JPH0417221B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a method for producing a polyethylene resin foam having excellent heat resistance and closed cell properties by an extrusion foaming method. (Prior Art) A polyethylene foam obtained by foaming by an extrusion foaming method using a volatile foaming agent is widely used as a heat insulating material or a cushioning material. High-pressure polyethylene, which can be easily extruded and foam-molded, is used as the raw material for the polyethylene foam. This is because this high-pressure polyethylene is stable in the molten state over a relatively wide temperature range and has unique flow and crystallization properties. In the production of foam using this high-pressure polyethylene, the process is simple and no complicated equipment is required. However, the obtained foam does not have sufficient heat resistance because the raw material high-pressure polyethylene has a low melting point and does not have a crosslinked structure, and therefore, the uses of the foam are significantly limited. In order to improve the heat resistance of such polyethylene foams, for example, Japanese Patent Publication No. 53-34226, Japanese Patent Publication No. 58-47408, and Japanese Patent Application Laid-Open No. 54-161671 have been proposed.
JP-A-55-40739 proposes foams using medium-low pressure normal polyethylene or medium-low pressure normal polypropylene. Polyethylene and polypropylene produced by these medium-low pressure methods have excellent heat resistance, but on the other hand, when used alone, they can only be extruded and foamed within a specific temperature range, and may partially crystallize during kneading. . As a result, the extrusion foamability is extremely poor and a foam with a high closed cell ratio cannot be obtained. Therefore, in the above-mentioned publication, an attempt is made to improve the extrusion foamability by introducing a crosslinked structure into the molecules of normal polyethylene or polypropylene at medium and low pressures or by mixing an elastomer. For example, Japanese Patent Publication No. 58-47408 discloses a method of obtaining a foam by adding polybutene-1 to medium-low pressure polyethylene. polybutene-1
When added, medium-low pressure polyethylene becomes stable in a molten state over a relatively wide temperature range, making extrusion molding easier. However, although the obtained foam has excellent heat resistance, it has poor thermal stability, and if left in a high temperature atmosphere for a long time, it will shrink significantly. The independent foaming property of the foam is also not sufficient. The methods disclosed in the other three publications mentioned above are similarly insufficient in terms of thermal stability and heat resistance of the obtained foam, extrusion foamability in the manufacturing process, production cost, etc. JP-A No. 54-33569 discloses a method of obtaining a foam by mixing a specific low-melting point organic solvent type blowing agent with a mixture of high-pressure polyethylene and high-melting point polyolefin and extruding the mixture into a low-temperature, low-pressure zone. ing. However, even with this method, a foam having a heat resistance higher than the melting point of high-pressure polyethylene cannot be obtained. There are also examples in which the formed foam has a crosslinked structure to improve heat resistance. For example, JP-A-55-
No. 152724, JP-A No. 58-61129, and JP-A No. 58-1530 disclose methods of reacting high-pressure polyethylene with a silyl compound to obtain crosslinkable high-pressure polyethylene having hydrolyzable silyl groups, and using this. A method for obtaining a foam is disclosed. Although these methods can provide foams with excellent heat resistance, they have the fatal drawback of poor thermal stability and large shrinkage when heated. (Objective of the Invention) An object of the present invention is to provide a method for producing a polyethylene foam that has excellent heat resistance and thermal stability, has a high closed cell ratio, and can be produced at low cost. Another object of the present invention is to provide a method for producing a polyethylene foam that has excellent extrusion moldability and is therefore free from uneven foaming. (Structure of the Invention) The present invention provides a crosslinked structure by foaming a crosslinkable high-pressure branched polyethylene having a hydrolyzable silyl group, a high melting point linear polyethylene, and a polybutene resin in the presence of a catalyst and bringing them into contact with water. This was completed based on the inventor's knowledge that it is possible to obtain a foam with excellent heat resistance and a high closed cell ratio. Therefore, the method for producing polyethylene resin foam of the present invention consists of 95 to 50% by weight of crosslinkable high-pressure