JP2018095860A - Porous material, adhesive tape, and production method for porous material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous material filled with inorganic filler in which the yield, the expansion ratio and the surface smoothness are enhanced as well as the reworkability is improved.SOLUTION: The porous material of the present invention is a porous material containing an elastomer and an inorganic filler dispersed in the elastomer and in which the elongational viscosity of the porous material has an elongation viscosity rupture time of 1.7 seconds or more as measured at 240°C and strain rate of 0.2/second as well as has an elongation viscosity at rupture of 1×10Pa-s or more and 5×10Pa-s or less as made into a state containing no air bubbles and measured at 240°C and strain rate of 0.2/second.SELECTED DRAWING: None

Description

  The present invention relates to a porous body filled with an inorganic filler, an adhesive tape using the porous body, and a method for producing the porous body.

  Conventionally, in order to impart various properties such as electrical conductivity and thermal conductivity to an elastomer, it is generally performed to add an inorganic filler having characteristics according to the property to be imparted to the elastomer or thermoplastic resin. . Moreover, when it is necessary to give a softness | flexibility etc. further to the elastomer or thermoplastic resin which mix | blended the inorganic filler, it may be set as the porous body which provided many air bubbles inside. As such a porous body, for example, as described in Patent Documents 1 and 2, it is known to be produced by foaming a composition in which a large number of inorganic fillers are kneaded into an elastomer or a thermoplastic resin. ing.

Here, in patent document 1, while using heat conductor fillers, such as aluminum oxide, magnesium oxide, and boron nitride, as an inorganic filler, acrylic butadiene rubber, ethylene-propylene rubber, etc. are used as an elastomer. Moreover, in patent document 2, while using electroconductive fillers, such as carbon black, as an inorganic filler, the olefin resin containing high melt strength polyethylene is used as a thermoplastic resin. High melt strength polyethylene is a mixture of low density and high density polyethylene, measured for elongation viscosity at 110 ° C. and strain angular velocity 0.5 rad / min, breaking time 3 to 4.5 seconds, elongation at break The viscosity is 1.0 × 10 ^{6 to} 1.8 × 10 ⁶ Pa · s.

  In addition, in order to assemble the porous body described above inside the electronic device, an adhesive tape may be provided on one surface of the porous body to form an adhesive tape. Since the porous body used as the adhesive tape may be reattached, generally, peelability and reattachability (hereinafter collectively referred to as “reworkability”) are required. .

WO2014 / 083890 JP 2013-213103 A

  By the way, in the porous body which mix | blended the inorganic filler, it is calculated | required to further improve various performances, such as electrical conductivity and heat conductivity. For this reason, it has been studied to increase the filling rate of the inorganic filler or to use an inorganic filler having a special shape such as a plate-like filler whose electric conductivity, thermal conductivity, etc. are increased in one direction. Inorganic fillers such as boron nitride, which have a relatively low density, have high thermal conductivity, but the filling rate tends to be high with a small blending amount, and it may be difficult to increase the filling rate of the filler. Furthermore, the porous body is also required to have a higher expansion ratio in order to increase flexibility.

However, if the filling rate of the inorganic filler is increased, or if an inorganic filler having a special shape or material is used, defective foaming tends to occur during foam molding. When foaming failure occurs, it is difficult to produce a porous body having a high foaming ratio and a smooth porous surface. Furthermore, the porous body having low foamability and no smooth porous surface has a problem that the surface adhesion is low, and the reworkability is poor because the foam is torn at the time of peeling or reapplying. .
The present invention has been made in view of the above problems, and the object of the present invention is to increase the filling rate in a porous body highly filled with a filler, or to have a special shape and type as an inorganic filler. Even if it is used, it is to obtain a porous body having a sufficient expansion ratio and surface smoothness and good reworkability.

As a result of intensive studies, the present inventors have found that the above problems can be solved by setting the extensional viscosity to a certain range, and have completed the following present invention.
That is, the present invention provides the following [1] to [11].
[1] A porous body containing an elastomer and an inorganic filler dispersed in the elastomer, and the breaking time is 1 when the elongational viscosity is measured at 240 ° C. and the strain rate is 0.2 / sec. The elongational viscosity at break when measured at 240 ° C. and a strain rate of 0.2 / second is 1 × 10 ⁴ Pa · s or more 5 × 10 ⁶ Pa · s or less porous body.
[2] The porous body according to [1], wherein a filling rate of the inorganic filler is 30% by volume or more.
[3] The porous body according to the above [1] or [2], wherein the inorganic filler has a thermal conductivity of 30 W / m · K or more.
[4] The porous body according to any one of [1] to [3], wherein the inorganic filler contains boron nitride.
[5] The porous body according to [4], wherein the inorganic filler further contains magnesium oxide.
[6] The porous body according to any one of [1] to [5], wherein the inorganic filler includes a spherical filler having a diameter of 20 μm to 150 μm and a plate-shaped filler having a diameter of 10 μm to 100 μm.
[7] The porous body according to any one of [1] to [6], wherein the elastomer contains 30% by mass or more of ethylene-propylene-diene rubber.
[8] The porous body according to any one of [1] to [7] above, wherein the apparent density of the porous body is 0.2 g / cm ³ or more and 3.0 g / cm ³ or less.
[9] The porous body according to any one of [1] to [8], further containing a softening agent.
[10] An adhesive tape comprising the porous material according to any one of [1] to [9] above and an adhesive material provided on at least one surface of the porous material.
[11] A method for producing a porous body, wherein an elastomer is blended with at least an inorganic filler to obtain a resin composition, and the resin composition is foamed to obtain a porous body,
The resin composition has an elongational viscosity at break of 1 × 10 ⁴ Pa · s or more and 5 × 10 ⁶ Pa · s or less when measured at 240 ° C. and a strain rate of 0.2 / second, and the porous The method for producing a porous body, wherein the body has a breaking time of 1.7 seconds or longer when the elongational viscosity is measured at 240 ° C. and a strain rate of 0.2 / second.

  According to the present invention, an inorganic filler is filled into a porous body, and the filling rate is increased, or even when a special shape or type of inorganic filler is used, with a high yield, It is possible to obtain a porous body having high expansion ratio and surface smoothness and good reworkability.

