)trimethylammonium chloride, 2,6-dichlorostyrene, 2-fluorostyrene, 2-isopropenylaniline, 3-(trifluoromethyl)styrene, 3-fluorostyrene, α-methylstyrene, 3-vinylbenzoic acid, 4-vinylbenzyl chloride, α-bromostyrene, 9-vinylanthracene, and combinations thereof.

[0044] Preferred monomers containing primary amide groups are (meth)acrylamide. Suitable monomers containing amide groups include, but are not limited to, N-vinylformamide or any vinylamide, N,N-dimethyl(meth)acrylamide, N-(1,1-dimethyl-3-oxobutyl)(meth)acrylamide, N-(hydroxymethyl)(meth)acrylamide, N-(3-methoxypropyl)(meth)acrylamide, N-(butoxymethyl)(meth)acrylamide, N-(isobutoxymethyl)acryloyl(meth)acrylamide, N-[tris(hydroxymethyl)methyl]acryloyl(meth)acrylamide, 7-[4-(trifluoromethyl)coumarin](meth)acrylamide, 3-(3-fluorophenyl)-2-propenamide, 3-(4-methylphenyl)(meth)acrylamide, N-(tert-butyl)(meth)acrylamide, and combinations thereof. These monomers can be polymerized with the acrylic monomers listed above. The general formula for vinyl (meth)amide is:

[0045]

[0046] And the general formula for (meth)acrylamide is:

[0047]

[0048] Wherein R1 and R2 can be -H, -CH3, -CH2CH3, and other substituted organic functional groups, and R3 can be -H, alkyl, or aryl.

[0049] In one embodiment, styrene monomers, such as styrene, methylstyrene, chlorostyrene, methoxystyrene, and the like, are preferably copolymerized with (meth)acrylamide monomers.

[0050] In one embodiment, the aqueous latex polymer can also contain vinyl monomers. Monomers of this type suitable for the uses according to the present invention include any compound having a vinyl functional group (i.e., -CH=CH2 group). Preferably, the vinyl monomers are selected from the group consisting of vinyl esters, vinyl aromatics, vinyl aliphatic hydrocarbons, vinyl alkyl ethers, and mixtures thereof.

[0051] Suitable vinyl monomers include vinyl esters such as, for example, vinyl acetate, vinyl propionate, vinyl laurate, vinyl pivalate, vinyl nonanoate, vinyl decanoate, vinyl neodecanoate, vinyl butyrate, vinyl caproate, vinyl benzoate, vinyl isopropyl acetate, and similar vinyl esters; nitrile monomers such as (meth)acrylonitrile and the like; vinyl aromatics such as, for example, styrene, methylstyrene, and similar lower alkyl styrenes, chlorostyrene, vinyltoluene, vinylnaphthalene, and divinylbenzene; vinyl aliphatic hydrocarbon monomers such as, for example, vinyl chloride and vinylidene chloride, and alpha-olefins such as, for example, ethylene, propylene, isobutene, and conjugated dienes such as 1,3-butadiene, methyl-2-butadiene, 1,3-pentadiene, 2,3-dimethylbutadiene, isoprene, cyclohexene, cyclopentadiene, and dicyclopentadiene; and vinyl alkyl ethers such as, for example, methyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether.

[0052] Suitable CTAs include, but are not limited to, monofunctional thiols such as monothiol or compounds having a sulfur-hydrogen (S-H) functional group. A preferred chain transfer agent is isooctyl 3-mercaptopropionate (iOMP), which is disclosed in U.S. Patent No. 7,642,314 jointly owned by Gharapetian et al. Preferred iOMP (C 11 H 22 O2S) chain transfer agents have the following structure:

[0053]

[0054] Other suitable thiol chain transfer agents include, but are not limited to, n-dodecyl mercaptan (n-DDM), tert-dodecyl mercaptan, n-octyl mercaptan, tert-octyl mercaptan, sec-octyl mercaptan, n-tetradecyl mercaptan, n-octadecyl mercaptan, n-hexyl mercaptan, n-pentyl mercaptan, n-butyl mercaptan, tert-butyl mercaptan, n-butyl 3-mercaptopropionate (BMP), methyl 3-mercaptopropionate, etc., and mixtures thereof, which are disclosed in U.S. Patent Nos. 4,593,081 and 7,256,226. The '081 patent further discloses other non-thiol chain transfer agents. All patent references cited in this paragraph are incorporated herein by reference in their entirety. n-DDM is another preferred chain transfer agent.

[0055]

[0056] As discussed above, the latex particles can have crosslinking monomers that are added to the monomer mixture for the internal stage (such as the core or two internal cores / stages) or to the first part of the monomer mixture. Crosslinking can improve the toughness of the dry paint film, for example, improve its scrub resistance or have improved scrub resistance. Suitable self-crosslinking moieties are formed from monomers such as diacetone acrylamide (“DAAM”), and suitable crosslinking agents include adipic dihydrazide (“ADH”).

[0057] Suitable crosslinking monomers include, but are not limited to, DAAM, diacetone methacrylamide (DAMAM), acetoacetoxyethyl methacrylate (AAEM), allyl methacrylate (AMA), and / or 1,4-butanediol diacrylate, which are added to the pre-emulsion composition and can copolymerize with the film-forming monomers to form latex particles.

[0058] It has been reported that crosslinking of polymers containing DAAM and the ADH crosslinking agent by the keto-hydrazide reaction has a significant reaction rate in aqueous solution (“The diacetone acrylamide cross-linking reaction and its influence on the film formation of an acrylic latex”, Journal of Coatings Technology and Research, 5(3), 285-297, 2008.). To minimize this premature crosslinking, the ADH hydrazide is substantially replaced by a hydrazone, or a blocked hydrazide particle, which is discussed in co-owned U.S. Published Patent Application No. 2012 / 0142847 and co-owned U.S. Patent No. 9,040,617, which are incorporated herein by reference in their entirety. The hydrazone crosslinking particles do not react with the DAAM moiety during storage and are converted to hydrazide crosslinking particles when the aqueous component evaporates after application to a substrate.

