JP5089920B2 - Expandable polyethylene resin particles and method for producing the same - Google Patents

Description

  The present invention relates to an expandable polyethylene resin particle and a method for producing the same, an expanded bead obtained by expanding the expandable polyethylene resin particle, and an expanded foam obtained by foam molding the expandable polyethylene resin particle or expanded bead. The present invention relates to a polyethylene resin molded product.

  Compared with expanded polystyrene resin molded products, expanded polyethylene resin molded products make use of the characteristics of excellent resilience of impact resistance, bending deflection, and repeated stress strain, and as packaging materials for precision parts and heavy products, Taking advantage of its excellent heat resistance and oil resistance, it is widely used as automotive parts such as shock absorbers, bumpers and floor spacers.

  Expandable polyethylene resin particles obtained by impregnating a polyethylene resin with a foaming agent are known. However, polyethylene has the property of easily permeating the foaming agent, and therefore, the foaming agent dissipates within a few hours after production, and the foamability is significantly reduced. There was a need to do. For this reason, it was necessary to install a pre-foaming machine and a molding machine near the foaming agent impregnation equipment, and the production base was limited. As a result, the transportation cost of the expanded particles and the molded product is high, which is economically disadvantageous.

  As a method for solving these problems, polyethylene resin particles and a cross-linking agent are added to a dispersion medium composed of water, low-boiling alcohols and ketones, and this is heated to perform a cross-linking treatment. A method of impregnating crosslinked resin particles as a foaming agent has been proposed (Patent Document 1).

  Many methods have been proposed for obtaining modified polyethylene resin particles by impregnating polyethylene resin particles with a vinyl aromatic monomer in which a polymerization initiator and a crosslinking agent are dispersed to perform polymerization and crosslinking. (Patent Documents 2 to 7).

JP 50-139167 A Japanese Patent Laid-Open No. 52-32990 Japanese Examined Patent Publication No. 45-32623 JP-A-1-284536 JP-A-48-101457 JP 49-5473 A JP 49-97884 A

  However, although the method described in Patent Document 1 described above has excellent retention of the foaming agent, the foamability is extremely low. That is, low-boiling alcohols and ketones do not perform a sufficient function as a foaming agent for polyethylene resin particles.

  On the other hand, in the methods described in Patent Documents 2 to 7, in order to obtain sufficient foaming agent retention, although the retention of the foaming agent is improved by increasing the ratio of the vinyl aromatic monomer to the polyethylene resin particles. It is necessary to considerably increase the ratio of the vinyl aromatic monomer. In this case, bending resilience, which is a characteristic of polyethylene, and resilience of repeated stress strain are impaired.

  The present invention has been made in view of the above, and suppresses the dissipation of the foaming agent, is excellent in foam moldability for a long period of time, and is further characterized by bending deflection, repeated stress strain, which is a feature of the foamed olefin resin molded product. An object of the present invention is to provide an expandable polyethylene-based resin particle that does not impair the recoverability and a method for producing the same.

  According to the first aspect of the present invention, polyethylene resin core particles are prepared from an acrylonitrile-styrene copolymer and a polyethylene polymer having a tensile fracture stress of 20 to 50 MPa according to JISK6924-2. Provided is a method for producing expandable polyethylene resin particles in which resin core particles are suspended in an aqueous medium, a styrene monomer is added to the suspension, and polymerization and impregnation with a foaming agent are performed.

  According to the 2nd aspect of this invention, the manufacturing method of the expandable polyethylene-type resin particle whose weight average molecular weights of the acrylonitrile styrene copolymer mix | blended with a polyethylene-type resin core particle are 70-400,000 is provided.

  According to the third aspect of the present invention, the ratio of the acrylonitrile-styrene copolymer to the total of the acrylonitrile-styrene copolymer and the polyethylene polymer in the polyethylene resin core particles is 1 to 50% by weight. A method for producing expandable polyethylene resin particles is provided.

  According to the fourth aspect of the present invention, the ratio of the polyethylene resin core particles to the total of the polyethylene resin core particles and the styrene monomer in the expandable polyethylene resin particles is 10 to 60% by weight. A method for producing certain expandable polyethylene resin particles is provided.

