JP2001240693A - Method for producing expanded polyolefin resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an expanded polyolefin resin necessitating decreased installation cost, giving a crosslinked expanded product having excellent uniformity, enabling easy adjustment of the expansion ratio and giving an expanded product having excellent recyclability. SOLUTION: An expanded sheet having excellent appearance is produced by supplying 100 pts.wt. of a polyolefin resin such as polypropylene, 0.5 pt.wt. of a dioxime compound (preferably p-quinone dioxime) and a heat-decomposable chemical foaming agent (preferably azodicarbonamide) to a screw extruder, melting and kneading at 170-165 deg.C and heating the obtained expandable resin composition at 180-220 deg.C (e.g. 210 deg.C) to perform the crosslinking reaction and the expansion of the polyolefin resin in one step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a polyolefin resin foam having excellent recyclability.

[0002]

2. Description of the Related Art Polyolefin resin foams are widely used as industrial materials because they have an excellent balance between mechanical and thermal properties and can be heated and shaped later. BACKGROUND ART For interior materials such as doors and ceilings of automobiles, for example, foams mainly composed of polypropylene resin have become mainstream because of their good heat resistance. In addition, foams mainly composed of polyethylene resin are mainly used for heat insulating materials for folded-plate roofs, pipe covers, and the like because of their good heat insulating properties, flexibility, and durability.

[0003] Conventionally, in order to produce a sheet-like foam of a polyolefin resin, it is necessary to crosslink the resin so that the resin has a foamable melt strength.
For example, a foaming agent is added to a polyolefin-based resin composition, the composition is shaped into a sheet, and this is crosslinked until it shows a gel fraction of about 30 to 50%. Is thermally decomposed and foamed. Examples of the method for crosslinking the sheet-like polyolefin-based resin include a method using radiation or electron beam irradiation, a method using ultraviolet irradiation, and a method using a thermal decomposition type chemical crosslinking agent such as an organic peroxide. In addition, by improving the melt strength by crosslinking the resin, it is possible to shape the obtained foam into an arbitrary shape in a later step.

Among the above-mentioned crosslinking methods, the crosslinking method using an electron beam is excellent in productivity and is widely practiced industrially. However, since it occurs only in the non-crystal part, the subsequent foaming becomes non-uniform, and there is a tendency that defective products having pinholes or the like are generated. On the other hand, as a method using a thermal decomposition type chemical crosslinking agent, for example, Japanese Patent Publication No. 58-5745.
No. 2 discloses a crosslinked foam which is obtained by adding a specific polyfunctional monomer such as triallyl cyanurate and a pyrolytic foaming agent to a polypropylene resin and melt-mixing the whole, and then subjecting the composition to crosslinking and foaming by heating. A manufacturing method is disclosed. Also, JP-A-11-1570 discloses that 100 parts by weight of polyolefin resin and 0.05 parts of dioxime compound are used.
５5 parts by weight are melt-mixed at a temperature of 170 ° C. or higher to modify the resin, the modified resin composition is kneaded with a thermal decomposition type chemical foaming agent, and the obtained foamable resin composition is heated. A method for producing a polyolefin resin foam which is foamed by decomposition of a foaming agent is disclosed.

[0005]

[Problems to be Solved by the Invention]
The method described in Japanese Patent Application Laid-Open No. 8-57452 has the advantages of requiring less capital investment and excellent homogeneity of the obtained crosslinked foam as compared with the crosslinking method using an electron beam or radiation. In order to improve this point because the crosslinking reaction takes a long time, a heat treatment for 10 to 100 minutes is often required before foaming, so that the productivity is very poor, and the obtained foam is a gel. The fact was that the fraction was too high to be suitable for recycling.

In the method described in Japanese Patent Application Laid-Open No. H11-1570, a step of melt-mixing a polyolefin resin and a dioxime compound, and a step of kneading a thermally decomposable chemical blowing agent into the obtained modified resin composition are further performed. This requires two steps, which makes the manufacturing process complicated and ultimately requires a large capital investment. The point that the obtained foam is not suitable for recycling because it is crosslinked is the same as the technique described in Japanese Patent Publication No. 58-57452. Unsuitable for recycling is because, for example, it cannot be re-melted even if collected after use, or it is difficult to reuse it as a raw material because of its high melt viscosity.

