Method for manufacturing thickeners

Abstract

The objective of the present invention is to produce a thickening agent that can be suitably used as a thickening agent, can obtain the desired viscosity with a small amount of addition due to its high molecular weight, and does not string after dissolution. [Solution] A method for producing a thickening agent containing 90% by mass or more of methacrylic resin, comprising the step of polymerizing monomers using two or more chain transfer agents with a Bertz complexity index (BertzCT) of 40 or more to produce the methacrylic resin, wherein the weight-average molecular weight of the methacrylic resin is 400,000 to 1,000,000.

Description

Technical Field

[0001] The present invention relates to a method for producing a thickener.

Background Art

[0002] In the production of paints or adhesives, etc., organic thickeners are used for the purpose of adjusting the viscosity of products to improve handling properties. Among organic thickeners, thickeners using methacrylic resin compositions have high transparency and weather resistance as transparent resins, and also have excellent affinity and chemical resistance with alkyl cyanoacrylates, etc. Since the methacrylic resin composition rapidly dissolves in the monomer while maintaining transparency, it is widely used as a thickener for adhesives.

[0003] Among adhesives, especially cyanoacrylate adhesives can start polymerization by weak anions such as a small amount of moisture or impurities due to the high anionic polymerization property of the main component alkyl cyanoacrylate, and can firmly bond various materials in a short time. Therefore, as an instant adhesive, it is used in a wide range of fields such as industrial, medical, and household uses.

[0004] Methacrylic resin compositions are generally used in cyanoacrylate adhesives, etc. Higher molecular weight methacrylic resins can obtain the desired viscosity with a small amount of addition, and the influence on adhesives, etc. becomes small, so they are preferable.

[0005] However, when a methacrylic resin with a very high molecular weight is dissolved in an organic solvent as a thickener, there is a problem that stringing occurs during use or when dividing into small portions.

[0006] As a thickener containing a methacrylic resin, for example, Patent Document 1 discloses an acrylic thickener in which the alkyl group of the alkyl acrylate monomer unit of the copolymer component of the methacrylic resin has 4 or more carbon atoms.

[0007] Patent Document 2 discloses a thickening agent containing a methacrylic resin that exhibits excellent stability when exposed to methyl methacrylate at 50°C / 95% Rh.

[0008] Patent Document 3 describes the inclusion of an alkyl poly(meth)acrylate having a weight-average molecular weight of 200,000 to 500,000 as a thickening agent in a cyanoacrylate-based adhesive composition. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2022 / 07068 [Patent Document 2] Japanese Patent Publication No. 2018-178076 [Patent Document 3] Special Publication No. 4-15267 [Overview of the project] [Problems that the invention aims to solve]

[0010] Patent documents 1 to 3 do not describe a thickening agent that has a higher molecular weight, allows for a smaller amount to be added, and also exhibits excellent resistance to stringing when dissolved in an adhesive.

[0011] Therefore, the object of the present invention is to provide a method for producing a thickener that can be suitably used as a thickener, can obtain the desired viscosity with a small amount of addition due to its high molecular weight, does not string after dissolution, and has excellent storage stability when used as a thickener for cyanoacrylate adhesives. [Means for solving the problem]

[0012] To solve the above problems, the present inventors conducted extensive research and, as a result, have surprisingly discovered a method for producing a thickening agent that includes a step of polymerizing monomers using a chain transfer agent with a Belz complexity index of 40 or higher to produce the methacrylic resin, and in which the weight-average molecular weight of the methacrylic resin is 400,000 to 1,000,000. This method produces a thickening agent that can achieve the desired viscosity with only a small amount of addition, does not string after dissolution, and has excellent storage stability when used as a thickening agent for cyanoacrylate adhesives.

[0013] In other words, the present invention is as follows. [1] A method for producing a thickening agent containing 90% by mass or more of methacrylic resin, The process includes polymerizing monomers using two or more chain transfer agents with a Bertz complexity index (BertzCT) of 40 or higher to produce the methacrylic resin, The weight-average molecular weight of the methacrylic resin is 400,000 to 1,000,000. A method for producing a thickening agent. [2] The method for producing a thickener according to [1], wherein at least one of the chain transfer agents is a chain transfer agent with a Bertz complexity index (BertzCT) of 150 or higher. [3] A method for producing a thickener according to [1] or [2], wherein at least two of the chain transfer agents are a chain transfer agent with a Bertz complexity index (BertzCT) of 40 or more and less than 150, and a chain transfer agent with a Bertz complexity index (BertzCT) of 150 or more. [4] A method for producing a thickener according to any one of [1] to [3], wherein the weight-average molecular weight of the methacrylic resin is 800,000 to 1,000,000. [5] A method for producing a thickener according to any one of [1] to [4], wherein the methacrylic resin is bead-shaped and has a D90 (90% particle size) of less than 300. [6] At least one of the aforementioned chain transfer agents, A chain transfer agent having a thiol group and a bond dissociation energy ΔH of a C-S bond when bonded to the end of a methyl methacrylate (MMA) trimer of 50 kcal / mol or more. The method for producing a thickener according to any one of [1] to [5]. [7] A method for producing a thickener containing 90% by mass or more of a methacrylic resin, including a step of polymerizing a monomer using a chain transfer agent having a Bertz complexity index (BertzCT) of 150 or more to produce the methacrylic resin, where the weight average molecular weight of the methacrylic resin is 400,000 to 1,000,000. The method for producing a thickener.

