JP7597111B2 - Method for manufacturing a thermally conductive sheet, laminate and thermally conductive sheet - Google Patents

Description

The present invention relates to a method for manufacturing a thermally conductive sheet, a laminate, and a thermally conductive sheet.

These heat dissipation measures are becoming increasingly important against the backdrop of higher integration of electronic devices such as semiconductor elements, and smaller, more dense modules. For this reason, heat dissipation components made of highly thermally conductive materials such as aluminum and copper are sometimes attached to heat generating elements such as electronic components. Furthermore, to further improve the heat dissipation effect, a thermally conductive sheet containing resin and a thermally conductive material may be placed between the heat generating element and the heat dissipation component.

In recent years, the amount of heat generated by electronic components has been increasing, and there is a demand for further improvement in the thermal conductivity of thermal conductive sheets. One possible method for increasing the thermal conductivity of thermal conductive sheets is to increase the amount of thermal conductive material contained in the thermal conductive sheet, but increasing the amount of thermal conductive material tends to make the sheet hard and brittle.
In view of this, it has been proposed to increase thermal conductivity in the thickness direction while reducing the use of thermally conductive material by orienting thermally conductive material in anisotropic shapes such as scales or fibers in the thickness direction of the sheet (see, for example, JP 2002-26202 A and JP 2015-73067 A).

The thermally conductive sheet described in JP 2002-26202 A is obtained by producing a primary sheet by molding a kneaded material containing resin and thermally conductive inorganic particles, stacking a number of primary sheets to a predetermined thickness, and slicing the laminate in a direction approximately perpendicular to the sheet surfaces.
The thermally conductive sheet described in JP 2015-73067 A is obtained by producing a thin resin sheet in which thermally conductive particles are oriented, folding it vertically, and welding it.
The methods described in these documents require complicated operations and special equipment, and therefore there is room for improvement in terms of productivity and cost.
Furthermore, there is room for improvement in the heat resistance of thermally conductive sheets produced by conventional methods.

In view of the above circumstances, an object of the present invention is to provide a method for producing a thermally conductive sheet that can be carried out without using special equipment and has excellent productivity.
Another object of the present invention is to provide a laminate that can be used to produce a thermally conductive sheet without using any special equipment and with good productivity, and a thermally conductive sheet obtained from the laminate.
Another object of the present invention is to provide a thermally conductive sheet having excellent heat resistance.

Means for solving the above problems include the following aspects.
<1> A primary sheet forming step of forming a primary sheet containing an organic polymer compound and thermally conductive particles on a substrate unwound from a roll;
a laminate forming step of winding the primary sheet to form a laminate of the primary sheets;
A slicing step of slicing the laminate of primary sheets along a thickness direction.
<2> The method for manufacturing a thermal conductive sheet described in <1>, wherein the thermal conductive particles contained in the primary sheet have anisotropic shape and are oriented along the surface direction of the primary sheet.
<3> The method for producing a thermal conductive sheet according to <1> or <2>, wherein the thermal conductive particles contained in the thermal conductive sheet are oriented in the thickness direction of the thermal conductive sheet.
<4> The method for producing a thermal conductive sheet according to any one of <1> to <3>, wherein the organic polymer compound contains an acrylic elastomer made of a block copolymer.
<5> The method for producing a thermal conductive sheet according to any one of <1> to <4>, wherein the primary sheet is formed using a coating machine.
<6> The method for producing a thermal conductive sheet described in any one of <1> to <5>, wherein the substrate has a release treatment applied to the surface on which the primary sheet is formed.
<7> A laminate in a wound state of a primary sheet containing an organic polymer compound and thermally conductive particles.
<8> A thermally conductive sheet produced from the laminate according to <7>.
<9> A thermally conductive sheet containing an organic polymer compound and thermally conductive particles,
the thermally conductive particles are oriented in the thickness direction of the thermally conductive sheet,
The organic polymer compound includes an acrylic elastomer composed of a block copolymer.
Thermal conductive sheet.

According to the present invention, there is provided a method for producing a thermally conductive sheet which can be carried out without using any special equipment and has excellent productivity.
The present invention further provides a laminate that can be used to produce a thermally conductive sheet without using any special equipment and with good productivity, and a thermally conductive sheet obtained from the laminate.
The present invention further provides a thermally conductive sheet having excellent heat resistance.

FIG. 2 is a diagram illustrating an example of a configuration of an apparatus used in a method for producing a thermally conductive sheet.

