JP2753039B2 - Method for producing carbon-containing styrene-modified foamable olefin-based resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] The present invention relates to a method for easily producing styrene-modified foamable olefin-based resin particles (including spherical bodies and columnar bodies) containing carbon particles.

[Industrial applications]

Since the styrene-modified expandable olefin-based resin particles containing carbon particles obtained by the production method of the present invention are expandable resin particles containing carbon uniformly, foamed resin particles obtained by pre-expanding using these are used. It is placed in a mold, steam-heated to expand the particles and fuse them together, and then cooled to obtain a foamed molded product having a good appearance and a good fusion ratio, uniformly colored black to the inside, and It is a foamed resin molded product having good antistatic properties and conductivity.

This foamed resin molded product is useful as an electromagnetic wave shielding wall material and an antistatic container.

(Prior art)

Packaging materials and return boxes for transporting various products such as electrical appliances, fish, fruits, etc. are made of expanded polystyrene, expanded polyethylene, expanded polypropylene, styrene-modified expanded polyethylene (Mitsubishi A synthetic resin foamed molded article such as Ellenpol (made by Yuka Birdsie) is used. However, these synthetic resin foam moldings have a disadvantage that they are easily charged with static electricity,
When used as a packaging material or returnable box for electrical products such as floppy disks, microcomputers, printers, and other electrical components such as ICs, (a) an antistatic agent may be attached to the surface as foamable resin particles. Used.

(B) Apply an antistatic agent to the surface of the foam molded article.

(C) A conductive sheet is attached to the surface of the foamed molded article.

(D) Apply a conductive paint to the surface of the foam molded article.

(E) Carbon particle-containing expandable resin particles are used as expandable resin particles.

Methods and the like are used.

However, in the methods (a) and (b), the antistatic function is as low as 1 × 10 ¹¹ to 1 × 10 ¹³ Ω in terms of the surface specific resistance. The rise is great.

According to the method (c), a molded product having good conductivity is obtained, but only planar attachment is possible, and the shape of the molded product is restricted.
Further, as in the case of the method (b), the sticking operation leads to an increase in the price of the product.

The method (d) results in a molded article having good conductivity, but the coating film is easily peeled off, and the price of the foam molded article due to the coating operation is undesirably increased.

In the method (e), a foam molded article of any shape is obtained,
And this product has the advantage of having excellent conductivity.

As a method for uniformly containing carbon in the styrene-based expandable resin particles, a method in which polystyrene is mixed with carbon and a foaming agent (expanding agent) by heating in an extruder and pelletized by quenching, and a method in which polystyrene and carbon are mixed in an extruder After heating and mixing to form a pellet, the pellet and the blowing agent are placed in a closed container and heated to impregnate the blowing agent, and styrene monomer having carbon dispersed therein is subjected to suspension polymerization in an aqueous medium, and the polymerization is carried out. There has been known a method of impregnating by adding a blowing agent during the process or after polymerization. However, in the methods of (1) and (2), small particles and large particles are less likely to be generated, and particles having a desired size can be obtained relatively uniformly.However, since the particles have a pellet-like shape, Has poor filling properties and the surface appearance of the foamed molded article is poor. The method of (1) can obtain true spherical expandable resin particles, but the generation of unnecessary small particles and large particles cannot be avoided, it is necessary to separate them, and to prevent contamination between product grades In addition, many equipment such as a mixing and dispersing tank for monomer and carbon, a drying line for resin particles, and a sieve need to be prepared for each product, which is disadvantageous in that equipment costs increase. Further, a serious disadvantage of the method is that the carbon dispersed in the monomer during the polymerization is transferred to the aqueous phase of the polymerization medium, causing loss of carbon, wastewater treatment is troublesome, and suspension polymerization is also problematic. There are drawbacks that the system becomes unstable, resulting in delay of polymerization or incomplete polymerization (increase in the amount of unreacted monomers).

