JPH0417220B2 - - 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) Polyethylene foams obtained by foaming by an extrusion foaming method using a volatile foaming agent are widely used as heat insulating materials and cushioning materials. 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 over a wide temperature range and has unique fluidity 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. 1983-34226, Japanese Patent Publication No. 58-47408, Japanese Patent Application Laid-open No. 54-161671, and Japanese Patent Application Laid-Open No. 1982-1989 have been proposed.
Publication No. 40739 proposes a foam 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, 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. However, none of these conventional methods can be said to be sufficient in terms of heat resistance, thermal stability, and production costs of extruded foams and other foams obtained. JP-A-54-33569 discloses a method of obtaining a foam by mixing a specific low-melting-point organic solvent 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. There is.
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. (Structure of the Invention) The present invention involves foaming crosslinkable high-pressure branched polyethylene having a hydrolyzable silyl group and linear medium-low density polyethylene having a melting point within a specific range in the presence of a catalyst and contacting it with water. This was completed based on the inventor's knowledge that a foam having a crosslinked structure and excellent heat resistance could be obtained by doing so. Therefore,
The method for producing the polyethylene resin foam of the present invention uses 95 to 50% by weight of crosslinkable high-pressure branched polyethylene in which a hydrolyzable silyl group is bonded to high-pressure branched polyethylene, and a melting point that satisfies the following formula (1). 100 parts by weight of a polyethylene composition containing 5% to 50% by weight of medium-low density polyethylene is heated and melted, and 5% to 50% by weight of a volatile blowing agent is added to this in the presence of a silanol condensation catalyst.
It is characterized in that 50 parts by weight are added and extruded into a low pressure zone and brought into contact with moisture, thereby achieving the above object. 120℃＜Melting point of linear medium-low density polyethylene＜Melting point of high-pressure branched polyethylene+10℃...(1) The crosslinkable high-pressure branched polyethylene of the present invention is unsaturated with an organic group that can be hydrolyzed into high-pressure branched polyethylene. It can be obtained by grafting silane in the presence of a radical generator, or by copolymerizing ethylene and an unsaturated silane having a hydrolyzable organic group 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, particularly preferably 0.3 to 5.0. A higher melting point is desirable. Melting point measured by DSC is 110
℃ or higher, but it is more preferably 112℃ or higher, and if it is 110℃ or lower, the difference in melting point with linear medium-low density polyethylene will be within 10℃, and the above-mentioned
Equation (1) cannot be satisfied. The production of crosslinkable high-pressure branched polyethylene by the method described in or above and its composition do not need to be special;
This is disclosed in detail in Publication No. 1711 and Japanese Unexamined Patent Publication 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 medium-low density polyethylene of the present invention is obtained by adding a small amount of α-olefin to ethylene and copolymerizing the mixture. Examples of α-olefins include propylene, 1-butene, and 4-methyl-1-pentene. The density of linear medium-low density polyethylene is
It is 0.915-0.945g/ ^cm3 . Its melting point is 120℃ ~
(Melting point of high-pressure branched polyethylene +10°C).
