JP4680715B2 - Manufacturing method of plastic optical fiber cable - Google Patents

Description

  The present invention relates to a method of manufacturing a plastic optical fiber cable that can be used, for example, for information transmission in a moving body such as an automobile and sensor applications in the field of food and semiconductors.

  Conventionally, silica-based optical fibers are mainly used for trunk systems because optical fibers can perform excellent optical transmission over a wide wavelength range. However, silica-based optical fibers are expensive and workable. There is a problem that is low. Therefore, an optical fiber made of plastic (plastic optical fiber) has been developed that has advantages such as low cost, light weight, large diameter, and easy end face processing and handling. Plastic optical fibers have been put to practical use in illumination / decoration applications, sensor applications in the food / semiconductor field, and optical information transmission applications in short and medium distances such as FA, OA, and LAN.

The plastic optical fiber is generally used in the form of a plastic optical fiber cable in which the outer peripheral portion of the plastic optical fiber is coated with a coating layer made of a thermoplastic resin.
Here, the plastic optical fiber is composed of a core that is a main optical transmission path formed of polymethyl methacrylate (PMMA) having excellent transparency, and a material having a lower refractive index than the core on the outer peripheral surface of the core. And a clad layer.

  In recent years, plastic optical fiber cables are sometimes used for information transmission in mobile bodies such as automobiles. When used for information transmission in automobiles and other moving bodies, it is used in the presence of chemicals such as oil, electrolytes, and flammable substances such as gasoline. In addition to excellent properties, it is required to have excellent chemical resistance. Therefore, as a coating layer, it is highly transparent, has a lower refractive index than a material generally used as a cladding layer of a plastic optical fiber, and further has excellent oxygen barrier properties, oil resistance, and organic solvent resistance, It has been proposed to use an ethylene-vinyl alcohol copolymer (hereinafter referred to as an EVAL copolymer).

For example, Patent Document 1 proposes a plastic optical fiber in which a plastic optical fiber having a core made of PMMA resin and a cladding layer made of a fluoroalkyl methacrylate copolymer is coated with a transparent EVAL copolymer. . According to this plastic optical fiber, the transmission loss of the light amount when bent is small.
Patent Document 2 proposes a plastic optical fiber in which a protective layer made of an EVAL copolymer having a refractive index lower than the cladding layer by 0.001 or more is provided outside a specific plastic optical fiber. In this plastic optical fiber, an increase in transmission loss when bent is prevented, and further, an increase in transmission loss due to oxidation is prevented, and heat resistance (95 dB, 15 dB / km or less at 1000 hours) is improved.
Patent Document 3 and Patent Document 4 describe a plastic optical fiber cord in which a plastic optical fiber is coated with a saponified ethylene-vinyl acetate copolymer, and further coated with a flame retardant material or a thermoplastic resin. Has been.
Patent Document 5 discloses a plastic optical fiber cable in which an EVAL copolymer is provided as a blocking layer on a plastic optical fiber having a clad layer made of a vinylidene fluoride (VdF) -tetrafluoroethylene (TFE) copolymer. Are listed. In this plastic optical fiber cable, it is possible to prevent the plasticizer contained in the polyvinyl chloride coating layer from being transferred to the plastic optical fiber, and as a result, transmission loss when exposed at 80 ° C. for 100 hours. The increase of is prevented.
JP-A-9-101422 JP-A-11-183738 Japanese Utility Model Publication No. 57-74403 Japanese Utility Model Publication No. 58-71703 JP-A-63-113511

By the way, when a plastic optical fiber cable is used for information transmission in a moving body such as an automobile, a high-temperature and high-humidity environment in which the operating environment temperature reaches around 100 to 105 ° C. Long-term heat resistance is required for laying underneath. Specifically, the increase in transmission loss is required to be small over a long period of up to 5000 hours in an environment of 100 to 105 ° C.
However, in the plastic optical fiber cables described in Patent Documents 1 to 5, increase in transmission loss when bent is prevented, but long-term heat resistance in a high temperature environment of about 100 to 105 ° C. is insufficient. It was. For example, the plastic optical fiber cable described in Patent Document 2 has only excellent heat resistance in about 1000 hours at around 95 ° C., and is applied to information transmission applications that require heat resistance at 100 to 105 ° C. It was difficult to do.
An object of the present invention is to provide a method for producing a plastic optical fiber cable that can produce a plastic optical fiber cable having excellent chemical resistance and excellent long-term heat resistance in a high temperature environment of about 100 to 105 ° C. is there.