[Porous body]
The porous body of the present invention is a porous body containing an elastomer and an inorganic filler dispersed in the elastomer, and having a large number of bubbles in the elastomer. The porous body does not contain bubbles and has an elongational viscosity at break (hereinafter also referred to as “breaking elongational viscosity”) of 1 × 10 ⁴ Pa when measured at 240 ° C. and a strain rate of 0.2 / second. -It becomes s or more and 5 * 10 < ⁶ > Pa * s or less. In the porous body, when the breaking elongation viscosity is higher than 5 × 10 ⁶ Pa · s, the foaming property of the porous body is deteriorated, and the yield in producing the porous body is reduced. Surface smoothness tends to deteriorate. Furthermore, it becomes difficult to produce a porous body having a high expansion ratio. On the other hand, if it is less than 1 × 10 ⁴ Pa · s, it is difficult to increase the expansion ratio.
In order to increase the expansion ratio, the yield when manufacturing the porous body, and the surface smoothness, the elongation at break should be 5 × 10 ⁴ Pa · s or more and 2 × 10 ⁶ Pa · s or less. Preferably, it is 1 × 10 ⁵ Pa · s or more and 1 × 10 ⁶ Pa · s or less.

Here, the elongation at break is the compression and heating of the porous body so that the bubbles in the porous body are completely crushed, obtaining a sample in which all the bubbles are crushed, and using the sample. The elongational viscosity is measured when the elongational viscosity is measured at 240 ° C. and the strain rate is 0.2 / second, and the sample is broken. Further, the breaking time is the time when the sample is broken at the time of measuring the elongation at break.
In addition, the elongation at break is a resin composition obtained by crosslinking the resin composition under the same conditions when the porous body is crosslinked without foaming the resin composition for forming the porous body. Alternatively, it can be confirmed by measuring the extensional viscosity of the sample. By confirming the elongation at break by such a method, the yield of the porous body can be predicted without manufacturing the porous body.

Moreover, in this invention, the fracture | rupture time at the time of a fracture | rupture when measuring an elongation viscosity at 240 degreeC and strain rate 0.2 / sec of a porous body will be 1.7 second or more. When the breaking time is less than 1.7 seconds, even when the elongation at break is in the above-described range, the porous body is damaged when the porous body is peeled off from the adherend, and the reworkability is not improved. . From the viewpoint of improving reworkability, the breaking time is preferably 1.9 seconds or more, more preferably 2.5 seconds or more, and further preferably 3 seconds or more. Further, the upper limit of the breaking time is not particularly limited, but is preferably 7 seconds or less, more preferably 5 seconds or less in order to obtain a practical porous body.
The breaking time here is the breaking time when the elongational viscosity is measured for a porous body having bubbles without crushing the bubbles by compression.

The porous body is preferably a foam that is foamed by a foaming agent blended in the resin composition. The expansion ratio of the porous body is usually 1.6 times or more, preferably 2.1 times or more and 8.0 times or less, more preferably 2.8 times or more and 7.0 times or less. In the present invention, as described later, for example, even when an inorganic filler is highly filled and a special shape and type of filler is used, by setting the elongation at break to a certain range, high foaming is achieved as described above. It is possible to obtain a porous body with a magnification. Moreover, when the porous body has a high magnification, flexibility and the like are easily improved. Furthermore, by setting the expansion ratio to be equal to or less than the above upper limit, the rupture time becomes long and the reworkability tends to be good.
The porous body is more preferably a crosslinked foam that is further crosslinked and foamed. When the porous body is cross-linked, the above-described breaking elongation viscosity is likely to be high, and various mechanical performances are easily improved. Moreover, it becomes easy to lengthen a fracture | rupture time by bridge | crosslinking.

The apparent density of the porous body is preferably 0.2 g / cm ³ or more and 3.0 g / cm ³ or less, and more preferably 0.3 g / cm ³ or more and 2.0 g / cm ³ or less. By setting the apparent density to be equal to or higher than these lower limit values, the fracture time becomes long and the reworkability of the porous body tends to be good. Moreover, it becomes easy to make the softness | flexibility of a foam sheet, mechanical strength, thermal conductivity etc. favorable by making an apparent density into these ranges.
Although the shape of a porous body is not specifically limited, It is preferable that it is a sheet form. The thickness of the sheet-like porous body is, for example, 0.01 mm or more and 10 mm or less, preferably 0.05 mm or more and 1 mm or less.

[Elastomer]
The elastomer (that is, first and second elastomers described later) is preferably a thermoplastic elastomer having thermoplasticity. Specifically, the elastomer is acrylonitrile butadiene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber, natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene block copolymer, hydrogenated styrene-butadiene block copolymer. , Hydrogenated styrene-butadiene-styrene block copolymer, hydrogenated styrene-isoprene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, olefin-based dynamically crosslinked thermoplastic elastomer, and the like. These elastomers may be used alone or in a combination of two or more.
Among these, an elastomer having a double bond such as acrylonitrile butadiene rubber, ethylene-propylene-diene rubber, natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene block copolymer is preferable. Since these elastomers have a double bond in the molecule, it is easy to increase the degree of cross-linking of the porous body, and it is easy to set the elongation at break to the above lower limit value or more.

Moreover, it is particularly preferable to use ethylene-propylene-diene rubber as the elastomer from the viewpoint of easily setting the breaking elongation viscosity and the breaking time within the above-described desired ranges.
When ethylene-propylene-diene rubber is used as the elastomer, ethylene-propylene-diene rubber may be used alone as the elastomer, but may be used in combination with other elastomers described above. The elastomer preferably contains 30% by mass or more of ethylene-propylene-diene rubber, more preferably 50% by mass or more and 100% by mass or less, and more preferably 60% by mass or more and 100% by mass or less, based on the total amount of elastomer. .

