JP2007231441A - Carbon fiber strand for reinforcing thermoplastic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a carbon fiber for reinforcing a thermoplastic resin, which is applied a sizing agent having excellent adhesion to a polyamide resin. <P>SOLUTION: The carbon fiber strand applied with a sizing agent including a polyurethane resin. The breaking elongation of a dried film of the sizing agent is ≤400%, and the amount thereof attached to the carbon fiber is 0.1-5.0 mass%. The carbon fiber-reinforced thermoplastic resin obtained by blending the carbon fiber strand has excellent mechanical strength such as flexural strength because the resin having high compatibility with the carbon fiber and a matrix resin is attached to the filaments. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carbon fiber strand for reinforcing a thermoplastic resin provided with a sizing agent having excellent adhesion to a thermoplastic resin matrix, and a thermoplastic resin reinforced by the carbon fiber strand.

  Carbon fiber and carbon fiber composite material have high tensile strength / tensile modulus, excellent heat resistance, chemical resistance, fatigue characteristics, wear resistance, low linear expansion coefficient, excellent dimensional stability, electromagnetic shielding, X It has excellent features such as high line transparency. Therefore, it is widely applied to sports / leisure, aviation / space, and general industrial applications. Conventionally, a thermosetting resin such as an epoxy resin is often used as a matrix resin of a composite material, but recently, a thermoplastic resin has attracted attention from the viewpoint of recyclability and high-speed moldability.

  As a matrix resin of the carbon fiber reinforced thermoplastic resin composite material, acrylonitrile-butadiene-styrene copolymer (ABS), polyamide (nylon 6, nylon 66, etc.), polyacetal, polycarbonate, polypropylene, high density polyethylene, polyethylene terephthalate, poly Examples include butylene terephthalate, polyetherimide, polystyrene, polyether sulfone, polyphenylene sulfide, polyether ketone, and polyether ether ketone.

  Of these thermoplastic resins, polyamide resins are inexpensive and have properties excellent in heat resistance, mechanical properties (strength, elastic modulus), and chemical resistance. Therefore, dramatic growth is expected in the future as a matrix for carbon fiber reinforced thermoplastic resin composite materials.

  The carbon fiber is manufactured as a fiber bundle (strand) shape in which a large number of ultrafine filaments are bundled, and fluff is likely to occur due to mechanical friction during handling. Therefore, a sizing agent is generally added to the carbon fiber in order to improve the bundling property of the carbon fiber to improve the handleability and to improve the affinity and adhesiveness with the matrix.

  Carbon fiber composite material with thermoplastic resin as matrix is compound pellet injection molding, resin-containing long fiber strand cut, injection molding of fiber reinforced resin composite material (so-called long fiber pellet), injection compression molding These are used as molding materials such as extrusion molding and stamping molding using a random mat, and carbon fibers contained in these are often used in a relatively short fiber form.

  For this reason, the mechanical properties such as strength and elastic modulus of the carbon fiber composite material are greatly influenced by the affinity and adhesiveness between the carbon fiber and the thermoplastic resin as the matrix. In particular, in recent years, further improvement in performance has been demanded for carbon fiber reinforced thermoplastic resin composite materials, and the required strength may not be obtained in the case of the above molding method.

  Many proposals have been made regarding carbon fiber sizing agents in consideration of the affinity between the sizing agent and the thermoplastic resin matrix (see, for example, Patent Documents 1 and 2). Patent Document 1 proposes a carbon fiber strand coated with polyurethane. According to this proposal, it is disclosed that the handleability of carbon fiber strands can be improved and the mechanical properties of the carbon fiber reinforced thermoplastic resin can be improved.

  Patent Document 2 proposes a sizing agent containing bisphenol A type epoxy resin that is liquid at room temperature, bisphenol A type epoxy resin that is solid at room temperature, unsaturated polyester resin, and stearic acid as essential components. Furthermore, Patent Document 2 describes that the sizing agent gives good scratch resistance to carbon fiber strands.

