Polyurethane resin composition

Abstract

The present invention provides a polyurethane resin composition that exhibits excellent compatibility between hydroxyl group-containing compounds and crosslinking agents, and in which the cured product can exhibit hardness, elongation, and tensile strength suitable for following stress changes in parts, as well as excellent moisture resistance. [Solution] A polyurethane resin composition containing (A) an isocyanate group-containing compound, (B) a hydroxyl group-containing compound, and (C) a crosslinking agent, The (C) crosslinking agent comprises a secondary alcohol group and / or a tertiary alcohol group. The crosslinking agent (C) has a number average molecular weight of 900 or less. A polyurethane resin composition characterized by the following features.

Description

Technical Field

[0001] The present invention relates to a polyurethane resin composition.

Background Art

[0002] Conventionally, the density and integration of members such as electronic circuit boards and electronic components have been increasing, and improvement in reliability has been required for each component. For this reason, the above-mentioned electrical components and the like are sealed with a polyurethane resin to protect the components and the like.

[0003] As a polyurethane resin composition for forming the above-mentioned polyurethane resin, a two-component curable adhesive has been proposed. The two-component curable adhesive described in Patent Document 1 uses an alkoxylated aromatic diol and a diol having two hydroxyl groups bonded to primary carbon and having a number average molecular weight of 60 or more and 150 or less (see Patent Document 1).

[0004] However, in the polyurethane resin composition as described above, the primary carbon diol acting as a crosslinking agent is often solid, does not dissolve in polyols other than castor oil, and has a problem of poor compatibility.

[0005] In addition, the cured product obtained by curing the above-mentioned polyurethane resin composition has too high hardness, so the elongation rate is low, and when used for electrical and electronic components, cracks occur because it cannot follow the stress change of the components, resulting in insufficient sealing of the electronic components.

[0006] Furthermore, the above-mentioned electronic components and the like may be used under humid conditions, and the cured product obtained by curing the polyurethane resin composition used for sealing to protect the components and the like is required to have moisture resistance.

[0007] Therefore, it is desired to develop a polyurethane resin composition having excellent compatibility between a hydroxyl group-containing compound and a crosslinking agent, capable of showing a hardness, elongation rate, and tensile strength suitable for following the stress change of components in the cured product, and excellent moisture resistance. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7330820 [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a polyurethane resin composition that exhibits excellent compatibility between a hydroxyl group-containing compound and a crosslinking agent, and in which the cured product can exhibit hardness, elongation, and tensile strength suitable for following stress changes in a component, as well as excellent moisture resistance. [Means for solving the problem]

[0010] The present invention relates to the following polyurethane resin compositions, encapsulants, and electrical and electronic components. 1. A polyurethane resin composition containing (A) an isocyanate group-containing compound, (B) a hydroxyl group-containing compound, and (C) a crosslinking agent, The (C) crosslinking agent comprises a secondary alcohol group and / or a tertiary alcohol group. The crosslinking agent (C) has a number average molecular weight of 900 or less. A polyurethane resin composition characterized by the following features. 2. The polyurethane resin composition according to item 1, wherein the content of the crosslinking agent (C) is 20% by mass or less, with the polyurethane resin composition being 100% by mass. 3. The (C) crosslinking agent is a polyurethane resin composition according to item 1 or 2, wherein the molecular weight is 60 to 250. 4. The polyurethane resin composition according to any one of items 1 to 3, wherein the (C) crosslinking agent is a compound containing two or more hydroxyl groups. 5. The (C) crosslinking agent is a polyurethane resin composition according to any one of items 1 to 4, having an asymmetric structure. 6. The polyurethane resin composition according to any one of items 1 to 5, wherein the (C) crosslinking agent is a diol compound. 7. The polyurethane resin composition according to item 6, wherein the crosslinking agent (C) is greater than the total number of carbon atoms in all side chains branching from the main chain, which has hydroxyl groups at both ends. 8. The polyurethane resin composition according to any one of claims 1 to 7, wherein the (C) crosslinking agent is at least one selected from the group consisting of 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,3-butanediol, 2-ethyl-2,4-pentanediol, and 3-methyl-1,3-butanediol. 9. The polyurethane resin composition according to any one of claims 1 to 8, wherein the (B) hydroxyl group-containing compound is at least one selected from the group consisting of polybutadiene-based polyols and castor oil-based polyols. 10. A polyurethane resin composition according to any one of items 1 to 9, wherein the hardness change rate of the cured product, as measured by the measurement method described below, is -50 to -5%. (Hardness change rate) A test specimen (inner diameter 30 mm, height 10 mm) is prepared. The temperature of the test specimen is adjusted to 23°C, and the initial hardness (Type A) is measured using a hardness tester (Asker Rubber Hardness Tester Type A, manufactured by Polymer Instruments Co., Ltd.) according to the measurement method in accordance with JIS K6253. Next, the test specimen is left to stand for 100 hours in an environment of 121°C and 100% humidity, and after cooling to room temperature (23°C), the hardness of the test specimen (final hardness) is measured in the same manner as the initial hardness. From the initial hardness and final hardness, the hardness change rate (hydrolysis resistance) is calculated based on the following formula. (Hardness change rate (%)) = [(Final hardness - Initial hardness) / Initial hardness] × 100 11. A sealing material comprising a polyurethane resin composition as described in any of items 1 to 10. 12. An electrical or electronic component having the sealing material described in item 11. [Effects of the Invention]

