Thickener and adhesive composition

Abstract

A purpose of the present invention is to provide a thickener which is suitable for use as a thickener for adhesives and which, when used as a thickener for adhesives, especially cyanoacrylate-based adhesives, makes the adhesives have excellent long-term storage stability. The thickener includes a methacrylic resin having an Mw of 85,000-1,500,000. When the 25°C viscosity of an ethyl cyanoacrylate solution of the methacrylic resin is expressed by ƞ1 and the 25°C viscosity of the solution which has been allowed to stand at 60°C for 48 hours and then cooled to 25°C is expressed by ƞ2, then 1.0≤ƞ2 / ƞ1≤5.0 is satisfied (the solution has a methacrylic resin concentration of 20, 10, or 7 mass% depending on the Mw of the methacrylic resin).

Description

Technical Field

[0001] The present invention relates to a thickener and an adhesive composition.

Background Art

[0002] In the production of paints or adhesives, organic thickeners are used for the purpose of adjusting the viscosity of products to improve handleability. 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 cyanoacrylate and the like. Since the methacrylic resin composition dissolves rapidly in the monomer while maintaining transparency, it is widely used as a thickener for adhesives.

[0003] Among adhesives, cyanoacrylate adhesives in particular can start polymerization by weak anions such as slight moisture or impurities due to the high anionic polymerizability of the main component, alkyl cyanoacrylate, and can firmly bond various materials in a short time. Therefore, as instant adhesives, they are used in a wide range of fields such as industrial, medical, and household applications.

[0004] Due to its high polymerizability, cyanoacrylate adhesives are transported and stored in an environment that is somewhat blocked from the outside air, such as in a sealed container. However, cyanoacrylate adhesives may be handled under high-temperature and high-humidity conditions depending on the transportation, storage, or use conditions. When left under such conditions for a long time, the viscosity of the cyanoacrylate adhesive may increase, so improvements are required.

[0005] In addition, cyanoacrylate adhesives may have a peculiar odor due to the thickener contained in the adhesive, and reduction of the odor is also required.

[0006] Patent Document 1 discloses an acrylic thickener having excellent solubility in methyl methacrylate and having a characteristic molecular weight distribution.

[0007] Patent Document 2 discloses a thickener containing a methacrylic resin having excellent stability when exposed in methyl methacrylate at 50 ° C. under 95% Rh.

[0008] Patent Document 3 describes that a poly(alkyl methacrylate) having a weight average molecular weight of 200,000 to 500,000 is contained as a thickener in a cyanoacrylate-based adhesive composition.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] Patent Document 1 does not describe the solubility in alkyl cyanoacrylate and the long-term storage stability when dissolved in alkyl cyanoacrylate which is likely to polymerize due to the influence of a small amount of moisture or impurities.

[0011] Patent Document 2 provides a thickener having excellent long-term stability in methyl methacrylate by introducing a specific structure at the end of the resin, but does not describe the long-term stability in alkyl cyanoacrylate.

[0012] Patent Document 3 constitutes a cyanoacrylate-based adhesive by adding various stabilizers, and does not describe the contribution of the acrylic thickener itself to stabilization.

[0013] Therefore, in the present invention, it is an object to provide a thickener that can be suitably used as a thickener for adhesives, and particularly has excellent long-term storage stability when used as a thickener for cyanoacrylate adhesives.

Means for Solving the Problems

[0014] As a result of intensive studies to solve the above problems, the present inventors surprisingly found that a thickener with excellent long-term storage stability can be obtained when the viscosity change rate when left at 60°C for 48 hours after dissolving in ethyl cyanoacrylate is within a specific range, and thus completed the present invention.

[0015] That is, the present invention is as follows. [1] A thickener containing a methacrylic resin having a weight average molecular weight (Mw) of 85,000 to 1,500,000, wherein the viscosity (Pa·s) of the ethyl cyanoacrylate solution of the methacrylic resin at 25°C is η1, when the solution is left at 60°C for 48 hours and then cooled to 25°C, and the viscosity (Pa·s) of the solution at 25°C after cooling is η2, η1 and η2 satisfy 1.0 ≦ η2 / η1 ≦ 5.0 (provided that when the Mw of the methacrylic resin is 85,000 or more and less than 300,000, the concentration of the methacrylic resin in the solution is 20% by mass, when the Mw of the methacrylic resin is 300,000 or more and less than 800,000, the concentration of the methacrylic resin in the solution is 10% by mass, when the Mw of the methacrylic resin is 800,000 or more and 1,500,000 or less, the concentration of the methacrylic resin in the solution is 7% by mass)), a thickener. [2] The thickener according to [1], wherein the methacrylic resin contains 90 to 99.9% by mass of methyl methacrylate monomer units and 0.1 to 10% by mass of alkyl acrylate monomer units. [3] The thickener according to [2], wherein the alkyl group of the alkyl acrylate monomer unit has 4 or more carbon atoms. [4] The thickener according to [1], wherein the methacrylic resin contains 90 to 99.9% by mass of methyl methacrylate monomer units and 0.1 to 10% by mass of aromatic vinyl monomer units. [5] The methacrylic resin contains 90 to 99.8% by mass of methyl methacrylate monomer units, 0.1 to 8% by mass of aromatic vinyl monomer units and Alkyl 0.1 to 8% by mass of acrylic acid monomer units. The thickener according to [4]. [6] The thickener according to [5], wherein the alkyl group of the alkyl acrylate monomer unit has 4 or more carbon atoms. [7] The thickener according to any one of [1] to [3], wherein the methacrylic resin has a moisture content of 0.01% or more and 1% or less as measured by the drying method. [8] The thickener according to any one of [1] to [4], wherein the methacrylic resin is in the form of beads having an average particle diameter of 50 to 500 μm. [9] The thickener according to [5], wherein the mass ratio of particles having a particle diameter of 710 μm or more is 5% or less with respect to 100% by mass of the thickener.

[10] A cyanoacrylate-based adhesive composition containing 1 to 30% of the thickener according to any one of [1] to [6].

Advantages of the Invention

[0016] According to the present invention, it can be suitably used as a thickener for adhesives. In particular, when used as a thickener for cyanoacrylate-based adhesives, it can suppress an increase in viscosity and solidification during storage of the thickening target, and improve the storage stability of the product. A thickener can be provided.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments 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 can be variously modified and implemented within the scope of the gist thereof.

[0018] In the present embodiment, the "methacrylic resin" refers to a resin containing 80% by mass or more of methyl methacrylate monomer units as monomer units and having a weight average molecular weight (Mw) of 85,000 to 1,500,000, unless otherwise specified.

[0019] [Thickener] The thickener of the present embodiment contains at least a methacrylic resin. The thickener may contain only the methacrylic resin, or may contain the methacrylic resin and other resins. It is preferable that the resin component of the thickener is only the methacrylic resin. Also, the thickener may contain the methacrylic resin alone or in combination of two or more. In one example, it is more preferable that the thickener consists of only a single methacrylic resin as the resin component.

[0020] The thickener can be suitably used as a thickener for adhesives, particularly as a thickener for cyanoacrylate adhesives.

[0021] [Viscosity ratio] In the present embodiment, when the viscosity (Pa·s) of the ethyl cyanoacrylate solution of the methacrylic resin at 25°C is η1, the solution is left at 60°C for 48 hours, cooled to 25°C, and the viscosity (Pa·s) of the solution at 25°C after cooling is η2, 1.0 ≤ η2 / η1 ≤ 5.0 is satisfied for η1 and η2. By making η2 / η1 (hereinafter sometimes simply referred to as "the ratio of η") be 1.0 or more and 5.0 or less, even when the thickener is dissolved in alkyl cyanoacrylate and left at room temperature for a long time (for example, several months), the viscosity and adhesive performance can be maintained.

[0022] The temperature for dissolving the methacrylic resin in ethyl cyanoacrylate is preferably 50°C or higher. After dissolving the methacrylic resin, the temperature of the solution is set to 25°C and the viscosity η1 is measured.