[0059] Another method of reducing premature crosslinking during storage is to substantially remove the hydrazide (ADH) crosslinking agent and introduce a second crosslinkable moiety, such as methacrylamide (MAM) and / or acrylamide (AM) monomers, onto the latex particles. This second crosslinkable monomer copolymerizes as part of the latex particles and acts as another self-crosslinking moiety of the film-forming latex particles. A small amount of the hydrazide crosslinking agent (e.g., less than its stoichiometric ratio with DAAM) can remain in the aqueous phase. Latex particles having multiple crosslinkable moieties are disclosed in co-owned U.S. Published Patent Application Nos. US2014 / 0323635 and US 2014 / 0228514.

[0060] Also suitable are pre-crosslinked monomers such as diethylene glycol dimethacrylate (DEGDMA), ethylene glycol dimethacrylate (EGDMA), and 1,3-butanediol diacrylate (BGDA), which crosslink during the polymerization process.

[0061] Additives can be added during the polymerization process, including surfactants, initiators, promoter systems, biocides, rheology modifiers, etc.

[0062] Examples of surfactants that can be used in the polymerization process can include, but are not limited to, nonionic and / or anionic surfactants such as ammonium nonoxynol-4 sulfate, nonylphenol (10) ethoxylate, nonylphenol (~10 mol%) ethoxylate, nonylphenol (~40 mol%) ethoxylate, octylphenol (~40 mol%) ethoxylate, octylphenol (9-10) ethoxylate, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, polyether phosphate esters, alcohol ethoxylate phosphates, those compounds sold under the trade name Triton TM (e.g., QS series, CF series, X series, etc.), those compounds sold under the trade name Rhodapon TM under, those compounds sold under the trade name Rhodapex TM under, those compounds sold under the trade name Rhodacal TM under, those compounds sold under the trade name Rhodafac TM etc., and the like, and combinations thereof.

[0063] Examples of initiators and promoter systems that can be used in the polymerization process can include, but are not limited to, ammonium persulfate, sodium persulfate (SPS), azo initiators (such as azoisobutyronitrile), redox systems (such as sodium hydroxymethanesulfinate (rongalite; reducing agent) and tert-butyl hydroperoxide (oxidizing agent), and the like, and combinations thereof, typically in aqueous solution. If a stable emulsion is desired, any one or both of these components can optionally contain additional surfactants and / or pH regulators.

[0064] Examples of pH regulators that can be used in the polymerization process can include, but are not limited to, ammonium hydroxide, sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, ammonia, amines such as trimethylamine, triethylamine, dimethylaminoethanol, diethylaminoethanol, AMP-95, and the like, and combinations thereof. In some cases, compounds that meet the requirements of a pH regulator can be added for purposes other than adjusting the pH, for example, emulsion stabilization, but are still characterized as pH regulators herein.

[0065] Preferably, a redox pair (a reducing agent and an oxidizing agent) is added to the latex emulsion polymer to reduce odor and neutralize unreacted monomers without performing a lengthy or time-consuming stripping step or requiring additional stripping equipment.

[0066] Suitable oxidizing agents include, but are not limited to, water-soluble hydroperoxides, tert-butyl hydroperoxide, cumene hydroperoxide, hydrogen peroxide, sodium peroxide, potassium peroxide, sodium perborate, potassium persulfate, sodium persulfate, ammonium persulfate, persulfuric acid and its salts, perphosphoric acid and its salts, potassium permanganate, and ammonium or alkali metal salts of peroxydisulfuric acid. A preferred oxidizing agent is tert-butyl hydroperoxide (tBHP).

[0067] Suitable reducing agents include, but are not limited to, sodium formaldehyde sulfoxylate (SFS), ascorbic acid, isoascorbic acid, organic compounds containing thiol or disulfide groups, reducing inorganic bases and ammonium salts of sulfur-containing acids (such as sodium sulfite, metabisulfite, thiosulfate, bisulfite, sulfide, hydrosulfide or dithionite), formadinesulfinic acid, hydroxymethanesulfonic acid, acetone bisulfite, amines (such as ethanolamine), glycolic acid, glyoxylic acid hydrate, lactic acid, glyceric acid, malic acid and tartaric acid. Preferred reducing agents include formaldehyde-free SFS and sodium salts of organic sulfinic acid derivatives.

[0068] The following non-limiting emulsion examples illustrate the polymerization of the latex particles of the present invention. In Examples 1-2, different amounts of the same set of monomers were used in all stages of the polymer to achieve several different Tg stages. However, different monomer combinations can be used to achieve different stages. For polymers having at least three stages, the Tg of the innermost core is usually not detectable by DSC - when this stage represents a small percentage of the total monomer weight of the polymer or when the phase change is small, and is therefore calculated by Fox's equation. The Tg of the other two stages and the Tg of the two-stage polymer can be measured by DSC. In Examples 1-2, a crosslinking monomer (such as DAAM) was incorporated into the core or two cores, and a CTA such as iOMP was included in the shell stage. In Example 3 (which is a single-stage polymer), the crosslinking monomer was added to the monomer mixture at the start of the polymerization, and the CTA was added to the monomer mixture at the end of the polymerization.

[0069] Example 1: 3-stage polymer

[0070] Deionized water, surfactant, and buffer were charged into a reactor and heated to 80 °C. Monomer pre-emulsion mixtures for core 1, core 2, and shell were prepared separately. A seed (13% of the core 1 pre-emulsion monomer mixture) and initiator solution 1 were charged into the reactor and held for 15 minutes, then the remaining core 1 monomer mixture was fed into the reactor. Once the monomers of core 1 were completely reacted, the core 2 pre-emulsion monomer mixture was fed in, and then the shell pre-emulsion monomer mixture was fed in. The total feeding time was 3.5 hours. The holding time was 30 minutes. Then an additive was added dropwise at 55 - 60 °C over 30 minutes. It was cooled to 35 °C, neutralized with ammonia, and then a biocide solution was added.

