JP2011221450A - Plastic clad optical fiber - Google Patents

Abstract

The present invention provides a plastic clad optical fiber in which an increase in transmission loss is suppressed even in a humid heat environment.
A plastic clad optical fiber is provided with a clad layer formed by curing a curable resin composition on the outer periphery of a core layer made of quartz glass. The rate is 30 MPa or more and 35 MPa or less. The equilibrium elastic modulus can be calculated from the result of the storage elastic modulus in dynamic viscoelasticity. The curable resin composition for forming the clad layer 3 contains a trifunctional or higher functional monomer.
[Selection] Figure 1

Description

  The present invention relates to a plastic clad optical fiber in which a clad layer formed by curing a curable resin composition is provided on the outer periphery of a core layer made of quartz glass.

  One type of optical fiber is called a plastic clad optical fiber (see, for example, Patent Document 1). This plastic-clad optical fiber has a core layer made of quartz glass such as pure silica and a clad layer made of plastic provided on the outer periphery of the core glass. A plastic clad optical fiber having such a structure is usually cured after a quartz glass base material is melt-drawn by a drawing machine to form a core layer of the optical fiber, and then the outer circumference of the core layer is cured by a coating die or the like. It is formed by applying and curing a functional resin.

JP 2008-208225 A

  Since the clad layer is made of plastic as described above, the plastic clad optical fiber may cause an increase in transmission loss when placed in a humid heat environment.

  The present invention has been made in view of the above problems in the conventional plastic clad optical fiber, and its object is to provide a plastic clad optical fiber in which an increase in transmission loss is suppressed even in a humid heat environment. is there.

  As a result of intensive studies to achieve the above object, the present inventors have paid attention to the relationship between the elastic modulus of the clad layer of the plastic clad optical fiber and the crosslinking density, and set the equilibrium elastic modulus of the clad layer to 30 MPa or more and 35 MPa. By setting it as the following, it discovered that the transmission loss increase could be suppressed also in a wet heat environment, and came to completion of this invention.

  That is, the plastic clad optical fiber of the present invention is a plastic clad optical fiber in which a clad layer formed by curing a curable resin composition is provided on the outer periphery of a core layer made of quartz glass. The equilibrium elastic modulus is 30 MPa or more and 35 MPa or less (claim 1).

  According to another preferred embodiment of the plastic clad optical fiber of the present invention, the curable resin composition for forming the clad layer contains 100 parts by weight of a base resin containing a trifunctional or higher monomer other than the trifunctional or higher monomer. On the other hand, it is contained in an amount of 0.5 to 13 parts by weight (claim 2).

  In another preferred embodiment of the plastic clad optical fiber of the present invention, the trifunctional or higher functional monomer is a monomer having 3 to 6 groups represented by the following formula in the molecule (claims). 3).

  In another preferred embodiment of the plastic clad optical fiber of the present invention, the core layer has a diameter of 50 μm to 200 μm, and the clad layer has a thickness of 15 μm to 25 μm.

  According to the present invention, it is possible to provide a plastic clad optical fiber in which an increase in transmission loss is suppressed even in a humid heat environment.

It is a schematic sectional drawing which shows an example of the plastic clad optical fiber of this invention. It is the schematic explaining an equilibrium elastic modulus.

Hereinafter, the plastic clad optical fiber of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic sectional view showing an example of the plastic clad optical fiber of the present invention.
The plastic clad optical fiber 1 has a clad layer 3 formed by curing an ultraviolet curable resin or the like on the outer periphery of a core layer 2 made of quartz glass such as pure silica.
For example, the outer diameter of the core layer 2 can be 50 μm to 200 μm, and the thickness of the cladding layer 3 can be 15 μm to 25 μm. However, when used for a home optical composite USB cable or HDMI cable, the minimum allowable bending radius In order to make the core layer 2 small and easy to handle, the outer diameter of the core layer 2 is preferably 50 μm to 80 μm, and the thickness of the cladding layer 3 is preferably 15 μm to 22.5 μm.

