JPS6223977B2 - - Google Patents

Description

[Detailed description of the invention]

[] BACKGROUND TECHNICAL FIELD OF THE INVENTION The present invention relates to a crosslinked polyethylene resin pipe with excellent characteristics. Specifically, the present invention relates to a crosslinked polyethylene resin pipe made of a water crosslinked product of an ethylene-unsaturated silane compound copolymer that has excellent heat resistance and excellent heat fusion properties. Conventionally, polyethylene resin pipes have been used for the purpose of transporting gaseous and liquid substances, and in this case, polyethylene resin pipes that are not crosslinked have good heat resistance, abrasion resistance, ESC resistance, and other physical properties. Therefore, crosslinked polyethylene resin pipes are used in fields where the above-mentioned physical properties are required (for example, when transporting relatively high temperature substances). Prior art As a method for producing cross-linked polyethylene, silicone graft polyethylene (Special Publication No. 48-1711
A method using the following methods has been proposed.
When silicone-grafted polyethylene is brought into contact with moisture, the silicone portion is hydrolyzed and a crosslinking reaction proceeds, and this hydrolysis occurs at a relatively low temperature, so crosslinking methods using radiation irradiation and peroxide This eliminates the need for special and expensive crosslinking equipment, which is required when using crosslinking methods.
Application to the crosslinked polyethylene resin pipe is being considered. However, silicone grafted polyethylene
Materials in which the degree of crosslinking is increased in order to improve heat resistance, abrasion resistance, ESC resistance, and other physical properties inevitably have the disadvantage of deteriorating heat fusion properties. Although this problem can be partially solved by crosslinking before crosslinking treatment or after heat fusion bonding of materials with low crosslinking, strict control of the period until use (blocking moisture) or Strict control of processing conditions is required to obtain a low degree of cross-linking, and in addition, when performing secondary processing such as welding during remodeling, such as repairing damaged parts during use after cross-linking, cross-linking Since it is a material, its adhesive strength is weak, and it has been impossible to overcome the drawbacks such as damage occurring at the welded joint. [] Summary of the Invention The present invention aims to solve the above-mentioned problems, and attempts to achieve this purpose by using a copolymer of ethylene and an unsaturated silane compound. It is. Therefore, the crosslinked polyethylene resin pipe according to the present invention is a water-crosslinked copolymer mainly composed of ethylene and an olefinic unsaturated silane compound represented by the general formula RSiR' _o Y _3-o (however, the degree of crosslinking is 5 % or more) (in the above general formula, R is an olefinic unsaturated hydrocarbon or hydrocarbonoxy group, R' is an aliphatic saturated hydrocarbon group, Y is a hydrolyzable organic group, n is 0,
Represents 1 or 2. When there are multiple Y's, they do not have to be the same. The above degree of crosslinking is expressed in weight percent of the undissolved portion when extraction was performed with boiling xylene for 10 hours using a Soxhlet extractor). Effects As described above, the present invention does not involve grafting, but
By using a polyethylene resin into which an unsaturated silane compound has been introduced through copolymerization, the problem of poor thermal fusion properties that was observed when using silicone-grafted polyethylene has been successfully solved. Therefore, the product of the present invention is a crosslinked polyethylene resin pipe that has excellent heat resistance and excellent heat fusion properties, and can be easily subjected to secondary processing such as joining, repair, and remodeling. The fact that the heat fusion property is good even after water cross-linking means that pipes that have been processed into relatively short lengths for convenience of transportation can be fused to each other (pad fusion) after water cross-linking to make the desired length. It means that. Further, it also leads to the advantage in construction that secondary processing can be performed into shapes such as T-shape and cross-shape. [] Specific description of the invention (1) Ethylene-unsaturated silane compound copolymer The unsaturated silane compound is represented by the following formula. RSiR′ _o Y _3-o (where R is an ethylenically unsaturated hydrocarbon or hydrocarbonoxy group, R′ is an aliphatic saturated hydrocarbon group, Y is a hydrolyzable organic group, n is 0, 1 or Represents 2.
When there are a plurality of Y's, they do not have to be the same. ) Specific examples of this unsaturated silane compound include R being vinyl, allyl, propenyl, butenyl, cyclohexenyl, γ-(meth)acryloyloxypropyl, and Y being methoxy, ethoxy, formyloxy, acetoxy, propionoxy, alkyl or Arylamino, R' is methyl, ethyl, propyl, decyl, phenyl. Particularly preferred unsaturated silane compounds are those represented by the following formula. CH ₂ =CHSi(OA) ₃ (where A has 1 to 8 carbon atoms, preferably 1 to 8 carbon atoms)
