Cyclic olefin-based polymer resin foamed sheet

Abstract

The purpose of the present invention is to provide a cyclic olefin-based polymer resin foamed sheet with which the stability of mechanical properties or thermal properties is maintained and excellent light reflection characteristics, dielectric characteristics (low relative dielectric constant, low dielectric loss tangent), and surface quality are achieved.　According to the present invention, a cyclic olefin-based polymer resin foamed sheet is obtained, which is characterized by comprising a cyclic olefin homopolymer (A), a cyclic olefin copolymer (B), or a mixture of the cyclic olefin homopolymer (A) and the cyclic olefin copolymer (B) and having an average foam diameter of 1-20 μm. Consequently, a cyclic olefin-based polymer resin foamed sheet having excellent light reflection characteristics, dielectric characteristics (low relative dielectric constant, low dielectric loss tangent), and surface quality can be obtained.

Description

Cyclic olefin polymer resin foam sheet

[0001] The present invention relates to a cyclic olefin polymer resin foam sheet.

[0002] Cyclic olefin resins have superior physical properties such as thermal stability, chemical stability, and elastic modulus compared to conventional non-cyclic olefin resins, and are widely used in the fields of optics (e.g., optical films), packaging materials, medical and testing equipment, electronic devices, etc. Also in the field of foams, various resin foams using cyclic olefins as the base resin have been proposed.

[0003] Patent Document 1 discloses a cyclic polyolefin resin obtained by gas foaming with a porosity of 95% or more. It claims that this resin foam has excellent thermal insulation performance, environmental friendliness, and moist heat resistance. It also discloses a resin foam with a peak bubble size distribution of 36 μm to 80 μm.

[0004] Patent Document 2 discloses a cycloolefin copolymer derived from a norbornene-based compound obtained by crosslinking foaming. It is said to be particularly suitable for such applications because it has high resistance to warm and hot water and does not absorb water due to its chemical structure. It discloses an average cell diameter of about 40 μm to about 200 μm.

[0005] Patent Document 3 discloses an ethylene-cyclic olefin random copolymer obtained by copolymerizing ethylene and a norbornene compound by injection foaming using carbon dioxide. It is said that this copolymer provides a cyclic olefin resin foam that is excellent in rigidity, heat resistance, heat aging resistance, chemical resistance, solvent resistance, dielectric properties, etc., as well as exhibiting vibration damping properties over a wide temperature range and excellent heat resistance. There is no mention of the cell diameter of the foam.

[0006] Patent Document 4 discloses a coaxial cable having an insulation layer material made of a resin composition containing a cyclic olefin resin and low-density polyethylene and / or linear low-density polyethylene, which is obtained by extrusion foaming with nitrogen gas, and has a foaming degree of 80% to 90%. This is said to provide a coaxial cable having a high degree of foaming in the insulation layer, which has sufficient lateral pressure resistance for use as a coaxial cable. Furthermore, the high foaming degree of the insulation layer in the coaxial cable reduces the dielectric loss tangent and relative permittivity of the insulation layer, making it suitable for use as a high-frequency coaxial cable.

[0007] Patent Document 5 discloses a method for producing expanded cyclic olefin resin beads, which comprises expanding expandable beads containing a cyclic olefin resin as a base resin and an inorganic physical blowing agent to produce expanded beads for in-mold molding. It is said that this method produces expanded molded articles with good appearance. There is no mention of cell diameter.

[0008] Japanese Patent Laid-Open No. 2013-189484 Japanese Patent Laid-Open No. 11-514680 Japanese Patent Laid-Open No. 11-100454 International Publication WO2009 / 041116 Japanese Patent Laid-Open No. 2017-179238

[0009] On the other hand, cyclic olefin resins have a unique low dielectric constant and low dielectric dissipation factor due to their molecular structure, and are therefore expected to be used particularly in high-frequency components. In particular, their foams are expected to be used in terahertz wave components, which are expected to expand in the future. However, in order to achieve similar low dielectric properties for terahertz waves, it is believed that micro-foamed fine cells are required. Therefore, the present invention aims to provide a cyclic olefin polymer resin foam sheet that maintains stable mechanical and thermal properties while achieving excellent light reflectivity, dielectric properties (low dielectric constant, low dielectric dissipation factor), and surface quality.

[0010] In view of the above problems, the present inventors conducted extensive research and found that the above-mentioned required properties can be satisfied by forming fine bubbles having a specific average bubble diameter or less in a resin sheet. The present invention was completed based on this finding. That is, the present invention is a cyclic olefin polymer resin foam sheet composed of either a cyclic olefin homopolymer (A) or a cyclic olefin copolymer (B) alone, or a mixture of a cyclic olefin homopolymer (A) and a cyclic olefin copolymer (B), and having an average bubble diameter of 20 μm or less.

[0011] The cyclic olefin copolymer (B) may be a cyclic olefin elastomer, and the cyclic olefin elastomer may be added in an amount of 1 to 20 parts by mass per 100 parts by mass of the cyclic olefin homopolymer (A), to form a cyclic olefin polymer resin foam sheet.

[0012] The cyclic olefin homopolymer (A) or the cyclic olefin copolymer (B) may be a cyclic olefin polymer resin foam sheet having a repeating unit represented by any one of the following formulas (a3), (b3), (c2), (d1), (e3), and (f3): In the formula, R １ and R ２ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, a halogen atom, or a carboxyl group; R １ and R ２ may be bonded to each other to form a ring. ３ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, a halogen atom, a carboxyl group, an acyl group having 2 to 12 carbon atoms, or an alkyloxycarbonyl group having 2 to 12 carbon atoms.

[0013] The cyclic olefin homopolymer (A) or the cyclic olefin copolymer (B) may be a cyclic olefin resin foamed sheet having a repeating unit represented by any one of the following formulas (b3-1) to (b3-7).