[0071]

[0072]

[0073] Total latex:

[0074]

[0075] DW is deionized water; the emulsifier is phosphate ester; the buffer is sodium bicarbonate; the initiator is sodium persulfate (SPS); the wetting agent is neutralized alcohol phosphate ester; the oxidizer is tert-butyl hydroperoxide (tBHP) oxidizer; the reducing agent is the sodium salt of an organic sulfinic acid derivative; and MEEU is N-(2-methacryloyloxyethyl)-ethyleneurea and acts as a wet adhesion monomer. Due to the functionality of the crosslinking monomer in the present invention (as described herein), the DAAM monomer is not included in the total monomer solids and is tracked separately.

[0076] The weight percentages of each stage are as follows: core 1 is 35 wt%, core 2 is 25 wt%, and shell is 40 wt%. The Tg of core 1 is 20 °C (Fox), the Tg of core 2 is 50 °C (DSC), and the Tg of the shell is -6 °C (DSC).

[0077] Example 2: 2-stage polymer

[0078] Deionized water, surfactant, and buffer were charged into a reactor and heated to 80 °C. Monomer pre-emulsion mixtures for the core and shell were prepared separately. A seed (6% of the core pre-emulsion) and initiator solution 1 were charged into the reactor and held for 15 minutes, then the remaining core pre-emulsion monomer mixture was fed into the reactor. Once the core was completely reacted, the shell pre-emulsion monomer mixture was fed in. The total feeding time was 3.5 hours. The holding time was 30 minutes. Then an additive was added dropwise at 55 - 60 °C over 30 minutes. It was cooled to 35 °C, neutralized with ammonia, and then a biocide solution was added.

[0079]

[0080]

[0081] Total latex:

[0082]

[0083] The weight percentages of each stage are as follows: the core is 50% by weight and the shell is 50% by weight. The Tg of the core is 50 °C (DSC), and the Tg of the shell is -6 °C (DSC).

[0084] Example 3: 1-stage polymer

[0085] Deionized water, surfactant, and buffer are charged into a reactor and heated to 80 °C. A monomer pre-emulsion mixture without DAAM crosslinker or iOMP chain transfer agent is prepared. The seed (4.8% of the total pre-emulsion mixture) and initiator solution 1 are charged into the reactor, held for 15 minutes, and then the remaining emulsion is fed in. The DAAM solution is fed into the first 70% of the pre-emulsion. The iOMP is fed into the last 30% of the pre-emulsion. The total feeding time is 3.5 hours. Hold for 30 minutes. Then, the additive is added dropwise at 55 - 60 °C over 30 minutes. Cool to 35 °C, neutralize with ammonia, and then add the biocide solution.

[0086]

[0087]

[0088] Total latex:

[0089]

[0090]

[0091] In this example, the emulsifier 2 is sodium alpha olefin sulfonate.

[0092] The Tg of this one-stage latex is about 20 °C (DSC).

[0093] For the present invention, which relates to anti-blocking properties within a short time after paint application, the standard blocking test (ASTM D4946 - 89) is modified to have a shorter timing after paint application, and different numerical scales are selected as follows:

[0094] 1. Apply the paint composition on a white panel with a 3 - mil bar and dry for 1 hour at a controlled temperature (77 °F or 25 °C) and controlled humidity (50%) (CTCH).

[0095] 2. Cut 1 - inch × 1 - inch squares and arrange these squares such that the painted surfaces face each other.

[0096] 3. Place a 1-inch x 1-inch x 1-inch block weighing 100 grams-force on the square and place it under CTCH for 3 hours, and then place it in an oven at 120°F (49°C) for 3 hours.

[0097] 4. Remove the heavy weight and let the square stand at room temperature (77°F) for 30 minutes.

[0098] 5. Pull the square apart.

[0099] 6. Rate the antiblocking as follows:

[0100] 1. Film transfer; indicate the percentage of paint transfer.

[0101] 2. Heavy tack; no paint transfer.

[0102] 3. Medium tack; no paint transfer.

[0103] 4. Light tack; no paint transfer, and

[0104] 5. No tack; no paint transfer.

[0105] 7. Repeat steps 2 - 6 two more times.

[0106] 8. Take the average of the three measurements.

[0107] Samples of the 1-phase, 2-phase, and 3-phase polymers of the present invention polymerize similarly to those shown in Examples 1 - 3. DAAM and iOMP were used in the following examples. The polymers of the present invention can be used in both uncolored and colored paints. The uncolored paints used herein include paints having a binder resin and an opacifying pigment (such as TiO2), in addition to 4-base pastel pigments and optional extender pigments and additives. The uncolored paints are suitable for painting / plastering the walls of building structures (such as houses, adobe houses, and commercial buildings). Due to the presence of the opacifying pigment, the uncolored paints are usually white. Colored paints are obtained by adding colorants to the uncolored paints to achieve the desired final color. The colorants usually contain additional thickeners, rheology modifiers, and polymer surfactants, which can increase the blocking tendency of the paint film. The antiblocking test using colored paints is more difficult to pass and is included to show the enhanced antiblocking ability of the polymeric latex resins of the present invention. As discussed above, the paints used in the tests reported below do not contain any antiblocking additives.

[0108] Table 1. Performance data and results of 3-phase polymers in uncolored paints.

[0109]

[0110]

[0111] Table 2. Properties of the 3 - stage polymer

[0112]

[0113] (By DSC) Measure the Tg of core 2 and the shell. Calculate the Tg of core 1 (by the Fox equation) as it does not appear on the DSC scan. The calculated Tg (Fox) of core 2 is 38 °C. The Tg (DSC) is approximately 12 °C higher than the Tg (Fox). The calculated Tg (Fox) of the shell is - 6 °C. The Tg (DSC) is approximately 2 °C lower than the Tg (Fox).