In view of the above-mentioned problems of the conventional method for producing a polyolefin-based resin foam, the object of the present invention is to reduce the capital investment, obtain excellent uniformity of the obtained cross-linked foam, and adjust the expansion ratio. An object of the present invention is to provide a method for producing a polyolefin-based resin foam which is easy and can obtain a foam having excellent recyclability.

[0008]

The method for producing a polyolefin-based resin foam of the present invention has been devised to achieve the above object, and the amount of the dioxime compound 0.05 to 100 parts by weight based on 100 parts by weight of the polyolefin-based resin. 5 parts by weight and the thermal decomposition type chemical foaming agent are simultaneously melt-mixed at a temperature of 170 ° C. or less, and the obtained foamable resin composition is heated at 180 ° C. or more to 220 ° C.
It is characterized in that the crosslinking reaction and foaming of the polyolefin-based resin are carried out in one stage by heating to a temperature range of not more than ° C.

The polyolefin as the main component of the polyolefin resin in the present invention is a homopolymer of an olefinic monomer or a copolymer of a main component olefinic monomer and another monomer, and is not particularly limited. Examples include polyethylene, polypropylene, and polybutene. Examples of the polyethylene include homo-type polyethylenes such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and high-density polyethylene, and random or block copolymers containing ethylene as a main component. As the ethylene-based copolymer, ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, Examples thereof include an ethylene-acrylate copolymer.

Examples of the polypropylene include a homo-type polypropylene and a random or block copolymer containing propylene as a main component. Examples of the propylene-based copolymer include a random copolymer of propylene and an α-olefin, and a block copolymer of propylene and an α-olefin (provided that the α-olefin is ethylene, 1-hexene, -Methyl-1-pentene, 1-octene, 1-butene, 1-pentene and the like are exemplified). The above-mentioned examples of polyolefins may be used alone or in combination of two or more. In the method of the present invention, in particular, polypropylene is preferably used in terms of heat resistance and moldability, and polyethylene is preferably used in terms of heat insulation, flexibility, and durability.

In the present invention, the polyolefin resin means that the above polyolefin may be a blend with another resin. In the case of a polypropylene-based resin, examples of other resins include an ethylene-vinyl acetate copolymer, an olefin-based thermoplastic elastomer, polystyrene, and a styrene-based thermoplastic elastomer. The proportion of polyolefin is 50 to 1 of the whole blend.
It is preferably 00% by weight. If the proportion is less than 50% by weight, the heat resistance and rigidity, which are characteristics of polyolefin, cannot be exhibited, or in the case of blending with another polyolefin resin, it is difficult to secure the melt viscosity required for foaming. May be.

The dioxime compound used in the present invention refers to an oxime group represented by the following chemical formula (1), or a hydrogen atom of an oxime group represented by another chemical group (mainly a hydrocarbon group) represented by the following chemical formula (2). ) In the molecule. Representative examples of such dioxime compounds include p-quinone dioxime represented by the chemical formula (3) and p, p'-dibenzoylquinone dioxime represented by the chemical formula (4). These compounds may be used alone or in combination of two or more.

[0013]

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[0014]

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[0015]

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[0016]

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The amount of the dioxime compound is 0.05 to 5 parts by weight, preferably 0.1 to 3 parts by weight, based on 100 parts by weight of the polyolefin resin. If the amount is less than 0.05 parts by weight, the melt viscosity required for foaming cannot be imparted. If the amount exceeds 5 parts by weight, the gel fraction becomes unnecessarily too high, and the magnification decreases due to the decrease in melt viscosity. Happens. In addition, the ratio of the dioxime compound remaining as an unreacted substance in the product is increased, which irritates the human body and lowers the efficiency of producing the product with respect to the raw material.