The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, the word "to" is used to mean that the numerical values before and after it are included as the lower limit and upper limit.
In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples.
In this specification, “(meth)acrylic” is used to mean both “acrylic and methacrylic” and “acrylic or methacrylic”, and “A and/or B” is used to mean both “A and B” and “A or B”.
In the present invention, a combination of two or more preferred embodiments is a more preferred embodiment.

<Method of manufacturing thermal conductive sheet>
The method for producing a thermally conductive sheet according to the present disclosure includes a primary sheet forming step of forming a primary sheet containing an organic polymer compound and thermally conductive particles on a substrate unwound from a roll;
a laminate forming step of winding the primary sheet to form a laminate of the primary sheets;
A slicing step of slicing the laminate of primary sheets along the thickness direction.

According to the above method, a thermally conductive sheet in which thermally conductive particles are oriented in the thickness direction can be manufactured without using a special device. For example, in the primary sheet forming step in the above method, a roll-to-roll type device that is generally used as a coating machine for forming a coating film on a substrate unwound from a roll can be used. In addition, in this method, a primary sheet is formed on a substrate unwound from a roll. Therefore, compared to the case where a primary sheet is formed for each substrate cut to a predetermined size, a primary sheet can be formed on a large amount of substrates at once, and productivity is excellent.
In the laminate formation step of the above method, the primary sheet is wound to form the laminate, which makes it possible to form a laminate of primary sheets more efficiently than in a method in which a plurality of individual primary sheets are laminated.

(Primary sheet forming process)
In the primary sheet forming step, a primary sheet containing an organic polymer compound and thermally conductive particles is formed on a substrate unwound from a roll.

There are no particular limitations on the method for forming the primary sheet on the substrate unwound from the roll. For example, the primary sheet may be formed by applying a composition containing an organic polymer compound and thermally conductive particles using a coater equipped with a coating head arranged at a predetermined distance from the surface of the substrate, and drying as necessary. Alternatively, the primary sheet may be formed by extrusion molding the composition containing the organic polymer compound and thermally conductive particles using an extruder equipped with a T-die at the tip.

When a coating machine is used, the coating head of the coating machine can be any known head without any particular restrictions. Specific coating heads include die coaters, roll coaters, comma coaters, gravure coaters, knife coaters, etc. Among these, die coaters, roll coaters, and comma coaters are preferred because they can be applied to coating fluids with a relatively wide viscosity range.

The configuration of the coater is not particularly limited, and a known coater can be used.
In addition to a roll for unwinding the substrate (unwinding roll) and the above-mentioned coating head, the coater may also include a drying oven, rolls other than the unwinding roll (such as a take-up roll and a guide roll), various sensors, etc. The above sensors can detect the coating amount, tension, amount of residual solvent, as well as the temperatures of the coating liquid and the drying oven, etc.

From the viewpoint of increasing the thermal conductivity of the thermally conductive sheet, it is preferable that the thermally conductive particles contained in the formed primary sheet have anisotropic shape and are oriented along the surface direction of the primary sheet (the direction perpendicular to the thickness direction).

When the thermally conductive particles contained in the primary sheet are oriented along the surface direction of the primary sheet, the thermally conductive particles contained in the thermally conductive sheet obtained by slicing the laminate of the primary sheets along the thickness direction tend to be oriented along the thickness direction of the thermally conductive sheet. This improves the thermal conductivity of the thermally conductive sheet in the thickness direction.

In this disclosure, "a state in which thermally conductive particles are oriented along the surface direction of the primary sheet" means a state in which thermally conductive particles having anisotropic shape contained in the primary sheet form an angle between their major axes and the surface direction of the primary sheet in the range of 0° to 30°, preferably in the range of 0° to 15°.

In the present disclosure, "particles having anisotropic shape" refers to particles having a ratio of the long axis to the short axis (long axis/short axis, aspect ratio) of greater than 1. The state of particles having anisotropic shape is not particularly limited, and may be ellipsoidal, plate-like, scaly, fibrous, rod-like, etc.

In this disclosure, "a state in which the thermally conductive particles are oriented along the surface direction of the primary sheet" includes both a state in which all of the thermally conductive particles contained in the primary sheet are oriented along the surface direction of the primary sheet, and a state in which some of the thermally conductive particles are oriented along the surface direction of the primary sheet.

From the standpoint of thermal conductivity, it is preferable that the proportion of thermally conductive particles that are oriented along the surface direction of the primary sheet is 50% or more by number, more preferably 70% or more, and even more preferably 80% or more.