A method for producing a plastic optical fiber cable according to the present invention includes a plastic optical fiber comprising a core made of a polymer containing methyl methacrylate units, and one or more cladding layers formed on the outer peripheral surface of the core. A plastic optical fiber cable manufacturing method for manufacturing a plastic optical fiber cable having a strand and a coating layer covering an outer peripheral portion of the plastic optical fiber strand,
The outermost layer of the clad layer in the plastic optical fiber is composed of a ternary copolymer consisting of 10 to 60% by mass of vinylidene fluoride units, 20 to 70% by mass of tetrafluoroethylene units and 5 to 35% by mass of hexafluoropropylene units. Or 10 to 30% by mass of vinylidene fluoride units, 40 to 80% by mass of tetrafluoroethylene units, 5 to 40% by mass of hexafluoropropylene units, and 0.1 to 15% by mass of perfluoro (fluoro) alkyl vinyl ether units And a vinylidene fluoride-based resin having a heat of crystal melting of 40 mJ / mg or less in differential scanning calorimetry (DSC).
The coating layer is formed from a coating material containing an ethylene-vinyl alcohol copolymer containing 30 to 39 mol% of ethylene units and a content of vinyl alcohol units of 61 to 70 mol% and a light shielding agent,
And a coating step in which a coating layer is provided by coating the outer peripheral portion of a previously produced plastic optical fiber with a coating material using an extrusion coating apparatus equipped with a crosshead die, and in the coating step, the ethylene -When the melting point of the vinyl alcohol copolymer is T ₁ (° C) and the coating temperature is T ₂ (° C), the following formulas (1) to (3) are satisfied.
T ₁ ≦ 195 (1)
T ₂ ≦ 220 (2)
30 ≦ T ₂ −T ₁ ≦ 65 (3)
In the manufacturing method of the plastic optical fiber cable of the present invention, it is preferable that the covering layer is provided in the covering step so that the drawing strength between the plastic optical fiber and the covering layer is 35 N or more.
Moreover, in the manufacturing method of the plastic optical fiber cable of this invention, it is preferable to provide a coating layer in a coating process, after heat-processing at 95-120 degreeC to the plastic optical fiber strand produced by the said composite melt spinning.

  According to the method for producing a plastic optical fiber cable of the present invention, it is possible to produce a plastic optical fiber cable having excellent chemical resistance and excellent long-term heat resistance in a high temperature environment of about 100 to 105 ° C. Therefore, the plastic optical fiber cable obtained by the manufacturing method of the present invention can be suitably used for information transmission in an automobile.

  The method for producing a plastic optical fiber cable (hereinafter referred to as POF cable) of the present invention is a plastic optical fiber strand (hereinafter referred to as POF strand) provided with a core and a cladding layer formed on the outer peripheral surface of the core. ) And a coating layer covering the outer periphery of the POF strand.

  As a material (core material) for forming a core in a POF strand, a polymer containing methyl methacrylate (MMA) units is used because of its excellent balance between transparency and mechanical strength. Polymethyl methacrylate (PMMA), which is a homopolymer of methyl acid, is preferred.

The clad layer in the POF strand may be one layer or two or more layers. When the clad layer is composed of two or more layers, it is preferable to have a two-layer structure in which the second clad layer (outermost layer) is provided concentrically on the outer periphery of the first clad layer from the viewpoint of reducing the manufacturing cost. .
When the clad layer has such a two-layer structure, the refractive index n ₁ of the core, the refractive index n ₂ of the first clad layer, and the refractive index n ₃ of the second clad layer are expressed by the following relational expression (4).
n ₁ > n ₂ > n ₃ (4)
Alternatively, the following relational expressions (5) and (6)
n ₁ > n ₂ (5)
n ₃ > n ₂ (6)
It is preferable to satisfy. In addition, the refractive index in this invention says the refractive index in 25 degreeC by a sodium D line | wire.
In particular, when the above relational expression (4) is satisfied, light leaked from the first cladding layer when the POF cable is bent can be reflected by the second cladding layer having a lower refractive index. it can.

  As the resin forming the first cladding layer (first cladding material), a known material used as a POF cladding material such as a fluorinated methacrylate polymer or a vinylidene fluoride polymer may be appropriately selected. it can. Among them, in the present invention, it is preferable to use a fluorinated methacrylate-based polymer from the viewpoint of easy adjustment of the refractive index, high transparency and heat resistance, excellent flexibility and workability. .

More specifically, the fluorinated methacrylate polymer is 15 to 90% by mass of a fluoroalkyl (meth) acrylate unit (A) represented by the following general formula (I), and other copolymerizable compounds. Mention may be made of copolymers having a monomer unit (B) of 10 to 85% by mass and a refractive index in the range of 1.39 to 1.475.
_{CH 2 = CX-COO (CH} 2) m (CF 2) n Y (I)
(In the formula, X represents a hydrogen atom or a methyl group, Y represents a hydrogen atom or a fluorine atom, m represents 1 or 2, and n represents an integer of 1 to 12.)

Further, as the fluorinated methacrylate polymer, 0 to 50% by mass of a long-chain fluoroalkyl methacrylate unit (C) represented by the following general formula (II) and a short-chain fluoroalkyl methacrylate represented by the following general formula (III) Unit (D) 0 to 50% by mass and another copolymerizable monomer unit (E) 50 to 80% by mass (including at least one of units (C) and (D)) And a fluorinated methacrylate polymer having a refractive index in the range of 1.45 to 1.48. When such a fluorinated methacrylate polymer is used, the transmission band of the POF cable can be further widened.
_{CH 2 = C (CH 3)} COO- (CH 2) m (CF 2) n CF 3 (II)
(In the formula, m represents 1 or 2, and n represents an integer of 5 to 12.)
_{CH 2 = C (CH 3)} COO-CH 2 (CF 2) m X (III)
(In the formula, X represents a hydrogen atom or a fluorine atom, and m represents an integer of 1 to 4.)