The thermal decomposition type chemical blowing agent used in the present invention is not particularly limited as long as it generates a decomposition gas by heating. Representative examples of the thermal decomposition type chemical blowing agent are azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, and 4,4-oxybis (benzenesulfonyl hydrazide). These may be used alone or in combination of two or more. Among them, azodicarbonamide is preferably used.

In order to obtain the above foamable resin composition, 0.05 to 5 parts by weight of a dioxime compound and 170 parts by weight of a thermal decomposition type chemical blowing agent are added to 100 parts by weight of a polyolefin resin.
Melt and mix simultaneously at a temperature of below ℃. Specifically, for example, the above-mentioned substances are put into kneading apparatuses such as a screw extruder and a kneader in required amounts, and are melt-mixed at a temperature of 170 ° C. or lower. The temperature at the time of melt mixing is 170 ° C or less,
Usually, the melting point is higher than the melting point of the polyolefin resin. When the melt mixing temperature exceeds 170 ° C., the reaction of the dioxime compound and the decomposition of the blowing agent occur. When a gel is formed by the reaction of the dioxime compound, poor dispersion and stagnation of the resin occur in the melt mixing step. Further, when a part of the foaming agent is decomposed, air bubbles are entrapped in the resin composition, and these become nuclei, so that the air bubbles of the final foam become coarse, which causes a reduction in expansion ratio and a reduction in strength.

The apparatus used for the melt mixing may be a screw kneader or a melt kneading apparatus which can be generally used in plastic molding, and examples thereof include a kneader, a rotor and a continuous kneader. Among these, a screw extruder that can be continuously performed is preferable, and a single-screw extruder, a twin-screw extruder, a multi-screw extruder having three or more screws, and the like are all suitably used. Examples of the single screw extruder include an extruder having a discontinuous flight screw, a pin barrel, a mixing head, and the like, in addition to a general full flight screw. Further, as the twin screw extruder, a meshing co-rotating extruder, a meshing different direction rotating extruder, a non-meshing different direction rotating extruder and the like can be suitably used. Providing a vacuum vent at the latter stage of the extruder is effective for preventing volatiles from remaining in the resin composition. When a screw extruder is used, the polyolefin-based resin is charged from a normal hopper, but it is also preferable to use a screw type feeder, a weight control type feeder, or the like in order to increase quantitativeness.

The method of supplying the dioxime compound and the thermal decomposition type chemical blowing agent is not particularly limited, but for example, the following method is preferably used. 1) A method in which a polyolefin-based resin, a dioxime compound, and a pyrolytic chemical blowing agent are dry-blended and then collectively charged into an ordinary hopper. 2) After dry-blending the dioxime compound and the blowing agent, the mixture and the polyolefin-based resin are charged into the extruder using separate feeders. For example, the mixture and the polyolefin-based resin are charged into the extruder from the same portion using separate quantitative feeders. Alternatively, a method in which the mixture is introduced from the middle of the extruder using a side feeder. 3) The polyolefin-based resin, the dioxime compound, and the pyrolytic chemical blowing agent are charged into the extruder using separate feeders. For example, separate quantitative feeders are used. Or
A method using a side feeder, etc.

The above melt-blended foamable resin composition comprises:
Furthermore, it may be shaped. The shaping method is extrusion molding,
A method generally performed in plastic molding, such as press molding, blow molding, calendaring molding, or injection molding, can be applied. The foamable resin composition has 180
By heating under a temperature condition of not less than 220 ° C. or more,
Cross-linking reaction and foaming of the polyolefin resin occur simultaneously, and foaming can be performed to a desired expansion ratio. As a foaming apparatus for performing this, a vertical or horizontal foaming furnace, a hot air thermostat, or a heat bath such as an oil bath, a metal bath, or a salt bath, which is operated in an air atmosphere, is generally used.

If the foaming temperature is lower than 180 ° C., the crosslinking reaction does not occur or the reaction is very slow, so that the decomposition of the foaming agent is completed before the gel required for foaming is formed, and the foam is I can't get it. When the foaming temperature exceeds 220 ° C., the decomposition of the thermal decomposition type chemical foaming agent is fast, so the decomposition of the foaming agent ends before the gel required for foaming is generated,
Again, no foam is obtained.