The clad layer 3 has an equilibrium elastic modulus of 30 MPa or more. The equilibrium elastic modulus can be calculated from the result of storage elastic modulus measurement in dynamic viscoelasticity.
In the storage elastic modulus measurement, a resin sheet having a predetermined thickness is prepared as a sample. The resin sheet is formed by curing the curable resin composition by ultraviolet irradiation. Next, the storage elastic modulus is measured using a dynamic viscoelasticity measuring device while applying a vibration at a constant period in the major axis direction of the sample while changing the temperature. The storage elastic modulus at a predetermined temperature is obtained from the relationship between the storage elastic modulus and the temperature, and the equilibrium elastic modulus G1 in the equilibrium state (T1 (° C.)) is obtained (see FIG. 2).

  The storage elastic modulus is related to the ability to elastically store energy against the strain applied to the material, and is a kind of mechanical property, and is an index that represents the elastic property of the material (curable resin composition). It will be. Above the glass transition temperature (Tg (° C.) shown in FIG. 2) representing the transition from the glass region to the rubber region (that is, the rubber-like elastic region), the polymer segment of the resin is in a relaxed state. The storage elastic modulus component of is caused by a cross-linking point that is a bonding portion. Therefore, the equilibrium elastic modulus, which is the storage elastic modulus of the rubber-like elastic region, is related to the crosslink density of the resin.

  The reason why an increase in transmission loss is caused when a plastic clad optical fiber is placed in a humid heat environment is considered as follows.

When the plastic clad optical fiber is placed in a humid heat environment, the resin constituting the clad layer is decomposed by a chemical change, or fluorine atoms contained in the resin are aggregated to form an aggregate. And it is thought that the increase in transmission loss is caused by making the refractive index of the cladding layer non-uniform.
Causes of resin decomposition and aggregate formation include heat, ultraviolet rays, radiation, moisture, various additives such as plasticizers, salt content, microorganisms, metal catalysts, etc., especially due to moisture and plasticizers. These are usually not contained in the cladding layer itself, but are brought about by, for example, a thermoplastic resin layer formed on the outer periphery of the cladding layer or an external environment.
Then, scatterers are generated in the vicinity of the interface with the core layer due to the water and plasticizer flowing into the clad layer, which diffuses light and increases transmission loss. Moisture and plasticizers (and their degradation products) themselves become scatterers, and moisture also causes the resin to hydrolyze and cause the refractive index of the cladding layer to become non-uniform. This causes an increase in transmission loss.
On the other hand, when energy such as heat is applied from the outside to the resin containing fluorine atoms, fluorine aggregates that are more advantageous for energy are easily generated. At this time, fluorine atoms contained in the cladding layer are more likely to aggregate due to the presence of the plasticizer, and the refractive index of the cladding layer is made non-uniform by the generated aggregate, which causes an increase in transmission loss. It is.

The clad layer 3 of the polymer clad optical fiber 1 of the present invention has an equilibrium elastic modulus of 30 MPa or more and 35 MPa or less. By setting the equilibrium elastic modulus to 30 MPa or more, it is possible to achieve miniaturization of the resin network structure, that is, it is possible to form a resin network structure smaller than the molecular size of moisture, plasticizer, or the like. As a result, it is possible to prevent a substance that causes an increase in transmission loss from flowing into the cladding layer 3. In this way, the increase in transmission loss is small even when placed in a humid heat environment.
On the other hand, when the equilibrium elastic modulus is larger than 35 MPa, cracks (minute cracks) are generated due to curing shrinkage, which may lead to an increase in transmission loss in a humid heat environment.

  The equilibrium elastic modulus can be obtained by adding a trifunctional or higher monomer to the curable resin composition. However, if the content is too large, the flexibility of the resin cannot be ensured and the breaking strength deteriorates. Curing shrinkage is likely to occur during curing by ultraviolet irradiation. For this reason, it is desirable that the curable resin composition contains a trifunctional or higher functional monomer in an amount of 0.5 to 13 parts by weight with respect to 100 parts by weight of the base resin including other than the trifunctional or higher functional monomer. By containing a monomer having a trifunctional or higher functional group in the above range, the flexibility of the resin can be ensured, and the desired crosslink density can be achieved while minimizing the influence on the core layer 2 due to curing shrinkage. Can do.