[0114] The blocking resistance results of the 3 - stage polymer of the present invention show that after drying for 1 hour at room temperature or 77 °F, the painted surface exhibits only slight tackiness or better, and at a high temperature of 120 °F, the painted surface exhibits only slight to moderately slight tackiness. The scrub resistance of the paint film is below the normal range but still acceptable. The scrub resistance test is carried out 7 days after the paint film is dried. The paint film is easy to clean and the total score is below 6. The higher the value, the more difficult it is to remove the stain from the paint film, and a lower value is preferred. The reported numbers are the sum of the color reading changes (δE values in CIE2000) of the paint film before pre - soiling and after soiling with various different stains (coffee, red wine, ketchup, yellow mustard, and graphite) and then cleaning. The presented stain tests also include TTP stains (which contain raw sienna, white petrolatum, and mineral spirits) and junk stains (which contain lanolin, petrolatum, carbon black, and mineral oil). Lower junk and TTP scores are preferred.

[0115] Table 3. Performance data and results of the 2 - stage polymer in colored paint.

[0116]

[0117] Polymer # Scrubbing Total cleaning ability Garbage / TTP Invention 4 342 2.93 0.70 / 0.32 Invention 5 492 2.90 0.87 / 1.12 Invention 6 208 3.83 0.68 / 0.60 Control 1 663 3.73 0.81 / 0.24

[0118] Table 4. Properties of the 2 - stage polymer

[0119]

[0120] Measure the Tg of the core and the shell by DSC. The Tg (DSC) of 50 °C also corresponds to the Tg (Fox) of 38 °C. The Tg (DSC) of 63 °C corresponds to the Tg (Fox) of 55 °C.

[0121] Tables 3 and 4 illustrate the advantages of adding CTA to the shell of the two-stage polymer. For example, about 1% of iOMP is incorporated in the shell and about 4% of DAAM is incorporated in the core of the crosslinking monomer. The 1-hour blocking resistance at 77°F is 4.0 - 4.5 (lightly tacky - non-tacky), and the 1-hour blocking resistance at elevated 120°F is 3 (moderately tacky). These examples include control two-stage polymers that contain crosslinking monomers in the core but no CTA in the shell. The Tg of the core and shell is similar to that of the examples of the present invention. The blocking resistance is significantly improved. The 1-hour blocking resistance at 77°F is significantly improved from 3 (moderately tacky) to 4.0 - 4.5 (lightly tacky - non-tacky), and the 1-hour blocking resistance at 120°F is significantly improved from 1 (10% film transfer) to 3 (moderately tacky). These examples demonstrate the advantages of using CTA in the outermost stage.

[0122] The inventors of the present invention believe that although the scrub resistance of Samples 4 and 6 of the present invention is not as high as that of other samples of the present invention, adding more crosslinking monomers (such as DAAM) to the core (which will crosslink with hydrazine or hydrazone crosslinking compounds during film formation) can improve the scrub resistance. In addition, as shown in Samples 1 - 3 of the present invention, adding an internal core stage can improve the scrub resistance and blocking resistance.

[0123] Using gel permeation chromatography (GPC) data of substantially the same polymer, the molecular weights of the shells of the blocking-resistant polymers of the present invention were calculated to be 11,612 and 17,688 daltons. GPC is discussed in commonly-owned U.S. Patent No. 8,895,658, which is incorporated herein in its entirety. The preferred molecular weight range of the shell or outermost stage is from about 8,000 daltons to about 30,000 daltons, and preferably from about 10,000 daltons to about 25,000 daltons, or preferably from about 10,000 daltons to about 20,000 daltons. As described above, the molecular weight is reported as the weight average molecular weight.

[0124] Table 5. Performance data and results of the second-preferred single-stage polymer in uncolored paint.

[0125]

[0126] Table 6. Performance of single-stage polymers

[0127]

[0128] Samples of the single-stage polymers of the present invention show that the difference between Tg (Fox) and Tg (DSC) is 5°C. At both temperatures, the blocking resistance is better than that of Control 2 without crosslinking monomers and without CTA, and at higher temperatures, it is better than that of Control 2 with more crosslinking monomers and without CTA.

[0129] A novel aspect of the single-stage polymers of the present invention (such as Example 3 and Sample 7 of the present invention) is that in a single stage (i.e., a stage formed from the same monomer mixture), a crosslinkable monomer and a CTA are added sequentially, wherein the crosslinkable monomer is added at the beginning of the polymerization and the CTA is added when the polymerization approaches completion. Preferably, the addition of the crosslinkable monomer and the CTA does not overlap.

[0130] Table 7. Comparative Examples of Two-Stage Polymers in Uncolored Paints

[0131]

[0132] Monomers: MMA, 2EHA, and styrene.

[0133] Controls 3 and 4 are two-stage polymers and do not contain crosslinking monomers, and Control 4 contains a small amount of CTA in the shell. Neither material has acceptable blocking resistance at high temperatures; however, even Control 4, which has no crosslinking monomers in the core and only a small amount of CTA in the shell, exhibits acceptable blocking resistance (no paint transfer) superior to that of Control 3 at room temperature. These comparative examples demonstrate the efficacy of CTA in the shell and a high core Tg.

[0134] The inventors of the present invention have also found that crosslinking monomers (such as DAAM) not only provide crosslinking in the internal stage or internal portion but also maintain the scrub resistance of the paint film.

