Title of Invention

A PROCESS OF PREPARING A RESIN COMPOSITION FOR OPTICAL FIBER LOOSE TUBES

Abstract

There is provided a resin composition for optical fiber loose tubes which enables the production of both colored loose tubes and non-colored loose tubes under the same extrusion molding conditions, even the production of optical fiber loose tubes of the same quality, particularly the same quality in terms of extra length and post-shrinkage, and has excellent hydrolysis resistance as well as an optical fiber loose tube. The resin composition is obtained by blending a master batch (A) produced by melt kneading 100 parts by weight of (a) polybutylene terephthalate and 0.1 to 5 parts by weight of (b) a crystal nucleating agent with polybutylene terephthalate (B) in an amount 10 to 100 times the weight of the master batch. The amount of the crystal nucleating agent is 0.01 to 0.5 wt% based on the total amount of the resin composition and the polybutylene terephthalate (B) has a terminal carboxyl group concentration of 30 eq/ton or less and an intrinsic viscosity of 1.0 to 1.2.

Full Text

[Field of the Invention] The present invention relates to a resin composition for optical fiber loose tubes which has excellent hydrolysis resistance and little variations in characteristic properties caused by coloration and to an optical fiber loose tube. More specifically, it relates to a resin composition for optical fiber loose tubes which enables the production of optical fiber loose tubes having the same characteristic properties without changing extrusion production conditions whether they are colored or not colored. [Prior Art] An optical fiber loose tube (may be referred to as "loose tube" hereinafter) contains optical fibers loose therein and has a structure such as a jelly-like intimate mixture filled in a space therein. Some of the optical fiber loose tubes are tied up into an optical fiber cable. Heretofore, polybutylene terephthalate and compositions thereof have been widely used in the loose tube thanks to their excellent mechanical strength and chemical resistance. A loose tube constituting an optical fiber cable is generally colored for identification. A known method of coloring a loose tube is disclosed by JP-A 2-242210 (the term " JP-A" as used herein means an "unexamined published Japanese patent application"). An optical fiber cable generally contains colored optical fiber loose tubes (may be referred to as "colored loose tubes" hereinafter) and non-colored, that is, natural colored optical fiber loose tubes (may be referred to as "non-colored loose tubes" hereinafter). Preferably, glass fibers contained in the colored loose tubes and the non- colored loose tubes have the same extra length. Preferably, the colored loose tubes and the non-colored loose tubes have the same post-shrinkage. When the colored loose tube and the non-colored loose tube are produced under the same production conditions, glass fibers contained therein become different in extra length and the loose tubes also become different in post-shrinkage. The differences of extra length and post-shrinkage are observed between a colored loose tube and a non-colored loose tube, particularly marked between a colored loose tube colored by an inorganic pigment and a non-colored loose tube, further between colored loose tubes which differ from each other in the type and cunount of a colorant blended. The term "extra length" as used herein means the length of a glass fiber projecting from a loose tube when the loose tube containing the glass fiber is cut. When the extra length is small, tensile stress is applied to the fiber while optical fiber loose tubes are tied up into an optical fiber cable, fatigue proceeds, and the optical fiber may break after the passage of a certain period. When the extra length is large, flexure stress is applied to a glass fiber even with a loose tube structure, resulting in a large transmission loss. The term "post-shrinkage" as used herein means the shrinkage of a loose tube caused by the crystallization of a resin constituting the loose tube in a high-temperature high-humidity environment. When post-shrinkage is large, the size of the loose tube changes, thereby giving flexure stress to a glass fiber contained therein and further generating internal strain in an optical fiber cable itself with the result of great deterioration in performance. These problems can be eliminated by optimally controlling production conditions such as resin temperature, the temperature of a cooling water tank and the haul-off speed of a loose tube in the production process of the loose tube. In this case, the number of production control steps increases, thereby