[0011] The polyurethane resin composition of the present invention exhibits excellent compatibility between the hydroxyl group-containing compound and the crosslinking agent, and the cured product can exhibit hardness, elongation, and tensile strength suitable for following stress changes in the component, and can also exhibit excellent moisture resistance. [Modes for carrying out the invention]

[0012] 1. Polyurethane resin composition The polyurethane resin composition of the present invention is a polyurethane resin composition containing (A) an isocyanate group-containing compound, (B) a hydroxyl group-containing compound, and (C) a crosslinking agent, wherein the (C) crosslinking agent contains a secondary alcohol group and / or a tertiary alcohol group, and the (C) crosslinking agent has a weight-average molecular weight of 900 or less.

[0013] The polyurethane resin composition of the present invention having the above characteristics has a crosslinking agent (C) with a weight-average molecular weight of 900 or less that contains a secondary alcohol group and / or a tertiary alcohol group, so that the crosslinking agent can exhibit excellent compatibility with hydroxyl group-containing compounds such as polybutadiene polyols and castor oil. Furthermore, because the polyurethane resin composition of the present invention uses the above crosslinking agent (C), the cured product can exhibit hardness, elongation, and tensile strength suitable for following stress changes in the part. In other words, the polyurethane resin composition of the present invention, having the above configuration, exhibits excellent compatibility between hydroxyl group-containing compounds and the crosslinking agent, and the cured product can exhibit hardness, elongation, and tensile strength suitable for following stress changes in the part.

[0014] Furthermore, the polyurethane resin composition of the present invention contains (A) an isocyanate group-containing compound, (B) a hydroxyl group-containing compound, and (C) a crosslinking agent. By using the above-mentioned specific crosslinking agent, the excellent compatibility between the hydroxyl group-containing compound and the crosslinking agent, combined with the fact that the cured product exhibits excellent moisture resistance, is possible. For this reason, even when the cured product of the polyurethane resin composition of the present invention is used in a high-temperature, high-humidity environment, changes in hardness are suppressed.

[0015] The polyurethane resin composition of the present invention will be described in detail below.

[0016] ((A) Isocyanate group-containing compound) The isocyanate group-containing compound is not particularly limited, and known isocyanate group-containing compounds used in polyurethane resins can be used. Examples of such isocyanate group-containing compounds include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, aromatic polyisocyanate compounds, and araliphatic polyisocyanate compounds. Further, in order to further improve the heat resistance of the polyurethane resin composition, an isocyanurate-modified product of the above isocyanate group-containing compound may be used.

[0017] Examples of the aliphatic polyisocyanate compound include tetramethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2-methylpentane-1,5-diisocyanate, 3-methylpentane-1,5-diisocyanate, and the like.

[0018] Examples of the alicyclic polyisocyanate compound include isophorone diisocyanate, hydrogenated xylylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, methylcyclohexylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, and the like.

[0019] Examples of the aromatic polyisocyanate compound include tolylene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate, xylylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, and the like.

[0020] Examples of aromatic aliphatic polyisocyanate compounds include dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, and α,α,α,α-tetramethylxylylene diisocyanate.

[0021] The above-mentioned isocyanate group-containing compound may be a modified form of the above-mentioned polyisocyanate compound, and examples include isocyanurate, carbodiimide, adduct, biuret, allophanate, and carbodiimide compounds.

[0022] The above isocyanate group-containing compound is preferably 4,4'-diphenylmethane diisocyanate (MDI), and more preferably carbodiimide-modified 4,4'-diphenylmethane diisocyanate (MDI).

[0023] The above-mentioned isocyanate group-containing compounds may be used individually or as a mixture of two or more.

[0024] The molecular weight of the above isocyanate group-containing compound is preferably 50 to 1000, more preferably 100 to 500, and even more preferably 150 to 300.

[0025] In the polyurethane resin composition of the present invention, the content of the isocyanate group-containing compound used is not particularly limited as long as it is an amount that can be used in a polyurethane resin composition (especially a polyurethane resin composition for electrical and electronic components), and is appropriately adjusted according to the desired NCO / OH ratio, with 1 to 50% by mass being preferred, 5 to 45% by mass being more preferred, 10 to 40% by mass being even more preferred, and 15 to 35% by mass being particularly preferred, based on 100% by mass of the polyurethane resin composition. By setting the upper limit of the isocyanate group-containing compound content within the above range, curing defects of the polyurethane resin composition are further suppressed. By setting the lower limit of the isocyanate group-containing compound content within the above range, the heat resistance of the cured polyurethane resin composition is further improved.