[0135] Based on Examples 1 and 2 and Samples 1-6 of the present invention, as well as Example 3 and Sample 7 of the present invention, the preferred amounts of the components in the polymer latex resin of the present invention are as follows. The amount of CTA in the entire polymer (such as those within the outer shell) or in the single-stage polymer is from about 0.2 wt% to about 2.0 wt% of the entire polymer, preferably from about 0.5 wt% to about 1.5 wt%, and more preferably from about 0.75 wt% to about 1.25 wt%

[0136] The amount of crosslinking monomer to be added to the entire multi-stage or core-shell polymer (such as those within one or more core stages) or to the single-stage polymer is from about 1 wt% to about 8 wt% of the entire polymer, preferably from about 2 wt% to about 7 wt%, and more preferably from about 3 wt% to about 5 wt%

[0137] The weight percentage range of the soft, low molecular weight outermost stage is from about 40 wt% to about 65 wt%, preferably from about 45 wt% to about 60 wt%. The weight percentage range of the hardest inner stage is from about 20 wt% to about 55 wt%, preferably from about 25 wt% to about 50 wt%.

[0138] When there are three stages, the third stage is the innermost stage and accounts for from about 20% to about 50% by weight, preferably from 30% to about 40% by weight. The weight percentage range of the hardest inner stage is from about 15% to about 35% by weight, preferably from about 20% to about 30% by weight. The soft, low molecular weight outermost stage ranges from about 30% to about 50% by weight, preferably from about 35% to about 45% by weight.

[0139] The Tg value of the polymer of the present invention is defined as Tg(DSC) or Tgm (measured Tg) and Tg(Fox) or Tgc (calculated Tg). For multi-stage polymers (including 2-stage, 3-stage and 3 + -stage polymers), the hardest stage within the polymer is one of the inner stages, i.e., not the outermost shell. The hardest stage can be one of the innermost core or the intermediate stage. The Tgc range of the hardest stage is from about 25 °C to about 100 °C, preferably from about 25 °C to about 75 °C and preferably from about 35 °C to about 60 °C. The Tgm range of the hardest stage is from about 30 °C to about 120 °C, preferably from about 40 °C to about 100 °C and preferably from about 45 °C to about 80 °C.

[0140] The Tgc or Tgm of the outermost stage or shell is preferably about 45 °C to about 90 °C lower, preferably about 50 °C to about 80 °C lower, preferably about 55 °C to about 75 °C lower than the Tgc or Tgm of the hardest stage.

[0141] The Tgm of the outermost stage is preferably less than about 5 °C, preferably less than about 0 °C and preferably less than -5 °C, and higher than about -25 °C. The Tgc of the outermost stage is preferably less than about 0 °C, preferably less than about -5 °C and preferably less than about -10 °C, and higher than about -35 °C.

[0142] The present invention can be defined by Tg(Fox) / Tgc or Tg(DSC) / Tgm, as long as Tg is used consistently.

[0143] As described above, the weight average molecular weight range of the outermost stage or the softest stage is from about 8,000 daltons to about 30,000 daltons, and preferably from about 10,000 daltons to about 25,000 daltons, or preferably from about 10,000 daltons to about 20,000 daltons.

[0144] Another embodiment of the present invention relates to a two-stage or more-stage polymer that contains a certain amount of crosslinkable monomer in the shell and a certain amount of CTA in the shell. Preferably, the core also contains a crosslinkable monomer, and preferably the crust contains more than half of the total monomer weight of the polymer. In this embodiment, the crosslinkable monomer is added to the core monomer mixture feed and continues at the start of the addition of the shell monomer mixture feed. The CTA is added to the latter part of the second-stage monomer mixture feed. Preferably, the addition of the CTA and the crosslinkable monomer do not overlap and can be added sequentially one after the other, or can be added in sequence with a stage in between where neither is added. Alternatively, in another embodiment, the CTA and the crosslinkable monomer overlap. This embodiment is a combination of the single-stage embodiment shown in Example 3 and Sample 7 of the present invention with a core containing a crosslinkable monomer.

[0145] Preferably, the shell stage of this embodiment is relatively large, i.e., at least 60% by weight, preferably at least 70% by weight, and up to at least 80% by weight of the total monomer weight of the latex particles. Without being bound by any particular theory, the inventors of the present invention believe that at these relative weight percentages, the shell stage of the latex polymer forms a continuous phase in the dry paint film. In other words, the shell forms a matrix in the dry film.

[0146] The method for preparing the polymer according to this embodiment is shown in Example 4 below.

[0147] Example 4: 2-stage polymer

[0148] Deionized water, surfactant, and buffer were charged into a reactor and heated to 80 °C. Pre-emulsions of monomers for the core / stage 1 and shell / stage 2 were prepared separately. DAAM in stage 1 was added throughout the addition of the first-stage monomer mixture. DAAM in stage 2 was added to the first 60% by weight of the stage 2 monomer mixture. The chain transfer agent was added to the last 30% by weight of the stage 2 monomer mixture. Seeds (15% of the weight of the stage 1 emulsion) and initiator solution 1 were charged into the reactor, held for 15 minutes, and then the remaining stage 1 monomer mixture was fed into the reactor over one hour together with 30% by weight of initiator 2. Once the core was completely reacted, the shell monomer mixture was fed in together with the remainder of initiator 2. The total feeding time was 3.5 hours. Held for 30 minutes. Then the additive was added dropwise over 30 minutes at 55 - 60 °C. Cooled to 35 °C, neutralized with ammonia, and then the biocide solution was added.

[0149]

[0150]

[0151] Samples 8 - 15 of the present invention were prepared using the polymerization method discussed in Example 4. The values reported in Example 4 reflect Sample 14 of the present invention. MMA, 2 - EHA, and a small amount of MAA were used in the monomer mixture to achieve the Tg reported below. The glass transition temperatures of the monomers used in Example 4 and Samples 8 - 15 of the present invention are as follows: MMA is 105 °C, 2 - EHA is - 50 °C, and MAA is 228 °C, and the combined Tg was calculated using Fox's equation. A small amount of wet - adhesion monomer (less than 1 wt%) can be omitted from the Tg calculation, and the cross - linking monomer and CTA are omitted from the Tg calculation.

