Expandable microspheres with excellent barrier properties

Abstract

To provide thermoplastic thermally expandable microspheres with excellent barrier properties and thermal stability, wherein the thermoplastic thermally expandable microspheres comprise a polymer shell and a propellant.SOLUTION: A polymer shell is formed from ethylenically unsaturated monomers and encapsulates a propellant, wherein the ethylenically unsaturated monomers comprise acrylonitrile in an amount from 45 to 80 weight %, methacrylonitrile in an amount of from 10 to 45 weight %, and methyl acrylate and / or methyl methacrylate in an amount of 5 to 35 weight %, each based on the total weight of ethylenically unsaturated monomers, and wherein the thermoplastic thermally expandable microspheres comprise the propellant in an amount of 5 to 17 weight %, based on the total weight of the thermoplastic thermally expandable microspheres. The disclosure further relates to a process for preparing such thermoplastic thermally expandable microspheres and an aqueous slurry comprising such thermoplastic thermally expandable microspheres.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to thermoplastic, thermally expandable microspheres and expandable microspheres made from thermoplastic, thermally expandable microspheres having excellent barrier properties and thermal stability. The present invention further relates to such thermoplastic, thermally expandable microspheres and methods for preparing aqueous slurries containing such thermoplastic, thermally expandable microspheres. [Background technology]

[0002] Thermally expandable microspheres are known in the art and are described, for example, in U.S. Patent No. 3,615,972, International Patent Publication No. 00 / 37547, and International Patent Publication No. 2007 / 091960. Several examples are marketed under the trademark name ExpanseL®. These can be expanded to form extremely low-weight and low-density fillers and can be found in applications such as foamed resins or low-density resins, paints and coatings, cements, inks, and crack fillers. Consumer goods that often contain expandable microspheres include lightweight shoe soles (e.g., for running shoes), textured coatings such as wallpaper, sun-reflective and heat-insulating coatings, food packaging sealants, wine corks, artificial leather, foamed materials for protective helmet liners, and automotive weatherstrips.

[0003] Thermally expandable polymer microspheres typically consist of a thermoplastic polymer shell, and the hollow core contains a propellant (or, in some cases, a blowing agent) that expands upon heating. Examples of propellants include low-boiling point hydrocarbons or halogenated hydrocarbons that are either condensable or liquid at room temperature and vaporize upon heating. To produce expandable microspheres, the expandable microspheres are heated so that the thermoplastic polymer shell softens, and the propellant vaporizes and expands, thereby causing the microspheres to expand. Typically, the diameter of the microspheres may increase between 1.5 and 8 times during expansion. Expandable microspheres are commercially available in various forms, for example, as dry free-flowing particles, as aqueous slurries, or as partially dehydrated wet cakes. Heating of expandable microspheres may be carried out using various techniques. One commonly used technique is the so-called wet expansion technique, in which the microspheres expand in water heated to its boiling point. If higher temperatures are required for expansion, expansion may be carried out using, for example, high-energy steam techniques.

[0004] Inflatable microspheres may be produced, for example, by polymerizing ethylenically unsaturated monomers in the presence of a propellant using a suspension polymerization method. Typical monomers include halogen-containing monomers such as acrylates, acrylonitrile, acrylamide, and vinylidene dichloride (VDC), as well as styrene-based monomers. Typically, mixtures of such monomers are used to produce inflatable microspheres having copolymer shells.

[0005] Expandable microspheres having a copolymer shell based on either VDC and acrylonitrile (AN), or AN and methacrylonitrile (MAN), are often used in the manufacture of wet-heat-expandable microspheres. These microspheres are distinguished in that the polymer shell has excellent barrier properties against encapsulated propellant, even in wet conditions, despite the possibility of water acting as a plasticizer within the microsphere shell. When the polymer shell is plasticized, the propellant is lost by diffusion, degrading the properties of the microsphere. This can already be observed during expansion in a watery environment or during storage of wet-expandable, heat-expandable microspheres.

[0006] Halogen-containing microspheres, particularly VDC-containing microspheres, have been found to possess excellent barrier properties due to the crystalline polyvinylidene chloride (PVDC) portion within the polymer shell, which also limits the plasticizing effect of water due to the hydrophobic nature of PVDC. Another advantage of these expandable VDC-containing microspheres is their expansion at relatively low temperatures due to their low glass transition temperature (Tg), i.e., the low softening point of the polymer shell, which allows these expandable VDC-containing microspheres to expand even in boiling water. However, the main drawback of these microspheres is the high halogen content due to PVDC, which makes the microspheres unsustainable. Furthermore, there are health, safety, and environmental (HSE) concerns regarding these VDC-containing microspheres due to the significant amount of residual VDC, as polymerizing VDC to PVDC is often difficult.

[0007] Attempts have been made to overcome these sustainability and HSE issues using halogen-free AN-co-MAN polymer shells. However, these microspheres typically require temperatures above 150°C for efficient expansion, and the inability to use boiling water presents other challenges. Instead, steam is usually used as the energy source during expansion. This increases the demands on the expansion apparatus, reducing the flexibility of using these microspheres and also creating HSE issues when working with high-energy steam. Furthermore, several drawbacks have been found, particularly regarding the storage stability of expandable microspheres made from such halogen-free expandable microspheres, such as those described in International Patent Publication 2007 / 091960 A1. In particular, the storage stability of such halogen-free expandable microspheres that are wet-expanded and then stored in a wet state has been found to be unsatisfactory. Storage stability is a highly commercial issue because, for logistical and economic reasons, customers tend to order larger batches of expandable microspheres, which are then used over specific periods, such as at least three weeks, preferably at least four weeks, and more preferably at least six weeks. The time required to transport the expandable microspheres from the manufacturing site to the customer must also be taken into account. Furthermore, there are many applications of expandable microspheres where they are not completely embedded in a robust matrix. In such applications, long-term storage stability of the expandable microspheres is crucial.

[0008] Wet storage of expandable microspheres is preferable because handling wet microspheres is far easier than handling completely dry microspheres, which are dust powders. However, as already mentioned above, water acts as a plasticizer for the polymer shell, thus impairing the barrier properties of the polymer shell and leading to reduced storage stability.

[0009] Therefore, there remains a need for thermoplastic thermal expandable microspheres that are essentially halogen-containing monomer-free, particularly VDC-free, and yet possess excellent barrier stability and very good storage stability after expansion. Furthermore, it is desirable that such thermoplastic thermal expandable microspheres can be expanded at lower temperatures, preferably by using aqueous wet expansion. In particular, it is desirable to provide such thermal expandable microspheres that are essentially halogen-containing monomer-free, particularly VDC-free, can be wet-expanded, and, after wet expansion, possess excellent barrier stability and very good storage stability even when stored in a wet state.