The elastomer preferably includes a first elastomer and a second elastomer. Specifically, the first elastomer is a liquid elastomer that is solid at room temperature (23 ° C.) and normal pressure, and the second elastomer is liquid at room temperature and normal pressure.
More specifically, the first elastomer is an elastomer having a Mooney viscosity (ML _{1 + 4} , 125 ° C.) of 10 or more and 100 or less, and the second elastomer has a viscosity at 23 ° C. of 1 Pa · s or more and 1000 Pa · s. The following elastomers are mentioned. When these two kinds of elastomers are used as the elastomer of the porous body, the above-mentioned breaking elongation viscosity is lowered, the foamability of the porous body is improved, and the breaking time of the porous body is easily increased. And it becomes easy to make the yield of a porous body, a moldability, foamability, mechanical strength, etc. favorable.

  In the present invention, it is possible to improve the mechanical strength and the like of the porous body by increasing the content of the first elastomer. Further, by increasing the content of the second elastomer, it becomes easy to lower the breaking elongation viscosity and lengthen the breaking time. From these viewpoints, on the basis of the total amount of elastomer, the content of the first elastomer is preferably 40% by mass or more and less than 70% by mass, and the second elastomer is preferably more than 30% by mass and 60% by mass or less. It is more preferable that the content of the first elastomer is 50% by mass or more and 65% by mass or less, and the content of the second elastomer is 35% by mass or more and 50% by mass or less, and the content of the first elastomer Is more preferably 55% by mass or more and 65% by mass or less, and the content of the second elastomer is further preferably 35% by mass or more and 45% by mass or less.

In the present invention, it is possible to adjust the breaking elongation viscosity and the breaking time of the porous body by the Mooney viscosity of the first elastomer. For example, by lowering the Mooney viscosity of the first elastomer, the breaking elongation viscosity is lowered. Is possible. Here, the Mooney viscosity (ML _{1 + 4} , 125 ° C.) of the first elastomer is more preferably 10 or more and 50 or less in order to easily adjust the breaking elongation viscosity and the breaking time to the above-described ranges. Since the first elastomer has such a relatively low Mooney viscosity (ML _{1 + 4} , 125 ° C.), even if the content of the first elastomer is relatively large (for example, 50 mass% or more and 65 mass%). Hereinafter, it becomes easy to adjust the breaking elongation viscosity and the breaking time to the above-described ranges. Moreover, when the elastomer having a double bond such as EPDM is used and the porous body is crosslinked, the elongation at break may be too high, but the Mooney viscosity of the first elastomer is low. , Preventing the elongation at break from becoming too high. Further, when the Mooney viscosity is lowered, it becomes easy to adjust the elongation at break to a predetermined range without using a softening agent such as process oil.

Further, the Mooney viscosity (ML _{1 + 4} , 125 ° C.) of the first elastomer is more preferably 10 or more and 23 or less from the viewpoint of easily setting the breaking elongation viscosity within a desired range. Since the first elastomer has such a Mooney viscosity (ML _{1 + 4} , 125 ° C.), even if the content of the first elastomer is further increased (for example, 55 mass% or more and 65 mass% or less), the fracture occurs. It is possible to make extensional viscosity into the above-mentioned range.
In addition, the Mooney viscosity (ML _{1 + 4} , 125 ° C.) of the first elastomer is more preferably higher than 23 and 50 or lower from the viewpoint of easily setting the breaking time within a desired range. Since the first elastomer has such a Mooney viscosity (ML _{1 + 4} , 125 ° C.), the break time can be easily set in the desired range described above.

Further, by adjusting the contents of the first and second elastomers, it is possible to lower the breaking elongation viscosity of the porous body and lengthen the breaking time. Specifically, by decreasing the content of the first elastomer and increasing the content of the second elastomer, it is possible to lower the elongation at break and increase the break time.
Furthermore, for example, when the first elastomer is 45% by mass to 55% by mass and the second elastomer is 45% by mass to 55% by mass, the Mooney viscosity of the first elastomer is not so much. Even if it is not lowered (for example, even when the Mooney viscosity (ML _{1 + 4} , 125 ° C.) is greater than 23), the extensional viscosity is easily set within the predetermined range described above.

  The viscosity of the second elastomer at 23 ° C. is preferably 5 Pa · s to 500 Pa · s, more preferably 5 Pa · s to 100 Pa · s. By setting the viscosity of the second elastomer within these ranges, the kneadability when the inorganic filler is kneaded with the elastomer becomes good.

The first and second elastomers may be appropriately selected and used from the various types of elastomers described above, but the first and second elastomers are preferably the same type of elastomer. Therefore, it is more preferable that the first and second elastomers both contain ethylene-propylene-diene rubber. When the first and second elastomers contain ethylene-propylene-diene rubber, the content of ethylene-propylene-diene rubber in each of the first and second elastomers is preferably 30% by mass or more, and 60% by mass or more and 100% by mass. The following is more preferable, and 80% by mass or more and 100% by mass or less is more preferable. Further, both the first and second elastomers may be made of ethylene-propylene-diene rubber.
Although the elastomer is not particularly limited, it is usually preferably 30% by volume or more, more preferably 35% by volume or more and 60% by volume or less, based on the total volume of the resin composition for forming the porous body. More preferably, it is 40 volume% or more and 57 volume% or less.

[Softener]
In the present invention, the porous body may contain a softening agent. Since the elongation at break can be lowered by the softening agent, the elongation at break can be easily adjusted to the desired range by using the softening agent. Moreover, it becomes easy to lengthen a fracture | rupture time. When the softening agent is blended, it may be a porous body in which the softening agent is blended with the elastomer including both the first and second elastomers, or the elastomer containing the first elastomer is replaced with the second elastomer. It is good also as a porous body which mix | blended the softening agent. The softening agent can be used in place of the second elastomer since it becomes easy to adjust the breaking extension viscosity and the breaking time of the porous body to predetermined values by blending in the same manner as the second elastomer.
As the softener, those having good compatibility with the elastomer are used, specifically, process oil, more specifically mineral oil softener such as paraffin oil, vegetable oil softener, and other than process oil. Examples thereof include synthetic softeners, and among these, process oil is preferable.
When using a process oil, it is preferable to use an oil-extended elastomer obtained by adding a process oil in advance to the first elastomer. By using an oil-extended elastomer, it becomes easy to uniformly mix the process oil into the elastomer.