[0152] During the polymerization process, a cross - linkable monomer (i.e., DAAM) accounting for about 4 wt% of the total monomers and a CTA (i.e., IOMP) accounting for about 0.4% of the total monomers were used. The DAAM monomer was added to the first 70% of the total monomer mixture added (which includes the first and second stages), and the CTA / IOMP was added to the last 20% of the total monomer mixture (which only includes the second stage or the shell stage). After polymerization was completed, about 60 wt% of the second stage or shell stage contained DAAM, and about 30 wt% of the second stage contained CTA. The samples of the present invention and the control samples in Tables 8 and 9 below are all low - VOC (<50 g / l), semi - gloss, 1 - base uncolored paint compositions without anti - blocking additives such as fluorosurfactants. An adequate amount of the opacifying pigment TiO2 was added to the latex resin during the paint - making stage to prepare 1 - base paints. All paint samples passed the low - temperature coalescence (LTC) test at 10 °C. Similar to the Tgc discussed above in connection with Examples 1 - 3 and their related samples of the present invention, the Tgc for Example 4 and Samples 8 - 15 in Table 8 does not include the DAAM cross - linking monomer.

[0153] Table 8

[0154]

[0155] Table 9

[0156]

[0157] RT or room temperature is about 77 °F or 25 °C.

[0158] The weight - average molecular weights (Mw) of the control and Invention 14 are shown in Table 10 below. The molecular weight of Invention 14 represents the molecular weights of Inventions 8 - 15.

[0159] Table 10

[0160]

[0161] As shown in Table 8 - 10, Samples 8 - 15 of the present invention exhibit good anti - blocking at room temperature and acceptable anti - blocking at 50°C. Samples with a lower calculated Tg in the core or a lower ΔTg generally have lower anti - blocking (Sample 8 - 10), although the anti - blocking is acceptable. Samples with a higher Tg or a higher ΔTg generally have higher anti - blocking (Samples 13 - 15). As the core Tg or ΔTg increases, the scrub resistance or scourability generally decreases. As the core Tg or ΔTg increases, the cleaning ability slightly decreases.

[0162] The hardness of the dry film (Persoz hardness) is evaluated by monitoring the damping of the pendulum vibration by the dry film, which is directly related to the softness of the sample. The harder the dry film, the higher the Persoz value. The Persoz hardness value is higher at 4 weeks compared to 1 week, indicating that the anti - blocking property improves as the paint film ages.

[0163] The ΔTg of Samples 8 - 15 and Example 4 can be lower than 45°C. The amount of CTA used in these samples is lower than those in Samples 1 - 6 and Examples 1 - 2 of the present invention, and thus the weight - average molecular weight of Sample 8 - 15 is higher than those of Samples 1 - 6.

[0164] Example 5. Another experiment was conducted where DAAM monomer was mixed throughout the shell stage, and CTA (iOMP) was added to the last 20% of the shell monomer mixture. In this experiment, the core accounts for about 30 wt% of the polymer latex, and the shell accounts for about 70 wt% of the polymer latex.

[0165]

[0166]

[0167] Example 6 is similar to Example 5, except that DAAM is mixed with the first 70% of the two - monomer mixture, whereby the entire core contains DAAM and the inner part of the shell also contains DAAM. CTA (0.4 wt%) is also added to the last 20% of the total monomers for the latex particles containing the core and the shell, or to the last 30% of the shell monomer mixture in Examples 5 and 6.

[0168] Example 5 studied the film properties when the cross - linking monomer was mixed throughout the shell. Example 6 is the inventive Sample 8 discussed above and is used here for comparison with Example 5. The properties of the paint films of Examples 5 and 6 of the present invention are shown below.

[0169]

[0170]

[0171]

[0172] The inventive samples in Examples 5 and 6 showed that when the crosslinking monomer was uniformly mixed or distributed in the shell stage but not in the core stage, and at the same time the CTA was mixed into the outer 20% of the shell, the polymer resin passed the anti-blocking standard (2 - 3 at room temperature and 2 at 120°F), and had good cleaning ability and scrub resistance. These results also showed that when the crosslinking monomer was mixed with the core and the shell of the inner part and the CTA was mixed into the last 20% of the shell, the anti-blocking property increased (5 at room temperature and 4 at 120°F), and the scrub resistance also increased, while the cleaning ability remained basically unchanged.

[0173] The preferred amounts of the components in the inventive polymer latex resins in the embodiments of Examples 3 and 4 and inventive samples 7 and 8 - 15 and inventive Examples 5 and 6 are discussed in the following paragraphs. The amount of CTA in the whole polymer (such as those in the shell) or in a single-stage polymer is from about 0.20 wt% to about 1.0 wt% of the whole polymer, preferably from about 0.25 wt% to about 0.90 wt%, and more preferably from about 0.30 wt% to about 0.80 wt%.

[0174] The amount of the crosslinking monomer to be incorporated into the whole multi-stage or core-shell polymer (such as those within one or more core stages) or into a single-stage polymer is from about 1 wt% to about 8 wt% of the whole polymer, preferably from about 2 wt% to about 7 wt%, and more preferably from about 3 wt% to about 5 wt%.

[0175] The weight percentage range of the soft, low molecular weight outermost stage is from about 60 wt% to about 80 wt%, preferably from about 65 wt% to about 75 wt%, or from 67.5 wt% to 72.5 wt%. The weight percentage range of the hardest inner stage is from about 20 wt% to about 40 wt%, preferably from about 25 wt% to about 35 wt%.