[0014] The cyclic olefin polymer resin foamed sheet may be characterized in that the cyclic olefin polymer (A) is a crystalline olefin polymer.

[0015] The cyclic olefin polymer resin foam sheet has a relative dielectric constant of 1.10 to 2.00 and a dielectric loss tangent of 0.5×10 as measured at a frequency of 2 GHz using a cavity resonator perturbation method. －４ From 4.5 x 10 －４ The cyclic olefin polymer resin foam sheet may be characterized by satisfying the following range.

[0016] The cyclic olefin polymer resin foamed sheet may have a total reflectance of 90% or more relative to the reflectance of an aluminum oxide reflector in the visible light band at a wavelength of 555 nm, which reflectance is taken as 100%.

[0017] The cyclic olefin polymer foamed sheet may also satisfy the requirement that the average arithmetic mean surface roughness Ra in the MD and TD directions of the cyclic olefin polymer foamed sheet is 0.50 μm or less.

[0018] The cyclic olefin polymer resin foam sheet may be used as a housing for electric / electronic parts, an electric insulating material, a sealing material, a protective material, a high frequency substrate, or a substrate for an electromagnetic wave control member.

[0019] The cyclic olefin polymer resin foam sheet may be used as a light reflector for a lighting device.

[0020] The cyclic olefin polymer resin foam sheet may be used as a housing for electric / electronic parts, an electric insulating material, a sealing material, a protective material, a high-frequency substrate, or a substrate for an electromagnetic wave control member. The cyclic olefin polymer resin foam sheet may be used as a light reflector for a lighting device.

[0021] According to the present invention, it is possible to provide a cyclic olefin polymer resin foam sheet that maintains the stability of mechanical and thermal properties and achieves excellent light reflectance, dielectric properties (low relative dielectric constant, low dielectric dissipation factor), and surface quality, and a method for producing the same.

[0022] Cyclic olefin polymers (COP) and cyclic olefin copolymers (COC) have glass transition temperatures and transparency comparable to those of polycarbonate, but have very low water absorption like polyolefins and excellent dielectric properties, making them particularly useful materials for optical and electrical / electronic systems. The present invention relates to a resin foam sheet using a cyclic olefin polymer or a cyclic olefin copolymer.

[0023] The cyclic olefin polymer resin foam sheet of the present invention is composed of either a cyclic olefin homopolymer (A) or a cyclic olefin copolymer (B) alone, or a mixture of the cyclic olefin homopolymer (A) and the cyclic olefin copolymer (B). The cyclic olefin polymer resin foam sheet will be described in detail below.

[0024] (Cyclic Olefin Polymer) A cyclic olefin homopolymer (COP) or cyclic olefin copolymer (COC) refers to a homopolymer or copolymer having an alicyclic structure in the chain, synthesized using a cyclic olefin as a raw material. In this specification, homopolymers and copolymers may be simply referred to as polymers. For example, a cyclic olefin polymer may also refer to a cyclic olefin homopolymer and a cyclic olefin copolymer. The cyclic olefin polymer that can be used in the present invention is preferably a polymer (homopolymer or copolymer) obtained using norbornenes or cycloalkadienes as raw materials. Representative examples include homopolymers or copolymers obtained by the following formulas (I) to (VI). Note that the term "cyclic olefin polymer resin" is not limited to cyclic olefin polymers alone, but also includes mixtures of cyclic olefin polymers with other polymers and compositions containing additives, etc.

[0025]

[0026] The above formula (I) provides an addition copolymer of norbornenes represented by formula (a1). The formula (II) provides a hydrogenated ring-opening metathesis polymer of norbornenes represented by formula (a1). The formula (III) provides a transannular polymer of alkylidenenorbornenes represented by formula (c1). The formula (IV) provides an addition polymer (d1) of norbornenes represented by formula (a1). The formula (V) provides a hydrogenated polymer of cyclopentadiene represented by formula (e1). The formula (VI) provides a hydrogenated polymer of cyclohexadiene represented by formula (f1). In this specification, polymers using norbornene as a substrate represented by formulas (I) to (IV) may be referred to as norbornene-based resins.

[0027] In the formula, R １ and R ２ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, a halogen atom, or a carboxyl group; R１ and R ２ may be bonded to each other to form a ring. １ and R ２ An example of a compound in which R forms a ring is dicyclopentadiene. １ and R ２ Examples of the ring formed by bonding include a cyclopentane ring and a norbornane ring which may have an alkyl group having 1 to 3 carbon atoms or a carboxyl group.

[0028] In the formula, R ３ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, a halogen atom, a carboxyl group, an acyl group having 2 to 10 carbon atoms, or an alkyloxycarbonyl group (preferably having 2 to 12 carbon atoms, more preferably having 2 to 6 carbon atoms, and even more preferably having 2 or 3 carbon atoms).

[0029] R １ ~R ３ The moiety may have an arbitrary substituent.

[0030] Examples of polymers used in the present invention include the cyclic olefin copolymer represented by the above formula (a3), the cyclic olefin homopolymer represented by the formula (b3), the cyclic olefin homopolymer represented by the formula (c2), the cyclic olefin homopolymer represented by the formula (d1), the cyclic olefin copolymer represented by the formula (e3), and the cyclic olefin copolymer represented by the formula (f3). Among these, the cyclic olefin copolymer represented by the formula (a3), the cyclic olefin homopolymer represented by the formula (b3), and the cyclic olefin homopolymer represented by the formula (d1) are preferred, and the cyclic olefin homopolymer represented by the formula (b3) is more preferred.

[0031] The hydrogenated ring-opening metathesis polymer of norbornenes of formula (b3) is preferably a polymer containing structural units represented by the following (b3-1) to (b3-7).

