Method for producing acrylic resin

Abstract

To provide a method for producing an acrylic resin by suspension polymerization, by which solid-liquid separation after polymerization can efficiently be carried out while using a modified cellulose and a slightly water-soluble inorganic salt in combination as a dispersion stabilizer, and the acrylic resin having good physical properties can be obtained.SOLUTION: A method for producing an acrylic resin, comprising a step of performing suspension polymerization in the presence of a modified cellulose and a poorly water-soluble inorganic salt as dispersion stabilizers to obtain a suspension containing an acrylic resin, a step of adding a cellulolytic enzyme to the suspension to degrade the modified cellulose, a step of adding an acid to the suspension after degradation of the modified cellulose to dissolve the poorly water-soluble inorganic salt, and a step of recovering the acrylic resin from the suspension after dissolution of the poorly water-soluble inorganic salt.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an acrylic resin. [Background technology]

[0002] Acrylic resins are widely used as glass substitutes, or as the main resin raw material for paints and adhesives, and are also known for use as hot melt adhesives.

[0003] One known method for producing acrylic resins is radical polymerization, which forms resin particles with diameters ranging from several tens to several thousand microns. These particles are washed and dried to obtain spherical powder.

[0004] Suspension polymerization is carried out by adding a dispersion stabilizer to the polymerization system to maintain a stable dispersion of the monomer or polymer droplets. Known examples of such dispersion stabilizers include modified cellulose such as methyl cellulose, polyvinyl alcohol, polyacrylic acid or its salts, gelatin, polyethylene glycol, polyvinylpyrrolidone, polyacrylamide, and poorly water-soluble inorganic salts such as tertiary phosphates (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-185645 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-198938 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when modified cellulose is used as a dispersion stabilizer in the suspension polymerization of acrylic resins, a large amount of nano-sized fine particles is generated, which may make it difficult to recover the resin. On the other hand, when a poorly water-soluble inorganic salt is used as a dispersion stabilizer, it becomes easier to adjust the particle size, but depending on the molecular weight of the resin, the dispersion stability of the polymerization system may decrease, making it difficult for the polymerization reaction to proceed. In response to these problems, the present inventors have found that by using a modified cellulose and a poorly water-soluble inorganic salt in combination as a dispersion stabilizer in the suspension polymerization of an acrylic resin, it becomes easier to adjust the particle size, the dispersion stability of the polymerization system is improved, and an acrylic resin powder with excellent physical properties can be efficiently produced.

[0007] However, it was found that using these two types of dispersion stabilizers in combination increases the viscosity of the suspension, which can hinder the separation of the acrylic resin from water after polymerization, making it difficult to carry out solid-liquid separation efficiently.

[0008] It has also been found that even if solid-liquid separation can be carried out, when the resulting acrylic resin powder is used as a hot melt powder, the adhesiveness may be reduced.

[0009] In view of the above-described current situation, an object of the present invention is to provide a production method for producing an acrylic resin by suspension polymerization, which can efficiently carry out solid-liquid separation after polymerization while using modified cellulose and a poorly water-soluble inorganic salt as dispersion stabilizers, and can also provide an acrylic resin with good physical properties. [Means for solving the problem]

[0010] The present inventors conducted extensive research to solve the above-mentioned problems, and found that the problems can be solved by carrying out suspension polymerization using a combination of modified cellulose and poorly water-soluble inorganic particles as a dispersion stabilizer, then adding a cellulose-degrading enzyme to the suspension to decompose the modified cellulose, then adding an acid to dissolve the poorly water-soluble inorganic salt, and then recovering the acrylic resin, thereby completing the present invention.

[0011] That is, the present invention provides a method for producing a suspension containing an acrylic resin by carrying out suspension polymerization in the presence of modified cellulose and a poorly water-soluble inorganic salt as dispersion stabilizers; adding a cellulolytic enzyme to the suspension to decompose the modified cellulose; adding an acid to the suspension after decomposition of the modified cellulose to dissolve the poorly water-soluble inorganic salt; and and recovering the acrylic resin from the suspension after dissolving the poorly water-soluble inorganic salt. [Effects of the Invention]

[0012] According to the present invention, there can be provided a production method which, when producing an acrylic resin by suspension polymerization, can efficiently carry out solid-liquid separation after polymerization while using modified cellulose and a poorly water-soluble inorganic salt in combination as dispersion stabilizers, and can also provide an acrylic resin having good physical properties.