  As a trifunctional or higher functional monomer, those having 3 to 6 groups represented by the following formula in the molecule are desirable from the viewpoint of convenience.

Such monomers include the following.
Trifunctional monomers include trimethylolpropane tri (meth) acrylate (TMPTA), tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, and pentaerythritol triacrylate. Tetrafunctional monomers include pentaerythritol tetra (meth) acrylate (PETA) and ditrimethylolpropane tetra (meth) acrylate. The hexafunctional monomer includes dipentaerythritol hexa (meth) acrylate (DPHA).

  Next, the base resin of the cladding layer 3 will be described. Although the material which comprises base resin is not specifically limited, For example, the following material can be mentioned.

  The clad layer 3 is formed by curing a curable composition containing a fluorine-based ultraviolet curable resin. The fluorine-based ultraviolet curable resin has a low refractive index with respect to quartz glass forming the core layer 2 and can be cured with active energy rays such as ultraviolet rays. Further, a curable composition containing this resin is cured. It is preferable that the resin has mechanical strength, flexibility, and a cured product with excellent transparency. Examples of such resins include fluorine atom-containing urethane (meth) acrylate compounds, (meth) acrylate compounds having a fluorinated polyether in the structure, and (meth) acrylated fluorine atom-containing vinyl polymers. .

  Among them, the base resin of the cladding layer 3 contains the following (A) to (C) from the viewpoints of a low refractive index, stable transparency, good coatability, adhesion to the core layer, strength and flexibility. It is preferable to further include (D) if necessary.

(A) An ethylenically unsaturated group-containing fluorine-containing copolymer.
(B) a compound represented by the following formula,
^{_{CH 2 = CR 8 COO (CH}} 2) x (CF 2) y X
[Wherein R ⁸ represents a hydrogen atom or a methyl group, X represents a hydrogen atom or a fluorine atom, x represents 1 to 2, and y represents 2 to 8].
(C) A compound other than the components (A) and (B), which does not have an aromatic structure and a polar group and has a monofunctional or bifunctional ethylenically unsaturated group.
(D) (Meth) acrylic acid or a dimer thereof.
Hereinafter, each component will be described.

(A) Ethylenically unsaturated group-containing fluoropolymer:
The ethylenically unsaturated group-containing fluorinated polymer (A) is not particularly limited as long as it is a polymer having an ethylenically unsaturated group and a fluorine atom, but a fluorinated olefin-based polymer having an ethylenically unsaturated group in the side chain A copolymer is preferred. With the component (A), the curable resin composition exhibits basic performance as a clad forming material for polymer clad optical fibers, such as low refractive index, high mechanical strength, and adhesion to a core layer such as glass or quartz.

  The ethylenically unsaturated group-containing fluorine-containing polymer is obtained by reacting the compound containing an ethylenically unsaturated group and an isocyanate group described below with the hydroxyl group of the hydroxyl group-containing fluorine-containing polymer.

(1) A compound containing an ethylenically unsaturated group and an isocyanate group:
The compound containing an ethylenically unsaturated group and an isocyanate group is particularly limited as long as it is a compound containing at least one ethylenically unsaturated group and at least one isocyanate group in the molecule. is not.
Moreover, since the curable resin composition mentioned later can be hardened more easily as said ethylenically unsaturated group, the compound which has a (meth) acryloyl group is more preferable.
Such compounds include (meth) acrylic acid, (meth) acryloyl chloride, anhydrous (meth) acrylic acid, 2- (meth) acryloyloxyethyl isocyanate, 2- (meth) acryloyloxypropyl isocyanate, 1,1- (Bisacryloyloxymethyl) ethyl isocyanate may be used alone or in combination of two or more.
In addition, as a commercial item of the (meth) acrylate which has an isocyanate group, the Showa Denko Co., Ltd. make, brand name Karenz MOI, AOI, BEI etc. are mentioned, for example.

Such a compound can also be synthesized by reacting diisocyanate and a hydroxyl group-containing (meth) acrylate.
As examples of diisocyanates, 2,4-tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, methylene bis (4-cyclohexyl isocyanate), and 1,3-bis (isocyanate methyl) cyclohexane are preferred.