[0032]

[0033] The crystallinity and Tg (Tm) of each compound are as follows: Compound No. Crystallinity Tg (Tm) Transparency Abbreviation b3-1 Crystalline 134°C Opaque NB b3-2 Amorphous 75°C Transparent b3-3 Amorphous 86°C Transparent b3-4 Amorphous 96°C Transparent DCP b3-5 Amorphous 150°C Transparent b3-6 Amorphous 162°C Transparent TCD b3-7 Amorphous 171°C Transparent

[0034] The following documents can be referenced for examples of the COP polymers and COC polymers listed above: - Yosuke Harauchi et al., "Zeon Corporation Cycloolefin Polymer Development Trends," Society of Polymer Science, Journal of Polymer Science, Vol. 75, No. 6, pp. 477-485 (Nov., 2018) https: / / www.jstage.jst.go.jp / article / koron / 75 / 6 / 75_2018-0025 / _pdf - Teiji Obara, "Development and Applications of Cycloolefin Polymers," Kobunshi, Vol. 57, August issue (2008) https: / / www.jstage.jst.go.jp / article / kobunshi1952 / 57 / 8 / 57_8_613 / _pdf - Teiji Obara, "Development and Practical Use of Cycloolefin Polymers," Recent Advances in Polyimides and Aromatic Polymers 2008 http: / / fibertech.or.jp / JPIC / pdf / 2008_04.pdf

[0035] Specific examples of cyclic olefin homopolymers include polymers obtained by ring-opening polymerization of norbornene. Examples of commercial products include hydrogenated ring-opening polymers of norbornene-based monomers, such as ZEONEX (registered trademark; manufactured by Zeon Corporation), ZEONOR (registered trademark; manufactured by Zeon Corporation), and ARTON (registered trademark; manufactured by JSR Corporation) (formulas b3-1 to b3-7). Examples of cyclic olefin copolymers include addition polymers of norbornene-based monomers and ethylene, such as APEL (registered trademark; manufactured by Mitsui Chemicals, Inc.) and TOPAS (registered trademark; manufactured by Polyplastics Co., Ltd.) (formula a-3).

[0036] The resin foam sheet of the present invention is composed of either a cyclic olefin homopolymer (A) or a cyclic olefin copolymer (B), or a mixture of a cyclic olefin homopolymer (A) and a cyclic olefin copolymer (B). In the case of a mixture, the cyclic olefin copolymer (B) is preferably an elastomer (exhibiting rubber elasticity at room temperature). When the cyclic olefin-based polymer resin foam sheet is composed of a mixture of a cyclic olefin homopolymer (A) and a cyclic olefin copolymer (B), the amount of the cyclic olefin copolymer added is preferably 1 to 20 parts by mass per 100 parts by mass of the cyclic olefin homopolymer (A). It is also possible to use a cyclic olefin-based polymer resin foam sheet composed solely of a cyclic olefin copolymer (B).

[0037] The cyclic olefin polymer resin foam sheet used in the present invention may be used as a resin foam sheet made of a resin composition combined with functional additives. For example, a flame retardant, a viscosity modifier, an antibacterial / antifungal agent, a hydrophilic / lipophilicity modifier, a dimensional stabilizer, an antistatic agent, a colorant, etc. may be added. The amount of additive added is not particularly limited, but if an additive is added, it can be added within a range that does not impair the properties of the cyclic olefin polymer resin foam sheet, such as the cell structure, dielectric properties, surface quality, and light reflectance (total reflectance).

[0038] Alternatively, the cyclic olefin polymer according to the present invention may be mixed with another resin to impart mechanical properties such as strength and impact value, and functionality such as moldability and heat resistance, and the resulting cyclic olefin resin foam sheet may be made from a resin mixture or a resin alloy. There are no restrictions on the resin to be mixed, and an appropriate resin may be selected and used according to the needs. The mixing ratio of the cyclic olefin polymer according to the present invention to the functional resin is not particularly limited, but, as with additives, the resin may be added within a range that does not impair the cell structure, dielectric properties, surface quality, light reflectance (total reflectance), and other properties of the cyclic olefin polymer foam sheet after mixing.

[0039] (Average Cell Diameter) The resin foam sheet of the cyclic olefin polymer of the present invention has an average cell diameter of 1 to 20 μm for the bubbles present in the resin constituting the sheet. The resin foam sheet of the present invention has the advantage that the average cell diameter is small as described above, allowing the relative dielectric constant and dielectric loss tangent to be maintained low, thereby providing excellent properties as an insulating material. The average cell diameter is preferably 1 to 18 μm, more preferably 1 to 10 μm, even more preferably 1 to 8 μm, and even more preferably 1 to 6 μm.

[0040] (Bubble Number Density) The bubble number density (bubbles / mm ) in the resin foam sheet of the cyclic olefin polymer of the present invention. ３ ) is 1.0 x 10 ５ ~6.0 x 10 ８ The preferred range of the bubble number density is 1.6 × 10 ５ ~4.8 x 10 ８ and more preferably 1.0 × 10 ６ ~4.8 x 10 ８ and further 6.0 × 10 ６ ~4.8 x 10 ８ Furthermore, the bubble number density is somewhat related to the average bubble diameter, and generally tends to decrease as the average bubble diameter increases. In other words, it is preferable that the bubble diameter is small and the bubble number density is high, so that the two satisfy a predetermined relationship.

[0041] (Density, Expansion Ratio) In the cyclic olefin polymer resin foam sheet of the present invention, the density of the resin composition is 0.85 g / cm３ Preferably, the density is 0.125 g / cm or less. ３ ~0.80 g / cm ３ It is more preferable that:

[0042] The preferred expansion ratio of the cyclic olefin polymer resin foamed sheet of the present invention can be estimated from the density described above, but for the sake of certainty, it is preferably 1.2 times or more, more preferably 1.3 times or more. There is no particular upper limit, but it may be 10 times or less, or may be 8 times or less.

