JP7651095B2 - Resin molding material and method for manufacturing molded product - Google Patents

Description

The present invention relates to a resin molding material and a method for manufacturing a molded article. More specifically, the present invention relates to a resin molding material used to manufacture magnets by transfer molding, and a method for manufacturing a molded article that is a magnet by molding the resin molding material by transfer molding.

There are several known attempts to manufacture magnets by molding a resin molding material containing magnetic particles.
Magnets obtained by molding a resin molding material containing magnetic particles are sometimes called "bonded magnets" or "plastic magnets".

For example, Example 1 of Patent Document 1 describes how a bonded magnet composition is obtained by mixing and stirring Sm-Fe-N magnetic powder, an unsaturated polyester resin that is a thermosetting resin with radical polymerization reactivity, and a peroxyester peroxide that is a curing agent. The same Example also describes how the bonded magnet composition is molded by injection molding to obtain a bonded magnet.

Patent document 2 describes how a bonded magnet can be obtained by "compression molding" a resin compound containing a resin composition and magnet powder.

JP 2007-109963 A JP 2017-073479 A

According to the inventor's findings, the unsaturated polyester resin contained in the bonded magnet composition described in the examples of Patent Document 1 is liquid at room temperature. For this reason, the composition described in Patent Document 1 has problems such as (i) being difficult to distribute and store as a molding material, and (ii) being difficult to "pulverize" at room temperature, making it difficult to turn it into a granular or tablet-like resin molding material that is often used in resin molding, making it "difficult to handle as a material."

In addition, the "compression molding" described in Patent Document 2 has problems such as being unsuitable for molding complex shapes and tending to be less suitable for mass production than other resin molding methods.

The present invention was made in consideration of these circumstances. One of the objects of the present invention is to provide a resin molding material for manufacturing magnets that is easy to handle and suitable for mass-producing magnets with complex shapes.

As a result of extensive research, the inventors have completed the invention provided below and solved the above problems.

According to the present invention,
A resin molding material used to manufacture a magnet by transfer molding,
The composition includes an epoxy resin, a curing agent, and hard magnetic particles,
The resin molding material is provided, in which 70 mass % or more of the epoxy resin is an epoxy resin that is solid at 23°C, and 70 mass % or more of the curing agent is a curing agent that is solid at 23°C.

Further, according to the present invention,
There is also provided a method for producing a molded article, which comprises using a transfer molding device to inject a melt of the above-mentioned resin molding material into a mold, and obtaining a molded article by hardening the melt.

The present invention provides a resin molding material for manufacturing magnets that is easy to handle and suitable for mass-producing magnets with complex shapes.

Hereinafter, an embodiment of the present invention will be described in detail.
In this specification, the expression "a to b" in the description of a numerical range means from a to b, unless otherwise specified. For example, "1 to 5% by mass" means "1% by mass to 5% by mass."

In the description of groups (atomic groups) in this specification, when a notation does not specify whether the group is substituted or unsubstituted, the notation includes both groups having no substituents and groups having a substituent. For example, an "alkyl group" includes not only an alkyl group having no substituents (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group).
In this specification, the term "(meth)acrylic" refers to a concept that includes both acrylic and methacrylic. The same applies to similar terms such as "(meth)acrylate."
In this specification, the term "organic group" means an atomic group obtained by removing one or more hydrogen atoms from an organic compound, unless otherwise specified. For example, a "monovalent organic group" refers to an atomic group obtained by removing one hydrogen atom from any organic compound.

<Resin molding material>
The resin molding material of this embodiment is used to manufacture a magnet by transfer molding.
The resin molding material of the present embodiment contains an epoxy resin, a curing agent, and hard magnetic particles.
70% by mass or more of the epoxy resin is an epoxy resin that is solid at 23°C, and 70% by mass or more of the curing agent is a curing agent that is solid at 23°C.

The resin molding material of this embodiment contains a relatively large amount of an epoxy resin that is "solid" at 23° C. and a curing agent that is "solid" at 23° C. This makes it possible to design a resin molding material that is not liquid like the composition described in Patent Document 1 and that generally has substantially no fluidity at 23° C. This improves the handleability of the resin molding material.
In addition, the resin molding material of this embodiment is a resin molding material for "transfer molding". Therefore, it can be said that the resin molding material of this embodiment is easier to mass-produce molded products, i.e., bonded magnets, with more complex shapes than the material described in Patent Document 2 (material for compression molding).

The components and properties of the resin molding material of this embodiment will be described below.
Hereinafter, an epoxy resin that is solid at 23° C. may be referred to as a "specific epoxy resin", and a curing agent that is solid at 23° C. may be referred to as a "specific curing agent".