The gel fraction of the foam produced by the above method is preferably 10% or more and less than 60%, more preferably 15% or more and less than 40%.
If the gel fraction is less than 10%, the melt viscosity is low,
When foaming, bubbles cannot be maintained and gas escapes. When the gel fraction is 60% or more, the viscosity of the resin composition is too high in a general screw extruder and the composition does not melt and flow, so that the recycling and recycling of the used product may not be possible. . The lower the gel fraction, the better the melt moldability during recycling.

The expansion ratio (foam specific volume) of the foam produced by the method of the present invention is preferably 10 times (cm ³ / cm ³ ).
g) or more, more preferably 12 times (cm ³ / g) or more. When the expansion ratio is less than 10 times, heat insulation, cushioning,
This is because a foam excellent in sound insulation, flexibility, buoyancy and the like may not be obtained.

(Function) In the method for producing a polyolefin resin foam of the present invention, 0.05 to 5 parts by weight of a dioxime compound and a thermal decomposition type chemical blowing agent are added to 100 parts by weight of a polyolefin resin at 170 ° C. or less. Melt at the same time at a temperature, the resulting foamable resin composition is 180 ° C or more and 220 ° C or more.
By heating to a temperature of not more than ℃, the cross-linking reaction and foaming of the polyolefin resin are performed in one step, thereby obtaining a foam having excellent homogeneity and further excellent recyclability. Although the detailed reaction mechanism that can be performed is unknown, it is roughly estimated as follows.

Since the polyolefin resin, the dioxime compound and the pyrolytic chemical blowing agent are simultaneously melt-blended at a temperature of 170 ° C. or lower, they can be melt-blended without generating polymer radicals due to the polyolefin resin. . At this stage, since the polyolefin-based resin is not crosslinked, the melt viscosity during the process is stable, and the foamable resin composition of stable quality can be obtained without staying in the process.

The foamable resin composition thus obtained is
When heated to a temperature range of 180 ° C. or more and 220 ° C. or less, the thermal decomposition type chemical foaming agent is decomposed to generate gas and also generate radicals, which extract hydrogen from the polyolefin-based resin and generate polymer radicals. Furthermore,
The dioxime compound undergoes a graft reaction with the polymer radical to produce a trace amount of crosslinked modified resin having a structure in which the dioxime compound bridges the polymers. Thus, the crosslinking reaction and foaming are performed in one step, that is,
It proceeds almost simultaneously, and finally a polyolefin-based resin foam can be obtained.

Since the reaction rate of the dioxime compound used here is higher than that of other polyfunctional monomers generally used as a cross-linking agent, the cross-linking reaction and foaming proceed almost simultaneously, and the bubbles are maintained in a short time. A sufficient crosslinked structure can be formed. Since the foam obtained by the production method of the present invention is a slightly crosslinked molded article, the melt tension required for foaming can be maintained by the crosslinked portion, while a large amount of components not contributing to crosslinkage are present. , The melt fluidity can be maintained to the extent that kneading and shaping are possible. For this reason, in addition to being able to be molded in a different shape, the foam is melted again even after molding as a foam, thereby exhibiting recyclability for reuse.

[0030]

EXAMPLES The present invention will be described more specifically with reference to examples. (Example 1) Melt kneading apparatus The screw extruder shown in Fig. 1 was used. In FIG. 1, 1 is a screw extruder, 2 is a forming die, 3 is a feeder for resin, 4 is a quantitative feeder for dioxime compounds, 5 is a quantitative feeder for foaming agent, 6 is a vent for suction, 7 is a suction pump, and 8 9 is a thermocouple for measuring resin temperature, 10 is a cooling roll, 11 is a foamable resin sheet, and C1 to C12 are first to first.
It is a two cylinder barrel. The screw extruder has the following configuration.