[0043] (Method for Producing Foamed Sheet (Fine Foaming Process)) The fine foaming process is a batch process in which a high-pressure inert gas (e.g., nitrogen gas or carbon dioxide gas) serving as a foaming agent is dissolved in a solid resin sheet at room temperature in a high-pressure vessel until the gas reaches a saturated dissolution amount. The gas in the high-pressure vessel is then depressurized or heated to induce phase separation by utilizing the thermodynamic instability of the gas contained in the resin, thereby foaming the resin. A specific example of the process includes the following three steps. First, the method for producing a resin foamed sheet of this embodiment employs a step of incorporating a non-reactive gas into the resin under pressure (hereinafter referred to as the "first step"). Next, the resulting thermoplastic resin is heated under no pressure within a temperature range above the crystallization peak temperature and below the melting point peak temperature of the resin measured by a differential scanning calorimeter to foam the resin (hereinafter referred to as the "second step"). Finally, the resulting thermoplastic resin is cooled (hereinafter referred to as the "third step"). The average cell diameter of the foamed sheet can be adjusted by the holding time and temperature in the second step.

[0044] (Definition of total optical reflectance) The cyclic olefin polymer resin foam sheet of the present invention preferably has a total optical reflectance of 90% or more, relative to the reflectance of an aluminum oxide reflector in the visible light band at a wavelength of 555 nm, which is taken as 100%. The total reflectance is more preferably 94% or more, and even more preferably 98% or more. Depending on the intended use, the cyclic olefin polymer resin foam sheet of the present invention can be used by laminating the transparent cycloolefin polymer resin on another resin.

[0045] (Relative dielectric constant, dielectric loss tangent) The foamed sheet has a low relative dielectric constant and a low dielectric loss tangent, and therefore can exhibit favorable performance when used in housings for electric and electronic components, electrical insulating materials, sealing materials, protective materials, or substrates for high-frequency electromagnetic wave control members. From this viewpoint, the relative dielectric constant of the foamed sheet is preferably 1.10 to 2.00, more preferably 1.10 to 1.50, and particularly preferably 1.10 to 1.35. The dielectric loss tangent (tan δ) is 0.5 to 4.5 × 10 －４ is preferably 1.0 to 3.5 × 10 －４ More preferably, it is 1.0 to 2.5 × 10 －４ It is particularly preferable that the ratio is 1.0 to 2.0 × 10 －４ It is even more preferable that:

[0046] (Arithmetic Mean Surface Roughness) When AC current flows through a conductor, the higher the frequency of the current, the more difficult it is to pass through the center of the conductor, resulting in a skin effect that causes the current to flow only through the surface layer. Regarding the relationship between surface roughness and transmission loss in high-frequency copper circuits, if the surface roughness is greater than the skin depth, the signal transmission path becomes longer, increasing signal loss. Conversely, if the surface roughness is smaller than the skin depth, the transmission path becomes shorter, reducing signal loss. Therefore, a lower surface roughness for foam sheets is preferable. Particularly in high-frequency bands such as the GHz and THz bands, the surface properties of the foam sheet may affect the surface properties of the circuit material, thereby affecting loss. Furthermore, for resin foam sheets expected to be used as circuit board materials, considering the future trend toward higher circuit precision and the influence of surface irregularities on the surface properties of the laminated circuits, the surface roughness of the foam sheet must be reduced. Here, the average surface irregularities of the sheet are important, and therefore the arithmetic mean surface roughness Ra is used as the surface roughness in the present invention. From such a viewpoint, the arithmetic mean surface roughness Ra of the cyclic olefin polymer resin foam sheet is 0.08 to 0.50 μm, preferably 0.10 to 0.50 μm, more preferably 0.10 to 0.35 μm, even more preferably 0.10 to 0.30 μm, and particularly preferably 0.10 to 0.25 μm.

[0047] The thickness of the cyclic olefin polymer resin foam sheet of the present invention is a maximum of 2 to 3 mm. Specifically, the thickness can be determined depending on the application. Considering applications such as housings for electronic components and reflectors, the thickness can be set, for example, in the range of 50 μm to 2 mm, preferably 100 μm to 1 mm, and more preferably 0.5 mm to 1 mm. The cyclic olefin polymer resin foam sheet of the present invention is produced by impregnating a cyclic olefin polymer resin foam sheet as described above with a foaming gas and then foaming the gas under specified conditions, thereby producing a resin foam sheet with excellent surface quality, as described above. Furthermore, after the micro-foaming process is completed, roll rolling may be performed as needed to adjust the sheet thickness and surface properties. Thus, the excellent surface roughness of the resin foam sheet of the present invention is due to the fact that the gas penetration process and the foaming process are separated, resulting in small cell diameters and a stable cell size distribution. Therefore, the surface properties are easily stabilized, and the arithmetic mean surface roughness Ra, an index of surface roughness, can be kept low by combining the above-mentioned roll processing.

[0048] (Uses) The cyclic olefin polymer resin foam sheet of the present invention can be used for housings for high-quality electric and electronic components, electrical insulating materials, sealing materials, protective materials, substrates for high-frequency electromagnetic wave control members, or light reflectors for lighting devices, taking advantage of its low dielectric constant and low dielectric loss tangent. In this case, its excellent surface properties and light reflectance are advantageous when using the above materials.