4, is a hydrocarbon group. ) The most preferred compounds are vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriacetoxysilane. The copolymerization of ethylene and the unsaturated silane compound may be carried out under any conditions that allow copolymerization of both. Specifically, for example, the pressure is 500 to 4000Kg/
^cm2 , preferably 1000-4000Kg/ ^cm2 , temperature 100
~400°C, preferably 150~350°C, in the presence of a radical polymerization initiator, and if necessary, a comonomer copolymerizable with ethylene, and a chain transfer agent, in a tank or tube type. Each monomer is contacted simultaneously or stepwise in a reactor, preferably a tank reactor. In the present invention, any radical polymerization initiator, comonomer, and chain transfer agent known for use in homopolymerization or copolymerization of ethylene can be used. As a polymerization initiator, lauroyl peroxide, dipropionyl peroxide, benzoyl peroxide, di-t-butyl peroxide,
These include organic peroxides such as t-butyl hydroperoxide and t-butyl peroxyisobutyrate, molecular oxygen, and azo compounds such as azobisisobutyronitrile and azoisobutylvaleronitrile. Examples of comonomers include (a) vinyl carboxylate esters such as vinyl acetate and vinyl pivalate, (b) methyl (meth)acrylate,
(meth)acrylic acid esters such as butyl (meth)acrylate; (iii) olefinic unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, fumaric acid; ) Acrylamide-like (meth)
Acrylic acid derivative, (v)vinyl methyl ether,
Examples include vinyl ethers such as vinyl phenyl ether. Among these, preferred are:
Vinyl esters of monocarboxylic acids having about 1 to 4 carbon atoms, such as vinyl acetate, and about 1 to 4 carbon atoms.
(meth)acrylic acid esters of alcohols of about 4, such as methyl (meth)acrylate. Such olefinically unsaturated compounds are
Multiple types can be used together. In addition, "(meth)acrylic acid" shall mean both acrylic acid and methacrylic acid. Examples of chain transfer agents include paraffinic hydrocarbons such as methane, ethane, propane, butane, pentane, hexane, and heptane, α-olefins such as propylene, butene-1, and hexene-1, formaldehyde, acetaldehyde, n- Examples include aldehydes such as butyraldehyde, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, aromatic hydrocarbons, and chlorinated hydrocarbons. The copolymer used in the present invention has an unsaturated silane compound unit content of 0.01 to 15% by weight, preferably 0.05 to 5% by weight, particularly preferably 0.1 to 2% by weight. In general, water-crosslinked copolymers with a higher content of unsaturated silane compounds have better mechanical strength, ESC resistance, and heat resistance, but if the content is too high, tensile elongation and heat fusion properties decrease. The content range of 0.01 to 15% by weight was determined from this point of view. The content of comonomer units (if used) is usually between 0.5 and 40% by weight, especially between 0.5 and 35% by weight, especially between 1 and 25% by weight. (2) Silanol condensation catalyst A silanol condensation catalyst is usually used to crosslink such water-crosslinkable copolymers. The present invention is generally directed to catalysts that can be used to promote dehydration condensation between silanols of silicones. Such silanol condensation catalysts are generally carboxylic acid salts of metals such as tin, zinc, iron, lead, cobalt, organic bases, inorganic acids, and organic acids. Specific examples of silanol condensation catalysts are as follows. Dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, stannous acetate, stannous caprylate, lead naphthenate, zinc caprylate, cobalt naphthenate, ethylamine, dibutylamine, hexylamine, pyridine, sulfuric acid, hydrochloric acid, etc. inorganic acid,
Organic acids include toluenesulfonic acid, acetic acid, stearic acid, and maleic acid. The amount of the silanol condensation catalyst to be used may be appropriately determined by a practitioner with reference to the Examples described below for a given copolymer and a given catalyst. Generally speaking, for the total amount of copolymer
The amount is about 0.001 to 10% by weight, preferably 0.01 to 5% by weight, particularly preferably 0.01 to 3% by weight. (3) Composition Preparation and Pipe Forming The resin composition to be subjected to water crosslinking can be prepared by any means that can be used to incorporate various additives into a thermoplastic resin. Various methods can be used to prepare the composition. Composition preparation methods generally involve melting or dissolving (particularly the former) an ethylene-unsaturated silane compound copolymer or a silanol catalyst; for example, the copolymer and silanol are combined in an extruder. The condensation catalyst (as it is or as a solution or dispersion) and a compensating material to be added as necessary may be kneaded and extruded into a pipe. As mentioned above, the amount of silanol condensation catalyst is small compared to the copolymer. Therefore, as is often done when blending small amounts of components, it is possible to create a masterbatch in which a silanol condensation catalyst is blended in a dispersion medium such as polyethylene at a high concentration, and then blend this into a copolymer at a predetermined catalyst concentration. It's convenient. Another method is to mold the copolymer into a pipe and then immerse the molded product in a solution or dispersion containing a silanol catalyst to impregnate it. According to this method, a composition in a molded state can be obtained. The composition can include various auxiliary materials, as are often found in resin compositions. Such auxiliary materials include miscible thermoplastics, stabilizers, lubricants, fillers, colorants, blowing agents,