Whether or not the thermally conductive particles contained in the primary sheet are oriented along the surface direction of the primary sheet can be confirmed, for example, by observing a cut surface of the primary sheet using an electron microscope.

There are no particular limitations on the method for orienting the thermally conductive particles contained in the primary sheet along the surface direction of the primary sheet. For example, there is a method in which a shear stress is applied to the composition containing the organic polymer compound and the thermally conductive particles when the composition is applied to the substrate.

The thickness of the primary sheet formed on the substrate is not particularly limited. For example, it may be in the range of 10 μm to 500 μm, 20 μm to 300 μm, or 50 μm to 100 μm.

The material of the substrate is not particularly limited, and for example, resin, paper, metal, a combination of these, etc. can be used.
Examples of the resin include polyethylene terephthalate, polyethylene, polyester, polypropylene, polyimide, polyamide, polyetherimide, polyether naphthalate, and methylpentene film.
In order to facilitate separation from the primary sheet, the surface of the substrate on which the primary sheet is formed may be subjected to a release treatment.
The substrate may be recycled or non-recycled.

(Laminate Forming Process)
In the laminate formation step, the primary sheet obtained in the primary sheet formation step is wound to form a laminate of primary sheets.

In this disclosure, "rolling a primary sheet to form a laminate of primary sheets" means that a multilayer structure is formed by rolling up the primary sheet and stacking multiple layers of the primary sheet. The rolling method is not particularly limited, and can be selected from, for example, a method of rolling up the primary sheet around a core, a method of rolling up the primary sheet into a spiral roll, and the like.

When the primary sheet is wound using a winding core, the winding core may be provided as part of the device used in the primary sheet formation process (for example, a winding roll in a coating machine), or it may be provided in a device separate from the device.

When the primary sheet is wound around a winding core, the cross-sectional shape of the winding core is not particularly limited and may be circular or a shape other than circular. For example, it may be an ellipse, an oval, a polygon, or other shape that includes a portion of low curvature or a straight portion. If the cross-sectional shape of the winding core includes a portion of low curvature or a straight portion, at least a portion of the laminate of primary sheets formed around the winding core can be made flat. This is advantageous in that it makes it easier to slice the laminate of primary sheets in the slicing process and allows the thickness of the heat conductive sheet obtained by slicing to be uniform.

In one embodiment of the laminate formation process, a primary sheet formed on a substrate is separated from the substrate, and the primary sheet separated from the substrate is wound onto a take-up roll to form a laminate of primary sheets.

In another embodiment of the laminate formation process, the substrate on which the primary sheet is formed is wound onto a take-up roll, and then when the substrate is rewound, the primary sheet is separated from the substrate and rolled up to form a laminate of the primary sheets.

There are no particular limitations on the method for separating the primary sheet from the substrate in the laminate formation process. For example, the separated primary sheet and substrate may be wound up on separate rolls.

When the primary sheet is wound, the laminate of the primary sheets may be pressurized, heated, or the like to improve the adhesion between the layers constituting the laminate. Pressure may be applied by adjusting the tension (winding pressure) when winding the primary sheet, or the nip pressure with the nip roll, etc.

(Slicing process)
In the slicing process, the laminate of primary sheets is sliced along the thickness direction to obtain a thermally conductive sheet. The thickness direction of the thermally conductive sheet obtained by slicing the laminate corresponds to the surface direction of the primary sheets included in the laminate. Therefore, when the thermally conductive particles are oriented along the surface direction of the primary sheets, the thermally conductive particles included in the thermally conductive sheet obtained by slicing the laminate of primary sheets along the thickness direction are oriented along the thickness direction of the thermally conductive sheet. As a result, the thermal conductivity of the thermally conductive sheet in the thickness direction is improved.

The method for carrying out the slicing process is not particularly limited, and can be carried out using known means such as a knife, a rotary blade, or an ultrasonic cutter. The slice width (thickness of the thermally conductive sheet) is not particularly limited, and can be set according to the performance and use of the resulting thermally conductive sheet. For example, it may be in the range of 0.1 mm to 5 mm, 0.2 mm to 3 mm, 0.3 mm to 2 mm, or 0.5 mm to 1.0 mm.

The slicing direction is not particularly limited as long as it is along the thickness direction of the primary sheet laminate. For example, the slicing may be performed so that the angle between the plane parallel to the thickness direction and the sliced surface is in the range of 0° to 30°, or in the range of 0° to 15°.