Extruder: TEX-44 type (manufactured by Nippon Steel Works) Co-rotating twin screw extruder Screw: self-wiping 2 strips, L / D: 45.
5, D: 47 mm Cylinder barrel: 1st from upstream to downstream of extruder
12 cylinder barrel [Temperature setting section] 1st barrel is always cooled 1st zone; 2nd to 4th barrel 2nd zone; 5th barrel 3rd zone; 6th to 12th barrel 4th zone; Die and adapter part

Molding die: T die (width 200 mm, thickness 1 mm) Suction vent: Installed in the ninth barrel to collect volatiles Thermocouple for measuring resin temperature: Eighth barrel and ninth by thermocouple 7 Measure the resin temperature (T1) between the barrels, and measure the resin temperature (T2) at the adapter section using a thermocouple 8.

I) Preparation of a foamable resin composition and preparation of a foam using a reforming melt-kneading apparatus having the above structure, a polypropylene random copolymer ("EG8", MI;
8 g / 10 min, density; 0.9 g / cm ³ ) and p-
Quinone dioxime (p-QDO) and azodicarbonamide (ADCA) are supplied from the hopper to the first cylinder barrel C1 using the feeders 3, 4, and 5 under the following mixing conditions, and these materials are melted. They were mixed and extruded from a forming die into a sheet. The sheet-like foamable resin composition thus obtained was heated and foamed to obtain a polypropylene resin foam.

[Operation conditions] Screw rotation speed: 100 rpm Polypropylene supply amount: 14 kg / h p-Quinone dioxime compounding amount: polypropylene 100
0.5 parts by weight per part by weight-Blending amount of foaming agent: 6 parts by weight of ADCA per 100 parts by weight of modified resin composition-Resin temperature: T1; 164 ° C, T2; 166 ° C-Foaming: 210 ° C This was carried out by charging the hot air dryer for 5 minutes.

Ii) Physical properties of foam The physical properties of the obtained foam were measured by the following methods. a) Expansion ratio It is a specific volume measurement value of a foam sample. b) Gel Fraction The foam sample was heated in xylene at 130 ° C. for 24 hours to elute the dissolved components into xylene, and the remaining solid was collected by filtration through a 200-mesh metal net, and dried at 80 ° C. under vacuum. It is a weight% calculated by the formula: (weight of insoluble matter / weight of foam) × 100.

C) Reflowability (evaluation method is as follows): good sheet formability, no foreign matter. Crushed foam sample 2
0% by weight and 80% by weight of the original polyolefin resin were kneaded and extruded, and the appearance of the extruded product was checked. The same extruder and die as those in the above-mentioned melt kneading apparatus were used, and the operating conditions were also the same.

The evaluation results are as follows: foaming ratio: 15 cm ³ / g gel fraction: 16% reflowability: good sheet moldability, no foreign matter.

Example 2 As a polyolefin-based resin, polypropylene manufactured by Mitsubishi Chemical Corporation (homotype, "EA
8 ", MI = 0.8, density = 0.9 g / cm ³ ), and p, p'-dibenzoylquinonedioxime (p, p'-DBQDO) was used as a dioxime compound with respect to 100 parts by weight of polyolefin. The same operation as in Example 1 was performed except that the amount was supplied to be 1.0 part by weight. However, resin temperature: T1: 162 ° C, T2: 165 ° C. The physical properties of the obtained foam were measured in the same manner as in Example 1. The results are as follows.・ Expansion ratio: 18 cm ³ / g ・ Gel fraction: 25% ・ Reflowability: good sheet formability, no foreign matter

Comparative Example 1 Example 2 was repeated except that the amount of p, p'-dibenzoylquinone dioxime was changed to 0.03 parts by weight based on 100 parts by weight of the polyolefin resin.
The same operation as described above was performed. However, resin temperature: T1; 16
5 ° C, T2; 168 ° C. The physical properties of the obtained foam were measured in the same manner as in Example 1. The results are as follows.・ Expansion ratio: 5 cm ³ / g ・ Gel fraction: 3%

Comparative Example 2 The same operation as in Example 1 was carried out except that the amount of p-quinone dioxime was changed to 7 parts by weight with respect to 100 parts by weight of the polyolefin resin. However, resin temperature: T1; 160 ° C, T2; 163 ° C. The physical properties of the obtained foam were measured in the same manner as in Example 1. The results are as follows.・ Expansion ratio: 16 cm ³ / g ・ Gel fraction: 70% ・ Reflowability: good sheet moldability, no foreign matter, melt fracture occurred during extrusion, and the extrusion load was significantly increased. Further, when extruding the sheet-like foamable resin composition, the surface properties of the sheet were poor, and the foaming agent was not evenly kneaded. The obtained sheet-like foamable resin composition was heated and foamed, but foamed unevenly and could not be evaluated.