[0013] According to the present invention, a powdered acrylic resin suitable for use as a hot-melt powder can be obtained. The acrylic resin exhibits excellent adhesion as a hot-melt powder. In particular, the acrylic resin is suitable for use as a hot-melt powder for forming a binder resin layer that adheres ink to an object. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described in detail. The present embodiment relates to a method for producing an acrylic resin, in which an acrylic resin is synthesized by suspension polymerization and then the acrylic resin is recovered from the suspension.

[0015] In the present disclosure, an acrylic resin refers to a thermoplastic resin containing a (meth)acrylic monomer as a constituent monomer. However, the acrylic resin may further contain a monomer other than the (meth)acrylic monomer as a constituent monomer. The term "(meth)acrylic" is used to refer collectively to acrylic and methacrylic.

[0016] The content of the (meth)acrylic monomer is preferably 50% by weight or more and 100% by weight or less of the total amount of monomers constituting the acrylic resin, and the lower limit may be 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 99% by weight or more.

[0017] The (meth)acrylic monomer is not particularly limited, and examples thereof include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and behenyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as phenoxyethyl (meth)acrylate and benzyl (meth)acrylate; hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; glycidyl (meth)acrylates such as glycidyl (meth)acrylate and glycidyl alkyl (meth)acrylate; alkoxy(meth)alkyl acrylates; (meth)acrylonitrile, substituted (meth)acrylonitrile, (meth)acrylamide, and 2-(dimethylamino)ethyl (meth)acrylate. The (meth)acrylic monomer may be used alone or in combination of two or more kinds.

[0018] Among these, it is preferable to use a (meth)acrylic acid alkyl ester, and a methacrylic acid alkyl ester is particularly preferable. In this case, the methacrylic acid alkyl ester may be used alone, or the methacrylic acid alkyl ester may be used in combination with an acrylic acid alkyl ester and / or an aromatic vinyl compound described below.

[0019] In the present disclosure, suspension polymerization can be suitably carried out using a (meth)acrylic acid alkyl ester having an alkyl group with 4 to 12 carbon atoms. In particular, it is preferable to use a methacrylic acid alkyl ester having at least an alkyl group with 4 to 12 carbon atoms. The content of such an alkyl ester is preferably 50% by weight or more, and more preferably 60% by weight or more, of the total amount of monomers constituting the acrylic resin.

[0020] The constituent monomer other than the (meth)acrylic monomer is not particularly limited as long as it is a vinyl compound copolymerizable with the (meth)acrylic monomer, such as an aromatic vinyl compound.

[0021] The aromatic vinyl compound is not particularly limited, and examples thereof include unsubstituted vinyl aromatic compounds such as styrene and 2-vinylnaphthalene; substituted vinyl aromatic compounds such as α-methylstyrene; ring-alkylated vinyl aromatic compounds such as 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene; ring-alkoxylated vinyl aromatic compounds such as 4-methoxystyrene and 4-ethoxystyrene; ring-halogenated vinyl aromatic compounds such as 2-chlorostyrene and 3-chlorostyrene; ring-ester-substituted vinyl aromatic compounds such as 4-acetoxystyrene; and ring-hydroxylated vinyl aromatic compounds such as 4-hydroxystyrene. Among these, substituted or unsubstituted styrene is preferred, styrene and / or α-methylstyrene is more preferred, and styrene is particularly preferred. The aromatic vinyl compound may be used alone or in combination of two or more.

[0022] When the acrylic resin is used as a hot-melt powder described later, it is preferable that the acrylic resin is a non-crosslinked acrylic resin having no crosslinked structure, i.e., it is preferable that the acrylic resin does not contain a polyfunctional monomer such as allyl methacrylate or divinylbenzene as a constituent monomer.

[0023] In the manufacturing method according to the present disclosure, the acrylic resin is synthesized by suspension polymerization, in which the monomer and water are mechanically stirred and the polymerization reaction is carried out in a suspended state, and spherical resin particles can be obtained by suspension polymerization.

[0024] The molecular weight of the acrylic resin obtained by the production method according to this embodiment is not particularly limited. However, the production method according to this embodiment makes it possible to produce an acrylic resin with a relatively low molecular weight without reducing the dispersion stability of the polymerization system. The weight-average molecular weight of such an acrylic resin may be, for example, 150,000 or less. The lower limit is not particularly limited, but may be, for example, 50,000 or more. The weight-average molecular weight is a polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC).