branched polyethylene in which hydrolyzable silyl groups are bonded to high-pressure branched polyethylene, and linear polyethylene with a melting point of 120°C or higher. A polyethylene composition prepared by adding 3 to 30 parts by weight of a polybutene resin to 100 parts by weight of a mixture with 5 to 50% by weight of polyethylene is heated and melted, and a volatile blowing agent is added to this in the presence of a silanol condensation catalyst. In addition, it is characterized by extrusion into a low pressure zone and contact with moisture, whereby the above object is achieved. The crosslinkable high-pressure branched polyethylene of the present invention can be obtained by grafting an unsaturated silane having a hydrolyzable organic group to the high-pressure branched polyethylene in the presence of a radical generator, or by grafting an unsaturated silane having a hydrolyzable organic group to ethylene. It is obtained by a method of copolymerizing saturated silane under high pressure. Hydrolyzable organic groups of the above and above include alkoxy groups such as methoxy, ethoxy and butoxy groups; acyloxy groups such as formyloxy, acetoxy and propionoxy groups; -ON=C
(CH ₃ ) ₂ , −ON=CCH ₃ C ₂ H ₅ , −ON=C (C ₆ H ₅ ) ₂
Oxime groups such as -NHCH ₃ , -NHC ₂ H ₅ , -
Examples include substituted amino groups such as NH (C ₆ H ₅ ). Among these, methoxy group and ethoxy group are particularly preferred. Among such unsaturated silanes having a hydrolyzable organic group, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, etc. are preferably used. The density of high-pressure branched polyethylene is 0.915 to 0.935 g/cm ³ . The melt index (MI) is preferably in the range of 0.1 to 20.0. A higher melting point is preferable. It is sufficient if the melting point measured by DSC is 108°C or higher, but preferably 112°C or higher. The object of the present invention can be achieved even at temperatures below 108°C. The production of crosslinkable high-pressure branched polyethylene by the above method and its composition do not need to be special, and are disclosed in detail in, for example, Japanese Patent Publication No. 48-1711 and Japanese Patent Application Laid-Open No. 55-9611. The crosslinkable high-pressure branched polyethylene thus obtained has the property of being easily crosslinked when it comes into contact with water in the presence of a silanol condensation catalyst. The linear polyethylene of the present invention refers to a. high-density polyethylene with few long chain branches and a density of 0.940 g/cm ³ or more obtained by medium-low pressure polymerization methods such as the Ziegler process; or b. Obtained by adding olefin and copolymerizing it, density 0.915
~0.945g/ ^cm3 linear low density polyethylene.
There are no particular limitations on the MI of linear polyethylene, but
The melting point must be 120°C or higher. If the melting point is below 120°C, the resulting foam will have insufficient heat resistance. When the linear polyethylene has a hydrolyzable silyl group, the reactivity with the crosslinkable high-pressure branched polyethylene is further improved. Linear polyethylene having hydrolyzable silyl groups can be easily obtained by grafting unsaturated silane to linear polyethylene in the same manner as in the case of obtaining crosslinkable high-pressure branched polyethylene. In the present invention, the polyethylene composition is a mixture of the high-pressure branched polyethylene and linear polyethylene, and a polybutene resin such as a copolymer of butene-1 and a small amount of olefin or polybutene-1. can be obtained. Butene
The olefin copolymer and polybutene-1 may be used alone or in combination. Its MI is 0.1 ~
Preferably in the 10.0 range. Especially 0.3~5.0
It is preferable that As such a polybutene resin, a commercially available polybutene resin can also be used. A mixture of 95 to 5% by weight of the above crosslinkable high-pressure branched polyethylene and 5 to 50% by weight of linear polyethylene
A polyethylene composition obtained by adding 3 to 30 parts by weight of a polybutene resin to 100 parts by weight is heated and melted, and a silanol condensation catalyst and a volatile blowing agent are added thereto to obtain a foam composition. A foam is obtained by extruding this into a low pressure zone, foaming it and bringing it into contact with moisture. If the amount of linear polyethylene in the mixture is less than 5% by weight, the resulting foam will have poor heat resistance. If it is in excess, the closed foam rate of the resulting foam will be low. The polyethylene composition obtained by adding a polybutene resin to this mixture is stable over a relatively wide temperature range when heated and melted, making it possible to perform extrusion foam molding. Since the viscosity of this molten composition is uniform throughout,
The resulting foam is not partially deformed.