  According to the 5th aspect of this invention, the manufacturing method of the expandable polyethylene-type resin particle whose particle diameter of a polyethylene-type resin core particle is 0.1 mm or more and 3.0 mm or less is provided.

  According to the sixth aspect of the present invention, there is provided a method for producing expandable polyethylene resin particles, wherein the styrene monomer added to the suspension is a styrene monomer in which a polymerization initiator and a crosslinking agent are dispersed. Is done.

  According to the 7th aspect of this invention, the expandable polyethylene-type resin particle obtained by said manufacturing method is provided.

  According to the 8th aspect of this invention, the polyethylene-type foam bead obtained by foaming said foamable polyethylene-type resin particle is provided.

  According to the ninth aspect of the present invention, there is provided a polyethylene resin molded product obtained by foam molding the above expandable polyethylene resin particles or the above polyethylene foam beads.

  According to the present invention, the foamable polyethylene that suppresses the dissipation of the foaming agent, has excellent foam moldability for a long period of time, and does not impair the bending deflection and the repeated stress-strain resilience characteristic of the foamed olefin resin molded product. -Based resin particles and a method for producing the same can be provided.

Hereinafter, embodiments of the present invention will be described.
The present invention includes (1) a polyethylene resin core particle preparation step of preparing polyethylene resin core particles from an acrylonitrile-styrene copolymer and a polyethylene polymer having a tensile fracture stress of 20 to 50 MPa according to JIS K6924-2; (2) A polymerization step in which the polyethylene resin core particles are suspended in an aqueous medium, and a styrene monomer is added to the suspension to polymerize; (3) a blowing agent impregnation step in which a foaming agent is impregnated Have

(1) Polyethylene resin core particle production step The polyethylene resin core particles in the present invention are composed of a mixture in which an acrylonitrile-styrene copolymer is blended with a polyethylene polymer. , Not only ethylene homopolymers, but also copolymers such as ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, ethylene-vinyl chloride copolymers, ethylene-acrylic acid ester copolymers, It can be used alone or as a mixture of two or more.

In the present invention, the tensile fracture stress of the polyethylene polymer used for the polyethylene resin particles is 20 to 50 MPa, preferably 30 to 45 MPa. When the tensile fracture stress is less than 20 MPa, the bending deflection of the foamed molded product is lowered, and when the tensile fracture stress exceeds 50 MPa, the foamability is lowered.
In the present invention, the tensile fracture stress is measured according to JISK6924-2.

The weight average molecular weight of the acrylonitrile-styrene copolymer blended with the polyethylene resin core particles is preferably 70,000 to 400,000, more preferably 100,000 to 250,000. When the weight average molecular weight is less than 70,000, the retention of the foaming agent is lowered, and when the weight average molecular weight is more than 400,000, the foamability and moldability may be lowered.
The weight average molecular weight can be determined by gel permeation chromatogram method and converted into standard polystyrene.

  The ratio of the acrylonitrile-styrene copolymer to the total of the acrylonitrile-styrene copolymer and the polyethylene polymer in the polyethylene resin core particles is preferably 1 to 50% by weight, more preferably 2 to 10% by weight. It is.

  The polyethylene resin core particles used in the present invention can contain an air conditioner, a pigment, a slip agent and the like as long as the effect is not impaired in addition to the acrylonitrile-styrene copolymer and the polyethylene polymer.

The polyethylene resin core particles of the present invention can be prepared by blending an acrylonitrile-styrene copolymer with a polyethylene polymer.
It can mix | blend and granulate by kneading | mixing using an extruder. At this time, in order to uniformly knead, it is preferable to extrude after mixing a polyethylene polymer and an acrylonitrile-styrene copolymer in advance. Mixing of the polyethylene polymer and the acrylonitrile-styrene copolymer can be performed by a conventionally known means. For example, a blender such as a ribbon blender, a V blender, a Henschel mixer, or a ready game mixer can be used.