Effect of the Invention

[0014] According to the present invention, the present invention can be suitably used as a thickener, and due to its high molecular weight, a desired viscosity can be obtained with a small amount of addition, and furthermore, a thickener without stringing after dissolution can be produced.

Mode for Carrying Out the Invention

[0015] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist thereof.

[0016] [Thickener] The thickener of this embodiment contains at least methacrylic resin. The thickener may contain only methacrylic resin, or it may contain methacrylic resin and other resins. Preferably, the resin component of the thickener is methacrylic resin only. The thickener may also contain one type of methacrylic resin alone, or a combination of two or more types. In one example, it is more preferable that the thickener consists of only a single methacrylic resin as the resin component. The methacrylic resin content in the thickener is 90% by mass or more, preferably 95% by mass or more, and more preferably 97% by mass or more. It is particularly preferable that the thickener consists of methacrylic resin (with a methacrylic resin content of 100% by mass).

[0017] The thickener in this embodiment is preferably a thickener for cyanoacrylate adhesives.

[0018] (Methacrylic resin) The methacrylic resin contained in the thickener of this embodiment has a weight-average molecular weight of 400,000 to 1,000,000.

[0019] <Weight average molecular weight> The methacrylic resin has a weight-average molecular weight (Mw) of 400,000 to 1,000,000, as measured by gel permeation chromatography (GPC). If the Mw is less than 400,000, the amount of methacrylic resin used to achieve the desired viscosity of the syrup (solution of methacrylic resin) increases, which may result in inferior mechanical properties of the resulting adhesive, and is therefore undesirable. On the other hand, from the viewpoint of suppressing stringing when used as a thickening agent, the Mw should be 1,000,000 or less. Since the desired viscosity can be obtained with a small amount of addition, the Mw is preferably greater than 405,000, more preferably 410,000 or more, even more preferably 420,000 or more, even more preferably 430,000 or more, even more preferably 550,000 or more, even more preferably 800,000 or more, preferably 980,000 or less, and more preferably 950,000 or less.

[0020] The molecular weight distribution Mw / Mn, which is the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of the methacrylic resin as measured by gel permeation chromatography (GPC), is preferably 1.7 or more and 2.5 or less. From the viewpoint of ease of manufacture, it is more preferably 1.8 or more. Furthermore, from the viewpoint of suppressing undissolved residue during dissolution and improving solubility, it is more preferably less than 2.5, even more preferably 2.4 or less, particularly preferably 2.3 or less, and especially preferably less than 2.3.

[0021] The weight-average molecular weight and number-average molecular weight are measured by GPC. A calibration curve is prepared beforehand using a standard methacrylic resin, available as a reagent with a known monodisperse weight-average molecular weight, and an analytical gel column that elutes from high molecular weight components, based on the elution time and weight-average molecular weight. The molecular weight of each sample can then be measured from this calibration curve. Specifically, this can be done by the method described in the examples below.

[0022] <Chain movement agent> The methacrylic resin is manufactured by radical polymerization, and a chain transfer agent is used to adjust the molecular weight. In this embodiment, a chain transfer agent with a Bertz complexity index (BertzCT) of 40 or higher is used, thereby improving the stability of the thickening agent and the storage stability when dissolved in adhesives, especially cyanoacrylate-based adhesives. The Bertz complexity index (BertzCT) is preferably 100 or higher. From the viewpoint of improving storage stability, it is even more preferable to use a chain transfer agent with a Bertz complexity index (BertzCT) of 150 or higher. Chain transfer agents having thiol groups are preferred. When a chain transfer agent having thiol groups is used, during polymerization, the H of the thiol group SH of the chain transfer agent is removed and bonded to the polymer end, forming a CS bond.

[0023] As the chain transfer agent with a Bertz complexity index of 40 or more and less than 150, among the compounds having a thiol group, a compound calculated to have a Bertz complexity index of 40 or more and less than 150 can be used. For example, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, 2-ethylhexyl thioglycolate, methoxybutyl thioglycolic acid, and 2-ethylhexyl-3-mercaptopropionate are preferably used. As the chain transfer agent with a Bertz complexity index of 150 or more, among the compounds having a thiol group, a compound calculated to have a Bertz complexity index of 150 or more can be used. For example, tridecyl 3-mercaptopropionate can be mentioned.

[0024] The chain transfer agent may be used in the range of 0.001 to 1% by mass based on 100% by mass of the total mass of the monomers. The amount of the chain transfer agent is determined depending on the desired molecular weight.

[0025] The Bertz complexity index (BertzCT) can be calculated from the molecular structure. Specifically, it can be calculated by inputting the molecular structure using the library RDKit.

[0026] The methacrylic resin is preferably polymerized using two or more types of chain transfer agents. In the present invention, surprisingly, using two or more types of chain transfer agents little by little is more effective in improving the stability of the thickening target, particularly the storage stability when dissolved in a cyanoacrylate-based adhesive, than increasing the amount of one type of chain transfer agent to adjust the molecular weight. It is preferable that the methacrylic resin is polymerized using a chain transfer agent with a Bertz complexity index of 40 or more and less than 150 and a chain transfer agent with a Bertz complexity index of 150 or more, and it is more preferable to polymerize using a chain transfer agent with a Bertz complexity index of 100 or more and less than 150 and a chain transfer agent with a Bertz complexity index of 150 or more. Further, the methacrylic resin may be polymerized using one or two or more chain transfer agents with a Bertz complexity index (BertzCT) of 150 or more.