As examples of the hydroxyl group-containing (meth) acrylate, 2-hydroxyethyl (meth) acrylate and pentaerythritol tri (meth) acrylate are preferable.
Examples of commercially available hydroxyl group-containing polyfunctional (meth) acrylates include, for example, Osaka Organic Chemical Co., Ltd., trade name HEA; Nippon Kayaku Co., Ltd., trade name KAYARAD DPHA, PET-30; Toagosei Co., Ltd., trade name. Aronix M-215, M-233, M-305, M-400, etc. can be obtained.

(2) Hydroxyl-containing fluoropolymer:
The hydroxyl group-containing fluoropolymer preferably comprises the following structural units (a), (b) and (c ′).
(A) A structural unit represented by the following formula (1).
(B) A structural unit represented by the following formula (2).
(C ′) A structural unit represented by the following formula (6).

Structural unit (a):

[In the formula (1), R ¹ represents a hydrogen atom or a methyl group, m represents 1 to 8, and n represents 1 to 20]

Structural unit (b):

[In Formula (2), R ² represents a hydrogen atom or a methyl group, and R ³ represents a monovalent organic group having an alicyclic structure]

Structural unit (c ')

[In the formula (6), R ⁷ represents a hydrogen atom or a methyl group, and v represents a number of 1 to 20]

(I) Structural unit (a):
In said formula (1), m is 1-8, Preferably it is 1-4, More preferably, it is 2. n is 1 to 20, preferably 3 to 12, more preferably 4 to 8, and most preferably 8.
The structural unit (a) can be introduced by using a compound represented by the following formula (7) as a polymerization component. Typical examples of such compounds include perfluorooctylethyl (meth) acrylate.

Wherein (7), R ^1, m and n are each identical to R ^1, m and n in formula (1)]
The content of the structural unit (a) in the hydroxyl group-containing fluoropolymer is 20 to 70 mol%, where the total amount of the structural units (a), (b) and (c ′) is 100 mol%, preferably Is 30-60 mol%, More preferably, it is 35-60 mol%. When the content of the structural unit (a) exceeds 70 mol%, the solubility of the hydroxyl group-containing fluoropolymer may be lowered and may be precipitated during the polymerization reaction, or the polymer may be insoluble in the solvent. . On the other hand, if it is less than 20 mol%, the fluorine content of the hydroxyl group-containing fluoropolymer (weight ratio of fluorine atoms in the polymerization pair) decreases, and the refractive index of the hydroxyl group-containing fluoropolymer increases.

(Ii) Structural unit (b):
R ³ in the above formula (2) is a monovalent organic group having an alicyclic structure. When R ³ has an aliphatic structure, the Young's modulus of the cured product obtained by curing the curable resin composition is too low, and when R ³ has an aromatic structure, the refractive index of the cured product is too high. In either case, the characteristics of the cladding layer are not suitable. When R ³ is a monovalent organic group having an alicyclic structure, the balance between the Young's modulus and the refractive index of the cured product is suitable. Here, the alicyclic structure includes a heterocyclic structure.

  The structural unit (b) can be introduced by using a compound represented by the following formula (8) as a polymerization component. Examples of such a compound include cyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentenyl (meth) acrylate, and the like.

Wherein (8), R ² and R ³ are each the same as R ² and R ³ in the formula (2). ]
The content of the structural unit (b) in the hydroxyl group-containing fluoropolymer is preferably 10 to 70 mol%, with the total amount of the structural units (a), (b) and (c ′) being 100 mol%, preferably Is 20-60 mol%, More preferably, it is 20-55 mol%. When the content of the structural unit (b) exceeds 70 mol%, there is a side effect of increasing the refractive index of the fluoropolymer. On the other hand, if it is less than 20 mol%, there is a side effect of lowering the solubility of the fluoropolymer.

(Iii) Structural unit (c ′):
The structural unit (c ′) can be introduced by using a compound represented by the following formula (9) as a polymerization component. Such compounds include 2-hydroxyethyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, caprolactone (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol ( A (meth) acrylate etc. can be used.