reducing productivity. That is, in the production of a loose tube, when production conditions are changed according to a colorant contained in the loose tube, production control becomes complicated and production efficiency greatly lowers. It is an object of the present invention to provide a process for preparing a resin composition for optical fiber loose tubes which enables the production of loose tubes under the same production conditions whether they are colored or non-colored, even the production of loose tubes having the same quality, particularly the same quality in terms of extra length and post-shrinkage, and has excellent hydrolysis resistance. It is another object of the present invention to provide an optical fiber loose tube which is formed from the resin composition for optical fiber loose tubes of the present invention. Other objects and advantages of the present invention will become apparent from the following description. Accordingly the present invention relates to a process of preparing a resin composition for optical fiber loose tubes comprising the step of blending (A) a master batch produced by melt kneading 100 parts by weight of (a) polybutylene terephthalate and 0.1 to 5 parts by weight of (b) a crystal nucleating agent with (B) polybutylene terephthalate in an amount 10 to 100 times the weight of the master batch, wherein the amount of the crystal nucleating agent (b) is 0.01 to 0.5 wt% based on the total amount of the resin composition and the polybutylene terephthalate (B) has a terminal carboxyl group concentration of 30 eq/ton or less and an intrinsic viscosity of 1.0 to 1.2. According to the present invention, secondly, the above objects and advantages of the present invention are attained by an optical fiber loose tube prepared by extrusion molding the resin composition of the present invention, wherein polybutylene terephthalate constituting the optical fiber loose tube has a terminal carboxyl group concentration of 30 eq/ton or less and an intrinsic viscosity of 1.0 to 1.2. The present Invention will be described in detail hereinafter. Polybutylene terephthalate la) The polybutylene terephthalate (a) is a polyester comprising terephthalic acid as the main acid component and 1.4-butanediol as the main glycol component. The expression "main" as used herein means that the component is contained in an amount of 80 mol% or more, preferably 90 mol% or more based on the total of all the dicarboxylic acid components or all the glycol components. The polybutylene terephthalate (a) encompasses not only a homopolymer but also a copolymer comprising a comonomer. When the comonomer is copolymerized, the proportion of the comonomer is 20 mol% or less, preferably 10 mol% or less based on the total of all the dicarboxylic acid components or all the glycol components. The copolymerizable acid component is an aromatic dicarboxylic acid other than terephthalic acid, such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ketone dicarboxylic acid or diphenylsulfone dicarboxylic acid; aliphatic dicarboxylic acid such as succinic acid, adipic acid or sebacic acid; or alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid, tetralindicarboxylic acid or decalindicarboxylic acid. The copolymerizable glycol component other than butanediol is ethylene glycol, hexamethylene glycol. neopentyl glycol, cyclohexane dimethanol, tricyclodecane dimethylol, xylylene glycol, bisphenol A, bisphenol B, bishydroxyethoxy bisphenol A or the like- A polyfunctional compound having a functionality of 3 or more, such as glycerin, trimethylol propane, pentaerythritol, trimellitic acid, trimesic acid or pyromellitic acid may be copolymerlzed in limits that the polyester does not lose its raoldability substantially. Crystal nucleating aoftnt (b^ The crystal nucleating agent (b) is either an organic crystal nucleating agent or inorganic crystal nucleating agent. They may be used alone or in admixture of two or more kinds of agents. The crystal nucleating agent preferably generates no scum. The scum is sublimate or volatile matter adhered to a dice portion. When the scum is formed, it falls off from the dice portion and adheres to a molten resin, thereby greatly impairing the quality of a loose tube. Examples of the organic crystal nucleating agent include the salt of at least one metal selected from the group I and II metals of the periodic table of carboxylic acid; polymers such as polyesters, polyethylene and polypropylene; and crosslinked polymers- They may be used alone or in admixture of two or more. Examples of the carboxylic acid of the above metal salt include aliphatic monocarboxylic acids such as acetic acid, propionic