(Epoxy resin)
The resin molding material of the present embodiment contains an epoxy resin. 70% by mass or more, preferably 80% by mass or more, and more preferably 95% by mass or more of the epoxy resin is a specific epoxy resin, that is, an epoxy resin that is solid at 23° C. All of the epoxy resin (100%) may be the specific epoxy resin.
Examples of the epoxy resin include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, tetramethyl bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol E type epoxy resin, bisphenol M type epoxy resin, bisphenol P type epoxy resin, and bisphenol Z type epoxy resin; novolac type epoxy resins such as phenol novolac type epoxy resin and cresol novolac type epoxy resin; biphenyl type epoxy resin, biphenyl aralkyl type epoxy resin, aryl alkylene type epoxy resin, naphthalene type epoxy resin, anthracene type epoxy resin, phenoxy type epoxy resin, dicyclopentadiene type epoxy resin, norbornene type epoxy resin, adamantane type epoxy resin, fluorene type epoxy resin, and triphenyl methane type epoxy resin. Examples of the specific epoxy resin include those that are solid at 23°C among these.
The resin molding material of the present embodiment may contain only one type of epoxy resin, or may contain two or more types of epoxy resins. In addition, epoxy resins of the same type but different molecular weights may be used in combination.

The epoxy resin is preferably at least one selected from the group consisting of epoxy resins containing a triphenylmethane structure and/or epoxy resins containing a biphenyl structure, particularly as a specific epoxy resin. The moderate rigidity of the structure of these epoxy resins can improve the heat resistance and durability of the resulting magnet.

From another viewpoint, the epoxy resin preferably contains, as the specific epoxy resin, a bisphenol A type or F type epoxy resin. Since the resin skeleton of this epoxy resin is appropriately flexible, it is easy to improve the flow characteristics during transfer molding, and the set temperature during transfer molding can be lowered.
In particular, it is preferable to use (i) at least one selected from the group consisting of an epoxy resin containing a triphenylmethane structure and/or an epoxy resin containing a biphenyl structure in combination with (ii) a bisphenol A-type or F-type epoxy resin in terms of the balance of various performances.

Specifically, the epoxy resin containing a triphenylmethane structure is an epoxy resin containing a partial structure in which three of the four hydrogen atoms of methane (CH ₄ ) are substituted with a benzene ring. The benzene ring may be unsubstituted or substituted with a substituent. Examples of the substituent include a hydroxyl group and a glycidyloxy group.
Specifically, the epoxy resin containing a triphenylmethane structure contains a structural unit represented by the following general formula (a1): Two or more of these structural units are linked together to form a triphenylmethane skeleton.

In general formula (a1),
R ¹¹ , when present in a plurality, each independently represents a monovalent organic group, a halogen atom, a hydroxyl group, or a cyano group;
R ¹² , when present in a plurality, each independently represents a monovalent organic group, a halogen atom, a hydroxyl group, or a cyano group;
i is an integer from 0 to 3;
j is an integer from 0 to 4.

Examples of the monovalent organic group for R ¹¹ and R ¹² include those listed as the monovalent organic groups for R ^a and R ^b in general formula (BP) described later.
Each of i and j independently is preferably 0 to 2, and more preferably 0 to 1.
In one embodiment, both i and j are 0. That is, in one embodiment, all of the benzene rings in general formula (a1) have no substituents other than the explicitly stated glycidyloxy group as monovalent substituents.

Specifically, the epoxy resin containing a biphenyl structure is an epoxy resin containing a structure in which two benzene rings are linked by a single bond. The benzene ring here may or may not have a substituent.
Specifically, the epoxy resin containing a biphenyl structure has a partial structure represented by the following general formula (BP).

In general formula (BP),
R ^a and R ^b , when present in a plurality, each independently represent a monovalent organic group, a hydroxyl group, or a halogen atom;
r and s each independently represent 0 to 4;
* indicates that the group is connected to another group.

Specific examples of the monovalent organic group of R ^a and R ^b include an alkyl group, an alkenyl group, an alkynyl group, an alkylidene group, an aryl group, an aralkyl group, an alkaryl group, a cycloalkyl group, an alkoxy group, a heterocyclic group, and a carboxyl group.
Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a neopentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group.
Examples of the alkenyl group include an allyl group, a pentenyl group, and a vinyl group.
The alkynyl group includes, for example, an ethynyl group.
Examples of the alkylidene group include a methylidene group and an ethylidene group.
Examples of the aryl group include a tolyl group, a xylyl group, a phenyl group, a naphthyl group, and an anthracenyl group.
Examples of the aralkyl group include a benzyl group and a phenethyl group.
Examples of the alkaryl group include a tolyl group and a xylyl group.
Examples of the cycloalkyl group include an adamantyl group, a cyclopentyl group, a cyclohexyl group, and a cyclooctyl group.
Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an s-butoxy group, an isobutoxy group, a t-butoxy group, an n-pentyloxy group, a neopentyloxy group, and an n-hexyloxy group.
Examples of the heterocyclic group include an epoxy group and an oxetanyl group.

The monovalent organic groups of R ^a and R ^b each have a total carbon number of, for example, 1 to 30, preferably 1 to 20, more preferably 1 to 10, and particularly preferably 1 to 6.

r and s are each independently preferably 0 to 2, more preferably 0 to 1. In one embodiment, r and s are both 0.

