JP2007112917A - Acrylic rubber material for shielding electromagnetic waves - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acrylic rubber material for shielding electromagnetic waves, giving vulcanized formed articles (rubber materials) having low hardness and excellent electromagnetic wave-shielding properties, even when a carbon-based filler is compounded in an amount capable of keeping the sealing property. <P>SOLUTION: This acrylic rubber material for shielding the electromagnetic waves is characterized by compounding 100 pts.wt. of a composition containing (A) an acrylic polymer having at least one alkenyl group capable of being hydrosilylated, (B) a hydrosilyl group-containing compound, and (C) a hydrosilylation catalyst as essential components with ≥5 pts.wt. of conductive carbon black or graphite. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an acrylic rubber material for electromagnetic wave shielding. More specifically, the present invention relates to an electromagnetic wave shielding acrylic rubber material containing a carbon-based filler.

  Conventional electromagnetic shielding materials include methods that use a metal plate such as an aluminum plate, methods that use a metal fiber wire mesh such as a stainless steel wire mesh, and methods that apply plating, coating, etc. to the housing. It is used properly according to.

  Here, the method of giving conductivity to the rubber material and exhibiting the shielding effect is slightly inferior in electromagnetic wave shielding property, but is excellent in cost, durability, and weight reduction, and also has the effect of adding the sealing property of the attachment site. For this reason, it has been applied to a joint portion of a casing, a wire covering, and the like.

However, in response to the recent strong demands for weight reduction and downsizing, metal plates are heavy and there are problems in terms of space efficiency, so the case has been converted from metal plates to composite materials such as resin, metal fibers, and plating. It is out. In the case of a metal casing, since the strength is high, even a conventional electromagnetic shielding rubber material can maintain a sufficient sealing property. However, in the case of a resin casing, the conventional electromagnetic shielding rubber material has a problem such as deformation of the resin due to reaction force. It may occur. In addition, conventional electromagnetic wave shielding rubbers require the addition of a large amount of a conductivity-imparting agent, but this has caused a problem that the hardness is increased. On the other hand, in response to the addition of a softening agent and a decrease in the filler, since the electromagnetic shielding property is greatly lowered, it is difficult to cope with low hardness.
JP 2000-332483 A JP-A-11-167825 JP-A-10-298355

As such countermeasures, as disclosed in Patent Document 4, a method of blending a large amount of carbon fiber and a softening agent with good conductivity has been proposed. There is a problem above.
JP 2002-167654 A

In addition, a method has been proposed in which two or more types of polymers are mixed and the amount of the conductivity-imparting agent is reduced by unevenly distributing the conductivity-imparting agent in one polymer, thereby reducing the hardness, but there is a problem in workability. There is a problem that the non-polar liquid such as oil is poor in sealing properties.
JP 2002-309107 A

  An object of the present invention is to provide an electromagnetic wave shielding acrylic rubber that can provide a vulcanized molded article (rubber material) having a low hardness and excellent electromagnetic wave shielding properties even when an amount of a carbon-based filler capable of maintaining sealing properties is blended. To provide materials.

  An object of the present invention is to provide a composition containing (A) an acrylic polymer having at least one alkenyl group capable of hydrosilylation reaction, (B) a hydrosilyl group-containing compound and (C) a hydrosilylation catalyst as essential components. This is achieved by an acrylic rubber material for electromagnetic wave shielding in which 5 parts by weight or more of conductive carbon black or graphite is blended with respect to 100 parts by weight.

  The vulcanized product obtained from the acrylic rubber material for electromagnetic wave shielding according to the present invention has a low hardness without impairing the sealing property and sufficient electromagnetic wave shielding property. This vulcanized molded product is suitably used as a rubber material for electromagnetic shielding for resin casings that require particularly low hardness. In addition, as a normal rubber material for electromagnetic shielding, it can be suitably used for any part that requires sealing properties.