[0010] The present invention therefore aims to find such expandable polymer microspheres whose polymer shells are essentially free of halogen-containing monomers, particularly VDCs, and nevertheless possess excellent barrier stability and very good storage stability after expansion, and can preferably be expanded at lower temperatures, such as by using aqueous wet expansion, and also possess very good storage stability even when stored in a wet state after wet expansion. Surprisingly, it has been found that these objectives can be achieved by specific combinations of a specific range of amounts of monomers for the polymer shell of the expandable microspheres, further combined with a specific range of amounts of propellant contained in the expandable microspheres. [Overview of the project]

[0011] In a first aspect, the present invention is directed to thermoplastic thermally expandable microspheres comprising a polymer shell and a propellant, the polymer shell being made from ethylenically unsaturated monomers encapsulating the propellant, the ethylenically unsaturated monomers each comprising acrylonitrile in an amount of 45 to 80% by weight, methacrylonitrile in an amount of 10 to 45% by weight, and methyl acrylate and / or methyl methacrylate in an amount of 5 to 35% by weight, based on the total weight of the ethylenically unsaturated monomers, and the thermoplastic thermally expandable microspheres comprising the propellant in an amount of 5 to 17% by weight, based on the total weight of the thermoplastic thermally expandable microspheres.

[0012] In a second aspect, the present invention is further directed to a method for preparing thermoplastic thermally expandable microspheres comprising a polymer shell and a propellant, the method comprising the step of polymerizing ethylenically unsaturated monomers in the presence of a propellant in a polymerization mixture, the ethylenically unsaturated monomers each comprising acrylonitrile in an amount of 45 to 80% by weight, methacrylonitrile in an amount of 10 to 45% by weight, and methyl acrylate and / or methyl methacrylate in an amount of 5 to 35% by weight, based on the total weight of the ethylenically unsaturated monomers, the propellant comprising at least one of propane, isobutane, and n-butane, and being present in an amount of 5 to 30% by weight, based on the total weight of the ethylenically unsaturated monomers and the propellant.

[0013] In a third aspect, the present invention is further directed to an aqueous slurry comprising the above thermoplastic thermally expandable microspheres according to the first aspect, or an aqueous slurry obtained from the above method according to the second aspect.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 illustrates the difference in microspheres between single core (FIG. 1A) and multi-core (FIG. 1B). [Figure 2] FIG. 2 shows the storage stability of the expandable microspheres from the examples over a period of up to 42 days. [Modes for carrying out the invention]

[0015] In a first aspect, the present invention relates to a thermoplastic, thermally expandable microsphere comprising a polymer shell and a propellant, wherein the polymer shell is made from an ethylenically unsaturated monomer and contains a propellant, the ethylenically unsaturated monomer comprising acrylonitrile in an amount of 45-80% by weight, methacrylonitrile in an amount of 10-45% by weight, and methyl acrylate and / or methyl methacrylate in an amount of 5-35% by weight, based on the total weight of the ethylenically unsaturated monomer, and the thermoplastic, thermally expandable microsphere comprises the propellant in an amount of 5-17% by weight, based on the total weight of the thermoplastic, thermally expandable microsphere.

[0016] The ethylenically unsaturated monomers preferably contain acrylonitrile in an amount of 50-75% by weight, more preferably 53-70% by weight, and most preferably 55-65% by weight, for example, 57-61% by weight, based on the total weight of each ethylenically unsaturated monomer.

[0017] The ethylenically unsaturated monomers preferably contain methacrylonitrile in an amount of 15-40% by weight, more preferably 20-35% by weight, for example 21-33% by weight, and most preferably 22-30% by weight, for example 23-28% by weight, based on the total weight of each ethylenically unsaturated monomer.

[0018] The ethylenically unsaturated monomers preferably contain methyl acrylate and / or methyl methacrylate in amounts of 6 to 34% by weight, for example, 7 to 33% by weight, 8 to 32% by weight, or 10 to 30% by weight, preferably 12 to 25% by weight, and most preferably 13 to 23% by weight, for example, 14 to 20% by weight, based on the total weight of the ethylenically unsaturated monomers.

[0019] The total weight of the ethylenically unsaturated monomers in the polymer shell of the thermoplastic, thermally expandable microspheres is 100% by weight.

[0020] Accordingly, according to a preferred embodiment, the polymer shell of the thermoplastic thermally expandable microsphere of the present invention is made from ethylenically unsaturated monomers, each comprising 50-75% by weight of acrylonitrile, 15-40% by weight of methacrylonitrile, and 10-30% by weight of methyl acrylate and / or methyl methacrylate, based on the total weight of the ethylenically unsaturated monomers.

[0021] According to a more preferred embodiment, the polymer shell of the thermoplastic, thermally expandable microsphere of the present invention is made from ethylenically unsaturated monomers, each comprising 53-70% by weight of acrylonitrile, 20-35% by weight of methacrylonitrile, and 12-25% by weight of methyl acrylate and / or methyl methacrylate, based on the total weight of the ethylenically unsaturated monomers.

[0022] In a more preferred embodiment, the polymer shell of the thermoplastic, thermally expandable microsphere of the present invention is made from ethylenically unsaturated monomers, each comprising 55-65% by weight of acrylonitrile, 22-30% by weight of methacrylonitrile, and 13-23% by weight of methyl acrylate and / or methyl methacrylate, based on the total weight of the ethylenically unsaturated monomers.

[0023] According to a particularly preferred embodiment, the polymer shell of the thermoplastic, thermally expandable microsphere of the present invention is made from ethylenically unsaturated monomers, each comprising 57-61% by weight of acrylonitrile, 23-28% by weight of methacrylonitrile, and 14-20% by weight of methyl acrylate and / or methyl methacrylate, based on the total weight of the ethylenically unsaturated monomers.

[0024] Surprisingly, this particular combination of specific monomers and their range of amounts has been found to provide a polymer mixture for polymer shells that is suitable for providing desirable properties such as a low expansion temperature and, at the same time, excellent barrier properties and good long-term stability of expandable microspheres obtained from expandable microspheres having polymer shells containing this particular polymer mixture.

[0025] In a more preferred embodiment, the polymer shell of the thermoplastic, thermally expandable microsphere of the present invention is made from an ethylenically unsaturated monomer containing methyl acrylate and / or methyl methacrylate in the range specified above.

[0026] In a more preferred embodiment, the ethylenically unsaturated monomer is substantially free of VDC. If present, the amount of VDC is less than 5% by weight, most preferably less than 2% by weight, or even less than 1% by weight of the ethylenically unsaturated monomer, for example, less than 0.5% by weight, or even less than 0.1% by weight of the ethylenically unsaturated monomer. It is even more preferable that the ethylenically unsaturated monomer is substantially free of halogen-containing monomers. If present, the amount of halogen-containing monomer is preferably less than 5% by weight, most preferably less than 2% by weight, or even less than 1% by weight of the ethylenically unsaturated monomer, for example, less than 0.5% by weight, or even less than 0.1% by weight of the ethylenically unsaturated monomer. In some embodiments, the ethylenically unsaturated monomer is completely free of any VDC and / or halogen-containing monomers.