More specifically, epoxy resins containing a biphenyl structure have a structural unit represented by the following general formula (BP1):

In general formula (BP1),
The definitions and specific embodiments of R ^a and R ^b are the same as those of general formula (BP).
The definitions and preferred ranges of r and s are the same as those of general formula (BP),
R ^c , when present in a plurality, each independently represents a monovalent organic group, a hydroxyl group, or a halogen atom;
t is an integer from 0 to 3.

Specific examples of the monovalent organic group for ^Rc include the same as those given as specific examples for ^Ra and ^Rb .
t is preferably 0 to 2, and more preferably 0 to 1.

Specific examples of bisphenol A or F type epoxy resins (epoxy resins produced by the condensation reaction of bisphenol A or bisphenol F with epichlorohydrin) include epoxy resins represented by the following general formula (EP):

In general formula (EP),
Each of the R's is independently a hydrogen atom or a methyl group, preferably a methyl group;
R ^a , R ^b , R ^c and R ^d each independently represent, when a plurality of R a , R b , R c and R d are present, a monovalent organic group, a hydroxyl group or a halogen atom;
p, q, r and s each independently represent an integer from 0 to 4, preferably from 0 to 2;
n is an integer of 0 or more, usually 0 to 10, and preferably 0 to 5.

Specific examples of the monovalent organic groups of R ^a , R ^b , R ^c and R ^d include the same as those exemplified as the monovalent organic groups of R ^a and R ^b in general formula (BP).

The amount of the epoxy resin in the resin molding material of this embodiment is, for example, 0.1 to 20 mass %, and preferably 0.5 to 10 mass %.
The amount of the epoxy resin in the resin molding material of this embodiment is, for example, 0.5 to 60% by volume, and preferably 3 to 40% by volume.

(Other resins)
The resin molding material of the present embodiment may contain resins other than the epoxy resin, so long as handling properties and the like are not excessively impaired.
Examples of other resins include thermosetting resins such as phenol resin, urea resin, melamine resin, unsaturated polyester resin, and polyimide resin.
Other examples of the thermoplastic resin include polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymers, modified polyolefins, polyamides (nylons), thermoplastic polyimides, and liquid crystal polymers such as aromatic polyesters, and thermoplastic resins such as polyphenylene oxide, polyphenylene sulfide, polycarbonate, polymethyl methacrylate, polyether, polyether ether ketone, polyetherimide, polyacetal, styrene-based, polyolefin-based, polyvinyl chloride-based, polyurethane-based, polyester-based, polyamide-based, polybutadiene-based, trans-polyisoprene-based, fluororubber-based, and chlorinated polyethylene-based.

(Hardening agent)
The resin molding material of the present embodiment contains a curing agent. 70% by mass or more, preferably 80% by mass or more, and more preferably 95% by mass or more of the curing agent is a specific curing agent, that is, a curing agent that is solid at 23° C. All of the curing agent (100%) may be the specific curing agent.
The curing agent is not particularly limited as long as it can react with the epoxy group of the epoxy resin to form a bond. For example, it can be an amine compound such as an aliphatic polyamine, an aromatic polyamine, an aromatic diamine, or a diamine diamide, an acid anhydride such as an alicyclic acid anhydride or an aromatic acid anhydride, a phenolic compound such as a novolac phenolic resin, or an imidazole compound. As the specific curing agent, it can be one that is solid at 23°C among these.

The hardener preferably contains a phenol-based hardener (phenol compound) as a specific hardener. This is expected to further improve the durability of the final magnet. A phenol-based hardener typically has two or more hydroxyl groups per molecule.

The phenol-based hardener preferably contains a skeleton selected from the group consisting of a novolac skeleton and a biphenyl skeleton. When the phenol-based hardener contains one of these skeletons, the durability of the magnet can be particularly improved.

Specifically, the "biphenyl skeleton" is a structure in which two benzene rings are linked by a single bond, as in the general formula (BP) in the above description of the epoxy resin.
Specific examples of phenol-based curing agents having a biphenyl skeleton include those having a structure in which the glycidyl group in the general formula (BP1) in the above description of epoxy resins is replaced with a hydrogen atom.

Specific examples of phenol-based curing agents having a novolac skeleton include those having a structural unit represented by the following general formula (N):

In general formula (N),
^R4 represents a monovalent substituent;
u is an integer from 0 to 3.

Specific examples of the monovalent substituent for R ⁴ include the same as those explained as the monovalent substituents for R ^a and R ^b in general formula (BP).
u is preferably 0 to 2, more preferably 0 to 1, and further preferably 0.

When the curing agent is a polymer or oligomer, the number average molecular weight of the curing agent (standard polystyrene equivalent value measured by GPC) is, for example, about 200 to 800.

The content of the curing agent in the resin molding material is, for example, 0.1 to 20% by mass, and preferably 0.5 to 10% by mass.
The content of the hardener in the resin molding material is, for example, 0.5 to 60% by volume, and preferably 3 to 40% by volume.
By appropriately adjusting the amount of curing agent, it is possible to further improve moldability and to improve the mechanical and magnetic properties of the resulting cured product (magnet).

