JP2009179771A - Thermally conductive resin paste and optical disk apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally conductive resin paste which is curable and has a high thermal conductivity, and an optical disk apparatus. <P>SOLUTION: The thermally conductive resin paste comprises particles which meet the equation: 1.0X+0.4Y≥700 when the thermally conductive resin paste comprises, based on 100 pts.wt. curable base resin, X pts.wt. aluminum nitride particles having a thermal conductivity of not less than 150 W/m×K and Y pts.wt. aluminum oxide particles having a thermal conductivity of not less than 20 W/m×K, the surface of the paste being a metal oxide. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a thermally conductive resin paste that functions as a medium for releasing heat of a heating element to other peripheral members, and an optical disk device using the same.

  Various optical discs such as DVD (digital versatile disc), CD-R (writable compact disc), CD-RW (rewritable compact disc) have been developed as optical recording media. In a DVD, information is recorded or reproduced by a laser beam having a wavelength of about 650 nm. On the other hand, in CD-R and CD-RW, information is recorded or reproduced by laser light having a wavelength of about 780 nm. An optical disc apparatus that records or reproduces information on a plurality of types of optical discs has been proposed.

  Further, in such an optical disc apparatus that records or reproduces information on a plurality of types of optical discs, a single laser element that emits light beams of different wavelengths is used as a light source of an optical pickup mounted on the optical disc apparatus. A hybrid two-wavelength semiconductor laser disposed adjacent to a package, a monolithic two-wavelength semiconductor laser in which light sources having a plurality of wavelengths are integrated on one semiconductor substrate, and the like are used.

  When a hybrid type two-wavelength semiconductor laser is used as the light source, since the distance between the light sources is relatively wide, the amount of heat generated by the light source is not very large. However, if a monolithic type two-wavelength semiconductor laser is used, it is monoblock. Since the light beam emission positions are very close to each other, there is a problem that there is an extremely high amount of heat generation, and there is a problem that the life of the light source is shortened.

  In addition, since this light source needs to be adjusted in angle, it is not fixedly provided on the base of the optical pickup, but is provided in a state slightly separated from the base. The temperature of the light source itself rises to 80 ° C. Therefore, the heat of the light source is released to the base.

  Conventionally, a silicone grease having thermal conductivity is applied to the gap between the light source and the base, and the heat generated by the light source is conducted to the base. Thermally conductive silicone grease is an oil compound containing a thermally conductive substance. Silicone has good wettability to the filler and is suitable for filling many particles. It had a thermal conductivity of m · K.

  However, since the silicone grease is not curable, a “pumping out phenomenon” in which the silicone oil as a medium bleeds with time has occurred. Therefore, after oil bleed, the function of conducting heat of the heating element that rises to about 80 ° C. cannot be sufficiently performed, and there is a possibility that the apparatus may be defective.

In order to solve the above-described problem, conventionally, a thermally conductive material is used in a curable form by blending a thermally conductive substance with an epoxy resin (see, for example, Patent Documents 1 and 2). As a result, the pumping-out phenomenon was prevented and stable thermal conductivity was ensured.
Japanese Patent No. 1943804 Japanese Patent No. 2658399

  However, in the conventional technique, the following problems have occurred.

  That is, the conventional thermal conductive adhesive does not necessarily have a high thermal conductivity of about 0.5 to 4 W / m · K, and it absorbs the heat of the heating element sufficiently and conducts it to the base of the optical pickup. There was a problem that could not be done.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a thermally conductive resin paste that is curable and has a high thermal conductivity, and an optical disk device using the same.

  The present invention has been made to solve the above-mentioned problems, and particles having a thermal conductivity of 150 W / m · K or more are X parts by weight and 20 W / m · K or more with respect to 100 parts by weight of the curable base resin. Thermally conductive resin paste characterized by containing particles satisfying 1.0X + 0.4Y ≧ 700 when Y parts by weight of particles having a thermal conductivity and at least the particle surface is a metal oxide are mixed It is.

  According to the present invention, since the composition of the heat conductive resin in the heat conductive resin paste can be blended in an extremely large proportion of the heat conductive resin paste with respect to the curable base resin, the heat conductive resin is curable and has high heat conductivity. Can provide paste.

  The invention according to claim 1 has particles having a thermal conductivity of 150 W / m · K or more with respect to 100 parts by weight of the curable base resin, X parts by weight, and a thermal conductivity of 20 W / m · K or more. It is a heat conductive resin paste characterized in that particles satisfying 1.0X + 0.4Y ≧ 700 are blended when at least particles whose surface is a metal oxide is blended in Y parts by weight. As a result, the thermal conductivity of the thermally conductive resin paste can be increased by including a very large proportion of the thermally conductive material particles in the thermally conductive resin paste with respect to the curable base resin. The product can be a heat conductive resin paste having a heat conductivity of 6 W / m · K or more.

  The invention described in claim 2 is the thermal conductive resin paste according to claim 1, wherein the particles having a thermal conductivity of 150 W / m · K or more are aluminum nitride particles. Thereby, it is possible to obtain a thermal conductivity of 6 W / m · K or higher with a low viscosity, and by using an insulating material, a cured product of the resin paste can be used as an insulator.

  A third aspect of the present invention is the thermally conductive resin paste according to the second aspect, wherein the aluminum nitride particles have an average particle size in the range of 40 to 100 μm. Thereby, even if it mix | blends a lot of particle | grains in base resin, a raise of a viscosity can be suppressed and it can discharge using a dispenser, maintaining high thermal conductivity.

  A fourth aspect of the present invention is the thermally conductive resin paste according to the second to third aspects, wherein the aluminum nitride particles are formed into a substantially spherical shape by granulating and sintering small-sized aluminum nitride. It is formed. Thereby, even if it mix | blends a lot of particle | grains in base resin, a raise of a viscosity can be suppressed and it can discharge using a dispenser, maintaining high thermal conductivity.