In this invention, in order to adjust the bubble of a foam, a bubble regulator can be added to a polyethylene-type resin core particle. Higher fatty acid bisamides, higher fatty acid metal salts, inorganic substances, and the like can be used as the bubble regulator.
The blending amount of the higher fatty acid bisamide and higher fatty acid metal salt that can be used as the bubble regulator is preferably in the range of 0.01 to 2 parts by weight with respect to 100 parts by weight of the resin component in the polyethylene resin core particles. . If the amount is less than 0.01 part by weight, there is a tendency that a sufficient effect of reducing the bubble size cannot be obtained. There is a tendency to get worse.

  It is preferable that the compounding quantity of the inorganic substance which can be used as a bubble regulator is the range of 0.1-5 weight part with respect to 100 weight part of resin components in a polyethylene-type resin core particle. If the amount is less than 0.1 parts by weight, there is a tendency that a sufficient effect of reducing the bubble size cannot be obtained. If the amount exceeds 5 parts by weight, the bubble size becomes extremely small, and the resin melts at the time of molding and the appearance of the molded product deteriorates. Tend to.

  In the present invention, the particle diameter of the polyethylene resin core particles is preferably 0.1 to 3.0 mm. A more preferable particle diameter is 0.4 to 2.0 mm. If the particle diameter is less than 0.1 mm, the retention of the foaming agent tends to decrease, and if it exceeds 3.0 mm, the mold filling property tends to decrease during molding, which is not preferable. Such a polyethylene resin core particle can be made fine by an extruder, but other methods may be used as long as a desired particle diameter is obtained. When using an extruder, it can adjust by extruding from the hole which has the diameter in the said particle diameter range, and cut | disconnecting to the length in the said particle diameter range with a pelletizer, for example.

(2) Polymerization step The polyethylene resin core particles obtained above are suspended in an aqueous medium to form a suspension. Dispersion in an aqueous medium is usually performed using an apparatus equipped with a stirring blade, and there are no restrictions on the conditions. Examples of the aqueous medium used in the present invention include ion exchange water.

  The polyethylene-based resin core particles are preferably dispersed together with a dispersant. Examples of the dispersant include organic dispersants such as polyvinyl alcohol, polyvinyl pyrrolidone, and methyl cellulose, and poorly soluble inorganic salts such as magnesium phosphate and tricalcium phosphate.

Furthermore, a surfactant can also be used for dispersion in an aqueous medium. Examples of the surfactant include sodium oleate, sodium dodecylbenzenesulfonate, and other anionic surfactants and nonionic surfactants commonly used in suspension polymerization.
Among these dispersants, it is particularly preferable to use an organic dispersant.

Next, a styrene monomer is added to the suspension and polymerized. Preferably, in order to uniformly polymerize styrene in the polyethylene resin particles, the polyethylene resin core particles are impregnated with the styrene monomer and polymerized. When the polyethylene-based resin core particles are impregnated and polymerized, crosslinking occurs with polymerization. If necessary, a polymerization initiator and a crosslinking agent are used. Preferably, the polymerization initiator and / or the crosslinking agent are preferably dissolved in the styrene monomer in advance.
In the polymerization process of the styrenic monomer, polyethylene may be cross-linked. In this specification, “polymerization” may include “cross-linking”.

  The styrenic monomer that can be used in the present invention is one or more of styrene and styrene derivatives such as α-methylstyrene and vinyltoluene, or these and methacrylic such as methyl methacrylate and ethyl methacrylate. It is a combination with other polymerizable monomers such as acid esters and corresponding acrylic acid esters, vinyl cyanide such as acrylonitrile and methacrylonitrile, and vinyl chloride. In the case of a combination, the ratio of styrene and / or styrene derivative is preferably 50% by weight or more based on the total monomers.

  In the obtained expandable polyethylene resin particles, the ratio of the polyethylene resin core particles to the total of the polyethylene resin core particles and the styrene monomer is preferably 10% by weight or more and 60% by weight or less, more preferably. Is 20% by weight or more and 50% by weight or less. If it exceeds 60% by weight, the particles are difficult to spheroidize, and if it is less than 10% by weight, the impact resistance, heat resistance, and chemical resistance, which are the characteristics of the polyethylene resin particles, tend to decrease.