When the primary sheet formed on the substrate is formed using a composition containing an organic polymer compound and thermally conductive particles, the composition may contain only the organic polymer compound and thermally conductive particles, or may further contain other components. Details of the organic polymer compound and thermally conductive particles contained in the composition and other components contained as needed are the same as those of the organic polymer compound and thermally conductive particles and other components contained as needed described below.
The composition may contain a solvent for adjusting the viscosity, etc. The solvent may be removed by drying after the composition is applied.
The composition may be prepared without containing a solvent by, if necessary, heating and kneading the organic polymer compound, the thermally conductive particles, and other components that are included as required.
The composition may optionally contain a crosslinking agent to crosslink the organic polymer compound.

(Organic polymer compound)
The type of organic polymer compound used in the above method is not particularly limited. From the viewpoint of flexibility of the thermal conductive sheet and ease of forming a laminate of the primary sheet, it is preferable that the glass transition temperature (Tg) is 50° C. or less. The organic polymer compound is preferably

Specific examples of organic polymer compounds with a Tg of 50°C or less include flexible organic polymer compounds generally referred to as elastomers or rubber, such as poly(meth)acrylic acid ester polymer compounds (so-called acrylic elastomers) whose main structure is derived from (meth)acrylic monomers with low Tg, such as butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate, polymer compounds whose main structure is a polydimethylsiloxane structure (so-called silicone rubber), polymer compounds whose main structure is a polyisoprene structure (so-called isoprene rubber, natural rubber), polymer compounds whose main raw material component is chloroprene (polychloroprene, so-called neoprene rubber), polymer compounds whose main structure is a polybutadiene structure (so-called butadiene rubber), and urethane polymer compounds having polyester or polyether soft segments (so-called urethane elastomers).

Among these, acrylic elastomers are preferred because they have excellent flexibility, chemical stability and processability, and their adhesion is easy to control and they are relatively inexpensive.

The poly(meth)acrylic acid ester-based polymer compound constituting the acrylic elastomer may use an alkyl (meth)acrylic acid ester compound and/or an alkoxyalkyl (meth)acrylic acid ester compound as a constituent monomer.
The proportion of the (meth)acrylic acid alkyl ester compound and/or the (meth)acrylic acid alkoxyalkyl ester compound may be 50% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more based on the total constituent monomers of the poly(meth)acrylic acid ester-based polymer compound. It may also be 99.9% by mass or less, 99% by mass or less, 95% by mass or less, 90% by mass or less, or 80% by mass or less. When the proportion is 50% by mass or more, it is easy to obtain a flexible polymer with a low Tg.

Specific examples of the (meth)acrylic acid alkyl ester compound include linear or branched alkyl ester compounds of (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate;
Examples of the ester compounds include aliphatic cyclic ester compounds of (meth)acrylic acid, such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, isobornyl (meth)acrylate, adamantyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentanyl (meth)acrylate.

Specific examples of (meth)acrylic acid alkoxyalkyl ester compounds include methoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, n-propoxyethyl (meth)acrylate, n-butoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, n-propoxypropyl (meth)acrylate, n-butoxypropyl (meth)acrylate, methoxybutyl (meth)acrylate, ethoxybutyl (meth)acrylate, n-propoxybutyl (meth)acrylate, and n-butoxybutyl (meth)acrylate.

The poly(meth)acrylic acid ester polymer compound may contain a crosslinkable functional group. The crosslinkable functional group can be introduced, for example, by copolymerizing a vinyl compound having a crosslinkable functional group. Examples of the vinyl compound having a crosslinkable functional group include unsaturated carboxylic acids, hydroxyl group-containing vinyl compounds, and epoxy group-containing vinyl compounds. These compounds may be used alone or in combination of two or more.

Examples of unsaturated carboxylic acids include (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, citraconic acid, cinnamic acid, and monoalkyl esters of unsaturated dicarboxylic acids (monoalkyl esters of maleic acid, fumaric acid, itaconic acid, citraconic acid, maleic anhydride, itaconic anhydride, citraconic anhydride, etc.). These compounds may be used alone or in combination of two or more.

Examples of hydroxy group-containing vinyl compounds include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and mono(meth)acrylic acid esters of polyalkylene glycols such as polyethylene glycol and polypropylene glycol. These compounds may be used alone or in combination of two or more.

Examples of epoxy group-containing vinyl compounds include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, etc. These compounds may be used alone or in combination of two or more.