[0026] In the polyurethane resin composition of the present invention, the content of the isocyanate group-containing compound used is not particularly limited as long as it is an amount that can be used in a polyurethane resin composition (especially a polyurethane resin composition for electrical and electronic components), and is appropriately adjusted according to the desired NCO / OH ratio, with (B) being preferably 5 to 50 parts by mass, more preferably 10 to 45 parts by mass, and even more preferably 15 to 40 parts by mass per 100 parts by mass of the hydroxyl group-containing compound. By setting the upper limit of the isocyanate group-containing compound content within the above range, curing defects of the polyurethane resin composition are further suppressed. By setting the lower limit of the isocyanate group-containing compound content within the above range, the heat resistance of the cured polyurethane resin composition is further improved.

[0027] ((B) Hydroxyl group-containing compounds) The hydroxyl group-containing compound used in the polyurethane resin composition of the present invention is not particularly limited, and various hydroxyl group-containing compounds other than the crosslinking agent (C) described later can be used from among those conventionally used as polyol components in polyurethane resin compositions.

[0028] Examples of the polyol components mentioned above include polyolefin polyols, castor oil polyols, polyester polyols, polybutadiene polyols, or their hydrogenated products. Specifically, examples include polybutadiene polyols, polylactone diols, polylactone triols, ester glycols, polyester polyols, polyether polyols, polycarbonate polyols, acrylic polyols, silicone polyols, fluorinated polyols, polytetramethylene glycols, polypropylene glycols, polyethylene glycols, polycaprolactone polyols, castor oil, hydrogenated castor oil, hydrogenated hydroxyl group-containing liquid polyisoprene, hydrogenated hydroxyl group-containing liquid polybutadiene, and the like.

[0029] Among the polyol components mentioned above, polyolefin polyols, polyester polyols, and their hydrogenated products are preferred, polybutadiene polyols, castor oil polyols, and their hydrogenated products are more preferred, and at least one selected from the group consisting of polybutadiene polyols and castor oil polyols is even more preferred.

[0030] Examples of the above-mentioned castor oil-based polyols and their hydrogenated products include castor oil or castor oil derivatives. Examples of the above-mentioned castor oil derivatives include castor oil fatty acids; hydrogenated castor oil obtained by hydrogenating castor oil or castor oil fatty acids; transesterified products of castor oil and other oils and fats; reaction products of castor oil and polyhydric alcohols; esterification reaction products of castor oil fatty acids and polyhydric alcohols; and products obtained by addition polymerization of these with alkylene oxides.

[0031] The above hydroxyl group-containing compounds may be used individually or as a mixture of two or more.

[0032] The weight-average molecular weight Mw of the above hydroxyl group-containing compound is preferably 500 to 5000, more preferably 800 to 4800, even more preferably 900 to 4000, and particularly preferably 1000 to 3000.

[0033] The lower limit of the number average molecular weight Mn of the above hydroxyl group-containing compound is preferably greater than 900, more preferably 1000 or more, and even more preferably 1200 or more. The upper limit of the number average molecular weight Mn of the above hydroxyl group-containing compound is preferably 6000 or less, more preferably 5000 or less, even more preferably 4000 or less, and particularly preferably 3500 or less. The lower limit of the number average molecular weight Mn of the above hydroxyl group-containing compound is preferably greater than 900, particularly from the viewpoint of distinguishing it from the (C) crosslinking agent described later.

[0034] In the polyurethane resin composition of the present invention, the content of the hydroxyl group-containing compound is preferably 30 to 98.5% by mass, more preferably 40 to 90% by mass, even more preferably 50 to 85% by mass, and particularly preferably 60 to 80% by mass, based on 100% by mass of the polyurethane resin composition. By setting the upper limit of the hydroxyl group-containing compound content within the above range, curing defects of the polyurethane resin composition are further suppressed. By setting the lower limit of the hydroxyl group-containing compound content within the above range, the elastic modulus of the polyurethane resin composition is further reduced, and the rise in glass transition temperature can be further suppressed.

[0035] In the polyurethane resin composition of the present invention, the content of the hydroxyl group-containing compound is preferably 30 to 98.5% by mass, more preferably 40 to 90% by mass, even more preferably 50 to 85% by mass, and particularly preferably 60 to 80% by mass, based on 100 parts by mass of the polyurethane resin composition. By setting the upper limit of the hydroxyl group-containing compound content within the above range, curing defects of the polyurethane resin composition are further suppressed. By setting the lower limit of the hydroxyl group-containing compound content within the above range, the elastic modulus of the polyurethane resin composition is further reduced, and the rise in glass transition temperature can be further suppressed.