If the melting point is below 120°C, the resulting foam will have insufficient heat resistance. If the melting point is too high, it will be difficult to obtain a foam with a high closed cell ratio. As such linear medium-low density polyethylene, commercially available medium-density polyethylene or linear low-density polyethylene can be used. When the linear medium-low density polyethylene has a hydrolyzable silyl group, the reactivity with the crosslinkable high-pressure branched polyethylene is further improved. Linear medium-low density polyethylene having hydrolyzable silyl groups can be easily obtained by grafting unsaturated silane to linear medium-low density polyethylene in the same manner as in the case of obtaining crosslinkable high-pressure branched polyethylene. A mixture of 95 to 5% by weight of the above-mentioned crosslinkable high-pressure branched polyethylene and 5 to 50% by weight of linear medium-low density polyethylene is heated and melted, and a silanol condensation catalyst and a volatile blowing agent are added thereto to form a foam. Obtain a composition. A foam is obtained by extruding this into a low pressure zone, foaming it and bringing it into contact with moisture. If the linear medium-low density 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. In addition, if unsaturated silane is grafted onto a mixture of high-pressure branched polyethylene that does not have hydrolyzable silyl groups and linear medium-low density polyethylene that does not have hydrolyzable silyl groups, it is possible to Hydrolyzable silyl groups are introduced into both the medium and low density polyethylene. As the silanol condensation catalyst in the above 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 melting point solvents belonging to fluorocarbons, chlorocarbons, and hydrocarbons can be used. Among them, dichlorodifluoromethane,
Trichlorofluoromethane, 1,2-dichlorotetrafluoroethane, trichlorotrifluoroethane, pentane, butane, etc. 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 can be obtained. (Example) The present invention will be described below with reference to Examples. 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 rate 15Kg/hr using twin screw extruder with L/D=26
Silane-grafted polyethylene pellets (MI=
1.1, the achieved gel fraction was 75%). The temperature conditions are 160℃, 180℃, 200℃, 200℃ for the barrel, and 200℃ for the mold.
200℃ and 180℃. (B) Preparation of foam: Yucalon LL9150M (manufactured by Mitsubishi Yuka Co., Ltd., density 0.936 g/cm ³ MI5.0, melting point 125
30 parts by weight of pellets (°C) were added. Additionally, 100 parts by weight of Yucalon NF-90, 2 parts by weight of dibutyltin dilaurate, 5 parts by weight of talc, and a hindered phenol antioxidant (manufactured by Adaka Argus Co., Ltd.)
5 parts by weight of masterbatch pellets consisting of 3 parts by weight (MARK AO-60) were added and mixed uniformly with a tumbler mixer. This was extruded and foamed at an extrusion rate of 8 kg/hr using an extruder with a diameter of 40 mm and L/D = 30 equipped with a nozzle mold having a diameter of 3 mm. Barrel temperature is 120℃, 150℃, 160℃, 140℃
And the mold temperature is 115℃. Incidentally, 28 parts by weight of 1,2-dichlorotetrafluoroethane per 100 parts by weight of the above-mentioned compound was pressurized from the middle of the barrel using a high-pressure pump. (C) Performance evaluation of foam: The foam obtained in section (B) had a smooth surface and elasticity. The density and closed cell ratio of the foam were measured. Further foam at 120℃
The sample was left in a dryer 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 medium-low density polyethylene were used. In addition, in Examples 2 to 5 and Comparative Examples 1 to 3, the mold temperature was adjusted to the optimum temperature for each foam composition. (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 medium-low density 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 medium-low density 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 50 parts by weight of silane grafted polyethylene and 50 parts by weight of linear medium-low density polyethylene were used. (C) Performance evaluation of foam: The foam obtained in section (B) shrank slightly after foaming, but the foamed state was good. 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 medium-low density polyethylene was 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 1 (B) except that 40 parts by weight of silane grafted polyethylene and 60 parts by weight of linear medium-low density polyethylene were used. (C) Performance evaluation of foam: The foam obtained in section (B) shrunk immediately after foaming. The density and closed cell ratio of the foam were measured. The results are shown in Table 1. Comparative Example 3 (A) Preparation of foam Same as Example 1 (B) except that silane grafted polyethylene was not used and 100 parts by weight of linear medium-low density polyethylene was used. Although it was extruded using an extruder, there was almost no foaming and no foam was obtained.

【table】

[Table] Example 6 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) NEOSEX 3510F (manufactured by Mitsui Petrochemical Co., Ltd.: density 0.955,
The procedure was the same as in Example 1 (B) except that MI1.6, melting point 122°C) was used. (C) Performance evaluation of foam: The density and closed cell ratio of the obtained foam were measured. Further, the foam was left in a dryer at 120°C for 24 hours, and its volumetric shrinkage rate was measured. The results are shown in Table 2. Table 2 also shows the types of high-pressure branched polyethylene and linear medium-low density polyethylene used. For comparison, the results of Example 1 are also shown in Table 2. Example 7 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Urtozex 2020L (Mitsui Petrochemical Co., Ltd.) as linear medium-low density polyethylene
The procedure was the same as in Example 1 (B) except that a material (density 0.920, MI 2.1, melting point 120°C) was used. (C) Performance evaluation of foam: Same as Example 6 (C). Comparative Example 4 (A) Preparation of foam: Example 1 except that Yucalon NF-90 without silane grafting was used.