When the poly(meth)acrylic acid ester-based polymer compound has a crosslinkable functional group, the amount of the crosslinkable functional group introduced is preferably 0.01 mol % or more, more preferably 0.1 mol % or more, even more preferably 1.0 mol % or more, and particularly preferably 2.0 mol % or more, based on the total structural units of the poly(meth)acrylic acid ester-based polymer compound.

From the viewpoint of heat resistance, the organic polymer compound preferably contains an acrylic elastomer made of a block copolymer.
The acrylic elastomer made of a block copolymer has at least one polymer block (A) as a hard segment and at least one polymer block (B) as a soft segment. There is no particular limitation on the structure of the block copolymer, and various linear or branched block copolymers such as AB type diblock polymers, or ABA type and ABC type triblock polymers can be used.

In terms of obtaining good performance as an elastomer material, those having an A-(BA)n type structure, such as an ABA triblock copolymer consisting of polymer block (A)-polymer block (B)-polymer block (A), are preferred. When the block copolymer has two or more of the above polymer blocks (A) and/or polymer blocks (B), the structures of the individual blocks may be the same or different.

The Tg of the polymer constituting the polymer block (A) is preferably 100° C. or higher, more preferably 120° C. or higher, and even more preferably 150° C. or higher, from the viewpoint of heat resistance. The Tg may be 170° C. or higher, or may be 200° C. or higher. Due to limitations on the constituent monomer units that can be used, the upper limit of the Tg may be 350° C.
The Tg value of the polymer constituting the polymer block can be obtained by differential scanning calorimetry (DSC) or can be calculated from the monomer units constituting the polymer block.

The polymer block (A) may have structural units derived from styrenes and maleimide compounds. The polymer block (A) may also be made of polymethyl methacrylate.

The styrenes include styrene and its derivatives. In the polymer block (A), the proportion of the structural units derived from the styrenes is preferably 1% by mass to 70% by mass, more preferably 5% by mass to 70% by mass, even more preferably 10% by mass to 70% by mass, and even more preferably 20% by mass to 60% by mass, based on the total structural units of the polymer block (A). When the structural units derived from styrenes are 1% by mass or more, a block copolymer with excellent moldability tends to be obtained.

The maleimide compounds include maleimide and N-substituted maleimide compounds. In the polymer block (A), the proportion of the structural units derived from the maleimide compound is preferably 30% by mass to 99% by mass, more preferably 30% by mass to 95% by mass, even more preferably 30% by mass to 90% by mass, and even more preferably 40% by mass to 80% by mass, based on the total structural units of the polymer block (A). When the structural units derived from the maleimide compound are 30% by mass or more, the heat resistance of the resulting block copolymer tends to be good.

The Tg of the polymer constituting the polymer block (B) is preferably 20° C. or lower, more preferably 0° C. or lower, and even more preferably −10° C. or lower. When the Tg is 20° C. or lower, the resulting block copolymer tends to have sufficient flexibility. Due to restrictions on the constituent monomer units that can be used, the lower limit of the Tg is, for example, −80° C.
Moreover, a Tg of −20° C. or less is preferable in that flexibility is ensured even in a low-temperature environment. Taking cold resistance into consideration, a Tg of −30° C. or less is more preferable, and a Tg of −40° C. or less is even more preferable.

The polymer block (B) can be obtained by polymerizing a monomer containing an acrylic ester monomer. Among the acrylic ester monomers, an acrylic acid alkyl ester compound having an alkyl group having 1 to 12 carbon atoms or an alkoxyalkyl group having 2 to 8 carbon atoms is preferred in that a block copolymer having excellent flexibility can be obtained.
In the polymer block (B), the proportion of the structural units derived from the acrylic ester monomer is, from the viewpoint of mechanical properties, preferably in the range of 20% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, even more preferably 80% by mass to 100% by mass, and still more preferably 90% by mass to 100% by mass, based on the total structural units of the polymer block (B).

The Tg of the organic polymer compound is preferably 50° C. or less, more preferably 20° C. or less, and even more preferably 0° C. or less.
The Tg of the organic polymer compound can be measured by a dynamic viscoelasticity measuring apparatus (DMA). As the dynamic viscoelasticity measuring apparatus (DMA), for example, a DMS6100 manufactured by Seiko Instruments Inc. can be used. The measurement conditions are a temperature rise rate of 2° C./min and a measurement frequency of 1.0 Hz. Alternatively, the Tg can be calculated from the Tg when the monomer, which is the raw material of the organic polymer compound, is made into a homopolymer.