  The acrylic rubber serving as the base rubber of the conductive rubber is formed by curing a composition containing the components (A), (B) and (C) as essential components.

  The acrylate ester monomer constituting the main chain of the acrylic polymer having at least one alkenyl group capable of hydrosilylation reaction as component (A), preferably at least one at the terminal, is not particularly limited, Any thing can be used.

  For example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, n-pentyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-heptyl acrylate, n-octyl Acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, phenyl acrylate, toluyl acrylate, benzyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, stearyl Acrylate, glycidyl acrylate, 2-aminoethyl acrylate, trifluoromethylmethyl Chryrate, 2-trifluoromethyl ethyl acrylate, 2-perfluoroethyl ethyl acrylate, 2-perfluoroethyl-2-perfluorobutyl ethyl acrylate, perfluoroethyl acrylate, perfluoromethyl acrylate, diperfluoromethyl methyl acrylate, 2 -Acrylic acid esters such as perfluoromethyl-2-perfluoroethylethyl acrylate, 2-perfluorohexylethyl acrylate, 2-perfluorodecylethyl acrylate, 2-perfluorohexadecylethyl acrylate, or the corresponding methacrylic acid An ester, an ethylene oxide adduct of acrylic acid, γ- (methacryloyloxypropyl) trimethoxysilane, or the like is used. Alternatively, acrylic acid or methacrylic acid can also be used.

  Of these, acrylic acid esters or methacrylic acid esters are preferably used from the viewpoint of physical properties of the product, and acrylic acid esters such as butyl acrylate, ethyl acrylate, 2-methoxyethyl acrylate, 2-ethoxy are particularly preferable. Ethyl acrylate or the like is used alone or in combination of two or more.

  In the present invention, these preferred monomers may be randomly copolymerized with other monomers or further block copolymerized, and in this case, 60% by weight of these preferred monomers, acrylate ester or methacrylate ester. It is preferable that the copolymer is copolymerized in the above ratio.

  In addition to these acrylic acid or methacrylic acid monomers, other monomers can be copolymerized at a ratio of about 30% by weight or less. Examples of such monomers include styrene, vinyltoluene, α-methylstyrene, chloro Styrene monomers such as styrene, styrenesulfonic acid or salts thereof; fluorine-containing vinyl monomers such as perfluoroethylene, perfluoropropylene, and vinylidene fluoride; silicon-containing vinyl monomers such as vinyltrimethoxysilane and vinyltriethoxysilane; Maleic anhydride, maleic acid, monoalkyl or dialkyl esters of maleic acid; fumaric acid, monoalkyl or dialkyl esters of fumaric acid; maleimide, methylmaleimide, ethylmaleimide, propylmaleimide, butylmaleimide , Hexylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide, cyclohexylmaleimide and other maleimide monomers; acrylonitrile, methacrylonitrile and other nitrile group-containing vinyl monomers; acrylamide, methacrylamide and other amide group-containing vinyls Monomers; Vinyl esters such as vinyl acetate, vinyl propionate, vinyl pivalate, vinyl benzoate, vinyl cinnamate; olefins such as ethylene and propylene; conjugated dienes such as butadiene and isoprene; vinyl chloride, vinylidene chloride, Examples include allyl chloride and allyl alcohol.

In the acrylic polymer obtained by copolymerizing these monomers, at least one alkenyl group capable of hydrosilylation reaction is introduced, preferably at least one at the terminal. The introduced alkenyl group has the general formula
CH ₂ = C (R)-
Wherein R is a hydrogen atom or an organic group having 1 to 20 carbon atoms, such an organic group is an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, or 7 to 7 carbon atoms. 20 aralkyl groups and the like are mentioned. From the viewpoint of reactivity with the hydrosilyl group-containing compound, an alkenyl group in which R is a hydrogen atom or a methyl group, preferably a hydrogen atom, is introduced.

