JP5440444B2 - Fluoro rubber magnetic material - Google Patents

Description

  The present invention relates to a fluororubber magnetic material. More specifically, the present invention relates to a fluororubber magnetic material having improved dough roll kneadability and product mold releasability.

  Polar rubbers such as nitrile rubber and chloroprene rubber are used as rubber magnetic materials for the position detection magnetic rubber ring for auto switches. When using polar liquids such as water-soluble cutting oil for hydraulic oil, Fluorine rubber with less swelling is preferably used.

The present applicant has previously proposed a fluororubber composition in which 200 to 500 parts by weight of magnetic powder is added to 100 parts by weight of a polyol vulcanized fluororubber having a Mooney viscosity ML _{1 + 10} (121 ° C.) of 8 to 15. However, for example, when magnetic powder is blended in a proportion of 400 parts by weight or more, good heat resistance and magnetic properties are exhibited, but dough roll kneadability and product mold releasability are exhibited. In some cases, problems were observed.

JP 2007-284604 A JP 2000-228308 A JP-A-8-120178

  An object of the present invention is to provide a fluororubber magnetic material excellent in roll kneading property of a dough and mold release property of a product even when a low viscosity millable type fluororubber is highly filled with magnetic powder. is there.

The object of the present invention is to provide 1 to 7 parts by weight of a perfluoroalkyl group-containing acrylic ester polymer per 100 parts by weight of a polyol vulcanized fluororubber having a Mooney viscosity ML _{1 + 10} (121 ° C.) of 15 to 40 And a fluororubber magnetic material to which 200 to 500 parts by weight of magnetic powder is added.

  The fluororubber magnetic material according to the present invention uses a low-viscosity millable type fluororubber with a polymer of a perfluoroalkyl group-containing acrylic acid ester added as a processing aid, so that the magnetic powder is 200 to 500 parts by weight. Even when filled, fabric sticking may occur during roll wrapping processing, resulting in deterioration of workability, and mold releasability such as cracking of vulcanized products after vulcanization molding. It can be effectively prevented.

  Thus, the fluororubber magnetic material of the present invention that enables high-concentration filling of magnetic powder while maintaining good dough roll kneadability and product mold releasability is a bonded magnet for sensors, particularly pneumatic pressure. It can be effectively used as a vulcanization molding material for position detection magnetic rubber rings (sensitive to magnetic sensors) for cylinder auto switches and encoders for detecting the number of revolutions in a high temperature environment.

  For the magnetic rubber ring, in order to attach it to the concave part of the cylinder, a part of the ring connected in a circumferential shape is cut in a direction perpendicular to the circumference, and the part is expanded and then assembled to the cylinder. The cutting part is fixed with an adhesive during assembly. Therefore, the rubber needs to be flexible, and the material is required to have an elongation of 50% or more. In addition, since the detected magnetic force varies depending on the shape of the product and the distance to the magnetic sensor, the larger the magnetic force as the material (saturated magnetization as an evaluation index of the magnetic property of the material), the higher the degree of freedom in shape design, which is preferable. become.

  Various types of fluororubbers are on the market and can be broadly classified into three types: amine vulcanization systems, peroxide crosslinking systems, and polyol vulcanization systems. Patent Document 2 describes a flexible magnetic sheet made of magnetic powder and vinylidene fluoride copolymer rubber. In all of the examples, an amine vulcanization system is used. The amine vulcanization system has a problem that the vulcanization is very slow, so that the productivity is poor, and in order to obtain a vulcanizate having good physical properties, a lead compound which is an environmental load substance must be used. In the peroxide crosslinking system, unreacted peroxide decomposition gas generated at the time of crosslinking may remain in the crosslinked rubber, resulting in foaming.

  In the present invention, a polyol vulcanized fluororubber which does not have such problems is used.

  The fluororubber vulcanized by the polyol vulcanization system is a highly fluorinated elastic copolymer, and for example, a copolymer of vinylidene fluoride and other fluorinated olefins can be used. Specifically, vinylidene fluoride and hexafluoropropylene, pentafluoropropylene, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, vinyl fluoride, perfluoroacrylic acid ester, perfluoroalkyl acrylate, perfluoromethyl vinyl ether , Perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, or a copolymer with one or more thereof, preferably vinylidene fluoride-hexafluoropropylene binary copolymer and vinylidene fluoride-tetrafluoroethylene- A hexafluoropropylene terpolymer is used.