(Comparative Example 3) The same operation as in Example 2 was performed except that the cylinder barrel set temperature was changed as follows. When extruding a sheet-like foamable resin composition,
The resin stayed in the T-die, and the extrusion amount gradually decreased. In addition, the sheet contains a large number of fine air bubbles, the surface of the sheet is poor, and the obtained sheet-like foamable resin composition is heated and foamed, but the foam is unevenly foamed and cannot be evaluated. Was. 1st zone; 180 ° C 2nd zone; 180 ° C 3rd zone; 180 ° C 4th zone; 180 ° C

Comparative Example 4 The same operation as in Example 1 was carried out except that the set temperature of the hot air dryer for foaming was changed to 175 ° C., and the foaming time was changed to 30 minutes. The physical properties of the obtained foam were measured in the same manner as in Example 1. The results are as follows.・ Expansion ratio: 1.5 cm ³ / g ・ Gel fraction: 2%

Comparative Example 5 The same operation as in Example 1 was performed except that the set temperature of the hot air dryer for foaming was changed to 230 ° C., and the foaming time was changed to 5 minutes. The physical properties of the obtained foam were measured in the same manner as in Example 1. The results are as follows.・ Expansion ratio: 6 cm ³ / g ・ Gel fraction: 4%

The operating conditions of Examples 1 and 2 and Comparative Examples 1 to 5 and the properties of the obtained foams are summarized in Table 1.

[0045]

[Table 1]

In Table 1, "Appearance of molded sheet"
○ means good, and × means bad. In the "expansion ratio and gel fraction",-means that the foaming was non-uniform and could not be evaluated. Also, "reflowability"
In, ○ is good, × is bad,-is poor foamability,
This means that reflowability was not evaluated.

According to the present invention, the crosslinking reaction and foaming of the above-mentioned polyolefin resin are performed in one step, so that kneading and shaping with a foaming agent can be performed later. While maintaining a certain degree of melt fluidity, it is possible to obtain a modified resin composition having a melt strength that allows foaming at the same time, and by using this modified resin composition,
Highly recyclable polyolefin-based resin foam with excellent homogeneity, easy adjustment of expansion ratio, and recyclability of used foam that can be collected, melted, and molded again with low capital investment It can be provided with productivity.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a melt-kneading apparatus suitable for use in the method for producing a polyolefin-based resin foam of the present invention.

[Explanation of symbols]

 1: screw extruder 2: molding die 3: resin feeder 4: quantitative feeder for dioxime compound 5: quantitative feeder for foaming agent 6: suction vent 7: suction pump 8, 9: thermocouple for measuring resin temperature 10: Cooling roll 11: Foamable resin sheet

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F070 AA13 AA15 AA16 AB08 AC45 AC50 AE08 AE12 BA02 GA06 GA10 GB02 GB09 4F074 AA24 AA25 AD13 AG20 BA13 BB07 DA02 DA24 DA32 DA33 DA35 4J002 BB031 BB051 BB061 BB071 BB011 BG041 BP021 EQ017 ES007 ES016 EV267 FD146 FD327

Claims (1)

[Claims] 1. A foamable resin composition obtained by simultaneously melt-blending 0.05 to 5 parts by weight of a dioxime compound and a thermal decomposition type chemical foaming agent at a temperature of 170 ° C. or lower with respect to 100 parts by weight of a polyolefin resin. 180 ° C to 220 ° C
A method for producing a polyolefin-based resin body, wherein a cross-linking reaction and foaming of a polyolefin-based resin are performed in one stage by heating to the following temperature range.