  The polymerization initiator that can be used in the present invention is not particularly limited as long as it is used in a suspension polymerization method of a styrene monomer, and examples thereof include t-butyl peroxide, benzoyl peroxide, and t-butyl peroxy. One or more organic peroxides such as 2-ethylhexyl carbonate and t-butyl perbenzoate, and azo compounds such as azobisisobutyronitrile can be used.

The polymerization initiator may be added after being dissolved in a solvent, and impregnated into the polyethylene resin core particles. In this case, as a solvent for dissolving the polymerization initiator, aromatic hydrocarbons such as ethylbenzene and toluene, aliphatic hydrocarbons such as heptane and octane, and the like are used. In this case, the amount is usually 3% by weight or less based on the styrene monomer.
Although the usage-amount of a polymerization initiator changes with kinds of polymerization initiator, generally the range of 0.1-1.0 weight% is preferable with respect to a styrene-type monomer.

  In the present invention, fatty acid monoamides such as oleic acid amide and stearic acid amide, fatty acid bisamides such as methylene bis stearic acid amide and ethylene bis stearic acid amide, etc. are dissolved in the styrenic monomer or the solvent as a bubble regulator. May be used. In this case, it is preferable to use 0.01 to 2 parts by weight of the bubble regulator based on 100 parts by weight of the styrene monomer.

The cross-linking agent that can be used in the present invention is mainly one having a function of cross-linking polyethylene resin particles, preferably one that does not decompose at the polymerization temperature of the styrene-based monomer, but decomposes at the cross-linking temperature, Examples include peroxides such as dicumyl peroxide, 2,5-t-butyl perbenzoate, and 1.1-bismutual butyl peroxycyclohexane, which are used alone or in combination of two or more thereof. It is usually 0.1 to 5% by weight based on the monomer.
In the present invention, the polymerization initiator and the crosslinking agent may be the same compound.

  The addition of the styrenic monomer (including a polymerization initiator and / or a cross-linking agent as necessary) may be performed all at once or dividedly.

  The polymerization temperature varies depending on the type of polymerization initiator used, but is preferably in the range of 60 to 105 ° C. Moreover, although a crosslinking temperature changes with kinds of crosslinking agent to be used, the range of 100-150 degreeC is preferable.

(3) Foaming agent impregnation step Subsequently, the foaming agent is impregnated into the resin particles during or after polymerization (and crosslinking). For impregnation of the foaming agent, the foaming agent is press-fitted into a container, and the temperature is usually raised to a temperature equal to or higher than the softening point of the polyethylene resin particles, and the resin particles are impregnated.

As the foaming agent, a foaming agent that does not dissolve the polyethylene-based resin particles, or those that slightly swell are preferable, specifically, aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane, Alicyclic hydrocarbons such as cyclohexane and cyclopentane are used. These may be used alone or in combination of two or more.
These foaming agents are usually used in an amount of 5 to 30% by weight based on the polyethylene resin particles before impregnation with the foaming agent.

  The impregnation temperature of the foaming agent is preferably 80 ° C to 140 ° C, more preferably 90 ° C to 120 ° C. If the impregnation temperature of the foaming agent is less than 80 ° C., the impregnation of the foaming agent may be insufficient. If it exceeds 140 ° C, the resin particles may be flattened. After the impregnation of the foaming agent is completed, the expandable polyethylene resin particles can be obtained by discharging from the polymerization system.

  After dehydrating and drying the expandable polyethylene resin particles, a surface coating agent can be coated as necessary. For example, zinc stearate, stearic acid triglyceride, stearic acid monoglyceride, castor oil, antistatic agent, etc. can be used as the surface coating material.

  The expandable polyethylene resin particles produced by the method of the present invention are excellent in retention of the foaming agent and have excellent foamability and moldability for a long period of time.

  The polyethylene foam beads of the present invention are obtained by foaming the above expandable polyethylene resin particles by a conventional method. The polyethylene resin molded article of the present invention can be obtained by foam molding the above expandable polyethylene resin particles or polyethylene foam beads by a conventional method.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following Example.