[0036] In the polyurethane resin composition of the present invention, the content of the hydroxyl group-containing compound is preferably 200 to 900 parts by mass, more preferably 250 to 850 parts by mass, even more preferably 300 to 700 parts by mass, and particularly preferably 320 to 500 parts by mass, per 100 parts by mass of the isocyanate group-containing compound (A). By setting the upper limit of the hydroxyl group-containing compound content within the above range, curing defects of the polyurethane resin composition are further suppressed. By setting the lower limit of the hydroxyl group-containing compound content within the above range, the heat resistance of the cured polyurethane resin composition is further improved.

[0037] The polyurethane resin composition of the present invention preferably has an NCO / OH ratio of 0.6 to 2.0 between the isocyanate group-containing compound and the hydroxyl group-containing compound, and more preferably 0.7 to 1.5. Having the lower limit of the NCO / OH ratio within this range further improves the heat resistance of the polyurethane resin composition. Having the upper limit of the NCO / OH ratio within this range further suppresses curing defects in the polyurethane resin composition.

[0038] ((C) Crosslinking agent) The crosslinking agent used in the polyurethane resin composition of the present invention is not particularly limited as long as it contains a secondary alcohol group and / or a tertiary alcohol group and has a molecular weight of 900 or less. As such a crosslinking agent, a polyol compound can be used, with short-chain polyol compounds being preferred and short-chain diol compounds being more preferred.

[0039] Examples of crosslinking agents include 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,2-hexanediol, 1,3-butanediol, 2-ethyl-2,4-pentanediol, N,N-bis(2-hydroxypropyl)aniline, and 3-methyl-1,3-butanediol.

[0040] The crosslinking agent constituting the polyurethane resin composition of the present invention has a molecular weight of 900 or less. If the molecular weight exceeds 900, the crosslinking density decreases, and the hardness and tensile strength of the cured polyurethane resin composition decrease. The molecular weight of the crosslinking agent is preferably 700 or less, more preferably 500 or less, even more preferably 300 or less, particularly preferably 250 or less, and most preferably 200 or less. Furthermore, the lower limit of the molecular weight of the crosslinking agent is not particularly limited and may be 80 or 100.

[0041] In this specification, the molecular weight of the crosslinking agent is calculated by the following method. That is, since the molecular weight is equal to the mass per mole (g / mol), the molar mass (g / mol) is calculated using Avogadro's number (6.02 × 10⁻¹⁰). 23Divide by (number of atoms / mol) to calculate the relative mass of each atom, and the sum of these is the molecular weight.

[0042] The crosslinking agent constituting the polyurethane resin composition of the present invention comprises a secondary alcohol group and / or a tertiary alcohol group.

[0043] A secondary alcohol group is a group in which two carbon atoms are bonded to the carbon atom to which a hydroxyl group is bonded. For example, it is a group in which a hydroxyl group is bonded to a carbon atom other than the terminal carbon of the carbon chain.

[0044] Examples of compounds containing a secondary alcohol group include 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,3-butanediol, 2-ethyl-2,4-pentanediol, and N,N-bis(2-hydroxypropyl)aniline.

[0045] A tertiary alcohol group is a group in which three carbon atoms are bonded to a carbon atom to which a hydroxyl group is attached. For example, it is a carbon atom other than the terminal carbon in a carbon chain, and to which a carbon atom containing a side chain is bonded, to which a hydroxyl group is attached.

[0046] Examples of compounds containing a tertiary alcohol group include 3-methyl-1,3-butanediol.

[0047] Furthermore, the compounds containing the above-mentioned secondary alcohol group and / or tertiary alcohol group only need to contain a secondary alcohol group and / or a tertiary alcohol group in their molecule, and may also contain a primary alcohol group.

[0048] The primary alcohol group described above is a group in which zero or one carbon atom is bonded to the carbon atom to which a hydroxyl group is bonded. For example, it is a group in which a hydroxyl group is bonded to the end of a carbon chain.

[0049] Examples of compounds containing primary and secondary alcohol groups include 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, and 1,3-butanediol.

[0050] The crosslinking agent preferably has an asymmetric molecular structure. This asymmetric structure improves the compatibility between the hydroxyl group-containing compound and the crosslinking agent, and also improves the elongation of the cured product.

[0051] The crosslinking agent is preferably a diol compound, and it is preferable that the total number of carbon atoms in all the side chains branching from the main chain is greater than the total number of carbon atoms in the main chain which has hydroxyl groups at both ends. By using such a crosslinking agent, the compatibility between the hydroxyl group-containing compound and the crosslinking agent is further improved, and the elongation of the cured product is further improved.

[0052] The crosslinking agent content in the polyurethane resin composition of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the polyurethane resin composition. By limiting the upper limit of the crosslinking agent content to the above range, the compatibility between the hydroxyl group-containing compound and the crosslinking agent is further improved. Furthermore, the lower limit of the crosslinking agent content is not particularly limited and may be 0.5% by mass, 1% by mass, 2% by mass, or 3% by mass, based on 100% by mass of the polyurethane resin composition.