There are others. (4) Crosslinking When the resin composition (ie, copolymer + silanol condensation catalyst) used for manufacturing the pipe of the present invention is exposed to moisture, a crosslinking reaction occurs. Exposure to water involves exposing the molded product to water (liquid or vapor) at room temperature to 200°C, usually room temperature to 100°C.
The contact may be carried out for about 10 seconds to about 1 week, usually for about 1 minute to 1 day. In order to improve wetting of the molded article, the water may contain a wetting agent, a surfactant, a water-soluble organic solvent, and the like. Besides regular water, the water can also be in the form of heated steam or moisture in the air. Crosslinking of the resin composition used for manufacturing the pipe of the present invention can be carried out after or simultaneously with the molding of the composition. The degree of crosslinking of the crosslinked polyethylene resin pipe according to the present invention must be 5% or more from the viewpoint of various physical properties such as heat resistance, 30% or more from the viewpoint of ESC resistance, and 90% or less from the viewpoint of heat fusion property. It is preferable. The most preferred degree of crosslinking is 50-85%. Here, the "degree of crosslinking" is expressed as a percentage of the undissolved matter relative to the weight before extraction when extraction was performed with boiling xylene for 10 hours using a Soxhlet extractor. Experimental Examples Examples 1-2 A mixture of ethylene, vinyltrimethoxysilane, and propylene as a chain transfer agent was introduced into a stirred autoclave having an internal volume of 1.5 liters,
Add t-butyl peroxide isobutyrate as a polymerization initiator, pressure 2400 Kg/cm ² , temperature 220
An ethylene-vinyltrimethoxysilane copolymer was continuously synthesized under conditions of .degree. Table 1 shows the polymerization conditions and physical properties of the produced copolymer. To this copolymer, 1% by weight of dibutyltin dilaurate (the remainder is "Yukalon EH-30" manufactured by Mitsubishi Yuka Co., Ltd.)
5 wt. Pipe with diameter 48mm and wall thickness 4.4mm and (C) outer diameter
After forming the pipe into a 68 mm long pipe with a wall thickness of 4 mm, it was immersed in hot water at 90°C for one day to crosslink it. Using the obtained crosslinked pipe, a hot internal pressure creep test (using the crosslinked pipe (A)) and a stress cracking test (using the crosslinked pipe (B)) were conducted. Next, using the crosslinked pipe (C), fusion bonding was performed by the patch fusion method (heating temperature: 200° C., heating time: 1 minute), and after cooling for 1 minute, the fusion jig was removed. From the pipe, so that the joint is in the center,
A No. 2 dumbbell based on JIS K6301 was prepared and a tensile test was conducted at a tensile speed of 50 mm/min. Display the results -
Shown in 2. Comparative Example 1 Melt index 2g/10min, density 0.919
2% by weight of vinyltrimethoxysilane and 0.06% by weight of dicumyl peroxide were dispersed in low-density polyethylene (Yukalon EH-30 manufactured by Mitsubishi Yuka Co., Ltd.) of Graft polymerization was carried out by extrusion using a 50 mm diameter extruder at an extrusion temperature of 200°C. Using the obtained silicone grafted polyethylene, the pipe was formed and crosslinked by the method shown in Examples 1 and 2, and then the physical properties of the crosslinked pipe were measured, and the fused joint was subjected to a tensile test. The results are shown in Table-2. Comparative Example 2 Melt index 0.3g/10min, density 0.925
A pipe was formed using the method shown in Examples 1 and 2 using low-density polyethylene (Yukalon ZC-52, manufactured by Mitsubishi Yuka Co., Ltd.) of g/cc, and the physical properties of the pipe were measured and fusion bonded. A tensile test was conducted on the parts. The results are shown in Table-2.

【table】

【table】

Claims (1)

[Claims] 1 A water-crosslinked copolymer mainly composed of ethylene and an olefinic unsaturated silane compound represented by the general formula RSiR′ _o Y _3-o (however, the degree of crosslinking is 5%)
A cross-linked polyethylene resin pipe characterized by being made of a resin containing (the above general formula:
R is an olefinic unsaturated hydrocarbon or hydrocarbonoxy group, R' is an aliphatic saturated hydrocarbon group, Y is a hydrolyzable organic group,
n represents 0, 1 or 2. When there are multiple Y's, they do not have to be the same. The above degree of crosslinking is the weight percent of the uneluted content when extracted with boiling xylene using a Soxhlet extractor for 10 hours.
).