[0023] After measuring the viscosity η1 of the solution at 25°C, the temperature of the solution is raised to 60°C. Then, the solution is left standing at 60°C for 48 hours, cooled to 25°C, and the viscosity η2 of the solution at 25°C after cooling is measured. Here, leaving the solution standing at 60°C for 48 hours means that the elapsed time since the solution was placed in an oven at 60°C is between 48 ± 1 hours.

[0024] As means for adjusting the ratio of η to be 1.0 or more and 5.0 or less, copolymerizing a certain amount of an alkyl acrylate monomer unit, copolymerizing a small amount of an aromatic vinyl monomer unit, adjusting the moisture content of the methacrylic resin, reducing the weight ratio of particles with a particle size of 710 μm or more, performing acid / alkali washing so that the pH of the aqueous phase when the thickener is dispersed in water is 2 or more and 9 or less, reducing impurities in the thickener as much as possible, etc. can be mentioned, and it is preferable to combine a plurality of these.

[0025] The ratio of η is preferably 1.0 or more and 4.5 or less, more preferably 1.0 or more and 4.0 or less. If the ratio of η is less than 1.0, the viscosity will decrease after dissolution and it will not function as a thickener. If the ratio of η exceeds 5.0, there is a risk of solidification when stored for a long time such as several months or when the temperature rises during transportation, or the strength as an adhesive after solidification may be inferior.

[0026] The concentration of the methacrylic resin in the ethyl cyanoacrylate solution is 20% by mass when the Mw of the methacrylic resin is 85,000 or more and less than 300,000, 10% by mass when the Mw of the methacrylic resin is 300,000 or more and less than 800,000, and 7% by mass when the Mw of the methacrylic resin is 800,000 or more and 1,500,000 or less.

[0027] When the ethyl cyanoacrylate solution contains methacrylic resins with different Mw ranges, the Mw of the entire methacrylic resin may be measured, and the above concentration may be determined from the Mw.

[0028] (Methacrylic resin) The methacrylic resin preferably contains 90 to 99.9% by mass of methyl methacrylate monomer units and 0.1 to 10% 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. As the alkyl acrylate monomer unit having an alkyl group having 4 or more carbon atoms, monomer units derived from alkyl acrylates having an alkyl group having 4 to 8 carbon atoms such as n-butyl acrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, etc. are preferably used. From the viewpoint of reducing the odor of the cyanoacrylate solution of the methacrylic resin, the number of carbon atoms of the alkyl group of the alkyl acrylate monomer unit is preferably 4 to 8. From the viewpoints of easy availability and reducing the odor during dissolution in cyanoacrylate, the n-butyl acrylate monomer unit is particularly preferred.

[0030] The methacrylic resin may be composed only of methyl methacrylate monomer units and alkyl acrylate monomer units having an alkyl group having 4 or more carbon atoms, or 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, they include alkyl methacrylates having an alkyl group with 2 to 18 carbon atoms; alkyl acrylates having an alkyl group with 1 to 3 carbon atoms; α,β-unsaturated acids such as acrylic acid and methacrylic acid; unsaturated group-containing dibasic carboxylic acids such as maleic acid, fumaric acid, and itaconic acid and their alkyl esters; aromatic vinyl compounds such as styrene, α-methylstyrene, and styrene having a substituent on the benzene ring; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; maleic anhydride, maleimide, N-substituted maleimide; ethylene glycol or its oligomer with both terminal hydroxyl groups esterified with acrylic acid or methacrylic acid, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate; compounds obtained by esterifying the hydroxyl groups of two alcohols such as neopentyl glycol di(meth)acrylate and di(meth)acrylate with acrylic acid or methacrylic acid; compounds obtained by esterifying polyhydric alcohol derivatives such as trimethylolpropane and pentaerythritol with acrylic acid or methacrylic acid; polyfunctional monomers such as divinylbenzene; etc. These can be used alone or in combination of two or more. From the perspective of odor suppression, when containing an alkyl acrylate having an alkyl group with 1 to 3 carbon atoms, the mass ratio of the monomer unit derived from the alkyl acrylate having an alkyl group with 1 to 3 carbon atoms is preferably less than 0.1% by mass, more preferably not containing, based on 100% by mass of all monomer units constituting the methacrylic resin.

[0032] From the perspective of odor suppression when dissolved (for example, when dissolved in alkyl cyanoacrylate), the mass ratio of the monomer unit derived from methyl methacrylate is preferably 90 to 99.9% by mass based on 100% by mass of the methacrylic resin. More preferably 95 to 99.8% by mass, still more preferably 97 to 99.8% by mass, and particularly preferably 98 to 99.8% by mass.

[0033] The mass ratio of the alkyl acrylate monomer unit to 100% by mass of the methacrylic resin is preferably 0.1 to 10% by mass. More preferably, it is 0.2 to 5% by mass, still more preferably 0.2 to 3% by mass, and particularly preferably 0.2 to 2% by mass. When it exceeds 5% by mass, when dissolved in alkyl cyanoacrylate or the like, a peculiar odor is generated due to the remaining alkyl acrylate monomer, impurities derived therefrom, etc., which is not preferable. When it is less than 0.1% by mass, the effect of improving the odor obtained by copolymerizing the alkyl acrylate monomer unit is not exhibited, which is not preferable.

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

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

[0036] From the viewpoint of improving the storage stability of the cyanoacrylate-based adhesive, the methacrylic resin preferably contains an aromatic vinyl monomer unit. Regarding the mechanism by which the storage stability of the cyanoacrylate-based adhesive can be improved by the aromatic vinyl monomer unit, it is presumed that a monomer having a weak electron-withdrawing property of the aromatic group and a low anionic polymerizability is incorporated.

[0037] The methacrylic resin preferably contains 90 to 99.9% by mass of methyl methacrylate monomer units and 0.1 to 10% by mass of aromatic vinyl monomer units. In one embodiment, the aromatic vinyl monomer units are monomer units derived from styrene.

[0038] In one embodiment, the content of the aromatic vinyl monomer units is 0.2% by mass or more, 0.3% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, 2.0% by mass or more, 2.5% by mass or more, 3.0% by mass or more, 3.5% by mass or more, 4.0% by mass or more, 4.5% by mass or more, 5.0% by mass or more, 6.0% by mass or more, 7.0% by mass or more, 8.0% by mass or more, or 9.0% by mass or more with respect to 100% by mass of the methacrylic resin. In another embodiment, the content of the aromatic vinyl monomer units is 10.0% by mass or less, 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, 4.5% by mass or less, 4.0% by mass or less, 3.5% by mass or less, 3.0% by mass or less, 2.5% by mass or less, 2.0% by mass or less, 1.5% by mass or less, 1.0% by mass or less, or 0.5% by mass or less with respect to 100% by mass of the methacrylic resin. If it exceeds 10% by mass, the production efficiency deteriorates, and a peculiar odor may be generated by the remaining aromatic vinyl monomer, which is not preferable. If it is less than 0.1% by mass, the effect of improving the storage stability when added as a thickener to the cyanoacrylate adhesive cannot be obtained, which is not preferable.

[0039] In one embodiment, the methacrylic resin contains 90 to 99.9% by mass of methyl methacrylate monomer units and a total of 0.1 to 10% by mass of one or more selected from the group consisting of alkyl acrylate monomer units and aromatic vinyl monomer units.

[0040] <Weight average molecular weight> The methacrylic resin has a weight-average molecular weight measured by gel permeation chromatography (GPC) of 85,000 to 1,500,000. If Mw is less than 85,000, the amount of thickener used to make the syrup (a solution in which the methacrylic resin is dissolved) reach a predetermined viscosity increases, and the mechanical properties of the resulting adhesive or the like may be inferior, which is not preferable. On the other hand, from the viewpoints of solubility and property stability, Mw is 1,500,000 or less. Particularly preferred molecular weights vary depending on the desired viscosity and required properties when dissolved. However, when used at a relatively low viscosity or when it is desired to improve the dissolution rate, 85,000 or more and less than 300,000 is preferable. On the other hand, when used at a high viscosity or when it is desired to obtain the desired viscosity with a small addition, 300,000 or more and 1,500,000 or less is preferable.