  A fifth aspect of the present invention is the thermally conductive resin paste according to the second to fourth aspects, wherein the aluminum nitride particles are surface-treated with a polysaccharide or silicon oxide. Aluminum nitride reacts with water to generate ammonia, but these treatments can improve water resistance.

  Invention of Claim 6 is the heat conductive resin paste of Claim 1, Comprising: The particle | grains which have the heat conductivity of 20 W / m * K or more, and the particle | grain surface is a metal oxide at least, It is characterized by being aluminum oxide particles. Thereby, it is possible to obtain a thermal conductivity of 6 W / m · K or higher with low viscosity, and by using an insulating material, a cured product of the resin paste can be used as an insulator.

  Invention of Claim 7 is the heat conductive resin paste of Claim 1, Comprising: The particle | grains which have the heat conductivity of 20 W / m * K or more, and the particle | grain surface is a metal oxide at least, It is characterized by being aluminum oxide particles. Thereby, it is possible to obtain a thermal conductivity of 6 W / m · K or higher with low viscosity, and by using an insulating material, a cured product of the resin paste can be used as an insulator.

  The invention according to an eighth aspect is the heat conductive resin paste according to the sixth to seventh aspects, wherein the aluminum oxide particles are surface-treated with a surface treatment agent. Thereby, it can inject | pour smoothly into a narrow space without resistance, and also can improve dispersion stability.

  The invention according to claim 9 is the heat conductive resin paste according to claim 8, wherein the surface treatment agent is a silane coupling agent having a phenyl group and an amino group. This surface treatment agent exhibits a high flow effect and dispersion stability with respect to various curable base resins and particles among the surface treatment agents, so that the width of the resin composition can be widened and the application range is widened. be able to.

  A tenth aspect of the present invention is the thermally conductive resin paste according to the sixth to ninth aspects, in which 100 to 100 parts by weight of the curable base resin contains 100 to 100 aluminum oxide particles having an average particle diameter of about 0.7 μm. 300 weight part is mix | blended, It is characterized by the above-mentioned. Thereby, the discharge rate with a dispenser can be increased while maintaining high thermal conductivity. Furthermore, the dispersion stability of the heat conductive resin paste can be improved, and a heat conductive resin paste having excellent storage properties can be obtained.

  An eleventh aspect of the invention is the heat conductive resin paste according to the sixth to tenth aspects, wherein the aluminum oxide particles are substantially spherical. Thereby, even if it mix | blends a lot of particle | grains in base resin, a raise of a viscosity can be suppressed and it can discharge using a dispenser, maintaining high thermal conductivity.

  The invention according to claim 12 is the thermally conductive resin paste according to claim 1, wherein the particles having a thermal conductivity of 150 W / m · K or more are aluminum nitride particles, and the 20 W / The particles having a thermal conductivity of m · K or more and at least the particle surface of which is a metal oxide are aluminum oxide particles. As a result, the cured product can be a curable resin paste having a thermal conductivity of 6 W / m · K or more, and since it is curable, it prevents the heat conductive resin paste from fluidizing. It can conduct heat sufficiently. Furthermore, since an insulating material is used, the cured product can be an insulator, and even when applied to an electronic component, it can be used without causing a short circuit between terminals.

  Invention of Claim 13 is the heat conductive resin paste of Claim 12, Comprising: The mixing ratio of an aluminum nitride particle and an aluminum oxide particle is about 4: 6-6: 4 by weight ratio. Features. As a result, the viscosity of the heat conductive resin paste can be reduced while maintaining high heat conductivity, and can be injected into a narrow gap. Moreover, application | coating is possible with general purpose apparatuses, such as a dispenser, and it can be set as the heat conductive resin paste useful also in terms of workability | operativity.

  The invention according to claim 14 is the thermally conductive resin paste according to claim 1, wherein the curable base resin is a curable resin selected from a thermosetting resin, a room temperature curable resin, and a moisture curable resin. It is characterized by being. As a result, curing is possible even when a large amount of particles having poor light transmittance is filled, and high thermal conductivity can be ensured.

  Invention of Claim 15 is the heat conductive resin paste of Claim 1 or 14, Comprising: In the said curable base resin, the hydroxyl group was added to the side chain contained in the hardened | cured material after hardening. It is a structure. When a large amount of particles are blended in the base resin, the amount of the base resin that serves as a binder is very small, so that the cured product of the resin paste tends to be brittle. However, by adopting a structure in which a hydroxyl group is added to the side chain of the cured product, the cured product can be made sticky and tough.

  The invention described in claim 16 is the heat conductive resin paste according to claim 15, wherein the curable base resin contains a monofunctional monomer having a hydroxyl group. Thereby, the hardened | cured material becomes a structure which has a hydroxyl group in a side chain, and tough hardened | cured material can be obtained.

  The invention described in claim 17 is the thermally conductive resin paste according to claim 1 or 14 to 16, wherein the curable base resin contains a latent curing agent. Thereby, the reactivity of curable base resin can be raised, or conversely, it can be set as curable base resin which hardly reacts at room temperature. For this reason, the hardening time of a heat conductive resin paste can be shortened, hardening temperature can be reduced, or pot life can be lengthened.

  The invention described in claim 18 is the heat conductive resin paste according to claim 1 or 14 to 17, wherein the curable base resin is an epoxy resin. Epoxy resins have high durability against heat and chemicals, and cured products having various physical properties can be produced. Therefore, a heat conductive resin paste that can be used in a wide range of fields can be obtained.

  A nineteenth aspect of the present invention is the heat conductive resin paste according to the eighteenth aspect, wherein the epoxy resin includes an amine-based curing agent as a curing agent. Thereby, according to the reactivity of a hardening | curing agent, it can be set as thermosetting and room temperature curable resin, and also it can be made into moisture curable resin by ketiminizing. Moreover, since a hydroxyl group is generated as a result of the curing reaction, a tough cured product can be obtained.