(Hard Magnetic Particles)
The resin molding material of the present embodiment contains hard magnetic particles. The hard magnetic particles are magnetic particles that have a large coercive force and can be regarded as permanent magnets. As the hard magnetic particles, any type can be selected depending on the strength of the magnetic force, cost, and the like.

In terms of magnetic strength, the hard magnetic particles are preferably hard magnetic particles containing a rare earth element, such as Sm, Nd, Pr, Y, La, Ce, or Gd.
Specifically, preferred examples of hard magnetic particles include samarium iron nitrogen magnets (Sm-Fe-N magnetic particles), samarium cobalt magnets (Sm-Co magnetic particles), and neodymium magnets (Nd-Fe-B magnetic particles). The ratio of each element in these magnets is not particularly limited. It is sufficient that the final molded product (bonded magnet) has the necessary magnetic force and other magnetic properties.

Ferrite magnets (hard ferrites) are also an example of hard magnetic particles that can be used. Ferrite magnets are inferior in magnetic strength to the samarium magnets and neodymium magnets mentioned above, but are relatively inexpensive. Depending on the application, ferrite magnets are often sufficient. There are no particular limitations on the crystal structure of the ferrite magnet, as long as it exhibits hard magnetic properties.

Two or more types of hard magnetic particles may be used in combination. By using two or more types of hard magnetic particles having different chemical compositions and/or particle size distributions in combination, the flowability during molding can be further improved and the magnetic properties can be further improved.
A preferred combination of hard magnetic particles is a neodymium magnet and a samarium iron nitrogen magnet. Neodymium magnets have extremely strong magnetic force, but are expensive. By using a combination of a neodymium magnet and a samarium iron nitrogen magnet as hard magnetic particles, it is possible to obtain a strong magnetic force while reducing manufacturing costs.

The surface of the hard magnetic particles may be subjected to some kind of treatment. For example, the surface of the hard magnetic particles may be treated with a coupling agent or plasma. The surface treatment may modify the surface of the hard magnetic particles, which may result in improved compatibility with epoxy resins and improved flowability.

For example, it is possible to surface treat the hard magnetic particles with a silane compound such as a silane coupling agent before mixing with an epoxy resin, etc. Specific examples of the silane compound include compounds having an alkoxysilyl group, which will be described later.
Specific examples of the surface treatment method include immersing the hard magnetic particles in a diluted solution of a silane compound, and directly spraying the silane compound onto the hard magnetic particles.

As part of the surface treatment, plasma treatment may be performed before the surface treatment with a silane compound. For example, oxygen plasma treatment generates OH groups on the surface of the hard magnetic particles, facilitating bonding between the hard magnetic particles and the silane compound. This allows the functional groups to be bonded more firmly.

The shape of the hard magnetic particles is not particularly limited. The shape of the hard magnetic particles can be crushed, spherical, scaly, etc.

The volume-based median diameter _D50 of the hard magnetic particles is, for example, 1 to 200 μm, preferably 1 to 150 μm, and more preferably 1 to 135 μm. When two or more types of hard magnetic particles are used in combination, it is preferable that the median diameter _D50 of the hard magnetic particles as a whole (as a mixture of two or more types of hard magnetic particles) is within this numerical range. When _D50 is 1 μm or more, it is easy to further increase the fluidity during transfer molding. Also, when _D50 is 150 μm or less, it is easy to sufficiently improve the magnetic properties of the cured product (bonded magnet).

The hard magnetic particles may include first hard magnetic particles having a median diameter D ₅₀ of preferably 1 to 10 μm (more preferably 1 to 5 μm) and second hard magnetic particles having a median diameter D ₅₀ of preferably 50 to 150 μm (more preferably 100 to 150 μm). The first hard magnetic particles and the second hard magnetic particles usually differ from each other in chemical composition and/or particle size distribution. By using the first hard magnetic particles and the second hard magnetic particles in combination, it is considered that the relatively small first hard magnetic particles enter the "gaps" of the second hard magnetic particles having a relatively large particle size. It is considered that the filling amount of the hard magnetic particles per unit volume can be increased. It is considered that this further improves the magnetic properties while maintaining the flowability during molding.

Preferably, the first hard magnetic particles are samarium iron nitrogen magnets, and the second hard magnetic particles are neodymium magnets. Samarium iron nitrogen magnets generally have better magnetic properties when their particle size is smaller. On the other hand, neodymium magnets have very strong magnetic forces, but are generally expensive and difficult to use in large quantities. For these reasons, it is very reasonable to use samarium iron nitrogen magnets, which have small median diameters, in combination with neodymium magnets.

The ratio of the first hard magnetic particles to the second hard magnetic particles is not particularly limited. However, from the viewpoint of obtaining a sufficient effect from the combined use, a volume ratio of first hard magnetic particles/second hard magnetic particles=10/90 to 50/50 is preferable, and a volume ratio of first hard magnetic particles/second hard magnetic particles=20/80 to 30/70 is more preferable.