[0053] The crosslinking agent content in the polyurethane resin composition of the present invention is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 9 parts by mass or less, based on the total content of (A) isocyanate group-containing compound and (B) hydroxyl group-containing compound per 100 parts by mass. The upper limit of the crosslinking agent content is within the above range, which further improves the compatibility between the hydroxyl group-containing compound and the crosslinking agent. Furthermore, the lower limit of the crosslinking agent content is not particularly limited and may be 0.5 parts by mass, 1 part by mass, 2 parts by mass, or 3 parts by mass, based on the total content of (A) isocyanate group-containing compound and (B) hydroxyl group-containing compound per 100 parts by mass.

[0054] The crosslinking agent has a melting point upper limit that is preferably 150°C, more preferably 100°C, even more preferably 80°C, and particularly preferably 60°C, as measured by visual inspection. This range of upper limit improves the compatibility between the hydroxyl group-containing compound and the crosslinking agent. Furthermore, the lower limit of the melting point of the crosslinking agent is not particularly limited and may be 0°C, 10°C, 20°C, 30°C, 40°C, or 50°C.

[0055] The crosslinking agent described above preferably has an upper viscosity limit of 2000 mPa·s, and more preferably 1500 mPa·s, when measured at a temperature of 50°C. Having the upper viscosity limit of the plasticizer within this range further improves the compatibility between the hydroxyl group-containing compound and the crosslinking agent. Furthermore, the lower viscosity limit of the plasticizer is not particularly limited and may be 100 mPa·s, 300 mPa·s, 500 mPa·s, or 700 mPa·s.

[0056] The viscosity of the crosslinking agent mentioned above is measured using a Brookfield BH viscometer after adjusting the crosslinking agent to 50°C.

[0057] ((D) Inorganic fillers) The polyurethane resin composition of the present invention may contain an inorganic filler. The inorganic filler is not particularly limited, and conventionally known inorganic fillers can be used. Examples of such inorganic fillers include calcium carbonate, fused silica, amorphous silica, talc, alumina, aluminum hydroxide, aluminum nitride, boron nitride, magnesium hydroxide, and magnesium oxide. Among these, metal hydrate compounds such as aluminum hydroxide and magnesium hydroxide are preferred in terms of excellent flame retardancy and thermal conductivity. Examples of inorganic fillers with excellent thermal conductivity include alumina, magnesium hydroxide, aluminum hydroxide, and alumina nitride.

[0058] From the viewpoint of lowering the coefficient of linear expansion of the polyurethane resin composition of the present invention, reducing the stress of the urethane resin, and improving the tensile strength, and from the viewpoint of suppressing wear of surrounding materials when sealing the polyurethane resin composition and further improving workability, it is preferable to use an inorganic filler with a low Mohs hardness. The Mohs hardness of such an inorganic filler is preferably 4 or less, and more preferably 3 or less. Examples of such inorganic fillers include aluminum hydroxide (Mohs hardness 3), magnesium hydroxide (Mohs hardness 2.5), and talc (Mohs hardness 1).

[0059] The Mohs hardness of the inorganic filler described above is a value measured by the Mohs hardness test method using standard minerals. Specifically, the Mohs hardness of the inorganic filler is determined by relative comparison with the Mohs hardness of the standard mineral when scratches are made by rubbing the sample material against the standard mineral.

[0060] In the polyurethane resin composition of the present invention, the content of the inorganic filler is preferably 20 to 80% by mass, and more preferably 50 to 80% by mass, based on 100% by mass of the polyurethane resin composition. By setting the lower limit of the inorganic filler content within the above range, the flame retardancy of the polyurethane resin composition is further improved. By setting the upper limit of the inorganic filler content within the above range, the mixing viscosity during the manufacture of the polyurethane resin composition is suppressed, further improving workability, and further improving heat resistance, moisture resistance, strength, and flame retardancy without impairing the fluidity and flexibility after mixing.

[0061] (Additives) The polyurethane resin composition of the present invention may contain various additives as needed, such as antioxidants, polymerization catalysts, hygroscopic agents, fungicides, and silane coupling agents.

[0062] The antioxidant is not particularly limited, but conventionally known antioxidants used in urethane resin compositions can be used. Suitable antioxidants include pentaerythritol compounds, and more specifically, pentaerythritol=tetrakis[3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate].

[0063] The polymerization catalyst is not particularly limited, but conventionally known polymerization catalysts used in urethane resin compositions can be used. Examples of such polymerization catalysts include tin catalysts such as dioctyl tin dilaurate, dibutyl tin dilaurate, and dioctyl tin diacetate; lead catalysts such as lead octoate, lead octate, and lead naphthenate; bismuth catalysts such as bismuth octoate and bismuth neodecanoate; and amine catalysts such as diethylenetriamine. In addition, organometallic compounds and metal complex compounds may be used as catalysts.