acid, caproic acid, palmitic acid, stearic acid, oleic acid, behenic acid, montanic acid, methacrylic acid and acrylic acid; aliphatic dicarboxylic acids such as oxalic acid, adipic acid, succinic acid, sebacic acid, maleic acid and fumaric acid; aromatic carboxylic acids such as benzoic acid, terephthalic acid and phthalic acid. Examples of the metal salt of the carboxylic acid include the salts of group I metals of the periodic table such as Na, K and Li; and the salts of metals such as Mg, Ca, Ba and Zn. In these carboxylic acid metal salts, all the carboxyl groups do not need to form a salt. Some of the carboxyl groups may be neutralized and the other carboxyl groups may remain in the form of an acid or ester. Examples of the inorganic nucleating agent preferably include clays such as talc, kaolin and clay; metal oxides jsuch as zinc oxide, titanium oxide, alumina and silica gel; nitrides such as silicon nitride and titanium nitride; and simple substances such as Zn powder, Al powder, graphite and carbon black. When a crystal nucleating agent is added, it is possible to make the crystallization rate of polybutylene terephthalate resin compositions constituting a colored loose tube and a non-colored loose tube close to the crystallization speed of a polybutylene terephthalate resin composition having a higher crystallization speed, thereby making it possible to achieve the same crystallization speed while producing loose tubes under the same production conditions. When a crystal nucleating agent is not added, the shrinkage behaviors of polybutylene terephthalate resin compositions constituting a colored loose tube and a non-colored loose tube cannot be made substantially the same, thereby making it impossible to achieve the same extra length and post-shrinkage. The amount of the crystal nucleating agent (b) is 0.1 to 5 parts by weight based on 100 parts by weight of polybutylene terephthalate (a) in the master batch and 0.01 to 0.5 wt% based on the resin composition for optical fiber loose tubes. When the amount of the crystal nucleating agent is smaller than 0.01 wt% based on the resin composition for optical fiber loose tubes, it is difficult to reduce the difference of crystallization speed between a colored loose / tube and a non-colored loose tube to such an extent that the same extra length and post-shrinkage can be obtained. When the amount is larger than 0.5 wt%, the mechanical properties such as elongation of an optical fiber loose tube are impaired. The crystal nucleating agent (b) is preferably talc, more preferably talc having an average particle diameter of 10 µm or less, particularly preferably talc which all passes through a 50 µm sieve and has an average particle diameter of 10 µm or less. When this talc is used, the effect of the crystal nucleating agent is good and the characteristic properties of polybutylene terephthalate are not impaired advantageously. When talc having an average particle diameter of more than 50 vmi is used, the elongation of the resulting loose tube lowers and when talc having an average particle diameter of more than 10 µm is used, the effect of the crystal nucleating agent becomes poor disadvantageously. The average particle diameter is a value measured with the SA-CP3L particle size distribution measuring instrument of Shimadzu Corporation* Polybutylene terephthalate (B) The polybutylene terephthalate (B) is a polyester comprising terephthalic acid as the main acid component and 1,4-butanediol as the main glycol component. The expression "main" as used herein means that the component is contained in an 2unount of 80 mol% or more, preferably 90 mol% or more based on the total of all the dicarboxylic acid components or all the glycol components. The polybutylene terephthalate (B) encompasses not only a homopolymer but also a copolymer comprising a comonomer. When the comonomer is copolymerized, the proportion of the comonomer is 20 mol% or less, preferably 10 mol% or less based on the total of all the dicarboxylic acid components or all the glycol components. The copolymerizable acid component is an aromatic dicarboxylic acid other than terephthalic acid, such as isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ketone dicarboxylic acid or diphenylsulfone dicarboxylic acid; aliphatic dicarboxylic acid such as succinic acid, adipic acid or sebacic acid; or alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid, tetralindicarboxylic acid or deoalindicarboxylic acid. The copolymerizable glycol component other than butanediol is ethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexane dimethanol, tricyclodecane dimethylol, xylylene glycol, bisphenol A, bisphenol B, bishydroxyethoxy