[0027] In a more preferred embodiment, the ethylenically unsaturated monomer contains, by weight, more methacrylonitrile than methyl acrylate and / or methyl methacrylate. Particularly preferred, the ethylenically unsaturated monomer contains, by weight, more methacrylonitrile than methyl acrylate. For example, the ethylenically unsaturated monomer contains, by weight, at least 1% by weight more, preferably at least 2% by weight more, more preferably at least 3% by weight more, and most preferably at least 5% by weight more, methacrylonitrile than methyl acrylate and / or methyl methacrylate. It has been found that such an excess weight of methacrylonitrile, compared to methyl acrylate, further improves the storage stability of the microspheres after expansion.

[0028] The ethylenically unsaturated monomer may also contain additional monomers in amounts up to 20% by weight, for example, 0 to 15% by weight, or 0.1 to 12% by weight, preferably up to 10% by weight, for example, 0.2 to 8% by weight, and more preferably up to 5% by weight, for example, up to 2% by weight, based on the total weight of each ethylenically unsaturated monomer. Suitable additional monomers include, for example, (meth)acrylates, vinyl esters, styrene (styrene and α-methylstyrene, etc.), nitrile-containing monomers, (meth)acrylamides, vinyl ethers (for example, methyl vinyl ether and ethyl vinyl ether, etc.), N-substituted maleimides, dienes (butadiene, isoprene, etc.), vinylpyridines, and any combination thereof.

[0029] In further embodiments, the ethylenically unsaturated monomer may include, as an additional monomer, a lactone according to formula (1): [ka] In the formula, each of R1, R2, R3, and R4 is selected separately from each other from the group consisting of H and alkyl groups. The alkyl group preferably contains 1 to 4 carbon atoms. Particularly preferred alkyl groups are methyl and ethyl. More preferably, each of R1, R2, R3, and R4 is selected separately from each other from the group consisting of H and CH3.

[0030] In a preferred embodiment, R1, R2, R3, and R4 in formula (1) are selected as follows: R1=H, R2=H, R3=CH3, R4=H (α-methylene-γ-valerolactone (MVL), identical to γ-methyl-α-methylene-γ-butyrolactone), R1=H, R2=H, R3=H, R4=H (α-methylene-γ-butyrolactone (MBL)), R1=CH3, R2=H, R3=H, R4=H (β-methyl-α-methylene-γ-butyrolactone (MMBL)), or R1=H, R2=H, R3=CH3, R4=CH3(γ,γ-dimethyl-α-methylene-γ-butyrolactone).

[0031] When the ethylenically unsaturated monomer contains a lactone according to formula (1), the lactone is most preferably either MVL or MBL.

[0032] In further embodiments, the ethylenically unsaturated monomer may include an itaconate dialkyl ester according to formula (2) as an additional monomer: [ka] In the formula, each of R1 and R2 is an alkyl group having 1 to 4 carbon atoms, separately from each other. Suitable alkyl groups include methyl, ethyl, n-propyl, isopropyl, and butyl groups. In particular, the itaconate dialkyl ester is preferably selected from the group consisting of dimethyl itaconate (DMI), diethyl itaconate (DEI), di(n-propyl) itaconate, diisopropyl itaconate, and dibutyl itaconate (DBI).

[0033] In a further embodiment, the ethylenically unsaturated monomer may contain the monomer of formula (3) as an additional monomer.

Chemical formula

[0034] In a more preferred embodiment, the ethylenically unsaturated monomer contains small amounts of one or more crosslinked polyfunctional monomers, for example, divinylbenzene, ethylene glycol di(meth)acrylate, di(ethylene glycol) di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,10-decanediol di(meth)acrylate One or more of the following can be mentioned: pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallylformal tri(meth)acrylate, allyl methacrylate, trimethylolpropane tri(meth)acrylate, tributanediol di(meth)acrylate, PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate, PEG#600 di(meth)acrylate, 3-acryloyloxyglycol monoacrylate, triacrylic formal, triallyl isocyanate, and triallyl isocynurate. Particularly preferred are crosslinked monomers that are at least trifunctional, examples of which include pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tolylformal tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, triacrylicformal, tolyl isocyanate, and tolyl isocyanurate. The amount of crosslinked functional monomer may be, for example, 0.1 to 6% by weight, or 0.1 to 1% by weight, or 1 to 3% by weight of the ethylenically unsaturated monomer, with 0.1 to 1% by weight being particularly preferred when one or more polyfunctional monomers are at least trifunctional, and 1 to 3% by weight being particularly preferred when one or more polyfunctional monomers are bifunctional.If the mixture contains ethylenically unsaturated monomers other than acrylonitrile, methacrylonitrile, methyl acrylate and / or methyl methacrylate, and mixtures thereof, and one or more crosslinked polyfunctional monomers, the amount is preferably 0 to 6% by weight, and most preferably 0 to 5% by weight. Examples of other types of monomers that may be included include nitrile-containing monomers (such as α-ethoxyacrylonitrile, fumaronitrile, or crotonitrile), vinylpyridine, vinyl esters (such as vinyl acetate), styrene (such as styrene, halogenated styrene, or α-methylstyrene), dienes (such as butadiene, isoprene, and chloroprene), unsaturated carboxylic acid compounds (such as acrylic acid, methacrylic acid, and their salts), or other unsaturated monomers (such as acrylamide, methacrylamide, or N-substituted maleimide).

[0035] In some embodiments, the ethylenically unsaturated monomer used to prepare the thermoplastic, thermally expandable microspheres of the present invention comprises less than 5% by weight, preferably less than 2% by weight, and more preferably less than 1% by weight of halogen-containing monomer, where the weight percentage is based on the total weight of the ethylenically unsaturated monomer. In some embodiments, the ethylenically unsaturated monomer is substantially free of halogen-containing monomer.

[0036] In a more preferred embodiment, the ethylenically unsaturated monomer substantially consists of acrylonitrile, methacrylonitrile, methyl acrylate and / or methyl methacrylate, and mixtures thereof, and optionally one or more crosslinked polyfunctional monomers, each monomer in the respective amount specified above. In a particular embodiment, the ethylenically unsaturated monomer substantially consists of acrylonitrile, methacrylonitrile, methyl acrylate and / or methyl methacrylate, and mixtures thereof, and one or more crosslinked polyfunctional monomers, each monomer in the respective amount specified above. In a further particular embodiment, the ethylenically unsaturated monomer substantially consists of acrylonitrile, methacrylonitrile, methyl acrylate, and one or more crosslinked polyfunctional monomers, each monomer in the respective amount specified above.

[0037] Thermoplastic, thermally expandable microspheres are hollow, with a shell containing a polymer made from the ethylenically unsaturated monomers described above, and a hollow center or core containing one or more propellants. In expandable microspheres, the density is typically 1 g / cm³. 3 It is less than 0.005 to 0.8 g / cm³, preferably 0.005 to 0.8 g / cm³. 3 , or 0.01~0.6 g / cm³ 3 This range is used. In preferred embodiments, the density of the expandable microspheres is 0.01 to 0.4 g / cm³. 3 It is within the range of higher densities, especially 1 g / cm³. 3 The densities mentioned above generally indicate that the microsphere sample is unsuitable for use.