Wherein (9), R ⁷ and v are each identical to R ⁷ and v in equation (6). ]

  The content of the structural unit (c ′) in the hydroxyl group-containing fluoropolymer is 5 to 70 mol%, where the total amount of the structural units (a), (b) and (c ′) is 100 mol%, Preferably, it is 10-40 mol%, More preferably, it is 10-20 mol%. When the content of the structural unit (c ′) exceeds 70 mol%, there is a side effect of increasing the refractive index of the fluoropolymer. On the other hand, if it is less than 5 mol%, there is a side effect that the ethylenically unsaturated group may not be sufficiently introduced.

(3) Ethylenically unsaturated group-containing fluoropolymer:
The (A) component ethylenically unsaturated group-containing fluoropolymer is a compound containing a hydroxyl group, an ethylenically unsaturated group and an isocyanate group in the structural unit (c ′) of the hydroxyl group-containing fluoropolymer. It is obtained by reacting with a reactive group such as an isocyanate group. In this case, the number of moles of isocyanate groups contained in the compound containing an ethylenically unsaturated group and an isocyanate group is 0.5 to 1.0 times the number of moles of hydroxyl groups contained in the hydroxyl group-containing fluoropolymer. It is preferable.

  Accordingly, (A) the ethylenically unsaturated group-containing fluoropolymer is a structural unit of a hydroxyl group-containing fluoropolymer in addition to the structural unit (a) and the structural unit (b) derived from the hydroxyl group-containing fluoropolymer. c ′) has the following structural unit (c) produced by reacting with a compound containing an ethylenically unsaturated group and an isocyanate group.

Structural unit (c);

[In Formula (3), R ⁴ represents a hydrogen atom or a methyl group, R ⁵ represents a group represented by the following Formula (4) or (5), and v represents 1 to 20.

(In formulas (4) and (5), R ⁶ represents a hydrogen atom or a methyl group)]

The content of the structural unit (a) in the ethylenically unsaturated group-containing fluorine-containing copolymer is the same as that of the hydroxyl group-containing fluorine-containing copolymer, and the structural units (a), (b) and (c ) Is 100-mol%, it is 20-70 mol%, preferably 30-60 mol%, more preferably 35-60 mol%.
The content of the structural unit (b) in the ethylenically unsaturated group-containing fluorine-containing copolymer is the same as that of the hydroxyl group-containing fluorine-containing copolymer, and the structural units (a), (b) and (c ) Is 100 to 70 mol%, preferably 20 to 60 mol%, more preferably 20 to 55 mol%.
The content of the structural unit (c) in the ethylenically unsaturated group-containing fluorine-containing copolymer is the same as that of the hydroxyl group-containing fluorine-containing copolymer, and the structural units (a), (b) and (c ) Is 25 to 70 mol%, preferably 5 to 40 mol%, and more preferably 5 to 20 mol%. When the content of the structural unit (c) exceeds 70 mol%, there is a side effect of increasing the refractive index of the fluoropolymer. On the other hand, if it is less than 5 mol%, the physical strength of the cured product tends to decrease.

The molecular weight of the ethylenically unsaturated group-containing fluorine-containing copolymer is preferably 5,000 to 500,000 as a polystyrene-equivalent number average molecular weight measured with tetrahydrofuran as a solvent by gel permeation chromatography (GPC). This is because when the number average molecular weight is less than 5,000, the mechanical strength of the cured product may be reduced. On the other hand, when the number average molecular weight exceeds 500,000, This is because the viscosity increases and coating may become difficult.
For these reasons, the number average molecular weight in terms of polystyrene of the ethylenically unsaturated group-containing fluorine-containing copolymer is more preferably 10,000 to 300,000, and is preferably 10,000 to 100,000. Is more preferable.

  These (A) component ethylenically unsaturated group-containing fluorine-containing copolymers are usually blended in an amount of 20 to 65 mass% with respect to the sum of (A), (B), (C) and (D). Desirably, more preferably 20 to 50% by mass, and particularly preferably 30 to 40% by mass. If it is less than 20% by mass, the viscosity of the curable resin composition tends to be too low, so that the applicability at the time of optical fiber production tends to be reduced. As a result of the compression, the solubility of the component (A) may be reduced, and it may be difficult to obtain a highly transparent cured product.