However, the sizing agents disclosed in Patent Documents 1 and 2 have not been able to ensure a satisfactory reinforcing effect in response to the recent demand for further performance improvement of carbon fiber reinforced thermoplastic resin composite materials.
JP 58-126375 A (Claims) JP-A-7-197381 (Claims)

  An object of the present invention is to provide a carbon fiber strand for reinforcing a thermoplastic resin excellent in affinity and adhesiveness with a thermoplastic resin matrix, and a carbon fiber reinforced thermoplastic resin containing the carbon fiber strand.

  The present invention for achieving the above object is as follows.

  [1] A carbon fiber strand provided with a sizing agent containing a polyurethane resin, wherein the rupture elongation of the dry film of the sizing agent is 400% or less, and the amount of adhesion is 0.1 to carbon fiber. Carbon fiber strands for reinforcing thermoplastic resin that are 5.0% by mass.

  [2] The carbon fiber strand for reinforcing a thermoplastic resin according to [1], wherein the softening temperature of the dried film of the sizing agent is 50 to 150 ° C.

  [3] The carbon fiber strand for reinforcing a thermoplastic resin according to [1] or [2], wherein the polyol component of the polyurethane resin is ester-based.

  [4] A carbon fiber reinforced thermoplastic resin obtained by blending 5 to 70% by mass of the thermoplastic resin reinforcing carbon fiber strand according to any one of [1] to [3].

  [5] The carbon fiber reinforced thermoplastic resin according to [4], wherein the thermoplastic resin is a polyamide resin.

  In the carbon fiber strand of the present invention, a predetermined polyurethane adheres to the carbon fiber to form a film having excellent adhesion to the polyamide resin.

  The carbon fiber strand of the present invention is an injection molding of compound pellets, a resin-containing long fiber strand cut, an injection molding of an intermediate material for fiber reinforced resin composite material (so-called long fiber pellets), injection compression molding, extrusion molding, etc. It is suitably used for molding. The carbon fiber reinforced thermoplastic resin obtained by these moldings is excellent in mechanical strength such as bending strength since the affinity between the coating covering the filament and the polyamide resin is high.

  The present invention will be described in detail below.

  The sizing agent applied to the carbon fiber strand of the present invention has a dry elongation at break of 400% or less, preferably 350% or less. When the elongation at break exceeds 400%, the adhesion with the polyamide resin is lowered, so that a carbon fiber reinforced thermoplastic resin having good mechanical strength cannot be obtained. The reason why a sizing agent having a breaking elongation of 400% or less is good is not clear, but the elongation of the unstretched film of polyamide resin is 400% while the elongation of the carbon fiber strand is 1.5 to 2.5%. Therefore, it is considered that the sizing agent present between the carbon fiber and the polyamide resin preferably has a breaking elongation of 400% or less.

  The sizing agent applied to the carbon fiber strand of the present invention preferably has a dry film softening temperature of 50 to 150 ° C, more preferably 70 to 130 ° C. When the softening temperature exceeds 150 ° C., the adhesiveness with the polyamide resin is lowered, so that a carbon fiber reinforced thermoplastic resin having good mechanical strength may not be obtained. The case where the softening temperature is less than 50 ° C. is the same as the case where the softening temperature exceeds 150 ° C.

  The polyol component of the polyurethane resin in the sizing agent attached to the carbon fiber strand of the present invention is preferably an ester system. That is, examples of the polyol component of the raw material for producing the polyurethane resin include polyester polyol, polyether polyol, polycarbonate polyol, and the like, but the polyol component having good adhesion to the polyamide resin is polyester polyol.

  As the polyester polyol, a polyester polyol obtained by subjecting the following glycol component and the following acid component to a dehydration condensation reaction can be used.

  Examples of the glycol component that can be used in obtaining the polyester polyol include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1, 5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol (molecular weight 300 to 6000), dipropylene glycol, tripropylene glycol, bishydroxyethoxybenzene, 1, Examples include 4-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, hydrogenated bisphenol A, hydroquinone, and their alkylene oxide adducts.