The content of the softening agent may be adjusted so that the elongation at break is within the above range, but when the softening agent is a process oil, the content of the process oil is 100 parts by mass of the elastomer. The amount is preferably 1 part by mass or more and 50 parts by mass or less. By using 1 part by mass or more of procell oil, it becomes easy to lower the elongation at break by the process oil. Moreover, it is prevented that various physical properties, such as the mechanical strength of a porous body, fall by procell oil as it is 50 mass parts or less.
From these viewpoints, the content of the process oil is more preferably 10 parts by mass or more and 50 parts by mass or less, and further preferably 25 parts by mass or more and 50 parts by mass or less. Further, when the process oil is contained in these contents, even if the Mooney viscosity of the first elastomer is high (for example, Mooney viscosity (ML _{1 + 4} , 125 ° C.) is higher than 40), the elongation at break is determined as described above. It becomes easy to adjust to the range.

[Inorganic filler]
Examples of the inorganic filler include a heat conductive filler that has high heat conductivity and improves the heat conductivity of the porous body, and a conductive filler that has high conductivity and improves the conductivity of the porous body.
Specific inorganic fillers include silica, aluminum oxide, magnesium oxide, and composite oxides containing these oxides, boron nitride, aluminum nitride, and composite nitrides containing these nitrides, talc, and carbon-based fillers. Or at least 1 sort (s) chosen from the various metal filler which consists of titanium, copper, nickel, tin, silver, gold | metal | money, and the alloy containing these metals is used. Examples of the carbon filler include graphite, graphene, carbon nanotube, carbon black, and graphite. These inorganic fillers may be used alone or in combination of two or more.
Among these, silica, aluminum oxide, magnesium oxide, boron nitride, talc, aluminum nitride, graphite, graphene, carbon nanotubes, and the like can be used as thermally conductive fillers. On the other hand, carbon black, graphite, various metal fillers, and the like can be used as conductive fillers.

The inorganic filler is preferably a heat conductive filler. The inorganic filler used as the thermally conductive filler preferably has a thermal conductivity of 30 W / m · K or more, more preferably 40 W / m · K or more and 100 W / m · K or less.
The inorganic filler is preferably one or more selected from magnesium oxide, boron nitride, aluminum oxide, and aluminum nitride. These inorganic fillers generally have a thermal conductivity of 30 W / m · K or more, and the thermal conductivity of the porous body is easily improved. Moreover, it is more preferable that an inorganic filler contains boron nitride from a viewpoint of thermal conductivity and breaking elongation viscosity, and it is still more preferable to use both boron nitride and magnesium oxide.

  The inorganic filler may have any shape, and examples thereof include a spherical filler and a plate filler. The spherical filler has a filler shape close to a sphere and a sphere, and the ratio of the major axis to the minor axis of each filler is close to 1 or 1, and the ratio is, for example, 0.6 or more and 1.7 or less, preferably 0. .8 or more and 1.5 or less. Further, the plate-like filler is a filler having a flaky or flaky filler shape, and the major axis of each filler is sufficiently larger than the thickness. For example, the ratio of the thickness to the major axis is 2 or more, preferably 3. That's it.

In general, the plate-like filler tends to improve performance such as thermal conductivity and electrical conductivity, but tends to be a factor that deteriorates foamability. However, in the present invention, as described above, the elongation at break is set in the above range, thereby preventing the foaming property from being deteriorated due to the plate-like filler. On the other hand, by using a spherical filler, while maintaining various performances of the porous body such as thermal conductivity and electrical conductivity, the elongation at break is lowered and the elongation at break is within the above range. Easy to adjust.
From the above viewpoint, the inorganic filler preferably contains at least one of a plate-like filler and a spherical filler, more preferably contains a plate-like filler, and more preferably contains both of them.

The diameter of the inorganic filler is, for example, 10 μm or more and 150 μm or less. By setting the diameter of the inorganic filler within the above range, it becomes easy to improve the thermal conductivity while keeping the breaking elongation viscosity within a predetermined range. Moreover, the suitable value of the diameter of an inorganic filler changes with shapes of a filler, The diameter of a spherical filler becomes like this. Preferably it is 20 micrometers or more and 150 micrometers or less, and the diameter of a plate-like filler becomes like this.
In the present invention, the elongation at break can be adjusted also by the diameter of the inorganic filler. For example, when the diameter of the spherical filler is increased, the specific surface area of the inorganic filler is decreased, and thereby the elongation at break can be decreased. From the viewpoint of setting the elongation at break to a desired range, the diameter of the spherical filler is more preferably 30 μm or more and 100 μm or less, and further preferably more than 40 μm and 80 μm or less.

  On the other hand, if the diameter of the plate filler is too large, it tends to be a factor that hinders foamability. Accordingly, the diameter of the plate-like filler is preferably smaller than the diameter of the spherical filler, and specifically, the diameter of the plate-like filler is more preferably 10 μm or more and 50 μm or less, and 15 μm or more and 40 μm or less. Is more preferable.

In the porous body, the filling rate of the inorganic filler is preferably 30% by volume or more. The filling rate means volume% of the inorganic filler based on the total volume of the porous body component (resin composition). When the filling rate of the inorganic filler is increased, the performance imparted by the inorganic filler by the inorganic filler such as thermal conductivity and conductivity is easily improved. From the viewpoints of thermal conductivity, conductivity, etc., the filling rate of the inorganic filler is preferably high, but if the filling rate is too high, the elongation at break tends to be high as well. Therefore, from the viewpoint of adjusting the breaking elongation viscosity and the breaking time within the predetermined ranges described above, the filling rate of the inorganic filler is preferably 70% by volume or less.
Moreover, in order to improve various performances imparted by the inorganic filler while adjusting the breaking elongation viscosity and the breaking time within the desired ranges, the filling rate of the inorganic filler is more preferably 35% by volume or more and 60% by volume or less. Preferably, 40 volume% or more and 50 volume% or less are more preferable.
In addition, the volume of each component mix | blended with a resin composition is computable from the mass of each component mix | blended, For example, it can calculate by multiplying the density in 23 degreeC of each component to the mass of each component. . The filling rate of the inorganic filler can be calculated by the ratio of the sum of the volume of the inorganic filler to the sum of the volumes of all the components blended in the resin composition. The volume% of the elastomer described above can be calculated in the same manner.