(B) component:
(B) A component is a compound represented by following formula (10).
^{_{CH 2 = CR 8 COO (CH}} 2) x (CF 2) y X (10)
[Wherein R ⁸ represents a hydrogen atom or a methyl group, X represents a hydrogen atom or a fluorine atom, x represents 1 to 2, and y represents 2 to 8]

  (B) A component is mix | blended in order to reduce the refractive index of hardened | cured material other than the objective of ensuring the solubility of (A) component with (C) component mentioned later. Specific examples of the component (B) are not particularly limited as long as they are compounds corresponding to the above formula (10), but 2-perfluorooctylethyl (meth) acrylate, 2,2,3,3, -tetrafluoropropyl (Meth) acrylate, 1H, 1H, 5H-octafluoropentyl (meth) acrylate and the like can be mentioned. Examples of these commercially available products include Biscote 17F, 4F, 8F, etc. (manufactured by Osaka Organic Chemical Industry Co., Ltd.). Among these, 2-perfluorooctylethyl (meth) acrylate is preferable because it is suitable for dissolving the component (A) and is easily available.

  The component (B) is preferably blended in an amount of usually 20 to 60% by mass, more preferably 20 to 50% by mass, based on the sum of (A), (B), (C) and (D). Preferably it is 20-45 mass%. If it is less than 20% by mass, the solubility of the component (A) is impaired, and the refractive index of the cured product may increase. If it exceeds 70% by mass, the viscosity of the curable resin composition decreases, The applicability is impaired.

  The compatibility between the (A) component ethylenically unsaturated group-containing fluorine-containing copolymer and the (meth) acrylate monomer is limited in many cases, but the (B) component and the later-described (C) component By mixing with a combination, solubility is improved and a uniform curable resin composition can be obtained. In particular, the mixing ratio of the component (B) and the component (C) is preferably 2: 3 to 5: 1 as a mass ratio, and more preferably 2: 3 to 4: 1.

(C) Compound having no aromatic structure and no polar group and having a monofunctional or bifunctional ethylenically unsaturated group:
The component (C) blended in the curable resin composition is a component other than the component (A) and the component (B), has no aromatic structure and a polar group, and is monofunctional or bifunctional ethylenically unsaturated. A compound having a group. Since the component (C) does not have a polar group, when used in combination with the component (B), the solubility of the component (A) is increased to give a uniform curable resin composition. Moreover, (C) component gives the hardened | cured material which has a low refractive index because it does not have an aromatic structure.
Here, the polar group includes polar groups such as a carbonyl group and an alkylene oxide group having 3 or less carbon atoms in addition to a dissociable group such as a carboxyl group and an amino group, but a hydroxyl group is excluded. The component (C) is not particularly limited as long as it has a structure that satisfies the above requirements.

Specific examples of the component (C) include vinyl group-containing lactams such as N-vinylpyrrolidone and N-vinylcaprolactam;
Vinyl ethers such as hydroxybutyl vinyl ether, lauryl vinyl ether, cetyl vinyl ether, 2-ethylhexyl vinyl ether;
Acrylamides such as diacetone (meth) acrylamide, isobutoxymethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide t-octyl (meth) acrylamide;
Alicyclic structure-containing (meth) acrylates such as isobornyl (meth) acrylate, bornyl (meth) acrylate, tricyclodecanyl (meth) acrylate, dicyclopentanyl (meth) acrylate, 4-butylcyclohexyl (meth) acrylate;
2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate , Butyl (meth) acrylate, amyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate , Octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meta Acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (Meth) acrylate, neopentyl glycol di (meth) acrylate, neopentyl glycol hydroxypivalate ester di (meth) acrylate, trimethylolpropane trioxyethyl (meth) acrylate, polyester di (meth) acrylate, 1,4-butanediol Examples include aliphatic structure-containing (meth) acrylates such as di (meth) acrylate and 1,6-hexanediol di (meth) acrylate.

  Among the components (C) listed above, monofunctional or bifunctional aliphatic structure-containing (meth) acrylates are preferable, and neopentyl glycol di (meth) acrylate or neopentyl glycol hydroxypivalate ester di (meth) acrylate is preferable. Particularly preferred. (C) A component may be used individually by 1 type and may use 2 or more types together.