[0027] <Bond dissociation energy of C-S bond> Furthermore, it is preferable that at least one of the chain transfer agents has a thiol group and that the bond dissociation energy ΔH of the CS bond when bonded to the methyl methacrylate (MMA) trimer end is 50 kcal / mol or more. The bond dissociation energy can be calculated by the method described in the examples below.

[0028] <Monomer> The methacrylic resin preferably contains 90 to 99.9% by mass of monomer units derived from methyl methacrylate (hereinafter also simply referred to as "methyl methacrylate monomer units") and 0.1 to 10% by mass of monomer units derived from alkyl acrylate (hereinafter also simply referred to as "alkyl acrylate monomer units"). More preferably, it contains 92 to 99.8% by mass of methyl methacrylate monomer units and 0.2 to 8% by mass of alkyl acrylate monomer units, and even more preferably, it contains 95 to 99.7% by mass of methyl methacrylate monomer units and 0.3 to 5% by mass of alkyl acrylate monomer units. The methacrylic resin may or may not contain other monomer units other than methyl methacrylate monomer units and alkyl acrylate monomer units.

[0029] The alkyl acrylate monomer unit preferably has an alkyl group having 4 or more carbon atoms. Preferred alkyl acrylate monomer units having 4 or more carbon atoms include those having 4 to 8 carbon atoms, such as n-butyl acrylate, sec-butyl acrylate, and 2-ethylhexyl acrylate. From the viewpoint of reducing the odor of the cyanoacrylate solution of the methacrylic resin, the number of carbon atoms in the alkyl group of the alkyl acrylate monomer unit is preferably 4 to 8. From the viewpoint of ease of availability and odor reduction when dissolved in cyanoacrylate, the n-butyl acrylate monomer unit is particularly preferred.

[0030] The methacrylic resin may consist only of methyl methacrylate monomer units and alkyl acrylate monomer units having an alkyl group with 4 or more carbon atoms, or it may further contain other monomer units such as other vinyl monomer units copolymerizable with methyl methacrylate.

[0031] Other monomer units may be vinyl monomers copolymerizable with methyl methacrylate, specifically including alkyl methacrylates with 2 to 18 carbon atoms in the alkyl group; alkyl acrylates with 1 to 3 carbon atoms in the alkyl group; α,β-unsaturated acids such as acrylic acid and methacrylic acid; divalent carboxylic acids containing unsaturated groups such as maleic acid, fumaric acid, and itaconic acid, and their alkyl esters; aromatic vinyl compounds such as styrene, α-methylstyrene, and styrene having substituents on the benzene ring; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; maleic anhydride, maleimide, and N-substituted maleimide; and these can be used individually or in combination of two or more. From the viewpoint of odor suppression, when alkyl acrylates with 1 to 3 carbon atoms in the alkyl group are included, it is preferable that the mass ratio of alkyl acrylate monomer units with 1 to 3 carbon atoms in the alkyl group is less than 0.1% by mass relative to 100% by mass of all monomer units constituting the methacrylic resin, and it is more preferable that they are not included.

[0032] The mass ratio of methyl methacrylate monomer units to 100% by mass of methacrylic resin is preferably 90 to 99.9% by mass, from the viewpoint of suppressing odor when dissolved (for example, when dissolved in alkylcyanoacrylate). More preferably 95 to 99.8% by mass, even more preferably 97 to 99.8% by mass, and particularly preferably 98 to 99.8% by mass.

[0033] The mass ratio of alkyl acrylate monomer units to 100% by mass of methacrylic resin is preferably 0.1 to 10% by mass. More preferably 0.2 to 5% by mass, even more preferably 0.2 to 3% by mass, and particularly preferably 0.2 to 2% by mass. If it exceeds 10% by mass, a peculiar odor tends to be generated when dissolved (for example, when dissolved in alkyl cyanoacrylate, etc.) due to residual alkyl acrylate monomers and impurities derived therefrom, which is undesirable. If it is less than 0.1% by mass, the odor-improving effect obtained by copolymerizing alkyl acrylate monomer units tends not to be exhibited, which is undesirable.

[0034] In this embodiment, other monomer units may be copolymerized to the extent that the effects of the present invention are not impaired. Considering solubility in alkyl cyanoacrylates and odor during dissolution, when the total amount of methyl methacrylate monomer units and alkyl acrylate monomer units having an alkyl group with 4 or more carbon atoms is 100 parts by mass, the mass ratio of monomer units derived from other vinyl monomers copolymerizable with methyl methacrylate is preferably 0 to 20 parts by mass, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less.

[0035] In 100 parts by mass of methacrylic resin, the total mass proportion of methyl methacrylate monomer units and alkyl acrylate monomer units having an alkyl group with 4 or more carbon atoms is preferably 80 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, and particularly preferably 100 parts by mass.

[0036] <Moisture percentage> The methacrylic resin preferably has a moisture content of 0.01% to 1%. Trying to keep the moisture content even lower may necessitate long drying times. From the viewpoint of productivity, a moisture content of 0.01% or more is preferable. On the other hand, if it exceeds 1%, the storage stability after dissolution in cyanoacrylates such as ethyl cyanoacrylate tends to deteriorate, so a moisture content of 1% or less is preferable. More preferably, it is 0.01% or more, even more preferably 0.02% or more, most preferably more than 0.03%, more preferably 0.8% or less, even more preferably 0.7% or less, and most preferably less than 0.5%.