In addition, when the spherical filler and the plate-like filler are used as the inorganic filler as described above, the volume fraction of the spherical filler is 50% or more and 90% or less based on the total inorganic filler, and the volume fraction of the plate-like filler. Is preferably 10% or more and 50% or less. Furthermore, the volume ratio of the spherical filler is 65% to 85%, the volume ratio of the plate filler is more preferably 15% to 35%, and the volume ratio of the spherical filler is 70% to 80%. In addition, the volume ratio of the plate-like filler is more preferably 20% or more and 30% or less.
The filler material used as the spherical filler and the plate-like filler may be appropriately selected and used from the above-mentioned materials, but the spherical filler is preferably magnesium oxide and the plate-like filler is preferably boron nitride. .

[Foaming agent]
The porous body is preferably foamed with a foaming agent blended in the resin composition. Here, the foaming agent used is preferably a pyrolytic foaming agent. By using a foaming agent such as a thermally decomposable foaming agent, the foamability when foaming and molding the porous body is improved. Furthermore, it becomes possible to make the air bubbles of the porous body substantially closed cells, and various mechanical strengths are improved.

Specific examples of the thermal decomposition type foaming agent include organic or inorganic chemical foaming agents having a decomposition temperature of about 140 to 270 ° C.
Examples of organic foaming agents include azodicarbonamide, azodicarboxylic acid metal salts (such as barium azodicarboxylate), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N′-dinitrosopentamethylenetetramine, Examples thereof include hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate, and the like.
Among these, azo compounds and nitroso compounds are preferable from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety, and azodicarbonamide, azobisisobutyronitrile, N, N′-dinitrosopentamethylene. Tetramine is more preferred, and azodicarbonamide is particularly preferred. These pyrolytic foaming agents can be used alone or in combination of two or more.
The blending amount of the pyrolytic foaming agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the elastomer so that the foam of the foam sheet can be appropriately foamed without rupturing, and 5 parts by mass or more. 25 parts by mass or less is more preferable, and 10 parts by mass or more and 25 parts by mass or less is more preferable.

[Optional ingredients]
The resin composition may be composed of an elastomer, an inorganic filler, and preferably a foaming agent to be blended, but may contain components other than these components. For example, the above-described softener and various additives described below. It may contain. The kind of additive is not specifically limited, The various additive normally used for a foam can be used. Examples of such additives include foaming aids, lubricants, shrinkage inhibitors, cell nucleating agents, crystal nucleating agents, colorants (pigments, dyes, etc.), ultraviolet absorbers, antioxidants, anti-aging agents, and fillers described above. Other fillers, reinforcing agents, flame retardants, flame retardant aids, antistatic agents, surfactants, vulcanizing agents, surface treatment agents, and the like. Such additives can be used alone or in combination of two or more.
The optional component blended in the resin composition is preferably an antioxidant. Examples of the antioxidant include phenolic antioxidants, sulfur antioxidants, phosphorus antioxidants, amine antioxidants, etc. Among them, phenolic antioxidants are preferable. An antioxidant may be used independently and 2 or more types may be used together.
The content of the antioxidant is preferably 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.2 parts by mass or more and 6 parts by mass or less with respect to 100 parts by mass of the elastomer.
The blending amount of optional components other than the elastomer, the inorganic filler, and the foaming agent can be appropriately selected within a range that does not impair the formation of bubbles and the like, and the addition amount used for foaming and molding of ordinary resins can be adopted.

<Method for producing porous body>
Examples of the method for producing a porous body of the present invention include a method in which an inorganic filler is blended in an elastomer to obtain a resin composition, and the resin composition is foamed to obtain a porous body.
In this production method, the resin composition is prepared by, for example, supplying an elastomer, an inorganic filler, and, if necessary, a foaming agent and other optional components to the extruder, melt-kneading, and extruding from the extruder. It may be formed into At this time, the resin composition is preferably extruded into a sheet. Alternatively, an elastomer, an inorganic filler, and further, if necessary, a foaming agent and other optional components are continuously conveyed while kneading using a calendar, conveyor belt casting, etc., to obtain a sheet-shaped resin composition. May be.
Moreover, you may obtain a resin composition by knead | mixing an elastomer, an inorganic filler, and also a foaming agent and other arbitrary components as needed by methods other than the above. Such a resin composition is preferably formed into a sheet by pressing, for example.

The method of foaming the resin composition is preferably foamed with a foaming agent such as a pyrolytic foaming agent as described above. In the case of foaming with a thermally decomposable foaming agent, the resin composition may be heated at a temperature higher than the decomposition temperature of the thermally decomposable foaming agent. Specifically, the heating temperature is about 200 to 400 ° C.
The method for decomposing and foaming the pyrolytic foaming agent is not particularly limited. For example, the method of heating the resin composition with hot air, the method of heating with infrared rays, the method of heating with a salt bath, or heating with an oil bath. The method etc. are mentioned, These may be used together.

In this production method, it is preferable to crosslink the resin composition before foaming. Examples of the method for crosslinking the resin composition include a method of irradiating the resin composition with ionizing radiation such as an electron beam, α-ray, β-ray, and γ-ray, an organic peroxide or a sulfur compound in advance on the resin composition. And a method in which the resin composition is heated to decompose the organic peroxide or vulcanize with a sulfur compound. These methods may be used in combination. In these, the method of irradiating ionizing radiation is preferable.
Furthermore, when the porous body (or resin composition) is in the form of a sheet, it may be stretched after foaming or while foaming.
In addition, the manufacturing method of a foam sheet is not limited to the said method, You may manufacture by another method.