Such an alkenyl group can be introduced, for example, by the following method.
(a) When synthesizing an acrylic polymer by living radical polymerization, together with a predetermined acrylic monomer, a general formula
CH ₂ = CR ¹ -R ² -R ³ -CR ¹ = CH ₂
R ¹ : hydrogen atom or methyl group
R ² : ester group or o-, m- or p-phenylene group
In the case of an ester group, a (meth) acrylate compound
In the case of phenylene group, styrenic compound
R ³ : a C _{1 to} C ₂₀ organic group that may have a direct bond or one or more ether bonds, and having both a highly polymerizable alkenyl group and a less polymerizable alkenyl group in one molecule Compounds, for example
CH ₂ = CHCOO (CH ₂ ) nCH = CH ₂
CH ₂ = C (CH ₃ ) COO (CH ₂ ) nCH = CH ₂
Method of reacting o-, m- or p-divinylbenzene
(b) when synthesizing an acrylic polymer by living radical polymerization, a compound having at least two low-polymerizable alkenyl groups as the second monomer after the end of the polymerization reaction or after completion of the reaction of the predetermined monomer, That is, the general formula
CH ₂ = CR ¹ -R ⁴ -CR ¹ = CH ₂
R ¹ : hydrogen atom or methyl group
R ⁴ : A compound represented by a C _{1 to} C ₂₀ organic group which may contain one or more ether bonds, for example, 1,5-hexadiene, 1,7-octadiene, 1,9-decadiene and the like are reacted. Method This method makes it easier to control the alkenyl groups introduced per molecule.
(c) halogens in acrylic polymers, such as a method in which various organometallic compounds having an alkenyl group are allowed to act on an acrylic polymer having at least one halogen to replace the halogen in the polymer with an alkenyl group. Of substituting an alkenyl group with

  The alkenyl group introduced into the acrylic polymer by these methods is 1 to 10, preferably 2 to 8, per molecule of the polymer.

  As the acrylic polymer having an alkenyl group, those having a liquid number average molecular weight Mn of 500 to 1,000,000, preferably 1,000 to 100,000 at room temperature are generally used. If the molecular weight is too low, the original properties of the acrylic polymer are hardly expressed, while if it is too high, handling becomes difficult.

  The molecular weight distribution of this acrylic polymer, that is, the ratio (Mw / Mn) of the weight average molecular weight and number average molecular weight measured by gel permeation chromatography (GPC) is generally 1.8 or less, preferably 1.5 or less, particularly preferably. 1.3 or less is used. Use of a material having this ratio of 1.8 or more is not preferable because it causes a decrease in physical properties. In addition, the molecular weight by GPC measurement was calculated | required in polystyrene conversion using the polystyrene gel column by using chloroform as a mobile phase.

  The alkenyl group-containing acrylic polymer can be obtained by various polymerization methods, and the method is not particularly limited, but the radical polymerization method is preferable from the viewpoint of versatility of the monomer and ease of control. Of the radical polymerization methods, the living polymerization method is more preferable, and the atom transfer radical polymerization method is particularly preferable.

  The radical polymerization reaction is considered to be difficult to control because the polymerization rate is high and the termination reaction due to coupling between radicals is likely to occur, but the living radical polymerization method uses a special polymerization system. As a result, a side reaction such as a termination reaction at the polymer growth end hardly occurs, and a polymer having a narrow molecular weight distribution (Mw / Mn: about 1.1 to 1.5) is obtained. Further, the molecular weight depends on the charging ratio of the monomer and the initiator. It can be controlled freely.

  Therefore, the living polymerization method has a narrow molecular weight distribution, and when the resulting polymer is liquid, not only can a polymer having a low viscosity be obtained, but also a monomer having a specific functional group can be placed in almost any position of the polymer. Therefore, it can be said to be preferable as a method for producing an acrylic polymer having an alkenyl group.

  The living polymerization method, in a narrow sense, refers to a polymerization in which molecular ends grow while the terminal always has activity, but in general, it is activated when the terminal is inactivated. Pseudo-living polymerization that grows in a balanced state is also included, and the living polymerization method in the present invention is the latter.