[0025] The volume average particle diameter of the acrylic resin particles obtained by the production method according to this embodiment may be in the range of several μm to 1000 μm, which is typically achievable by suspension polymerization. However, when the acrylic particles are used as a hot-melt powder (described later), the volume average particle diameter is preferably in the range of 80 μm to 250 μm. The volume average particle diameter of the acrylic resin can be controlled by the type and amount of dispersion stabilizer, emulsifier, etc. used in suspension polymerization, the solids concentration during particle dispersion, and dispersion conditions.

[0026] Suspension polymerization can be carried out by charging the above-mentioned monomers, dispersion stabilizer, polymerization initiator, chain transfer agent, etc. all at once, in portions, or continuously as needed, and maintaining a predetermined polymerization temperature with stirring.

[0027] As mentioned above, many types of dispersion stabilizers are known for use in suspension polymerization. In contrast, the production method according to the present disclosure uses a combination of modified cellulose and a poorly water-soluble inorganic salt as dispersion stabilizers, improving the stability of the polymerization system and enabling the efficient production of acrylic resin powder with excellent physical properties.

[0028] The modified cellulose can be any cellulose known to be usable as a dispersion stabilizer or suspension stabilizer in suspension polymerization. Specific examples include, but are not limited to, methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and carboxymethyl cellulose. Among these, hydroxypropyl methyl cellulose and carboxymethyl cellulose are preferred. Only one type of modified cellulose may be used, or two or more types may be used in combination.

[0029] A poorly water-soluble inorganic salt refers to an inorganic salt that is difficult to dissolve in water and has extremely low water solubility under room temperature conditions, and is known to be usable as a dispersion stabilizer or suspension stabilizer in suspension polymerization. Specific examples include, but are not limited to, tribasic calcium phosphate, calcium sulfate, barium sulfate, sodium pyrophosphate, magnesium pyrophosphate, calcium carbonate, magnesium carbonate, and hydroxyapatite. Among these, tribasic calcium phosphate, calcium sulfate, and sodium pyrophosphate are preferred. Only one type of poorly water-soluble inorganic salt may be used, or two or more types may be used in combination.

[0030] The ratio of modified cellulose to poorly water-soluble inorganic salt used is not particularly limited, but since the combined use of both components makes it easier to achieve the desired effect, it is preferable that the weight ratio of modified cellulose to poorly water-soluble inorganic salt is approximately 0.1 to 10, more preferably 0.5 to 5, and particularly preferably 1 to 3.

[0031] From the viewpoints of dispersion stability and cost, the total amount of the modified cellulose and the poorly water-soluble inorganic salt used is preferably 0.2 parts by weight or more and 15 parts by weight or less, and more preferably 0.5 parts by weight or more and 10 parts by weight or less, per 100 parts by weight of the total amount of the monomers.

[0032] An emulsifier can also be used in combination as an auxiliary for the dispersion stabilizer. The emulsifier is not particularly limited, and anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, etc. can be used. From the viewpoint of maintaining stability during polymerization, anionic surfactants and nonionic surfactants are preferred. These emulsifiers may be used alone or in combination.

[0033] Furthermore, for the purpose of preventing emulsification, neutral salts such as sodium chloride, sodium sulfate, sodium dodecyl sulfate, and sodium nitrite may be added.

[0034] The polymerization initiator is preferably an initiator soluble in the monomer used, and is not particularly limited, but examples thereof include azo or diazo polymerization initiators such as 2,2'-azobis(dimethyl isobutyrate) and 2,2'-azobisisobutyronitrile; and peroxide polymerization initiators such as benzoyl peroxide, methyl ethyl ketone peroxide, and lauryl peroxide. From the viewpoint of a balance between molecular weight adjustment and polymerization temperature control, lauryl peroxide is particularly preferred.

[0035] The amount of the polymerization initiator used is not particularly limited, but is preferably in the range of 0.02 to 2 parts by weight, more preferably 0.1 to 1 part by weight, per 100 parts by weight of the total amount of the monomers.

[0036] It is preferable to use a chain transfer agent to adjust the molecular weight of the acrylic resin. The chain transfer agent is not particularly limited, but examples thereof include mercaptans such as n-dodecyl mercaptan; thioglycolic acid esters such as octyl thioglycolate; and α-methylstyrene dimer. These may be used alone or in combination. Among these, n-dodecyl mercaptan is preferred because it has a large chain transfer constant and is relatively easy to suppress odor during melting.