[0064] The amount of these additives used should be determined appropriately from the range of normal additive amounts and identifications, depending on the intended use, so as not to impair the desired properties of the polyurethane resin composition.

[0065] (Polyurethane resin composition)

[0066] When the polyurethane resin composition of the present invention is in a liquid state before curing, its viscosity is preferably 500 to 100,000 mPa·s, more preferably 1,000 to 10,000 mPa·s, and even more preferably 1,500 to 5,000 mPa·s. By setting the viscosity within the above range, the polyurethane resin composition of the present invention can exhibit higher workability, improve flow into parts, enhance adhesion to electrical and electronic components, reduce the occurrence of voids, and further improve resin strength, thermal conductivity, and waterproofing. Furthermore, because the upper limit of viscosity is within the above range, a larger amount of inorganic filler can be incorporated, thus further improving flame retardancy.

[0067] In this specification, the viscosity of the polyurethane resin composition before curing is measured by the following method: The polyurethane resin composition is adjusted to 23°C, and the viscosity is measured 3 minutes after mixing (A) an isocyanate group-containing compound, (B) a hydroxyl group-containing compound, and (C) a crosslinking agent, as well as other additives as necessary, using a Brookfield BH viscometer.

[0068] The method for producing the polyurethane resin composition of the present invention is not particularly limited and can be produced by conventionally known methods used for producing polyurethane resin compositions.

[0069] Such a manufacturing method includes, for example, preparing a component containing an isocyanate group-containing compound to form a first component (polyisocyanate component), preparing a component containing a hydroxyl group-containing compound to form a second component (polyol component), and reacting the first and second components by mixing them to produce a polyurethane resin, thereby producing a polyurethane resin composition containing the polyurethane resin.

[0070] If the first component contains an isocyanate group-containing compound and the second component contains a hydroxyl group-containing compound, the other components may be contained in either the first or second component. In particular, a configuration in which the second component contains an inorganic filler is preferred. By adopting such a configuration, it is possible to suppress curing defects of the polyurethane resin caused by the reaction between the water contained in the inorganic filler and the polyisocyanate group-containing compound.

[0071] Specifically, a preferred combination of the compositions of the first and second components is one in which the first component contains only an isocyanate group-containing compound, and the second component contains a hydroxyl group-containing compound, a plasticizer, and optionally an inorganic filler, antioxidant, and polymerization catalyst. With such a composition, the first and second components exhibit excellent liquid stability.

[0072] A polyurethane resin composition is a liquid composition before curing, and its cured product is also called polyurethane resin. One method for curing a polyurethane resin composition is to react an isocyanate group-containing compound with a hydroxyl group-containing compound by mixing the first and second components described above, thereby curing the polyurethane resin composition over time. However, it may also be cured by heating. In this case, the heating temperature is preferably around 40°C to 120°C, and the heating time is preferably around 0.1 hours to 24 hours.

[0073] The hardness (A) of the cured polyurethane resin composition, as measured by the measurement method described in the examples below, is preferably 25 to 85, more preferably 30 to 80, and even more preferably 40 to 75. Having the hardness (A) of the cured product within this range allows the cured product to exhibit superior conformability to stress changes in the component.

[0074] The elongation of the cured polyurethane resin composition, as measured by the measurement method described in the examples below, is preferably 100 to 400%, more preferably 160 to 380%, and even more preferably 170 to 360%. Having the elongation of the cured product within this range allows the cured product to exhibit superior conformability to stress changes in the component.

[0075] The tensile strength of the cured polyurethane resin composition, as measured by the measurement method described in the examples below, is preferably 0.8 to 9.0 MPa, more preferably 1.8 to 8.5 MPa, and even more preferably 2.0 to 8.0 MPa. Having the tensile strength of the cured product within this range allows the cured product to exhibit superior conformability to stress changes in the component.

[0076] 2. Encapsulating materials, electrical and electronic components The present invention also relates to a encapsulant comprising the above-mentioned polyurethane resin composition. Specifically, the polyurethane resin composition hardens to form a cured product of the polyurethane resin composition (polyurethane resin), which becomes an encapsulant. The encapsulant comprising the above-mentioned polyurethane resin composition has excellent compatibility, heat resistance, and heat cycle properties, making it suitable for use in electrical and electronic components used in high-temperature environments and electrical and electronic components that generate heat. Furthermore, the encapsulant comprising the above-mentioned polyurethane resin composition also exhibits excellent flexibility in low-temperature ranges, making it suitable for use in electrical and electronic components used in low-temperature environments. Examples of such electrical and electronic components include transformers such as transformer coils, choke coils, and reactor coils, equipment control boards, and various sensors. Such electrical and electronic components are also part of the present invention. The electrical and electronic components of the present invention can be used in electric washing machines, toilet seats, water heaters, water purifiers, baths, dishwashers, power tools, automobiles, motorcycles, and the like. [Examples]

[0077] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

[0078] The raw materials used in the examples and comparative examples are shown below.