R⁸,R⁹：C₁〜C₆のアルキル基またはフェニル基
R¹⁰：C₁〜C₁₀のアルキル基またはアラルキル基
0≦d≦8
2≦e≦10
0≦f≦8
3≦d+e+f≦10
で表わされる化合物等が用いられる。 The hydrosilyl group-containing compound of component (B) is not particularly limited as long as it is a compound that can be cured by crosslinking with an acrylic polymer having at least one alkenyl group at the end of component (A).
R ⁵ ₃ SiO [SiR ⁵ ₂ O] a [SiHR ⁶ O] b [SiR ⁶ R ⁷ O] c SiR ⁶ ₃
R ⁵ ₂ HSiO [SiR ⁵ ₂ O] a [SiHR ⁶ O] b [SiR ⁶ R ⁷ O] c SiHR ⁵ ₂
R ^5, R ^6: an alkyl group or a phenyl group of C ₁ -C ₆
R ^7: alkyl or aralkyl group of C ₁ -C ₁₀
0 ≦ a ≦ 100
2 ≦ b ≦ 100
0 ≦ c ≦ 100

R ^8, R ^9: alkyl or phenyl C ₁ -C ₆
R ¹⁰ : C _{1 to} C ₁₀ alkyl group or aralkyl group
0 ≦ d ≦ 8
2 ≦ e ≦ 10
0 ≦ f ≦ 8
3 ≦ d + e + f ≦ 10
The compound etc. which are represented by these are used.

  Of these, compounds such as chain polysiloxanes having at least 1.1 hydrosilyl groups in the molecule on average and cyclic siloxanes are preferably used. From the viewpoint of compatibility with acrylic polymers, hydrosilyl groups are preferred. A siloxane compound having an alkyl group, a phenyl group, an alkylphenyl group or the like in addition to the group is more preferable. These hydrosilyl group-containing compounds may be used alone or in combination of two or more.

  The alkenyl group-containing acrylic polymer and the hydrosilyl group-containing compound can be mixed and used in an arbitrary ratio. From the viewpoint of curability, the alkenyl group-containing hydrosilyl group-containing compound in the acrylic polymer is hydrosilylated. The molar ratio of groups is 5 to 0.2, preferably 2.5 to 0.4. When this molar ratio is 5 or more, curing is insufficient, and only a cured product having a sticky and low strength can be obtained. On the other hand, when the molar ratio is 0.2 or less, a large amount of active hydrosilyl groups remain in the cured product even after curing. Therefore, cracks and voids are generated, and a uniform and strong cured product cannot be obtained.

Further, the hydrosilylation catalyst of component (C) is not particularly controlled, and any one can be used. Specifically, solid platinum supported on a carrier such as chloroplatinic acid, platinum alone, alumina, silica, carbon black, etc., and platinum-vinylsiloxane complex Ptn (CH ₂ = CHMe ₂ SiOSiMe ₂ CH = CH ₂ ) n
Pt [(MeCH = CHSiO) ₄ ] m
Platinum-phosphine complex Pt (PPh ₃ ) ₄
Pt (PBu ₃ ) ₄
Platinum-phosphite complex Pt [P (OPh) ₃ ] ₄
Pt [P (OBu) ₃ ] ₄
Me: Methyl group
Bu: Butyl group
Ph: Phenyl group
n, m: Catalysts other than positive integers and platinum compounds RhCl (PPh ₃ ) ₃ , RhCl ₃ , Rh / Al ₂ O ₃ , RuCl ₃ , IrCl ₃ , FeCl ₃ , AlCl ₃ , PdCl ₂ · 2H ₂ 0 NiCl ₂ , TiCl _{4 and the} like, and platinum-hydrocarbon complexes (US Pat. Nos. 3,159,601 and 3,159,662) and platinum-alcolate complexes (US Pat. No. 3,220,972) are also used. These are used alone or in combination of two or more. Of these hydrosilylation catalysts, chloroplatinic acid, platinum-olefin complexes, platinum-vinylsiloxane complexes and the like are preferably used from the viewpoint of catalytic activity.