[0049] The need for low-dielectric materials is increasing. For example, in the mobile phone service field, the fifth-generation (5G) mobile communication system began to be introduced overseas in 2019 and in Japan in 2020, introducing new systems with high speed, large capacity, low latency, and multiple simultaneous connections. In the automotive field, the development of advanced driver assistance systems (ADAS) is progressing, and new technologies are being put to practical use, such as the release of Level 3 autonomous vehicles. These technologies are supported by printed wiring boards and antenna substrates compatible with high frequencies such as the Sub-6 band and millimeter wave band. Because transmission loss increases with increasing frequency of radio waves, low-dielectric substrates that suppress loss are playing an increasingly important role. Furthermore, as mentioned at the beginning, there is a demand for compatibility with terahertz waves, and the cyclic olefin polymer resin foam sheet of the present invention can be suitably used for this purpose.

[0050] The cyclic olefin polymer resin foam sheet of the present invention has an extremely high total light reflectance. Its applications include light reflectors for lighting devices, as mentioned above. Growing awareness of energy conservation has led to the widespread adoption of LED lighting in homes, offices, stores, and other general lighting applications. Even within automobiles, the benefits of compact lighting, improved luminous efficiency, lower costs for LED light sources, and room lamps, illumination, and design freedom have led to enhanced interior space and commercial value. The cyclic olefin polymer resin foam sheet of the present invention can meet the above-mentioned needs by providing an extremely high total light reflectance. Furthermore, its excellent moldability allows it to be processed into shapes that accommodate the lighting configuration and installation location constraints to provide a reflector.

[0051] (Materials used) Cyclic olefin polymer (1) Zeonex C2420 manufactured by Zeon Corporation (estimated from the melting point to be a DCP syndiotactic resin) (2) Zeonex 790R manufactured by Zeon Corporation (norbornene-based resin) (3) Zeonor 1420R manufactured by Zeon Corporation (norbornene-based resin) (4) Zeonex K22R manufactured by Zeon Corporation (norbornene-based resin) Glass transition temperature (JIS K7121): 143 ° C. (5) Zeonex T62R manufactured by Zeon Corporation (norbornene-based resin) Glass transition temperature (JIS K7121): 154 ° C. (6) Cycloolefin copolymer (COC) elastomer: TOPAS E-140 TOPAS Advanced manufactured by Polyplastics Co., Ltd. Amorphous resin produced by Polyplastics Polymers GmbH (norbornene-based resin). It has a tensile modulus of 50 MPa and a tensile elongation at break of over 500% (ISO 527-T2 / 1A), making it an elastomer that maintains excellent ductility even at low temperatures below freezing. (7) Cycloolefin copolymer (COC): TOPAS 5013L-10 (norbornene-based resin) manufactured by Polyplastics Co., Ltd. (8) Cycloolefin copolymer (COC): TOPAS 6015 (norbornene-based resin) manufactured by Polyplastics Co., Ltd.

[0052] <Production of Example Materials as Test Specimens> The above-described rolled cyclic olefin polymer sheet was obtained, placed in a pressure vessel, and pressurized to 5.2 MPa with carbon dioxide gas. The carbon dioxide gas was allowed to penetrate into the resin film for 24 hours. After this process, the rolled cyclic olefin polymer sheet was removed from the pressure vessel and continuously fed into a hot air circulation foaming oven set at 140°C to 260°C. The sheet was then held for a predetermined time to foam the cyclic olefin polymer sheet, thereby obtaining a cyclic olefin polymer resin foam sheet. For the comparative example, an unfoamed resin sheet was used without carbon dioxide gas penetration. The foaming temperatures for each test material were 260°C for Example Materials 1 to 4, 170°C for Example Materials 5 to 8, and 140°C for Example Materials 9 and 10.

[0053] (Measurement Method) The expansion ratio and foam density were measured as follows. <Method for Measuring Expansion Ratio> The expansion ratio is an apparent ratio commonly used for resin foams. This apparent ratio can be calculated by cutting a specimen having dimensions of 10 cm x 10 cm from a resin foam sheet, weighing the specimen (W1 [g]), measuring the thickness at the four corners and at the center of the specimen (using a measuring machine conforming to JIS K6767), and using the average value (T [cm]) of the five measurements, according to the following formula (1): apparent ratio (expansion ratio) = 10 x 10 x T / W1 (1)

[0054] <Method for measuring foam density> The density of the resin foam sheet was measured in accordance with JIS K7222-1999 "Foamed plastics and rubber - Method for measuring apparent density." Test specimens were cut into 10 cm x 10 cm pieces from resin foam sheets that had been conditioned at 23°C ± 2°C for 72 hours or more after molding. Specifically, the foam density was calculated using the following formula (2). The unit is g / cm. ３ [Equation 1] ρ ａ = {(m + ma)} / V ... (2) m is the mass of the test piece (g), V is the volume of the test piece (cm ３ ), ma: mass of replaced air (g). Note that ma: mass of replaced air is negligible due to the low expansion ratio, so calculations were made ignoring this. Measurements were performed five times, and the average value was calculated from the measurement results of all test pieces, and this was used as the density.

[0055] <Method for measuring bubble diameter> The bubble diameter was determined in accordance with ASTM D3576-77. An SEM photograph of the longitudinal cross section of the sheet was taken, and straight lines were drawn horizontally and vertically on the SEM photograph, and the lengths t of the chords of the bubbles crossed by the straight lines were averaged. The magnification of the photograph, M, was substituted into the following formula to determine the average bubble diameter d (d = t / (0.616 × M)). The average bubble diameter was determined by measuring SEM photographs of three different fields of view at the center in the width direction, and averaging the results.