  Further, as the fluorinated methacrylate copolymer, the above-mentioned long-chain fluoroalkyl methacrylate unit (C) 0 to 80% by mass, the above-mentioned short-chain fluoroalkyl methacrylate unit (D) 10 to 90% by mass, and other copolymers are possible. And a copolymer having a refractive index in the range of 1.39 to 1.435. When such a polymer is used, it is possible to further reduce the bending light amount loss when the POF cable is bent.

The unit (E) of another copolymerizable monomer in the fluorinated methacrylate polymer is not particularly limited, but a methyl (meth) acrylate unit is preferable for improving the transparency. In order to improve mechanical properties, units of (meth) acrylic acid alkyl esters such as ethyl (meth) acrylate and butyl (meth) acrylate are preferred. For improving heat resistance, (meth) acrylic such as cyclohexyl (meth) acrylate, methyl cyclohexyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, adamantyl (meth) acrylate, etc. Unit of acid cycloalkyl ester, unit of (meth) acrylic acid aromatic ester such as phenyl (meth) acrylate, benzyl (meth) acrylate, unit of hexafluoroneopentyl (meth) acrylate, N-methylmaleimide, N-substituted maleimide units such as N-ethylmaleimide, N-propylmaleimide, N-isopropylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, α-methylene-γ-butyrolactone, α-methylene-γ-methyl-γ -Butyrolactone, α-methylene-γ, γ-di Units of γ-butyrolactone compounds such as methyl-γ-butyrolactone, α-methylene-γ-ethyl-γ-butyrolactone, α-methylene-γ-cyclohexyl-γ-butyrolactone are preferred.
Of these, methyl (meth) acrylate is used as another copolymerizable monomer (E) from the viewpoint of obtaining a POF cable excellent in transparency, long-term heat resistance near 100 to 105 ° C., and mechanical strength. It is particularly preferable to use the unit of

  The glass transition temperature (Tg) of the first cladding material is preferably around 100 ° C. or higher because the heat resistance near 100 ° C. becomes higher. However, in the present invention, long-term heat resistance at 100 to 105 ° C. can be satisfied even when a known fluorinated methacrylate polymer having a Tg of about 70 to 90 ° C. is used for the first cladding layer. . A fluorinated methacrylate polymer having a Tg of 70 ° C. to 90 ° C. is characterized by being more flexible and less susceptible to cracking than a fluorinated methacrylate polymer having a Tg of around 100 ° C. or higher. When used as a layer, a POF cable having particularly excellent bending characteristics can be obtained.

  The higher the refractive index of the first cladding layer, the wider the transmission band, but there is a tendency that the effect of suppressing the bending light amount loss by the second cladding layer becomes insufficient. Therefore, it is desirable to design the first cladding layer as appropriate in consideration of the balance between the transmission band and the bending light amount loss required according to the environment in which the POF cable is used.

The outermost layer of the cladding layer in the POF strand is composed of 10 to 60% by mass of vinylidene fluoride (VdF) units, 20 to 70% by mass of tetrafluoroethylene (TFE) units, and 5 to 35% by mass of hexafluoropropylene (HFP) units. A terpolymer comprising 10 to 30% by weight of vinylidene fluoride (VdF) units, 40 to 80% by weight of tetrafluoroethylene (TFE) units, 5 to 40% by weight of hexafluoropropylene (HFP) units and Any of quaternary copolymers comprising 0.1 to 15% by mass of fluoro (fluoro) alkyl vinyl ether (PFPVE) units, and the heat of crystal melting in differential scanning calorimetry (DSC) is 40 mJ / mg or less It is formed from the vinylidene fluoride resin which is.
When there is one clad layer, the one clad layer is the outermost layer.

The content of VdF units in the VdF resin forming the clad outermost layer is preferably 60% by mass or less, more preferably 30% by mass or less, in all the structural units of the resin.
In the terpolymer, when the vinylidene fluoride unit exceeds 60% by mass, the crystallinity of the resin increases. Therefore, when the non-crystalline inner layer resin (core material or clad consists of two or more layers) A compatible layer may be formed with the first cladding material. Therefore, when the POF cable is exposed to a high temperature and high humidity environment such as a temperature of 85 ° C. and a humidity of 95% RH for a long time, the compatible layer tends to phase-separate and increase transmission loss. When the vinylidene fluoride unit is less than 10% by mass, the terpolymer and an amorphous inner layer resin (a core material, or a first clad material when the clad is composed of two or more layers), There is a tendency for the adhesion of the to decrease. In the terpolymer, the vinylidene fluoride unit is preferably 40% by mass or less.
If the tetrafluoroethylene unit exceeds 70% by mass, the melting point of the copolymer tends to increase, and the molding stability near the spinning temperature of POF (200 to 240 ° C.) may be lowered. If the tetrafluoroethylene unit is less than 20% by mass, the elastomeric property of the copolymer tends to be high, so that the molding stability in POF melt spinning is lowered and the hardness is low, so that POF is machined. The protective function may be reduced.
If the hexafluoropropylene unit exceeds 35% by mass, the elastomeric property of the copolymer tends to be high, so that the molding stability in POF melt spinning is lowered and the hardness is reduced, so that POF is mechanically reduced. There is a risk that the protective function will be reduced. Further, if the hexafluoropropylene unit is less than 5% by mass, the copolymer has high crystallinity, so that it becomes cloudy at room temperature or when the POF cable is exposed to a high temperature and high humidity environment for a long time. Since it gradually becomes cloudy, the transmission loss of POF may be impaired.