[0037] The moisture content can be measured by the method described in the examples below, and is measured by the drying method. The drying method involves holding 10.0 g of methacrylic resin at 70°C and ending the measurement when the weight loss rate over 10 seconds becomes 0.02% or less, and the total weight loss rate is taken as the moisture content.

[0038] The moisture content of methacrylic resin (for example, methacrylic resin in pellet or bead form) can be adjusted by drying methods such as the slurry after polymerization.

[0039] Methods for drying methacrylic resin include hot air drying, which involves blowing hot air into a tank from a hot air fan or blow heater; vacuum drying, which involves reducing the pressure in the system and heating it as needed; barrel drying, which involves rotating the resulting polymer in a container to remove moisture; spin drying, which utilizes centrifugal force; airflow drying, which involves transferring the resin through pipes with hot air while drying; and fluidized bed drying, which dries the resin at a specific temperature for a certain period of time, after which the bottom of the tank opens and closes to allow it to fall into the next drying tank.

[0040] To achieve the above moisture content, it is preferable to dry the resulting slurry in an air-jet dryer and / or fluidized bed dryer after suspension polymerization is complete. However, if the final moisture content is significantly low, the processing time will be long, resulting in poor productivity, and problems such as pump-up failures may occur in the slurry delivery process.

[0041] The shape of the methacrylic resin is not particularly specified, but it is preferably in the form of pellets, flakes, beads, or powder. From the viewpoint of shortening the dissolution time and reducing unmelted material, it is preferably in the form of beads or powder.

[0042] <Volume-average particle diameter> For methacrylic resin, the volume-average particle size when used in bead form is preferably 50 to 500 μm. Since the dissolution time decreases as the particle size decreases, it is preferable that the particle size is 500 μm or less, and from the viewpoint of suppressing bead scattering during handling and reducing unmelted material, it is preferable that the particle size is 50 μm or more. The volume-average particle size is more preferably 70 μm or more, most preferably 100 μm or more, more preferably 400 μm or less, and most preferably 350 μm or less.

[0043] In this specification, volume-average particle diameter refers to the volume particle diameter that can be measured by the method described in the examples below.

[0044] <d90> The 90% particle size D90 (particle size distribution) of the methacrylic resin is preferably less than 300 μm. Because methacrylic resin has a high molecular weight, if the particle size is large, it takes a long time to dissolve. In particular, if there are beads with a particle size of 300 μm or more, there is a problem that it takes a long time for the large particle size beads to dissolve when dissolving at relatively low temperatures below 55°C. By setting the D90 to less than 300 μm, a thickening agent that dissolves easily can be obtained even when dissolving at low temperatures. A D90 of 280 μm or less is more preferable, and 260 μm or less is even more preferable. Methods for setting D90 to less than or equal to a predetermined value (e.g., less than 300 μm) include setting the particle size of the suspension to less than or equal to a predetermined value (e.g., 35 μm or less if D90 is to be less than 300 μm) or preheating the suspension as described later.

[0045] The methacrylic resin content in the thickener is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and particularly preferably 99 to 100% by mass, based on 100% by mass of the thickener.

[0046] <Polymerization method> Methacrylic resin can be manufactured, for example, using monomers that constitute the methacrylic resin, along with polymerization initiators, chain transfer agents, suspending agents, and other additives.

[0047] When using free radical polymerization, general radical polymerization initiators such as peroxide-based initiators like di-t-butyl peroxide, lauryl peroxide, dilauroyl peroxide, t-butyl peroxy 2-ethylhexanoate, 1,1-bis(t-butyl peroxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butyl peroxy)cyclohexane, or azo-based initiators like azobisisobutyronitrile, azobisisovaleronitrile, and 1,1-azobis(1-cyclohexanecavonitrile) can be used as polymerization initiators. These may be used individually or in combination of two or more. These radical initiators may also be combined with appropriate reducing agents to create redox initiators.

[0048] Polymerization initiators are generally used in amounts ranging from 0.001% to 1% by mass relative to 100% by mass of the total monomer mass. When using dilauroyl peroxide, it is preferable to use it in amounts ranging from 0.01% to 0.5% by mass relative to the total amount of monomer, more preferably in amounts ranging from 0.03% to 0.3% by mass, even more preferably in amounts ranging from 0.04% to 0.18% by mass, and most preferably in amounts ranging from 0.05% to 0.13% by mass (polymerized by including it in the monomer solution).

[0049] For polymerizing methacrylic resin, suspension polymerization or emulsion polymerization is preferred. Suspension polymerization yields particulate resin beads, while emulsion polymerization yields powdered resin beads, which is advantageous in terms of operation when dissolving an appropriate amount as a thickener to adjust the syrup to the desired viscosity.

[0050] Suspension polymerization is preferred over emulsion polymerization because its polymerization time is shorter.

[0051] In particular, when using suspension polymerization, it is preferable to keep the molecular weight distribution within the range described above. When it is required to suppress the generation of unmelted material due to a broad molecular weight distribution during dissolution in alkyl cyanoacrylates, etc., and to maintain high storage stability after dissolution at a high level, it is preferable to obtain the product by single-stage suspension polymerization rather than multi-stage polymerization which results in a broad molecular weight distribution. Two-stage polymerization is undesirable because it increases the amount of impurities derived from the suspension agent.

[0052] Furthermore, as a polymerization method for methacrylic resin, it is preferable to use a method in which a suspension agent with an average particle size of 10 to 40 μm is dispersed in water and polymerized. In particular, it is preferable to perform a one-step suspension polymerization by dispersing a suspension agent with an average particle size of 10 to 40 μm in water.