bisphenol A or the like. A polyfunctional compound having a functionality of 3 or more, such as glycerin, trimethylol propane, pentaerythritol, trimellitic acid, trimesic acid or pyromellitic acid may be copolymerized in limits that the polyester does not loose its moldability substantially. The terminal carboxyl group concentration of polybutylene terephthalate (B) is 30 eq/ton or less, preferably 20 eq/ton or less, more preferably 10 eq/ton or less. When the terminal carboxyl group concentration is higher than 30 eq/ton, the obtained optical fiber loose tube is easily hydrolyzed. That is, hydrolysis resistance which is high enough to stand the use environment is impaired. In other words, when the terminal carboxyl group concentration is higher than 30 eq/ton, in a humidity resistance promotion deterioration test based on a pressure cooker test (test conditions: 121°C x 100 %RH x 80 hours) . the resulting optical fiber loose tube cannot have such hydrolysis resistance that intrinsic viscosity retention is 50 % or more, has low mechanical strength retention when it is used under high-temperature and high-humidity conditions and is easily cracked or broken by slight external force, thereby losing the function of protecting an optical fiber. The intrinsic viscosity of polybutylene terephthalate (B) is 1.0 to 1.2, preferably 1.1 to 1.2. When the intrinsic viscosity is lower than 1.0, the resulting composition deteriorates in moldability for the extrusion molding of a tube and does not have satisfactory shapability. Further when external force is applied, the obtained loose tube is easily cracked or broken, thereby impairing the function of protecting an optical fiber. When the intrinsic viscosity is higher than 1.2, the extrusion moldability of an optical fiber loose tube deteriorates and the production cost of polybutylene terephthalate boosts. The above polybutylene terephthalate (B) is preferably produced by solid-phase polymerization, more preferably the solid-phase polymerization of polybutylene terephthalate containing an alkaline metal compound in an amount of 20 wt%. The alkaline metal compound is the hydroxide, inorganic acid salt or organic acid salt such as acetate, carbonate or hydrate thereof, complex salt or ammonium salt of an alkali metal or alkali earth metal. They may be used alone or in combination of two or more. Illustrative examples of the alkaline metal compound include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, francium hydroxide, beryllium hydroxide, magnesium hydroxide, strontium hydroxide, barium hydroxide, lithium acetate, sodium acetate, potassium acetate, magnesium acetate, calcium acetate, lithium carbonate, sodium carbonate, potassium carbonate, lithium benzoate, sodium benzoate, potassium benzoate and the like. Out of these, sodium compounds and potassium compounds are preferred. The resin composition for optical fiber loose tubes may contain a colorant. The colorant is a dye or pigment. Known pigments and dyes which have been used to color thermoplastic resins may be used. The dye is preferably a dye which does not sublime or volatilize at 300'C or less, such as some of perinone-based and anthraquinone-based dyes. The pigment may be either organic or inorganic. Examples of the inorganic pigment include zinc oxide, titanium oxide, red oxide, chromium oxide, barium sulfate. Titanium Yellow, ultramarine blue, cobalt blue, cobalt green, iron blue, zinc yellow, chrome yellow, white lead, transparent iron oxide, aluminum powder and carbon black. Examples of the organic pigment include azo-, quinacridone-, anthraquinone-, perylene-, isoindolinone-, phthalocyanine-. dioxazine- indanthrene-, perinone-, quinophthalone-, triphenylmethane-, quinoline-, thioindigo-, dioxane- and metal complex salt-based organic pigments. These pigments may be used alone or in combination of two or more. The colorant may be suitably added in limits that a loose tube can be colored. Additives The resin composition for optical fiber loose tubes of the present invention may contain a hindered phenol compound, phosphorus-based compound and thioether-based compound to prevent oxidative deterioration under high-temperature and high-humidity conditions. Examples of the hindered phenol compound include 2,6-di-t-butyl-p-cresol, 2,2'-methylene-bis-(4-methyl-6-di-t-butylphenol), 4,4'-thiobis(3-methyl-t-butylphenol), 1,1,3- tris (2 -methyl- 4 -hydroxy- 5 -1 -butylphenyl') butane, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate. Examples of the phosphorus-based compound include phosphite-based organic compounds, phosphonite-based organic compounds, phosphoric acid esters, phosphorous acid esters, and metal salts