Radical polymerizable resin composition

Abstract

The present application provides a radical polymerizable resin composition which is excellent in moldability and curing property and also excellent in workability. The radical polymerizable resin composition contains urethane (meth) acrylate (A) having a structural unit derived from 1,6-hexamethylene diisocyanate and a structural unit derived from 2-hydroxyethyl methacrylate, the urethane (meth) acrylate (A) being a crystalline urethane (meth) acrylate, and contains a radical polymerization initiator (C) and an N-oxyl compound (D), the content of the N-oxyl compound (D) being 0.20 to 0.60 parts by mass per 100 parts by mass of the urethane (meth) acrylate (A).

Description

Technical Field

[0001] This invention relates to free radical polymerizable resin compositions. Background Technology

[0002] Magnets used in household appliances are mainly manufactured through sintering, but this process makes it difficult to shape them into complex forms. In contrast, bonded magnets, which are made by molding microparticle magnets using resins or similar binders, are widely used in various applications such as electrical and electronic components, motors in household appliances and automobiles due to their high degree of shape freedom.

[0003] As applications expand and products become more high-performance, the performance requirements for adhesives such as resins are becoming increasingly complex. In particular, resin compositions for bonding magnets using thermosetting resins are being developed as adhesives with excellent heat resistance.

[0004] For example, Patent Document 1 discloses a thermosetting composition for the purpose of improving flowability and curing speed, comprising a crystalline free radical polymerizable compound having a melting point in the range of 30 to 150°C and magnetic powder.

[0005] Patent Document 1: International Publication No. 2022 / 255217 Summary of the Invention

[0006] As described above, a resin composition comprising microparticle-shaped magnets as raw materials for bonding magnets and thermosetting resins, etc., is molded to obtain the desired shape. However, the curing time is short, which cannot ensure sufficient usable time, resulting in problems with moldability. On the other hand, rapid curing is required after molding, posing a challenge to balance moldability and curing performance.

[0007] Furthermore, the composition before molding and processing also presents problems with workability due to the stickiness of the thermosetting resin raw materials. Therefore, there is a need for a composition that can balance moldability and curing properties while also being workable as a raw material for bonding magnets.

[0008] Therefore, the objective of this invention is to provide a free radical polymerizable resin composition that has excellent moldability, curability, and workability.

[0009] The inventors have discovered that compositions containing specific urethane (meth)acrylates, magnetic powder, free radical polymerization initiators, and specific amounts of N-oxygen compounds can solve the above-mentioned problems.

[0010] That is, the present invention relates to the following.

[0011] [1] A free radical polymerizable resin composition comprising urethane (meth)acrylate (A) and magnetic powder (B), wherein the urethane (meth)acrylate (A) has structural units derived from 1,6-hexamethylene diisocyanate and structural units derived from 2-hydroxyethyl methacrylate, wherein the urethane (meth)acrylate (A) is crystalline urethane (meth)acrylate, wherein the free radical polymerizable resin composition comprises a free radical polymerization initiator (C) and an N-oxygen compound (D), wherein the content of the N-oxygen compound (D) is 0.20 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate (A).

[0012] [2] According to the free radical polymerizable resin composition described in [1] above, wherein the melting point of the urethane (meth) acrylate (A) is 30 to 150°C.

[0013] [3] The free radical polymerizable resin composition according to [1] or [2] above, wherein the above-mentioned urethane (meth)acrylate (A) is solid at 23°C.

[0014] [4] The free radical polymerizable resin composition according to any one of [1] to [3] above, wherein the total content of the structural units from 1,6-hexamethylene diisocyanate and the structural units from 2-hydroxyethyl methacrylate in the above urethane (meth) acrylate (A) is 90 to 100 by mass.

[0015] [5] The free radical polymerizable resin composition according to any one of [1] to [4] above, wherein the above-mentioned N-oxy compound (D) is 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy.

[0016] [6] The free radical polymerizable resin composition according to any one of [1] to [5] above, wherein the content of the above-mentioned N-oxygen compound (D) is 0.35 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate (A).

[0017] [7] The free radical polymerizable resin composition according to any one of [1] to [6] above, wherein the content of the phenolic polymerization inhibitor is 0.05 parts by weight or less relative to 100 parts by weight of urethane (meth)acrylate (A).

[0018] [8] The free radical polymerizable resin composition according to any one of [1] to [7] above, wherein the 10-hour half-life temperature of the free radical polymerization initiator (C) is 80 to 150°C.

[0019] [9] The free radical polymerizable resin composition according to any one of [1] to [8] above, wherein the content of the magnetic powder (B) is 100 to 500 parts by weight relative to 100 parts by weight of urethane (meth)acrylate (A).