[0053] In a method for producing methacrylic resin, it is preferable to polymerize the suspension agent dispersed in the suspension polymerization water with an average particle size of 10 to 40 μm. This allows control of the standard deviation of the volume particle size of the methacrylic resin (e.g., methacrylic resin beads), stabilizes the polymerization behavior, reduces the amount of heat removed, and improves productivity.

[0054] The average particle size of a suspension can be adjusted by appropriately selecting the particle size of the suspension used. Furthermore, by mixing powders with different particle sizes, a suspension with an appropriate average particle size can be obtained.

[0055] In the method for producing methacrylic resin, it is preferable to adjust the pH of the aqueous phase to a range of 4 to 7. By setting the pH within this range, the standard deviation of the bead particle size can be controlled, and the polymerization behavior can be stabilized.

[0056] In the method for producing methacrylic resin, it is preferable to first heat the suspension to 50°C to 90°C and then add it to the water (50°C to 90°C) in the reactor. This allows for adjustment of the average particle size and its variation in the methacrylic resin (e.g., methacrylic resin beads).

[0057] Depending on the method of producing methacrylic resin, it is preferable to use an inorganic suspension agent rather than an organic suspension agent. In the case of organic suspension agents, the variation in the average particle size of the beads tends to become too small. Examples of organic suspension agents include polyvinyl alcohol, methylcellulose, ethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, gelatin, and polyvinyl acetate.

[0058] As an inorganic suspension agent, it is preferable to include an inorganic compound containing calcium and / or aluminum, considering stability after dissolution in alkylcyanoacrylate. Examples of inorganic compounds include calcium phosphate such as tricalcium phosphate (tricalcium phosphate), calcium carbonate, and aluminum hydroxide. In particular, from the viewpoint of stability after dissolution, it is more preferable to include an inorganic compound containing aluminum.

[0059] Furthermore, the suspension agent may also contain suspension aids such as polyethylene glycol, sodium ethylenediaminetetraacetate, and sodium lauryl sulfate. The suspension aid may be present in an amount of 0.01 to 10% by mass relative to 100% by mass of the suspension agent.

[0060] The suspension is preferably used by mixing it with the monomer raw material in water.

[0061] <Cleaning method> In the method for producing methacrylic resin, it is preferable to perform operations such as acid washing, water washing, or alkaline washing to remove the suspension agent. The number of times these washing operations are performed can be selected to be optimal based on work efficiency and the efficiency of suspension agent removal, and may be repeated once or multiple times.

[0062] The temperature used for washing should be selected to be optimal considering the efficiency of removing the suspension and the degree of coloration of the resulting polymer, and is preferably between 20 and 100°C. More preferably 30°C or higher, even more preferably 40°C or higher, particularly preferably 50°C or higher, more preferably 95°C or lower, and particularly preferably 80°C or lower.

[0063] Furthermore, the washing time per wash is preferably 10 minutes or more, more preferably 20 minutes or more, preferably 180 minutes or less, and more preferably 150 minutes or less, from the viewpoint of washing efficiency, odor reduction when used as a thickening agent, and solubility in cyanoacrylate.

[0064] The pH of the washing solution used during washing should be within a range that allows for the removal of the suspension agent, but is preferably pH 1 to 12. When acid washing is performed, the pH is preferably pH 1 to 5, and more preferably pH 1.2 to 4, from the viewpoint of the efficiency of suspension agent removal and the color tone of the resulting polymer. The acid used should be one that can remove the suspension agent, and is not particularly specified, but conventionally known inorganic acids and organic acids can be used. Examples of suitable acids include, as inorganic acids, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, etc., and these may be used as diluted solutions diluted with water, etc. Examples of organic acids include those having carboxyl groups, sulfo groups, hydroxyl groups, thiol groups, and enols. Considering the effect of suspension agent removal and the color tone of the resulting resin, nitric acid, sulfuric acid, and organic acids having carboxyl groups are more preferable.

[0065] After acid washing, it is preferable to further wash with water or alkaline water to suppress any undissolved residue in the cyanoacrylate. More preferably, the washing is carried out with hot water at 50°C or higher, and even more preferably, the washing is carried out with hot water at 50°C or higher, followed by further alkaline washing and / or washing with hot water at 50°C or higher.

[0066] By adjusting the pH of the slurry after washing to 2 to 9, preferably 4 to 7, more preferably 5 to 6.8, and especially preferably 5.5 to 6.5, a thickening agent with excellent storage stability and light resistance when dissolved in cyanoacrylate can be obtained.

[0067] (Additives) The thickener of this embodiment may optionally contain other additives. The additives are not particularly limited as long as they exert the effects of the present invention, and may be appropriately selected according to the purpose.

[0068] Examples of additives, though not limited to those listed below, include ultraviolet absorbers, heat stabilizers, light stabilizers; plasticizers; flame retardants; flame retardant aids; curing agents; curing accelerators; antistatic agents; conductivity imparters; stress relaxants; mold release agents; crystallization accelerators; hydrolysis inhibitors; lubricants; impact imparters; sliding properties improvers; compatibilizers; nucleating agents; strengthening agents; flow regulators; dyes; sensitizers; colorants; settling inhibitors; sagging inhibitors; fillers; defoaming agents; light-diffusing fine particles; rust inhibitors; antibacterial agents; antifungal agents; antifouling agents; conductive polymers, etc. The content of additives in the thickener is not particularly limited, but may be, for example, 0.1% by mass or less.