  Examples of acid components that can be used in obtaining the polyester polyol include succinic acid, adipic acid, azelaic acid, sabatic acid, dodecanedicarboxylic acid, maleic anhydride, fumaric acid, 1,3-cyclopentanedicarboxylic acid, 1, 4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, 1,2- Bis (phenoxy) ethane-p, p'-dicarboxylic acid and anhydride or ester-forming derivatives of these dicarboxylic acids, as well as p-hydroxybenzoic acid, p- (2-hydroxyethoxy) benzoic acid and the hydroxycarboxylic acids Examples thereof include ester-forming derivatives.

  In addition, polyesters obtained by ring-opening polymerization reaction of cyclic ester compounds such as ε-caprolactone and copolymerized polyesters thereof can also be used.

  In addition to the above polyurethane resins, sizing agents include synthetic lubricants such as methyl oleate and dioctyl sebacate, higher alcohols such as vegetable oil and macco alcohol, emulsifiers such as polyethylene glycol type nonionic surfactants and low-sulfated oils, etc. May be included.

  As the carbon fiber strand to which the sizing agent is applied, any carbon fiber such as polyacrylonitrile (PAN), petroleum / coal pitch, rayon, and lignin can be used. In particular, PAN-based carbon fibers using PAN as a raw material are preferable because they are excellent in productivity and mechanical properties on an industrial scale. These are available as commercial products.

  The number of filaments constituting the carbon fiber strand is not particularly limited, but the number of filaments of the carbon fiber strand obtained in a normal production process is about 1000 to 50000.

  The diameter of the filament constituting the carbon fiber strand is preferably 4 to 10 μm, and more preferably 6 to 8 μm.

  The PAN-based carbon fiber is manufactured through the following steps.

  In the first flameproofing step, the acrylic fiber is heated in an air atmosphere at 200 to 300 ° C., the nitrile group is closed, oxygen is introduced into the acrylic polymer, and a stable structure is obtained even at high temperatures.

  In the carbonization step, the carbon fiber is baked at a high temperature of 1000 ° C. or higher in an inert gas atmosphere to increase the carbon content to 90% by mass or higher.

  In the surface treatment step, an oxygen-containing functional group is introduced on the surface of the carbon fiber to enhance the adhesion with the matrix resin.

  Examples of the carbon fiber surface treatment include chemical liquid oxidation / electrolytic oxidation in a liquid phase, gas phase oxidation, and the like. Among these surface treatments, an electrolytic oxidation treatment in a liquid phase is preferable from the viewpoint of productivity and treatment uniformity. Examples of the electrolytic solution used for the electrolytic oxidation treatment include inorganic acids such as sulfuric acid, nitric acid, and hydrochloric acid, inorganic hydroxides such as sodium hydroxide and potassium hydroxide, and inorganic salts such as ammonium sulfate, sodium carbonate, and sodium bicarbonate. Can be mentioned.

  The adhesion amount of the sizing agent to the carbon fiber strand is 0.1 to 5.0% by mass, preferably 0.5 to 2.0% by mass with respect to the carbon fiber. When the adhesion amount is less than 0.1% by mass, the handleability of the carbon fiber strand during molding is inferior. On the other hand, if it exceeds 5.0% by mass, the texture of the carbon fiber strand is lowered, and the winding density when wound on the bobbin is lowered, so that problems such as collapse during transportation are likely to occur.

  Hereinafter, an example of the manufacturing method of the carbon fiber strand of this invention is demonstrated.

[Sizing liquid]
In general, the polyurethane resin is used in a form dispersed in water. The polyurethane resin may be self-emulsified by introducing a hydrophilic group into the molecule, or may be forcedly emulsified using a known surfactant.

[Sizing agent]
In the present invention, the sizing agent refers to a composition in the sizing liquid attached to the carbon fiber surface.

[Sizing process]
Examples of sizing methods for carbon fiber strands include spraying, roller dipping, and roller transfer. Among these sizing methods, a roller dipping method excellent in productivity and uniformity is preferable. When dipping the carbon fiber strand in the sizing liquid, it is important to repeat the opening and drawing through an immersion roller provided in the sizing bath and impregnate the sizing liquid into the strand.

  After impregnating the carbon fiber strand with the sizing liquid, the moisture or solvent is removed by the subsequent drying treatment to obtain the carbon fiber strand to which the target sizing agent is applied. The amount of the sizing agent attached to the carbon fiber is adjusted by adjusting the concentration of the sizing liquid or adjusting the squeezing roller.