[0020]

[10] The free radical polymerizable resin composition according to any one of [1] to [9] above, wherein the magnetic powder (B) is at least one selected from ferrite magnetic powder, AlNiCo magnetic powder and rare earth magnetic powder.

[0021]

[11] The free radical polymerizable resin composition according to any one of [1] to

[10] above, wherein the magnetic powder (B) is at least one selected from samarium iron nitrogen magnetic powder, samarium cobalt magnetic powder and neodymium magnetic powder.

[0022]

[12] The free radical polymerizable resin composition according to any one of [1] to

[11] above, wherein the magnetic powder (B) is samarium iron nitrogen magnetic powder.

[0023]

[13] A magnet is obtained by molding the free radical polymerizable resin composition described in any one of [1] to

[12] above.

[0024] According to the present invention, a free radical polymerizable resin composition with excellent moldability, curability, and workability can be provided. Therefore, the free radical polymerizable resin composition of the present invention is suitable for use as a raw material for bonding magnets. Detailed Implementation

[0025] [Free radical polymerizable resin composition]

[0026] The free radical polymerizable resin composition of the present invention contains urethane (meth)acrylate (A) and magnetic powder (B), wherein the urethane (meth)acrylate (A) has structural units derived from 1,6-hexamethylene diisocyanate and structural units derived from 2-hydroxyethyl methacrylate, wherein the urethane (meth)acrylate (A) is crystalline urethane (meth)acrylate, and wherein the free radical polymerizable resin composition contains a free radical polymerization initiator (C) and an N-oxygen compound (D), wherein the content of the N-oxygen compound (D) is 0.20 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate (A).

[0027] The free radical polymerizable resin composition of the present invention has excellent moldability and curability, as well as excellent workability.

[0028] The reasons for the excellent moldability, curability, and operability of the free radical polymerizable resin composition of the present invention are not yet certain, but the following are possible considerations.

[0029] The urethane (meth)acrylate contained in the free radical polymerizable resin composition of the present invention is synthesized from hexamethylene diisocyanate and hydroxyethyl methacrylate. Due to the presence of a symmetrical and relatively long methylene chain backbone, such as hexamethylene diisocyanate, it readily exhibits crystallinity and has a low melting point, thus exhibiting excellent workability, curability, and moldability. Furthermore, the free radical polymerizable resin composition of the present invention contains a specific amount of N-oxygen compounds. These N-oxygen compounds can capture excess free radicals but decompose again to revert to their original form, thus providing a prolonged curing delay effect. Moreover, due to the specific amount contained, excellent curability is achieved while simultaneously providing a curing delay effect. Therefore, compared to other polymerization inhibitors, especially in the presence of magnetic powder, which is considered to promote free radical decomposition, it extends the usable time and provides excellent moldability.

[0030] <Carbamate (Meth)acrylate (A)>

[0031] The free radical polymerizable resin composition of the present invention contains urethane (meth)acrylate (A), which has structural units derived from 1,6-hexamethylene diisocyanate and structural units derived from 2-hydroxyethyl methacrylate, and is a crystalline urethane (meth)acrylate.

[0032] By giving urethane (meth)acrylate (A) the above-described composition, the free radical polymerizable resin composition possesses the magnetic properties required as a raw material for bonding magnets, and its shape can be freely adjusted, resulting in excellent moldability, curability, and workability.

[0033] Carbamate (meth)acrylates are (meth)acrylate adducts of polyisocyanates having an isocyanate group, and more specifically, are compounds obtained by forming a carbamate bond between the isocyanate group of a polyisocyanate and the hydroxyl group (-OH) of a (meth)acrylate having a hydroxyl group. However, for carbamate (meth)acrylate (A), as a polyisocyanate, it contains 1,6-hexamethylene diisocyanate, and as a (meth)acrylate having a hydroxyl group, it contains 2-hydroxyethyl methacrylate.

[0034] In this invention, "(meth)acrylate" refers to at least one selected from "acrylate" and "methacrylate".

[0035] The urethane (meth)acrylate (A) has structural units from 1,6-hexamethylene diisocyanate and structural units from 2-hydroxyethyl methacrylate, but may also contain structural units other than those.

[0036] Specifically, examples include structural units from polyisocyanates other than 1,6-hexamethylene diisocyanate, structural units from alcohol compounds containing (meth)acryloyl groups other than 2-hydroxyethyl methacrylate, structural units from polyols, and structural units from polyester polyols.