In the quaternary copolymer, when the vinylidene fluoride unit exceeds 30% by mass, the crystallinity of the copolymer increases, so that the copolymer is cloudy at room temperature or the POF cable is long in a high temperature and high humidity environment. When it is exposed to time, it gradually becomes cloudy, and there is a risk that the transmission loss of POF is impaired. When the vinylidene fluoride unit is less than 10% by mass, the adhesion between the quaternary copolymer and the amorphous inner layer resin (the core material or the first clad material when the clad is composed of two or more layers) is improved. There is a tendency to decrease. When the tetrafluoroethylene unit exceeds 80% by mass, the melting point of the copolymer tends to be high, and the molding stability near the spinning temperature of POF (200 to 240 ° C.) may be lowered. If the tetrafluoroethylene unit is less than 40% by mass, the elastomeric property of the copolymer tends to be high, so that the molding stability in POF melt spinning is lowered and the hardness is reduced, so that POF is machined. The protective function may be reduced.
If the hexafluoropropylene unit exceeds 40% by mass, the elastomeric property of the copolymer tends to be high, so that the molding stability in POF melt spinning is lowered or the hardness of the copolymer is reduced. In addition, since the adhesion to the above-described non-crystalline inner layer resin is lowered, the POF clad material may be peeled off. When the hexafluoropropylene unit is less than 5% by mass, the effect of reducing the crystallinity of the copolymer is insufficient, so that it becomes cloudy at room temperature or the POF cable is exposed to a high temperature and high humidity environment for a long time. In this case, the cloudiness gradually becomes cloudy, and there is a risk that the POF transmission loss may be impaired.
Further, when the perfluoro (fluoro) alkyl vinyl ether unit exceeds 15% by mass, or when the perfluoro (fluoro) alkyl vinyl ether unit is less than 0.1% by mass, the same tendency as in the case of the hexafluoropropylene unit is observed. Indicates.

The perfluoro (fluoro) alkyl vinyl ether is represented by the general formula (IV).
_{CF 2 = CF- (OCF 2 CF} (CF 3)) a O-R f2 (IV)
(In the formula, R _f2 represents an alkyl group having 1 to 8 carbon atoms, a fluoroalkyl group, an alkoxylalkyl group, or a fluoroalkoxylalkyl group, and a is an integer of 0-3.)
The perfluoro (fluoro) alkyl vinyl ether is preferably selected from the following general formulas (V) to (VIII).
_{CF 2 = CFO (CF 2)} n -OCF 3 (V)
(Where n is an integer from 1 to 3)
CF ₂ = CF (OCF ₂ CF (CF ₃ )) _n O (CF ₂ ) _m CF ₃ (VI)
(Where n is an integer from 1 to 3, m is an integer from 0 to 3)
CF ₂ = CFO (CH ₂ ) _n (CF ₂ ) _m CF ₃ (VII)
(Where n is an integer from 1 to 3, m is an integer from 0 to 3)
CF ₂ = CFO (CH ₂ ) _n CH ₃ (VIII)
(Where n is an integer from 1 to 3)

Among these, from the viewpoint which can reduce the cost of the raw _{material, CF 2 = CFOCF 3, CF} 2 = CFOCF 2 CF 3, CF 2 = CFOCF 2 CF 2 CF 3, CF 2 = CFOCH 2 CF 3, CF ₂ = CFOCH selected from _{2 CF 2 CF 3, CF 2} = CFOCH 2 CF 2 CF 2 CF 3, CF 2 = CFOCH 3, CF 2 = CFOCH 2 CH 3 and _{CF 2} = CFOCH 2 CH 2 group consisting of CH ₃ At least one of them is preferred.

  The material forming the outermost layer of the clad layer is a resin having a heat of crystal melting of 40 mJ / mg or less in differential scanning calorimetry (DSC), preferably a resin of 30 mJ / mg or less, preferably 15 mJ / mg or less. Some resins are more preferred. The heat of crystal melting is the amount of heat generated due to heat melting, and the smaller the amount of heat, the lower the crystallinity. Therefore, since a resin having a heat of crystal melting of 40 mJ / mg or less can suppress white turbidity due to crystals, the use of such a resin for the outermost layer of the cladding exposes the POF cable to an initial transmission loss and a high temperature environment for a long time. This can further suppress an increase in transmission loss of the POF cable.

The coating layer covering the outer periphery of the POF strand is a layer made of a coating material containing an EVAL copolymer having a specific copolymer composition and a light shielding agent.
The melting point of the EVAL copolymer contained in the coating material is preferably 195 ° C. or less, and more preferably 180 ° C. or less. When the melting point of the EVAL copolymer is higher than 195 ° C., it is necessary to set the temperature when forming the coating layer on the POF strand higher than 220 ° C., and the optical performance of the POF strand may be lowered. This is because if the temperature at which the coating layer is formed on the POF strand is set higher than 220 ° C., the POF strand may be damaged by heat.