[0056] <Method for measuring cell number density> A SEM photograph of the longitudinal section of a cyclic olefin polymer resin foam sheet was taken, and five regions of 100 μm × 100 μm were randomly selected on the SEM photograph, and the number of cells present in each region was counted. ２ By calculating the number of bubbles per 1 mm based on each area, ３ The number of bubbles per 1 mm was calculated based on each of the five regions. 2 The average number of bubbles per square centimeter was calculated, and the bubble density ( 2 The obtained 1 mm ２ The number of bubbles per square meter is multiplied by (3 / 2) to obtain a square meter of 1 mm based on each area. ３ The number of bubbles per 1 mm was calculated based on each of the five regions. ３ The average number of bubbles per square centimeter was calculated, and the bubble density ( ３ When measuring the bubble diameter and bubble number density, it is desirable to prepare a plurality of SEM photographs (preferably three or more) and calculate the average value of the values ​​calculated for each SEM photograph.

[0057] <Method of determining total optical reflectance> The total optical reflectance was measured as follows. The total reflectance of the sample was measured at a wavelength of 550 nm using a Hitachi High-Tech spectrophotometer U-4100 (trade name). An aluminum oxide white plate (210-0740 (trade name), manufactured by Hitachi High-Tech Fielding Corporation) was used as a reference, and the measured value was expressed as a relative value to the reference.

[0058] <Measurement of relative permittivity and dielectric loss tangent> The relative permittivity and dielectric loss tangent were measured using a cavity resonator perturbation method, with the measurement frequency set to 2 GHz. ｒThe complex dielectric constant in the planar direction of the cyclic olefin polymer resin foam sheet can be measured by a cavity resonator method, where tanδ is the dielectric loss tangent and tanδ is the dielectric constant. In the present invention, the dielectric constant was measured by the cavity resonator method at a resonance frequency of 2 GHz using a sample having a length of 78 mm, a width of 2.4 mm, and a thickness of 1 mm. The measurement equipment used for this measurement can be, for example, a CP461 cavity resonator manufactured by Kanto Electronics Application Development Co., Ltd., and an E8361A network analyzer manufactured by Agilent Technologies.

[0059] <Surface Roughness Measurement> To evaluate the overall surface quality of a foam sheet, the surface quality of the foam sheet of the present invention was evaluated by measuring Ra rather than Rz, which is significantly affected by factors such as maximum irregularities. The arithmetic mean roughness Ra was determined in accordance with JIS B0601:2013. A Handysurf E-30A (manufactured by Tokyo Seimitsu Co., Ltd.) was used for this measurement. Each measurement had a reference length of 2.5 mm. In the present invention, a surface roughness Ra of, for example, 1.0 μm or less means that five measurement lines were randomly selected in the MD direction on the surface of the foam sheet, the arithmetic mean roughness of the measurements on each measurement line was measured, and the average of the five measurements was taken. Additionally, five measurement lines were randomly selected in the TD direction, the arithmetic mean roughness of the measurements on each measurement line was measured, and the average of the five measurements in both directions was taken, resulting in a value of 1.0 μm or less. In other words, the surface roughness in the present invention is evaluated as an average in both the MD and TD directions. Here, the surface characteristics are calculated by taking into account the influence of surface roughness in not only the MD direction but also the TD direction, and are therefore averaged in both directions. This is because, when manufacturing sheet material, the sheet may be passed through rolls, and in this case, in addition to the pressing effect of the roll on the surface, tension is applied to the sheet in the MD direction to stretch it, so the surface properties in the MD direction are often better than those in the TD direction.

[0060] <Materials Used in the Test> The materials used in the test were a total of 12 types of COP resins, namely, Example Materials 1 to 10 and Comparative Examples 1 and 2. Comparative Examples 1 and 2 are non-foamed sheets having the same composition as the specified materials of the Example Materials.

[0061] Example 1 is a foam sheet using Zeonex C2420 alone as the COP resin, while Examples 2 to 4 are foam sheets in which Zeonex C2420 is the primary COP resin and TOPAS E140, a COC elastomer, is gradually added in increasing amounts. Example 2 is a foam sheet containing 95% by weight of Zeonex C2420 and 5% by weight of COC elastomer TOPAS E140. Example 3 is a foam sheet containing 90% by weight of Zeonex C2420 and 10% by weight of COC elastomer TOPAS E140. Example 4 is a foam sheet containing 80% by weight of Zeonex C2420 and 20% by weight of COC elastomer TOPAS E140. Examples 5 to 8 are foams containing various types of COP resin. Specifically, Example Material 5 is a foam using Zeonor 790R as the COP resin, and Example Material 6 is a foam using Zeonor 1430R. Example Material 7 is a foam sheet using Zeonex K22R, and Example Material 8 is a foam sheet using Zeonex T62R. Example Material 9 is a COC resin foam sheet using TOPAS 5013L-10 as the COC resin, and Example Material 10 is a COC resin foam sheet using TOPAS 6015 alone as the COC resin. Comparative Example Material 1 shows the relative permittivity and dielectric loss tangent of Zeonex C2420 as a non-foamed COP resin, and Comparative Example Material 2 is a non-foamed sheet material composed of a mixture of 80% by mass of COP resin and 20% by mass of COC elastomer. The composition of Comparative Example Material 1 is the same as that of Example Material 1, and the composition of Comparative Example Material 2 is the same as that of Example Material 4.

[0062] <Test Results for Evaluating the Physical Properties of Test Foam Sheets> Table 1 shows the results of evaluating the physical properties of Example Materials 1 to 10 and Comparative Materials 1 and 2 used in the test.

[0063] <Expansion Ratio and Density of COP Resin Foam Sheets> When the foamability of the example materials was evaluated in terms of expansion ratio and density, the expansion ratios of example materials 1 to 10 were in the range of 1.4 to 6.7 times, which were low expansion ratios of 10 times or less. In particular, except for example materials 4 and 2, which had a maximum cell diameter of 16.0 μm, the expansion ratios of the other example materials were less than 6 times. In contrast, example materials 9 and 10, which were foam sheets using only COC resin, had low expansion ratios of less than 2 times. In contrast, the foam density of example materials 1 to 10 was 0.15 to 0.72 g / cm ３ The foamed sheet of Example 4, which gave a maximum cell diameter of 16.0 μm, had the lowest density, at 0.15 g / cm. ３ In addition, in Example Materials 9 and 10, the foaming ratios are low at 1.4 times and 1.6 times, respectively, and the foam densities are 0.72 and 0.64 g / cm ３ showed high values.