The amount of the catalyst is not particularly limited, but it is used within the range of 10 ^-1 to 10 ^-8 mol, preferably 10 ^-2 to 10 ^-6 mol, relative to 1 mol of the alkenyl group in component (A) . The hydrosilylation catalyst is generally expensive and corrosive, and may generate a large amount of hydrogen to foam the cured product. Therefore, it is better not to use 10 ^-1 mol or more.

  These (A), (B), (C) three components, if any one of these essential components is missing, a vulcanized molded product (cured product) cannot be obtained, or even if obtained, rubber elasticity or Problems such as a decrease in elongation occur.

  The acrylic rubber containing these components (A), (B) and (C) as essential components is 5 parts by weight or more, preferably 10 to 30 parts by weight of conductive carbon black, preferably kettle per 100 parts by weight thereof. Chain black or graphite is used in an amount of 5 parts by weight or more, preferably 5 to 30 parts by weight.

  Ketjen black is a highly conductive carbon black, and if it is used at a ratio below this, the desired electromagnetic shielding properties cannot be obtained. Further, when graphite is used at a ratio less than this, a desired electromagnetic shielding property cannot be obtained.

  In the composition containing the above-mentioned components as essential components, as rubber compounding agents or thermoplastic elastomer compounding agents, reinforcing agents such as carbon black and white carbon other than ketjen black, diatomaceous earth, talc, clay Powdered solid fillers such as calcium silicate, barium sulfate, calcium carbonate, magnesium carbonate, aluminum hydroxide, metal oxide, mica, etc., various metal powders, glass powder, ceramic powder, granular or powdery polymer A small amount of thermoplastic resin or rubber that improves wear and moldability, short fibers that improve strength, rigidity, or electromagnetic shielding properties, processing aids such as stearic acid, palmitic acid, paraffin wax, zinc oxide, magnesium oxide Acid acceptors such as hydrotalcite, amines, phenols, imidazoles Or various additives commonly used in the rubber industry such as anti-aging agents, stabilizers, plasticizers, tackifiers, mold release agents, flame retardants, pigments and the like of these derivatives, if necessary. Used as appropriate. In these various compounding agents, it is preferable to use liquid ones from the viewpoint of operation.

  In the composition, a curing modifier such as 3,5-dimethyl-1-hexyn-3-ol, 3,5-dimethyl-1-hexyne-5-ol, (A), (B), (C) About 5 parts by weight or less, preferably about 0.01 to 1 part by weight can be added per 100 parts by weight of the total amount of each component. The curing modifier functions to adjust the curing rate and prevent scorching.

  Preparation of the composition used for each of the above applications is generally about 100 to 180 ° C. using an injection molding machine, compression molding machine, vulcanizing press, etc. after mixing and dispersing with a mixer and pouring it into a mold. And heating for about 1 to 24 hours at about 120 to 200 ° C., if necessary. Curing can also be achieved by leaving it to stand at room temperature for 24 hours or more without performing any heating.

  Next, the present invention will be described with reference to examples.

Example 1
Acrylic polymer 100 parts by weight Conductive carbon black 15 〃
(Lion Product Ketjen Black EC-600JD)
Hydrosilyl group-containing compound 6 〃
Hydrosilylation catalyst 0.05 〃
Curing modifier (3,5-dimethyl-1-hexyn-3-ol; 0.1 〃
Nissin Chemical Products Surfinol 61)
Anti-aging agent (Ciba Specialty Chemicals product 2)
(Irganox 1010)

Each of the above components are kneaded with a planetary mixer, left to stand at room temperature for 24 hours, defoamed, and then poured into a test sheet mold, which is subjected to press vulcanization at 180 ° C, 100 MPa for 10 minutes, and vulcanized. A sheet (150 × 150 × 2 mm) was obtained.