In the present invention, the resin composition has a breaking elongation viscosity of 1 × 10 ⁴ Pa · s to 5 × 10 ⁶ Pa · s, preferably 5 × 10 ⁴ Pa · s to 2 × when producing a porous body. It may be adjusted to be 10 ⁶ Pa · s or less, more preferably 1 × 10 ⁵ Pa · s or more and 1 × 10 ⁶ Pa · s or less. The porous body is preferably cross-linked as described above. However, in the case of cross-linking, the breaking elongation viscosity of the resin composition after cross-linking may be adjusted to be within the above range.
Furthermore, what is necessary is just to adjust so that the above-mentioned fracture | rupture time of a porous body may be 1.7 second or more. As described above, the break time is preferably 1.9 seconds or more, more preferably 2.5 seconds or more, further preferably 3 seconds or more, and preferably 7 seconds or less, more preferably 5 seconds or less. It may be adjusted so that
In the resin composition of the present invention, the filling rate and size of the inorganic filler, the type of elastomer, the Mooney viscosity of the first elastomer, the contents of the first and second elastomers, the presence or absence of a softener, the content of the softener The presence or absence of crosslinking and at least one factor of the degree of crosslinking can be appropriately adjusted. Thus, what is necessary is just to adjust a resin composition so that breaking elongation viscosity and breaking time may become the said range.

Specifically, when the filling rate of the inorganic filler is increased, the elongation at break is increased and the breaking time is shortened, whereas when the filling rate is decreased, the breaking elongation viscosity is lowered and the breaking time is increased. By appropriately adjusting the filling rate of the inorganic filler, it is possible to make the breaking elongation viscosity and the breaking time within the above ranges. In addition, for example, if the particle size of the spherical filler is increased, the elongation at break is reduced and the breaking time is shortened. On the other hand, if the particle size is decreased, the elongation at break is increased and the breaking time tends to be increased. Therefore, it is possible to adjust the breaking elongation viscosity and the breaking time by appropriately selecting the particle size of the spherical filler according to other factors of the resin composition.
Furthermore, the elongation at break tends to increase by using an elastomer having a double bond, such as ethylene-propylene-diene rubber, and crosslinking the porous body. On the other hand, by lowering the Mooney viscosity of the first elastomer or relatively increasing the content of the second elastomer, the elongation at break tends to decrease and the break time tends to increase. Therefore, the elongation at break can also be adjusted by appropriately adjusting the type of elastomer, Mooney viscosity, the contents of the first and second elastomers, the presence or absence of crosslinking of the porous body, and the degree thereof. Furthermore, the break elongation viscosity decreases as the softener is added and the content of the softener is increased. Therefore, the elongation at break can be adjusted by the presence or absence of the softener and the content of the softener.
In addition, since the preferable aspect of each factor, such as the filling rate of an inorganic filler and content of 1st and 2nd elastomer, is as above-mentioned, the detail is abbreviate | omitted.

<Usage method of porous body>
When the inorganic filler is a heat conductive filler, the porous body of the present invention can be used as a heat dissipation material, for example. The heat dissipation material is used, for example, for electronic equipment. As the electronic device, a mobile device such as a mobile phone such as a smartphone, a tablet terminal, electronic paper, a notebook PC, a video camera, or a digital camera is preferable.
The heat dissipating material is disposed in the vicinity of the heat source inside the electronic device, and diffuses or dissipates heat generated from the heat source. Specifically, the heat dissipating material is disposed, for example, in a space between a heat source and a heat sink, and constitutes a heat dissipating mechanism that dissipates heat generated from the heat source together with the heat sink. The heat source is an electronic component that generates heat when driven or used, and specifically includes a CPU, a battery, a power amplifier, and the like. Examples of the heat sink include a metal member such as iron or stainless steel, a material having high thermal conductivity such as graphite, or a composite or laminate of these, and preferably constitutes a casing of an electronic device.
Since the porous body of the present invention is highly flexible due to the presence of bubbles, it can be placed inside an electronic device or the like in close contact with other members. Can also be arranged. Furthermore, since the porous body of the present invention is excellent in smoothness, it is easy to adhere to other members, and furthermore, in portable devices such as smartphones, even when the space where the heat dissipating material is arranged is narrow, It is possible to arrange appropriately.

Further, when the inorganic filler is a conductive filler, the porous body of the present invention has a large electric resistance because the conductive fillers are separated from each other in a state where the inorganic filler is not compressed. Contact, a conductive path is formed, and the electrical resistance decreases. Therefore, it can be used as various sensors for detecting pressure, pressure distribution, and the like using such properties.
In addition, it can be applied to members that require electrical conductivity and flexibility, such as a grounding application, a static eliminating member for a touch panel, a buffer sealing material between components in a display device, and an electromagnetic wave shielding application.

The porous body of the present invention may be used as an adhesive tape by providing an adhesive material on at least one surface. The adhesive material may be provided on one surface or both surfaces of a sheet-like porous body, for example. The pressure-sensitive adhesive material includes at least a pressure-sensitive adhesive layer, and the porous body is bonded to another member by the pressure-sensitive adhesive layer. More specifically, the adhesive material may be a single adhesive layer laminated directly on the surface of the porous body, or may be a double-sided adhesive tape attached to the surface of the porous body, The pressure-sensitive adhesive layer is preferably a simple substance. In addition, a double-sided adhesive tape is provided with a base material and the adhesive layer provided in both surfaces of the base material. Moreover, the method of forming the pressure-sensitive adhesive layer on the porous body may be carried out by directly applying the pressure-sensitive adhesive to the porous body, or the pressure-sensitive adhesive layer formed on the release film is formed on the porous body. You may transcribe.
As for the thickness of an adhesive material, 5-200 micrometers is preferable, More preferably, it is 10-100 micrometers. The thickness of the pressure-sensitive adhesive means the thickness of the pressure-sensitive adhesive layer when the pressure-sensitive adhesive consists of a single pressure-sensitive adhesive layer, and the total thickness of the double-sided pressure-sensitive adhesive tape when it is a double-sided pressure-sensitive adhesive tape. To do.
Also when using a porous body as an adhesive tape, it can be used by the method similar to the usage method of a porous body mentioned above.

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

In addition, the measuring method and evaluation method of each physical property in this invention are as follows.
[Break elongation viscosity, break time]
Samples were prepared from the porous bodies of the examples and comparative examples and the resin composition after cross-linking, and using a mechanical spectrometer (ARES manufactured by TA Instruments) under the following conditions, The elongational viscosity of each resin composition was measured.
Measurement temperature: 240 ° C. Strain rate 0.2 (1 / second)
Sample size: length 10 mm × width 20 mm × thickness 0.05 to 1 mm (thickness may be arbitrarily selected)
Specifically, after placing the sample in the oven and stabilizing the sample temperature to a state where the set temperature ± 0.3 ° C. continues for 30 seconds, the elongation viscosity at break and the time until break Were measured, and each was regarded as a breaking elongation viscosity and a breaking time. Table 1 shows the breaking elongation viscosity of the crosslinked resin composition and the breaking time of the porous body.
In the examples and comparative examples, the porous body was pressurized for 2 hours under the conditions of 200 ° C. and 20 MPa, and the porous body was compressed to create a sample of the porous body free of bubbles. When the elongation at break was measured, it was confirmed that the value was the same as that of the sample obtained from the crosslinked resin composition.