  The EVAL copolymer is a copolymer containing 30 to 39 mol% of ethylene units and 61 to 70 mol% of vinyl alcohol units (total of ethylene units and vinyl alcohol units is 100 mol%). When the ethylene unit content is less than 30 mol%, the vinyl alcohol unit content is high and the water absorption is high, so that the moist heat resistance of the POF cable may be lowered. Further, the melting point of the EVAL copolymer becomes higher than 195 ° C. On the other hand, if the ethylene unit content is more than 39 mol%, the glass transition temperature of the EVAL copolymer is lower than 60 ° C and the melting point is 160 ° C or higher, but the POF cable is 100 to 105 ° C The cable may be deformed when used in

The melt viscosity of the EVAL copolymer preferably has a melt flow index measured at 210 ° C. and a load of 5 kgf (49 N) in the range of 25 to 80 g / 10 minutes. If the melt flow index is less than 25 g / 10 min, the viscosity of the EVAL copolymer is increased, and therefore the resin pressure applied to the POF inside the crosshead increases when the outer peripheral portion of the POF is coated with the coating layer. Therefore, there is a tendency that the POF strand is damaged, or the orientation strain becomes large when the POF strand is coated with the coating layer. When the processing temperature is raised to suppress the orientation strain, the POF strand may be thermally deteriorated.
If the melt flow index is larger than 80 g / 10 min, the viscosity of the EVAL copolymer tends to be low, and it becomes difficult to provide a coating layer with a uniform thickness, and the strength of the coating layer tends to be weak.

  Examples of commercially available EVAL copolymers include Eval E105, G156, F104, FP104, EP105, and EU105 manufactured by Kuraray.

  As the light shielding agent contained in the coating material, one that can prevent the incidence of external light to the POF strand and makes the coating layer achromatic is used, and examples thereof include carbon black. The content of the light shielding agent is preferably 0.1 to 2.0% by mass.

  The coating layer is preferably not stretched. If the coating layer is not stretched, the orientation of the coating layer can be further suppressed, so that thermal shrinkage under a high temperature environment of about 105 ° C. can be further reduced.

  Various thermoplastic resins may be contained in the coating material as long as the function as the coating layer is not impaired. For example, a polyethylene resin or a polypropylene resin may be contained in an amount of 5 to 30 parts by mass with respect to 100 parts by mass of the EVAL copolymer. Since the EVAL copolymer has high water absorption, the moisture resistance of the POF cable tends to be low. However, when the polyethylene resin or polypropylene resin is contained in the range of 5 to 30 parts by mass, The water vapor shielding property is increased, and the moisture resistance of the POF cable can be ensured.

  The thickness of the coating layer is preferably 150 to 750 μm, and more preferably 250 to 350 μm. When the thickness of the coating layer is less than 150 μm, the effect of mechanically protecting the POF strand is insufficient, and the drawing strength between the POF strand and the coating layer may not be sufficiently maintained. On the other hand, when the thickness of the coating layer exceeds 750 μm, the cost of the material used for the coating layer increases. Further, as the coating layer becomes thicker, the amount of heat transferred to the POF strand during the coating process increases, and the optical performance of the POF strand tends to deteriorate.

  In the POF cable, a secondary coating layer made of a thermoplastic resin may be provided on the outer periphery of the coating layer in order to enhance durability, environmental resistance characteristics, and the like. Examples of the thermoplastic resin forming the secondary coating layer include polyvinyl chloride, polyethylene, polypropylene, chlorinated polyethylene, polyamide, polyurethane, fluorine-based resin, and ethylene-vinyl acetate copolymer. These can be used singly or in a combination of two or more appropriately selected according to the use environment of the POF cable.

  For wiring in automobiles and the like, it is preferable to use a polyamide resin excellent in oil resistance, heat resistance, etc. as the secondary coating layer. Specifically, nylon 11, nylon 12, nylon 6, nylon 66, nylon 6-12 and other homopolymers, nylon copolymers composed of combinations of monomer units of these polymers, and flexible to these polymers Nylon elastomer into which various segments are introduced, and a mixture containing nylon elastomer and other polyamide resins are preferable. Of these, nylon-based elastomers or mixtures of nylon-based elastomers and other polyamide-based resins are preferable because they have good moldability and can prevent thermal and mechanical damage during secondary coating layer formation. .

  In order to manufacture the POF cable, first, a POF strand is formed by a known composite melt spinning method in a POF strand forming step, and then an extrusion coating apparatus equipped with a crosshead die in a covering step. Is used to coat the outer periphery of the POF strand with a coating material to provide a coating layer. Thereby, a POF cable having a POF strand and a coating layer is obtained.

  In the POF strand forming step, the draw ratio is preferably 1.3 to 2.2, and more preferably 1.5 to 2.0. If the draw ratio is less than 1.3, the mechanical strength of the POF strands becomes insufficient, so that the POF cable may be broken when it is bent. If the draw ratio is larger than 2.2, a very long heat treatment may be required to reduce thermal shrinkage, or the number of relaxation treatments may need to be increased.