  For drying the carbon fiber strand, for example, hot air, a hot plate, a roller, an infrared heater or the like can be used, and the carbon fiber strand is preferably held at a temperature of 120 to 150 ° C. for 1 to 10 minutes.

  The carbon fiber strands of the present invention produced by the above method are processed into compound pellets, intermediate materials (so-called long fiber pellets) obtained by cutting resin-containing long fiber strands, random mats, unidirectional reinforcing prepregs, etc., and molded. It can be set as a molded product (carbon fiber reinforced thermoplastic resin). The carbon fiber strand of the present invention is particularly suitable for producing molded products such as injection molding, injection compression molding, extrusion molding, etc., which are processed into compound pellets and long fiber pellets.

  The blending amount of the carbon fiber strand of the present invention to be blended with the carbon fiber reinforced thermoplastic resin varies depending on the form, molding method, use, etc. of the carbon fiber, but is preferably in the range of 5 to 70% by mass from the viewpoint of cost performance. -40 mass% is more preferable.

  Carbon fiber strands to which a sizing agent was adhered were produced under the conditions described in Examples 1 to 3 and Comparative Examples 1 to 4 below. Various physical properties of the obtained carbon fiber strand were measured by the following methods.

[Measurement of interfacial bond strength]
The interfacial adhesive strength was evaluated by a microdroplet test using a composite material interface property evaluation apparatus (manufactured by Toei Sangyo Co., Ltd.).

  First, the carbon fiber monofilament was taken out from the carbon fiber strand. As shown in FIG. 1, both ends of the carbon fiber monofilament 11 are fixed to the protrusions 13 a and 13 b provided on both ends of the U-shaped mount 13 with an adhesive 12, and the carbon fiber monofilament 11 is stretched on the mount 13. did. This mount was set in the mount holder of the apparatus. The mount holder is connected to a sample moving device including a load cell, and the mount 13 can be moved at a constant speed in the fiber axis direction of the carbon fiber monofilament 11. A polyamide resin heated to 250 ° C. and melted (Ube Industries, Ube Nylon 1011FB) is suspended in the form of droplets from the mesh of a sample container provided in the apparatus and brought into contact with the carbon fiber monofilament 11 stretched on the mount 13. I let you. By this operation, the microdroplet 14 was adhered to the carbon fiber monofilament 11 to obtain a measurement sample. After the microdroplet was sufficiently cooled at room temperature, the carbon fiber monofilament 11 was sandwiched between SUS blades 15a and 15b. Thereafter, the mount 13 was moved in the fiber axis direction of the carbon fiber monofilament 11 at a speed of 0.06 mm / min, the carbon fiber monofilament 11 was pulled out from the microdroplet 14, and the maximum load F at the time of pulling out was measured with a load cell. Ten or more measurement samples were prepared and measured, and the average value of the maximum load F was obtained for microdroplets having a diameter of 30 to 100 μm. The measurement was performed under a nitrogen atmosphere at an ambient temperature of 23 ° C., and the number of samples measured with one measurement sample was five.

The interfacial shear strength τ was calculated by the following formula (iii), and the adhesive strength between the carbon fiber filament and the polypropylene resin was evaluated.
τ = F / πdl (iii)
In the formula (iii), F represents the maximum load during drawing, d represents the carbon fiber filament diameter, and l represents the particle diameter in the drawing direction of the microdroplet.

[Bending test of unidirectional laminate]
A carbon fiber reinforced strand prepreg was produced by impregnating a carbon fiber provided with a sizing agent with a polyamide resin (manufactured by Ube Industries, Ube Nylon 1022B) using the apparatus shown in FIG.

  The carbon fiber 31 provided with a sizing agent is continuously immersed at 30 cm / min in a polyamide resin bath 39 (width 10 cm × length 30 cm) set in a thermostatic chamber 38 maintained at 270 ° C. After surplus resin was squeezed out by the squeezing roller 34 on the side, it was wound up by a winder 37. The carbon fiber volume content in the obtained carbon fiber reinforced strand prepreg was 30%. In FIG. 2, 32 is a guide roller, 33 is an immersion roller, and 35 is a carbon fiber strand package.