The size of the cells in the foam is uniform and the closed cell ratio is high. If the amount of polybutene resin is less than 3 parts by weight per 100 parts by weight of the polyethylene composition, the above effects cannot be obtained. Although there is no problem even if the content of the polybutene resin is excessive, the effect is the same as when 30 parts by weight is contained. Since polybutene resin is expensive, if a large amount is used, a foam cannot be provided at a low price. Therefore, the content of the polybutene resin is more preferably 100%
The amount is 5 to 20 parts by weight. In addition, if unsaturated silane is grafted onto a mixture of high-pressure branched polyethylene that does not have a hydrolyzable silyl group and linear polyethylene that does not have a hydrolyzable silyl group, the high-pressure branched polyethylene and linear polyethylene can be grafted. Hydrolyzable silyl groups are introduced into both. As the silanol condensation catalyst in the above-mentioned foam composition, for example, the compounds disclosed in Japanese Patent Publication No. 1711/1982 can be used. Among them, dibutyltin dilaurate, dioctyltin dilaurate, etc. are preferably used. As the volatile blowing agent, low boiling point solvents belonging to fluorocarbons, chlorocarbons, and hydrocarbons can be used. Among them, dichlorodifluoromethane, trichlorofluoromethane, 1,2-dichlorotetrafluoroethane, trichlorotrifluoroethane, pentane,
Butane and the like are preferably used. In addition to the silanol condensation catalyst and the blowing agent, a foaming nucleating agent, an antioxidant, a light stabilizer, a flame retardant, an antistatic agent, a coloring agent, and the like may be added to the composition as necessary. When the foam composition is extruded into a low pressure zone and the resulting foam is left in the air at room temperature, the crosslinking reaction proceeds due to moisture in the air. The crosslinking reaction is accelerated when the foam is left under high temperature and high humidity. In this way, a foam having a crosslinked structure and excellent heat resistance and moldability can be obtained. (Example) The present invention will be described with reference to an example. Example 1 (A) Preparation of crosslinkable high-pressure branched polyethylene: Yucalon NF-90 as high-pressure branched polyethylene
(Mitsubishi Yuka Co., Ltd.: density 0.930g/cm ³ , MI1.5, melting point
116°C). To 100 parts by weight of Yucalon NF-90 pellets, 1.2 parts by weight of vinyltrimethoxysilane (VTS-M, manufactured by Chitsuso Corporation) and dicumyl peroxide (Percumyl D, manufactured by NOF Corporation) were added.
0.06 part by weight was added. This is caliber 50mm,
Extrusion amount 15Kg/hr using twin screw extruder with L/D=26
Silane-grafted polyethylene pellets were obtained as extrusion-crosslinkable high-pressure branched polyethylene.
The MI of this silane grafted polyethylene is 1.1,
The achieved gel fraction (xylene insoluble fraction at 110℃) is 75
It was %. The extrusion temperature condition is 160℃ for the barrel.
180℃, 200℃, 200℃, mold temperature is 200℃, 180℃. (B) Preparation of foam: 70 parts by weight of the silane grafted polyethylene obtained in section (A) was added with Rinrex AR4810 (Nippon Petrochemical Co., Ltd.) as linear polyethylene.
30 parts by weight of pellets (density 0.940 g/cm ³ , MI 4.0, melting point 127°C) were added. To this was added 10 parts by weight of AA polybutene #8640 (manufactured by Adaka Argus Co., Ltd., density 0.908 g/cm ³ , MI 1.0) as a polybutene resin. In addition, masterbatch pellets consisting of 100 parts by weight of Yucalon NF-90, 2 parts by weight of dibutyltin dilaurate, 5 parts by weight of talc, and 3 parts by weight of a hindered phenolic antioxidant (manufactured by Adaka Argus Co., Ltd.: MARK AO-60) were prepared. 5 parts by weight were added and mixed uniformly using a tumbler mixer. This was extruded into a rod shape and foamed using an extruder with a diameter of 40 mm and L/D=30 equipped with a nozzle mold of 3 mm diameter at an extrusion rate of 8 kg/hr. Barrel temperature is 120℃, 150℃, 160℃, 140℃
And the mold temperature is 117℃. In addition, from the middle of the barrel, 1.2 dichlorotetrafluoroethane was added as a blowing agent to 100 parts by weight of the above compound.