[0037] The amount of the chain transfer agent used is preferably in the range of 0.1 to 2 parts by weight, more preferably 0.2 to 1 part by weight, and even more preferably 0.2 to 0.5 parts by weight, per 100 parts by weight of the total amount of monomers. By appropriately adjusting the amount within this range, it is possible to control the molecular weight of the polymer within the above-mentioned numerical range.

[0038] The temperature during polymerization is not particularly limited, but is, for example, 50 to 80° C., and preferably 60 to 80° C. After the polymerization progresses and the top of the exothermic peak can be confirmed, it is preferable to continue the polymerization at 80 to 90° C. for a certain period of time in order to increase the polymerization conversion rate.

[0039] The time required for polymerization varies depending on the type and amount of the polymerization initiator, the polymerization temperature, etc., but is usually 1 to 24 hours.

[0040] There are no particular limitations on the method for adding the polymerization initiator and the chain transfer agent, but the most preferred method is to dissolve both the polymerization initiator and the chain transfer agent in the monomer, suspend the monomer in water, and then carry out the polymerization reaction as is.

[0041] Alternatively, the polymerization reaction can be carried out by suspending a portion of the monomers in water to initiate the polymerization reaction, and as the polymerization reaction progresses, adding the remainder of the monomers or an aqueous suspension of the remainder of the monomers to the polymerization vessel in one stage or in several stages, or continuously.

[0042] The stirring conditions during suspension polymerization can be appropriately set within known ranges, and the apparatus used can be a polymerization vessel equipped with a stirrer equipped with known stirring blades, such as turbine blades, Pfaudle blades, propeller blades, blue margin blades, H-shaped blades, etc.

[0043] In suspension polymerization, a polymerization reaction of monomers proceeds in a suspension to form a suspension containing an acrylic resin. The suspension is then subjected to solid-liquid separation to separate and recover the acrylic resin from the water. However, since the suspension contains modified cellulose, the viscosity of the suspension increases due to the cellulose, making it difficult to perform solid-liquid separation.

[0044] Therefore, before carrying out solid-liquid separation, a cellulolytic enzyme is added to the suspension to decompose the modified cellulose, which reduces the viscosity of the suspension and makes solid-liquid separation easier.

[0045] Cellulolytic enzymes, also known as cellulases, are enzymes that hydrolyze the glycosidic bonds of cellulose. There are no particular limitations on the type of cellulolytic enzyme, and commercially available products can be used as appropriate.

[0046] The amount of cellulolytic enzyme to be added is not particularly limited and may be set appropriately from the viewpoint of decomposing the modified cellulose, but it is desirable that the amount be, for example, 0.001 to 0.1 parts by weight per 100 parts by weight of the modified cellulose.

[0047] Furthermore, if the suspension contains poorly water-soluble inorganic salts, it may be difficult to carry out solid-liquid separation, and the poorly water-soluble inorganic salts may remain in the acrylic resin, adversely affecting the physical properties of the acrylic resin. Therefore, before carrying out solid-liquid separation, an acid is added to the suspension to dissolve the poorly water-soluble inorganic salts in water. However, if an acid is added before or simultaneously with the treatment using a cellulose-degrading enzyme, decomposition of the modified cellulose is inhibited.

[0048] Therefore, in the production method according to the present disclosure, an acid is added to the suspension obtained after decomposition of the modified cellulose, thereby dissolving the poorly water-soluble inorganic salt in water. The acrylic resin is then recovered by solid-liquid separation. This allows both the decomposition of the modified cellulose and the dissolution of the poorly water-soluble inorganic salt, and enables efficient solid-liquid separation after polymerization to obtain an acrylic resin with good physical properties.

[0049] The acid used to dissolve the poorly water-soluble inorganic salt is not particularly limited, and may be either an organic acid or an inorganic acid. Examples of organic acids include formic acid and acetic acid, and examples of inorganic acids include hydrochloric acid, sulfuric acid, and nitric acid. Among these, hydrochloric acid is preferably used from the viewpoints of volatility and treatment during solid-liquid separation.

[0050] The amount of acid to be added is not particularly limited and may be appropriately set from the viewpoint of dissolving the poorly water-soluble inorganic salt, but is preferably, for example, 0.001 to 0.1 parts by weight per 100 parts by weight of the poorly water-soluble inorganic salt. In particular, in order to efficiently dissolve the poorly water-soluble inorganic salt, it is desirable to add the acid so that the molar ratio of the acid to the poorly water-soluble inorganic salt is 1 or more.