[0038] The propellant is preferably a hydrocarbon or a mixture of hydrocarbons having a boiling point below the softening point of the thermoplastic polymer shell. The boiling point at atmospheric pressure is preferably in the range of -50 to 100°C, most preferably -20 to 50°C, and most preferably -20 to 30°C. The propellant may substantially consist of at least one of methane, ethane, propane, isobutane, n-butane, and neopentane, and may further contain one or more hydrocarbons in an amount of, for example, 0 to 50% by weight of the propellant. Examples of such hydrocarbons include n-pentane, isopentane, cyclopentane, hexane, isohexane, neo-hexane, cyclohexane, heptane, isoheptane, octane, and isooctane. In addition, other hydrocarbon types such as petroleum ether, or chlorinated hydrocarbons or fluorinated hydrocarbons such as methyl chloride, methylene chloride, dichloroethane, dichloroethylene, trichloroethane, trichloroethylene, trichlorofluoromethane, perfluorinated hydrocarbons, and fluorine-containing ethers may be used. In preferred embodiments, the propellant comprises at least one of propane, isobutane, and n-butane, either alone or in a mixture with one or more other hydrocarbons. More preferably, the propellant consists of at least one of propane, isobutane, and n-butane. Even more preferably, the propellant comprises isobutane. Most preferably, the propellant consists of isobutane. The amount of isobutane in the propellant is preferably 50 to 100% by weight, most preferably 75 to 100% by weight, for example, 75 to 99% by weight.

[0039] The thermoplastic thermal expandable microspheres contain propellant in an amount of 5 to 17% by weight, based on the total weight of the thermoplastic thermal expandable microspheres. Preferably, the thermoplastic thermal expandable microspheres contain propellant in an amount of 7 to 16% by weight, for example, 9 to 15% by weight, most preferably 10 to 14% by weight, based on the total weight of the thermoplastic thermal expandable microspheres.

[0040] Surprisingly, by using such a small amount of propellant compared to the total weight of thermoplastic thermally expandable microspheres in an unexpanded, expandable microsphere, and combining it with the specific combination of ethylenically unsaturated monomers in the amounts specified above for the microsphere shell, it is possible to obtain an expanded microsphere that, on the one hand, has excellent barrier properties and good storage stability, while at the same time remaining expandable to meet the commercial demands for expandable microspheres.

[0041] The determination of the weight of propellant in microspheres can be achieved by measuring the volatile content of the microspheres (i.e., the weight of the volatile substance, i.e., propellant, encapsulated in the microspheres). Therefore, as used herein in the context of microspheres, the terms “weight of propellant” or “weight percentage of propellant” are considered equivalent and interchangeable. Determining the volatile content of microspheres is well known to those skilled in the art, and in principle, any suitable method for determining the volatile content of microspheres can be used.

[0042] For example, the propellant content of microspheres can be determined using gas chromatography techniques. In these techniques, microspheres are placed in a sealed, airtight vial and heated to release the sealed propellant. The gaseous sample is then introduced into a gas chromatograph to quantify the content of specific hydrocarbons.

[0043] In this invention, the temperature at which thermally expandable microspheres begin to expand, T Start This is not particularly limited. For example, thermally expandable microspheres are T Start It may have. However, it is preferable that the microspheres can be expanded using an aqueous wetting method. Therefore, T Start The temperature is preferably 60-120°C, for example, 70-110°C or 80-105°C. The temperature at which expansion begins is TStart It is called, and the temperature at which it reaches maximum expansion is T max It is called T Start and T Max This may be determined using standard measurement techniques that are generally known to those skilled in the art. For example, T Start and T Max This can be determined by a heating experiment using a Mettler-Toledo thermomechanical analyzer, such as the Mettler-Toledo TMA / SDTA 841e, with a heating rate of 20°C / min and a load (net) of 0.06 N. In such a heating experiment, a sample with a known weight of thermally expandable microspheres is heated at a constant heating rate of 20°C / min under a load (net) of 0.06 N. As the thermally expandable microspheres begin to expand, the volume of the sample increases and the load moves upward. From these measurements, an expansion thermogram is obtained, where the vertical axis represents the height to which the load moves upward and the horizontal axis represents temperature. Start and T Max This can be determined from this inflation thermogram, for example, using STARe software from Mettler-Toledo.

[0044] In a more preferred embodiment, the thermoplastic thermally expandable microspheres have an average particle size of 5 to 30 μm, preferably 7 to 28 μm, more preferably 8 to 25 μm, and most preferably 10 to 20 μm. When using specific combinations of monomers and their amounts relative to the amounts of polymer shell and propellant, such very low average particle sizes have been found to be particularly suitable for obtaining expandable microspheres that expand easily, have excellent barrier properties, and have good storage stability after expansion.

[0045] In further embodiments, the polymer shell may include particles that improve the mechanical properties and gas barrier properties of the polymer shell, and thus act as polymer shell enhancers. Examples of such particles include talc, montmorillonite, nanocrystalline cellulose, and various types of clay such as bentonite.

[0046] Apart from the polymer shell and propellant, the microspheres may contain further substances that are usually added during their manufacture in amounts of 0 to 20% by weight, preferably 1 to 10% by weight. Examples of such substances include solid suspensions, such as one or more starches, crosslinked polymers, gum agars, derivatized celluloses such as methylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, and carboxymethylcellulose, silica, colloidal clays such as chalk and bentonite, and / or one or more salts, oxides, or hydroxides of metals such as Al, Ca, Mg, Ba, Fe, Zn, Ni, and Mn, such as calcium phosphate, calcium carbonate, magnesium hydroxide, barium sulfate, calcium oxalate, and one or more hydroxides of aluminum, iron, zinc, nickel, or manganese. If present, these solid suspensions are usually mainly located on the outer surface of the polymer shell. However, even if suspensions are added during the manufacture of microspheres, they may be washed away in a later stage and therefore substantially absent from the final product.

[0047] Numerous factors can result in high density. For example, high density may be due to insufficient microsphere yield, i.e., too low a proportion of microspheres in the polymer material, preventing the overall density from being reduced to an acceptable level. Another problem is insufficient expansion properties, which can result in many microspheres containing insufficient propellant to allow for proper expansion. This can be due to the polymer shell being too permeable to the propellant, or to the formation of so-called "multicore" microspheres, i.e., having multiple propellant-containing cores within the shell instead of a single propellant-containing core (e.g., like a microsphere, foam, or sponge). In such multicore microspheres, the propellant concentration is typically too low to adequately reduce the density. Another cause is polymer aggregation or aggregation, resulting in poorly manufactured microspheres and higher-density material. Microspheres with too high a proportion of aggregated material or that do not expand sufficiently can also lead to significant heterogeneity in the expansion properties of the resulting microsphere product. This is particularly undesirable for surface-sensitive applications such as coatings where a smooth finish is desired.