[0041] <Moisture content> The methacrylic resin preferably has a moisture content of 0.01% or more and 1% or less. If an attempt is made to further suppress the moisture content, there may be a need for drying for a long time. From the viewpoint of productivity, it is preferably 0.01% or more. On the other hand, if it exceeds 1%, the storage stability after dissolution in cyanoacrylate such as ethyl cyanoacrylate tends to deteriorate, so it is preferably 1% or less. More preferably, it is 0.01% or more and 0.8% or less, still more preferably 0.02% or more and 0.7% or less, and most preferably more than 0.03% and less than 0.7%. Depending on the usage mode, the storage period of the thickener before dissolving the thickener of the present invention in an adhesive such as a cyanoacrylate-based adhesive may be long, and during that time, the methacrylic resin absorbs moisture, so it is preferable to reduce the initial moisture of the methacrylic resin as much as possible.

[0042] Here, the moisture content can be measured by the method described in the examples below and is measured by a drying method. The drying method is a method in which 10.0 g of the methacrylic resin is held at 70°C, the measurement is terminated when the weight loss rate for 10 seconds becomes 0.02% or less, and the total weight loss rate is taken as the moisture content.

[0043] The moisture content of the methacrylic resin (e.g., pellet or bead methacrylic resin) can be adjusted, for example, by a drying method such as that for a slurry after polymerization.

[0044] As methods for drying the methacrylic resin, there are hot air drying in which hot air is sent into a tank from a hot air blower or a blow heater to perform drying, vacuum drying in which the system is depressurized and then heated as necessary to perform drying, barrel drying in which the obtained polymer is rotated in a container to remove moisture, spin drying in which drying is performed using centrifugal force, pneumatic drying in which the resin in a pipe is dried while being transferred by hot air, fluidized bed dryers in which drying is performed at a specific temperature for a certain time and then the bottom of the tank opens and the material falls into the next drying tank, and the like.

[0045] In order to make the moisture content within the above range, after suspension polymerization is completed, it is preferable to dry the obtained slurry with a pneumatic dryer and / or a fluidized bed dryer. At this time, if the final moisture content is low, the treatment takes a long time, resulting in poor productivity, and problems such as poor pump-up may occur in the slurry feeding process.

[0046] The thickener of this embodiment can be used in the production of syrup for artificial marble, paints, adhesives, and the like.

[0047] The thickener of this embodiment is particularly preferably used for cyanoacrylate adhesives. Here, as the cyanoacrylate adhesive, those containing alkyl cyanoacrylate as the main component (for example, those having a mass ratio of alkyl cyanoacrylate of 50% by mass or more, more preferably 70% by mass or more, based on 100% by mass of the adhesive) are preferable.

[0048] Examples of the alkyl cyanoacrylate include cyanoacrylates having an alkyl group with 1 to 10 carbon atoms, such as methyl cyanoacrylate, ethyl cyanoacrylate, propyl cyanoacrylate, isopropyl cyanoacrylate, butyl cyanoacrylate, isobutyl cyanoacrylate, and octyl cyanoacrylate; and methoxyethyl cyanoacrylate, ethoxyethyl cyanoacrylate, etc. Generally, ethyl cyanoacrylate is often used.

[0049] The ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of the methacrylic resin, measured by gel permeation chromatography (GPC), is preferably 1.7 or more and 2.5 or less. From the viewpoint of ease of production, it is more preferably 1.8 or more. Also, from the viewpoints of suppressing undissolved residues during dissolution and improving solubility, it is more preferably less than 2.5, still more preferably 2.4 or less, particularly preferably 2.3 or less, and especially preferably less than 2.3.

[0050] The weight average molecular weight and the number average molecular weight are measured by GPC. In advance, a standard methacrylic resin that is available as a reagent with a known monodisperse weight average molecular weight and an analytical gel column eluted from a high molecular weight component are used to create a calibration curve from the elution time and the weight average molecular weight. The molecular weight of each sample can be measured from the calibration curve. Specifically, it may be measured by the method described in the examples below.

[0051] The shape of the methacrylic resin is not particularly defined, but it is preferably in the form of pellets, flakes, beads, or powder. From the viewpoints of shortening the dissolution time and reducing undissolved matter, it is preferably in the form of beads or powder.

[0052] <Volume average particle diameter> In the case of using methacrylic resin in the form of beads, the volume average particle diameter is preferably 50 to 500 μm. Since the dissolution time becomes shorter as the particle diameter becomes smaller, it is preferably 450 μm or less, and from the viewpoint of suppressing the scattering of beads during work and reducing undissolved matter, it is preferably 50 μm or more. The volume average particle diameter is more preferably 70 to 400 μm, and most preferably 100 to 350 μm.

[0053] In this specification, the volume average particle diameter refers to the volume particle diameter that can be measured by the method described in the examples below.

[0054] The mass ratio of particles having a particle diameter of 710 μm or more to 100% by mass of methacrylic resin (preferably methacrylic resin beads) is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, particularly preferably 0.5% by mass or less, and especially preferably 0.1% by mass or less, from the viewpoints of obtaining high solubility in alkyl cyanoacrylate and adjusting the ratio of η. The mass ratio of particles having a particle diameter of 710 μm or more can be measured, for example, by the method described in the examples below. Examples of the method for adjusting the mass ratio of particles having a particle diameter of 710 μm or more include reducing the particle diameter of the suspending agent and performing polymerization under stable conditions.

[0055] <Polymerization method> The methacrylic resin can be produced, for example, using a monomer constituting the methacrylic resin, a polymerization initiator, a chain transfer agent, a suspending agent, and other additives.

[0056] As polymerization initiators, when using free radical polymerization, peroxide-based initiators such as di-t-butyl peroxide, lauryl peroxide, dilauroyl peroxide, t-butyl peroxy 2-ethylhexanoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, etc., and azo-based general radical polymerization initiators such as azobisisobutyronitrile, azobisisovaleronitrile, 1,1-azobis(1-cyclohexanecarbonitrile), etc. can be used. These can be used alone or in combination of two or more. These radical initiators may be combined with a suitable reducing agent and implemented as a redox initiator.

[0057] The polymerization initiator is generally used in the range of 0.001 to 1% by mass based on 100% by mass of the total mass of the monomers.

[0058] In the method for producing a methacrylic resin, when produced by radical polymerization, a commonly used chain transfer agent can be used to adjust the molecular weight.

[0059] As the chain transfer agent, for example, mercaptans such as n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris(thioglycolate), pentaerythritol tetrakis(thioglycolate) are preferably used.

[0060] 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.

[0061] As the polymerization method of the methacrylic resin, suspension polymerization or emulsion polymerization is preferably used. Suspension polymerization gives particulate resins and emulsion polymerization gives powdered resin beads, which is operationally advantageous when dissolving an appropriate amount as a thickening agent to adjust the syrup to the desired viscosity.

[0062] Since the polymerization time of suspension polymerization is shorter than that of emulsion polymerization, suspension polymerization is preferred.

[0063] Especially when using the suspension polymerization method, it is preferable that the molecular weight distribution is within the above-mentioned range. When it is required to highly suppress the generation of unmelted matter due to the width of the molecular weight distribution during dissolution in cyanoalkyl acrylate or the like and maintain high storage stability after dissolution, it is preferable that it is obtained by suspension polymerization in one stage rather than multi-stage polymerization in which the molecular weight distribution becomes wide. In the case of two-stage polymerization, impurities derived from the suspending agent increase, which is not preferable.

[0064] Also, as a polymerization method of the methacrylic resin, it is preferable to use a method in which a suspending agent having an average particle diameter of 10 to 40 μm is dispersed in water and polymerized. Among them, it is preferable to perform one-stage suspension polymerization by dispersing a suspending agent having an average particle diameter of 10 to 40 μm in water.

