JPS6367165B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a light transmitting fiber,
More specifically, the present invention relates to a step-index type plastic optical fiber having excellent heat resistance.

(Technical Background) Inorganic glass optical fibers having excellent optical transmission properties over a wide range of wavelengths have been known as optical fibers. However, glass fibers have poor processability, are susceptible to bending stress, and are also expensive, so light transmitting fibers based on synthetic resins have been developed. Light transmitting fibers made of synthetic resin have a core component that is a polymer that has a high refractive index and good light transmittance, and a sheath component that is a transparent polymer that has a lower refractive index than the core component polymer. As,
It is obtained by producing fibers with a core-sheath dual structure. The polymer useful as a core component with high light transparency is preferably an amorphous material, and polymethyl methacrylate or polystyrene is generally used.

Among these, polymethyl methacrylate has excellent not only transparency but also mechanical properties and weather resistance, and is therefore used industrially as a core material for high-performance plastic optical fibers, and is used for short-distance optical communications, optical sensors, etc. Application development is progressing in the following fields. However, polymethyl methacrylate has a heat distortion temperature of 100
Since the heat resistance is not sufficient at around 100°C, there are many fields in which its application is restricted, and therefore there is a strong demand for improved heat resistance.

The following methods are known for improving the heat resistance of methacrylic resins.

(1) A method of copolymerizing methyl methacrylate and α-methylstyrene.

(2) A method in which poly-α-methylstyrene is dissolved in methyl methacrylate monomer and then methyl methacrylate is polymerized (Special Publication No. 43-1616,
No. 49-8718).

(3) Method of copolymerizing methyl methacrylate and N-allyl maleic acid imide (Japanese Patent Publication No. 43-9753
issue).

(4) Methyl methacrylate/α-methylstyrene/
A method of copolymerizing maleimide.

and (5) a method of polymerizing methyl methacrylate in the presence of a crosslinked polymer using a polyfunctional monomer (JP-A-48-95490, JP-A-48-95491).

However, in these conventional methods, although the heat resistance of the obtained polymer is improved, the one-sided polymerization rate is extremely low, resulting in a significant decrease in productivity and the resulting polymer is impractical. The mechanical properties of the material are insufficient, the optical properties are insufficient, the material is markedly colored when molded, or the moldability is low, making it impossible to put it into practical use. It's not up to the level you deserve.

(Objective of the Invention) The object of the present invention is to have not only excellent optical properties, mechanical properties, weather resistance, and moldability comparable to polymethacrylic acid ester resins, but also excellent heat resistance and moldability. The object of the present invention is to provide a light transmitting fiber having excellent light transmitting properties, which is composed of a core component polymer having high productivity and a sheath component polymer having excellent heat resistance and transparency.

(Structure of the Invention) As a result of intensive studies to achieve the above object, the present inventors have discovered that a polymer containing a ring structural unit composed of methacrylimide has excellent properties that could not be achieved with conventional copolymer resins. It exhibits excellent heat resistance, moldability, light transmission, and mechanical properties, as well as excellent productivity. By using a core component polymer with these excellent properties, it is possible to balance various performances. It has been discovered that a fiber with excellent optical transmission properties can be obtained.

That is, the present invention has the following formula: A core component substantially comprising a polymer consisting of 2% by weight or more of ring structural units represented by and 98% by weight or less of monomer units mainly composed of methyl methacrylate, and the core component is coated, The light transmitting fiber comprises a sheath component made of a polymer having a refractive index that is 1% or more lower than the refractive index of the core component polymer.

In the light transmitting fiber of the present invention, the core component polymer consists essentially of 2% by weight or more of methacrylimide ring structural units represented by the formula () and 98% by weight or less of monomer units mainly composed of methyl methacrylate. It is a polymer consisting of Among the above components, the methacrylimide ring structural unit is a component necessary for maintaining heat resistance and optical properties as a light transmitting fiber, and its content must be 2% by weight or more. In order to obtain especially excellent heat resistance, it is preferable to use 10% by weight or more. This is because if the methacrylimide ring structural unit content is less than 2% by weight, the effect of improving the heat resistance of the resulting polymer will be insufficient.

On the other hand, the methyl methacrylate component is a component necessary for maintaining basic optical properties, weather resistance, and mechanical properties as a light transmitting fiber.

