JPS60219236A - Production of polyethylene resin foam - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 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 resulting foam.

Since the high-pressure polyethylene used as the raw material has a low melting point and does not have a crosslinked structure, it does not have sufficient heat resistance, and therefore the uses of the 2-foam are extremely limited.

In order to improve the heat resistance of such polyethylene foams, for example, Japanese Patent Publication No. 53-34226, Japanese Patent Publication No. 5
8-47408, JP-A-54-161671, and JP-A-55-40739 propose 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 publication,
The extrusion foamability has been improved by introducing a crosslinked structure into the molecules of normal polyethylene or polypropylene at medium and low pressures, or by mixing elastomers. For example,
Japanese Patent No. 47408 discloses a method of obtaining a foam by adding polybutene-1 to medium-low pressure polyethylene. When polybutene-1 is added, medium-low pressure polyethylene becomes stable in the molten state over a relatively wide temperature range, making it easier to extrude. 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 above-mentioned publications also have the same effect (increasing the thermal stability and heat resistance of the obtained foam).

It is not sufficient in terms of extrusion foamability and production cost in the manufacturing process.

JP-A-54-33569 discloses a method of obtaining a foam by mixing a specific low-boiling 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-55-152724, JP-A-58-. Publication No. 61129 and JP-A-58
Publication No. 1530 discloses a method of reacting high-pressure polyethylene with a silyl compound to obtain crosslinkable high-pressure polyethylene having a hydrolyzable silyl group, and using this to obtain a foam. Although these methods can provide foams with excellent heat resistance, they have the fatal drawback of poor thermal stability and large shrinkage when heated.

(Purpose of the invention) The object of the present invention is to provide a material with excellent heat resistance and thermal stability.

It is an object of the present invention to provide a method for producing a polyethylene foam that 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. have This was completed based on the inventor's knowledge that a foam with excellent heat resistance and a high closed cell ratio could be obtained. Therefore, the method for producing polyethylene resin foam of the present invention is to use crosslinkable high-pressure branched polyethylene 95 in which a hydrolyzable silyl group is bonded to high-pressure branched polyethylene.
Heating and melting a polyethylene tissue obtained 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, The above object is achieved by adding a volatile blowing agent to this in the presence of a silanol condensation catalyst, extruding it into a low pressure zone and bringing it into contact with moisture.

The crosslinkable high-pressure branched polyethylene of the present invention can be produced by: (1) grafting unsaturated silane having a hydrolyzable organic group onto high-pressure branched polyethylene in the presence of a radical generator, or (2) grafting ethylene with a hydrolyzable organic group. It is obtained by a method of copolymerizing unsaturated silanes under high pressure.

Hydrolyzable organic groups in (1) and (2) above include alkoxy groups such as methoxy, ethoxy and butoxy groups; acyloxy groups such as formyloxy, acetoxy and propionoxy groups; -0N=C(CH3)
2+-0N=CCII+Czlls+-0N=C
(C611S,) an oxime group i-NHC such as 2
Examples include substituted amino groups such as Hz, -NHCJs, and -Nl((C6L). Among these, methoxy and ethoxy groups are particularly preferred.

Of these unsaturated silanes having a hydrolyzable organic group, vinyltrimethoxysilane, vinyltrier-1-xysilane, .gamma.-methacryloyloxypropyltrimethoxysilane, etc. are preferably used. The density of the high-pressure branched polyethylene is 0.915 to 0.935 g/cl. Meltoia 7'So'1 Su (Ml) is 0.1~
It is desirable that it is in the range of 20.0, especially 0.3 to 5.
．． Preferably, it is 0. A higher melting point is desirable.

I) It is sufficient if the melting point measured by SC is 108°C or higher, but the object of the present invention can be achieved even if the melting point is 108°C or lower, preferably 112°C or higher. The method for producing crosslinkable high-pressure branched polyethylene by method (1) or (2) and its composition need not be particularly specific, 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.

What is the cotton-like polyethylene of the present invention?a. It is obtained by a medium-low pressure polymerization method such as the Ziegler method. High-density polyethylene with little long chain branching and a density of 0.940 g/cm" or more; or b. Obtained by adding α-olefin to ethylene and copolymerizing this. Density 0.915 to 0.945 g
/cm3 linear low density polyethylene. Although there are no particular limitations on the type of linear polyethylene, it is necessary that the melting point is 120°C or higher.

When the melting point is below 120'C, the heat resistance of the resulting foam is insufficient. When the cotton-like 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.

It is obtained by further mixing a polybutene-based resin such as a copolymer of butene-1 and a small amount of olefin or polybutene-1 to the above-mentioned mixture of high-pressure branched polyethylene and linear polyethylene. The butate olefin copolymer and polybutene-1 may be used alone or in combination. That M
It is desirable that l is in the range of 0.1 to 10.0. In particular, it is preferably 50.3 to 5.0. As such a polybutene resin, a commercially available polybutene resin can also be used.