Same as paragraph (B). (B) Performance evaluation of foam: Same as Example 6 (C). Comparative Example 5 (A) Preparation of crosslinkable high-pressure branched polyethylene: Yucalon YK-30 as high-pressure branched polyethylene
(Mitsubishi Yuka Co., Ltd.: density 0.920, MI4.0 melting point 109℃)
The procedure was the same as in Example 1 (A) except that silane-grafted polyethylene (MI 3.1, achieved gel fraction 66%) was obtained using . (B) Preparation of foam: Same as Example 1 (B). (C) Performance evaluation of foam: Same as Example 6 (C). Comparative Example 6 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Comparative Example 5 (A). (B) Same as Example 1 (B) except that Urtozex 2020L was used as the linear medium-low density polyethylene. (C) Performance evaluation of foam: Same as Example 6 (C). Comparative Example 7 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Preparation of foam: Hi-Zex 3300F (manufactured by Mitsui Petrochemical Co., Ltd.) as linear medium-low density polyethylene.
The procedure is the same as in Example 1 (B) except that a material with a density of 0.954, an MI of 1.2, and a melting point of 131°C was used. (C) Performance evaluation of foam: Same as Example 6 (C).

[Table] Example 8 (A) Preparation of crosslinkable high-pressure branched polyethylene: Same as Example 1 (A). (B) Silylation of linear medium-low density polyethylene: 100 parts by weight of Yucalon LL9150M, 1.2 parts by weight of vinyltrimethoxysilane and dicumyl peroxide.
Silane-grafted linear medium-low density polyethylene (MI2.6, achieved gel fraction 66%) was obtained by adding 0.04 parts by weight of silylated silane-grafted linear polyethylene. (C) Preparation of foam: Example 1 (B) except that the silane-grafted linear medium-low density polyethylene obtained in section (B) was used instead of Yucalon LL9150M.
Same as section. (D) Performance evaluation of foam: Same as Example 1 (C). The results are shown in Table 3. For comparison, the results of Example 1 are also shown in Table 3. Example 9 (A) Preparation of foam: 100 parts by weight of a mixture of 70 parts by weight of Yucalon NF-90 and 30 parts by weight of Yucalon LL9150M uniformly mixed in a tumbler mixer, 1.2 parts by weight of vinyltrimethoxysilane and dicumyl peroxide. 0.05 part by weight was added to obtain silane grafted polyethylene (MI 1.8, achieved gel fraction 68%). Thereafter, masterbatch pellets similar to those in Example 1 were added to obtain a foam. (B) Performance evaluation of foam: Same as Example 1 (C). The results are shown in Table 3.

[Table] (Effects of the Invention) According to the present invention, crosslinkable high-pressure branched polyethylene having a hydrolyzable silyl group and linear medium-low density polyethylene having a melting point within a specific range are used. Since a foam having a crosslinked structure is produced, the resulting foam has excellent heat resistance.
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. The closed foam rate is also around 80%, which is significantly higher than conventional products. 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
100 parts by weight of a polyethylene composition containing 50% by weight and 5 to 50% by weight of linear medium-low density polyethylene whose melting point satisfies the following formula (1) is heated and melted, and the presence of a silanol condensation catalyst is added to the polyethylene composition. A method for producing a polyethylene resin foam, which comprises adding 5 to 50 parts by weight of a volatile blowing agent and extruding the foam into a low-pressure zone and bringing it into contact with moisture. 120°C<melting point of linear medium-low density polyethylene<melting point of high-pressure branched polyethylene+10°C... (1) 2. Claims in which the linear medium-low density polyethylene contains a hydrolyzable silyl group in its molecule The method described in paragraph 1.