[0064] <Characteristics of Cell Structure of COP Resin Foam Sheet> When Example Materials 1 to 10 were foamed, none of the test materials experienced foaming inhibition, and foaming proceeded without any particular problems, resulting in the production of the desired foamed sheets. The cell structure of the present invention can be appropriately adjusted by changing the composition of the materials constituting the foam and the foaming conditions. Looking at the average cell diameter, average cell number density, and foam density of the foamed sheet of the present invention, the Example Materials as a whole had an average cell diameter of 1.2 μm to 16.0 μm and a cell number density of 1.6×10 ５ ~4.8 x 10 ８ pieces / m ３The foam densities ranged from 0.15 to 0.72. Looking at the results for foam sheets made with Example Materials 1 to 4, which consist primarily of Zeonex C2420 as the COP resin and gradually increasing amounts of the COC elastomer TOPAS E140, it appears that increasing the amount of COC elastomer and expanding the bubbles through foaming increases the average bubble diameter, thereby reducing the bubble number density and foam density. In contrast, Example Materials 5 to 8, which contain only a COP resin other than Zeonex C2420 and do not contain a COC elastomer, exhibited smaller average bubble diameters and higher bubble number densities than Example Materials 2 to 4, which contain a predetermined amount of COC elastomer added to the COP resin. This is likely due to the improved viscoelastic properties, such as increased melt tension near the foaming temperature, of the resins containing the COC elastomer added to the COP resin. In addition, in the foam sheets of Example Materials 9 and 10, which use only COC resin, differences in foaming characteristics such as cell structure are observed depending on the type of COC resin. It goes without saying that the cell structure of the present invention can be obtained by appropriately changing the composition of the materials constituting the foam and the foaming conditions other than the cell structure disclosed in the examples, although the cell structure is different from that disclosed in the examples.

[0065] <Measurement Results of Total Reflectance of COP-Based Resin Foam Sheets> The ratio of the total reflectance of Example Materials 1 to 10 to the aluminum oxide standard plate at a wavelength of 550 nm in the visible light band was all 90% or higher. By incorporating bubbles with an average bubble diameter of 20 μm or less, specifically 1.2 to 16.0 μm or less, a resin foam sheet with high light reflectance can be obtained. Although diffuse reflectance data was not measured specifically, it is estimated that the resin foam sheet of the present invention also has high diffuse reflectance due to the incorporation of fine bubbles. The ratio of the total reflectance of Example Materials 1 to 8 to the aluminum oxide standard plate, consisting of COP resin alone or COP resin alone blended with 5% to 20% COC resin by weight, was 98.5 to 99.8%, whereas the total reflectance of Example Materials 9 and 10, which have a 100% COC resin composition, was 94.4% and 98.6%, respectively, indicating a tendency for these to be slightly inferior to Example Materials 1 to 8. This difference is thought to be due to the difference in the resin composition of the foam.

[0066] <Measurement Results of Relative Dielectric Constant and Dielectric Loss Tangent of COP Resin Foam Sheet> The relative dielectric constant of Example Materials 1 to 10 was in the range of 1.11 to 1.77, and the dielectric loss tangent was 1.0×10 －４ ~2.2 × 10 －４ The range of dielectric constants was 1.11 to 1.32, and the dielectric loss tangent was 1.0×10. The results of measuring the dielectric properties of the foamed sheets in which the COP resin of Example Materials 1 to 4 was Zeonex C2420 as the main component and TOPAS E140, a COC elastomer, was added in a stepwise increasing amount from 0 to 20 parts by mass. －４ ~2.0 x 10 －４ The dielectric constant and dielectric loss tangent of the material to which a specified amount of COC elastomer was added were low, and it is thought that materials with a larger amount of COC elastomer, which increased the average cell diameter and also set the cells to a specified cell number density, were slightly superior in dielectric properties. In contrast, Example Materials 5 to 8, which used different types of COP resin, had a dielectric constant of 1.21 to 1.32 and a dielectric loss tangent of 1.2 x 10 compared to a resin foam sheet that similarly used only C2420, a COP resin, as the substrate. －４ ~1.4 × 10 －４In contrast, Example Materials 9 and 10, which are made of 100% COC resin, have larger relative permittivity and dielectric loss tangent than Example Materials 1 to 8, with Example Material 9 having a relative permittivity of 1.77 and a dielectric loss tangent of 2.2×10 －４ The relative dielectric constant of Example Material 10 is 1.68, and the dielectric loss tangent is 2.1 × 10 －４ Here, it is presumed that the reason why Example Materials 9 and 10 have inferior dielectric properties compared to the other Example Materials is due to the difference in structure between the COP resin and the COC resin. In addition, the relative dielectric constants of non-foamed sheets having the same composition as Example Materials 1 and 4 are 2.34 and 2.13, respectively, and the dielectric loss tangent is 5.0 × 10 －４ , 2.8 × 10 －４ The relative dielectric constant is 2.00 or more, and the dielectric loss tangent is also 2.5 × 10 －４ It exceeded that.