These polyol vulcanized fluoro rubbers must have a Mooney viscosity ML _{1 + 10} (121 ° C.) of 15 to 40, preferably 20 to 40. However, even when the magnetic powder is highly filled, the adhesiveness at the time of roll kneading is large, and the roll processability as a dough is reduced. On the other hand, when a higher Mooney viscosity is used, the dough viscosity is low. It becomes very high and the dough becomes hard at the time of kneading, so that the winding property is deteriorated and the roll processability is also deteriorated.

  Actually, commercially available products such as Duton Viton A-200 (Mooney viscosity 20; vinylidene fluoride-hexafluoropropylene binary copolymer, F content 66%), Solvay Solexis technoflon N60HS (28 ; Vinylidene fluoride-hexafluoropropylene binary copolymer, F content 66%) and Dionion products FC-2120 (23), FC-2122 (25), FC-2123 (25), FC- 2170 (31), FC-2174 (40), FC-2176 (30), FC-2177 (33), FC-3009 (30), FE-5620Q (23), FE-5621 ( 23), FE-5641Q (same 40) <above, vinylidene fluoride-hexafluoropropylene binary copolymer, F content 65.9%>, FLS-2530 (same 38) <vinylidene fluoride-hexafluoropropylene 2 Original copolymer, F content 69.0%>, FE-5840Q (37) <vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, F content 70.1%> Use It has been.

  The polyhydroxy aromatic compound used as a vulcanizing agent for this fluororubber includes 2,2-bis (4-hydroxyphenyl) propane [bisphenol A], 2,2-bis (4-hydroxyphenyl) perfluoro Propane [bisphenol AF], hydroquinone, catechol, resorcin, 4,4'-dihydroxydiphenyl, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylsulfone, 2,2-bis (4-hydroxyphenyl) butane, etc. Preferably, bisphenol A, bisphenol AF, hydroquinone, etc. are used. These may also be in the form of alkali metal salts or alkaline earth metal salts. These vulcanizing agents are used in a proportion of about 0.5 to 10 parts by weight, preferably about 0.5 to 6 parts by weight, per 100 parts by weight of the fluororubber. If the ratio is less than this, the crosslinking density is insufficient, while if it is more than this, the crosslinking density becomes too high and the rubbery elasticity tends to be lost.

  For vulcanization of polyol vulcanized fluoro rubber, it is preferable to use an acid acceptor, and as the acid acceptor, an oxide or hydroxide of a divalent metal such as magnesium, calcium, barium, lead, zinc, etc. The product, hydroxide or hydrotalcite-related compound is used at a ratio of about 1 to 20 parts by weight, preferably about 3 to 6 parts by weight per 100 parts by weight of the fluororubber.

  Further, as vulcanization accelerators, quaternary onium salts (quaternary ammonium salts, quaternary phosphonium salts), N-alkyl-substituted amide compounds, active hydrogen-containing aromatic compounds-quaternary phosphonium salts, etc. The compound, the divalent metal amine complex compound, etc. can be used at a ratio of about 10 parts by weight or less, preferably about 0.1 to 5 parts by weight per 100 parts by weight of the fluororubber.

In the fluororubber magnetic material of the present invention, polyol vulcanized fluororubber having Mooney viscosity ML _{1 + 10} (121 ° C.) is used, while its dough roll kneading property and product mold releasability are ensured. In addition, a perfluoroalkyl group-containing acrylic ester polymer as a processing aid is 1 to 7 parts by weight, preferably 2 to 6 parts by weight, more preferably 3 to 6 parts by weight per 100 parts by weight of the polyol vulcanized rubber. It is used by adding at a ratio of parts.

  When the ratio of the specific processing aid is less than this, particularly when the amount of magnetic powder added is 300 parts by weight or more, the mold releasability of the product after vulcanization is deteriorated. On the other hand, when a specific processing aid is used at an addition ratio higher than this, it is not only preferable in terms of cost, but also the strength of the dough is lowered and roll processability is lowered.

Such a polymer of perfluoroalkyl group-containing acrylic acid ester is described in, for example, Patent Document 3,
CH ₂ = CB ¹ COOB ² Rf (C-1)
B ¹ : H, F, methyl group
B ² : an alkylene group having 1 to 6 carbon atoms
Rf: A homopolymer or copolymer of a perfluoroalkyl group-containing acrylic ester represented by a C6-21 perfluoroalkyl group. These polymers are said to have a number average molecular weight Mn of 1,000 to 100,000.

The comonomer forming the copolymer is preferably of the general formula
CH ₂ = CB ³ COOB ⁴ (C-2)
B ³ : H, F, methyl group
B ⁴ : (meth) acrylic acid ester represented by a hydrocarbon group having 1 to 24 carbon atoms and a glycidyl group, for example, methyl, butyl, 2-ethylhexyl, lauryl, stearyl, glycidyl ester of (meth) acrylic acid From the viewpoint of releasability, (meth) acrylates of higher alcohols such as 2-ethylhexyl, lauryl and stearyl, particularly acrylate are considered desirable.