[0048] Exemplary cross-sections of single-core and multi-core microspheres are provided in Figures 1A and 1B, respectively, where polymer region 1 is represented by a network-like area and propellant-containing region 2 is represented by a blank area.

[0049] In a second aspect, the present invention provides a process for preparing thermoplastic, thermally expandable microspheres comprising a polymer shell and a propellant, the process comprising polymerizing an ethylenically unsaturated monomer in the presence of a propellant in a polymerization mixture, wherein the ethylenically unsaturated monomer comprises acrylonitrile in an amount of 45-80% by weight, methacrylonitrile in an amount of 10-45% by weight, and methyl acrylate and / or methyl methacrylate in an amount of 5-35% by weight, and the propellant comprises at least one of propane, isobutane, and n-butane, and is present in an amount of 5-30% by weight based on the total weight of the ethylenically unsaturated monomer and the propellant. The method according to the second aspect of the present invention can be used to prepare thermoplastic, thermally expandable microspheres according to the first aspect of the present invention.

[0050] The method involves polymerizing the ethylenically unsaturated monomer described above, preferably in an aqueous suspension, in the presence of the propellant described above, to obtain microspheres comprising a polymer shell that encapsulates the propellant. The above description of expandable microspheres with respect to the type and amount of monomer, as well as any further additives described above, such as crosslinking agents, also applies equally to the method of this second embodiment of the present invention.

[0051] In a method according to a second aspect of the present invention, the propellant comprises at least one of propane, isobutane, and n-butane in an amount of, for example, 50 to 100% by weight or 50 to 99% by weight of the total propellant amount. In some embodiments, the propellant consists of propane, isobutane, n-butane, and mixtures thereof. In preferred embodiments, the propellant comprises, for example, isobutane in an amount of 50 to 100% by weight or 50 to 99% by weight of the total propellant amount. In particularly preferred embodiments, the propellant consists of isobutane.

[0052] In the method according to a second aspect of the present invention, the propellant is present in the polymerization mixture in an amount of 5 to 30% by weight, for example, 7 to 27% by weight, or 10 to 25% by weight, or 12 to 22% by weight, preferably 15 to 20% by weight, based on the total weight of the ethylenically unsaturated monomer and the propellant.

[0053] In principle, any known general method for preparing expandable microspheres can be used. A preferred method is, for example, suspension polymerization. For example, the method may follow the method described in U.S. Patent No. 3,615,972 or International Patent Publication No. 2019 / 043235 A1.

[0054] In one embodiment of the present invention, microspheres are produced by a batch method, and polymerization may then be carried out in a reaction vessel as described below. 100 parts by weight of monomer phase (preferably comprising monomer and propellant in a ratio that determines the proportion of monomer in the polymer shell and the amount of propellant in the final product), preferably 0.1 to 5 parts by weight of one or more polymerization initiators, preferably 100 to 800 parts by weight of aqueous phase, and preferably 1 to 20 parts by weight of one or more solid colloidal suspensions are mixed and homogenized. The diameter of the droplets of the resulting monomer phase determines the diameter of the final expandable microspheres. The temperature is preferably maintained at 40 to 90°C, preferably 50 to 80°C, while the preferred pH depends on the suspension used. For example, a high pH, ​​preferably 5 to 12, most preferably 6 to 10, is preferred when the suspension agent is selected from one or more salts, oxides, or hydroxides of metals such as Ca, Mg, Ba, Zn, Ni, and Mn, for example, calcium phosphate, calcium carbonate, magnesium hydroxide, magnesium oxide, barium sulfate, calcium oxalate, and hydroxides of zinc, nickel, or manganese. A low pH, preferably 1 to 6, most preferably 3 to 5, is preferred when the suspension agent is selected from the group consisting of starch, methylcellulose, hydroxypropyl methylcellulose, hydroxypropyl methylcellulose, carboxymethylcellulose, gum agar, silica, colloidal clay, or oxides or hydroxides of aluminum or iron. Each of the above agents has a different optimal pH, for example, depending on solubility data.

[0055] The suspension helps stabilize droplets of ethylenically unsaturated monomers containing the organic phase in the aqueous phase, and in embodiments, assists in the formation of an emulsion of the organic phase (i.e., an oil-in-water emulsion) in the aqueous phase.

[0056] Stabilization of droplets or emulsion droplets is preferable for several reasons. Without stabilization, droplet aggregation may occur, involving droplets containing ethylenically unsaturated monomers and propellants. Aggregation can have adverse effects, such as uneven droplet size and insufficient microsphere yield, and can increase microsphere aggregation.

[0057] The suspension agent is typically present in the aqueous phase in an amount of 0 to 20% by weight, for example, 0.01 to 20% by weight, 0.05 to 10% by weight, or 0.1 to 5% by weight. In further embodiments, the suspension agent is present in the aqueous phase in an amount of 0.1 to 1% by weight.

[0058] The choice of suspension agent is not particularly limited, but it may be selected from inorganic or organic suspension agents.

[0059] Examples of inorganic materials that can act as suspension agents include silica, particularly colloidal silica, which can be used in its unmodified "naked" form or, optionally, surface-modified to adjust its hydrophobic / hydrophilic properties, for example, using organosilane-modified silica or colloidal silica.

[0060] In this embodiment, the "organic" group in organosilane is C 1~20 Alkyl, C 1~20 Alkenil, C 5~6 C having an aryl group and one or more heteroatoms (e.g., 1 to 3) selected from O, S, and N. 5-6 A heteroaryl group may be selected. Each of these groups may be optionally a halide, hydroxyl, epoxy, thiol, amino, or C group. 1~20 Alkylamino, di-C 1~20 Alkylamino, hydroxyamino, hydroxy-C 1~20 Alkylamino, (Hydroxy-C 1~20 Alkyl)(C 1~20 Alkyl)amino, di(hydroxy-C) 1~20 Alkyl)amino C 1-20 Alkoxy, C 1~20 Amide, C 1~20 Ureid, C1~20 Mercapto, C 3~20 Epoxyalkoxy, C 1~20 The aliphatic group may be substituted with one or more groups selected from alkyl acrylates, ethylene glycol or its oligomer having 1 to 20 ethylene glycol groups, and propylene glycol or its oligomer having 1 to 20 propylene glycol groups. Any aliphatic group may be linear, branched, or cyclic.

[0061] Organosilane-modified silica or colloidal silica is silica (or colloidal silica) typically, R n SiX 4-n It can be produced by reacting with an organosilane compound having the following formula, where R is one of the organic groups identified above, and X is a halide, hydroxyl, or C 1~6 It is an alkoxy, where n is an integer in the range of 1 to 3, typically 1 or 2.