  As the acrylic polymer, a copolymer obtained by copolymerizing 1,7-octadiene into a copolymer of butyl acrylate, ethyl acrylate and 2-methoxyethyl acrylate and introducing an alkenyl group is used. The number average molecular weight Mn of the polymer is 18000, the molecular weight distribution (Mw / Mn) is 1.1, the average number of alkenyl groups introduced per molecule of the copolymer is 1.9, and the hydrosilyl group-containing compound is a molecule. A chain siloxane containing an average of 5 hydrosilyl groups and an average of 5 α-methylstyrene groups (amount of Si—H groups: 3.70 mmol / g) is used. Xylene solutions containing 3% by weight of 1,1,3,3-tetramethyl-1,3-divinyldisiloxane complex of platinum were used.

Example 2
In Example 1, the amount of conductive carbon black (Ketjen Black EC-600JD) was changed to 8 parts by weight.

Comparative Example 1
Acrylic rubber (Unimatec product PA-402) 100 parts by weight Conductive carbon black (Ketjen black EC-600JD) 15 部
Sedimented sulfur 0.3 〃
Sodium stearate 3 〃
Anti-aging agent (Irganox 1010) 2 〃

The above components were kneaded with a kneader and a roll, and vulcanized at 170 ° C. for 20 minutes to obtain a vulcanized sheet (150 × 150 × 2 mm).

Comparative Example 2
In Comparative Example 1, 40 parts by weight of dibutyl carbitol adipate (Asahi Denshi product RS-107) was further used as a softening agent.

The vulcanized sheets obtained in the above Examples and Comparative Examples were measured for hardness, tensile strength, elongation at break, volume resistivity, and electromagnetic shielding properties.
Hardness: 3 sheets of vulcanized sheets are overlapped and measured according to JIS K6253, and the value is evaluated as ○ when 65 or less, and x when 65 or more. Tensile strength, elongation at break: measured according to JIS K6251 Volume resistivity: Measured in accordance with JIS K6271 Electromagnetic shielding: Measure the shielding characteristics at 1 GHz with the advanced method, and evaluate the value as 15 dB or more as ○ and 15 dB or less as x

The results obtained are shown in the following table.
table
Measurement Item Example 1 Example 2 Comparative Example 1 Comparative Example 2
Normal physical properties Hardness (Duro A) 62 44 84 64
○ ○ × ○
Tensile strength (MPa) 6.13 5.86 10.3 9.81
Elongation at break (%) 170 200 120 240
Volume resistivity
500V (Ω ・ cm) 7 14 17 51
Electromagnetic shielding
1GHz (dB) 21 17 17 9
○ ○ ○ ×

Claims (5)

  (A) An acrylic polymer having at least one alkenyl group capable of hydrosilylation reaction, (B) a hydrosilyl group-containing compound, and (C) 100 parts by weight of a composition containing a hydrosilylation catalyst as essential components, Acrylic rubber material for electromagnetic wave shielding, containing more than parts by weight of conductive carbon black or graphite.   The acrylic resin for electromagnetic wave shielding according to claim 1, wherein a liquid acrylic polymer having a number average molecular weight Mn of 500 to 1,000,000 and a molecular weight distribution (Mw / Mn) of 1.8 or less is used as the component (A). Rubber material.   The acrylic rubber material for electromagnetic wave shielding according to claim 1 or 2, wherein the conductive carbon black is ketjen black.   An acrylic rubber material for electromagnetic wave shielding, vulcanized and molded from the acrylic rubber material for electromagnetic wave shielding according to claim 1, having a volume resistivity of 20 Ω · cm or less and an electromagnetic wave shielding property at 1 GHz of 15 dB or more. The acrylic rubber material for electromagnetic wave shielding according to claim 4, which has a hardness (JIS K6253 compliant; Duro A type) of 65 or less.