  The component (C) is desirably blended usually in an amount of 10 to 35% by mass, more preferably 15 to 35% by mass, based on the sum of (A), (B), (C) and (D). Preferably it is 15-30 mass%. If the amount is less than 10% by mass, the solubility of the component (A) may be impaired. If the amount exceeds 35% by mass, the blending amount of the component (A) and the component (B) is compressed. The rate increases and the adhesion to the core layer is impaired.

(D) (Meth) acrylic acid or its dimer (D) By mix | blending a (D) component, the adhesiveness of a core layer, especially the core layer which consists of glass or quartz, and a clad layer can be improved. The component (D) is usually blended in an amount of 0 to 10% by mass, preferably 1 to 7% by mass, based on the sum of (A), (B), (C) and (D). When it exceeds 10 mass%, the storage stability of the curable resin composition may be impaired.

  The curable resin composition preferably contains (E) a photopolymerization initiator in addition to the component serving as the base resin.

  Specific examples of (E) photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3 -Methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1- (4-isopropylphenyl) -2- Hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthioxanthate 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis- (2,6 -Dimethoxybenzoyl) -2,4,4-trimethylpentyl phosphine oxide; IRGACURE 184, 369, 651, 500, 907, CGI 1700, CGI 1750, CGI 1850, CG 24-61; Darocur 1116, 1173 Lucirin TPO (manufactured by BASF); Ubekrill P36 (manufactured by UCB) and the like.

  (E) When using a photoinitiator, a photosensitizer can also be used together. Examples of the photosensitizer include triethylamine, diethylamine, N-methyldiethanolamine, ethanolamine, 4-dimethylaminobenzoic acid, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, and 4-dimethylaminobenzoic acid. Isoamyl; Ubekryl P102, 103, 104, 105 (above, manufactured by UCB) and the like. (E) It is preferable to mix | blend a polymerization initiator 0.1-10 mass% with respect to curable resin composition whole quantity, especially 0.3-7 mass%.

  In the curable resin composition, various additives, for example, an antioxidant, a colorant, an ultraviolet absorber, a light stabilizer, a silane coupling agent, and a thermal polymerization, as long as they do not impair the characteristics of the present invention. Inhibitors, leveling agents, surfactants, storage stabilizers, plasticizers, lubricants, solvents, fillers, anti-aging agents, wettability improvers, coating surface improvers and the like can be blended.

  Hereinafter, the results of evaluation tests using examples and comparative examples according to the present invention will be shown, and the present invention will be described in more detail. The present invention is not limited to these examples.

[Production of plastic clad optical fiber cord]
A plastic clad optical fiber having an outer diameter of the core layer 2 of 80 μm, an outer diameter of the cladding layer 3 of 125 μm, an overcladding layer made of ETFE of 250 μm, an outer diameter of the core layer 2 of 200 μm, and an outer diameter of the cladding layer 3 A plastic clad optical fiber having a diameter of 230 μm and an overcladding layer made of ETFE having an outer diameter of 500 μm was produced. The prepared plastic clad optical fiber was further coated with an outermost layer of 2 mm in outer diameter made of polyvinyl chloride, which is a thermoplastic resin, to produce a plastic clad optical fiber cord.
The curable composition for constituting the cladding layer 3 was prepared by mixing the materials shown below with the formulation shown in Table 1.

(Base resin; common to all examples)
Ethylenically unsaturated group-containing fluoropolymer 35 parts by weight 2-perfluorooctylethyl methacrylate 45 parts by weight Neopentyl glycol diacrylate 16 parts by weight Acrylic acid 4 parts by weight

(Trifunctional or higher monomer)
Trimethylolpropane triacrylate (TMPTA) (trifunctional),
Pentaerythritol tetraacrylate (PETA) (tetrafunctional)
Or dipentaerythritol hexaacrylate (DPHA) (hexafunctional)

(Additive; common to all examples)
Photopolymerization initiator Antioxidant Silane coupling agent Thermal polymerization inhibitor It should be noted that the additives were adjusted to be contained in a total of several parts by weight with respect to 100 parts by weight of the base resin.