A polyethylene composition obtained by adding 3 to 30 parts by weight of a polybutene resin to 100 parts by weight of a mixture of 95 to 5% by weight of the above-mentioned crosslinkable high-pressure branched polyethylene and 5 to 50% linear polyethylene is heated and melted. A foam composition is obtained by adding a silanol condensation catalyst and a volatile blowing agent to the drippings. A foam is obtained by extruding this into a low-pressure zone, foaming it twice, 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. When the polyethylene composition obtained by adding polybutene resin to this mixture is heated and melted,
It is stable over a relatively wide temperature range, making extrusion foam molding possible. Since the viscosity of this molten composition is uniform throughout, the resulting foam will not be 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 based on 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 5 to 20 parts by weight based on 100 parts by weight of the mixture. In addition,
If unsaturated silane is grafted onto a mixture of high-pressure branched polyethylene that does not have hydrolyzable silyl groups and linear polyethylene that does not have hydrolyzable silyl groups, both high-pressure branched polyethylene and cotton-like polyethylene can be obtained. There are four hydrolyzable silyl groups. 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 diptyltin dilaurate.

Dioctyltin dilaurate and the like are preferably used. Fluorocarbons are volatile blowing agents.

Low boiling point solvents belonging to 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 blowing agent, the above composition may optionally contain a foaming nucleating agent.

Antioxidants, light stabilizers, flame retardants, antistatic agents, colorants, etc. may be added.

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. When the foam is left under high temperature and high humidity, the crosslinking reaction is accelerated. 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 below with reference to Examples.

(A) Preparation of cross-linkable high-pressure branched polyethylene: As high-pressure branched polyethylene, Yucalon NF-9 (1 (manufactured by Mitsubishi Yuka): density 0.930 g/cJ, MI 1.5, melting point 116°C ) was used. 1.2 parts by weight of vinyltrimethoxysilane (manufactured by Chisso: VTS-M) and dicumyl peroxide (manufactured by Bark Mill D Nippon Oil & Fats AI) were added to 10011 tkm of Yucalon NF-90 pellets.
．． 06 parts by weight were added. This has a diameter of 501m, L/
A silane-grafted polyethylene pellet was obtained as extrusion-crosslinkable high-pressure branched polyethylene using a twin-screw extruder with D = 26 at an extrusion rate of 15 kg/hr. The old version of this Silang shift polyethylene is 1.1. Achieved gel fraction (110°C
The xylene insoluble fraction) was 75%. The temperature conditions for extrusion are 160°C, 180°C, 200°C, and 200°C for the barrel.
, the mold temperature is 200°C and 180°C.

(B) Preparation of foam: Add linear polyethylene to 70 parts by weight of the silange-shifted polyethylene obtained in section (A) and add Linrex AR4810 (manufactured by Nippon Petrochemical Co., Ltd.: density 0).
．． 940g/cn, Ml 4.0. 30 parts by weight of pellets (melting point: 127° C.) were added. In addition, A, A, polybutene #8640 (manufactured by Adeka Argus Al: density 0.908 g/ct, former 1.0
) 10 parts by weight were added. Furthermore, Yucalon NF-901
00 parts by weight.

Add 5 parts by weight of master hatchet pellets consisting of 2 parts by weight of dibutyltin dilaurate, 5 parts by weight of talc, and 3 parts by weight of a hindered phenol antioxidant (Adeka Argus fI remanufactured by RK AO-60 to M), and mix in a tumbler mixer. Mixed evenly. This was extruded into a rond shape at an extrusion rate of 3 kg/hr using an extruder having a diameter of 40 mm and L/D = 30 equipped with a nozzle mold having a diameter of 3 mm, and was foamed. Barrel temperature is 120°C, 150'c.

160°C, 140°C and mold temperature 117°C. Note that 26 parts by weight of 1,2-dichlorotetrafluoroethane as a foaming agent was injected into the barrel from the middle of the barrel using a high-pressure pump based on 100 parts by weight of the above blend. 2 extruders
A rond-like foam was produced using the product for 4 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 rond foam. The density and closed cell ratio of the 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 1.

(A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (A).

(B) Preparation of foam Nijiran grafted polyethylene 9
The procedure is the same as in Example 1 (B) except that 0 parts by weight 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. Furthermore, the amount of blowing agent was adjusted so that the foam density was about 0.3 g/Ca.

(C) Performance evaluation of foam: Example 1 Same as section (C).

Example 3 (A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (A).

(B) Preparation of foam: silane grafted polyethylene
The procedure was the same as in Example 1 (B) except that 0 parts by weight and 20 parts by weight of linear polyethylene were used.

(C) Performance evaluation of foam: Example 1 Same as section (c).

Example 4 (A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (A).