The median diameter _D50 can be obtained, for example, by a laser diffraction/scattering particle size distribution measuring device. Specifically, a particle size distribution curve is obtained by measuring the magnetic particles in a dry state using a particle size distribution measuring device "LA-950" manufactured by HORIBA, and _D50 can be obtained by analyzing this distribution curve.

As the hard magnetic particles, publicly known or commercially available particles can be used as appropriate. An example of a commercially available product is samarium iron nitrogen magnetic powder (product name: SFN alloy fine powder) from Sumitomo Metal Mining Co., Ltd.

The content of the hard magnetic particles in the resin molding material is preferably 25% by volume or more, more preferably 25 to 80% by volume, and even more preferably 40 to 60% by volume.
By making the content of hard magnetic particles 25% by volume or more, the magnetic force of the resulting molded product (bonded magnet) can be further increased. Also, by making the content of hard magnetic particles 80% by volume or less, it is possible to use sufficient amounts of epoxy resin, hardener, etc. This is preferable in terms of further improving the flow characteristics and hardening properties.

(Curing catalyst)
The resin molding material of the present embodiment preferably contains a curing catalyst. The curing catalyst may also be called a curing accelerator. The curing catalyst is not particularly limited as long as it accelerates the curing reaction of the epoxy resin, and a known epoxy curing catalyst may be used.

Specific examples include phosphorus atom-containing compounds such as organic phosphines, tetra-substituted phosphonium compounds, phosphobetaine compounds, adducts of phosphine compounds and quinone compounds, and adducts of phosphonium compounds and silane compounds; imidazoles (imidazole-based curing accelerators) such as 2-methylimidazole; and nitrogen atom-containing compounds such as amidines and tertiary amines, exemplified by 1,8-diazabicyclo[5.4.0]undecene-7 and benzyldimethylamine, and quaternary salts of amidines and amines.

When a curing catalyst is used, only one type may be used, or two or more types may be used.
When a curing catalyst is used, its content is preferably 0.01 to 1 mass %, more preferably 0.05 to 0.8 mass %, based on the total resin molding material. By setting the content within such a numerical range, a sufficient curing acceleration effect can be obtained without excessively impairing other performances.

(Release Agent)
The resin molding material of the present embodiment preferably contains a mold release agent, which can improve the mold releasability after transfer molding.

Examples of release agents include natural waxes such as carnauba wax, synthetic waxes such as montan acid ester wax and oxidized polyethylene wax, higher fatty acids such as zinc stearate and their metal salts, and paraffin. These may be used alone or in combination of two or more.

When using a release agent, only one type may be used, or two or more types may be used.
When a mold release agent is used, its content in the entire resin molding material is preferably 0.01 to 3 mass %, and more preferably 0.05 to 2 mass %, so that the effect of improving mold releasability can be reliably obtained.

(Compound having an alkoxysilyl group)
The resin molding material of this embodiment preferably contains a compound having an alkoxysilyl group. The alkoxysilyl group of this compound reacts with the hard magnetic particles to form a bond (i.e., this compound modifies the surface of the hard magnetic particles), which makes it easy to obtain effects such as suppressing aggregation of the hard magnetic particles and improving flow characteristics by improving compatibility with the epoxy resin.

As an example, a compound having an alkoxysilyl group is a silane coupling agent. In other words, as an example, a compound having an alkoxysilyl group is a compound having, in one molecule, an alkoxysilyl group capable of forming a bond with a hard magnetic particle and a reactive functional group capable of forming a bond with an organic component.

Examples of silane coupling agents include amino group-containing silane coupling agents, epoxy group-containing silane coupling agents, (meth)acryloyl group-containing silane coupling agents, mercapto group-containing silane coupling agents, vinyl group-containing silane coupling agents, ureido group-containing silane coupling agents, and sulfide group-containing silane coupling agents.

In particular, the silane coupling agent is preferably a compound represented by the following general formula (S1). This silane coupling agent has good compatibility with epoxy resins, curing agents, etc., especially since L has 6 or more carbon atoms.

In general formula (S1),
Each of the three R's is independently an alkyl group, preferably a methyl group or an ethyl group;
L is a linear or branched alkylene group having 6 or more carbon atoms (preferably 6 to 10),
X is a reactive organic functional group such as a vinyl group, an epoxy group, a glycidyl group, an oxetanyl group, or a (meth)acryloyl group.

As another example, the compound having an alkoxysilyl group may be a compound having an alkoxysilyl group and a linear or branched alkyl group having 6 or more carbon atoms (preferably 6 to 10). The alkoxysilyl group bonds to the hard magnetic particles, while the presence of the alkyl group having 6 or more carbon atoms tends to improve compatibility with other components such as epoxy resins.
Specific examples of such compounds include compounds represented by the following general formula (S2).

In general formula (S2),
Each of the three R's is independently an alkyl group, preferably a methyl group or an ethyl group;
Y is a linear or branched alkyl group having 6 or more carbon atoms (preferably 6 to 10 carbon atoms).

When a compound having an alkoxysilyl group is used, only one type may be used, or two or more types may be used.
When a compound having an alkoxysilyl group is used, the amount thereof is preferably 0.1 to 5 mass %, more preferably 0.5 to 3 mass %, based on the total resin molding material.