The obtained carbon fiber reinforced strand prepreg was formed into a sheet shape with the orientation direction of the carbon fibers aligned in one direction, and seven sheets were laminated in the mold with the same orientation direction of the carbon fibers between the sheets. The carbon fiber reinforced strand prepreg laminated in the mold was heated under pressure at 6 kgf / cm ² (0.59 MPa) at 270 ° C. for 4 minutes to obtain a carbon fiber reinforced plastic (CFRTP) 10 mm wide × 2 mm thick × 12 mm long. ) A test piece was prepared. The carbon fiber volume content of the CFRTP test piece was 30%. A bending test (span / thickness ratio = 32, test speed 5.0 mm / min) was performed on five test pieces in accordance with JIS K7074.

(Measurement of elongation at break)
A sizing agent solution is applied on the film, dried at room temperature for 20 hours so that the film thickness after drying is 100 to 200 μm, then further dried at 140 ° C. for 5 minutes and peeled off from the film. Produced. Next, using this sample, the elongation at break when a tensile test was carried out at a crosshead speed of 50 mm / min in an atmosphere at 25 ° C. with a tensile tester (manufactured by Orientec) was measured.

[Measurement of softening temperature]
A sample is prepared by applying a sizing agent solution on the film, drying at room temperature for 20 hours so that the film thickness after drying is 100 to 200 μm, and further drying at 140 ° C. for 5 minutes and peeling from the film. did. Next, using this sample, the flow start temperature was measured with an orifice having a load of 98 N, an inner diameter of 1 mm, and a length of 1 mm using a Koka flow tester [CFT-500D manufactured by Shimadzu Corporation]. The softening temperature described later refers to this flow start temperature.

Example 1
(1) Production of carbon fiber strand As a sizing liquid, a water-based polyurethane resin [Hydran AP-40 manufactured by Dainippon Ink & Chemicals, Inc., elongation at break: 30%, softening temperature: 106 ° C.] was diluted with pure water, The resin concentration was adjusted to 25 g / L. Unsized carbon fiber strand [“BETHFITE STS-24K N00” manufactured by Toho Tenax Co., Ltd., diameter 7 μm × 24000 filament, fineness 1.6 g / m, tensile strength 4000 MPa (408 kgf / mm ² ), tensile elastic modulus 238 GPa (24.3 tonf / mm ² )] was continuously immersed, and the sizing solution was impregnated between the filaments. Subsequently, the moisture was evaporated by passing through a dryer at 140 ° C. for 3 minutes to obtain a carbon fiber strand having 1.0% by mass of a sizing agent attached thereto.

(2) Interfacial adhesive strength of carbon fiber strands and bending strength of unidirectional laminates As shown in Table 1, the interfacial adhesive strength and unidirectional laminate bending strengths measured for the obtained carbon fiber strands were 63 MPa and 733 MPa, respectively. It was expensive.

Example 2
(1) Production of carbon fiber strands Example 1 except that the sizing solution was changed to water-based polyurethane resin [Hydran AP-30F, Dainippon Ink & Chemicals, Inc., elongation at break: 30%, softening temperature: 105 ° C.] The same operation was performed to obtain a carbon fiber strand to which 1.0% by mass of the sizing agent was adhered.

(2) Interfacial adhesive strength of carbon fiber strands and bending strength of unidirectional laminates As shown in Table 1, the interfacial adhesive strength and unidirectional laminate bending strengths measured for the obtained carbon fiber strands were 59 MPa and 740 MPa, respectively. It was expensive.

Example 3
(1) Production of carbon fiber strands Example 1 except that the sizing solution was changed to water-based polyurethane resin [Hydran AP-20 manufactured by Dainippon Ink & Chemicals, Inc., elongation at break: 340%, softening temperature: 90 ° C.] The same operation was performed to obtain a carbon fiber strand to which 1.0% by mass of the sizing agent was adhered.

(2) Interfacial adhesive strength of carbon fiber strand and bending strength of unidirectional laminate As shown in Table 1, the interfacial adhesive strength and unidirectional laminate bending strength measured for the obtained carbon fiber strand were 58 MPa and 741 MPa, respectively. It was expensive.