  A twentieth aspect of the present invention is the thermally conductive resin paste according to any one of the eighteenth to nineteenth aspects, wherein the epoxy resin includes a monofunctional monomer. When a monofunctional monomer is blended using an amine-based curing agent, the cured product has a structure having a hydroxyl group in the side chain, so that a tough cured product can be obtained. In addition, since the monofunctional monomer usually has a low viscosity, the viscosity of the curable base resin can be reduced.

  The invention according to claim 21 is the heat conductive resin paste according to claim 1 or 14 to 20, characterized in that a dispersing agent is blended in the curable resin base resin or epoxy resin. To do. Thereby, the dispersibility of particle | grains increases, Therefore The viscosity of a resin paste falls and it can increase the discharge speed by a dispenser. In addition, it has a great effect in improving the wettability on the substrate and controlling the fluidity of the resin.

  The invention according to claim 22 is the heat conductive resin paste according to claim 1 or 14 to 21, wherein the viscosity of the curable base resin or epoxy resin is 380 mPa · s or less. Thereby, the viscosity of the curable resin paste can be lowered, and as a result, the discharge rate by the dispenser can be increased.

  The invention described in claim 23 is the thermally conductive resin paste according to any one of claims 1 to 22, wherein a 5 mL syringe and a needle having an inner diameter of 0.78 mm are used in a dispenser, and is discharged at a pressure of at least 0.5 MPa. It is possible to do. Thereby, the operation | work which inject | pours a heat conductive resin paste also in a very narrow clearance gap with a general purpose apparatus is attained.

  Invention of Claim 24 is the heat conductive resin paste of Claim 24, Comprising: Using a 5 mL syringe and a needle with an internal diameter of 0.78 mm with a dispenser, it is 200 mg / min or more at a pressure of 0.5 MPa. It can be discharged. Thereby, the operation | work which inject | pours a heat conductive resin paste also into a very narrow gap | interval with a general purpose apparatus becomes possible for a short time, and it can be set as the heat conductive resin paste with high workability | operativity.

  A twenty-fifth aspect of the invention is the heat conductive resin paste according to the first to twenty-fourth aspects, wherein the cured product of the heat conductive resin paste is an insulator. Thereby, even if it applies to an electronic component etc., it can be set as the heat conductive resin paste which can be used without short-circuiting between terminals.

  The invention described in claim 26 is based on 100 parts by weight of a curable base resin composed of an epoxy oligomer or epoxy monomer having two or more oxirane rings, a monofunctional epoxy monomer, an amine curing agent, and a dispersant. On the other hand, when X parts by weight of aluminum nitride particles and Y parts by weight of aluminum oxide particles are blended, particles satisfying 1.0X + 0.4Y ≧ 700 are blended, and the mixing ratio of aluminum nitride particles and aluminum oxide particles is a weight ratio. A curable resin paste having a ratio of about 4: 6 to 6: 4, a thermal conductivity of 6 W / m · K or more, a 5 mL syringe, and a dispenser equipped with a needle having an inner diameter of 0.78 mm. A thermal conductive resin paste characterized by having a discharge rate of 200 mg / min or more when discharged at a pressure of 5 MPa. Thereby, it is possible to fill a very narrow space with a high thermal conductivity material with general equipment while having high thermal conductivity. In addition, it has excellent workability due to good paintability on the base material, and uses an epoxy resin that is highly workable and highly resistant to heat and chemicals. The cured product is highly reliable because it is a tough physical property. Since it becomes an insulator, a heat conductive resin paste that can be used in various fields including electronic parts can be obtained.

  A twenty-seventh aspect of the present invention is an optical disc apparatus comprising a cured product that is filled or coated with the thermal conductive resin paste according to any of the first to twenty-sixth aspects and cured under predetermined conditions. As a result, heat of components that generate heat, such as a laser or a light receiving element, can be quickly diffused, so that an optical disk device with high reliability and long life can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a graph showing the relationship between the discharge rate of the resin paste dispenser according to the present invention and the thermal conductivity. The discharge speed by the dispenser at this time is a 5 mL syringe using a general dispenser device (Musashi Engineering Co., Ltd.), a needle having an outer diameter of 1.08 mm and an inner diameter of 0.78 mm (Musashi Engineering Co., Ltd. plastic needle, PN). −19G-B) was attached, and the discharge speed was set to discharge at a pressure of 0.5 MPa.

  Samples 1 to 8 are examples of the present invention, samples 9 to 11 are comparative examples, (Table 1) contains the curable base resin used in the present invention, and (Table 2) contains the particles. The manufacturing method and basic characteristics of each sample will be described later.

  Samples 9 and 10 in FIG. 1 are heat conductive resin pastes that have been commercially available so far. The heat conductive resin paste of Sample 9 has a discharge rate of about 200 mg / min with a dispenser and a heat conductivity of about 4 W / m · K, and is actually used among the heat conductive resin pastes currently on the market. As a level that can be used without any problem, it has the highest thermal conductivity. Depending on the location, about 500 mg of the thermally conductive resin paste may be injected into one place, and if the discharge rate with the dispenser becomes lower than this, the process takes too much time and the productivity becomes low. Therefore, it is preferable that the heat conductive resin paste has a discharge rate of 200 mg / min or more by a dispenser. The thermal conductive resin paste of Sample 10 has a thermal conductivity of about 6 W / m · K, which is the highest level in the market in terms of thermal conductivity, but the dispenser has a discharge rate of about 20 mg / min. There is a problem in use.

  FIG. 2 shows a graph showing the thermal conductivity when aluminum oxide and aluminum nitride are increased or decreased from the blend of particles in Sample 1. Increasing the amount of particles increases the thermal conductivity, and decreasing the amount of particles decreases the thermal conductivity. However, if either particle is reduced, it is 6 W / m · It will become the thermal conductivity of K or less. In addition, aluminum nitride having a high thermal conductivity has a larger contribution to the thermal conductivity. For this reason, a resin paste in which 600 parts by weight of aluminum nitride and 250 parts by weight of aluminum oxide are blended with respect to 100 parts by weight of the curable base resin, for example, in which the blending quantity of aluminum nitride is increased and the blending amount of aluminum oxide is reduced is also conceivable. .