(Other ingredients)
The resin molding material of the present embodiment may contain components other than those described above, such as one or more of a stress reducing agent, a colorant, an antioxidant, a corrosion resistant agent, a dye, a pigment, and a flame retardant.

(Volatile organic solvents)
The resin molding material of the present embodiment preferably does not contain any volatile organic solvents other than the various components described above, or if it does contain any, it contains only a small amount of such solvents, which makes the resin molding material easier to handle.
Specifically, the content of volatile organic solvents in the resin molding material of the present embodiment is preferably 3 mass% or less, more preferably 2 mass% or less, and even more preferably 1 mass% or less. It is particularly preferable that the resin molding material of the present embodiment is substantially free of volatile organic solvents.

(Form of resin molding material)
The resin molding material of the present embodiment is preferably in a tablet or granular form, more preferably in a tablet form, at 23° C. By using the resin molding material in a tablet or granular form, distribution and storage of the resin molding material are facilitated, and the resin molding material is easily applicable to transfer molding.

(Characteristics of resin molding material when melted)
By adjusting the composition of the resin molding material of this embodiment and setting the flow characteristics of the resin molding material when melted to an appropriate numerical range, it is possible to further improve moldability.
Specifically, the melt viscosity measured at a temperature of 175°C using a constant load capillary extrusion rheometer (flow tester) is preferably 0.1 to 500 Pa·s, more preferably 0.1 to 300 Pa·s, and even more preferably 0.1 to 200 Pa·s.
As the constant load capillary extrusion rheometer, for example, a flow tester "CFT-500D" manufactured by Shimadzu Corporation can be used. The die hole diameter can be, for example, 0.5 mm, the die length can be, for example, 1.0 mm, and the pressure (load) can be, for example, 40 kgf (392 N).

(Glass transition temperature of the cured product)
The resin molding material of this embodiment is melted at 175°C, molded, and then post-cured at 175°C under atmospheric conditions for 4 hours to obtain a cured product having a glass transition temperature of preferably 150 to 220°C, more preferably 160 to 200°C. By designing the resin molding material so that the glass transition temperature is 150°C or higher, it is easy to meet the heat resistance required for, for example, in-vehicle applications. By designing the resin molding material so that the glass transition temperature is 220°C or lower, molding can be performed at a relatively low temperature. This is preferable in terms of suppressing thermal demagnetization due to low-temperature processing.

(Method of manufacturing resin molding material)
The resin molding material of this embodiment can be industrially produced, for example, by first (1) mixing the components using a mixer, (2) kneading the mixture with a roll at about 120° C. for 5 minutes or more, preferably about 10 minutes, to obtain a kneaded mixture, (3) cooling the kneaded mixture, and (4) pulverizing the mixture (a powdered resin molding material can be obtained by the above steps).
The powdered resin molding material may be compressed into granules or tablets, which results in a resin molding material that is particularly suitable for use in transfer molding.

<Method of manufacturing molded products>
Using a transfer molding device, a molten resin molding material described above is injected into a mold and the molten material is hardened to produce a molded product (bonded magnet).

Transfer molding can be carried out by appropriately using a known transfer molding device. Specifically, first, a preheated resin molding material is placed in a heating chamber, also called a transfer chamber, and melted to obtain a molten material. The molten material is then injected into a mold with a plunger and held there to harden the molten material. This allows a desired molded product to be obtained.
Transfer molding is preferable to other molding methods in terms of the controllability of the dimensions of the molded product and the increased freedom of shape.

Various conditions in transfer molding can be set arbitrarily. For example, the preheating temperature can be adjusted between 60 and 100°C, the heating temperature during melting can be adjusted between 150 and 250°C, the mold temperature can be adjusted between 150 and 200°C, and the pressure during injection of the molten resin molding material into the mold can be adjusted between 1 and 20 MPa.
By not raising the die temperature too high, thermal demagnetization of the hard magnetic particles can be suppressed.

When manufacturing bonded magnets, the magnetic force of the final bonded magnet can be increased by applying a magnetic field during production. For example, when pouring the molten material into a mold for transfer molding, it is preferable to orient the hard magnetic particles by applying a magnetic field to the molten material while it is still fluid in the mold. It is also preferable to magnetize the hardened material removed from the mold by setting it in a magnetizing device.

The above describes the embodiments of the present invention, but these are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements that can achieve the object of the present invention are included in the present invention.

The embodiments of the present invention will be described in detail based on examples and comparative examples. Note that the present invention is not limited to the examples.

<Production of resin molding material and handling properties (room temperature grindability)>
First, the components shown in Table 1 were prepared in the ratios shown and mixed uniformly to obtain a mixture.
The mixture was then kneaded at 120° C. for 10 minutes. After kneading, the kneaded product was cooled to room temperature to solidify, and then crushed and tableted to obtain a tablet-shaped resin molding material.
For the avoidance of doubt, no volatile organic solvents were used during mixing or kneading.