As an improved method of the above method, instead of carbon, styrene, alkyl acrylate,
A method of preventing polymerization delay or incomplete polymerization by using a polymer obtained by graft polymerization of a monomer such as methacrylic acid ester or acrylonitrile, that is, a so-called polymer graft carbon has been proposed (JP-A-59-217715,
JP-A-60-31536). However, such a method using a polymer graft carbon is extremely disadvantageous industrially in that a special polymer graft carbon is required.

In Japanese Patent Application Laid-Open No. 60-31536, the polymerization reaction in the presence of such a polymer-grafted carbon is retarded or incomplete when a polymerization initiator having a benzene ring such as benzoyl peroxide is used. However, it is considered that there is a slight error in this point. That is, according to the study of the present inventors, the polymerization delay or incomplete polymerization in this type of suspension polymerization is not due to the presence of the benzene ring of the polymerization initiator, but the initiator does not generate a tertiary alkoxy radical. It is believed that it is generated by the use of a compound that generates a carboxy radical.

On the other hand, foamed polystyrene is superior to foamed polyethylene and polypropylene in terms of price and moldability, but is inferior to the latter olefin-based resin foam in compressive strain recovery, and is a foam molded product deformed by compressive load. Cannot be used repeatedly.

On the other hand, the olefin resin foam is rich in elasticity and compressive strain recovery, but has a drawback of poor moldability.

Therefore, in order to improve moldability, olefin resin particles are dispersed in water, styrene in which a polymerization initiator is dissolved is supplied to this dispersion, and then styrene is polymerized by heating to form a styrene-modified olefin resin. It is conceivable to use styrene-modified foamable olefin-based resin particles in which a volatile resin such as butane, pentane, dichlorodifluoroethane or the like is contained in a modified resin during the production or after the polymerization of resin particles. No.53-32972, No.58-57453
issue).

However, when carbon black particles are contained in the modified particles, there is a drawback that the presence of carbon inhibits the polymerization of styrene, as in the case of producing expandable styrene resin particles containing carbon particles.

As a method for remedying such a disadvantage of polymerization inhibition, it has been previously proposed to use a polymerization initiator which generates a tertiary alkoxy radical as a polymerization initiator (JP-A-62-1523).
8).

However, this method substitution (monomer transfer in industrial production scale 5 to 50 m ² to inert gas usually such as nitrogen gas in the vapor phase of the polymerization reactor is carried out at, ignition due to static electricity at the time of reactor stirring Is usually implemented to prevent).
That is, when the suspension polymerization is carried out in the absence of oxygen gas in the polymerization reactor gas phase, even if the particles obtained by pre-expanding the obtained expandable particles are subjected to bead foam molding in a mold, the surface blackness is still low. It has been found that an excellent foam molded article and a foam molded article excellent in conductivity cannot be stably obtained.

[Problems to be solved by the invention]

The present invention provides, during polymerization, a raw material that provides in-mold beads / molded foam having excellent blackness and excellent conductivity, even if replacement with an inert gas such as nitrogen gas in the reactor gas phase is carried out. The present invention provides a method for stably producing carbon-containing styrene-modified foamable olefin-based resin particles.

[Configuration of the invention]

(Means for Solving the Problems) In the present invention, a suspension polymerization is carried out in the presence of a water-soluble polymerization inhibitor such as sodium nitrite in a suspension system to obtain styrene-modified olefin resin particles having high conductivity. obtain.

That is, the present invention provides a styrene-based monomer in an aqueous medium in which olefin-based resin particles containing carbon particles are dispersed in water in a polymerization reactor, and a styrene-based monomer in the presence of a polymerization initiator and a polymerization inhibitor. Suspension polymerization of the monomer, at that time, during or after the polymerization reaction step of the styrene monomer, a boiling point lower than the glass transition temperature of the styrene resin is a polymer of the styrene monomer to be generated In a method for producing carbon-containing styrene-modified foamable olefin-based resin particles by impregnating the particles with a volatile expanding agent comprising an organic solvent or a gas, (i) a water-soluble polymerization inhibitor is used as a polymerization inhibitor.

(Ii) An organic peroxide that generates a tertiary alkoxy radical is used as a polymerization initiator.