[0065] In the method for producing a methacrylic resin, it is preferable to polymerize with the average particle diameter of the suspending agent dispersed in the suspension polymerization water being 10 to 40 μm. Thereby, the standard deviation of the volume particle diameter of the methacrylic resin (for example, methacrylic resin beads) can be controlled, the polymerization behavior is stabilized, the amount of heat generated gradually decreases, and the productivity can be improved.

[0066] The average particle diameter of the suspending agent can be adjusted by appropriately selecting the particle diameter of the suspending agent to be used. Furthermore, by mixing powders having different particle diameters, a suspending agent having an appropriate average particle diameter can be obtained.

[0067] In the method for producing a methacrylic resin, it is preferable to adjust the pH of the aqueous phase to the range of 4 to 7. By bringing the pH into the said range, the standard deviation of the particle diameter of the beads can be controlled and the polymerization behavior can be stabilized.

[0068] In the method for producing a methacrylic resin, it is preferable to preliminarily heat the suspending agent to 50°C to 90°C for adjustment and then introduce it into water (50°C to 90°C) in the reactor. Thereby, the average particle diameter of the methacrylic resin (for example, methacrylic resin beads) and its variation can be adjusted.

[0069] Depending on the method for producing a methacrylic resin, it is preferable to use an inorganic suspending agent rather than an organic suspending agent. In the case of an organic suspending agent, the variation in the average particle diameter of the beads tends to become too small. Here, examples of the organic suspending agent include polyvinyl alcohol, methyl cellulose, ethyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, gelatin, polyvinyl acetate, and the like.

[0070] As the inorganic suspending agent, considering the stability after dissolution in alkyl cyanoacrylate and the like, it is preferable to contain an inorganic compound containing calcium and / or aluminum. For example, calcium phosphates such as tricalcium phosphate (calcium phosphate tribasic), calcium carbonate, and inorganic compounds such as aluminum hydroxide can be mentioned. In particular, from the viewpoint of stability after dissolution, it is more preferable to contain an inorganic compound containing aluminum.

[0071] Further, the suspending agent may further contain suspending aids such as polyethylene glycol, sodium ethylenediaminetetraacetate, and sodium lauryl sulfate. The suspending aid may be contained in an amount of 0.01 to 10% by mass based on 100% by mass of the suspending agent.

[0072] The suspending agent is preferably mixed and used with the monomer raw material in water.

[0073] <Washing method> In the method for producing a methacrylic resin, for removing the suspending agent, it is preferable to perform operations such as acid washing, water washing, and alkali washing. The number of times of performing these washing operations may be selected as an optimal number from the working efficiency and the removal efficiency of the suspending agent, and it may be repeated once or a plurality of times.

[0074] When performing washing, an optimal temperature can be selected considering factors such as the removal efficiency of the suspending agent and the degree of coloring of the resulting polymer, and it is preferably 20 to 100 °C. More preferably, it is 30 to 95 °C, still more preferably 40 to 95 °C, and particularly preferably 50 to 80 °C.

[0075] Also, the washing time per wash during washing is preferably 10 to 180 minutes, more preferably 20 to 150 minutes, from the viewpoints of washing efficiency, reduction of odor when used as a thickener, and dissolution stability in cyanoacrylate.

[0076] The pH of the cleaning solution used during cleaning may be within a range where the suspending agent can be removed, but is preferably pH 1 to 12. When performing acid cleaning, the pH is preferably pH 1 to 5, more preferably pH 1.2 to 4, from the viewpoints of the removal efficiency of the suspending agent and the color tone of the resulting polymer. The acid used in that case may be any that can remove the suspending agent and is not particularly specified, but conventionally known inorganic acids and organic acids can be used. As an example of a preferably used acid, inorganic acids include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, etc., and they may be used as diluted solutions diluted with water or the like. Organic acids include those having a carboxyl group, a sulfo group, a hydroxy group, a thiol group, or an enol. Considering the removal effect of the suspending agent and the color tone of the resulting resin, nitric acid, sulfuric acid, and organic acids having a carboxyl group are more preferable.

[0077] After acid cleaning, it is preferably further washed with water or alkali washed from the viewpoint of suppressing undissolved matter during dissolution in cyanoacrylate. More preferably, it is a method of performing washing with warm water at 50 °C or higher, and still more preferably, after performing washing with warm water at 50 °C or higher, further alkali washing and / or washing with warm water at 50 °C or higher are performed.

[0078] By adjusting the pH of the slurry after washing to 2 or more and 9 or less, preferably 4 or more and 7 or less, more preferably 5 or more and 6.8 or less, and particularly preferably 5.5 or more and 6.5 or less, a thickener excellent in storage stability and light resistance when dissolved in cyanoacrylate can be obtained.

[0079] (Additive) The thickener of the present embodiment may optionally contain other additives. The additives are not particularly limited as long as the effects of the present invention can be exhibited, and may be appropriately selected according to the purpose.

[0080] Examples of the additives include, but are not limited to, ultraviolet absorbers, heat stabilizers, light stabilizers; plasticizers; flame retardants; flame retardant aids; curing agents; curing accelerators; antistatic agents; conductivity imparting agents; stress relaxants; mold release agents; crystallization accelerators; hydrolysis inhibitors; lubricants; impact imparting agents; sliding property improvers; compatibilizers; nucleating agents; reinforcing agents; flow regulators; dyes; sensitizers; colorants; anti-settling agents; anti-sagging agents; fillers; defoaming agents; light diffusing fine particles; rust preventives; antibacterial agents; antifungal agents; antifouling agents; conductive polymers, etc.

[0081] The thickener of the present embodiment may use the methacrylic resin obtained by the above method as the thickener as it is, or may be further mixed with other methacrylic resin compositions to be used as a thickener.

[0082] The thickener of the present embodiment can be suitably used particularly for applications of cyanoacrylate (preferably alkyl cyanoacrylate, more preferably ethyl cyanoacrylate) - based thickeners.

[0083] The mass ratio of the methacrylic resin 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 with respect to 100% by mass of the thickener.

[0084] <YI value of acetone solution> The tackifier preferably has a Yellowness Index (YI) value of 0.1 to 2, more preferably 0.2 to 1.9, and even more preferably 0.3 to 1.8, as measured in a 1 cm thick cell after dissolving the tackifier in acetone at a concentration of 10% by mass.

[0085] Also, the methacrylic resin contained in the tackifier preferably has a YI value of 0.1 to 2, more preferably 0.2 to 1.9, and even more preferably 0.3 to 1.8, as measured in a 1 cm thick cell after dissolving it in acetone at a concentration of 10% by mass.

[0086] By having the YI value within the above range, an adhesive excellent in stability, hue, and light resistance after dissolution can be obtained. Examples of the method for setting the YI value within the above range include a method of obtaining a methacrylic resin by one-stage polymerization instead of two-stage polymerization.

[0087] <pH of the aqueous phase when the tackifier is dispersed in water> For the tackifier, after stirring and dispersing 20 g of the tackifier and 100 g of pure water and then allowing it to stand to precipitate the solid content, the pH of the supernatant aqueous phase measured at room temperature is preferably 2 or more and 9 or less. From the viewpoint of maintaining a particularly good hue when the tackifier is dissolved and used, suppressing the solubility in cyanoacrylate, and the odor derived from the residue, it is more preferably 3 or more, and particularly preferably 3.5 or more. From the viewpoint of enhancing the storage stability after dissolution in cyanoacrylate or the like, it is preferably 8.5 or less, more preferably 8 or less, and particularly preferably 7.5 or less.

[0088] Also, after stirring and dispersing 20 g of methacrylic resin contained in the thickener and 100 g of pure water, and allowing it to stand, after sedimenting the solid content, the pH of the supernatant liquid aqueous phase measured at room temperature is preferably 2 or more and 9 or less. From the viewpoints of maintaining particularly good hue when dissolving and using the thickener, solubility in cyanoacrylate, and suppressing the odor derived from the residue, it is more preferably 3 or more, particularly preferably 3.5 or more. From the viewpoint of enhancing the storage stability after dissolution in cyanoacrylate or the like, it is preferably 8.5 or less, more preferably 8 or less, particularly preferably 7.5 or less.