  Samples 5, 7, and 8 are thermal conductive resin pastes using the same curable base resin and the cured product having a thermal conductivity of about 7 W / m · K. A plot of the particle composition of these samples in a graph is shown in FIG. These three points are located on a straight line represented by 1.0X + 0.4Y = 700 when X parts by weight of aluminum nitride and Y parts by weight of aluminum oxide are blended with respect to 100 parts by weight of the base resin. . In Samples 5, 7, and 8 using the resin composition 1, a thermal conductivity of about 7 W / m · K was obtained. Even if the thermal conductivity slightly changes depending on the resin composition, at least 1. When particles having a blending amount equal to or greater than 0X + 0.4Y = 700 are blended, a thermal conductivity of 6 W / m · K or more is obtained.

  In this example, aluminum nitride was blended as particles having a high thermal conductivity of 150 W / m · K or more. In general, in order to obtain a resin paste having a high thermal conductivity, the base resin has as high a thermal conductivity as possible. Since it is good to mix | blend particle | grains as much as possible, metal particles with high heat conductivity, such as aluminum, gold | metal | money, silver, copper, tungsten, beryllium, magnesium, can also be mix | blended. However, if a large amount of metal particles are blended, the cured product becomes conductive. Therefore, if there is a possibility that the cured product is applied to an electronic component as in the present invention, use insulating particles. Is desirable. When compounding metal particles, if the compounding amount is small, the resin cured product can also ensure insulation, so adding a small amount or coating the surface of the insulating particles thinly improves thermal conductivity Can be made.

  In addition to the above metal oxides and metal particles, any particles formed mainly of carbon and having a high thermal conductivity of 150 W / m · K or more can be used.

  There are several types of transmission methods for heat conduction. Among them, transmission by lattice vibration and transmission by free electrons are particularly efficient heat transfer methods. Therefore, a substance having a high thermal conductivity is generally a hard and very stable substance. Since such a stable substance has a small interaction with other substances, particles having a high thermal conductivity are generally unfamiliar with a resin. For this reason, it is necessary to improve the dispersion stability of the resin paste by blending a substance that is familiar with the resin even if the thermal conductivity is relatively low. Examples of the substance having such an action include metal oxides such as aluminum oxide, titanium oxide, and zinc oxide. The mechanism for improving the dispersion stability is considered to have a weak electrostatic action between the oxygen of the metal oxide and the carbon chain of the resin. Such a function is not a problem if the particle surface is a metal oxide. Therefore, the core shell structure of the metal particles and the metal oxide can be obtained by oxidizing the metal surface or coating the metal surface with gold oxide. Then, ideal inorganic particles having high thermal conductivity and good compatibility with the resin can be obtained.

  Among metal oxides, aluminum oxide has a relatively high thermal conductivity, is inexpensive, and has a spherical shape. In the case of blending aluminum oxide, when two or more kinds of particles having different particle diameters are mixed, particles having a small particle diameter enter a gap having a large particle diameter, and high filling becomes possible. Furthermore, by adjusting the two kinds of mixing ratios, the specific surface area of the whole particles can be controlled, and the viscosity of the resin paste can be freely controlled. In this example, 1 g of spherical aluminum oxide having an average particle size of about 0.7 μm and 4 g of spherical aluminum oxide having an average particle size of about 10 μm were blended with 1 g of curable base resin. The amount is preferably about 100 to 300 parts by weight with respect to 100 parts by weight of the base resin. If the amount is less than this, the effect of improving the dispersion stability is low.

  As described above, the particles having high thermal conductivity are poorly compatible with the resin, so that the specific surface area should be as small as possible. Therefore, it is preferable that the particles have a spherical shape and a large particle size. In this example, spherical aluminum nitride having an average particle diameter of about 50 μm was used. However, when the average particle size is smaller than 40 μm, the specific surface area increases, the viscosity increases, and the discharge rate by the dispenser decreases. On the other hand, if it is larger than 100 μm, clogging may occur in a narrow gap or dispersion stability may be deteriorated. Therefore, the particle size of the high thermal conductivity particles is suitably about 40 to 100 μm. By mixing such particles having high thermal conductivity and metal oxide particles, the metal oxide can be coated with particles having high thermal conductivity, and the dispersion stability of the resin paste can be improved. it can.

  FIG. 4 shows the thermal conductivity of the cured resin paste and the resin when the blending ratio of aluminum oxide and aluminum nitride is changed with the total blended particles being 1000 parts by weight with respect to 100 parts by weight of the curable base resin. The graph showing the discharge speed by the dispenser of a paste is shown. The thermal conductivity increases as the blending amount of aluminum nitride having high thermal conductivity increases. The discharge rate tends to decrease as the aluminum nitride is increased, with the peak of the mixing ratio of aluminum oxide and aluminum nitride being 4: 6 by weight. This is because the familiarity between the base resin and aluminum nitride is poor, and if the amount is increased too much, the dispersion stability deteriorates. The mixing ratio of aluminum oxide and aluminum nitride is suitably about 4: 6 to 6: 4 by weight. When there is less aluminum nitride, the thermal conductivity is low and the viscosity is high, and when there is more aluminum nitride than this, dispersion is achieved. The stability is poor, storage stability is low, and clogging with a dispenser is caused.

  The heat conductive resin paste of the present invention needs to contain a large amount of particles having low light transmittance unless expensive particles such as diamond are used. Therefore, the photocurable base resin can be expected to cure only about several tens of μm on the surface, and in order to cure the whole, it is desirable to be a thermosetting, room temperature curable, or moisture curable base resin.