In the coating step, the following formulas (1) to (3) are satisfied when the melting point of the EVAL copolymer is T ₁ (° C.) and the coating temperature (crosshead die temperature) is T ₂ (° C.).
T ₁ ≦ 195 (1)
T ₂ ≦ 220 (2)
30 ≦ T ₂ −T ₁ ≦ 65 (3)
Since the melting point (T ₁ ) of the EVAL copolymer is 195 ° C. or less and the coating temperature (T ₂ ) is 220 ° C. or less, the POF strand is not easily damaged by heat during the coating process. On the other hand, when the melting point (T ₁ ) of the EVAL copolymer exceeds 195 ° C. or the coating temperature (T ₂ ) exceeds 220 ° C., the POF strand is damaged by heat during the coating process.
Further, by setting T ₂ -T ₁ in the range of 30 to 65 (° C.), it is possible to form the coating layer without damaging the POF strand while suppressing the orientation of the coating layer. On the other hand, if T ₂ -T ₁ is less than 30 ° C., the orientation degree of the EVAL copolymer is increased during the coating process, and therefore, when the POF cable is exposed to a high temperature environment of 100 to 105 ° C. for a long time, Thermal contraction of the coating layer increases. As a result, contraction strain is imparted to the POF strand, so that the optical performance of the POF strand is degraded. On the other hand, if T ₂ -T ₁ is greater than 65 ° C., the temperature of the crosshead die during the coating process is merely set unnecessarily high, and the POF strand is damaged by heat.
As an extrusion coating apparatus provided with a crosshead die, a known apparatus used for cable manufacture can be used.

In the covering step, the covering layer is provided so that the drawing strength between the POF strand and the covering layer is 35 N or more, particularly 45 N or more. When the pulling strength is less than 35 N, when there is a difference in heat shrinkage characteristics at 100 to 105 ° C. between the POF strand and the coating layer, heat shrinkage strain is applied unevenly in the length direction of the POF strand. For this reason, the optical performance of the POF strand may be deteriorated, the protective effect of the coating layer against external force may be insufficient, or the pistoning of the POF cable in a high temperature environment may not be suppressed.
In order to make the drawing strength 35 N or more, it is preferable to appropriately select the temperature of the crosshead die and the shape of the die / nip during the coating process.
The pullout strength in the present invention is a value measured by a measurement method described later, and serves as an index of adhesion.

The POF cable manufacturing method may include a heat shrinkage reduction step of performing heat treatment or relaxation treatment on the POF strand between the POF strand forming step and the covering step.
Heat treatment and relaxation treatment include heating the POF strand with a heating medium such as water, water vapor, and heated gas, passing the POF strand through the heating medium while adjusting the supply rate or discharge rate of the POF strand. The method of making it, etc. are mentioned.
Further, when the heat treatment or relaxation treatment is performed, it is preferable to apply a tension of several hundred gf to the POF strand because the stretched orientation can be maintained.

The temperature of the heat treatment or relaxation treatment of the POF strand is preferably about 95 to 120 ° C. If the temperature of the heat treatment or relaxation treatment is higher than 120 ° C, the orientation of the POF strand tends to decrease and the strength tends to decrease. If the temperature is lower than 95 ° C, it takes a very long time to obtain the desired heat shrinkability. It is necessary to perform the heat treatment or increase the number of relaxation treatments.
In addition, since a POF strand excellent in mechanical properties can be obtained by suppressing a decrease in stretch orientation, heat shrinkage characteristics can be obtained, and the temperature of heat treatment or relaxation treatment can form the glass transition temperature of the core material and the cladding layer. It is preferable that it is below the lower one of the glass transition temperature of the material to do.

If the heat shrinkage reduction step is included, an increase in transmission loss of the POF cable in a high temperature environment can be prevented.
That is, the polymer containing methyl methacrylate units as the core material has a glass transition point of about 110 ° C., and the molecular orientation is relaxed and heat shrinks near that temperature. However, by reducing the heat shrinkability of the POF strand in the heat shrinkage reduction step, when the POF cable is exposed to a high temperature environment of 100 to 105 ° C., the POF strand and the coating layer The difference in thermal shrinkage becomes smaller. As a result, it becomes difficult for the POF cable to be pulled in (pistoning) in the POF cable, so that fluctuations in the distance between the light source or the light receiving element and the POF cable end face can be suppressed, and light loss due to the fluctuations can be prevented. Therefore, fluctuations in the amount of light emitted from the end face of the POF cable or the amount of light incident on the POF cable can be reduced.

  In the POF cable obtained by the above manufacturing method, the outermost layer of the cladding layer in the POF strand is a specific vinylidene fluoride copolymer, and a coating layer is provided on the POF strand at a specific temperature condition. It is a thing. Therefore, the orientation of the coating layer is suppressed, the thermal shrinkage difference between the POF strand and the coating layer is small, and excellent long-term heat resistance in a high temperature environment of about 100 to 105 ° C. Specifically, the transmission loss can be suppressed to 195 dB / km or less even after being exposed to a high temperature environment of 105 ° C. for 5000 hours. In addition, since the POF strand is not easily damaged by heat during the coating process, the initial transmission loss can be reduced to 150 dB / km or less.