of phosphoric acid and phosphorous acid. Examples of the thioether compound include di-tridecyl-thio-dipropionate, tetrakis[methylene-3-(dodecylthio)propionate], and bis[2-methyl-4-{3-n-alkyl (C12 or C14)thiopropionyloxy}-5-t-butylphenyl]sulfide. The resin composition of for optical fiber loose tubes of the present invention may further contain an ultraviolet light absorber which is generally used for fibers, films and resins, such as a benzophenone-based compound, triazole compound or salicylate compound; and others such as a lubricant, release agent, flame retardant and flame retarding aid- Optical fiber loose tube The terminal carboxyl group concentration of polybutylene terephthalate constituting an optical fiber loose tube is 30 eq/ton or less. When the terminal carboxyl group concentration is higher than 30 eq/ton, the obtained optical fiber loose tube is easily hydrolyzed. The intrinsic viscosity of polybutylene terephthalate constituting an optical fiber loose tube is 1.0 to 1.2. When the intrinsic viscosity is lower than 1.0, the tube is easily cracked or broken by external force. Process for producing master batch The master batch (A) may be produced by generally used methods . For example, the components of the master batch are blended together with a tumbler or V-shaped blender and the resulting blend is melt mixed with an extruder. To uniformly disperse a crystal nucleating agent, the component is preferably melt kneaded using an extruder having high kneading capability such as a twin-screw extruder. When a colorant is contained, a dispersant for well dispersing a colorant and a crystal nucleating agent into a resin composition is preferably added in a suitable amount to produce a master batch by melt kneading. Examples of the dispersant include aliphatic monocarboxylic acids such as polyethylene wax and montanic acid, esters thereof and salts thereof. The amount of the dispersant can be suitably determined according to the dispersibility of a colorant, Process for producing loose tube The resin composition for optical fiber loose tubes is obtained by blending the master batch (A) produced by the above process with polybutylene terephthalate (B) in an amount 10 to 100 times the weight of the master batch in the present invention. The obtained resin composition for optical fiber loose tubes is molten and kneaded using a general tube extrusion molding machine, extruded using a ring die and stretched to obtain a loose tube. Extrusion conditions include a resin temperature of preferably 250 to 270°C. When the extrusion temperature is lower than 250°C, melt viscosity becomes high and extrusion molding becomes difficult and when the resin temperature is higher than 270°C, the deterioration of polybutylene terephthalate is promoted disadvantageously. Since the crystallization of polybutylene terephthalate preferably proceeds to obtain a loose tube having excellent mechanical properties and a small difference in post-shrinkage, the cooling temperature of a loose tube is preferably 40 to 70°C, particularly preferably 50 to 70°C. The loose tube can be produced by a general tube forming machine. Methods for blending the master batch (A) with polybutylene terephthalate (B) include one in which (A) and (B) are uniformly blended using a tumbler or V-shaped blender and the resulting blend is charged into the supply port of an extrusion molding machine; one in which (A) and (B) are charged into the same supply port in a fixed ratio from different hoppers; and one in which (A) and (B) are charged from different supply ports and mixed together. The following examples are given to further illustrate the present invention. In the examples, characteristic properties were measured by the following methods. Polybutylene terephthalate (may be abbreviated as PBT) manufactured by Teijin Limited was used. (1) intrinsic viscosity The intrinsic viscosity [η] of a polymer is a value calculated from a solution viscosity measured at 25°C in an orthochlorophenol solvent. (2) terminal carboxyl group concentration The terminal carboxyl (COOH) group concentration is the number of equivalents per 106 g of a polymer measured by an A. Conix method (Makromol. Chem, 26, 226 (1958)). (3) tensile elongation at break The elongation at break of an optical fiber loose tube when it is pulled at a rate of 5 mm/min is obtained from the following equation. tensile elongation at break (%) = {L - Lo)/Lo x 100 wherein L is the distance between chucks at break and Lo is the original distance between the chucks- (4) crystallization temperature 3 to 5 mg of an optical fiber loose tube is cut out and the crystallization peak temperature of the loose tube is measured at