[0089] <Mass ratio of particles with a particle size of 710 μm or more> The mass ratio of particles with a particle size of 710 μm or more to 100% by mass of the thickener is preferably 5% by mass or less, more preferably 3% by mass or less, further preferably 1% by mass or less, particularly preferably 0.5% by mass or less, and especially preferably 0.1% by mass or less from the viewpoint of obtaining high solubility in the cyanoacrylate-based adhesive. The mass ratio of particles with a particle size of 710 μm or more can be measured, for example, by the method described in the examples below.

[0090] [Adhesive] The thickener of this embodiment is preferably used in a cyanoacrylate-based adhesive. Here, the cyanoacrylate-based adhesive contains the thickener of this embodiment and cyanoacrylate (preferably, alkyl cyanoacrylate). It may further contain an additive.

[0091] The adhesive preferably has a viscosity of 0.5 to 10 Pa·s at 25°C. Here, this viscosity is the viscosity measured with a B-type viscometer.

[0092] More preferably, it is 1 to 9 Pa·s, and still more preferably 2 to 8 Pa·s. By being in this range, an adhesive with excellent handleability can be obtained. As a method for adjusting the viscosity of the adhesive to the above range, adjusting the weight average molecular weight of the methacrylic resin, adjusting the concentration of the methacrylic resin or the thickener in the adhesive, etc. can be mentioned.

[0093] Specifically, it is preferably dissolved in cyanoacrylate (preferably alkyl cyanoacrylate, more preferably ethyl cyanoacrylate) at a mass percentage concentration of 10 to 30% with respect to 100% by mass of the adhesive, more preferably at a mass percentage concentration of 12 to 28%, and even more preferably at a mass percentage concentration of 15 to 25%.

[0094] The temperature for dissolution 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

[0095] It will be further specifically described using the following examples and comparative examples. <Raw materials> The raw materials used are as follows. Methyl methacrylate (MMA): manufactured by Asahi Kasei (containing 2.5 mass ppm of 2,4-dimethyl-6-t-butylphenol manufactured by Chugai Boeki as a polymerization inhibitor) Methyl acrylate (MA): manufactured by Mitsubishi Chemical (containing 15 ppm of 4-methoxyphenol as a polymerization inhibitor) Butyl acrylate (BA): manufactured by Toagosei (containing 15 mass ppm of 4-methoxyphenol as a polymerization inhibitor) Styrene (St): manufactured by Asahi Kasei Corporation (containing 12 ppm of 4-t-butylcatechol as a polymerization inhibitor) Ethylhexyl acrylate (EHA): manufactured by Tokyo Chemical Industry n-Octyl mercaptan (NOM): manufactured by Arkema 2-Ethylhexyl thioglycolate (EHTG): manufactured by Arkema Lauroyl peroxide (LPO): manufactured by NOF Corporation Tricalcium phosphate manufactured by Nippon Chemical Industry Calcium carbonate: manufactured by Nitto Funka Kogyo, NN#200, average particle size 14.8 μm Sodium lauryl sulfate: manufactured by Fujifilm Wako Pure Chemical Industries, used as a suspension aid Ethylenediaminetetraacetic acid tetrasodium dihydrate (EDTA): manufactured by Kishida Chemical Aluminum hydroxide: manufactured by Nippon Light Metal Co., Ltd., using SBX73, B303, B153, and B103, and adjusting the average particle size by appropriately mixing each of them

[0096] [I. Production of methacrylic resin beads used as a thickening agent] (Example 1) -Adjustment of suspending agent- Into a container equipped with a stirrer having four inclined paddle blades, 5 kg of water, 130 g of aluminum hydroxide with an average particle diameter of 33 μm, 0.39 g of sodium lauryl sulfate, and 2.3 g of EDTA were charged and mixed to obtain a mixed solution (a1). The average particle diameter of the suspending agent in the mixed solution (a1) was 33 μm, and the pH of the obtained mixed solution (a1) was 5.5. The obtained mixed solution (a1) was heated to 70°C.

[0097] -Polymerization reaction- Next, 25 kg of water was charged into a 60 L reactor and heated to 80°C, and a monomer solution obtained by mixing 3 kg of the mixed solution (a1), 21 kg of monomer raw materials with the formulation shown in Table 1, 60 g of EHTG, and 43 g of LPO was charged into the reactor. Then, suspension polymerization was carried out while maintaining a temperature of about 80°C, and a heat generation peak was observed 140 minutes after the monomer solution was charged. Then, after raising the temperature to 93°C at a rate of 1°C / min, the temperature was maintained at about 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 mass% sulfuric acid was charged into the polymer slurry to dissolve the suspending agent to obtain a polymerization reaction solution. Next, the obtained polymerization reaction solution was passed through a 1.68 mm mesh sieve 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.

[0098] -Washing process- Subsequently, approximately the same amount of ion-exchanged water at about 70°C as the bead-shaped methacrylic resin particles was added, followed by stirring, washing, and filtration. Similarly, washing with ion-exchanged water at about 70°C was performed one more time (for a total of two water washings) to obtain a slurry-like polymer solution. An aqueous sodium hydroxide solution was added dropwise to the obtained slurry-like polymer solution to adjust the pH to 8.5, followed by stirring and washing. The slurry-like polymer solution was filtered, and further ion-exchanged water at 70°C was added, followed by stirring and washing. The pH of the obtained slurry-like polymer solution was 6.1. Subsequently, the slurry-like polymer solution was filtered to obtain resin beads. The obtained resin beads were dried using an air current dryer at an air current of 150°C (30 Nm 3 / hr), and then dried in a fluidized bed dryer (25 Nm 3 / hr) at 90°C for 5 minutes to obtain methacrylic resin beads. The weight average molecular weight of the obtained methacrylic resin beads was 142,000, and Mw / Mn = 1.9.

[0099] (Example 2) A mixed solution (a1) was prepared in the same manner as in Example 1. Subsequently, a polymer slurry was formed, filtered, and bead-shaped methacrylic resin particles were obtained in the same manner as in Example 1, except that the formulation of the monomer raw materials was changed as shown in Table 1. Thereafter, washing was performed in the same manner as in Example 1, except that water washing was performed three times, to obtain a slurry-like polymer solution. The pH of the obtained slurry-like polymer solution was 6.0. Subsequently, the slurry-like polymer solution was filtered to obtain resin beads. The obtained resin beads were dried in the same manner as in Example 1 to obtain methacrylic resin beads. The weight average molecular weight of the obtained beads was 136,000, and Mw / Mn = 2.0.

[0100] (Examples 3 and 5) Methacrylic resin beads were obtained in the same manner as in Example 1, except that the formulation of the monomer raw materials was changed to the formulation described in Table 1.

[0101] (Example 4) Methacrylic resin beads were obtained in the same manner as in Example 1, except that the temperature of the air current dryer was set to 100°C.

[0102] (Comparative Example 1) 】Methacrylic resin beads were obtained in the same manner as in Example 1, except that the monomer raw material composition was MMA only.

[0103] (Comparative Example 2) Polymerization Example in Two-Stage Polymerization 2 kg of water, 65 g of tricalcium phosphate, 39 g of calcium carbonate, and 0.39 g of sodium lauryl sulfate were charged into a container equipped with a stirrer having four inclined paddle blades to obtain a suspension agent solution (A). 3900 g of methyl methacrylate, 20 g of butyl acrylate, 42 g of EHTG, and 28 g of LPO were blended to prepare a monomer raw material (1). Next, 26 kg of water was charged into a 60 L reactor and the temperature was raised to 80 °C, and then the entire amount of the suspension agent solution (A) and the monomer raw material (1) were charged. Suspension polymerization was carried out at a temperature of about 80 °C for 150 minutes, and the reaction was substantially completed to obtain a slurry of the polymer. Thereafter, the slurry of the polymer (I) was stirred at 80 °C for 60 minutes. Next, 20 kg of methyl methacrylate, 100 g of butyl acrylate, 35 g of NOM, and 40 g of LPO were blended to prepare a monomer raw material (2). The monomer raw material (2) was charged into the reactor, and suspension polymerization was continuously carried out at about 80 °C for 90 minutes. Then, the temperature was raised to 92 °C at a rate of 1 °C / min and held for 60 minutes, and the polymerization reaction was substantially completed to obtain a polymer slurry.