[0062] Suitable silane compounds include tris-(trimethoxy)silane, octyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, gamma-mercaptopropyltrimethoxysilane, beta-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, epoxy groups (epoxysilanes), glycidoxy groups and / or glycidoxypropyl groups, such as gamma-glycidoxypropyltrimethoxysilane, gamma-glycidoxypropylmethyldiethoxysilane, (3-glycidoxypropyl)trimethoxysilane, (3-glycidoxypropyl)hexyltrimethoxysilane, beta-(3,4-epoxycyclohexyl)-ethyltriethoxysilane, and vinyl groups containing glycidoxypropyl groups, such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris-(2-methoxyethoxy)silane, vinylmethyldiethoxysilane, etc. Examples include silanes containing vinyl groups, such as toxysilane and vinyltriisopropoxysilane; gamma-methacrylateoxypropyltrimethoxysilane, gamma-methacrylateoxypropyltriisopropoxysilane, gamma-methacrylateoxypropyltriethoxysilane, octyltrimethyloxysilane, ethyltrimethoxysilane, propyltriethoxysilane, phenyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, dimethyldiethoxysilane, 3-chloropropyltriethoxysilane, 3-methacrylateoxypropyltrimethoxysilane, i-butyltriethoxysilane, trimethylethoxysilane, phenyldimethylethoxysilane, hexamethyldisilozane, trimethylsilyl chloride, vinyltriethoxysilane, hexamethyldisilizane, and mixtures thereof. U.S. Patent No. 4,927,749 discloses more suitable silanes that may be used.

[0063] Examples of silica that can be used include silica sold under the trademark names Levasil®, Bindzil®, and Ludox®, which are related to colloidal silica. As for the solid form of silica, fumed silica is an option, and precipitated silica may also be used, which can be dispersed in water to form a fine suspension. Sources of fumed silica include silica sold under the trademark names Cab-o-Sil® and Aerosil®.

[0064] Other inorganic suspension agents include colloidal clays (e.g., chalk and bentonite), and salts, oxides, and hydroxides of Al, Ca, Mg, Ba, Fe, Zn, Ti, Ni, and Mn (e.g., calcium phosphate, calcium carbonate, magnesium hydroxide, barium sulfate, calcium oxalate, titanium dioxide, and hydroxides of aluminum, iron, zinc, nickel, or manganese).

[0065] When using solid inorganic suspensions, they can produce so-called "Pickering" emulsions, where the solid inorganic particles are at the interface between the aqueous and organic phases. One or more suspensions may be used. A mixture of organic and inorganic suspensions may also be used.

[0066] To enhance the effect of the suspension agent, one or more promoters in small amounts, for example, 0.001 to 1% by weight, may be added. Typically, such promoters are organic substances and may be selected from one or more of the following: water-soluble sulfonated polystyrene, alginates, carboxymethylcellulose, tetramethylammonium hydroxide or tetramethylammonium chloride, or water-soluble composite resinous amine condensates (e.g., water-soluble condensates of diethanolamine and adipic acid, water-soluble condensates of ethylene oxide, etc.), urea and formaldehyde, polyethyleneimine, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylamine, amphoteric substances such as proteinaceous substances (e.g., gelatin, glue, casein, albumin, glutin, and similar substances), nonionic substances such as methoxycellulose, ionic substances usually classified as suspension agents (e.g., soaps, alkyl sulfates, and sulfonates, etc.), and long-chain quaternary ammonium compounds.

[0067] Conventional radical polymerization initiators are selected from one or more organic peroxides such as dialkyl peroxides, diacyl peroxides, peroxide esters, dicarbonate peroxides, or azo compounds. Suitable initiators include dicetyl peroxydicarbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, dioctanyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, didecanoyl peroxide, tert-butyl peracetate, tert-butyl perlaurate, tert-butyl perbenzoate, tert-butyl hydroperoxide, cumene hydroperoxide, cumene ethyl peroxide, diisopropyl hydroxydicarboxylate, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitride), and 2,2' <1> -Azobis(2-methylpropionate, 2,2') <1> Examples include azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and similar compounds. Polymerization can also be initiated using radiation, such as high-energy ionization radiation.

[0068] Where appropriate, the microspheres may be treated at any stage to reduce the amount of residual unreacted monomer, for example, by any of the procedures described in International Patent Publication No. 2004 / 072160 or U.S. Patent No. 4287308.

[0069] In a further embodiment, the present invention also relates to thermoplastic, thermally expandable microspheres obtained by the method according to the second embodiment of the present invention described above.

[0070] In further embodiments, the present invention also relates to an aqueous slurry obtained by the method according to the first embodiment of the present invention described above, or the second embodiment of the present invention described above, which preferably contains expandable thermoplastic microspheres in an amount of 5 to 55% by weight, most preferably 20 to 55% by weight, based on the total weight of the slurry. Such slurries are useful for a variety of applications of expandable microspheres, including papermaking. The slurry also preferably contains at least one thickener and is preferably compatible with papermaking. Examples of such thickeners include copolymers made from monomers containing starch, gum, cellulose, chitin, chitosan, glycan, galactan, pectin, mannan, dextrin, acrylic acid or its salts (preferably up to 50 mol%, most preferably up to 20 mol%, of acrylic acid or its salts), homopolymers and copolymers made from monomers containing acrylic acid esters or amides, homopolymers and copolymers made from monomers containing methacrylic acid, its esters or amides, rubber latex and copolymers, polyvinyl esters and copolymers (e.g., including ethylene), polyvinyl alcohol, polyamines, polyethyleneimines, polyethylene / polypropylene oxides, polyurethanes, and precondensates of aminoplasts and phenoplasts, such as urea / formaldehyde, urea / melamine / formaldehyde, or phenol / formaldehyde, and polyamidoamine epichlorohydrin resins, which are at least partially water-soluble polymers. Suitable gums include guar gum, tamarind gum, locust bean gum, tara gum, karaya, okra, acacia, xanthan gum, and mixtures thereof, with guar gum being particularly preferred. Suitable celluloses include derivatives, such as optionally chemically modified CMC (carboxymethylcellulose), and cellulose ethers such as EHEC (ethylhydroxyethylcellulose) and HEC (hydroxyethylcellulose), and mixtures thereof.Examples of chemically modified cellulose derivatives include those modified with various functional groups such as quaternary amines, other amines, sulfates, sulfonates, phosphates, phosphonates, polyethylene oxide, and polypropylene oxide.

[0071] Polymers that are at least partially water-soluble may be linear, branched, or crosslinked. The average molecular weight can vary within a wide range depending on the type of polymer. In most cases, a preferred average molecular weight is at least 500, more preferably at least 2000, and most preferably at least 5000. The upper limit is not significant, and in most cases, the average molecular weight is preferably up to 50,000,000, more preferably up to 10,000,000, and most preferably up to 1,000,000.

[0072] Particularly preferred polymers include starch, CMC, EHEC, guar gum, polyamidoamine epichlorohydrin resin, copolymers of acrylic acid with other monomers (e.g., copolymers with acrylamide), and homopolymers or copolymers of polyacrylamide, polyamines, polyvinyl alcohol, and polyethylene / polypropylene oxide.