Further, since the material forming the outermost layer of the cladding layer is a specific vinylidene fluoride copolymer, a POF cable having a low refractive index and excellent transparency and heat resistance can be obtained. Furthermore, while acting as a protective layer in close contact with the inner clad layer or core, it relaxes stresses such as vibration and external pressure applied to the POF strands to increase flex resistance, and increase solvent resistance and chemical resistance. Can be.
Moreover, since the coating layer of the POF cable is made of a specific coating material containing a specific EVAL copolymer, it is excellent in chemical resistance, heat resistance, flex resistance, and workability. Moreover, since the oxygen barrier property is high, it is possible to prevent oxidative deterioration of the POF strand in a high temperature environment and to suppress an increase in transmission loss. In addition, it is possible to prevent a decrease in optical transmission characteristics due to the provision of the coating layer.

  For these reasons, the POF cable obtained by the production method of the present invention is suitable for applications such as in-car LAN cables that require long-term durability in an environment where chemicals are present and the temperature is high.

Hereinafter, the present invention will be described by way of examples. In addition, about the evaluation method in the Example of this invention, it implemented by the following method.
(Glass transition temperature (Tg), heat of crystal melting (ΔH))
A differential scanning calorimeter (DSC) (manufactured by Seiko Instruments Inc., DSC-220) was used for the measurement. The sample was heated to 200 ° C. at a rate of temperature increase of 10 ° C./min, held in that state for 5 minutes and melted, and then cooled to 0 ° C. at a rate of temperature decrease of 10 ° C./min. This operation was repeated again to determine the glass transition temperature and the heat of crystal melting.
(Refractive index)
A film-shaped test piece having a thickness of 200 μm was formed by a melt press, and the refractive index (n _D ²⁵ ) of sodium D-line at 25 ° C. was measured using an Abbe refractometer.
(Transmission loss)
Measurement was performed by a 25-1 m cut-back method using light having a wavelength of 650 nm under the condition of excitation NA = 0.1. The measurement was performed for the initial state of the POF cable, and after 1000 hours and 5000 hours had passed after leaving the POF cable in an oven at a temperature of 105 ° C.
(Melt flow index)
The melt flow index (MFI) was measured according to Japanese Industrial Standard JIS K7210. Specifically, the amount discharged from a nozzle having a diameter of 2 mm and a length of 8 mm under conditions of 210 ° C. and a load of 5 kgf (49 N) was measured for 10 minutes.

(Heat shrink)
A POF strand with a distance between test lengths of 1000 mm was suspended in a dryer at 105 ° C. for 24 hours, and then the distance between test lengths was measured. The amount of shrinkage was divided by the test length to determine the shrinkage in the length direction.

(Pullout strength)
The initial drawing strength of the coating layer (initial drawing strength between the optical fiber and the coating layer) is formed at one end of the jig 12 and the jig 12 for holding the optical fiber cable 10 as shown in FIG. The measurement was performed using a measuring device 20 including a chuck 8 that grips the protrusion 14 and a chuck 7 that grips the peeled portion 5 of the optical fiber cable 10. The jig 12 is formed with a holding chamber 13 in which the covering portion 4 of the optical fiber cable 10 is accommodated, and a through hole 15 that is larger than the peeling portion 5 of the optical fiber cable 10 and narrower than the covering portion 4.
In the measurement, an optical fiber cable from which the coating layer on one end side was peeled off was prepared and cut so that the length of the coating portion 4 of the optical fiber cable was 30 mm.
Next, the coated portion 4 of the optical fiber cable was accommodated in the holding chamber 13 formed in the jig 12, and the peeled portion 5 of the optical fiber cable was extracted from the through hole 15. Next, the protrusion 14 formed at one end of the jig 12 was gripped by the chuck 8, and the peeling portion 5 of the optical fiber cable was gripped by the chuck 7.
Next, the chuck 8 is moved at a constant speed of 50 mm / min along the central axis direction of the optical fiber cable 10 (arrow direction in the drawing) to pull the jig 12, so that the peeled portion of the coated portion 4 of the optical fiber cable 10 is pulled. The part thicker than 5 was pulled out. From the curve showing the relationship between the drawing stress at this time and the amount of displacement in the drawing direction of the portion thicker than the peeled portion 5 in the coated portion 4 of the optical fiber cable 10, the peak value of the stress at the time of drawing is read and the drawing strength did.

[ Reference Example 1]
PMMA (refractive index: 1.492) is used as the core material, and as shown in Table 1, 2,2,2-trifluoroethyl methacrylate (3FM) / 2- (perfluorooctyl) ethyl methacrylate is used as the first cladding material. (17FM) / MMA / methacrylic acid (MAA) (51/31/17/1 (mass%)) copolymer (refractive index 1.417), second clad material (material forming the outermost layer), VdF / TFE / HFP copolymer (48.0 / 42.7 / 9.3 (mass%), refractive index 1.374, heat of crystal melting 16 mJ / mg) was used. These polymers are melted, supplied to a spinning head at 220 ° C., subjected to composite spinning using a concentric composite nozzle, and then stretched twice in the length direction in a hot air heating furnace at 140 ° C. A POF strand having a layer thickness of 10 μm and a diameter of 1 mm was obtained. With this POF wire wound around a plastic bobbin, it is left in a thermostatic bath set at 100 ° C. for 24 hours to perform heat relaxation treatment, and the heat shrinkage rate (105 ° C., 24 hours) is 0.9%. did. The initial performance of this POF strand was 134 dB / km.
Next, as an EVAL copolymer, an ethylene-vinyl alcohol copolymer (ethylene (Et) 47 mol% / vinyl alcohol (EVOH) 53 mol%, MFI; 39 g / 10 min, see Table 1) is used as the POF. The strands were coated with a crosshead cable coating apparatus equipped with a crosshead die set at 210 ° C. Thereby, a coating layer having a thickness of 250 μm was formed, and a POF cable having an outer diameter of 1.5 mm was obtained .