[0051] In order to prevent blocking of the recovered acrylic resin, it is preferable to add inorganic particles to the acrylic resin. The timing of adding the inorganic particles is not particularly limited, and the inorganic particles may be added before solid-liquid separation or after solid-liquid separation and before drying.

[0052] As the material for forming the inorganic particles, a material having a large specific surface area is preferred, and examples thereof include silica, titanium dioxide, zinc oxide, and aluminum oxide. Considering the compatibility with acrylic resins, it is desirable to use hydrophilic inorganic particles, and among these, it is preferable to use titanium dioxide particles, especially hydrophilic titanium dioxide particles.

[0053] The amount of inorganic particles used can be appropriately set from the viewpoint of the blocking suppression effect, but is preferably 0.1 to 1 part by weight per 100 parts by weight of the acrylic resin. The lower limit is preferably 0.2 parts by weight or more, and the upper limit is preferably 0.8 parts by weight or less.

[0054] The acrylic resin obtained by solid-liquid separation can be obtained as a powder by washing, dehydrating, and drying using known methods.

[0055] (Applications of acrylic resins) The acrylic resin obtained by the production method according to this embodiment may be used for various applications as it is in the form of powder, or may be pelletized using an extruder and then used for various applications.

[0056] Specific applications of acrylic resins include molding materials, main resin materials for paints or adhesives, light diffusing materials, cosmetic additives, and pore-forming agents. In particular, the acrylic resin powder obtained by the present disclosure can be suitably used as a hot-melt powder, and since the poorly water-soluble inorganic salt used in suspension polymerization has been dissolved and removed from the acrylic resin obtained by the present disclosure, the acrylic resin can exhibit good adhesion when used as a hot-melt powder.

[0057] Hot-melt powder is used to form a binder resin layer by heating, melting, and solidifying it. There are no particular restrictions on the object to which the binder resin layer is to be adhered, but it is particularly suitable for use as a layer interposed between an ink layer and the surface of a printing object to ensure close contact of the ink with the printing object. Furthermore, the binder resin layer can achieve thermal transfer of the ink layer to the printing object. In particular, the acrylic resin powder obtained according to the present disclosure can be used as a hot melt powder required in DTF (Direct To Film) printing.

[0058] In DTF printing, a hot-melt powder is first applied to the surface of an ink layer placed on a release film, and then heated to melt and solidify the powder, producing a thermal transfer sheet consisting of a release film, an ink layer, and a binder resin layer laminated in that order. The binder resin layer and the ink layer are then thermally transferred onto the surface of the printing target using the thermal transfer sheet. DTF printing is particularly suitable for printing on textile products.

[0059] The following items list preferred aspects of the present disclosure, but the present invention is not limited to the following items. [Item 1] a step of carrying out suspension polymerization in the presence of modified cellulose and a poorly water-soluble inorganic salt as dispersion stabilizers to obtain a suspension containing an acrylic resin; adding a cellulolytic enzyme to the suspension to decompose the modified cellulose; adding an acid to the suspension after decomposition of the modified cellulose to dissolve the poorly water-soluble inorganic salt; and and recovering the acrylic resin from the suspension obtained after dissolving the poorly water-soluble inorganic salt. [Item 2] Item 2. The method according to item 1, wherein the modified cellulose is at least one selected from the group consisting of hydroxypropyl methylcellulose and carboxymethyl cellulose. [Item 3] 3. The method according to item 1 or 2, wherein the poorly water-soluble inorganic salt is at least one selected from the group consisting of calcium triphosphate, calcium sulfate, and sodium pyrophosphate. [Item 4] the acrylic resin contains alkyl (meth)acrylate as a constituent monomer, 4. The method according to any one of items 1 to 3, wherein the alkyl (meth)acrylate comprises an alkyl (meth)acrylate having an alkyl group having 4 to 12 carbon atoms. [Item 5] 5. The method according to any one of items 1 to 4, wherein the acrylic resin has a volume average particle size of 80 to 250 μm. [Item 6] 6. The production method according to any one of items 1 to 5, wherein lauryl peroxide is used as a polymerization initiator in the suspension polymerization. [Item 7] 7. The production method according to any one of items 1 to 6, wherein n-dodecyl mercaptan is used as a chain transfer agent in the suspension polymerization. [Example]

[0060] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0061] (Method for measuring volume average particle size) The volume average particle size of the powder was measured using a measuring device based on the laser diffraction / scattering method, MT3000II manufactured by Microtrac Corp. The measurement sample was prepared by dispersing the collected powder in soapy water.