  Other comonomer includes ethylene, propylene, vinyl chloride, vinyl acetate, butyl vinyl ether and the like.

  The monomer (C-1) is copolymerized in a proportion of 20% by weight or more in the copolymer, but is preferably 40% by weight or more, more preferably 80% by weight or more from the viewpoint of releasability. Yes, it may be a 100% by weight homopolymer. In practice, commercially available products such as Daikin Industries' product Die Free FB-962 are used as they are.

As magnetic powder, ferrite magnet powder or rare earth magnet powder whose particle size is about 0.5 to 10 μm is generally used. Ferrite magnets with lower magnetic force than rare earth magnet powder in terms of cost and adhesion to rubber. Powder is used. Among the ferrite magnet powders, strontium ferrite powder or barium ferrite powder is preferably used from the viewpoint of magnetic force. These magnet powders are prepared by adding 1.5 ml of 5 wt% polyvinyl alcohol aqueous solution to 20 g of magnetic powder, placing them in a cylindrical mold with a diameter of 25.4 mm, and press-molding them at a pressure of 1 ton / cm ² to produce samples. It is preferable to use a dust magnetism when Br is 1600 G or more and iHc is 2000 Oe or more when the residual magnetic flux density Br and coercive force iHc are measured by a magnetometer.

  Such magnetic powder is used in a proportion of about 200 to 500 parts by weight, preferably about 250 to 450 parts by weight, per 100 parts by weight of the polyol vulcanized fluororubber. If the blending ratio is less than this, not only the performance as a rubber magnet for the sensor cannot be exhibited, but also the dough viscosity is too low and the dough adheres to the roll, so that the kneading workability is deteriorated. On the other hand, when it is used at a blending ratio higher than this, the flexibility of the vulcanized molded product is significantly impaired.

  In the fluororubber composition containing each of the above components as essential components, reinforcing agents represented by carbon black, anti-aging agents, plasticizers, processing aids, vulcanization aids, and the like are added as necessary. These components are kneaded using a closed kneader and an open roll, etc., and the kneaded product is injection molded, compression molded, under conditions of about 150 to 200 ° C. and about 1/2 to 60 minutes. Molded by a pressure molding method such as transfer molding.

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

Example 1
Binary fluororubber (100 parts by weight of Solvay Solexis product)
Technoflon N60HS; ML _{1 + 10} (121 ℃) 28)
Strontium ferrite magnetic powder 300 〃
(DOMA F-Tech product SF-D630)
Processing aid (Daikin product Daifie FB-962) 2 〃
Magnesium oxide 3 〃
Calcium hydroxide 6 〃
Bisphenol AF (DuPont Elastomer Products 4 〃
Curative # 20)
4th onium salt (Corporate product # 30) 1.5 〃
The above components were kneaded using a closed kneader (pressure kneader) and an open roll, and the kneaded product was compression molded at 180 ° C. for 6 minutes to vulcanize a rubber sheet having a thickness of 2 mm.

The kneaded product and the vulcanized sheet were measured and evaluated for the following items.
Evaluation of roll kneadability (dough processability)
○: Good roll winding property during kneading
Δ: Slight adhesion is observed but kneading is not hindered
×: Roll adhesion is large and kneading work is difficult Evaluation of mold releasability after vulcanization
○: When the rubber sheet is released, there is no adhesion to the mold or damage to the rubber itself, and it is released smoothly
it can
Δ: Some adhesion to the mold is seen, but release is possible
×: Rubber sheet is severely damaged at the time of mold release, making it difficult to mold as a sheet Fabric fluidity: JIS K6300 compliant
Using Toyo Seiki Mooney Viscometer AM-3,
Measure Knee Viscosity Vm Normal properties: JIS K6253: 1997 compliant; Durometer A (instant)
JIS K6251 compliant; tensile strength, elongation magnetic force (saturation magnetization Ms) measurement:
A rubber sheet sample (3 x 5 x 2 mm) was used with a VSM-5 vibrating sample magnetometer manufactured by Toei Industries.
Measure saturation curve under applied magnetic field of 1.5 × 10 ⁴ Oe and vibration frequency of 80 Hz.
Obtained magnetization Ms

Example 2
In Example 1, the amount of processing aid was changed to 4 parts by weight.

Example 3
In Example 1, the amount of processing aid was changed to 6 parts by weight.