[0073] It is preferable that one or more at least partially water-soluble polymers effective as thickeners be present in an amount that stabilizes the slurry against substantial deposition or suspension of microspheres to the extent that they cannot be redispersed. Often, this can be achieved by adding enough polymer to obtain a preferred viscosity of slurry at 25°C of about 150 to about 1000 mPas, most preferably about 200 to about 600 mPas (referring to measurements using an Anton Paar DV-1P viscometer with spindle L3). The amount required to stabilize the slurry depends on the polymer and other factors such as pH. Often, the preferred content of at least partially water-soluble polymers in the slurry is about 0.1 to about 15% by weight, most preferably about 0.1 to about 10% by weight, and most preferably about 0.5 to about 10% by weight. [Examples]

[0074] The following examples are intended to illustrate the present invention.

[0075] The propellant content in microspheres was determined using headspace gas chromatography (HS-GC) with an Agilent 7697A static headspace connected to an Agilent 7890B gas chromatograph. 8–10 mg of sample was placed in a sealed, airtight vial and heated to 170°C. The gas phase sample was introduced into a gas chromatograph equipped with a CP-Sil 19cb column (30 m length, 0.32 mm inner diameter, 1 μm thickness, Agilent) using an airtight syringe. Evaluation was performed using Chromeleon software from Thermo, with isooctane used as a reference.

[0076] Expansion characteristics were evaluated using a Mettler TMA / SDTA 841e thermomechanical analyzer interfaced to a PC running STARe software. Samples were prepared from 0.5 mg (+ / -0.02 mg) of thermally expandable microspheres contained in an aluminum oxide crucible with a diameter of 6.8 mm and a depth of 4.0 mm. The crucible was sealed with a 6.1 mm diameter aluminum oxide lid. The sample temperature was increased to 20°C / min using a TMA expansion probe while applying a 0.06 N net load with the probe. -1 The temperature was increased from approximately 30°C to 240°C at the heating rate. The vertical displacement of the probe was measured to analyze the expansion characteristics. The initial temperature of expansion (T start ): The temperature (°C) at which the probe displacement began. Maximum expansion temperature (T max ) is the temperature (°C) when the probe displacement reaches its maximum. The TMA density is calculated by multiplying the sample weight (d) by the volume increase (dm) of the sample when the probe displacement reaches its maximum value. 3 This is the result of dividing by ).

[0077] Particle size was determined by laser light scattering on a wet sample using a Malvern Mastersizer Hydro 2000 SM instrument. The median particle size is presented as the volume median diameter d(0.5).

[0078] [Example 1] Microspheres were prepared using the following procedure. A reaction mixture containing Mg(OH)2-stabilized organic droplets in water was prepared by mixing the phases and vigorously stirring until a suitable droplet size was achieved. The aqueous dispersion contained 1.8 parts by weight of Mg(OH)2, 0.02 parts by weight of sodium 2-ethylhexyl sulfate, and 283 parts by weight of water. The organic droplets contained 2.0 parts by weight of dilauryl peroxide, 22.0 parts by weight of isobutane, 55.0 parts by weight of acrylonitrile, 30.0 parts by weight of methacrylonitrile, 15.0 parts by weight of methyl acrylate, and 0.3 parts by weight of trimethylolpropane trimethacrylate. Polymerization was carried out in a sealed reactor under stirring at 62°C. After cooling to room temperature, samples of the resulting microsphere slurry were removed, filtered, dehydrated, and dried before analysis by TMA and headspace gas chromatography. The microspheres contained approximately 14% by weight of isobutane, based on their total weight, and had an average particle size of approximately 38 μm. The TMA results can be found in Table 1 below.

[0079] [Example 2] 329 parts by weight of water, 22.7 parts by weight of 50% by weight of surface-modified colloidal silica (Bindzil, 80m 2A dispersion containing 32 nm particles surface-modified with 50% propylsilyl / 50% glycerolpropylsilyl was prepared and maintained at a pH of approximately 4.5. The aqueous dispersion was mixed with an organic phase containing 1.6 parts by weight of dilauryl peroxide, 38.0 parts by weight of isobutane, 55.0 parts by weight of acrylonitrile, 30.0 parts by weight of methacrylonitrile, 15.0 parts by weight of methyl acrylate, and 0.3 parts by weight of trimethylolpropane trimethacrylate. Polymerization was carried out in a sealed reactor under stirring at 62°C. After cooling to room temperature, samples of the resulting microsphere slurry were removed, filtered, dehydrated, and dried before analysis by TMA and headspace gas chromatography. The microspheres contained approximately 20% by weight of isobutane based on the total weight of microspheres and isobutane, and had an average particle size of approximately 14 μm. The TMA results can be found in Table 1 below.

[0080] [Examples 3-7] Further microspheres were prepared in additional polymerization examples carried out in the same manner as in Example 2. However, in these further examples, monomers and propellants were used in the amounts specified in Table 1 below. In Example 7, 0.5 parts by weight of acetylperoxydicarbonate was used as an initiator. The analytical results can be found in Table 1.

[0081] [Table 1]

[0082] [Storage stability test] Storage stability tests were conducted as follows. Expandable microspheres were obtained from the expandable microsphere slurries obtained in Examples 1-7 by expansion in boiling water, for example, as described in International Patent Publication No. 2014 / 198532A1. The expandable microspheres were stored in a sealed container at 40°C for at least 28 days. The initial amount of propellant contained in each expandable microsphere was determined after drying and set to 100%. Furthermore, the amount of propellant contained in each expandable microsphere was determined after 1, 3, 7, 14, 28, and 42 days, and the relative percentage of propellant content was calculated (in %) compared to the initial amount of propellant. The results are shown in Table 2 below. For further comparison, two commercially available microspheres were used: the VDC-containing benchmark expandable microsphere Expansionl 461 WE 40 (Comparative Example 8), and the commercially available unexpanded, VDC-free microsphere Expansionl 051 DU 40 (Comparative Example 9), which were investigated after wetting and expanding using the same procedure as in Examples 1-7.