[0079] (A) Compounds containing an isocyanate group (a-1): MTL, carbodiimide-modified MDI, trade name: Myrionate MTL, manufactured by Tosoh Corporation, molecular weight 250, specific gravity 1.22.

[0080] (B) Hydroxyl group-containing compounds (b-1): R-45HT: Polybutadiene polyol, trade name; Poly bd R-45 HT, manufactured by Idemitsu Petrochemical Co., Ltd., number average molecular weight 2800

[0081] (C) Crosslinking agent (c-1): 2,2,4-trimethyl-1,3-pentanediol, containing primary and secondary alcohol groups, asymmetric, manufactured by Tokyo Chemical Industry Co., Ltd., equivalent weight 73, molecular weight 146.23, number of functional groups (theoretical value) 2, solid at room temperature (23°C), melting point 54°C (c-2): 2-Ethyl-1,3-Hexanediol, containing primary and secondary alcohol groups, asymmetric, manufactured by KH Neochem, equivalent weight 73, molecular weight 146.23, number of functional groups (theoretical value) 2 (c-3): 1,3-Butanediol, containing primary and secondary alcohol groups, asymmetric, manufactured by KH Neochem, equivalent weight 45, molecular weight 90.12, number of functional groups (theoretical value) 2 (c-4): 2-Ethyl 2,4-pentanediol, containing secondary and tertiary alcohol groups, asymmetric, manufactured by Tokyo Chemical Industry Co., Ltd., equivalent weight 59, molecular weight 118.18, number of functional groups (theoretical value) 2 (c-5): N,N-bis(2-hydroxypropyl)aniline, containing secondary alcohol group, symmetrical, Okahata Sangyo Co., Ltd., product name OK All 100, equivalent weight 105, molecular weight 209.28, number of functional groups (theoretical value) 2, viscosity 1000~1500 mPa·s (50℃) (c-6): 3-methyl-1,3-butanediol, containing primary and tertiary alcohol groups, asymmetric, trade name isoprene glycol S, equivalent weight 52, molecular weight 104.15, number of functional groups (theoretical value) 2 (c-7): Polytetramethylene ether glycol, containing primary alcohol groups, manufactured by Mitsubishi Chemical Corporation, product name PTMG250, equivalent weight 108, molecular weight 225, number of functional groups (theoretical value) 2, viscosity 50 mPa·s (20℃) (c-8): 1,4-Cyclohexanedimethanol, containing primary alcohol group, symmetric, alicyclic, equivalent weight 72, molecular weight 144.21, number of functional groups (theoretical value) 2, solid at room temperature (23°C). (c-9): 1,6-Hexanediol, containing primary alcohol group, symmetric, manufactured by Ube Industries, equivalent weight 59, molecular weight 118.17, number of functional groups (theoretical value) 2, solid at room temperature (23°C), melting point 80°C

[0082] (Manufacturing of polyurethane resin compositions) The raw materials for the formulations of components (B) and (C) shown in Tables 1 and 2 were placed in a reaction vessel equipped with a heating, cooling, and vacuum device, and dehydrated for 21 hours at 100°C and a pressure of 10 mmHg or less to prepare the second component (polyol component).

[0083] As the first component (polyisocyanate component), the isocyanate group-containing compound (A) was prepared.

[0084] Polyurethane resin compositions were obtained by adding the polyisocyanate component to the polyol component in the proportions shown in Tables 1 and 2, stirring, degassing, and mixing. The polyol component and polyisocyanate component were mixed by adjusting the polyol component to 23°C, then adding the polyisocyanate component adjusted to 23°C, and stirring for 1 minute at a rotation speed of 2000 rpm using a rotation / revolving mixer (Awatori Rentaro, manufactured by Shinky Co., Ltd.).

[0085] The following tests were performed using the polyurethane resin compositions of the examples and comparative examples prepared as described above.

[0086] (Preparation of test specimens) The prepared polyurethane resin composition was injected into three molds: mold A (100mm x 100mm x 3mm), mold B (30mm inner diameter, 10mm height), and mold C (10mm x 80mm x 3mm). The polyurethane resin composition inside the molds was then heated at 80°C for 16 hours and left to cure at room temperature for 1 day. This prepared test specimens A (100mm x 100mm x 3mm) and B (30mm inner diameter, 10mm height). Test specimen A was also cut into the shape of a No. 3 dumbbell to prepare test specimen A-1.

[0087] The polyurethane resin compositions of the examples and comparative examples prepared as described above, as well as test specimens, were used to perform the following measurements and tests.

[0088] Hardness (A) (Initial hardness) The temperature of test piece B was adjusted to 23°C, and its hardness (Type A) was measured using a hardness tester (Asker Rubber Hardness Tester Type A, manufactured by Polymer Instruments Co., Ltd.) in accordance with the measurement method compliant with JIS K 6253.