Example 4
(1) Production of carbon fiber strands As in Example 1, except that the sizing solution was changed to water-based polyurethane resin [Hydran HW140SF, Dainippon Ink & Chemicals, Inc., elongation at break: 350%, softening temperature: 75 ° C.] A carbon fiber strand having 1.0% by mass of a sizing agent attached thereto was obtained by operation.

(2) Interfacial adhesive strength of carbon fiber strands and bending strength of unidirectional laminates As shown in Table 1, the interfacial adhesive strength and unidirectional laminate bending strengths measured for the obtained carbon fiber strands were 59 MPa and 730 MPa, respectively. It was expensive.

Comparative Example 1
(1) Production of carbon fiber strands As in Example 1, except that the sizing solution was changed to water-based polyurethane resin [Hydran HW930 manufactured by Dainippon Ink & Chemicals, Inc., elongation at break: 600%, softening temperature: 170 ° C.] A carbon fiber strand having 1.0% by mass of a sizing agent attached thereto was obtained by operation.

(2) Interfacial bond strength of carbon fiber strands and bending strength of unidirectional laminates As shown in Table 1, the interfacial adhesive strength and unidirectional laminate bending strengths measured for the obtained carbon fiber strands were 50 MPa and 655 MPa, respectively. It was low.

Comparative Example 2
(1) Production of carbon fiber strands As in Example 1, except that the sizing solution was changed to water-based polyurethane resin [Hydran HW940, Dainippon Ink & Chemicals, Inc., elongation at break: 700%, softening temperature: 180 ° C.] A carbon fiber strand having 1.0% by mass of a sizing agent attached thereto was obtained by operation.

(2) Interfacial bond strength of carbon fiber strands and bending strength of unidirectional laminates As shown in Table 1, the interfacial adhesive strength and unidirectional laminate bending strengths measured for the obtained carbon fiber strands were 48 MPa and 654 MPa, respectively. It was low.

Comparative Example 3
(1) Production of carbon fiber strands The same as Example 1 except that the sizing solution was changed to water-based polyurethane resin [Bondic 1310NE manufactured by Dainippon Ink & Chemicals, Inc., elongation at break: 450%, softening temperature: 173 ° C.] To obtain a carbon fiber strand having 1.0% by mass of a sizing agent attached thereto.

(2) Interfacial adhesive strength of carbon fiber strand and bending strength of unidirectional laminate As shown in Table 1, the interfacial adhesive strength and unidirectional laminate bending strength measured for the obtained carbon fiber strand were 52 MPa and 650 MPa, respectively. It was low.

It is a schematic explanatory drawing which shows the measuring method of interface adhesive strength. It is a schematic explanatory drawing which shows the apparatus used for manufacture of the carbon fiber reinforced strand prepreg in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Carbon fiber monofilament 12 Adhesive 13 Mount 13a, 13b Protrusion part 14 Microdroplet 15a, 15b Blade 31 Carbon fiber strand 32 Guide roller 33 Immersion roller 34 Drawing roller 35 Package 37 Winder 38 Constant temperature bath 39 Resin bath

Claims (5)

A carbon fiber strand to which a sizing agent containing a polyurethane resin is applied, wherein the rupture elongation of the dry film of the sizing agent is 400% or less, and the adhesion amount is 0.1 to 5.0 with respect to the carbon fiber. Carbon fiber strands for reinforcing thermoplastic resin in mass%. The carbon fiber strand for reinforcing a thermoplastic resin according to claim 1, wherein the softening temperature of the dry film of the sizing agent is 50 to 150 ° C. The carbon fiber strand for reinforcing a thermoplastic resin according to claim 1 or 2, wherein the polyol component of the polyurethane resin is ester-based. A carbon fiber reinforced thermoplastic resin comprising 5 to 70% by mass of the carbon fiber strand for reinforcing a thermoplastic resin according to any one of claims 1 to 3. The carbon fiber reinforced thermoplastic resin according to claim 4, wherein the thermoplastic resin is a polyamide resin.

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