The monomer component containing methyl methacrylate as a main component includes, in addition to methyl methacrylate, a small amount, preferably 20% by weight or less, of other components, such as methyl acrylate, ethyl methacrylate, butyl methacrylate, and cyclohexyl methacrylate. , benzyl methacrylate, methacrylic acid, acrylic acid, styrene, α-methylstyrene, and the like.

In addition to these copolymerized components, the following components may be included in an amount of 20% by weight or less.

Monomers with ethylenic double bonds such as methacrylic acid, acrylic acid, methyl acrylate, ethyl acrylate and vinyl acetate, as well as divinylbenzene, triallyl cyanurate, triallyl isocyanurate, ethylene glycol dimethacrylate, tri- It may consist of one or more types selected from polyfunctional reactive monomers such as ethylene glycol dimethacrylate and trimethylolpropane trimethacrylate.

To produce the core component polymer of the light transmitting fiber of the present invention, the copolymer containing polymethyl methacrylate or a methyl methacrylate monomer as a main component, an imidizing agent, such as anhydrous ammonia, an aqueous ammonia solution, and The desired methacrylimide polymer can be obtained by carrying out a heating condensation reaction with urea or the like that generates ammonia through a heating reaction.
The heat treatment temperature when producing the methacrylimide component of the present invention is in the temperature range of 100°C or higher, particularly 130 to 450°C, preferably 150 to 300°C, and nitrogen, argon, etc. Preferably, the heat treatment is carried out in an autoclave under an inert gas atmosphere.

Furthermore, in order to prevent thermal deterioration of the polymer during this heating reaction, it is also possible to add a thermal deterioration inhibitor such as an antioxidant.

The antioxidants mentioned here include phosphite-based antioxidants, hindered phenol-based antioxidants, sulfur-based antioxidants, amine-based antioxidants, and the like.

Specific examples of phosphite-based antioxidants include phosphite-based antioxidants, such as tricresyl phosphite, cresyl phenyl phosphite, tributyl phosphite, and tributoxyethyl phosphite.

Specific examples of hindered phenolic antioxidants include hydroxynon, cresol, and phenol derivatives.

Examples of sulfur-based antioxidants include alkyl mercaptans and dialkyl disulfide derivatives.

Examples of amine antioxidants include naphthylamine,
Examples include phenylenediamine and hydroquinoline derivatives.

To prepare polymethyl methacrylate or a polymer mainly composed of polymethyl methacrylate, which is the raw material for obtaining the above-mentioned methacrylimide component, conventional radical polymerization methods, ionic polymerization methods, etc. can be used. Radical polymerization is preferred from the viewpoint of properties.

The polymerization catalyst used to obtain the above polymer is one used in general radical polymerization, such as azobis-based catalysts such as azobisisobutyronitrile and 2,2'-azobis-(2,4-dimethylvaleronitrile). The catalyst can be selected from diacyl peroxide catalysts such as lauroyl peroxide, benzoyl peroxide, bis(3,5,5-trimethylhexanoyl) peroxide, and percarbonate catalysts.

In the light transmitting fiber of the present invention, the core component is covered with a sheath component. The sheath component is formed of a polymer having a refractive index that is at least 1% less than the refractive index of the core component copolymer. This polymer preferably has a glass transition point of 80° C. or higher and is substantially transparent.

As the sheath component polymer, for example, Japanese Patent Publication No. 43-8978
Polymers of fluorinated alcohol esters of methacrylic acid as described in Japanese Patent Publication No. 56-8321, Japanese Patent Publication No. 56-8322, Japanese Patent Publication No. 56-8323, and Japanese Patent Publication No. 53-60243, etc. and Special Public Interest Publication No. 53-42260
copolymers of vinylidene fluoride and tetrafluoroethylene, polymethyl methacrylate, polyvinylidene fluoride, polyvinyl fluoride, ethylene tetrafluoride, propylene hexafluoride copolymers, polysiloxanes, as described in It can be selected from poly-4-methylpentene-1, ethylene-vinyl acetate copolymer, and the like. The methacrylic acid-fluorinated alcohol ester has the following general formula: and [However, in the above formula, X represents an H, F or Cl atom, n represents an integer of 1 to 6, m represents an integer of 1 to 10, l represents an integer of 1 to 10, R ₁ and _R2
each represents an H atom or a CH ₃ , C ₂ H ₅ or CF ₃ group] There is a compound represented by the following. Such methacrylic acid fluoroalkyl ester may be polymerized alone or may be copolymerized with other polymerizable vinyl monomers. Such vinyl monomers include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, glycidyl methacrylate, methacrylic acid, acrylic acid,
Maleic anhydride, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, glycidyl methacrylate, glycidyl acrylate, styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, p-chloro Examples include styrene, 2,4-dichlorostyrene, p-methoxystyrene, acrylonitrile, methacrylonitrile, vinyl acetate, methyl vinyl ketone, hydroxypropyl acrylate, hydroxyethyl acrylate, and the like. Two types of these monomers may be combined and copolymerized. Among them, methyl methacrylate is particularly preferred from the standpoint of providing a transparent copolymer.