[0089] Tensile strength The tensile strength of test specimen A was measured using a measurement method compliant with JIS K 6301.

[0090] Growth rate The elongation (flexibility) of test specimen A-1 was calculated based on the following formula using a measurement method compliant with JIS K 6301. Elongation (%) = {[(gauge line distance at fracture)(gauge line distance)] ÷ (gauge line distance)} × 100

[0091] Hydrolysis resistance (rate of change in hardness) After measuring the initial hardness using test specimen B as described above, test specimen B was left to stand for 100 hours in an environment of 121°C and 100% humidity, cooled to room temperature (23°C), and then the hardness (final hardness) of test specimen B was measured in the same manner as the initial hardness. From the initial hardness and final hardness, the hardness change rate (hydrolysis resistance) was calculated based on the following formula. (Hardness change rate (%)) = [(Final hardness - Initial hardness) / Initial hardness] × 100

[0092] The results are shown in Tables 1 and 2.

[0093] [Table 1]

[0094] [Table 2]

[0095] compatibility The compatibility between (B) the hydroxyl group-containing compound and (C) the crosslinking agent was evaluated by the following method. Specifically, (B) the hydroxyl group-containing compound (polyol) and (C) the crosslinking agent were mixed in polypropylene cups in mass ratios of 9 / 1 and 9.5 / 0.5 to a total volume of 20 ml, and the mixtures for each example and comparative example were prepared by stirring thoroughly and transferred to 30 ml sample bottles. The sample bottles were left to stand for 7 days under conditions of 40°C (Table 3) and 5°C (Table 4). The appearance of the mixtures in the sample bottles after standing was observed visually and evaluated according to the evaluation criteria below. ◎:Transparent ○: Slight turbidity present △: Cloudy ×: Separation and coagulation present.

[0096] The results are shown in Tables 3 and 4.

[0097] [Table 3]

[0098] [Table 4] [Industrial applicability]

[0099] The polyurethane resin composition of the present invention exhibits excellent compatibility between hydroxyl group-containing compounds and crosslinking agents, and the cured product can exhibit hardness, elongation, and tensile strength suitable for following stress changes in components, as well as excellent moisture resistance. For this reason, it can be used in fields such as electrical products.

Claims

1. A polyurethane resin composition containing (A) an isocyanate group-containing compound, (B) a hydroxyl group-containing compound, and (C) a crosslinking agent, The (C) crosslinking agent comprises a secondary alcohol group and / or a tertiary alcohol group. The crosslinking agent (C) has a number average molecular weight of 900 or less. A polyurethane resin composition characterized by the following features.

2. The polyurethane resin composition according to claim 1, wherein the content of the crosslinking agent (C) is 20% by mass or less, with the polyurethane resin composition being 100% by mass.

3. The polyurethane resin composition according to claim 1, wherein the crosslinking agent (C) has a molecular weight of 60 to 250.

4. The polyurethane resin composition according to claim 1, wherein the (C) crosslinking agent is a compound containing two or more hydroxyl groups.

5. The (C) crosslinking agent is the polyurethane resin composition according to claim 1, having an asymmetric structure.

6. The polyurethane resin composition according to claim 1, wherein the (C) crosslinking agent is a diol compound.

7. The polyurethane resin composition according to claim 6, wherein the crosslinking agent (C) is greater than the total number of carbon atoms in all side chains branching from the main chain, which has hydroxyl groups at both ends.

8. The polyurethane resin composition according to claim 1, wherein the (C) crosslinking agent is at least one selected from the group consisting of 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 1,3-butanediol, 2-ethyl-2,4-pentanediol, and 3-methyl-1,3-butanediol.

9. The polyurethane resin composition according to claim 1, wherein the (B) hydroxyl group-containing compound is at least one selected from the group consisting of polybutadiene-based polyols and castor oil-based polyols.

10. The polyurethane resin composition according to claim 1, wherein the hardness change rate of the cured product, as measured by the measurement method described below, is -50 to -5%. (Hardness change rate) A test specimen (inner diameter 30 mm, height 10 mm) is prepared. The temperature of the test specimen is adjusted to 23°C, and the initial hardness (Type A) is measured using a hardness tester (Asker Rubber Hardness Tester Type A, manufactured by Polymer Instruments Co., Ltd.) according to the measurement method in accordance with JIS K6253. Next, the test specimen is left to stand for 100 hours in an environment of 121°C and 100% humidity, and after cooling to room temperature (23°C), the hardness of the test specimen (final hardness) is measured in the same manner as the initial hardness. From the initial hardness and final hardness, the hardness change rate (hydrolysis resistance) is calculated based on the following formula. (Hardness change rate (%)) = [(Final hardness - Initial hardness) / Initial hardness] × 100

11. A sealing material comprising the polyurethane resin composition according to any one of claims 1 to 10.

12. An electrical and electronic component having the sealing material described in claim 11.

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