[Inorganic filler diameter]
The diameter of an inorganic filler can be calculated | required using the observation screen measured with the scanning electron microscope. More specifically, the diameter of the inorganic filler in the foam sheet is determined by immersing the foam sheet in an epoxy resin and then embedding it by heating, along the ZD direction and MD direction by a cross sectional polisher. For the arbitrary cross section cut by cutting, the major axis of the filler can be determined using an observation screen measured with a scanning electron microscope. That is, for the spherical filler, the average value of the major axis obtained by measuring 50 different spherical fillers was used as the diameter. As for the plate-like fillers, the average value of 20 pieces from the longest one obtained by measuring 50 different plate-like fillers was used as the diameter. The observation screen of the scanning electron microscope for measuring the long diameter may be one sheet or a plurality of sheets.
The resin composition after cross-linking and the diameter of the inorganic filler in the porous state without bubbles are the cross section of the arbitrary cross section cut along the ZD direction and MD direction by a cross sectional polisher. It can also be determined using the measured observation screen. That is, for the spherical filler, the average value of the major axis obtained by measuring 50 different spherical fillers was used as the diameter. As for the plate-like fillers, the average value of 20 pieces from the longest one obtained by measuring 50 different plate-like fillers was used as the diameter. The observation screen of the scanning electron microscope for measuring the long diameter may be one sheet or a plurality of sheets.
[Foaming ratio]
The expansion ratio was calculated by dividing the specific gravity of the porous body by the specific gravity of the resin composition before foaming. Specific gravity was measured based on JISK7222.
[Apparent density]
The apparent density of the porous body was measured based on JIS K7222.
[Mooney viscosity and viscosity at 23 ° C.]
The Mooney viscosity (ML _{1 + 4} , 125 ° C.) of the elastomer is a value measured according to JIS K6300-1.
The viscosity at 23 ° C. is a value measured with a B-type rotational viscometer at a rotational speed of 1 rpm.

[Success rate and surface smoothness]
In accordance with the method described in each example and comparative example, the porous body was manufactured three times, and the success rate that the porous body could be manufactured was confirmed. In addition, the surface of the obtained porous body was observed, and when the surface was smooth, or a porous body having a level of practically no problem although the surface was uneven, The body was successfully manufactured. On the other hand, many irregularities based on foaming were found on the surface of the porous body, and the production of the porous body was not successful when the level was not practical.
Further, the surface of the porous body that was successfully produced was observed, and the smoothness was further evaluated in four stages of S, A, B, and C. “S” indicates that the smoothness is the best, and “C” indicates that the smoothness is the worst.
Various physical properties such as the expansion ratio shown in Table 1 are confirmed by selecting one porous body from the porous bodies that have been successfully manufactured and confirming the one porous body.

[Reworkability evaluation]
A test piece obtained by cutting a porous body into a size of 50 mm × 100 mm was coated with a pressure-sensitive adhesive previously applied to a release film in an environment of room temperature 23 ° C. and relative humidity 50% (manufactured by Sekisui Chemical Co., Ltd., After the product name “3801X”) was pasted, it was pasted on a SUS304 (mirror finish) plate and left for 30 minutes. Thereafter, one side of the test piece was turned up, and the peeled state when the one side was gripped and manually peeled was evaluated. “S” indicates that the porous body can be peeled in the same state as before peeling, and “A” indicates that the porous body is slightly deformed but can be peeled off in a state where it can be applied again. The case where it could not be applied again was evaluated as “B”.

The materials used in the examples and comparative examples are as follows.
(First elastomer)
8030M: Ethylene-propylene-diene rubber, manufactured by Mitsui Chemicals, trade name “8030M”, Mooney viscosity (ML _{1 + 4} , 125 ° C.): 18
EP21: Ethylene-propylene-diene rubber, manufactured by JSR Corporation, trade name “EP21”, Mooney viscosity (ML _{1 + 4} , 125 ° C.): 26
EP11: Ethylene-propylene rubber, manufactured by JSR Corporation, trade name “EP11”, Mooney viscosity (ML _{1 + 4} , 125 ° C.): 24
601F: Oil-extended elastomer, manufactured by Sumitomo Chemical Co., Ltd., trade name “Esprene 601F”, an elastomer in which 100 parts by mass of ethylene-propylene-diene rubber (resin component) is oil-extended with 70 parts by mass of process oil, ethylene-propylene-diene rubber Mooney Viscosity (ML _{1 + 4} , 125 ° C.): 73
(Second elastomer)
PX-068: Liquid ethylene-propylene-diene rubber, manufactured by Mitsui Chemicals, trade name “PX-068”, viscosity at 23 ° C .: 10 Pa · s
(Inorganic filler)
RF-70C: Magnesium oxide, manufactured by Ube Materials Co., Ltd., trade name “RF-70C-SC”, diameter: 70 μm, spherical filler, thermal conductivity: 50 W / m · K
RF-10C: Magnesium oxide, manufactured by Ube Materials Co., Ltd., trade name “RF-10C-SC”, diameter: 10 μm, spherical filler, thermal conductivity: 50 W / m · K
PTX25S: Boron nitride, manufactured by Momentive Co., Ltd., trade name “PTX25S”, diameter: 12 μm, plate filler, thermal conductivity: 60 W / m · K
Foaming agent: Azodicarbonamide, manufactured by Otsuka Chemical Co., Ltd., trade name “SO-L”
Phenol antioxidant: Ciba Specialty Chemicals Co., Ltd., trade name “Irganox 1010”

Example 1
60 parts by mass of ethylene-propylene-diene rubber (trade name “8030M”) was used as the first elastomer, and 40 parts by mass of liquid ethylene-propylene-diene rubber (trade name “PX-068”) was used as the second elastomer. In addition, 300 parts by mass of magnesium oxide (trade name “RF-70C-SC”) and 55 parts by weight of boron nitride (trade name “PTX25S”), 16 parts by weight of azodicarbonamide, and phenolic oxidation as inorganic fillers After melt-kneading 4 parts by mass of the inhibitor, a sheet-shaped resin composition having a thickness of 0.4 mm was obtained by pressing. Both surfaces of the obtained sheet-shaped resin composition were irradiated with 2.0 Mrad of an electron beam at an acceleration voltage of 500 keV to crosslink the resin composition. By heating the crosslinked resin composition to 250 ° C., the resin composition was foamed to obtain a sheet-like porous body having a thickness of 0.5 mm. About the obtained porous body, as shown in Table 1, each physical property and performance were evaluated.