a temperature falling rate of 20°C/min by a differential thermal analytical method based on JIS K7121 I after it is maintained at 280°C for 3 minutes. (5) extra length ratio An optical fiber loose tube is cut to a length of 10 m within 1 hour after production and the length (m) of a glass fiber contained therein is measured to obtain the extra length rate from the following equation, extra length ratio (%) = ({length of glass fiber - 10)/10) X 100 / (6) hydrolysis resistance Fibers and a jelly-like intimate mixture which are the contents of a colored optical fiber loose tube are removed, the inside of the tube is washed with hexane, and the tube is cut into flakes to carry out a pressure cooker test at 121'C and 100 %RH for 80 hours. The intrinsic viscosity is measured before and after the pressure cooker test to find intrinsic viscosity retention. Reference Example 1 (production of master batch) Red, green and non-colored master batches ("master" in the table) having compositions (PBT, pigment and crystal nucleating agent) shown in Table 1 were produced. That is, the components shown in Table 1 were uniformly blended together with a V-shaped blender, and the resulting blend was melt kneaded using a 44 mm-diameter twin-screw extruder at a barrel temperature of 260° C, and thread discharged from a die was cooled and cut to produce master batches A to G, Examples 1 to 6 and Comparative Examples 1 to 5 The master batches A to G produced in Reference Example 1 and PBT (of Teijin Limited, intrinsic viscosity of 1.14, terminal carboxyl group concentration of 4 eq/106 g) were prepared. These master batches and PBT were blended in a weight ratio shown in Tables 2 and 3 with a V-shaped blender. The obtained resin compositions were dried at 130°C for 5 hours and formed into optical fiber loose tubes (outer diameter of 3 mm, inner diameter of 2 mm) with a 40 mm-diameter extrusion molding machine for tubes at a cylinder temperature o,£ 260°C, a dice temperature of 260°C, a cooling bath water temperature of 50°C and a haul-off speed of 150 m/min. The obtained optical fiber loose tubes were evaluated. The results are shown in Tables 4 and 5. According to the present invention, it is possible to provide a resin composition for optical fiber loose tubes which enables the production of both colored loose tubes and non-colored loose tubes under the same production conditions, even the production of optical fiber loose tubes of the same quality, particularly the same quality in terms of extra length and post-shrinkage, and has excellent hydrolysis resistance as well as an optical fiber loose tube. We claim: 1. A process of preparing a resin composition for optical fiber loose tubes comprising the step of blending (A) a master batch produced by melt kneading 100 parts by weight of (a) polybutylene terephthalate and 0.1 to 5 parts by weight of (b) a crystal nucleating agent with (B) polybutylene terephthalate in an amount 10 to 100 times the weight of the master batch, wherein the amount of the crystal nucleating agent (b) is 0.01 to 0.5 wt% based on the total amount of the resin composition and the polybutylene terephthalate (B) has a terminal carboxyl group concentration of 30 eq / ton or less and an intrinsic viscosity of 1.0 to 1.2. 2. The process as claimed in claim 1, wherein the crystal nucleating agent (b) is at least one inorganic oxide selected from the group consisting of talc, kaolin, clay, zinc oxide, titanium oxide, alumina, silica, silicon nitride, titanium nitride, zinc powder, aluminum powder, graphite and carbon black. 3. The process as claimed in claim 1, wherein the crystal nucleating agent (b) is talc having an average particle diameter of 10 pm or less. 4. The process as claimed in claim 2, wherein the crystal nucleating agent (b) passes through a 50 pm sieve completely. 5. The process as claimed in claim 1, wherein the terminal carboxyl group concentration of the polybutylene terephthalate (B) is 20 eq/ton or less. 6. The process as claimed in claim 1, wherein the intrinsic viscosity of the polybutylene terephthalate (B) is 1.1 to 1.2. 7. The process as claimed in claim 1, wherein the polybutylene terephthalate (B) contains an alkaline metal compound. 8. An optical fiber loose tube produced by extrusion molding the resin composition of anyone of claims 1 to 7, wherein polybutylene terephthalate constituting the optical fiber loose tube has a terminal carboxyl group concentration 10 of 30 eq / ton or less and an intrinsic viscosity of 1.0 to 1.2. 9. A process of preparing a resin composition for optical fiber loose tubes, substantially as herein described and exemplified.

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