[0037] Examples of polyisocyanates other than 1,6-hexamethylene diisocyanate include aromatic isocyanate compounds, alicyclic isocyanate compounds, and aliphatic isocyanate compounds. Preferably, at least one of alicyclic and aliphatic isocyanate compounds is selected, and more preferably both alicyclic and aliphatic isocyanate compounds are used. Additionally, trifunctional isocyanates (ureate-type polyisocyanates) with isocyanurate rings formed by trimerization of difunctional isocyanate compounds, and isocyanate prepolymers modified with polyols may also be used.

[0038] Examples of aromatic isocyanate compounds include isophthalic dimethyl diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and m-tetramethylxylene diisocyanate.

[0039] Examples of alicyclic isocyanate compounds include hydrogenated xylene diisocyanate (1,3-bis(methyl isocyanate)cyclohexane), isophorone diisocyanate, norbornene diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated methylene bisphenylene diisocyanate, and 1,4-cyclohexane diisocyanate.

[0040] Examples of aliphatic isocyanate compounds include trimethylene diisocyanate. These isocyanate compounds can be used alone or in combination of two or more.

[0041] In addition, urea ester type polyisocyanates are preferred, such as isophorone diisocyanate. Urea ester type polyisocyanates are preferably selected from at least one of the trimers, pentamers, heptomers, nonamers and undecomers of the above-mentioned IPDI after the isophorone diisocyanate (IPDI) monomer forms a urea ester ring, or a mixture thereof.

[0042] The ratio of structural units derived from 1,6-hexamethylene diisocyanate in the polyisocyanate structural units is preferably 70-100 mol%, more preferably 80-100 mol%, even more preferably 90-100 mol%, even more preferably 95-100 mol%, even more preferably 99-100 mol%, even more preferably 100 mol%, and the polyisocyanate structural units may also consist solely of structural units derived from 1,6-hexamethylene diisocyanate.

[0043] Examples of alcohol compounds containing a (meth)acryloyl group other than 2-hydroxyethyl methacrylate include hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, and hydroxyphenoxypropyl methacrylate.

[0044] The ratio of structural units derived from 2-hydroxyethyl methacrylate in the structural units of the alcohol compound having a (meth)acryloyl group is preferably 70-100 mol%, more preferably 80-100 mol%, further preferably 90-100 mol%, even more preferably 95-100 mol%, even more preferably 99-100 mol%, and even more preferably 100 mol%. The structural units of the alcohol compound having a (meth)acryloyl group may also consist solely of structural units derived from 2-hydroxyethyl methacrylate.

[0045] Diols are preferred as polyols.

[0046] The diol is preferably selected from at least one of ethylene glycol, propylene glycol, bisphenols, hydrogenated bisphenols, etherified bisphenols, and neopentyl glycol.

[0047] Polyols can be used alone or in combination with two or more.

[0048] Polyester polyols can be exemplified by those formed by the condensation polymerization of diacids and diols.

[0049] As a dicarboxylic acid, it is preferably selected from at least one of phthalic acid, tetrahydrophthalic acid, succinic acid, adipic acid, sebacic acid and dimer acids, and more preferably from at least one of terephthalic acid and tetrahydrophthalic acid.

[0050] As a diol, it is preferably selected from at least one of bisphenols, hydrogenated bisphenols, neopentyl glycol, ethylene glycol, and propylene glycol; more preferably from at least one of bisphenols, hydrogenated bisphenols, and neopentyl glycol; and even more preferably from at least one of hydrogenated bisphenol A and neopentyl glycol.

[0051] Among polyester polyols, polyester polyols formed by the condensation polymerization of terephthalic acid and neopentyl glycol, and polyester polyols formed by the condensation polymerization of tetrahydrophthalic anhydride and hydrogenated bisphenol A are further preferred.

[0052] Components composed of polyester polyols can be used alone or in combination with two or more.

[0053] The total content of structural units from 1,6-hexamethylene diisocyanate and structural units from 2-hydroxyethyl methacrylate in urethane (meth)acrylate (A) is preferably 70-100% by mass, more preferably 80-100% by mass, further preferably 90-100% by mass, even more preferably 95-100% by mass, even more preferably 99-100% by mass, and even more preferably 100% by mass. Uraframinoacrylate (meth)acrylate (A) may also be composed solely of structural units from 1,6-hexamethylene diisocyanate and structural units from 2-hydroxyethyl methacrylate. By setting the total content of structural units from 1,6-hexamethylene diisocyanate and structural units from 2-hydroxyethyl methacrylate within the above range, the free radical polymerizable resin composition possesses the magnetic properties required as a raw material for bonding magnets, while also being able to freely adjust its shape. Furthermore, it exhibits excellent moldability, curability, and workability.