The sheath component polymer is produced by radical polymerization of polymerization components by a conventional method. As the polymerization catalyst at this time, an ordinary radical polymerization initiator can be used, and specific examples include, for example, di-tert
-Butyl peroxide, dicumyl peroxide,
Methyl ethyl ketone peroxide, tert-butyl perphthalate, tert-butyl perbenzoate, methyl isobutyl ketone peroxide, lauroyl peroxide, cyclohexane peroxide, 2,5-dimethyl-2,5-di-tert-butyl peroxyhexane, tert-butyl peroctano ate, tert-butyl perisobutyrate,
Organic peroxides such as tert-butylperoxyisopropyl carbonate, methyl 2,2'-azobisisobutyrate, 1,1'-azobiscyclohexanecarbonitrile, 2-phenylazo2,4-dimethyl-4-methoxyvaleronitrile , 2-carbamoyl-azobisisobutyronitrile, 2,2'-
azobis-2,4-dimethylpereronitrile,
Examples include azo compounds such as 2,2'-azobisisobutyronitrile.

Examples of polymerization methods include emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization, and bulk polymerization is preferred in order to obtain a highly pure polymer.

In the light transmitting fiber of the present invention, it is necessary that the refractive index value of the sheath component is at least 1% smaller than that of the core component. The difference in refractive index between both components is 1
When the amount is less than %, the openings of the light transmitting fiber obtained will be too small, making it difficult to use practically. Also,
If the refractive index of the sheath component is greater than that of the core component, the resulting fiber will not transmit light.

Since light transmitting fibers may be exposed to high temperatures for long periods of time, it is preferred that they have good durability under such conditions. For this purpose, it is desirable that the sheath component polymer has a heat distortion temperature as high as possible, preferably 70°C or higher, more preferably 90°C or higher. For this reason, the sheath component polymer preferably has a glass transition point of 80°C or higher.

The step index type light transmitting fiber of the present invention is manufactured by the method described below.

(1) A composite spinning method in which a core component copolymer and a sheath component polymer are each melted and extruded into a core-sheath structure through a special nozzle.

(2) A coating method in which core component fibers are formed from a core component copolymer, coated with a solution of a sheath component polymer, and then the solvent is removed from this coating layer.

When forming the core component, the core component polymer may be continuously polymerized in bulk according to the method disclosed in Japanese Patent Publication No. 48-131391, and then this may be spun to form the core component fiber. good. This method is effective in reducing the loss of optical transmission performance of the core component.

(Effects of the Invention) The light transmitting fiber of the present invention is significantly superior in heat resistance and durability compared to conventional plastic light transmitting fibers containing polymethyl methacrylate or polystyrene as a core component.

Furthermore, the optically transmitting fiber of the present invention is relatively inexpensive, easy to handle, and has an extremely well-balanced variety of properties.

Therefore, the optically transmitting fiber of the present invention can be used for wiring in the engine compartment of a car, and therefore has extremely high industrial significance and value as it can respond to the advancement of car electronics. be.

The features and effects of the present invention as described above will be further explained with reference to Examples.

(Embodiments of the invention) In the examples, the optical transmission performance of the fiber is
Measurement and evaluation were carried out using the apparatus shown in Figure 4 of Publication No. 58-7602. The measurement conditions are as follows: Interference filter (main wavelength) 650 μm I ₀ (total length of fiber) 5 ml (cut length of fiber) 4 m D (diameter of bobbin) 190 mm represents parts by weight.