[Example 1]
[Preparation of polyethylene resin core particles]
Henschel mixer (2850 g of low density polyethylene resin particles (Nisoron 9P51A, manufactured by Tosoh Corporation) having a tensile fracture stress of 40 MPa and 150 g of acrylonitrile-styrene copolymer resin particles (manufactured by Denka, AS-XGS, weight average molecular weight 1270,000) It was put into Mitsui Miike Chemical Industries, Ltd. FM10B) and mixed at 2000 rpm for 1 minute.
Next, a mixture of these resin particles was melt-extruded by an extruder (Ikegai Co., Ltd., PCM-30 twin screw type, die diameter 3 mm, cylinder temperature 230 ° C., head temperature 230 ° C.), cooled and solidified, and then pelletized by Nakatani Machinery Manufactured, cutter speed scale 0.5, roll speed scale 0.5) to 0.7 to 1.1 mm (average 0.9 mm) to obtain polyethylene resin core particles.

[Impregnation / polymerization / crosslinking process]
In a 5 L pressure-resistant stirring vessel, 385 g of the above polyethylene resin core particles, 2100 g of deionized water, 11 g of tricalcium phosphate, and 0.025 g of sodium dodecylbenzenesulfonate were charged and stirred.
Next, 0.55 g of t-butyl peroxide, 3.4 g of benzoyl peroxide, and 11.8 g of 1.1-starch butyl peroxycyclohexane are dissolved in 715 g of styrene monomer, and this styrene monomer is put in a container. The mixture was added and kept at 20 ° C. for 4 hours.
Thereafter, the temperature was raised to 88 ° C., and the temperature was maintained for 6 hours to polymerize the monomer. Subsequently, after adding 1.1 g of tricalcium phosphate, 0.03 g of sodium dodecylbenzenesulfonate, and 4.4 g of calcium carbonate, the temperature was raised to 135 ° C. and kept for 10 hours for crosslinking.

Thereafter, the mixture was cooled to 105 ° C., and 27 g of cyclohexane and 134 g of butane (isobutane / n-butane weight ratio = 4/6) were injected and held for 6 hours.
After cooling to room temperature, the polyethylene resin particles impregnated with the blowing agent were taken out and dehydrated and dried. Subsequently, the polymer particles were classified with a sieve having a mesh size of 3.35 mm and 1.7 mm to obtain resin particles. To 1000 g of the obtained resin particles, 1.0 g of fatty acid monoglyceride was added and mixed to obtain expandable polyethylene resin particles.
The obtained expandable polyethylene resin particles were pre-expanded into 30 ml / g expanded beads by heating with a steam using an expansion machine for expanded styrene resin (HBP-500LW manufactured by Hitachi Chemical Technoplant).
Then, after aging for about 18 hours, using a foamed styrene resin molding machine (VS-300 manufactured by Daisen Kogyo Co., Ltd.), the molded product was molded at a molding pressure of 0.12 MPa. )

The properties of the obtained expandable particles and molded products were evaluated by the following methods.
1. Foaming agent content (foaming agent amount)
The amount of the foaming agent after the obtained expandable polyethylene resin particles were allowed to stand at 20 ° C. for 24 hours in an open state was determined.
The amount of foaming agent was calculated by the following formula after heating the resin particles at 200 ° C. for 10 minutes.
Amount of foaming agent (% by weight) = (weight before heating−weight after heating) / weight before heating The amount of the foaming agent of the particles obtained in Example 1 was 7.3%.

2. Foaming degree This is the bulk magnification when foaming for 60 seconds in 100 ° C. boiling water.
The degree of foaming of the particles obtained in Example 1 was 33 ml / g.

3. Appearance of molded product The appearance of the molded product was visually determined in 5 stages, with 5 being the best and 1 being inferior.
The appearance of the molded product obtained in Example 1 was 4.0, which was good.

4). Bending deflection Measured according to JIS A9511.
The bending deflection of the molded product obtained in Example 1 was 41 mm.