[0054] Carbamate (meth)acrylate (A) is a crystalline carbamate (meth)acrylate. Because carbamate (meth)acrylate (A) is crystalline, it exhibits excellent workability, particularly in free radical polymerizable resin compositions.

[0055] The melting point of urethane (meth)acrylate (A) is preferably 30 to 150°C, more preferably 30 to 120°C.

[0056] The above-mentioned urethane (meth)acrylate (A) is preferably solid at 23°C.

[0057] By endowing urethane (meth)acrylate (A) with the aforementioned properties, the free radical polymerizable resin composition exhibits excellent workability, particularly. If urethane (meth)acrylate (A) is a solid, the shape of the composition does not change under the conditions of manufacturing, molding, and conveying the free radical polymerizable resin composition, thus enabling continuous production using general manufacturing equipment and conditions, which is therefore preferable. It should be noted that "solid" refers to a state in which the shape and volume are not easily changed by external forces.

[0058] The content of urethane (meth)acrylate (A) relative to the total amount of the free radical polymerizable resin composition is preferably 10-60% by mass, more preferably 10-50% by mass, even more preferably 10-40% by mass, even more preferably 15-35% by mass, even more preferably 15-30% by mass, and even more preferably 20-30% by mass. By setting the content of urethane (meth)acrylate (A) within the above range, the free radical polymerizable resin composition possesses the magnetic properties required as a raw material for bonding magnets, while also being able to freely adjust its shape. Furthermore, it exhibits excellent moldability, curability, and workability.

[0059] <Magnetic Powder (B)>

[0060] The free radical polymerizable resin composition of the present invention contains magnetic powder (B).

[0061] The magnetic powder (B) can be any magnetic powder, preferably selected from at least one of ferrite magnetic powder, AlNiCo magnetic powder and rare earth magnetic powder, more preferably selected from at least one of ferrite magnetic powder and rare earth magnetic powder, and from the viewpoint of formability and curability, rare earth magnetic powder is even more preferred.

[0062] Rare earth magnetic powder is a compound containing rare earth elements and transition metal elements.

[0063] Examples of rare earth elements include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, with at least one selected from Nd (neodymium) and Sm (samarium), and more preferably Sm.

[0064] Examples of transition metal elements include Fe, Co, Ni, and Mn, with at least one selected from Fe (iron) and Co (cobalt), and more preferably Fe.

[0065] As a rare earth magnetic powder, it is preferably selected from at least one of samarium iron nitrogen magnetic powder such as Sm-Fe-N, samarium cobalt magnetic powder such as Sm-Co, and neodymium magnetic powder such as Nd-Fe-B, and more preferably samarium iron nitrogen magnetic powder.

[0066] That is, from the viewpoint of formability and curability, the magnetic powder (B) is preferably selected from at least one of samarium iron nitrogen magnetic powder, samarium cobalt magnetic powder and neodymium magnetic powder, and from the viewpoint of formability and curability, samarium iron nitrogen magnetic powder is more preferred.

[0067] The preferred ferrite powder is selected from at least one of barium ferrite powder and strontium ferrite powder.

[0068] The magnetic powder (B) mentioned above can be used alone or in combination with two or more.

[0069] The content of magnetic powder (B) relative to 100 parts by weight of urethane (meth)acrylate (A) is preferably 100 to 500 parts by weight, more preferably 100 to 450 parts by weight, further preferably 100 to 400 parts by weight, even more preferably 120 to 400 parts by weight, even more preferably 150 to 400 parts by weight, even more preferably 200 to 400 parts by weight, and even more preferably 300 to 400 parts by weight. By setting the content of magnetic powder (B) within the above range, the free radical polymerizable resin composition possesses the magnetic properties required as a raw material for bonding magnets, while also allowing for free adjustment of shape. Furthermore, it exhibits excellent moldability, curability, and workability.

[0070] <Free Radical Polymerization Initiator (C)>

[0071] The free radical polymerizable resin composition of the present invention contains a free radical polymerization initiator (C).

[0072] Free radical polymerization initiators (C) are used to rapidly obtain homogeneous cured products during molding. Their types and amounts can be selected according to the application.

[0073] The free radical polymerization initiator (C) is preferably an organic peroxide.

[0074] The organic peroxide is preferably selected from at least one of ketone peroxide compounds, diacyl peroxide compounds, peroxide ester compounds, hydroperoxide compounds, dialkyl peroxide compounds, and peroxide ketal compounds, more preferably selected from at least one of peroxide ester compounds and dialkyl peroxide compounds, and even more preferably dialkyl peroxide compounds.

[0075] Examples of ketone peroxide compounds include methyl ethyl ketone peroxide and acetylacetone peroxide.