[0069] The thickener of this embodiment may be the methacrylic resin obtained by the method described above, or it may be mixed with other methacrylic resin compositions to form the thickener.

[0070] The thickener of this embodiment is particularly suitable for use as a thickener in cyanoacrylate (preferably alkyl cyanoacrylate, more preferably ethyl cyanoacrylate)-based adhesives.

[0071] Here, as the cyanoacrylate adhesive, it is preferable to have one that contains alkyl cyanoacrylate as the main component (for example, one in which the mass ratio of alkyl cyanoacrylate is 50% by mass or more, more preferably 70% by mass or more, relative to 100% by mass of the adhesive).

[0072] Examples of alkyl cyanoacrylates include cyanoacrylates having alkyl groups with 1 to 10 carbon atoms, such as methyl cyanoacrylate, ethyl cyanoacrylate, propyl cyanoacrylate, isopropyl cyanoacrylate, butyl cyanoacrylate, isobutyl cyanoacrylate, and octyl cyanoacrylate; as well as methoxyethyl cyanoacrylate and ethoxyethyl cyanoacrylate. Ethyl cyanoacrylate is generally the most commonly used.

[0073] [glue] The adhesive of this embodiment comprises the thickener of this embodiment described above and cyanoacrylate (preferably alkylcyanoacrylate). It may also contain the additives described above.

[0074] The adhesive preferably has a viscosity of 0.5 to 10 Pa·s at 25°C. More preferably, it is 1 to 9 Pa·s, and even more preferably, 2 to 8 Pa·s. This range provides an adhesive with excellent handling properties. Methods for adjusting the viscosity of the adhesive to the above range include adjusting the weight-average molecular weight of the methacrylic resin and adjusting the concentration of the methacrylic resin or thickener in the adhesive. Specifically, when using a methacrylic resin with a high weight-average molecular weight, the concentration should be lowered, and when using a methacrylic resin with a low weight-average molecular weight, the concentration should be increased. Generally, a higher weight-average molecular weight is preferable because it allows for a smaller amount to be added, but high molecular weight methacrylic resins may take longer to dissolve, so the concentration should be set appropriately according to the required characteristics of the adhesive. The viscosity is measured using a B-type viscometer.

[0075] Specifically, the concentration is preferably 5-30% by mass of the adhesive, dissolved in cyanoacrylate (preferably alkyl cyanoacrylate, more preferably ethyl cyanoacrylate), more preferably 6-28% by mass, and even more preferably 7-25% by mass.

[0076] The dissolution temperature is preferably 30°C or higher from the viewpoint of ease of dissolution, and preferably 80°C or lower from the viewpoint of stability. [Examples]

[0077] The following examples and comparative examples will provide a more detailed explanation.

[0078] <Raw materials> The raw materials used are as follows: Methyl methacrylate (MMA): Manufactured by Asahi Kasei (contains 2.5 ppm by mass of 2,4-dimethyl-6-t-butylphenol manufactured by Chugai Trading as a polymerization inhibitor) Butyl acrylate (BA): Manufactured by Toagosei (contains 15 ppm by mass of 4-methoxyphenol as a polymerization inhibitor) n-Octyl mercaptan (NOM): Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. 2-Ethylhexylthioglycolate (EHTG): Manufactured by Arkema 3-Tridecyl mercaptopropionate (TMP): Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. n-Dodecyl mercaptan (NDM): Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. t-Dodecyl mercaptan (TDM): Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Dilauroyl peroxide (LPO): Manufactured by Nippon Oil & Fats Co., Ltd. Sodium lauryl sulfate: Manufactured by Fujifilm Wako Pure Chemical Industries, used as a suspension aid. Ethylenediaminetetraacetate tetrasodium dihydrate (EDTA): Manufactured by Kishida Chemical Co., Ltd. Aluminum hydroxide: The average particle size was adjusted by using one or more of Nippon Light Metal's SBX73, B303, B153, and B103, and mixing them as appropriate.

[0079] <Bertz Complexity Index (BertzCT)> The Bertz complexity index (BertzCT) for each chain transfer agent was calculated by inputting the molecular structure into the RDKit library. The calculation results are as follows. NOM 37.8 EHTG 136.9 TMP 195.2 NDM 71.2 TDM 136.9

[0080] <End bond dissociation energy> The terminal bond dissociation energy of each chain transfer agent was determined by the following method. The software used for modeling and calculations was Biovia's Materials Studio 2021.

[0081] (1) Create a syndiotactic MMA trimer using Build Polymer. (2) Remove the hydrogen atom bonded to the terminal α-carbon of the MMA trimer created in (1) to create a model with a tertiary radical. (3) Assemble the molecular structure of the chain transfer agent. If there are many conformers and the stable structure is not obvious, use the COMPASS III force field with the Conformers tool and perform a conformer search including Optimize Geometry to adopt the most stable structure. Remove the hydrogen atoms bonded to the terminal sulfur atoms. (4) A bond is formed between the sulfur atom of (3) and the tertiary radical carbon of the model created in (2). (5) Using the DMol3 tool, optimize the structure with the PBE / DNP+ calculation accuracy, setting the spin multiplicity to Spin restricted and singlet, and selecting Frequency as the Properties. Verify that the optimized structure does not have imaginary frequencies. (6) For structures (2) and (3), the spin multiplicity is set to Spin unrestricted and doublet, and the other calculation conditions are the same as in (5) to perform structural optimization. Confirm that there are no imaginary frequencies in the optimized structure. (7) The bond dissociation energy ΔH is the enthalpy (H) obtained in (5) at a temperature of 298 K. PMMA-CTA ) and the enthalpy (H) at a temperature of 298K obtained in (6) PMMA and H CTA It is calculated using equation (1). ΔH=H PMMA +H CTA ―H PMMA-CTA (1)