[Example 2]
Example 1 Example 1 was conducted except that 2700 g of low density polyethylene resin particles (manufactured by Tosoh, Nipolon 9P51A) and 300 g of acrylonitrile-styrene copolymer resin particles (manufactured by Denka, AS-XGS, weight average molecular weight 1270,000) The same operation as in Example 1 was performed to obtain expandable polyethylene resin particles and a molded product.

  The foamable polyethylene resin particles obtained had an amount of foaming agent of 7.5%, a foaming degree of 35 ml / g, an appearance of the molded product of 4.0, and a bending deflection of the molded product of 39 mm.

[Comparative Example 1]
In Example 1, except that the low density polyethylene was changed to low density polyethylene having a tensile fracture stress of 13 MPa (manufactured by Tosoh, Petrocene 339), the same operation as in Example 1 was performed to obtain expandable polyethylene resin particles and a molded product. It was.

  The foamable polyethylene resin particles obtained had an amount of foaming agent of 7.2%, a foaming degree of 31 ml / g, an appearance of the molded product of 4.0, and a bending deflection of the molded product of 18 mm.

[Comparative Example 2]
Example 1 is the same as Example 1 except that the acrylonitrile-styrene copolymer resin is not used and the low-density polyethylene resin particles are ethylene vinyl acetate copolymer having a tensile fracture stress of 14 MPa (manufactured by Tosoh, Ultrasen 626). The same operation was performed to obtain expandable polyethylene resin particles and a molded product.

  The foamable polyethylene resin particles obtained had a foaming agent amount of 3.8%, a foaming degree of 6 ml / g, an appearance of the molded product of 2.0, and a bending deflection of the molded product of 20 mm.

[Comparative Example 3]
30 ml / g of expandable polystyrene resin particles (Hitachi Chemical Industries, High Beads SSB-TX-7) are heated with steam using a foaming machine for expanded styrene resin (HBP-500LW, manufactured by Hitachi Chemical Technoplant). The foamed beads were prefoamed.
Then, after aging for about 18 hours, using a foamed styrene resin molding machine (VS-300 manufactured by Daisen Industry), molding was performed at a molding pressure of 0.08 MPa to obtain a foamed polystyrene resin molded product.

  The appearance of the obtained molded product was 5.0, and the bending deflection was 18 mm.

The expandable polyethylene resin particles of the present invention and the foam molded products obtained therefrom can be used in various applications such as food containers, packaging materials for packing, cushioning materials, and heat insulating materials.

Claims (9)

From the acrylonitrile-styrene copolymer and a polyethylene polymer having a tensile fracture stress of 20 to 50 MPa according to JIS K6924-2, a polyethylene resin core particle is produced,
A method for producing expandable polyethylene resin particles in which the polyethylene resin core particles are suspended in an aqueous medium, a styrene monomer is added to the suspension, and polymerization and impregnation with a foaming agent are performed.   The method for producing expandable polyethylene resin particles according to claim 1, wherein the weight average molecular weight of the acrylonitrile-styrene copolymer is 70,000 to 400,000.   The expandable polyethylene according to claim 1 or 2, wherein the ratio of the acrylonitrile-styrene copolymer to the total of the acrylonitrile-styrene copolymer and the polyethylene polymer in the polyethylene resin core particles is 1 to 50% by weight. For producing resin-based resin particles.   The ratio of the polyethylene resin core particles to the total of the polyethylene resin core particles and the styrene monomer in the expandable polyethylene resin particles is 10 to 60% by weight. Method for producing expandable polyethylene resin particles.   The method for producing expandable polyethylene resin particles according to any one of claims 1 to 4, wherein the particle diameter of the polyethylene resin core particles is 0.1 mm to 3.0 mm.   The method for producing expandable polyethylene resin particles according to any one of claims 1 to 5, wherein the styrene monomer added to the suspension is a styrene monomer in which a polymerization initiator and a crosslinking agent are dispersed.   Expandable polyethylene resin particles obtained by the production method according to claim 1.   A polyethylene foam bead obtained by foaming the expandable polyethylene resin particles according to claim 7. A polyethylene resin molded product obtained by foam molding the expandable polyethylene resin particles according to claim 7 or the polyethylene foam beads according to claim 8.