[0104] Next, filtration, washing, and drying were carried out in the same manner as in Example 1 to obtain methacrylic resin beads. The weight average molecular weight of the obtained methacrylic resin beads was 124,000, and Mw / Mn = 2.6.

[0105] (Example 6) Treatment was carried out in the same manner as in Example 1, except that the temperature of the ion-exchanged water was changed to about 25 °C and the number of washing times was set to 1, to obtain methacrylic resin beads. The pH of the slurry liquid after washing was 4.6.

[0106] (Example 7) Treatment was carried out in the same manner as in Example 6, except that the amount of ion-exchanged water was changed to approximately half of the bead-like polymer and the number of washing times was set to 1, to obtain methacrylic resin beads. The pH of the slurry liquid was 3.5.

[0107] (Example 8) Treatment was carried out in the same manner as in Example 6 except that washing was performed using a small amount of 20% by mass sulfuric acid in addition to ion-exchanged water, and methacrylic resin beads were obtained. The pH of the slurry liquid was 2.0.

[0108] (Comparative Example 3) With the same formulation and treatment as in Example 3, separation was performed into bead-shaped methacrylic resin particles and suspension waste liquid. Thereafter, after adding approximately the same amount of normal-temperature water as the bead-shaped methacrylic resin particles, an aqueous sodium hydroxide solution was added to adjust the pH to 10.5, followed by stirring, washing, and filtration to obtain resin beads. The obtained resin beads were dried in the same manner as in Example 3 to obtain methacrylic resin beads.

[0109] (Example 9) With the same formulation and treatment as in Example 1, separation was performed into bead-shaped methacrylic resin particles and suspension waste liquid. Thereafter, treatment was carried out in the same manner as in Comparative Example 3 except that the pH was set to 9, and methacrylic resin beads were obtained.

[0110] (Comparative Example 4) Methacrylic resin beads were obtained with the same formulation and polymerization method as in Example 1 except that the temperature of the airflow dryer was set to 80°C.

[0111] (Example 10) -Suspending agent- Into a container equipped with a stirrer having 4 inclined paddle blades, 5 kg of water, 130 g of aluminum hydroxide with an average particle diameter of 23 μm, 0.39 g of sodium lauryl sulfate, and 2.3 g of EDTA were added and mixed to obtain a mixed solution (a2). The average particle diameter of the suspending agent in the mixed solution (a2) was 23 μm, and the pH of the obtained mixed solution was 5.5. The obtained mixed solution (a2) was heated to 70°C. 27 kg of water, 3 kg of the mixed solution (a2), 16 kg of monomer raw materials in the blending ratio shown in Table 2, 13 g of EHTG, and 25 g of LPO were added to a 60 L reactor and mixed. The reaction temperature of the reactor was polymerized at 80°C for 150 minutes. Then, after raising the temperature to 93°C at a rate of 1°C / min, it was aged for 45 minutes to substantially complete the polymerization reaction and obtain a polymer slurry. Next, it was cooled to 50°C and 20% by mass sulfuric acid was added to dissolve the suspending agent. Next, the polymerization reaction solution was passed through a 1.68 mm mesh sieve to remove aggregates, and then the obtained suspension was filtered through a filter cloth to separate it into bead-shaped methacrylic resin particles and suspension waste liquid. Then, ion-exchanged water heated to 70°C, approximately equal in amount to the bead-shaped polymer, was added, and the subsequent operations were carried out in the same manner as in Example 1 to obtain resin beads. The weight average molecular weight of the obtained resin beads was 402,000, and Mw / Mn = 2.2.

[0112] (Example 11) Methacrylic resin beads were obtained with the same composition and polymerization method as in Example 10, except that the amount of EHTG in the monomer raw materials was 8 g. The time from monomer addition until the exothermic peak was observed was 120 minutes. The weight average molecular weight of the obtained resin beads was 654,000, and Mw / Mn = 2.2.

[0113] (Example 12) Methacrylic resin beads were obtained with the same composition and polymerization method as in Example 10, except that the amount of water used was 30 kg and polymerization was carried out without adding EHTG. The time from monomer addition until the exothermic peak was observed was 100 minutes. The weight average molecular weight of the obtained resin beads was 1,250,000, and Mw / Mn = 2.4.

[0114] (Examples 13, 14, 15, 16) Methacrylic resin beads were obtained in the same manner as in Example 1, except that the monomer raw materials were changed to the types and formulations shown in Table 3.

[0115] (Comparative Example 5) 2 kg of water, 65 g of tricalcium phosphate, 39 g of calcium carbonate, and 0.39 g of sodium lauryl sulfate were charged into a container equipped with a stirrer having four inclined paddle blades to obtain a suspension agent solution (A). Next, 21 kg of water was charged into a 60 L reactor and heated to 80°C, and a prepared solution obtained by mixing the suspension agent solution (A), 21 kg of monomer raw materials in the blending ratio shown in Table 1, 60 g of EHTG, and 63 g of LPO was charged. Then, suspension polymerization was carried out while maintaining at about 80°C for 110 minutes. Next, after raising the temperature to 93°C at a rate of 1°C / min, the temperature of about 93°C was maintained for 45 minutes to substantially complete the polymerization reaction and obtain a polymer slurry. Since the amount of LPO as the initiator was increased, the polymerization time was shortened. Next, 20% by mass sulfuric acid was added to cool to 50°C to dissolve the suspension agent. Next, the polymerization reaction solution was filtered through a filter cloth to separate it into bead-shaped methacrylic resin particles and suspension waste liquid. The pH of the suspension waste liquid at that time was 3.3. Thereafter, ion-exchanged water warmed to about 70°C in an amount approximately equal to that of the bead-shaped polymer was added, followed by stirring, washing, and filtering, and the washing operation with ion-exchanged water at about 70°C was further carried out once more to obtain a slurry-shaped polymer solution (washed with water twice in total). An aqueous sodium hydroxide solution was dropped into the obtained slurry-shaped polymer solution to adjust the pH to 8.5, followed by stirring and washing. After filtering with a filter cloth and adding ion-exchanged water warmed to 70°C and stirring and washing, the pH of the obtained slurry-shaped polymer solution was 6.1. Thereafter, it was filtered with a filter cloth to obtain resin beads. The obtained undried resin beads were dried with an air flow of 150°C (30 Nm 3 / hr) using an air flow dryer, and then dried at 90°C for 5 minutes with a fluidized bed dryer (25 Nm 3 / hr) to obtain methacrylic resin beads. The proportion of particles of 710 μm or more in the obtained beads was 5.1%.

[0116] (Example 17) -Adjustment of suspension agent- Into a container equipped with a stirrer having 4 inclined paddle blades, 5 kg of water, 130 g of aluminum hydroxide with an average particle size of 33 μm, 0.39 g of sodium lauryl sulfate, and 2.3 g of EDTA were charged and mixed to obtain a mixed solution (a1). The average particle size of the suspending agent in the mixed solution (a1) was 33 μm, and the pH of the obtained mixed solution (a1) was 5.5. The obtained mixed solution (a1) was heated to 70 °C.

[0117] - Polymerization reaction - Next, 25 kg of water was charged into a 60 L reactor and heated to 80 °C. Into the reactor, a monomer solution obtained by mixing 3 kg of the mixed solution (a1), 21 kg of monomer raw materials with the formulation shown in Table 1, 60 g of EHTG, and 43 g of LPO was charged. Then, suspension polymerization was carried out while maintaining a temperature of about 80 °C. A heat generation peak was observed 140 minutes after the monomer solution was charged. After that, the temperature was raised to 93 °C at a rate of 1 °C / min, and then the temperature of about 93 °C was maintained 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 mass% sulfuric acid was added to the polymer slurry to dissolve the suspending agent and obtain a polymerization reaction solution. Next, the obtained polymerization reaction solution was filtered through a 1.68 mm mesh sieve to remove aggregates, and separated into bead-shaped methacrylic resin particles and suspension waste liquid. The pH of the suspension waste liquid was 3.3.