[0062] (Method for measuring weight-average molecular weight) The weight-average molecular weight was determined by dissolving a sample in tetrahydrofuran (THF), filtering the soluble fraction through a filter with a filter diameter of 0.2 μm, and then using a high-speed GPC system (HLC-8220, manufactured by Tosoh Corporation) (sample solution: 20 mg sample / 10 mL THF, columns: one TSKguardcolumn SuperHZ-H and two TSKgel SuperHZM-H, both manufactured by Tosoh Corporation, column temperature: 40°C, detector: differential refractometer, flow rate: 0.35 mL / min, injection volume: 10 μL, calibration curve: standard polystyrene).

[0063] Example 1 800g of deionized water, 0.55g of disodium hydrogen phosphate, 82.5g of 10% tribasic calcium phosphate solution, and 0.11g of sodium nitrite were charged into a 3L polymerization reactor. Separately, 330g of butyl methacrylate, 104.5g of butyl acrylate, and 115.5g of methyl methacrylate were mixed, and then 1.1g of normal dodecyl mercaptan and 3.3g of lauryl peroxide were dissolved in the mixture. After confirming dissolution, the monomer mixture was charged into the 3L polymerization reactor, allowed to stand for a while, and then stirred at 300 rpm for 10 minutes. After stirring, 200g of 2% hydroxypropyl methylcellulose was added and the temperature was raised to 70°C while flowing nitrogen to initiate polymerization. After confirming the exothermic peak due to polymerization, the temperature was raised to 85°C and held for 3 hours to complete the polymerization, yielding a suspension of acrylic resin particles.

[0064] After polymerization, the suspension was cooled to below 50°C, 0.01 g of cellulose-degrading enzyme was added, and the mixture was stirred for 30 minutes, resulting in the decomposition of the cellulose-derived structure of hydroxypropyl methylcellulose. Subsequently, 165 g of 10% hydrochloric acid was added to decompose the tribasic calcium phosphate. The suspension after the treatment was subjected to solid-liquid separation and then washed with water to obtain a dehydrated cake. This dehydrated cake was mixed with 2.8 g of hydrophilic titanium dioxide (AEROXIDE P25, manufactured by Nippon Aerosil Co., Ltd.) and then dried to obtain a spherical acrylic resin particle powder. The volume-average particle diameter of this powder was 132 μm, the weight-average molecular weight of the acrylic resin was 128,000, and the Tg was 14.8°C.

[0065] (Comparative Example 1) 800g of deionized water, 0.55g of disodium hydrogen phosphate, 82.5g of 10% tribasic calcium phosphate solution, and 0.11g of sodium nitrite were charged into a 3L polymerization reactor. Separately, 330g of butyl methacrylate, 104.5g of butyl acrylate, and 115.5g of methyl methacrylate were mixed, and then 1.1g of normal dodecyl mercaptan and 3.3g of lauryl peroxide were dissolved in the mixture. After confirming dissolution, the monomer mixture was charged into the 3L polymerization reactor, allowed to stand for a while, and then stirred at 300 rpm for 10 minutes. After stirring, 200g of 2% hydroxypropyl methylcellulose was added and the temperature was raised to 70°C while flowing nitrogen to initiate polymerization. After confirming the exothermic peak due to polymerization, the temperature was raised to 85°C and held for 3 hours to complete the polymerization, yielding a suspension of acrylic resin particles.

[0066] After polymerization, the suspension was cooled to below 50°C, and 165 g of 10% hydrochloric acid was added to decompose the tribasic calcium phosphate. 0.01 g of a cellulose-degrading enzyme was then added, and the mixture was stirred for 30 minutes. However, the suspension after the treatment could not be separated into solid and liquid, and a dehydrated cake could not be obtained.

[0067] (Comparative Example 2) After obtaining a suspension of acrylic resin particles in the same manner as in Comparative Example 1, the suspension was cooled to 50°C or below, and 165 g of 10% hydrochloric acid was added to decompose the tricalcium phosphate. After this treatment, the suspension could not be separated into solid and liquid, and a dehydrated cake could not be obtained.