Example 2
Except having changed the kind of 1st elastomer and the compounding quantity of an inorganic filler as shown in Table 1, it implemented similarly to Example 1 and obtained the porous body.
Example 3
Except having changed the compounding quantity of the 1st and 2nd elastomer and an inorganic filler as shown in Table 1, it implemented similarly to Example 2 and obtained the porous body.
Example 4
Example 1 except that the resin composition was obtained by blending 102 parts by mass of an oil-extended elastomer (trade name “Esprene 601F”) instead of 60 parts by mass of ethylene-propylene-diene rubber (trade name “8030M”). It carried out similarly and obtained the porous body.
Example 5
Except having changed the kind of 1st elastomer as shown in Table 1, it implemented similarly to Example 1 and obtained the porous body.
Example 6
Except having changed the compounding quantity of the 1st and 2nd elastomer and an inorganic filler as shown in Table 1, it implemented similarly to Example 2 and obtained the porous body.

Comparative Example 1
Except having changed the compounding quantity of the 1st and 2nd elastomer and the kind of inorganic filler as shown in Table 1, it implemented similarly to Example 1 and obtained the porous body.
Comparative Example 2
Except having changed the kind of 1st elastomer as shown in Table 1, it implemented similarly to Example 1 and obtained the porous body.
Comparative Example 3
Except having changed the compounding quantity of the 1st and 2nd elastomer and an inorganic filler as shown in Table 1, it implemented similarly to Example 5 and obtained the porous body.

* 1: In Table 1, the oil-extended elastomer (Esprene 601F) used in Example 4 is divided into ethylene-propylene-diene rubber (resin component) and process oil, and is shown in parts by mass.
* 2: In Table 1, filler volume% and elastomer volume% indicate the ratio of the total volume of each of the inorganic filler and elastomer to the total volume of the resin composition.
* 3: MgO / BN (volume% / volume%) indicates volume% of each of RF-70C or RF-10C and PTX25S based on the total amount of inorganic filler.

As is apparent from Table 1, in Examples 1 to 6, by adjusting the resin composition, that is, the elongation at break of the porous body without bubbles, and the break time of the porous body to a predetermined range, It was possible to obtain a porous body having a high success rate, excellent planar smoothness, a high expansion ratio, and excellent reworkability. On the other hand, in Comparative Examples 1 and 2, since the elongation at break was too high and the break time was short, it was possible to produce a porous body having a high success rate, excellent flatness and high foaming ratio. In addition, the reworkability was not good. As for Comparative Example 3, the surface smoothness was good because the elongation at break was within a predetermined range, but the reworkability was not good because the break time was short.
As is clear from the comparison between Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2, the breaking elongation viscosity and breaking time are adjusted to desired values by adjusting the size and blending amount of the inorganic filler. We were able to. Further, as is clear from the comparison between Examples 1 and 3 and Comparative Example 2, the Mooney viscosity of the first elastomer is lowered, the amount of the second elastomer is increased, and the type of the first elastomer is changed. It was possible to adjust the breaking elongation viscosity and the breaking time to desired values by adjusting. Furthermore, as apparent from Example 4, even when the Mooney viscosity of the first elastomer was relatively high, the elongation at break and the break time could be adjusted to desired values by blending a softener. .

Claims (11)

A porous body comprising an elastomer and an inorganic filler dispersed in the elastomer, the breaking time at breaking when measuring the elongational viscosity at 240 ° C. and a strain rate of 0.2 / second is 1.7 seconds. With the above,
When the porous body is free from bubbles and has an elongational viscosity at break of 1 × 10 ⁴ Pa · s to 5 × 10 ⁶ Pa · s when measured at 240 ° C. and a strain rate of 0.2 / sec. A porous body.   The porous body according to claim 1, wherein a filling rate of the inorganic filler is 30% by volume or more.   The porous body according to claim 1 or 2, wherein the inorganic filler has a thermal conductivity of 30 W / m · K or more.   The porous body according to any one of claims 1 to 3, wherein the inorganic filler contains boron nitride.   The porous body according to claim 4, wherein the inorganic filler further contains magnesium oxide.   The porous body according to any one of claims 1 to 5, wherein the inorganic filler includes a spherical filler having a diameter of 20 µm to 150 µm and a plate-like filler having a diameter of 10 µm to 100 µm.   The porous body according to any one of claims 1 to 6, wherein the elastomer contains 30% by mass or more of ethylene-propylene-diene rubber. The porous body according to any one of claims 1 to 7, wherein an apparent density of the porous body is 0.2 g / cm ³ or more and 3.0 g / cm ³ or less.   Furthermore, the porous body of any one of Claims 1-8 containing a softening agent.   An adhesive tape comprising: the porous body according to any one of claims 1 to 9; and an adhesive material provided on at least one surface of the porous body. A method for producing a porous body, wherein an elastomer is mixed with at least an inorganic filler to obtain a resin composition, and the resin composition is foamed to obtain a porous body,
The resin composition has an elongational viscosity at break of 1 × 10 ⁴ Pa · s or more and 5 × 10 ⁶ Pa · s or less when measured at 240 ° C. and a strain rate of 0.2 / second, and the porous The body is a method for producing a porous body, wherein the breaking time at the time of breaking when the elongational viscosity is measured at 240 ° C. and a strain rate of 0.2 / sec is 1.7 seconds or more.