[0118] - Washing process - After that, approximately the same amount of ion-exchanged water at about 70 °C as the bead-shaped methacrylic resin particles was added, and stirring, washing, and filtration were carried out. Similarly, washing with ion-exchanged water at about 70 °C was carried out one more time (a total of 2 water washings) to obtain a slurry-like polymer solution. An aqueous sodium hydroxide solution was dropped into the obtained slurry-like polymer solution to adjust the pH to 8.5, and stirring and washing were carried out. The slurry-like polymer solution was filtered, and further ion-exchanged water at 70 °C was added and stirred for washing. The pH of the obtained slurry-like polymer solution was 6.1. After that, the slurry-like polymer solution was filtered to obtain resin beads. The obtained resin beads were dried in an air flow dryer at an air flow of 150 °C (30 Nm 3 / hr), and then in a fluidized bed dryer (25 Nm3 It was dried at 90 °C for 5 minutes at 100 mL / hr to obtain methacrylic resin beads. The weight-average molecular weight of the obtained methacrylic resin beads was 143,000, and Mw / Mn = 1.9. As a result of NMR measurement, it was confirmed that a methacrylic resin having the composition as charged was obtained.

[0119] (Examples 18 to 24) Methacrylic resin beads were obtained in the same manner as in Example 17, except that the formulation of the monomer raw materials was changed to the formulation shown in Table 1.

[0120] (Example 25) - Suspending agent - Into a container having a stirrer equipped with four inclined paddle blades, 5 kg of water, 130 g of aluminum hydroxide with an average particle diameter of 23 μm, 0.39 g of sodium lauryl sulfate, and 2.3 g of EDTA were charged and mixed to obtain a mixed solution (a2). The average particle diameter of the suspending agent in the mixed solution (a2) was 23 μm, and the pH of the obtained mixed solution was 5.5. The obtained mixed solution (a2) was heated to 70 °C. 27 kg of water, 3 kg of the mixed solution (a2), 16 kg of monomer raw materials at the formulation ratio shown in Table 1, 13 g of EHTG, and 25 g of LPO were charged into a 60 L reactor and mixed, and the reaction temperature of the reactor was polymerized at 80 °C for 150 minutes. Then, after raising the temperature to 93 °C at a rate of 1 °C / min, it was aged for 45 minutes to substantially complete the polymerization reaction and obtain a polymer slurry. Next, it was cooled to 50 °C and 20 mass% sulfuric acid was added to dissolve the suspending agent. Next, the polymerization reaction solution was passed through a 1.68 mm mesh sieve to remove aggregates, and then the obtained suspension was filtered through a filter cloth to separate into bead-shaped methacrylic resin particles and suspension waste liquid. Then, ion-exchanged water heated to approximately 70 °C in an amount approximately equal to that of the bead-shaped polymer was added, and the subsequent operations were performed in the same manner as in Example 17 to obtain methacrylic resin beads. The weight-average molecular weight of the obtained methacrylic resin beads was 403,000, and Mw / Mn = 2.3.

[0121] (Example 26) Methacrylic resin beads were obtained in the same composition and polymerization method as in Example 9, except that the amount of EHTG was 8 g. The time from monomer charging until the exothermic peak was observed was 120 minutes. The weight-average molecular weight of the obtained methacrylic resin beads was 653,000, and Mw / Mn = 2.2.

[0122] (Example 27) Methacrylic resin beads were obtained in the same composition and polymerization method as in Example 9, except that the amount of water used was 30 kg and polymerization was carried out without adding EHTG. The time from monomer charging until the exothermic peak was observed was 100 minutes. The weight-average molecular weight of the obtained methacrylic resin beads was 1,250,000, and Mw / Mn = 2.4.

[0123] (Comparative Examples 6, 7) Methacrylic resin beads were obtained in the same manner as in Example 17, except that the formulation of the monomer raw materials was changed to the formulation described in Table 4.

[0124] [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 under the following apparatus and conditions. Measuring apparatus: Gel Permeation Chromatography (HLC-83 20GPC) manufactured by Tosoh Corporation Column: One TSKguardcolumn SuperH-H, two TSKgel SuperHM-M, and one TSKgel SuperH2500 were connected in series and used in order. In this column, high molecular weight components elute quickly, and low molecular weight components elute slowly. Detector: RI (Differential Refractometer) detector Detection sensitivity: 3.0 mV / min Column temperature: 40 °C Sample: 0.02 g of a solution of methacrylic resin in 20 mL of tetrahydrofuran Injection volume: 10 μL Developing solvent: Tetrahydrofuran, flow rate; 0.6 mL / min As an internal standard, 2,6-di-t-butyl-4-methylphenol (BHT) was added at 0.1 g / L. As calibration standard samples, the following 10 kinds of polymethyl methacrylate with known monodisperse peak top molecular weights and different molecular weights (manufactured by Polymer Laboratories; PMMA Calibration Kit M-M-10) 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 material 10 850 Under the above conditions, the RI detection intensity was measured with respect to the elution time of the methacrylic resin. Based on the area of the GPC elution curve and the calibration curve of the third-order approximation formula, the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the methacrylic resin were determined.

[0125] (II-2) (Volume average particle diameter, D 10 ) Measurement was carried out under the same conditions as in paragraph

[0045] of JP-A No. 2021-017561.

[0126] (II-3) (Moisture content) Using SHIMADZU MOISTURE BALANCE MOC-120H, 10.0 g of methacrylic resin beads were held at 70 °C, and the measurement was terminated when the weight loss rate for 10 seconds became 0.02% or less, and the total weight loss rate was taken as the moisture content.

[0127] (II-4) (MMA volatilization amount) Using an Agilent GC-6890 and MSD-5973, the MMA evaporation rate was measured. 5 mg of methacrylic resin beads were heated in a pyrolysis furnace at 60 °C for 10 minutes, and the generated gas was trapped by a column HP5-MS cooled with liquid nitrogen. The trapped generated gas was analyzed by GC / MS to quantify the MMA evaporation rate.

[0128] (II-5) (YI value of acetone solution) The obtained methacrylic resin beads were dissolved in acetone at a mass percentage concentration of 10%, placed in a 1 cm thick cell, and the YI value was measured in accordance with JIS K7105 using a color difference meter (manufactured by Tokyo Denshoku Co., Ltd., TC-8600A, light source: 10-C).

[0129] (II-6) (pH of the aqueous phase when the thickener is dispersed in water) After dispersing 20 g of methacrylic resin beads and 100 g of pure water and allowing them to stand, the solid content was allowed to settle, and then the pH of the supernatant was measured at room temperature. Measuring instrument: pH meter F-52 (HORIBA) Electrode: Standard ToupH electrode 9615S-10D

[0130] (II-7) (Ratio of particles with a size of 710 μm or more) Using approximately 100 g of methacrylic resin beads, based on JIS-Z8801, sieves (JTS-200-45-31 (aperture 710 μm), JTS-200-45-44 (aperture 500 μm), 35 (aperture 355 μm), 36 (aperture 300 μm), 37 (aperture 250 μm), 38 (aperture 150 μm), 61 (receiver) manufactured by Tokyo Screen) were used, and a sieving test machine TSK B-1 was used to perform sieving for 10 minutes at the maximum vibration force. The weight of the particles remaining on each sieve was measured, and the ratio of the particles remaining on the sieve with an aperture of 710 μm (the ratio of the particle size component of 710 μm or more) was measured. The measurement was carried out 3 times, and the ratio was calculated as the average value. [Ratio of particles with a size of 710 μm or more] = 100 × [Weight of particles remaining on the sieve with an aperture of 710 μm] / [Weight of the sample subjected to the sieving test machine] (%)