[0076] Examples of diacyl peroxide compounds include benzoyl peroxide.

[0077] Examples of peroxide ester compounds include tert-butyl peroxide, tert-butyl peroxyoctanoate, and tert-butyl peroxymonocarbonate-2-ethylhexyl.

[0078] Examples of dialkyl peroxide compounds include dicumyl peroxide and tert-butyl peroxide.

[0079] Examples of peroxide ketal compounds include 1,1-di(tert-hexylperoxy)cyclohexane, 1,1-di(tert-butylperoxy)cyclohexane, and 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane.

[0080] Organic peroxides can be used alone or in combination with two or more.

[0081] From the perspective of the degree of freedom in molding conditions and storage stability, it is preferred to select at least one of dicumyl peroxide, tert-butyl peroxide monocarbonate-2-ethylhexyl ester and tert-butyl peroxide, and more preferably dicumyl peroxide.

[0082] The 10-hour half-life temperature of the free radical polymerization initiator (C) is preferably 80–150°C, more preferably 100–130°C, and even more preferably 110–120°C. If the 10-hour half-life temperature of the free radical polymerization initiator (C) is within the above range, the resin composition can be stored for a long time, and the curing speed is also excellent. The polymerization initiator can be used alone or two or more can be used simultaneously.

[0083] The content of the free radical polymerization initiator (C) relative to 100 parts by weight of urethane (meth)acrylate (A) is preferably 0.1 to 3.0 parts by weight, more preferably 0.2 to 2.0 parts by weight, even more preferably 0.3 to 1.0 parts by weight, and even more preferably 0.3 to 0.8 parts by weight. By keeping the content of the free radical polymerization initiator (C) within the above range, the resin composition can be stored for a long time and has an excellent curing speed.

[0084] <N-oxygen compounds (D)>

[0085] The free radical polymerizable resin composition of the present invention contains an N-oxygen compound (D), wherein the content of the N-oxygen compound (D) is 0.20 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate (A).

[0086] Because the free radical polymerizable resin composition of the present invention contains N-oxygen compounds (D), the free radical polymerizable resin composition can maintain excellent curability while ensuring sufficient usable time and excellent moldability.

[0087] The N-oxy compound (D) is preferably selected from at least one of 2,2,6,6-tetraalkylpiperidine-1-oxy, 2,2,5,5-tetraalkylpyrrolidine-1-oxy, and 2-azaadamantane-N-oxy, more preferably 2,2,6,6-tetraalkylpiperidine-1-oxy. Each of the above N-oxy compounds may have substituents.

[0088] As a 2,2,6,6-tetraalkylpiperidine-1-oxy group, a 2,2,6,6-tetramethylpiperidine-1-oxy group is preferred.

[0089] The 2,2,6,6-tetramethylpiperidine-1-oxy group is preferably selected from at least one of 2,2,6,6-tetramethylpiperidine-1-oxy and 2,2,6,6-tetramethylpiperidine-1-oxy with a substituent at the 4-position, more preferably 2,2,6,6-tetramethylpiperidine-1-oxy with a substituent at the 4-position.

[0090] As a 2,2,6,6-tetramethylpiperidine-1-oxy group having a substituent at the 4-position, it is preferably selected from at least one of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy and 4-acyloxy-2,2,6,6-tetramethylpiperidine-1-oxy, more preferably 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy. That is, the N-oxy compound (D) is particularly preferably 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy.

[0091] Examples of acyl groups that can be 4-acyloxy-2,2,6,6-tetramethylpiperidine-1-oxy groups include acetyl and benzoyl groups.

[0092] The content of N-oxygen compounds (D) is 0.20 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate (A).

[0093] The content of N-oxygen compound (D) relative to 100 parts by weight of urethane (meth)acrylate (A) is preferably 0.25 to 0.60 parts by weight, more preferably 0.30 to 0.60 parts by weight, and even more preferably 0.40 to 0.60 parts by weight. With the content of N-oxygen compound (D) within the above range, the free radical polymerizable resin composition exhibits excellent moldability and curability.

[0094] <Other Ingredients>

[0095] The free radical polymerizable resin composition of the present invention may also contain mold release agents, colorants, reinforcing materials, thermoplastic resins, flame retardants, etc. as other components, without impairing the effects of the present invention.

[0096] It should be noted that the free radical polymerizable resin composition of the present invention preferably does not contain quinone-based polymerization inhibitors or phenol-based polymerization inhibitors, and is particularly preferably not containing phenol-based polymerization inhibitors.