[0082] The calculations revealed that the terminal bond dissociation energies were as follows: NOM 48.5kcal / mol EHTG 51.7kcal / mol TMP 51.1kcal / mol

[0083] [I. Manufacturing of methacrylic resin beads used as a thickening agent] (Example 1) -Preparation of suspension- In a container equipped with a stirrer featuring four inclined paddle blades, 5 kg of water, 130 g of aluminum hydroxide with an average particle size of 21 μm, 0.39 g of sodium lauryl sulfate, and 2.3 g of EDTA were added and mixed to obtain a mixture (a1). The average particle size of the suspension in the mixture (a1) was 33 μm, and the pH of the obtained mixture (a1) was 5.5. The obtained mixture (a1) was heated to 70°C.

[0084] -Polymerization reaction- Next, 25 kg of water was added to a 60 L reactor and heated to 80°C. 3 kg of mixed solution (a1), 21 kg of monomer raw materials according to the formulation shown in Table 1, and a monomer solution containing 14.7 g of EHTG, 4.2 g of TMP, and 21 g of LPO were added to the reactor. Suspension polymerization was then carried out while maintaining a temperature of approximately 80°C, and a peak in exothermic reaction was observed 180 minutes after the addition of the monomer solution. The temperature was then raised to 93°C at a rate of 1°C / min, and the temperature was maintained at approximately 93°C for 45 minutes to substantially complete the polymerization reaction and obtain a polymer slurry. Next, the obtained polymer slurry was cooled to 50°C. 20% by mass of sulfuric acid was added to the polymer slurry to dissolve the suspension agent and obtain a polymerization reaction solution. Next, the obtained polymerization reaction solution was sieved through a 1.68 mm mesh to remove aggregates, filtered, and separated into bead-shaped methacrylic resin particles and suspension waste liquid. The pH of the suspension waste liquid was 3.3.

[0085] -Cleaning process- Subsequently, approximately equal amounts of deionized water at about 70°C were added to the bead-shaped methacrylic resin particles, and the mixture was stirred, washed, and filtered. The mixture was then washed again with deionized water at about 70°C (a total of two water washes) to obtain a slurry polymer solution. Sodium hydroxide aqueous solution was added dropwise to the obtained slurry polymer solution to adjust the pH to 8.5, and the mixture was stirred and washed. The slurry polymer solution was filtered, and deionized water at 70°C was added again, followed by stirring and washing. The pH of the obtained slurry polymer solution was 6.1. The slurry polymer solution was then filtered to obtain resin beads. The obtained resin beads were dried using an air-flow dryer at 150°C with an airflow of 30 Nm². 3 After drying in a 25 Nm² fluidized bed dryer (25 Nm² / hr), 3 The methacrylic resin beads were dried at 90°C for 5 minutes at a rate of 1 / hr. The weight-average molecular weight Mw of the obtained methacrylic resin beads was 433,000, and the molecular weight distribution Mw / Mn was 1.9.

[0086] (Examples 2-10, Comparative Examples 1-5) It was prepared using the method described in Table 1 and Table 2.

[0087] [II. Physical Properties of Methacrylic Resin] (II-1)(Weight average molecular weight, molecular weight distribution) The weight-average molecular weight and molecular weight distribution of the methacrylic resin beads obtained in the examples and comparative examples were measured using the following apparatus and conditions. Measurement device: Gel permeation chromatography (HLC-83) manufactured by Tosoh Corporation (20 GPC) Columns used: 1 TSKguardcolumn SuperH-H, 2 TSKgel SuperHM-M, and 1 TSKgel SuperH2500, connected in series in that order. In this column, high molecular weight molecules elute quickly, while low molecular weight molecules elute more slowly. Detector: RI (Differential Refraction) Detector Detection sensitivity: 3.0mV / min Column temperature: 40℃ Sample: 0.02 g of methacrylic resin in a 20 mL solution of tetrahydrofuran. Injection volume: 10μL Developing solvent: tetrahydrofuran, flow rate: 0.6 mL / min 2,6-di-t-butyl-4-methylphenol (BHT) was added at a concentration of 0.1 g / L as an internal standard. As standard samples for the calibration curve, the following 10 types of polymethyl methacrylate (Polymer Laboratories; PMMA Calibration Kit MM-10) with different molecular weights and known monodisperse peak-top molecular weights were used. Peak top molecular weight (Mp) Standard sample 1: 1,916,000 Standard sample 2 625,500 Standard sample 3: 298,900 Standard sample 4 138,600 Standard sample 5 60,150 Standard sample 6 27,600 Standard sample 7 10,290 Standard sample 8 5,000 Standard sample 9 2,810 Standard Document 10 850 Under the above conditions, the RI detection intensity was measured in relation to the elution time of the methacrylic resin. Based on the area of ​​the GPC elution curve and the calibration curve using a cubic approximation formula, the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the methacrylic resin were determined.

[0088] (II-2) (Volume-average particle size) The volume-average particle size (μm) and D90 of methacrylic resin beads were measured using the laser scattering method of a Beckman Coulter LS13320.