Part by weight was press-fitted using a high-pressure pump. extruder
A rod-shaped foam was produced by using it for 24 hours, but
No pressure fluctuation was observed during extrusion. (C) Performance evaluation of foam: The foam obtained in section (B) had a smooth surface and elasticity. There was also no change in the diameter of the rod-shaped foam. The density and closed cell ratio of the foam were measured. More foam
The sample was left in a dryer at 120°C for 24 hours, and its volumetric shrinkage rate was measured. The results are shown in Table 1. Example 2 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 1 (B) except that 90 parts by weight of silane grafted polyethylene and 10 parts by weight of linear polyethylene were used. In addition, in Examples 2 to 6 and Comparative Examples 1 to 5, the mold temperature was adjusted to the optimum temperature for each foam composition. Additionally, the foam density is approximately
The amount of blowing agent was adjusted to 0.3 g/cm ³ . (C) Performance evaluation of foam: Same as Example 1 (C). Example 3 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 1 (B) except that 80 parts by weight of silane grafted polyethylene and 20 parts by weight of linear polyethylene were used. (C) Performance evaluation of foam: Same as Example 1 (C). Example 4 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 1 (B) except that 60 parts by weight of silane grafted polyethylene and 40 parts by weight of linear polyethylene were used. (C) Performance evaluation of foam: Same as Example 1 (C). Example 5 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 1 (B) except that 70 parts by weight of silane grafted polyethylene, 30 parts by weight of linear polyethylene, and 5 parts by weight of polybutene resin were used. (C) Performance evaluation of foam: Same as Example 1 (C). Example 6 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 1 (B) except that 70 parts by weight of silane grafted polyethylene, 30 parts by weight of linear polyethylene, and 20 parts by weight of polybutene resin were used. (C) Performance evaluation of foam: Same as Example 1 (C). Comparative Example 1 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 1 (B) except that 100 parts by weight of silane grafted polyethylene was used and linear polyethylene and polybutene resin were not used. (C) Performance evaluation of foam: Same as Example 1 (C). Comparative Example 2 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 2 except that polybutene resin was not used. The extrusion pressure fluctuated slightly when extruding. (C) Performance evaluation of foam: The foamed state of the rod-shaped foam obtained in section (B) was good, but after extrusion, the diameter varied slightly and became non-uniform. Example 1
The same test as in section (C) was conducted, and the results are shown in Table 1. Comparative Example 3 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 3 except that polybutene resin was not used. (C) Performance evaluation of foam: The diameter of the rod-shaped foam obtained in section (B) varied considerably and became non-uniform after extrusion. A test similar to that in Example 1 (C) was conducted, and the results are shown in Table 1. Comparative Example 4 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 5 except that polybutene resin was not used. (C) Performance evaluation of foam: The foam obtained in section (B) had a very high shrinkage rate after foaming. Comparative Example 5 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Same as Example 1 (B) except that 40 parts by weight of silane grafted polyethylene, 60 parts by weight of linear polyethylene, and 10 parts by weight of polybutene resin were used. (C) Performance evaluation of foam: The foam obtained in section (B) had a very high shrinkage rate after foaming.

[Table] Example 7 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Silylation of linear polyethylene: Rinrex
1.2 parts by weight of vinyltrimethoxysilane and 0.05 parts by weight of dicumyl peroxide in 100 parts by weight of AR4810
Parts by weight were added and silylated to obtain silane-grafted linear polyethylene (MI 1.2, achieved gel fraction 63%). (C) Preparation of foam: Same as Example 1 (B) except that the silane-grafted linear polyethylene obtained in Section (B) was used instead of Rinrex AR4810. (D) Performance evaluation of foam: Same as Example 1 (C). The results are shown in Table 2. For comparison, the results of Example 1 are also shown in Table 2. Example 8 (A) Preparation of foam: 70 parts by weight of Yucalon NF-90 and 30 parts by weight of Rinrex AR4810 were uniformly mixed using a tumbler mixer.100
1.2 parts by weight of vinyltrimethoxysilane and 0.05 parts by weight of dicumyl peroxide were added to the parts by weight to obtain silane grafted polyethylene (MI 1.8, achieved gel fraction 65%). Thereafter, a polybutene resin and masterbatch pellets were added in the same manner as in Example 1 (B) to obtain a foam. (B) Performance evaluation of foam: Same as Example 1 (C). The results are shown in Table 2.

[Table] (Effects of the Invention) According to the present invention, a foam composition containing a crosslinkable high-pressure branched polyethylene having a hydrolyzable silyl group and a linear polyethylene having a high melting point is used. Since a foam having a crosslinked structure is produced, the obtained foam has excellent heat resistance. Furthermore, since the foam composition contains a polybutene resin, it can be uniformly kneaded when the composition is heated and melted. Moreover, the composition does not partially crystallize. Therefore, the foam does not undergo dimensional changes after foaming. The size of the bubbles is uniform and the independent foaming rate is high. Thermal stability is also sufficient, and dimensional changes are minimal even when the resulting foam is left at high temperatures for a long period of time. Closed foam rate
80-90%, which is significantly higher than conventional ones.
Therefore, it can be used for a wide range of purposes including insulation and cushioning materials.

Claims (1)

[Scope of Claims] 1. Crosslinkable high-pressure branched polyethylene 95~ in which a hydrolyzable silyl group is bonded to high-pressure branched polyethylene
A polyethylene composition prepared by adding 3 to 30 parts by weight of a polybutene resin to 100 parts by weight of a mixture of 50% by weight and 5 to 50% by weight of linear polyethylene with a melting point of 120°C or higher is heated and melted. A method for producing a polyethylene resin foam, which comprises adding a volatile blowing agent to the foam in the presence of a silanol condensation catalyst, extruding the foam into a low-pressure zone, and bringing the foam into contact with moisture. 2. The method according to claim 1, wherein the polybutene resin is at least one of a copolymer of butene-1 and olefin and polybutene-1. 3. The method according to claim 1, wherein the linear polyethylene contains a hydrolyzable silyl group in the molecule.