[0131] (II-8) (Viscosity of Ethyl Cyanoacrylate Solution) Put silicone oil in an oil bath with a stirrer and heat it to 50°C. Place 16 g of a thickener, 64 g of ethyl cyanoacrylate (when the thickener is 20% by mass), and a rotor in a 110 mL screw-cap bottle (diameter 50 mm), and close the lid of the screw-cap bottle. Place the screw-cap bottle in the oil bath, rotate the stirrer (150 rpm), dissolve the methacrylic resin beads in ethyl cyanoacrylate, and obtain a syrup which is an ethyl cyanoacrylate solution of methacrylic resin. When the concentration of the thickener is 10% by mass, it is dissolved at a ratio of 8 g of the thickener and 72 g of ethyl cyanoacrylate. Thickeners with a weight average molecular weight of 85,000 or more and less than 300,000 are dissolved in ethyl cyanoacrylate at a concentration of 20% by mass, and thickeners with a weight average molecular weight of 300,000 or more and less than 800,000 are dissolved at a concentration of 10% by mass, 8 00,000 or more 1,5 00,000 Below of the thickener are dissolved at a concentration of 7% by mass, cooled, and the viscosity η1 is measured at 25°C. Also, after leaving the syrup standing at 60°C for 48 hours, the viscosity η2 is measured at 25°C. The viscosity measuring instrument used was a B-type viscometer (Digital Viscometer LVDV Next manufactured by Eiko Seiki Co., Ltd.). The syrup was weighed into a 40 mL measuring tube, the measuring tube was installed in the viscometer, and the viscosity measurement was started. The viscosity was measured at a spindle rotation speed of 60 rpm. If the measurement range was exceeded at 60 rpm, the rotation speed was decreased for measurement. For those with high viscosity, the addition amount can be adjusted during syrup production to adjust to an appropriate viscosity.

[0132] [III. Evaluation of Thickener] Using the methacrylic resin beads obtained in the examples and comparative examples as thickeners, the following evaluations were carried out.

[0133] (III-1) (Odor) 400 g of methacrylic resin beads were placed in a plastic container (sealed, 500 mL Iwaki wide-mouth bottle), heated at 60 °C for 2 hours, then cooled to 30 °C. After that, the odor was smelled by 5 evaluators and scored according to the following criteria. Then, based on the average value of the scores of the 5 people, the strength of the odor was ranked from A to D. 6: Intolerable odor 5: Very pungent odor 4: Pungent odor 3: Strongly felt but not pungent 2: Felt (slightly) but not pungent 1: Difficult to feel. This evaluation was conducted by 5 people, and from the average, A (odor is very weak): Average value of scores is 2 or less B (odor is very weak): Average value of scores is more than 2 and 3 or less C (good): Average value of scores is more than 3 and 4 or less D (bad): Average value of scores is more than 4 was determined.

[0134] (III-2) (Dissolution rate) Put silicone oil in an oil bath with a stirrer and heat it to 50 °C. Place 16 g of thickener, 64 g of ethyl cyanoacrylate (in the case of 20% by mass of thickener), and a rotor in an 110 mL screw-top bottle (diameter 50 mm), and close the lid of the screw-top bottle. Place the screw-top bottle in the oil bath, start the measurement by rotating the stirrer (150 rpm). The time until the thickener in the bottle dissolves in ethyl cyanoacrylate was measured. Thickeners with a weight average molecular weight of 85,000 or more and less than 300,000 were dissolved in ethyl cyanoacrylate at a concentration of 20% by mass, and thickeners with a weight average molecular weight of 300,000 or more and less than 800,000 were dissolved at a concentration of 10% by mass, 8 00,000 or more 1,5 00,000 Below and thickeners of A: All the thickener dissolved within 45 minutes B: All the thickener dissolved within 60 minutes C: The thickener was almost dissolved after more than 60 minutes D: The tackifier did not dissolve

[0135] (III-3) (Long-term stability after dissolution) In the same manner as above, methacrylic resin beads were dissolved in ethyl cyanoacrylate at a concentration corresponding to each molecular weight at 50 °C to prepare samples. After leaving the samples standing at 25 °C for 90 days, the long-term stability was evaluated according to the following criteria. A (Extremely excellent long-term stability): The sample maintained fluidity and could be used as an adhesive without problems B (Excellent long-term stability): Although the fluidity of the sample was slightly reduced, it could be used as an adhesive without problems C (Good long-term stability): The fluidity of the sample was reduced, but it did not solidify and could be applied and adhered D (Poor long-term stability): The sample solidified

[0136] (III-4) (Light resistance) Regarding the samples dissolved in ethyl cyanoacrylate in the evaluation of long-term stability, a part was extracted and placed in a sealed transparent 100 mL container and left outdoors under direct sunlight for 1 month. After leaving it standing, the light resistance was evaluated according to the following criteria. Criteria A and B indicate that the light resistance passed. A: The sample maintained fluidity B: The fluidity of the sample was greatly reduced C: The sample solidified

[0137] [Table 1]

[0138] [Table 2]

[0139] [Table 3]

[0140]

Table 4

[0141] Comparing Example 1 with Comparative Example 1, and Example 8 with Comparative Examples 2 and 3, it can be seen that the stability after dissolution is excellent due to the low value of the ratio of η. Comparing Example 1 with Comparative Example 4, it can be seen that the stability after dissolution is excellent due to the low value of the ratio of η, and by containing a predetermined amount of an alkyl acrylate monomer having an alkyl group with 4 or more carbon atoms, the odor after dissolution of cyanoacrylate can be reduced.

Industrial Applicability

[0142] According to the present invention, it can be suitably used as a thickener for adhesives, and in particular, when used as a thickener for cyanoacrylate adhesives, it can suppress the increase in viscosity and solidification during storage of the thickening target, and improve the storage stability of the product. A thickener can be provided.

Claims

1. A thickener containing 90 to 100% by mass of a methacrylic resin having a weight average molecular weight (Mw) of 136,000 to 1,500,000, wherein the methacrylic resin contains 90 to 99.9% by mass of methyl methacrylate monomer units and 0.1 to 10% by mass of acrylic acid alkyl monomer units having 4 or more carbon atoms in the alkyl group, the methacrylic resin has a moisture content of 0.01% or more and 1% or less as measured by a drying method, the mass ratio of particles of 710 μm or more is 5% or less with respect to 100% by mass of the thickener, taking the viscosity (Pa·s) at 25 °C of the ethyl cyanoacrylate solution of the methacrylic resin as η1, when the solution is left standing at 60 °C for 48 hours, cooled to 25 °C, and the viscosity (Pa·s) of the solution at 25 °C after cooling is taken as η2, η1 and η2 are such that 1.0 ≤ η2 / η1 ≤ 5.0 is satisfied (however, when the Mw of the methacrylic resin is 85,000 or more and less than 300,000, the concentration of the methacrylic resin in the solution is 20% by mass, when the Mw of the methacrylic resin is 300,000 or more and less than 800,000, the concentration of the methacrylic resin in the solution is 10% by mass, when the Mw of the methacrylic resin is 800,000 or more and 1,500,000 or less, the concentration of the methacrylic resin in the solution is 7% by mass), a thickener for a cyanoacrylate-based adhesive.

2. The thickener for a cyanoacrylate-based adhesive according to claim 1, wherein the methacrylic resin contains 90 to 99.9% by mass of methyl methacrylate monomer units and 0.1 to 10% by mass of aromatic vinyl monomer units.

3. The thickener for a cyanoacrylate-based adhesive according to claim 2, wherein the methacrylic resin contains 90 to 99.8% by mass of methyl methacrylate monomer units, 0.1 to 8% by mass of aromatic vinyl monomer units, and 0.1 to 8% by mass of alkyl acrylate monomer units.

4. The thickener for a cyanoacrylate-based adhesive according to claim 1, wherein the methacrylic resin is in the form of beads having an average particle diameter of 50 to 500 μm.

5. A cyanoacrylate-based adhesive composition containing 1 to 30% of the thickener for a cyanoacrylate-based adhesive according to claim 1.

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