However, in Comparative Examples 1 and 2 (wherein some components were liquid at 23° C.), the kneaded product did not become solid even when cooled to room temperature after kneading, and was not in a state suitable for pulverization or tableting. Therefore, no further evaluation was performed.
In Table 2 shown later, those materials which could be crushed at room temperature and then compressed into tablets to obtain a tablet-shaped resin molding material are indicated as "OK" for room temperature crushing, and those which could not be obtained are indicated as "NG".

The raw material ingredients listed in Table 1 are as follows:

(Hard Magnetic Particles)
SFN alloy fine powder: samarium iron nitrogen magnet manufactured by Sumitomo Metal Mining Co., Ltd., D ₅₀ =2.4 μm, crushed shape MF15P: neodymium (NdFeB) magnet manufactured by Aichi Steel Corporation, D ₅₀ =120 μm, crushed shape

(Epoxy resin)
jER1032H60: Epoxy resin containing a triphenylmethane structure manufactured by Mitsubishi Chemical Corporation, solid at 23° C., containing the structural unit represented by the above general formula (a1) YL-6810: Bisphenol A type epoxy resin manufactured by Mitsubishi Chemical Corporation, solid at 23° C., containing the structure represented by the above general formula (EP) NC-3000: Epoxy resin containing a biphenyl structure manufactured by Nippon Kayaku Co., Ltd., solid at 23° C., containing the structure represented by the above general formula (BP1) jER152 (for comparison): Phenol novolac type epoxy resin manufactured by Mitsubishi Chemical Corporation, liquid at 23° C.

(Hardening agent)
PR-HF-3: Novolac type phenolic resin manufactured by Sumitomo Bakelite Co., Ltd., solid at 23°C. MEH-7851SS: Phenol resin containing a biphenyl structure manufactured by Meiwa Kasei Co., Ltd., solid at 23°C, containing a structure in which the glycidyl group in the above general formula (BP1) is replaced with a hydrogen atom. MEH-8000H (for comparison): Phenol resin manufactured by Meiwa Kasei Co., Ltd., liquid at 23°C.

(Curing catalyst)
Curesol 2PZ-PW: Imidazole-based curing accelerator manufactured by Shikoku Chemical Industry Co., Ltd.

(Release Agent)
WE-4: Ester wax manufactured by Clariant Chemicals Co., Ltd.

(Compound having an alkoxysilyl group)
KBM-4803: Glycidoxyoctyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd. KBM-3103C: Decyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.

<Evaluation>
(Moldability)
A mold having a cylindrical cavity with a diameter of 5 mm and a height of 5 mm was prepared. A molten tablet-shaped resin molding material was injected into the mold using a low-pressure transfer molding machine (KOTAKISEIKI Co., Ltd., "KTS-15"). The injection conditions were a mold temperature of 175°C, an injection pressure of 10 MPa, and a curing time of 300 seconds.

After cooling, the cured product (molded product) was taken out of the mold and its appearance was observed, and the moldability was evaluated according to the following criteria.
◯ (Good): No unfilled areas were found in the obtained molding.
× (bad): Unfilled areas were found in the obtained molding.

(Spiral Flow)
Using a low pressure transfer molding machine ("KTS-15" manufactured by Kotaki Seiki Co., Ltd.), the resin molding material was injected into a metal mold for measuring spiral flow conforming to EMMI-1-66 under the conditions of a metal mold temperature of 175°C, an injection pressure of 6.9 MPa, and a curing time of 120 seconds, and the spiral flow was measured. The larger this value, the better the fluidity, and it indicates that it is possible to manufacture magnets with complex shapes by using a metal mold with complex shapes.

(Gel time)
A powdered resin molding material was placed on a hot plate set at 175°C. After the material melted, it was kneaded with a spatula and the time it took to harden (the time it could no longer be kneaded with the spatula) was measured. A relatively long time means that there is a certain amount of time between the injection of the molten material into the mold and complete hardening, and indicates that magnets with complex shapes can be manufactured by using molds with complex shapes.

(Glass transition temperature of the cured product)
The resin molding material was injected and molded using a low pressure transfer molding machine (KTS-30 manufactured by Kotaki Seiki Co., Ltd.) under conditions of a mold temperature of 175°C, an injection pressure of 9.8 MPa, and a curing time of 300 seconds, to obtain a molded product of 15 mm x 4 mm x 4 mm. The molded product was then post-cured at 175°C for 4 hours. This resulted in a test specimen.
The glass transition temperature (°C) of the obtained test piece was determined by measurement using a thermomechanical analyzer (TMA100, manufactured by Seiko Instruments Inc.) under conditions of a measurement temperature range of 0°C to 400°C and a temperature increase rate of 5°C/min. That is, in the measurement using the thermomechanical analyzer, the amount of elongation/compression was plotted on the vertical axis and the temperature on the horizontal axis, and the temperature was determined as the temperature at the intersection of the straight line portion on the low temperature side and the straight line portion on the high temperature side.