[0097] Therefore, the content of the phenolic polymerization inhibitor in the free radical polymerizable resin composition of the present invention is preferably 0.05 parts by weight or less, more preferably 0.01 parts by weight or less, further preferably 0.001 parts by weight or less, and even more preferably 0.0001 parts by weight or less, relative to 100 parts by weight of urethane (meth)acrylate (A). Furthermore, it is even more preferable that the composition does not contain the phenolic polymerization inhibitor.

[0098] Furthermore, similarly, the content of the quinone-based polymerization inhibitor in the free radical polymerizable resin composition of the present invention is preferably 0.05 parts by weight or less, more preferably 0.01 parts by weight or less, further preferably 0.001 parts by weight or less, and even more preferably 0.0001 parts by weight or less, relative to 100 parts by weight of urethane (meth)acrylate (A). Moreover, it is even more preferable that the composition does not contain the quinone-based polymerization inhibitor.

[0099] Carbon black is a preferred colorant.

[0100] The content of the colorant in the free radical polymerizable resin composition is preferably 0.02 to 1% by mass, more preferably 0.05 to 0.7% by mass, even more preferably 0.1 to 0.5% by mass, and even more preferably 0.1 to 0.4% by mass.

[0101] As a release agent, fatty acid-based release agents, fatty acid metal salt-based release agents, mineral-based waxes, etc., which are commonly used for thermosetting resins, can be used, with fatty acid metal salt-based release agents having excellent heat resistance and color change properties being preferred.

[0102] Examples of release agents include stearic acid, stearates, and paraffin wax, with stearates being preferred.

[0103] Examples of stearates include zinc stearate, aluminum stearate, and calcium stearate, with zinc stearate being preferred. Release agents can be used alone or in combination with two or more agents.

[0104] Release agents can also be used as needed, such as external release agents that are sprayed or coated onto the mold, and internal release agents that are formulated with molding materials containing release agents.

[0105] Glass fiber is a preferred reinforcing material.

[0106] Examples of glass fibers include E-glass (alkali-free glass for electrical applications), C-glass (alkali-containing glass for chemical applications), A-glass (acid-resistant glass), and S-glass (high-strength glass), all made from silicate glass and borosilicate glass. These glass fibers can be used in the form of long fibers (rovings), short fibers (chopped strands), or ground fibers. Furthermore, surface-treated glass fibers can also be used.

[0107] By using reinforcing materials, cured products with excellent strength properties and dimensional stability can be obtained.

[0108] Examples of thermoplastic resins include polystyrene, acrylic resins, polyvinyl acetate, and styrene-butadiene rubber.

[0109] As flame retardants, halogen-based, phosphorus-based, nitrogen-based, and composite organic flame retardants, as well as inorganic flame retardants such as metal hydroxides, antimony-based, red phosphorus-based, organosilicon-based, and borate-based flame retardants, can be used. Furthermore, these flame retardants can be additive flame retardants or reactive flame retardants that react with the resin and embed into the resin skeleton. These flame retardants can be used alone or in combination.

[0110] In addition, the free radical polymerizable resin composition of the present invention may also contain free radical polymerizable compounds other than urethane (meth)acrylate (A) to a extent that does not impair the effects of the present invention.

[0111] Examples of free radical polymerizable compounds other than urethane (meth)acrylate (A) include urethane (meth)acrylates other than urethane (meth)acrylate (A), epoxy (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, free radical polymerizable monomers, and free radical polymerizable prepolymers.

[0112] The proportion of urethane (meth)acrylate (A) in the free radical polymerizable compound contained in the free radical polymerizable resin composition of the present invention is preferably 70-100% by mass, more preferably 80-100% by mass, even more preferably 90-100% by mass, even more preferably 95-100% by mass, even more preferably 99-100% by mass, and even more preferably 100% by mass. The free radical polymerizable compound contained in the free radical polymerizable resin composition may also consist solely of urethane (meth)acrylate (A).

[0113] <Method for manufacturing free radical polymerizable resin compositions>

[0114] The free radical polymerizable resin composition of the present invention can be obtained by any method, by combining the components, mixing them thoroughly and uniformly using a mixer or blender, and then preparing and granulating them using a heatable and pressurized kneader or extruder.

[0115] The free radical polymerizable resin composition of the present invention can be selected in the form of granules, powder, flakes, etc., depending on the application, but is preferably granular, and the granules are preferably composed of the above-described free radical polymerizable resin composition. Furthermore, the granules are more preferably particles. These granules are preferably composed of the above-described free radical polymerizable resin composition.

[0116] [magnet]

[0117] The magnet of the present invention is obtained by molding the above-mentioned free radical polymerizable resin composition.