The weight average molecular weight of the organic polymer compound is not particularly limited. From the viewpoint of hardness and flexibility of the thermal conductive sheet, it is preferable that the weight average molecular weight is in the range of 10,000 to 5,000,000. The weight average molecular weight may be in the range of 50,000 to 2,000,000, 100,000 to 1,000,000, or 200,000 to 800,000.

The weight average molecular weight of the organic polymer compound can be measured by gel permeation chromatography using a calibration curve of standard polystyrene.
The organic polymer compound contained in the primary sheet and the thermally conductive sheet obtained by using the primary sheet may be of one type or of two or more types.

The content of the organic polymer compound contained in the primary sheet and the thermally conductive sheet obtained using the primary sheet is not particularly limited. From the viewpoint of the balance between the thermal conductivity and flexibility of the thermally conductive sheet, it is preferably 10% to 70% by mass of the total, more preferably 10% to 60% by mass, and even more preferably 10% to 50% by mass.

(Thermal Conduction Particles)
From the viewpoint of increasing the thermal conductivity in the thickness direction of the thermally conductive sheet, the thermally conductive particles used in the above method preferably contain particles having anisotropic shape.
From the viewpoint of increasing the thermal conductivity in the thickness direction of the thermal conductive sheet, the thermal conductive particles preferably include particles having an aspect ratio of 3 or more, and more preferably include particles having an aspect ratio of 10 or more. The aspect ratio of the thermal conductive particles may be 200 or less.

The material of the thermally conductive particles is not particularly limited. Examples include particles of boron nitride, aluminum nitride, alumina, silica, zinc oxide, magnesium oxide, aluminum hydroxide, silicon carbide, graphite, etc. Among these, boron nitride particles are preferred, and plate-shaped boron nitride particles are more preferred.

Plate-shaped boron nitride particles are boron nitride particles that have a layered, hexagonal crystal structure and a plate-like particle shape. Specifically, the ratio (a/c) of the sides parallel to the layers (a-axis direction) to the sides perpendicular to the layers (c-axis direction) is 1.5 or more.

The thermally conductive particles may be one type or a combination of two or more types with different materials or shapes. In addition, thermally conductive particles having anisotropic shapes and spherical thermally conductive particles may be used in combination. Examples of such thermally conductive sheets include a laminate of primary sheets containing both thermally conductive particles having anisotropic shapes and spherical thermally conductive particles, and a laminate consisting of a primary sheet containing only thermally conductive particles having anisotropic shapes and a primary sheet containing only spherical thermally conductive particles. In this case, the proportion of particles having anisotropic shapes (for example, satisfying the above aspect ratio) contained in the thermally conductive particles is preferably 50% or more by number, more preferably 70% or more, and even more preferably 80% or more.

The particle size of the thermally conductive particles is not particularly limited. For example, the volume average particle size (D50) measured by a laser diffraction/scattering method may be 2 μm to 1000 μm, 5 μm to 500 μm, 10 μm to 100 μm, or 10 μm to 50 μm.

The mass-based content of thermally conductive particles contained in the primary sheet and the thermally conductive sheet obtained using the primary sheet is not particularly limited. From the viewpoint of the balance between the thermal conductivity and flexibility of the thermally conductive sheet, it is preferably 30% to 90% by mass of the total, more preferably 40% to 90% by mass, and even more preferably 50% to 90% by mass.

The volumetric content of the thermally conductive particles contained in the primary sheet and the thermally conductive sheet obtained using the primary sheet is not particularly limited. From the viewpoint of the balance between the thermal conductivity and flexibility of the thermally conductive sheet, it is preferably 10% to 80% by volume of the total, more preferably 20% to 80% by volume, and even more preferably 30% to 80% by volume.

The primary sheet and the thermally conductive sheet obtained using the primary sheet may contain components other than the organic polymer compound and the thermally conductive particles, as necessary, such as various additives such as a flame retardant, a coupling agent, a surfactant, an ion trapping agent, a plasticizer, a tackifier, and a pigment.
When the primary sheet and the thermally conductive sheet obtained using the primary sheet contain components other than the organic polymer compound and the thermally conductive particles, the total content thereof may be 0.1% by mass to 20% by mass, 1% by mass to 10% by mass, or 2% by mass to 5% by mass or less of the total.

An example of a method for producing a thermally conductive sheet will now be described with reference to the drawings.
In the method described here, a primary sheet is formed on a substrate, and then the primary sheet formed on the substrate is separated from the substrate, and the primary sheet separated from the substrate is wound onto a winding roll to form a laminate of primary sheets.