[Examples 2 to 4, Example 6, Comparative Example 2]
As shown in Table 1, POF strands and POF cables were manufactured by the method described in Reference Example 1 except that the materials of the second cladding layer and the coating layer were changed. Table 2 shows the results of evaluating the obtained POF strands and the POF cable.

[Example 5]
As shown in Table 1, POF strands and POF cables were produced under the same conditions as in Example 4 except that the thermal relaxation treatment was performed in a thermostat set at 90 ° C. for 65 hours. The thermal contraction rate (105 ° C., 24 hours) of this POF strand was 2.2%. Table 2 shows the results of evaluating the obtained POF strands and the POF cable.

[Comparative Example 1]
A POF strand and a POF cable were produced under the same conditions as in Example 3 except that the coating temperature was 210 ° C. (T ₂ −T ₁ = 27 (° C.)). Table 2 shows the results of evaluating the obtained POF strands and the POF cable. When the POF cable was left in a thermostat set at 105 ° C. for 1000 hours, the cable was crimped.

[Comparative Examples 3 and 4]
As shown in Table 1, the same conditions as in Reference Example 1 except that the coating temperature was 230 ° C. using a high melting point (Comparative Example 3) or high viscosity (Comparative Example 4) EVAL copolymer for the coating layer. Manufactured POF strands and POF cables. Table 2 shows the results of evaluating the obtained POF strands and the POF cable.

The POF cables of Examples 2 to 6 manufactured by the manufacturing method according to claim 1 of the present application have good initial transmission characteristics (140 dB / km or less), and transmission loss after 5,000 hours at 105 ° C. (195 dB / km or less). ) Was also good.
The POF cable of Comparative Example 1 in which T ₂ -T ₁ during the coating process is less than 30 ° C., the POF cable of Comparative Example 2 in which the outermost layer of the cladding layer is not a specific copolymer, and the coating temperature T ₂ is from 220 ° C. In the high POF cables of Comparative Examples 3 to 4, the increase in transmission loss at 105 ° C. was large.

It is a figure for demonstrating the measuring method of drawing strength.

Explanation of symbols

4 Covering part 5 Peeling part 8, 7 Chuck 10 POF cable 12 Jig 13 Holding chamber 14 Protrusion 15 Through hole 20 Measuring device

Claims (3)

A plastic optical fiber having a core made of a polymer containing methyl methacrylate units, and one or more clad layers formed on the outer peripheral surface of the core, and an outer periphery of the plastic optical fiber A plastic optical fiber cable manufacturing method for manufacturing a plastic optical fiber cable having a coating layer covering a portion,
The outermost layer of the clad layer in the plastic optical fiber is composed of a ternary copolymer consisting of 10 to 60% by mass of vinylidene fluoride units, 20 to 70% by mass of tetrafluoroethylene units and 5 to 35% by mass of hexafluoropropylene units. Or 10 to 30% by mass of vinylidene fluoride units, 40 to 80% by mass of tetrafluoroethylene units, 5 to 40% by mass of hexafluoropropylene units, and 0.1 to 15% by mass of perfluoro (fluoro) alkyl vinyl ether units And a vinylidene fluoride-based resin having a heat of crystal melting of 40 mJ / mg or less in differential scanning calorimetry (DSC).
The coating layer is formed from a coating material containing an ethylene-vinyl alcohol copolymer containing 30 to 39 mol% of ethylene units and a content of vinyl alcohol units of 61 to 70 mol% and a light shielding agent,
And a coating step in which a coating layer is provided by coating the outer peripheral portion of a plastic optical fiber previously produced by composite melt spinning with a coating material using an extrusion coating apparatus equipped with a crosshead die, and the coating step Then, when the melting point of the ethylene-vinyl alcohol copolymer is T ₁ (° C.) and the coating temperature is T ₂ (° C.), the plastic optical fiber satisfies the following formulas (1) to (3): Cable manufacturing method.
T ₁ ≦ 195 (1)
T ₂ ≦ 220 (2)
30 ≦ T ₂ −T ₁ ≦ 65 (3)   2. The method of manufacturing a plastic optical fiber cable according to claim 1, wherein in the covering step, a covering layer is provided so that a pulling strength between the plastic optical fiber and the covering layer is 35 N or more. The plastic optical fiber cable according to claim 1 or 2, wherein a coating layer is provided in a coating step after heat-treating the plastic optical fiber strand produced by the composite melt spinning at 95 to 120 ° C. Method.

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