[0176] The Tg value of the inventive polymer in the embodiments of Examples 3 and 4 and inventive samples 7 and 8 - 15 is Tg(Fox) or Tgc (calculated Tg). The harder stage within the polymer is the inner stage or core, and the softer stage is the outer stage or shell. The Tgc range of the harder stage is from about 25°C to about 100°C, preferably from about 30°C to about 85°C and preferably from about 35°C to about 75°C. Alternatively, the Tgm (if used) range of the hardest stage is from about 30°C to about 120°C, preferably from about 40°C to about 100°C and preferably from about 45°C to about 80°C.

[0177] The Tgc or Tgm of the softer outermost stage or shell is preferably about 20 °C to about 90 °C lower than that of the harder stage, i.e., ΔTg, preferably about 50 °C to about 80 °C lower, preferably about 55 °C to about 75 °C lower. The Tgm of the softer outermost stage is preferably less than about 15 °C, preferably less than about 10 °C and preferably less than 0 °C, and higher than about -25 °C. The Tgc of the softer outermost stage is preferably less than about 15 °C, preferably less than about 10 °C and preferably less than about 0 °C, and higher than about -25 °C. The present invention can be defined by Tg(Fox) / Tgc or Tg(DSC) / Tgm, as long as Tg is used consistently.

[0178] The weight average molecular weight range of the entire outermost or softest stage, including the parts with and without CTA, is from about 30,000 Daltons to about 120,000 Daltons, and preferably from about 40,000 Daltons to about 110,000 Daltons, or preferably from about 50,000 Daltons to about 100,000 Daltons.

[0179] Within the softest or outermost stage, the weight average molecular weight of the part without CTA is from about 100,000 Daltons to about 150,000 Daltons, while the weight average molecular weight of the part with CTA is from about 8,000 Daltons to about 30,000 Daltons, preferably from about 10,000 Daltons to about 20,000 Daltons. The part with CTA accounts for about 10 wt% to about 60 wt% of the softest or outermost stage, preferably about 15 wt% to about 35 wt% of this stage, and more preferably about 20 wt% ± 1.5 wt% of this stage.

[0180] For the embodiment shown in Example 5, where the crosslinking monomer is distributed throughout the shell stage, the CTA part can account for about 15 wt% to about 90 wt% of the at least one stage, preferably about 15 wt% to about 70 wt%, about 15 wt% to about 35 wt% of the at least one stage, and more preferably about 20 wt% ± 1.5 wt%.

[0181] The weight average molecular weight range of the inner harder stage is from about 150,000 Daltons to about 260,000 Daltons, preferably from about 160,000 Daltons to about 250,000 Daltons, and more preferably from about 170,000 Daltons to about 240,000 Daltons.

[0182] The weight average molecular weight range of the multi-stage latex of aggregates including all stages is from about 100,000 Daltons to about 200,000 Daltons, preferably from about 110,000 Daltons to about 190,000 Daltons, and more preferably from about 120,000 Daltons to about 180,000 Daltons.

[0183] It is noted that the embodiments of Examples 3 and 4, Samples 7 and 8 - 15 of the present invention, and the embodiments of Examples 5 and 6 may have any number of stages from 1 (Example 3) to 2 (Example 4) or more, provided that the outermost stage has a crosslinkable monomer and a CTA incorporated into the monomer mixture of the outermost stage, as described herein. In other words, the embodiment may have any number of internal stages or cores.

[0184] In yet another embodiment, in Example 7, the internal stage or core is made of a softer monomer having a lower Tg, while the outer stage of the shell is made of a harder monomer having a higher Tg. The CTA is added to the last 30% - 50% of the outer stage / shell monomer mixture for the multi-stage polymer. MMA, 2-EHA, and styrene are the film-forming monomers used in combination to achieve the reported Tgc. Tables 11 and 12 below summarize the results of this embodiment.

[0185] Table 11. Additional Embodiment: Soft Core, Hard Shell

[0186]

[0187] DVB = divinylbenzene (0.8 wt%) used for crosslinking in addition to DAAM (4 wt%)

[0188] Additional compositional information for the experimental resins in Table 3 listed:

[0189] - MMA / 2EHA / styrene monomers used to achieve Tgc

[0190] - 4% DAAM

[0191] - 0.8% chain transfer agent in the last 30 - 50% of the particles

[0192]

[0193] Table 12. Additional Embodiment: Soft Core, Hard Shell

[0194]

[0195] The scrub resistance value represents the number of scrubbing cycles before the paint film is damaged, and a higher scrub resistance value indicates higher scrub resistance. The scrub resistance test results show the number of scrubbing cycles before damage, and the test is conducted according to Method B of ASTM D2486.

[0196] The stain removal tests (including stain types) conducted in these experiments are as described above and are similar to the MasterPaint Institute (MPI) COR-MTD-119 standard. The higher the value, the more difficult it is to remove the stain from the paint film. Lower values are preferred. The reported numbers are the sum of the color reading changes (δE values in CIE2000 units) of the paint film before staining and the paint film after applying various different stains and then cleaning. The stains include hot regular coffee, red wine, ketchup, yellow mustard, and graphite. The cleaning solution contains 0.5% nonylphenoxyethanol, 0.25% trisodium phosphate (TSP), and 99.25% deionized water. The cleaning solution is applied using a 430 g sponge / holder for 500 cycles. The color change caused by each stain is added and reported for each example. Alternatively, the less preferred and less stringent stain removal test MPI COR-MTD-083 can also be used.

[0197] The total number in the stain test is a combination of measured stains caused by various common substances. The lower the stain number, the fewer the measured stains and the better the stain resistance. The stain resistance values of the control and the samples of the present invention reported herein are both less than 6.0 and are within an acceptable range. A stain resistance value preferably less than 8.0, more preferably less than 7.0, and more preferably less than 6.0 is acceptable.

[0198] The presented stain tests also include TTP stains (which contain raw sienna, white petrolatum, and mineral spirits) and trash stains (which contain lanolin, petrolatum, carbon black, and mineral oil). Lower trash and TTP scores (e.g., less than about 1.5DE2000, or a ΔE value less than 1.25DE2000 units) are preferred.