Figure 1 is a schematic diagram showing an example of the configuration of an apparatus used in the manufacturing method of a thermally conductive sheet. The apparatus 100 shown in Figure 1 includes a first roll 1 for unwinding the substrate, a second roll 2 for winding up the primary sheet separated from the substrate, a third roll 3 for winding up the substrate separated from the primary sheet, a coating head 4 for forming the primary sheet on the substrate, a drying oven 5, and auxiliary rolls 6 and 7.

The substrate 11 is unwound from the first roll, and a primary sheet 12 is formed on the substrate 11. Specifically, a composition containing an organic polymer compound and thermally conductive particles is applied onto the substrate 11 by a coating head 4, and then the composition is passed through a drying oven 5 to form a primary sheet 12. When the composition contains a solvent, the solvent is evaporated in the drying oven 5.
The substrate 11 is then separated from the primary sheet 12, and the substrate 11 is wound onto a third roll 3. The primary sheet 12 is wound onto a second roll 2, forming a stack 13 of primary sheets around the second roll 2.

When the thickness (number of layers) of the primary sheet stack 13 formed around the second roll 2 reaches a predetermined level, the operation is terminated. The primary sheet stack 13 is then removed from the second roll 2 and sliced along the thickness direction to obtain a thermally conductive sheet. Alternatively, the primary sheet stack 13 is not removed from the second roll 2 and is sliced along the thickness direction to obtain a thermally conductive sheet.

<Laminate>
The laminate of the present disclosure is a laminate in a state in which a primary sheet containing an organic polymer compound and thermally conductive particles is wound.
By using the laminate of the present disclosure, a thermally conductive sheet can be produced without using special equipment and with high productivity.

The laminate of the present disclosure may be a laminate of primary sheets formed in the laminate formation step of the above-mentioned method for producing a thermally conductive sheet.
The details and preferred embodiments of the primary sheet included in the laminate of the present disclosure are the same as the details and preferred embodiments of the primary sheet used in the above-mentioned method for producing a thermally conductive sheet.

<Heat Conductive Sheet (First Embodiment)>
The thermally conductive sheet (first embodiment) of the present disclosure is a thermally conductive sheet produced from the above-described laminate. Specifically, the thermally conductive sheet is produced by slicing the laminate along the thickness direction of the primary sheet.
The details and preferred aspects of the method for producing a thermally conductive sheet from the laminate are the same as the details and preferred aspects of the method for producing a thermally conductive sheet in the above-mentioned method for producing a thermally conductive sheet.

<Heat Conductive Sheet (Second Embodiment)>
A thermally conductive sheet (second embodiment) of the present disclosure is a thermally conductive sheet including an organic polymer compound and thermally conductive particles, wherein the thermally conductive particles are oriented in the thickness direction of the thermally conductive sheet, and the polymer compound includes an acrylic elastomer consisting of a block copolymer.

The thermally conductive sheet of the present disclosure exhibits excellent heat resistance by containing an acrylic elastomer made of a block copolymer as an organic polymer compound.
The organic polymer compound and thermally conductive particles contained in the thermal conductive sheet of the second embodiment, as well as other details and preferred aspects, are similar to the organic polymer compound and thermally conductive particles described in the method for producing a thermal conductive sheet described above, as well as other details and preferred aspects.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

(1) Preparation of Composition The materials shown in Table 1 were mixed in the ratio (parts by mass) shown in Table 1, and diluted with the organic solvent contained in the organic polymer compound solution used to a solid content of 55 mass % to prepare a composition for producing a primary sheet. Details of the materials shown in Table 1 are as follows.

Organic polymer compound solution 1: Ethyl acetate solution of an acrylic elastomer, which is a random copolymer consisting of 30% by mass of methyl acrylate (MA), 40% by mass of butyl acrylate (BA), 25% by mass of methoxyethyl acrylate (MEA), and 5% by mass of 2-hydroxyethyl acrylate (HEA) (solid content: 40% by mass, weight average molecular weight: 450,000, Tg by DMA: -21°C)

Organic polymer compound solution 2: Acetonitrile solution of an acrylic elastomer (A/B mass ratio: 15/85) which is an ABA type block copolymer consisting of a polymer block A (Tg by DSC: 210°C) consisting of styrene (60% by mass) and phenylmaleimide (PhMI) 40% by mass, and a polymer block B (Tg by DSC: -50°C) consisting of butyl acrylate (100% by mass) (solid content: 40% by mass, weight average molecular weight: 130,000, Tg by DMA: -30°C)

Crosslinking agent: trimethylolpropane modified xylylene diisocyanate ("Takenate D-110N" manufactured by Mitsui Chemicals, Inc., solid content 75% by mass)
Thermally conductive particles: plate-shaped hexagonal boron nitride particles (D50: 12-13 μm)

(2) Preparation of Primary Sheet The composition obtained in (1) above was applied to a width of 200 mm on a release-treated surface of a polyethylene terephthalate substrate, one side of which had been subjected to a release treatment, using an apparatus having a configuration as shown in Fig. 1, and dried to form a primary sheet. The thickness of the primary sheet after drying was adjusted to 50 µm.