Example 1 After adding and dissolving 0.75 parts of tert-dodecyl mercaptan and 0.3 parts of lauroyl peroxide to 100 parts of methyl methacrylate, a glass plate was formed with two tempered glass plates facing each other with a gap of 3 mm through a polyvinyl chloride gasket. Set the thermocouple on the cell,
The above monomer solution was poured into this cell, and the cell was immersed in warm water at 80°C to polymerize and harden.

After immersing it in hot water, after the internal temperature reaches its peak due to polymerization exotherm, take it out from the hot water 30 minutes later.
Then, it was heat treated in an air heating furnace at 120°C for 2 hours.

After cooling, the cells were removed and the resulting resin plate with a thickness of about 6 mm was crushed in a clean box. The obtained polymer had an MI value (measured at 230°C under a load of 3.8 kg) of 11.5, a refractive index _nD of 1.4920, a specific gravity of 1.190,
The heat distortion temperature was 105°C. For 100 parts of this polymer, 9 parts of urea, 2.7 parts of water, and 0.01 part of Antige BHT (manufactured by Kawaguchi Kogyo Co., Ltd., 2,6-di-tert-butyl p-cresol) were charged into a 3-autoclave, and the mixture was replaced with nitrogen. The reaction was repeated by heating in a 230° C. oil bath for 4 hours to obtain a transparent resin body, methacrylimide-methyl methacrylate copolymer. The infrared absorption spectrum showed absorption characteristic of methacrylimide at 1680 cm ^-1 and 1210 cm ^-1 .

MI value of the obtained polymer (3.8Kg at 230℃
) is 4.0, refractive index 1.536, density
1.237, and the heat distortion temperature was 170℃.

The imidization rate measured from infrared absorption spectrum was 5.3%.

Separately, 50 parts of 2,2,2-trifluoroethyl methacrylate, 50 parts of methyl methacrylate, and 0.3 parts of n-octyl mercaptan were mixed and dissolved, and then 0.025 parts of azobisbutyronitrile was added and dissolved as a polymerization catalyst. The above mixture was then injected into a cell formed of two tempered glass plates facing each other at a 5 mm interval through a polyvinyl chloride gasket, and immersed in hot water at 70°C to polymerize and harden. Thirty minutes after reaching the peak temperature due to polymerization exotherm, the cell was taken out of the hot water and then heat treated in an air heating oven at 130°C for 2 hours. After cooling, the cell was removed and the resulting resin plate was crushed in a clean box, with an MI value (230℃, load 3.8Kg) of 5.0 and a refractive index n _D
A sheath component polymer with a heat distortion temperature of 1.445 and a heat distortion temperature HDT of 98°C was obtained.

The obtained core and sheath component polymers are
Supplied to a vented composite spinning machine with a two-layer sheath spinneret, spinning temperature 260℃, spinning speed 3m/min.
The film was then drawn up at 200°C, then continuously stretched 2.0 times at 200°C and rolled up.

The obtained fiber had a core component diameter of 980 μm, a sheath component thickness of 10 μm, and a weight ratio of core component to sheath component of 96:4.
It was a light transmitting fiber with a concentric structure.

The optical transmission loss of this optical transmission fiber is 890dB/Km
It was capable of sufficiently transmitting optical signals over a length of 10 meters.

The obtained light transmitting fibers are processed using a crosshead type cable processing machine, using aromatic polyamide fibers (Kevlar) as the first reinforcing fibers, and polyethylene with carbon black as the jacket polymer.
A second jacket was coated with polyester elastomer containing carbon black so as to have an outer diameter of 2.2 mm, thereby obtaining an optical cable with an optical transmission loss of 1050 dB/Km.

Cut 10m of this optical cable and fix one end to a light source (using a 650μm interference filter).
The other end was connected and fixed to a photodiode, and the 5 m middle portion of the optical cable was exposed to a hot air heating furnace at 130°C. Changes in the amount of light transmitted were tracked to evaluate the heat resistance and durability of the optical cable.

As a result, this optical cable exhibited stable heat resistance and durability, with no decrease in light intensity observed even after 1000 hours had passed.

Example 2 An optical cable was obtained in exactly the same manner as in Example 1, except that the sheath component polymer was polyvinylidene fluoride (refractive index: 1.43).