  In this example, an epoxy resin was used as the curable base resin, but any resin that can be cured by a method other than photocuring can be used. For example, an acrylic resin, a urethane resin, a silicone resin, and the like are thermally cured. , Room temperature curable, and moisture curable. In the case of using an acrylic resin, an organic peroxide is used to make it thermosetting or room temperature curable. However, the organic peroxide is a self-reactive substance, which is dangerous and it is difficult to control the reaction. Urethane resins often have high viscosity, and it is necessary to add plasticizers to mix a large amount of particles. However, plasticizers are not suitable for use in electronic parts because they may cause bleeding. . In order to make the silicone resin low in viscosity, it is necessary to use low molecular weight siloxane. However, since low molecular weight siloxane corrodes glass, it may cause fogging of optical components such as lenses. In view of these, it is preferable to use an epoxy resin as the curable base resin, which has high durability against heat and chemicals, has a degree of freedom in resin viscosity, and is easy to adjust physical properties.

  Epoxy oligomers are generally known as bisphenol A type and bisphenol F type. Recently, based on such a skeleton, oligomers that have various physical properties by adding monomers, etc., have been obtained from resin manufacturers. It has been released. In the present invention, the oligomer is not particularly limited, but it is preferable that the viscosity is as low as possible and the physical properties when cured are flexible. This is because the optical axis may be shifted if the cured product is too hard when used in an optical component such as an optical disk. In consideration of water resistance, it is desirable to use an oligomer structure having no ester bond.

  As a monofunctional or bifunctional monomer, a monomer having a long alkyl chain has a relatively low viscosity and is highly effective in reducing the viscosity of the resin paste. The monofunctional monomer has the effect of reducing the viscosity of the resin paste and making the resin cured product flexible and sticky. This is because, in addition to reducing the crosslinking density, when an amine curing agent is used, a structure in which a hydroxyl group is added to the side chain is taken. A side chain refers to a chain whose one end is not bound to another oligomer or monomer. When the monofunctional monomer and the amine curing agent are combined, the oxirane ring is opened, resulting in a hydroxyl group and a structure in which the hydroxyl group is added to the side chain.

  FIG. 5 is a graph showing the relationship between the blending amount of the monofunctional monomer and the elongation percentage of the cured base resin. It can be seen that the elongation increases as the blending amount of the monofunctional monomer increases. As in the present invention, when a large amount of particles are blended in the base resin, if the elongation percentage of the cured base resin is small, the cured resin paste becomes brittle. good. Therefore, although it is necessary to mix | blend a monofunctional monomer in large quantities, when a compounding quantity is increased too much, malfunctions, such as a deterioration of sclerosis | hardenability and the fall of durability by a crosslinking density fall, will arise. A suitable amount of the monofunctional monomer is about 30 to 60% by weight.

  When a cationic polymerization initiator or a curing agent that performs anionic polymerization such as imidazole is used as the curing agent, a hydroxyl group is not generated by the reaction. It is necessary to blend a monofunctional monomer having In this case, if a monofunctional monomer is added to the base resin by about 20% by weight, a remarkable effect appears, and the cured product of the base resin is tenacious and has soft physical properties.

  In this example, a modified polyamine was used as the curing agent, but as the curing agent for the epoxy resin, amine-based curing agents, polymercaptans, acid anhydrides, cationic polymerization initiators, amine complexes, and the like are known and cured. In consideration of temperature and pot life, it is necessary to select a curing agent according to the required performance.

  The thermal conductive resin paste of the present invention is assumed to be injected or applied near the laser element of the optical disk device. However, since the laser element does not oscillate when the temperature becomes high, the product is usually guaranteed only up to about 80 ° C. Not. For this reason, the curing temperature of the resin paste is desired to be 80 ° C. or less, but such a resin that cures at a low temperature has a problem that the pot life is short because it has a certain degree of reactivity even at room temperature. In order to solve such a problem, the pot life can be lengthened by using a latent curing agent that hardly reacts at room temperature.

  Among latent curing agents, those having a low curing temperature are known, such as modified polyamines and amine adducts that are solid at normal temperature and have a low melting point, cationic polymerization initiators, imidazoles, and amine complexes. Ketimine, which is moisture curable and has an amine active group blocked with a ketone, is also a kind of latent curing agent.

  FIG. 6 is a graph showing the relationship between the viscosity of the base resin and the viscosity of a resin paste in which particles are blended in the same manner as in Sample 1, and the relationship between the ejection speed of the dispenser at that time. The base resin used in this experiment is a resin having the resin composition 1 to 5 described in (Table 1). When 500 parts by weight of aluminum oxide and 500 parts by weight of aluminum nitride were blended with respect to 100 parts by weight of the base resin, discharging with a dispenser was possible with all resin compositions, but the discharging speed was 200 mg / min or more. Therefore, it is understood that the viscosity of the base resin may be at least 380 mPa · s or less. However, such a relationship is established only when the base resin of this system is used, when aluminum oxide and aluminum nitride are mixed in this blending amount. Since this relationship also changes when the type and amount of aluminum are changed, it is necessary to optimize the viscosity of the base resin according to each combination. The lower the viscosity of the base resin, the lower the viscosity of the resin paste, and the higher the discharge speed with the dispenser. Therefore, the lower the viscosity of the base resin, the better the working efficiency. However, in order to obtain a curable resin, the blending of about the resin composition 1 in (Table 1) is preferable.

  The mixing method of the curable base resin and the particles is not particularly limited. However, when mixing using an instrument such as a mortar, the aggregated particles can be well mixed by mixing and dispersing in order from the small particle size. Can be crushed and dispersibility is improved. Moreover, when using the granulated particle | grains like a present Example, since there is a possibility that the granulated particle may be destroyed, it is better not to apply too much force. When the resin paste is mixed by flowing, as in the case of a de-stirring device, the temperature easily rises due to friction between particles, and the curing reaction of the resin proceeds thereby, so that the temperature does not rise as much as possible. It is necessary to stir under mild conditions.

  Hereafter, the manufacturing method of each sample is shown.

  The heat conductive resin paste of Sample 1 is 5 g of spherical aluminum nitride (FAN-f50-JA made by Furukawa Electronics Co., Ltd.) having an average particle size of about 50 μm per 1 g of curable base resin of resin composition 3. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 4 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm, and the thermal conductivity was measured by a steady heat flow method to be 6.5 W / m · K. Furthermore, the discharge speed with the dispenser is 520 mg / min under the above-mentioned conditions, and is a heat conductive resin paste that combines high heat conductivity and high productivity that have never been achieved.