[0118] That is, the magnet of the present invention is a magnet obtained by molding a free radical polymerizable resin composition, wherein the free radical polymerizable resin composition contains urethane (meth)acrylate (A) and magnetic powder (B), wherein the urethane (meth)acrylate (A) has structural units derived from 1,6-hexamethylene diisocyanate and structural units derived from 2-hydroxyethyl methacrylate, wherein the urethane (meth)acrylate (A) is crystalline urethane (meth)acrylate, wherein the free radical polymerizable resin composition contains a free radical polymerization initiator (C) and an N-oxygen compound (D), wherein the content of the N-oxygen compound (D) is 0.20 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate (A).

[0119] The magnets of the present invention use the above-mentioned free radical polymerizable resin composition with excellent formability, curability and operability as raw materials, and therefore can be made into various shapes and are applicable to a wide range of uses.

[0120] There are no limitations on the method of manufacturing the magnet of the present invention. It can be obtained by molding various thermosetting compositions using conventional methods.

[0121] For the above-mentioned free radical polymerizable resin composition, injection molding, injection compression molding, transfer molding, and compression molding are suitable molding methods, such as melt heating molding. Among these, injection molding using an injection molding machine and transfer molding using a transfer molding machine are particularly suitable. Injection molding can further shorten the molding time, while transfer molding can mold more molded parts at once.

[0122] As described above, the magnet of the present invention preferably includes a step of molding granules composed of the above-described free radical polymerizable resin composition by injection molding or transfer molding.

[0123] There are no particular limitations on the temperature and pressure of the free radical polymerizable resin composition during injection molding. When using an injection molding machine, setting the temperature of the free radical polymerizable resin composition to 60–130°C, the mold temperature to 130–190°C, and the pressure of the free radical polymerizable resin composition to 0.1–10 MPa results in less damage to the magnet, which is therefore preferred. Furthermore, when using a transfer molding machine, setting the mold temperature to 130–190°C and the pressure of the free radical polymerizable resin composition to 0.1–10 MPa also results in less damage to the magnet, which is also preferred.

[0124] Example

[0125] The following describes one embodiment of the present invention in more detail through examples, but the present invention is not limited to these examples.

[0126] <Preparation of Free Radical Polymerizing Resin Compositions>

[0127] Examples 1-4 and Comparative Examples 1-3

[0128] The following components were combined in the manner described in Table 1, heated and mixed in a mixer until homogeneous, and then cooled to obtain a free radical polymerizable resin composition.

[0129] The following substances are used as cooperating ingredients.

[0130] (1) Crystalline carbamate (meth)acrylate

[0131] 1,6-Hexamethylene diisocyanate adduct of 2-hydroxyethyl methacrylate (melting point 77°C, solid at 23°C).

[0132] (2) Amorphous free radical polymerizable resin

[0133] Amorphous vinyl ester resin (a methacrylic acid adduct of bisphenol A type epoxy resin, with no melting point. Liquid at 23°C).

[0134] (3) Magnetic powder

[0135] Magnetic powder 1: Ferrite magnetic powder (Fe2O3)

[0136] Magnetic powder 2: Neodymium magnetic powder (Nd-Fe-B)

[0137] Magnetic powder 3: Samarium iron nitrogen magnetic powder (Sm-Fe-N)

[0138] (4) Free radical polymerization initiator

[0139] Dicumyl peroxide (PERCUMYL D-40, 40% purity, manufactured by Nippon Oil Co., Ltd.)

[0140] (5) N-oxygen compounds

[0141] 4-Hydroxy-2,2,6,6-Tetramethylpiperidin-1-oxy(4H-TEMPO)

[0142] (6) Polymerization inhibitor

[0143] p-Benzoquinone (PBQ, manufactured by Seiko Chemical Co., Ltd.)

[0144] <Evaluation Methods>

[0145] (1) Formability (T1-Tm)

[0146] 10 mg of the free radical polymerizable resin composition obtained in each example and comparative example was placed in an aluminum dish, sealed with a cap, and used as the test sample. Using a differential scanning calorimeter "DSC6220" (manufactured by SEIKO Instruments Co., Ltd.), the test sample was heated from -60°C to 200°C at a rate of 10°C / min to obtain a curve. The endothermic termination temperature of the obtained curve was set as Tm (°C), and the exothermic onset temperature was set as T1 (°C), and the difference between Tm and T1 was calculated. The larger the difference between Tm and T1, the more easily the usable time from plasticization to curing of the free radical polymerizable resin composition can be set, thus resulting in excellent moldability. It should be noted that the endothermic termination temperature is the temperature at which the DSC curve on the high-temperature side of the melt peak intersects with the baseline. Conversely, the exothermic onset temperature is the temperature at which the DSC curve on the low-temperature side of the exothermic peak intersects with the baseline.