[0089] (II-3)<Dissolution rate> Ethyl cyanoacrylate was placed in a 250 mL bottle, and the thickener was added at the concentrations listed in Tables 1 and 2. Dissolution was achieved by shaking at 50°C. Shaking was performed using a BR-40LF shaker manufactured by Taitec, under swirling conditions of 200 rpm and amplitude of 25 mm. A (Good): All dissolved 4 hours after shaking began. B (Good): All dissolved 6 hours after shaking began. C (Poor): Completely dissolved 18 hours after shaking began. D (Inferior): After 18 hours from the start of shaking, undissolved material still remained.

[0090] (II-4)<Initial viscosity> The viscosity η1 (Pa·s) was measured at 25℃. The cyanoacrylate adhesive, dissolved using the same method as described in (II-3) above, was measured using a Type B viscometer (LVDV Next digital viscometer manufactured by Eiko Seiki). 40 mL of syrup was measured into a measuring tube, and the tube was placed in the viscometer to begin viscosity measurement. Viscosity was measured at a spindle rotation speed of 60 rpm. If the measurement range was exceeded at 60 rpm, the rotation speed was reduced.

[0091] (II-5) <Initial Viscosity Evaluation> A (Good): Exceeds 1.0 Pa·s with an additive amount of 8% by weight relative to the weight of the adhesive. B (Good): Exceeds 1.0 Pa·s with an additive amount of 10% by weight relative to the weight of the adhesive. C (Poor): Exceeding 1.0 Pa·s with an additive amount of 12% by weight relative to the weight of the adhesive. D (Inferior): The amount of additive required to exceed 1.0 Pa·s exceeds 12% by weight.

[0092] [III. Evaluation of Thickening Agents] The methacrylic resin beads obtained in the examples and comparative examples were used as thickeners, and the following evaluations were performed.

[0093] (III-1) (Evaluation of stringing suppression) PMMA was dissolved in ethyl cyanoacrylate at a concentration that resulted in an initial viscosity of 0.7-1.0 (Pa·s). A cylindrical jig was then placed in contact with the solution from above, and the stringing was observed by pulling it up at an upward speed of 5 mm / s. A (Good): Stringing is 5mm or less. B (Defective): Stringing exceeds 5mm but is less than 20mm. C (Inferior): Stringiness of 20mm or more

[0094] (Initial viscosity) The viscosity η1 (Pa·s) was measured at 25℃.

[0095] (III-2) (Storage stability at 70°C) The cyanoacrylate adhesive dissolved in the same manner as in (II-3) above was stored (left standing) at 70°C for 10 days. A B-type viscometer (Eiko Seiki Digital Viscometer LVDV Next) was used for viscosity measurement. 40 mL of syrup was measured into a measuring tube, and the measuring tube was placed in the viscometer to start viscosity measurement. Viscosity was measured at a spindle rotation speed of 60 rpm. If the measurement range was exceeded at 60 rpm, the rotation speed was reduced and measurement was performed. Subsequently, viscosity η2 (Pa·s) was measured in the same manner as in (II-5) above. The ratio η2 / η1 of the obtained viscosity η2 to η1 obtained in (II-5) was calculated, and the storage stability at 70°C was evaluated according to the following evaluation criteria. A (Good): η2 / η1 is less than 1.5 B (Poor): η2 / η1 is 1.5 or greater and less than 2.0 C (Inferior): η2 / η1 is 2.0 or higher

[0096] The results of each measurement and evaluation are shown in Tables 1 and 2.

[0097] [Table 1]

[0098] [Table 2] [Industrial applicability]

[0099] According to the present invention, it is possible to provide a thickening agent that can achieve the desired viscosity with a small amount of addition and does not string after dissolution.

Claims

1. A method for producing a thickener containing 90% by mass or more of methacrylic resin, The process includes polymerizing monomers using two or more chain transfer agents with a Bertz complexity index (BertzCT) of 40 or higher to produce the methacrylic resin, The weight-average molecular weight of the methacrylic resin is 400,000 to 1,000,000. A method for producing a thickening agent.

2. The method for producing a thickening agent according to claim 1, wherein at least one of the chain transfer agents is a chain transfer agent with a Bertz complexity index (BertzCT) of 150 or more.

3. The method for producing a thickening agent according to claim 1 or 2, wherein at least two of the chain transfer agents are a chain transfer agent with a Bertz complexity index (BertzCT) of 40 or more and less than 150, and a chain transfer agent with a Bertz complexity index (BertzCT) of 150 or more.

4. A method for producing a thickener according to claim 1 or 2, wherein the weight-average molecular weight of the methacrylic resin is 800,000 to 1,000,000.

5. A method for producing a thickener according to claim 1 or 2, wherein the methacrylic resin is bead-shaped and has a D90 (90% particle size) of less than 300.

6. At least one of the aforementioned chain transfer agents, A chain transfer agent having a thiol group and a C-S bond dissociation energy ΔH of 50 kcal / mol or more when bonded to the end of a methyl methacrylate (MMA) trimer. A method for producing a thickening agent according to claim 1 or 2.

7. A method for producing a thickener containing 90% by mass or more of methacrylic resin, The process includes polymerizing monomers using a chain transfer agent with a Bertz complexity index (BertzCT) of 150 or higher to produce the methacrylic resin, The weight-average molecular weight of the methacrylic resin is 400,000 to 1,000,000. A method for producing a thickening agent.

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