The optical transmission loss of the obtained optical cable was 1530dB/
Km, but even after being exposed to a 160°C hot air heating furnace for 1000 hours, the light intensity decreased by only 4%, demonstrating excellent heat resistance and durability.

Example 3 The core component polymer obtained in Example 1 was spun using a pent-type spinning machine at a spinning temperature of 240°C and a spinning speed of 6 m/min.
Fiber containing only the core component (diameter 750 μm)
A precursor composition of polydimethylsiloxane (Shin-Etsu Silicone) is applied to the surface of this core component fiber.
After uniformly coating KE106LTU), 150
It was heated at ℃ for 10 minutes to form a polydimethylsiloxane film (refractive index: 1.42, thickness: 300 μm).

This optical fiber had an excellent optical transmission loss of 920 dB/Km, and exhibited extremely excellent heat resistance and durability, with a decrease in light intensity of 2% after exposure to 150°C for 1000 hours.

Example 4 Ammonia aqueous solution (40%) to 100 parts of polymethyl methacrylate obtained in Example 1
42.5g of the autoclave was charged into an autoclave, and the mixture was repeatedly purged with nitrogen and immersed in an oil bath at 230°C to react for 3 hours, yielding a transparent resin methacrylimide/methyl methacrylate copolymer.

The infrared absorption spectrum showed absorption characteristic of methacrylimide, and the imidization rate was 23%.

MI value of the obtained polymer (3.8Kg at 230℃
) is 6.2, refractive index 1.507, specific gravity
1.219, and the heat distortion temperature was 142°C.

This core component polymer was taken by a vent spinning machine at a spinning temperature of 240°C and a spinning speed of 6 m/min to obtain a fiber (diameter 750 μm) consisting only of the core component, and a precursor composition of polydimethylsiloxane was applied to the surface of the core component fiber. After uniformly coating a material (KE106LTU from Shin-Etsu Silicon Co., Ltd.), it was heated at 150℃ for 10 minutes to form a polydimethylsiloxane coating (refractive index 1.42, thickness 300μ).
m) was formed.

This optical fiber had an excellent optical transmission loss of 850 dB/Km, and exhibited excellent heat resistance and durability, with a decrease rate of light intensity of 1% after 1000 hours of exposure at 130°C.

Example 5 80 parts of methyl methacrylate, 10 parts of methacrylic acid,
Add and dissolve 10 parts of tert-butyl methacrylate, 0.75 parts of tert-dodecyl mercaptan and 0.4 parts of lauroyl peroxide, and use the same method as in Example 4 to obtain a copolymer of methyl methacrylate, tert-butyl methacrylate, and methacrylic acid. Ta.

A methacrylimide-methyl methacrylate copolymer was produced in exactly the same manner as the imidization method in Example 4.

The obtained polymer had an MI value (measured at 230°C under a load of 3.8 kg) of 7.0, a refractive index of 1.530, a specific gravity of 1.235,
The heat distortion temperature was 170℃.

The imidization rate from the infrared absorption spectrum was 47%.

In the same manner as in Example 4, fibers consisting only of the core component and sheath material were shaped.

This optical fiber has an excellent optical transmission loss of 970 dB/Km, and the decrease rate of light intensity after 1000 hours of exposure at 150°C was 1.0%, demonstrating excellent heat resistance and durability.

Comparative Example 1 The polymethyl methacrylate obtained in Example 1 was used as it was, and a sheath material according to Example 1 was used and supplied to a vented composite spinning machine, and the spinning temperature was 240°C.
Take off at a spinning speed of 3 m/min, and then continue
It was stretched 2.0 times at 140°C and rolled.

The obtained fiber has a core component diameter of 980 μm and a sheath component thickness.
It was 10 μm.

The optical transmission loss of this optical transmission fiber was 170 dB/Km.

After jacket coating processing similar to Example 1
When an exposure test was conducted at 120°C for 1000 hours, the light intensity decreased significantly, by 100%, and optical transmission was impossible.

Claims (1)

[Claims] 1 Formula: A core component substantially comprising a polymer consisting of 2% by weight or more of ring structural units represented by and 98% by weight or less of monomer units mainly composed of methyl methacrylate, and the core component is coated, A light transmitting fiber comprising a sheath component made of a polymer having a refractive index that is 1% or more lower than the refractive index of the core component polymer.