[0068] (Comparative Example 3) After obtaining a suspension of acrylic resin particles in the same manner as in Comparative Example 1, the suspension was cooled to below 50°C, 0.01 g of cellulose-degrading enzyme was added, and the mixture was stirred for 30 minutes to decompose the cellulose-derived structure of hydroxypropyl methylcellulose. The suspension after the treatment was subjected to solid-liquid separation and then washed with water to obtain a dehydrated cake. This dehydrated cake was mixed with 2.8 g of hydrophilic titanium dioxide (AEROXIDE P25, manufactured by Nippon Aerosil Co., Ltd.) and then dried to obtain a powder of spherical acrylic resin particles. The volume-average particle diameter of this powder was 135 μm, the weight-average molecular weight of the acrylic resin was 129,000, and the Tg was 14.8°C.

[0069] (Evaluation method) The acrylic resin particle powder obtained in Example 1 or Comparative Example 3 was subjected to the following evaluations.

[0070] (Coating onto polyester resin film) A 25% titanium oxide white pigment dispersion was applied to one entire surface of a polyester resin film (100 μm thick) coated with a release agent containing silicone wax using a No. 26 bar coater, followed by drying at 70°C for 1 minute to form a white ink layer. The acrylic resin particle powder obtained in Example 1 or Comparative Example 3 was sprinkled onto the surface of the white ink layer so that the powder adhered to the entire white ink layer. The film was then tapped to remove excess powder. The film was then heated at 125°C for 3 minutes and 30 seconds to melt and solidify the powder, forming a binder resin layer.

[0071] (Transfer process onto textile fabric) The film with the white ink layer and binder resin layer formed was placed on the surface of a black textile fabric with the binder resin layer facing the textile fabric, pressed at 150°C for 15 seconds, and cooled. After cooling, the polyester resin film was peeled off, and the fabric was pressed again at 150°C for 15 seconds, leaving the white ink printed on the textile fabric. The following evaluations were carried out using this textile fabric.

[0072] (Evaluation of Adhesion) After applying adhesive cloth tape to the white ink side of the textile fabric, the surface of the adhesive tape was rubbed with the cap of a pen 50 times to firmly adhere the tape to the textile fabric, and then the tape was peeled off in one go by pulling it vertically. After peeling, the adhesive surface of the adhesive tape was checked for any white ink residue and the adhesive strength to the textile fabric was evaluated.

[0073] As a result, the acrylic resin particle powder obtained in Example 1 was evaluated as having good adhesion of white ink to the textile fabric, with no white ink adhering to the adhesive surface, indicating that the powder obtained in Example 1 can be suitably used as a hot melt powder.

[0074] On the other hand, the acrylic resin particle powder obtained in Comparative Example 3 had visible white ink adhering to the adhesive surface, and was evaluated as having poor adhesion. This is presumably due to the influence of residual tricalcium phosphate remaining on the surface of the obtained particles, since the step of decomposing tricalcium phosphate was not carried out in Comparative Example 3. Therefore, the powder obtained in Comparative Example 3 is insufficient for use as a hot-melt powder.

Claims

1. a step of carrying out suspension polymerization in the presence of modified cellulose and a poorly water-soluble inorganic salt as dispersion stabilizers to obtain a suspension containing an acrylic resin; adding a cellulolytic enzyme to the suspension to decompose the modified cellulose; adding an acid to the suspension after decomposition of the modified cellulose to dissolve the poorly water-soluble inorganic salt; and and recovering the acrylic resin from the suspension obtained after dissolving the poorly water-soluble inorganic salt.

2. The method according to claim 1, wherein the modified cellulose is at least one selected from the group consisting of hydroxypropylmethylcellulose and carboxymethylcellulose.

3. 3. The method according to claim 1, wherein the poorly water-soluble inorganic salt is at least one selected from the group consisting of calcium triphosphate, calcium sulfate, and sodium pyrophosphate.

4. the acrylic resin contains alkyl (meth)acrylate as a constituent monomer, The method according to claim 1 or 2, wherein the alkyl (meth)acrylate comprises an alkyl (meth)acrylate having an alkyl group having from 4 to 12 carbon atoms.

5. The method according to claim 1 or 2, wherein the acrylic resin has a volume average particle size of 80 to 250 μm.

6. 3. The method according to claim 1, wherein lauryl peroxide is used as a polymerization initiator in the suspension polymerization.

7. 3. The production method according to claim 1, wherein n-dodecyl mercaptan is used as a chain transfer agent in the suspension polymerization.