[0147] In addition, since no melting peak is observed in amorphous vinyl ester resins, this evaluation is not performed.

[0148] (2) Curing properties

[0149] Curing end temperature (T2)

[0150] 10 mg of the free radical polymerizable resin composition obtained in each example and comparative example was placed in an aluminum dish, sealed with a cap, and used as the test sample. Using a differential scanning calorimeter "DSC6220" (manufactured by SEIKO Instruments Co., Ltd.), the test sample was heated from -60°C to 200°C at a rate of 10°C / min to obtain a curve. The exothermic termination temperature of the obtained curve was set as the curing termination temperature (T2). The lower the curing termination temperature (T2), the faster the curing ends, resulting in excellent curability. The exothermic termination temperature is the temperature at which the DSC curve on the high-temperature side of the exothermic peak intersects with the baseline.

[0151] (3) Operability

[0152] The free radical polymerizable resin compositions obtained in each example and comparative example were formed into cylindrical shapes with a diameter of 1 cm and a height of 3 cm, and then adjusted to 23°C in a constant temperature chamber. A 50 g weight was placed on top of the cylindrical free radical polymerizable resin composition at 23°C, and the deformation of the cylindrical shape (the height difference of the cylinder before and after placing the weight) and the adhesion of the free radical polymerizable resin composition to the weight were evaluated according to the following criteria after 15 minutes. The less deformation of the cylindrical shape and the less adhesion to the weight, the easier it is to maintain a solid state at room temperature, and the better the handling during molding.

[0153] (Evaluation Criteria)

[0154] ○: The deformation of the cylindrical shape is almost imperceptible (the height difference of the cylinder is less than 1mm). The composition has minimal adhesion to the weights.

[0155] △: The deformation of the cylindrical shape can be seen (the height difference of the cylinder is more than 1 mm but less than 15 mm). The composition adheres to the weights.

[0156] ×: Obvious deformation of the cylindrical shape can be seen (height difference of the cylinder is more than 15mm). The composition adheres heavily to the weights.

[0157]

[0158] As shown in Table 1, the free radical polymerizable resin composition of the embodiments exhibits a large temperature difference from plasticization to curing, allowing for a sufficient usable time. Furthermore, the curing end temperature is low, enabling curing to be completed in a short time. Additionally, it can maintain a solid state at room temperature without any stickiness. Therefore, the free radical polymerizable resin composition of the present invention exhibits excellent moldability and curability, as well as excellent workability, making it suitable as a raw material for bonding magnets.

Claims

1. A free radical polymerizable resin composition comprising urethane (meth)acrylate A and magnetic powder B, The urethane (meth)acrylate A has structural units derived from 1,6-hexamethylene diisocyanate and structural units derived from 2-hydroxyethyl methacrylate. The urethane (meth)acrylate A is a crystalline urethane (meth)acrylate. The free radical polymerizable resin composition contains a free radical polymerization initiator C and an N-oxygen compound D. The content of the N-oxygen compound D is 0.20 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate A.

2. The free radical polymerizable resin composition according to claim 1, wherein, The melting point of the urethane (meth)acrylate A is 30–150 °C.

3. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The urethane (meth)acrylate A is a solid at 23°C.

4. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The total content of the structural units from 1,6-hexamethylene diisocyanate and the structural units from 2-hydroxyethyl methacrylate in the urethane (meth) acrylate A is 90-100% by mass.

5. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The N-oxygen compound D is 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy.

6. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The content of the N-oxygen compound D is 0.35 to 0.60 parts by weight relative to 100 parts by weight of urethane (meth)acrylate A.

7. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The content of the phenolic polymerization inhibitor is less than 0.05 parts by weight relative to 100 parts by weight of urethane methacrylate A.

8. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The 10-hour half-life temperature of the free radical polymerization initiator C is 80–150 °C.

9. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The content of magnetic powder B is 100 to 500 parts by weight relative to 100 parts by weight of urethane (meth)acrylate A.

10. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The magnetic powder B is selected from at least one of ferrite magnetic powder, AlNiCo magnetic powder, and rare earth magnetic powder.

11. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The magnetic powder B is selected from at least one of samarium iron nitrogen magnetic powder, samarium cobalt magnetic powder and neodymium magnetic powder.

12. The free radical polymerizable resin composition according to claim 1 or 2, wherein, The magnetic powder B is samarium iron nitrogen magnetic powder.

13. A magnet formed from the free radical polymerizable resin composition of claim 1 or 2.

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