  The heat conductive resin paste of Sample 2 is composed of 7 g of spherical aluminum nitride (FAN-f50-JA made by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm per 1 g of curable base resin of resin composition 3. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 4 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm. The thermal conductivity was measured by a steady heat flow method and found to be 8.5 W / m · K. By increasing the amount of aluminum nitride having a high thermal conductivity, the thermal conductivity of the cured resin paste can be effectively improved. Moreover, the discharge speed with a dispenser was 60 mg / min in the said conditions. Since a large amount of particles are blended, the discharge speed is drastically reduced, making it difficult to use in the process. In the case of blending such a resin paste, it is necessary to use a dispenser needle having a large inner diameter.

  The heat conductive resin paste of Sample 3 is 5 g of spherical aluminum nitride (FAN-f50-JA, manufactured by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm with respect to 1 g of the curable base resin of resin composition 2. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 4 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm. The thermal conductivity was measured by a steady heat flow method, and found to be 6.8 W / m · K. Furthermore, the discharge rate with the dispenser was 1380 mg / min under the above conditions. When the viscosity of the curable base resin is lowered, the discharge speed is greatly increased, and the productivity can be greatly improved.

  The curable base resin used for sample 3 is a blend of resin composition 2 in (Table 1), but this has fewer oligomers than resin composition 3 used for sample 1, and instead a bifunctional monomer. The composition is blended. By setting it as such a composition, the effect which can make a viscosity low is high. When a large amount of oligomer is blended in the base resin, the cured product tends to have physical properties rich in elasticity. Conversely, when a large amount of monomer is blended, there is a tendency to have physical properties that cause plastic deformation.

  The heat conductive resin paste of Sample 4 is composed of 7 g of spherical aluminum nitride (FAN-f50-JA made by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm with respect to 1 g of curable base resin of resin composition 2. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 4 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm. The thermal conductivity was measured by a steady heat flow method, and found to be 8.7 W / m · K. Furthermore, the discharge rate with the dispenser was 150 mg / min under the above conditions.

  The heat conductive resin paste of Sample 5 is 5 g of spherical aluminum nitride (FAN-f50-JA made by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm per average particle of 1 g of the curable base resin of resin composition 1. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 4 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm. The thermal conductivity was measured by a steady heat flow method, and found to be 7.0 W / m · K. Furthermore, the discharge rate with the dispenser was 2970 mg / min under the above conditions.

  The curable base resin used for Sample 5 is a blend of the resin composition 1 of (Table 1). Unlike the resin compositions 2 and 3 of the base resin used for Samples 1 to 4, the base resin does not contain any oligomer and is a base resin specialized in low viscosity. When blended in such a manner, problems such as poor curability and poor compatibility with the particles are likely to occur. Therefore, it is necessary to carefully select the curing agent and the particles to be blended.

  The heat conductive resin paste of Sample 6 is composed of 7 g of spherical aluminum nitride (FAN-f50-JA made by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm with respect to 1 g of curable base resin of resin composition 1. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 4 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm, and the thermal conductivity was measured by a steady heat flow method. As a result, it was 8.9 W / m · K. Furthermore, the discharge rate with the dispenser was 300 mg / min under the above conditions.

  The heat conductive resin paste of Sample 7 is 3 g of spherical aluminum nitride (FAN-f50-JA made by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm per 1 g of curable base resin of resin composition 1. 1 g of spherical aluminum oxide having a diameter of approximately 0.7 μm (AC2500-SXH manufactured by Admatechs) and 9 g of spherical aluminum oxide having an average particle diameter of approximately 10 μm (AC9500-SXB manufactured by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm. The thermal conductivity was measured by a steady heat flow method to be 7.1 W / m · K. Furthermore, the discharge rate with the dispenser was 1030 mg / min under the above conditions.

  When the resin paste of Sample 5 having the same thermal conductivity as Sample 7 is compared, the discharge speed of Sample 7 is significantly small. In Sample 7, since a low-viscosity resin composition 1 was blended, a sufficient discharge speed was obtained. However, if a base resin having a slightly higher viscosity is used, a sufficient discharge speed cannot be obtained.

  The heat conductive resin paste of Sample 8 is 6 g of spherical aluminum nitride (FAN-f50-JA, manufactured by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm with respect to 1 g of curable base resin of resin composition 1. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 1.5 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm. The thermal conductivity was measured by a steady heat flow method to be 7.1 W / m · K. The discharge with the dispenser resulted in the needle being clogged immediately, and the discharge could not be performed sufficiently.

  The heat conductive resin paste of Sample 9 was produced by casting TB2955E manufactured by ThreeBond Co., Ltd. into a mold and curing it to prepare a flat plate having a thickness of 2 mm, and the thermal conductivity was measured by a steady heat flow method. m · K. Furthermore, the discharge rate with the dispenser was 220 mg / min under the above conditions.

  The heat conductive resin paste of sample 10 was made by casting X-32-2133 manufactured by Shin-Etsu Chemical Co., Ltd. into a mold and cured to produce a flat plate having a thickness of 2 mm, and the thermal conductivity was measured by a steady heat flow method. It was 5.9 W / m · K. Furthermore, the discharge rate with the dispenser was 20 mg / min under the above conditions.

  The heat conductive resin paste of sample 11 is 2 g of spherical aluminum nitride (FAN-f50-JA manufactured by Furukawa Electronics Co., Ltd.) having an average particle diameter of about 50 μm per 1 g of curable base resin of resin composition 3. 1 g of spherical aluminum oxide having a diameter of about 0.7 μm (AC2500-SXH made by Admatechs) and 4 g of spherical aluminum oxide having an average particle diameter of about 10 μm (AC9500-SXB made by Admatechs) were blended. The resin paste was poured into a mold and cured to produce a flat plate having a thickness of 2 mm. The thermal conductivity was measured by a steady heat flow method, and was 4.2 W / m · K. Furthermore, the discharge rate with the dispenser was 1480 mg / min under the above conditions.