[0199] In the LTC test, the paint is applied at various thicknesses, e.g., from 3 mils to 12 mils (1 mil = 1 / 1000 inch). The thickness at which the paint film cracks is the failure point. The LTC is the maximum thickness in mils at which a crack-free paint film is obtained. The higher the LTC value, the better the coalescence and the least amount of external plasticizer or coalescing agent required for film formation. LTC is used to determine the relative coalescence of a series of latex paints by observing how the samples dry at standard and low temperatures. Coalescence is the formation of a film of resin or polymer material when water evaporates from an emulsion or latex system, allowing adjacent latex particles to come into contact and fuse. Thus, this test evaluates paint film formation at standard and low temperatures. Cracking indicates poor film formation. Alternatively, the LTC test can be conducted according to ASTM D3793.

[0200] Although the exemplary embodiments of the present invention disclosed herein clearly achieve the above objects, it should be understood that those skilled in the art can design numerous modifications and other embodiments. Therefore, it should be understood that the appended claims are intended to cover all such modifications and embodiments that will fall within the spirit and scope of the present invention.

Claims

1. Copolymer latex particles comprising at least one stage, wherein the at least one stage is formed from a first monomer mixture of one or more film-forming monomers, wherein the at least one stage is copolymerized with at least one crosslinking monomer to form an inner portion of the at least one stage, and wherein an outer portion of the at least one stage is copolymerized in the presence of a chain transfer agent (CTA), wherein the at least one crosslinking monomer ranges from about 1 wt% to about 8 wt% of the entire polymer of the total monomers in the latex particles, wherein the CTA ranges from about 0.2 wt% to about 1 wt% of the entire polymer of the total monomers in the latex particles.

2. The copolymer latex particles of claim 1, wherein the at least one crosslinking monomer ranges from about 2 wt% to about 7 wt% of the entire polymer of the total monomers in the latex particles.

3. The copolymer latex particles of claim 2, wherein the at least one crosslinking monomer ranges from about 3 wt% to about 5 wt% of the entire polymer of the total monomers in the latex particles.

4. The copolymer latex particles of claim 1, wherein the CTA ranges from about 0.25 wt% to about 0.90 wt% of the entire polymer of the total monomers in the latex particles.

5. The copolymer latex particles of claim 4, wherein the CTA ranges from about 0.30 wt% to about 0.80 wt% of the entire polymer of the total monomers in the latex particles.

6. The copolymer latex particles of claim 1, wherein the inner portion and the outer portion do not overlap.

7. The copolymer latex particles of claim 6, wherein the inner portion and the outer portion are separated by an intermediate portion that does not contain the at least one crosslinking monomer and the CTA.

8. The copolymer latex particles of claim 1, wherein the outer portion accounts for about 10 wt% to about 60 wt% of the at least one stage.

9. The copolymer latex particles of claim 1, further comprising at least one inner stage formed from an inner monomer mixture of one or more film-forming monomers, the inner monomer mixture being different from the first monomer mixture, wherein the calculated glass transition temperature (Tgc) of the at least one inner stage ranges from about 25 °C to about 100 °C.

10. The copolymer latex particles of claim 9, wherein the inner monomer mixture further comprises the at least one crosslinking monomer.

11. The copolymer latex particles of claim 9, wherein the Tgc of the at least one inner stage is about 20 °C to about 90 °C higher than the Tgc of the at least one stage.

12. The copolymer latex particles of claim 9, further comprising an innermost stage located inside the at least one inner stage.

13. The copolymer latex particles of claim 9, further comprising a second inner stage located outside the at least one inner stage.

14. The copolymer latex according to claim 1, wherein the total weight average molecular weight of the at least one stage ranges from about 30,000 Daltons to about 120,000 Daltons, and preferably from about 40,000 Daltons to about 110,000 Daltons, or preferably from about 50,000 Daltons to about 100,000 Daltons.

15. The copolymer latex according to claim 9, wherein the total weight average molecular weight of the at least one stage ranges from about 30,000 Daltons to about 120,000 Daltons.

16. The copolymer latex according to claim 15, wherein the total weight average molecular weight of the at least one stage ranges from about 40,000 Daltons to about 110,000 Daltons.

17. The copolymer latex according to claim 16, wherein the total weight average molecular weight of the at least one stage ranges from about 50,000 Daltons to about 100,000 Daltons.

18. The copolymer latex according to claim 15, wherein the weight average molecular weight of the at least one internal stage ranges from about 150,000 Daltons to about 260,000 Daltons.

19. The copolymer latex according to claim 15, wherein the weight average molecular weight of the at least one stage of the aggregates and the at least one internal stage ranges from about 100,000 Daltons to about 200,000 Daltons.

20. Copolymer latex particles comprising at least a core stage and a shell stage, wherein the core stage is formed from a core monomer mixture of one or more film-forming monomers, wherein the calculated glass transition temperature (Tgc) of the core stage ranges from about 25 °C to about 100 °C, wherein the shell stage is formed from a shell monomer mixture of one or more film-forming monomers, the shell monomer mixture being different from the core monomer mixture, wherein the shell monomer mixture includes at least one crosslinking monomer and wherein the outer portion of the shell stage undergoes copolymerization in the presence of a chain transfer agent (CTA), wherein the at least one crosslinking monomer ranges from about 1 wt% to about 8 wt% of the entire polymer of the total monomers in the latex particles, wherein the CTA ranges from about 0.2 wt% to about 1 wt% of the entire polymer of the total monomers in the latex particles, and wherein the outer portion of the shell stage having CTA accounts for about 15 wt% to about 90 wt% of the outer stage, preferably about 15 wt% to about 70 wt%, about 15 wt% to about 35 wt% of the outer stage, more preferably about 20 wt% ± 1.5 wt%.

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