(Melt Viscosity)
The melt viscosity of the resin molding material was measured using a Shimadzu Corporation flow tester (a type of constant load capillary extrusion rheometer) "CFT-500D" under conditions of a temperature of 175°C, a die hole diameter of 0.5 mm, a die length of 1.0 mm, and a pressure of 40 kgf.

(Forming in a magnetic field and checking magnetic properties)
The resin molding material was melted at about 175° C. in a magnetic field and molded to produce a molded product (bonded magnet).
Specifically, a molding machine capable of melting and molding a resin molding material while applying a magnetic field was used to obtain a cubic molded product (bonded magnet) having a size of 7 mm on each side.
・Forming machine Name: Magnetic field forming hydraulic press Model: TM-MPH10525-10A2TM Manufacturer: Tamagawa Seisakusho Magnetic field: 25kOe

The residual magnetic flux density Br of the molded product (bonded magnet) obtained above was measured under the following measurement conditions using the following measuring device. It can be said that the higher the Br, the greater the magnetic power of the permanent magnet.
・Measuring device Name: Vibrating sample magnetometer (VSM)
Model name: TM-VSM331483-HGC Manufacturer: Tamagawa Manufacturing Co., Ltd. Measurement conditions Atmosphere: Room temperature Measurement magnetic field: 3.3T/Gap 14mm

And it was evaluated according to the following criteria.
Passable: Br is 0.5T or more and less than 0.7T Good: Br is 0.7T or more and less than 0.8T Excellent: Br is more than 0.8T

The composition of the resin molding material is shown in Table 1, and the evaluation results are shown in Table 2.
In Table 1, the amounts of components other than the hard magnetic particles are listed in mass % based on the entire composition including the hard magnetic particles, and the amount of the hard magnetic particles is listed in volume % (i.e., packing factor) based on the entire composition including the hard magnetic particles.

As summarized in Table 2, the resin molding materials of Examples 1 to 11 were pulverizable at room temperature (i.e., the handling properties were good). In addition, the resin molding materials of Examples 1 to 11 also had good performance in terms of moldability, spiral flow, gel time, etc. In other words, it was shown that the resin molding materials of Examples 1 to 11 are suitable for mass-producing magnets with complex shapes.
In addition, the results of confirming the magnetic properties confirmed that the products (bonded magnets) molded from the resin molding materials of Examples 1 to 11 functioned as permanent magnets. In particular, when neodymium magnets were used as the hard magnetic particles, and further when neodymium magnets with a relatively large median diameter and samarium-iron-nitrogen magnets with a relatively small median diameter were used as the hard magnetic particles, very good magnetic properties (large residual magnetic flux density Br) were obtained.

Claims (13)

A resin molding material used for producing a magnet by a transfer molding method , the melt viscosity of which, as measured at a temperature of 175°C using a constant load capillary extrusion rheometer, is 0.1 to 200 Pa s ,
The composition includes an epoxy resin, a curing agent, and hard magnetic particles,
The resin molding material, wherein 70 mass % or more of the epoxy resin is an epoxy resin that is solid at 23°C, and 70 mass % or more of the curing agent is a curing agent that is solid at 23°C. The resin molding material according to claim 1,
A resin molding material having a volatile organic solvent content of 3 mass % or less. The resin molding material according to claim 1 or 2,
The resin molding material has a content of the hard magnetic particles of 25 volume % or more. The resin molding material according to any one of claims 1 to 3,
The resin molding material, wherein the hard magnetic particles have a volume-based median diameter _D50 of 1 to 150 μm. The resin molding material according to any one of claims 1 to 4,
The hard magnetic particles include first hard magnetic particles having a median diameter D ₅₀ of 1 to 10 μm and second hard magnetic particles having a median diameter D ₅₀ of 50 to 150 μm. The resin molding material according to any one of claims 1 to 5,
The hard magnetic particles are at least one selected from the group consisting of ferrite magnets, samarium-iron-nitrogen magnets, samarium-cobalt magnets, and neodymium magnets. The resin molding material according to any one of claims 1 to 6,
The hard magnetic particles include a neodymium magnet and a samarium iron nitrogen magnet. The resin molding material according to any one of claims 1 to 7,
The resin molding material includes a phenol-based hardener. The resin molding material according to any one of claims 1 to 8,
The resin molding material further comprises a mold release agent. The resin molding material according to any one of claims 1 to 9,
The resin molding material further comprises a compound having an alkoxysilyl group. The resin molding material according to any one of claims 1 to 10,
A resin molding material that is in tablet form at 23°C. The resin molding material according to any one of claims 1 to 11 ,
The resin molding material is melted at 175°C, molded, and then post-cured at 175°C in the atmosphere for 4 days, to obtain a cured product having a glass transition temperature of 150 to 220°C. Using a transfer molding device,
A method for producing a molded product, comprising: injecting a melt of a resin molding material used for producing a magnet by a transfer molding method, the resin molding material comprising an epoxy resin, a curing agent, and hard magnetic particles, wherein 70% by mass or more of the epoxy resin is an epoxy resin that is solid at 23°C, and 70% by mass or more of the curing agent is a curing agent that is solid at 23°C, into a mold; and obtaining a molded product by hardening the melt.