  The case where the heat conductive paste of this invention is used for an optical disk is demonstrated using FIGS. FIG. 7 shows a perspective view of the optical disk device 71. The optical disk device 71 has a spindle motor 72 mounted with an optical disk such as a CD, a DVD, or a BD (Blu-ray Disc), and rotates light from the objective lens mounted on the optical pickup device 73 while rotating the optical disk. Data is recorded or reproduced by irradiating the data recording surface on the optical disc.

  FIG. 8 is an enlarged view of the optical pickup device 73. The optical pickup device 73 is equipped with a semiconductor laser element as a light source, an optical component for guiding light to the optical disk and irradiating the data recording surface of the optical disk, a light receiving element for detecting the light reflected from the optical disk, and the like. For example, when reproducing a BD, the light emitted from the semiconductor laser element 81a is guided to the objective lens 83 provided in the actuator 82 by various optical components, and is condensed and irradiated onto the recording surface of the BD by the objective lens 83. The Here, the objective lens 83 indicates two objective lenses, one of which is a BD objective lens, and the other is a CD and DVD objective lens. The irradiated light is reflected on the recording surface of the BD and returns to the prism 84a along the same path as the emitted light. The light returned by the prism 84a is reflected and incident on the light receiving element 85a. The light receiving element 85a converts the incident light into an electrical signal, and the electrical signal is sent to a circuit section of a signal generation system, which generates an RF signal and generates desired information.

  FIG. 9 is a simplified schematic diagram of the optical pickup device 73. Since the semiconductor laser elements 81a and 81b, which are light sources, need to be adjusted in the optical axis, there is a gap between the base 86 and the semiconductor laser elements 81a and 81b are fixed with an adhesive for precision fixing. Has been. Since the adhesive for precision fixing generally has a low thermal conductivity, the heat generated by the semiconductor laser elements 81a and 81b hardly transfers to the base 86. Further, since the light receiving elements 85a and 85b are also heat generating elements, the temperature around the semiconductor laser elements 81a and 81b may greatly exceed 80 ° C., and the semiconductor laser elements 81a and 81b oscillate when the temperature becomes high. In general, the product is guaranteed only up to 80 ° C. Therefore, means for efficiently diffusing heat to the base 86 is necessary so that the semiconductor laser elements 81a and 81b do not reach a temperature of 80 ° C. or higher.

  Up to now, a heat conductive adhesive having a thermal conductivity of about 4 W / m · K has been used as means for transferring heat from the semiconductor laser elements 81 a and 81 b to the base 86. However, the heat cannot be sufficiently diffused, and a device such as attaching a graphite sheet on the semiconductor laser elements 81a and 81b has been devised. However, in recent years, there has been a strong demand for an increase in the writing speed to the optical disc, and therefore, it is necessary to use a semiconductor laser element having a higher output. When a high-power semiconductor laser element is used, the amount of heat generated is larger than that of the currently used semiconductor laser elements 81a and 81b, so that it is necessary to diffuse heat more efficiently than before. As one of the means, it is conceivable to use a heat conductive material having high heat conductivity.

  In addition, the thermal conductive resin paste of the present invention achieves high thermal conductivity by blending a large amount of inorganic particles having high thermal conductivity with a curable base resin. If a large amount is blended, the viscosity of the resin paste becomes high, and it becomes impossible to inject the resin into a narrow gap using an instrument such as a dispenser. On the other hand, the distance between the heating element and the base of the optical pickup is such that the narrower one is more likely to conduct heat and the members are very close to each other due to downsizing and thinning. In many cases, the gap between the heating element and the base of the optical pickup is designed to be very narrow. Since the gap may be about 1 mm, it becomes necessary to inject the resin paste into the gap using a dispenser needle having a thin tip and an outer diameter of about 1 mm.

  Therefore, the heat conductive resin paste of the present invention is used for an optical disk, and as shown in FIG. 9 as an example of use, the heat conductive resin paste is used between the semiconductor laser elements 81a and 81b and the base 86, or the light receiving element 85a, After injecting between 85b and the base 86 or applying from above, the cured products 87a and 87b of the heat conductive resin paste are formed by curing.

  In addition, since the resin paste of a present Example has insulation, when apply | coating to the semiconductor laser elements 81a and 81b etc., it can apply | coat easily, without worrying about the influence of a short circuit etc.

  Since the cured products 87a and 87b of the above-described heat conductive resin paste have a thermal conductivity of 6 W / m · K or more, heat is efficiently diffused from the semiconductor laser elements 81a and 81b and the light receiving elements 85a and 85b to the base 86. can do. Moreover, since the heat conductive resin paste of the present invention is curable, it does not flow out to other places, so that high heat conductivity can be maintained and optical components are not contaminated.

  From the above, by using the thermally conductive resin paste of the present invention for an optical disk apparatus, an optical disk apparatus with high reliability and long life can be obtained.

  Examples of uses other than the optical disk device described above include electronic components that generate a large amount of heat and require heat dissipation, such as integrated elements such as CPUs and driver ICs, light sources such as LEDs, and the like. The heat from the CPU can be efficiently transferred to the heat receiving portion by using the heat receiving portion that receives the heat of the CPU and transferring the heat to the radiating fin and the CPU.

  Therefore, when a heat source such as a light source is provided with a gap with another member and has a structure in which it is difficult for heat to escape, as in an optical disc apparatus, a filler is provided in the gap to release heat from the heat source. It is preferable to use the resin paste of the present invention.

  In addition, since the resin paste of this embodiment has an insulating property, for example, it is used as an insulating layer of a wiring board by forming the resin paste on a flat plate, or as a protective material for protecting a conductive pattern on the wiring. The heat generated from the heat source can be efficiently diffused.