(B) Preparation of foam Niji Langshift polyethylene 6
The procedure is the same as in Example 1 (B) except that 0 parts by weight and 40 parts by weight of linear polyethylene were used.

(C) Performance evaluation of foam: Example 1 Same as section (c).

Example 5 (A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (A).

(B) Preparation of foam Nijirangrat polyethylene 7
0 parts by weight, and 30 parts by weight of linear polyethylene.

Example 1 except that 5 parts by weight of polybutene resin was used.
Same as item (B).

(C) Performance evaluation of foam: Example 1 Same as section (c).

(A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (A).

(B) Preparation of foam Nijilang shift polyethylene 7
0 parts by weight, and 30 parts by weight of linear polyethylene.

The procedure was the same as in Example 1 (B) except that 20 parts by weight of the polybutene resin was used.

(C) Performance evaluation of foam: Example 1 Same as section (C).

Preparation of cross-linkable high-pressure branched polyethylene of Hokkai Endo (A): Example 1
Same as item (A).

(B) Preparation of foam The procedure was the same as in Example 1 (B) except that 100 parts by weight of Nijiran grafted polyethylene was used and the linear polyethylene and polybutene resin were not used.

(C) Performance evaluation of foam: Example 1 Same as section (C).

Comparison 1 (A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as Section (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 rond foam obtained in section (B) was good, but after extrusion, its diameter varied slightly and became non-uniform. A test similar to that in Section (C) of Example 1 was conducted, and the results are shown in Table 1.

Comparative Example 3 (A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (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 rond foam obtained in section (B) varied considerably and became non-uniform after extrusion. A test similar to that in Section (C) of Example 1 was conducted, and the results are shown in Table 1.

(A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (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 one foaming.

(A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (A).

(B) Preparation of foam Nijiran grafted polyethylene 4
0 parts by weight, and 60 parts by weight of vA polyethylene.

The procedure was the same as in Example 1 (B) except that 10 parts by weight of the polybutene resin was used.

(C) Performance evaluation of foam: The foam obtained in section (B) had a very high shrinkage rate after two foamings.

(Left below) Hf117 (A) Preparation of crosslinkable high-pressure branched polyethylene: Example 1
Same as item (A).

(B) Silylation of kil-shaped polyethylene Nilinrex A 1.2 parts by weight of vinyltrimethoxysilane and 0.05 parts by weight of dicumyl peroxide are added to 100 parts by weight of R4810 to silylate the silane-grafted linear polyethylene (L+ 1.2 .Achieved gel fraction of 63%) was obtained.

(C) Preparation of foam Same as Example 1 (B) except that the silane grafted linear polyethylene obtained in (B) was used instead of Nilinrex AR4810.

(D) Performance evaluation of foam: Example 1 Same as section (C). The results are shown in Table 2. For comparison, the results of Example 1 are also shown in Table 2.

Example Day (A) Preparation of foam: 1.2 parts by weight of vinyltrimethoxysilane and 1.2 parts by weight of vinyltrimethoxysilane were added to 100 parts by weight of a mixture in which Yucalon IIF-9070 parts by weight and Linrex AR481030 parts by weight were uniformly mixed in a tumbler mixer. 0.05 parts by weight of mil peroxide was added to obtain silane grafted polyethylene (formerly 1.8. reached gel fraction 65%). Thereafter, a polybutene resin and master hatch pellets were added in the same manner as in Example 1 (B) to obtain a foam.

(B) Performance evaluation of foam: Example 1 Same as section (C). The results are shown in Table 2.

Table 2 (Effects of the Invention) According to the present invention, crosslinking is achieved using a foam composition containing a crosslinkable high-pressure branched polyethylene having a hydrolyzable silyl group and a linear polyethylene having a high melting point. Since a structured foam is produced, the resulting foam has excellent heat resistance. Furthermore, since the second foam composition contains a polybutene resin, it can be uniformly kneaded when the first composition is heated and melted. Moreover, the composition does not partially crystallize. Therefore, one 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. The independent foaming rate is also 80% to 90%, which is significantly higher than conventional products.

Therefore, it can be used for a wide range of purposes including insulation and cushioning materials.

that's all Applicant: Sekisui Chemical Co., Ltd.

Claims (1)

[Claims] 1. 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 5 to 50% by weight of linear polyethylene having a melting point of 120° C. or higher based on 100 parts by weight of the mixture. It is characterized by heating and melting a polyethylene composition to which 3 to 30 parts by weight of a polybutene resin has been added, adding a volatile blowing agent to this in the presence of a silanol condensation catalyst, extruding it into a low pressure zone, and bringing it into contact with moisture. A method for producing polyethylene resin foam. 2. The polybutene-based resin is at least one of a copolymer of butene-1 and olefin and polybutene-1.
The method according to claim 1, wherein the method is a species. 3. The method according to claim 1, wherein the linear polyethylene contains a hydrolyzable silyl group in the molecule.