[Measurement of equilibrium elastic modulus]
The equilibrium elastic moduli of the obtained clad materials of Examples and Comparative Examples were evaluated by the following methods.

A sample for measuring the dynamic viscoelasticity of the equilibrium elastic modulus was prepared as follows.
A stainless steel plate having a flat surface, the temperature of which was controlled at 40 to 42 ° C., was used as a mold, and each resin composition adjusted to 40 to 42 ° C. was applied to the mold surface so as to have a thickness of 200 μm. Using a metal halide type ultraviolet lamp, irradiation was performed under conditions of an integrated light amount of 2000 mJ / cm ² and a peak illuminance of 250 mW / cm ² to cure the resin composition, and then the cured product was peeled off to obtain a measurement sample. It was.

  The obtained sample was formed into a 30 mm × 3 mm × 0.2 mm strip, and the storage elastic modulus was measured by applying a 0.05% load strain to the sample using a dynamic viscoelasticity measuring device. . The frequency was 3.5 Hz, and the temperature range was −100 to 180 ° C. (temperature increase rate of 3 ° C./min). By this measurement, a temperature dependence curve of the storage elastic modulus was obtained. The value obtained when the value of the storage elastic modulus became almost constant regardless of the temperature was taken as the equilibrium elastic modulus.

[Measurement of increase in transmission loss]
About each plastic clad optical fiber cord of the obtained Example and the comparative example, the transmission loss increase amount was evaluated by the following method.
First, the plastic clad optical fiber cords of Examples and Comparative Examples were allowed to stand for 1500 hours at 85 ° C. and 85% RH, and the increase in transmission loss at 650 nm was measured at room temperature. +5.0 dB / km or less was regarded as acceptable.

  In each example and comparative example, a thin fiber with a core diameter of 80 μm and a normal fiber with a core diameter of 200 μm were measured. The results were similar for any fiber diameter. The results are summarized in Table 1.

  Examples 1-5 were good. The polyvinyl chloride resin contained a plasticizer, but the plasticizer did not reach the optical path of the clad layer even in a humid heat environment, and it is considered that a scatterer that diffuses light was not formed.

In Comparative Example 1, a trifunctional or higher monomer is not added and the equilibrium elastic modulus of the cladding layer is small. And the transmission loss increase amount is large. The reason is that the plasticizer from the outermost PVC layer of the optical cord reaches the cladding layer through the ETFE layer, and the refractive index of the cladding layer becomes non-uniform due to decomposition of the cladding layer or aggregation of fluorine atoms. it is conceivable that.
In Comparative Example 2, a trifunctional or higher monomer is added too much and the equilibrium elastic modulus of the cladding layer is too large. And the increase in transmission loss was remarkably large after the wet heat test, the signal could not be measured, and the loss value could not be obtained. As a result of excessive addition of a trifunctional or higher monomer, the cure shrinkage of the clad layer is large, and minute cracks in the clad layer are considered to cause the loss increase.

DESCRIPTION OF SYMBOLS 1 ... Plastic clad optical fiber, 2 ... Core layer, 3 ... Cladding layer, Tg ... Glass transition temperature, T1 ... Equilibrium temperature, G1 ... Equilibrium elastic modulus

Claims (4)

  A plastic clad optical fiber having a clad layer formed by curing a curable resin composition on the outer periphery of a core layer made of quartz glass, wherein the clad layer has an equilibrium elastic modulus of 30 MPa to 35 MPa. A plastic clad optical fiber characterized by that.   The curable resin composition for forming the clad layer contains a trifunctional or higher monomer in an amount of 0.5 to 13 parts by weight with respect to 100 parts by weight of a base resin composed of a monomer other than the trifunctional or higher monomer. Item 9. A plastic clad optical fiber according to Item 1. The plastic clad optical fiber according to claim 2, wherein the tri- or higher functional monomer has 3 to 6 functional groups represented by the following formula in the molecule.

  4. The plastic clad optical fiber according to claim 1, wherein the core layer has a diameter of 50 μm to 200 μm and the clad layer has a thickness of 80 μm to 250 μm.

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