[0067] <Measurement Results of Arithmetic Mean Surface Roughness Ra of COP Resin Foam Sheets> The arithmetic mean surface roughness Ra of Example Materials 1 to 10 was in the range of 0.10 to 0.50 μm. Looking more specifically at the differences between the materials, for Example Materials 1 to 4, which were foam sheets in which the amount of COC Elastomer TOPAS E-140 added to COP Zeonex C2420 was varied to change the expansion ratio and cell diameter, Example Material 4 had an average cell diameter of 16.0 μm, greater than 10 μm, and a large surface roughness of 0.50 μm. However, Example Materials 1 to 3 had average cell diameters of 2.7 to 3.8 μm, and although differences were observed between the materials, the differences were not significant. This is thought to be due to the large average cell diameter of 16.0 μm in Example Material 4, which likely resulted from changes in the cell structure within the foam due to cell growth during the foaming process, affecting the surface roughness of the foam sheet surface. In contrast, while differences were observed between the materials in Examples 5 to 8, which used different types of Zeon COP resin, and Examples 9 to 10, which used Polyplastics Co., Ltd.'s COC resin, the former had a surface roughness in the range of 0.15 μm to 0.23 μm, and the latter had a surface roughness in the range of 0.12 to 0.13 μm. Even when evaluating all of Examples 5 to 10, the surface roughness was in the range of 0.12 to 0.23 μm. With the exception of Example 4, the surface roughness of Examples 1 to 10 satisfied the requirement of 0.30 μm or less, even 0.25 μm or less, indicating that the difference in surface roughness between the materials was not significant. This is thought to be because the average bubble diameter of these foam sheets was small, at 5 μm or less, so bubble growth had little effect on the surface roughness of the foam surface. This is thought to be due to the combined effect of the effect of bubble growth increasing the surface roughness of the foam surface and the effect of stretching the resin in its softened state during foaming. In the case of the unfoamed sheet materials of Comparative Example 1 and Comparative Example 2, the surface roughness exceeded 0.20 μm.

[0068] <Summary of Test Results> From the results of the Examples, all foam sheets using cyclic olefin polymers (Example Materials 1 to 10) conforming to the provisions of the present invention had excellent light reflection characteristics, dielectric properties (low relative dielectric constant, low dielectric dissipation factor), and good surface quality. In particular, Example Materials 2 to 4, which are mixtures of cyclic olefin polymer (COP) and cyclic olefin copolymer (COC) in an amount of 20 mass% COC, as the cyclic olefin polymer, or Example Materials 5 to 8, which use different types of cyclic olefin polymer, and Example Materials 9 and 10, which use COC alone, achieved results showing even better light reflection characteristics, dielectric properties (low relative dielectric constant, low dielectric dissipation factor), and surface quality. In contrast, the cyclic olefin polymers of the comparative examples were not foamed and exhibited a relative dielectric constant at least about 0.4 higher than that of the Example Materials. The dielectric dissipation factor was also high, with the Example Materials exhibiting a dielectric dissipation factor of 1.0 x 10. －４ ~2.2 × 10 －４ In Comparative Example 1, the －４ showed extremely high values.

Claims

1. A cyclic olefin-based polymer resin foamed sheet is made of either a cyclic olefin homopolymer (A) or a cyclic olefin copolymer (B) alone, or a mixture of the cyclic olefin homopolymer (A) and the cyclic olefin copolymer (B), characterized in that the cyclic olefin-based polymer resin foamed sheet has an average cell diameter of 1 to 20 μm, and has a total reflectance of 90% or more relative to the reflectance of an aluminum oxide reflector in the visible light band at a wavelength of 550 nm, where the reflectance is taken as 100%.

2. 2. The cyclic olefin polymer resin foam sheet according to claim 1, wherein the cyclic olefin copolymer (B) is a cyclic olefin elastomer, and the cyclic olefin elastomer is added in an amount of 1 to 20 parts by mass per 100 parts by mass of the cyclic olefin homopolymer (A).

3. 2. The cyclic olefin polymer resin foam sheet according to claim 1, wherein the cyclic olefin homopolymer (A) or the cyclic olefin copolymer (B) has a repeating unit represented by any one of the following formulas (a3), (b3), (c2), (d1), (e3), and (f3): 【Chemistry 1】 In the formula, R １ and R ２ are each independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, a halogen atom, or a carboxyl group; R １ and R ２ may be bonded to each other to form a ring. ３ is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an aryl group having 6 to 18 carbon atoms, a hydroxyl group, a halogen atom, a carboxyl group, an acyl group having 2 to 12 carbon atoms, or an alkyloxycarbonyl group having 2 to 12 carbon atoms.

4. The cyclic olefin resin foamed sheet according to claim 3, wherein the cyclic olefin homopolymer (A) or the cyclic olefin copolymer (B) has a repeating unit represented by any one of the following formulas (b3-1) to (b3-7): 【Chemistry 2】

5. 5. The cyclic olefin polymer resin foamed sheet according to claim 1, wherein the cyclic olefin polymer (A) is a crystalline olefin polymer.

6. The cyclic olefin polymer resin foam sheet has a relative dielectric constant of 1.10 to 2.00 and a dielectric loss tangent of 0.5×10 as measured at a frequency of 2 GHz using a cavity resonator perturbation method. －４ From 4.5 x 10 －４ 5. The cyclic olefin polymer resin foam sheet according to claim 1, wherein the range of

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8. 5. The cyclic olefin polymer resin foamed sheet according to claim 1, wherein the arithmetic mean surface roughness Ra of the cyclic olefin polymer resin foamed sheet in the MD direction and the TD direction is 0.50 μm or less.

9. The cyclic olefin polymer resin foam sheet according to claim 6, characterized in that the cyclic olefin polymer resin foam sheet is used as a light reflector for a lighting device, a housing for electrical and electronic components, an electrical insulating material, a sealing material, a protective material, a high-frequency substrate, or a substrate for an electromagnetic wave control component.

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11. Use of the cyclic olefin polymer resin foam sheet according to claim 6 as a light reflector for a lighting device, a housing for electric / electronic components, an electric insulating material, a sealing material, a protective material, a high-frequency substrate, or a substrate for an electromagnetic wave control member.

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