  Since it functions as a medium for releasing the heat of the heating element to other peripheral members, it is possible to cool all devices that generate heat, such as a CPU of a personal computer, various integrated elements, and LEDs. Furthermore, since it can be injected into a narrow space, it is suitable for cooling a semiconductor laser element used in an optical disk apparatus.

Graph comparing performance in examples of the present invention Graph comparing performance in examples of the present invention Graph comparing performance in examples of the present invention The graph which compared the physical property in the Example of this invention Graph showing physical properties and performance in the examples of the present invention The graph which represented the compounding quantity of the appropriate particle | grain in the Example of this invention 1 is a perspective view of an optical disc apparatus according to an embodiment of the present invention. The enlarged view of the optical pick-up apparatus in the Example of this invention Schematic diagram of an optical pickup device in an embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 71 Optical disk apparatus 72 Spindle motor 73 Optical pick-up apparatus 81a Semiconductor laser element 81b Semiconductor laser element 82 Actuator 83 Objective lens 84a Prism 84b Prism 85a Light receiving element 85b Light receiving element 86 Base 87a Cured material of heat conductive resin paste 87b Heat conductive resin Cured paste

Claims (27)

With respect to 100 parts by weight of the curable base resin, particles having a thermal conductivity of 150 W / m · K or more have X parts by weight, thermal conductivity of 20 W / m · K or more, and at least the particle surface is a metal oxide. A thermally conductive resin paste, wherein particles satisfying 1.0X + 0.4Y ≧ 700 are blended when certain parts by weight of Y are blended. The thermally conductive resin paste according to claim 1, wherein the particles having a thermal conductivity of 150 W / m · K or more are aluminum nitride particles. The heat conductive resin paste according to claim 2, wherein the aluminum nitride particles have an average particle size in a range of 40 to 100 μm. The thermally conductive resin paste according to any one of claims 2 to 3, wherein the aluminum nitride particles are formed into a substantially spherical shape by granulating and sintering aluminum nitride having a small particle diameter. The thermally conductive resin paste according to claim 2, wherein the aluminum nitride particles are surface-treated with a polysaccharide or silicon oxide. The thermally conductive resin paste according to claim 1, wherein the particles having a thermal conductivity of 20 W / m · K or more and at least a particle surface of which is a metal oxide are aluminum oxide particles. The thermally conductive resin paste according to claim 6, wherein the aluminum oxide particles are particles obtained by mixing particles having an average particle diameter of approximately 0.7 μm and particles having an average particle diameter of approximately 10 μm. The thermally conductive resin paste according to claim 6, wherein the aluminum oxide particles are surface-treated with a surface treatment agent. The thermally conductive resin paste according to claim 8, wherein the surface treatment agent is a silane coupling agent having a phenyl group and an amino group. 10. The thermally conductive resin paste according to claim 6, wherein 100 to 300 parts by weight of aluminum oxide particles having an average particle diameter of about 0.7 μm are blended with 100 parts by weight of the curable base resin. . The heat conductive resin paste according to claim 6, wherein the aluminum oxide particles are substantially spherical. The particles having a thermal conductivity of 150 W / m · K or more are aluminum nitride particles, and the particles having a thermal conductivity of 20 W / m · K or more and at least the particle surface is a metal oxide. The thermally conductive resin paste according to claim 1, wherein the thermally conductive resin paste is aluminum oxide particles. The heat conductive resin paste according to claim 12, wherein a mixing ratio of the aluminum nitride particles and the aluminum oxide particles is approximately 4: 6 to 6: 4 by weight. 2. The thermally conductive resin paste according to claim 1, wherein the curable base resin is a curable resin selected from a thermosetting resin, a room temperature curable resin, and a moisture curable resin. The thermally conductive resin paste according to claim 1 or 14, wherein the curable base resin has a structure in which a hydroxyl group is added to a side chain contained in a cured product after curing. The thermally conductive resin paste according to claim 15, wherein the curable base resin contains a monofunctional monomer having a hydroxyl group. The thermally conductive resin paste according to claim 1 or 14 to 16, wherein the curable base resin contains a latent curing agent. The thermally conductive resin paste according to claim 1, wherein the curable base resin is an epoxy resin. The thermally conductive resin paste according to claim 18, wherein the epoxy resin includes an amine-based curing agent as a curing agent. The thermally conductive resin paste according to claim 18, wherein the epoxy resin contains a monofunctional monomer. 21. The thermally conductive resin paste according to claim 1, wherein a dispersing agent is blended in the curable resin base resin or the epoxy resin. The thermally conductive resin paste according to claim 1, wherein the curable base resin or the epoxy resin has a viscosity of 380 mPa · s or less. The thermally conductive resin paste according to any one of claims 1 to 22, wherein a 5 mL syringe and a needle having an inner diameter of 0.78 mm can be discharged with a dispenser at a pressure of at least 0.5 MPa. The thermally conductive resin paste according to claim 23, wherein a dispenser is capable of discharging 200 mg / min or more at a pressure of 0.5 MPa using a 5 mL syringe and a needle having an inner diameter of 0.78 mm with a dispenser. 25. The thermally conductive resin paste according to claim 1, wherein the cured product of the thermally conductive resin paste is an insulator. Aluminum nitride particles are X weight with respect to 100 parts by weight of a curable base resin composed of an epoxy oligomer or epoxy monomer having two or more oxirane rings, a monofunctional epoxy monomer, an amine curing agent, and a dispersant. Parts, when aluminum oxide particles are mixed in Y parts by weight, particles satisfying 1.0X + 0.4Y ≧ 700 are mixed, and the mixing ratio of aluminum nitride particles and aluminum oxide particles is about 4: 6 to 6: 4 is a curable resin paste having a thermal conductivity of 6 W / m · K or more, a 5 mL syringe, and a dispenser equipped with a needle having an inner diameter of 0.78 mm, and discharged at a pressure of 0.5 MPa. The thermal conductive resin paste is characterized by having a discharge rate of 200 mg / min or more. 27. An optical disc apparatus comprising a cured product that is cured after being filled or coated with the thermal conductive resin paste according to claim 1.

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