(3) Preparation of thermally conductive sheets Using an apparatus configured as shown in Fig. 1, a laminate (thickness of about 50 mm) of the primary sheets obtained in (2) above was prepared in a cylindrical shape around a roll. The laminate was then sliced in the thickness direction using a cutter to obtain thermally conductive sheets of Examples 1 to 4 with a thickness of 1.0 mm.
When the cross section of the thermally conductive sheet was observed under an electron microscope, it was found that the thermally conductive particles were oriented in the thickness direction of the thermally conductive sheet in all of the examples.

(4) Evaluation of thermal conductivity The thermal diffusivity in the thickness direction and the surface direction of the thermally conductive sheet obtained in (3) above was measured (using "LFA467" manufactured by Netzsch). Next, the specific heat was measured at the 25°C passing point when the temperature was raised from -20°C to +50°C using a DSC (TA Instruments, "Q100" was used) in accordance with JIS K7123:2012. In addition, the density was measured in water by the Archimedes method. From these measurement results, the thermal conductivity (W/m·K) was calculated according to the following formula. The results are shown in Table 1.
Thermal conductivity = specific heat x density x thermal diffusivity

(5) Evaluation of heat resistance The temperature (°C) at which the storage modulus E' in the dynamic viscoelasticity measurement of the thermal conductive sheet obtained in (3) above becomes 1 x 10 ⁴ Pa or less was regarded as the upper limit of the usable temperature, and was used to evaluate the heat resistance. The measurement was performed using a Seiko Instruments Inc. "DMS6100" under the conditions of a measurement range of -70°C to +250°C, a heating rate of 2°C/min, and a measurement frequency of 1 Hz. The results are shown in Table 1.

As shown in Table 1, the thermal conductivity of the thermally conductive sheets produced in Examples 1 to 4 all showed higher values in the thickness direction than in the surface direction. This is presumably because the thermally conductive particles were oriented along the thickness direction of the thermally conductive sheet, effectively enhancing thermal conductivity in the thickness direction. Additionally, each Example was found to have sufficient heat resistance. In particular, Examples 3 and 4, in which the acrylic elastomer is a block copolymer, were found to have superior heat resistance compared to Examples 1 and 2, in which the acrylic elastomer is a random copolymer.

The disclosure of Japanese Patent Application No. 2020-097217 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims (9)

a primary sheet forming step of forming a primary sheet containing an organic polymer compound and thermally conductive particles on a substrate unwound from a roll;
a laminate forming step of winding the primary sheet to form a laminate of the primary sheets;
A slicing step of slicing the laminate of primary sheets along a thickness direction. A method for manufacturing a thermally conductive sheet as described in claim 1, wherein the thermally conductive particles contained in the primary sheet have anisotropic shape and are oriented along the surface direction of the primary sheet. A method for manufacturing a thermally conductive sheet according to claim 1 or claim 2, wherein the thermally conductive particles contained in the thermally conductive sheet are oriented along the thickness direction of the thermally conductive sheet. A method for manufacturing a thermal conductive sheet according to any one of claims 1 to 3, wherein the organic polymer compound includes an acrylic elastomer consisting of a block copolymer. A method for manufacturing a thermal conductive sheet according to any one of claims 1 to 4, wherein the formation of the primary sheet is carried out using a coating machine. A method for manufacturing a thermal conductive sheet according to any one of claims 1 to 5, wherein the substrate has a release treatment applied to the surface on which the primary sheet is formed. A laminate in which a primary sheet containing an organic polymer compound and thermally conductive particles is wound. A thermally conductive sheet made from the laminate described in claim 7. A thermally conductive sheet comprising an organic polymer compound and thermally conductive particles,
the thermally conductive particles are oriented in the thickness direction of the thermally conductive sheet,
The organic polymer compound includes an acrylic elastomer composed of a block copolymer.
Thermal conductive sheet.