Comparative Example 1
In Example 3, the amount of processing aid was changed to 8 parts by weight.

Comparative Example 2
In Example 1, no processing aid was used.

Comparative Example 3
In Example 1, the same amount of carnauba wax (DuPont Elastomer VPA # 2) was used as a processing aid.

Comparative Example 4
In Example 1, the same amount of aliphatic monocarboxylic acid light metal salt (Technical Processing Company TE-58A) was used as a processing aid.

Comparative Example 5
In Example 2, no processing aid was used.
Comparative Example 6
In Example 2, the same amount of aliphatic monocarboxylic acid light metal salt (TE-58A) was used as a processing aid.

Example 4
In Example 2, the same amount of DuPont Viton A-200 (Mooney viscosity ML _{1 + 10} (121 ° C.) 20) was used as the fluororubber.

Example 5
In Example 2, the same amount of Dinion product FC-2123 (Mooney viscosity ML _{1 + 10} (121 ° C.) 25) was used as the fluororubber.
Comparative Example 7
In Example 1, the same amount of DuPont Viton A-100 (Mooney viscosity ML _{1 + 10} (121 ° C.) 12) was used as the fluororubber.

The measurement / evaluation results obtained in the above Examples and Comparative Examples are shown in the following table together with the types and blending amounts (unit: parts by weight) of the fluororubber, magnetic powder and processing aid used.
table
1 actual 2 actual 3 ratio 1 ratio 2 ratio 3 ratio 4 ratio 5 ratio 6 actual 4 actual 5 ratio 7
[Composition ingredients]
Fluoro rubber
N60HS 100 100 100 100 100 100 100 100 100 − − −
A-200 − − − − − − − − − 100 − −
FC-2123 − − − − − − − − − − 100 −
A-100-----------100
Magnetic powder 300 400 500 500 300 300 300 400 400 400 400 300
Processing aid
FB-962 2 4 6 8 − − − − − − 4 4 2
VPA # 2 − − − − − 2 − − 4 − − −
TE-58A − − − − − − 2 − − − − −
[Measurement and evaluation results]
Roll kneadability ○ ○ ○ △ △ ○ △ × ○ ○ ○ △
Mold releasability ○ ○ ○ △ △ △ × × × ○ ○ △
Vm 80 99 157 151 97 78 81 NG 98 72 76 60
Hardness (points) 93 96 97 96 92 93 NG NG NG 92 92 95
Tensile strength (MPa) 5.0 4.6 4.8 4.5 5.1 5.1 NG NG NG 4.7 4.9 4.7
Elongation (%) 270 190 100 110 280 270 NG NG NG 300 280 270
Ms (mT) 205 232 251 249 203 202 NG NG NG 230 228 200
Note 1) Comparative Examples 3 and 7 are both sheets after rubber sheet vulcanization molding
The shape could not be maintained and molding was impossible
Note 2) NG: Measurement not possible

From the above results, the following can be said.
(1) In Examples 1 to 5, both roll kneadability and mold releasability are good, and a large amount of magnetic powder can be filled, so that a molded product exhibiting high magnetic force can be formed.
(2) In Comparative Example 1, the strength of the dough is weakened and roll processability is reduced.
(3) In Comparative Examples 2 and 5, since a processing aid is not used even when a polymer having an appropriate viscosity is used, both roll kneadability and mold releasability are inferior.
(4) In Comparative Examples 3, 4, and 6, even when a polymer having an appropriate viscosity is used, the processing aid to be added is not appropriate, so that the moldability is poor.
(5) In Comparative Example 7, since the polymer viscosity is too low, the roll processability and mold releasability are inferior.

Claims (6)

_{1 to} 7 parts by weight of a polymer of perfluoroalkyl group-containing acrylic ester and 200 to 500 parts by weight per 100 parts by weight of polyol vulcanized fluororubber having Mooney viscosity ML _{1 + 10} (121 ° C.) of 15 to 40 Fluoro rubber magnetic material with magnetic powder added.   The fluororubber magnetic material according to claim 1, wherein the magnetic powder is a ferrite magnet powder or a rare earth magnet powder.   The fluororubber magnetic material according to claim 2, wherein the ferrite magnet powder is strontium ferrite powder or barium ferrite magnet powder.   4. The fluororubber magnetic material according to claim 1, which is used as a molding material for a bonded magnet for a sensor.   A bonded magnet for a sensor vulcanized and molded from the fluororubber magnetic material according to claim 4.   6. The bond magnet for a sensor according to claim 5, which is used as a position detecting magnetic rubber ring for an auto switch of a pneumatic cylinder.