[0083] [Table 2]

[0084] The results in Table 2 are shown in Figure 2. Figure 2 shows that the expandable microspheres according to the present invention (i.e., microspheres from Examples 1, 3, 4, and 6) have improved storage stability characteristics, and even when stored as wet microspheres, they have storage stability characteristics that are close to or better than those of other halogen-free expandable microspheres (i.e., microspheres from Comparative Examples 2, 5, 7, and 9), especially after storage for at least 28 days, and even compared to commercially available VDC-containing expandable microspheres (i.e., microspheres from Comparative Example 8). The present invention includes the following embodiments. Section 1. A thermoplastic, thermally expandable microsphere comprising a polymer shell and a propellant, wherein the polymer shell is made from an ethylenically unsaturated monomer and contains the propellant, the ethylenically unsaturated monomer comprising acrylonitrile in an amount of 45-80% by weight, methacrylonitrile in an amount of 10-45% by weight, and methyl acrylate and / or methyl methacrylate in an amount of 5-35% by weight, each based on the total weight of the ethylenically unsaturated monomer, and the thermoplastic, thermally expandable microsphere comprises the propellant in an amount of 5-17% by weight, based on the total weight of the thermoplastic, thermally expandable microsphere. Section 2. The thermoplastic, thermally expandable microsphere according to item 1, wherein the ethylenically unsaturated monomer comprises acrylonitrile in an amount of 50 to 75% by weight, preferably 53 to 70% by weight, most preferably 55 to 65% by weight, based on the total weight of each of the ethylenically unsaturated monomers. Section 3. The thermoplastic, thermally expandable microsphere according to item 1 or 2, wherein the ethylenically unsaturated monomer comprises methacrylonitrile in an amount of 15 to 40% by weight, preferably 20 to 35% by weight, most preferably 22 to 30% by weight, based on the total weight of the ethylenically unsaturated monomer. Section 4. The thermoplastic, thermally expandable microsphere according to any one of claims 1 to 3, wherein the ethylenically unsaturated monomer comprises methyl acrylate and / or methyl methacrylate in an amount of 6 to 34% by weight, for example, 7 to 33% by weight, 8 to 32% by weight, or 10 to 30% by weight, preferably 12 to 25% by weight, and most preferably 13 to 23% by weight, based on the total weight of the ethylenically unsaturated monomer. Section 5. The thermoplastic, thermally expandable microsphere according to any one of claims 1 to 4, wherein the ethylenically unsaturated monomer comprises, by weight, more methacrylonitrile than methyl acrylate and / or methyl methacrylate, preferably at least 1% by weight more methacrylonitrile than methyl acrylate and / or methyl methacrylate, and more preferably at least 1% by weight more methacrylonitrile than methyl acrylate and / or methyl methacrylate. Section 6. The thermoplastic thermal expandable microsphere according to any one of claims 1 to 5, wherein the thermoplastic thermal expandable microsphere contains the propellant in an amount of 7 to 16% by weight, preferably 9 to 15% by weight, most preferably 10 to 14% by weight, based on the total weight of the thermoplastic thermal expandable microsphere. Section 7. The thermoplastic, thermally expandable microsphere according to any one of claims 1 to 6, wherein the ethylenically unsaturated monomer comprises methyl acrylate. Section 8. The thermoplastic, thermally expandable microsphere according to any one of claims 1 to 7, wherein the ethylenically unsaturated monomer comprises a halogen-containing monomer in an amount of less than 5% by weight, preferably less than 2% by weight, and more preferably less than 1% by weight. Section 9. The thermoplastic, thermally expandable microsphere according to any one of claims 1 to 8, wherein the propellant comprises at least one of propane, isobutane, and n-butane, preferably isobutane. Section 10. A thermoplastic, thermally expandable microsphere according to any one of claims 1 to 9, wherein the propellant comprises 50 to 100% by weight of isobutane. Section 11. Thermoplastic, thermally expandable microspheres according to any one of claims 1 to 10, having an average particle diameter of 5 to 30 μm, preferably 7 to 28 μm, more preferably 8 to 25 μm, and most preferably 10 to 20 μm. Section 12. The thermoplastic, thermally expandable microsphere according to any one of claims 1 to 11, wherein the ethylenically unsaturated monomer further comprises 0.1 to 6.0% by weight of one or more crosslinking agents, preferably 0.2 to 1.0% by weight, based on the total weight of the ethylenically unsaturated monomer. Section 13. A process for preparing thermoplastic, thermally expandable microspheres comprising a polymer shell and a propellant, comprising the step of polymerizing an ethylenically unsaturated monomer in the presence of a propellant in a polymerization mixture, wherein the ethylenically unsaturated monomer comprises acrylonitrile in an amount of 45 to 80% by weight, methacrylonitrile in an amount of 10 to 45% by weight, and methyl acrylate and / or methyl methacrylate in an amount of 5 to 35% by weight, each based on the total weight of the ethylenically unsaturated monomer, and the propellant comprises at least one of propane, isobutane, and n-butane, and is present in an amount of 5 to 30% by weight based on the total weight of the ethylenically unsaturated monomer and the propellant. Section 14. The process according to item 13, wherein the polymerization mixture comprises inorganic particles, preferably magnesium hydroxide or colloidal silica, more preferably colloidal silica. Section 15. An aqueous slurry comprising the thermoplastic, thermally expandable microspheres obtained from any of the methods described in sections 1 to 12, or from any of the methods described in sections 13 and 14.

Claims

1. A thermoplastic, thermally expandable microsphere comprising a polymer shell and a propellant, wherein the polymer shell is made from an ethylenically unsaturated monomer and contains the propellant, the ethylenically unsaturated monomer comprising acrylonitrile in an amount of 45 to 80% by weight, methacrylonitrile in an amount of 10 to 45% by weight, and methyl acrylate in an amount of 13 to 23% by weight, each based on the total weight of the ethylenically unsaturated monomer, and the thermoplastic, thermally expandable microsphere comprises the propellant in an amount of 5 to 17% by weight, based on the total weight of the thermoplastic, thermally expandable microsphere.

2. The thermoplastic, thermally expandable microsphere according to claim 1, wherein the ethylenically unsaturated monomer comprises acrylonitrile in an amount of 50 to 75% by weight, based on the total weight of the ethylenically unsaturated monomer.

3. The thermoplastic, thermally expandable microsphere according to claim 1, wherein the ethylenically unsaturated monomer comprises methacrylonitrile in an amount of 15 to 40% by weight, based on the total weight of the ethylenically unsaturated monomer.

4. The thermoplastic, thermally expandable microsphere according to claim 1, wherein the ethylenically unsaturated monomer contains, by weight, more methacrylonitrile than methyl acrylate.

5. The thermoplastic thermal expandable microsphere according to claim 1, wherein the thermoplastic thermal expandable microsphere contains the propellant in an amount of 7 to 16% by weight, based on the total weight of the thermoplastic thermal expandable microsphere.

6. The thermoplastic, thermally expandable microsphere according to claim 1, wherein the ethylenically unsaturated monomer comprises less than 5% by weight of a halogen-containing monomer.

7. The thermoplastic, thermally expandable microsphere according to claim 1, wherein the propellant comprises at least one of propane, isobutane, and n-butane.

8. The thermoplastic, thermally expandable microsphere according to claim 1, wherein the propellant comprises 50 to 100% by weight of isobutane.

9. A thermoplastic, thermally expandable microsphere according to claim 1, having an average particle diameter of 5 to 30 μm.

10. The thermoplastic, thermally expandable microsphere according to claim 1, wherein the ethylenically unsaturated monomer further comprises one or more crosslinking agents in an amount of 0.1 to 6.0% by weight, based on the total weight of each of the ethylenically unsaturated monomers.

11. An aqueous slurry comprising thermoplastic, thermally expandable microspheres according to any one of claims 1 to 10.

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