Another object of the present invention is to provide a method for producing carbon-containing styrene-modified foamable olefin-based resin particles.

(Carbon-containing olefin-based resin) Examples of the carbon-containing olefin-based resin particles used in the present invention include carbon and olefin-based resin,
If necessary, zinc stearate, aluminum stearate,
Nucleating agents such as ethylene bisstearic acid amide, flame retardants,
Carbon particles such as those obtained by heating and mixing an antioxidant, an ultraviolet absorber and the like in an extruder and granulating into pellets with a strand cut, an underwater cut, a hot cut, or the like, are uniformly dispersed in an olefin resin.

Examples of the carbon used in the production of the carbon-containing olefin-based resin used in the present invention include furnace black, channel black, thermal black, acetylene black, graphite, and carbon fiber. In particular, Ketchen Black EC (trade name of Akzo), which is a kind of furnace black, is preferable because of its good conductivity.

Examples of the olefin resin containing carbon include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ethylene-butene- Ethylene resins such as 1 copolymer, ethylene / vinyl acetate copolymer, ethylene / acrylic acid copolymer, ethylene / acrylic acid alkyl ester copolymer, ethylene / methacrylic acid alkyl ester copolymer; propylene homopolymer , Propylene / ethylene copolymer, propylene / butene-1 copolymer, propylene / ethylene / butene / 1 copolymer, propylene-4-
Propylene-based resins such as methylpentene-1 copolymer, or a mixture of two or more of these or a mixture containing two or more of these olefin-based resins as main components and containing polystyrene, polyamide, polyvinyl chloride, polyethylene terephthalate, or the like. Available.

The content ratio of carbon in the carbon-containing olefin-based resin used in the present invention varies depending on the required blackness or conductivity of the foamed molded article. Usually, carbon is 1 to 50% by weight of the olefin-based resin, Preferably 2 to 30% by weight
Is appropriately selected from the range. The size of the carbon-containing olefin-based resin particles used in the present invention is not particularly limited, but is usually preferably about 0.1 to 5 mg / piece.

(Vinyl monomer) As described above, it is known to produce expandable styrene-modified olefin-based resin particles by suspension polymerization of a styrene monomer, and this known technique is used unless it is contrary to the gist of the present invention. Can be used.

Accordingly, as the vinyl monomer, styrene alone, styrene and chlorostyrenes, vinyltoluenes such as p-methylstyrene, a mixture of α-methylstyrene and the like, or styrene and other copolymerizable small amounts of other Monomers such as acrylonitrile, alkyl methacrylate (alkyl portion having about 1 to 8 carbon atoms), alkyl acrylate ester (alkyl portion having about 1 to 8 carbon atoms), mono- to dialkyl maleate (alkyl portion having 1 to 4 carbon atoms)
Degree), divinylbenzene, mono- or diacrylic acid or methacrylic acid esters of ethylene glycol, maleic anhydride, N-phenylmaleimide, and mixtures with others.

It is preferable that the amount of the vinyl monomer containing styrene is usually 20 to 300 parts by weight based on 100 parts by weight of the carbon-containing olefin-based resin particles. If the amount of the vinyl monomer is less than 20 parts by weight, the foamability and moldability of the resulting styrene-modified foamable olefin-based resin particles are difficult to be satisfied. The amount of vinyl monomer used is such that the carbon content of the resulting styrene-modified foamable olefin resin particles is 0.1%.
It is desirable that the content be about 30% by weight, preferably 1% to 15% by weight. If the carbon content in the styrene-modified foamable olefin-based resin particles is too small, the blackness of the foamed molded article, and the conductivity and antistatic imparting become insufficient,
If the amount is too large, the mechanical strength of the foamed molded article decreases.

(Polymerization initiator) The polymerization initiator used in the suspension polymerization of the present invention includes:
An initiator that generates a tertiary alkoxy radical (CO.),
Desirable is an initiator mainly containing an initiator that generates a tertiary alkoxy radical and does not generate a carboxy radical (RCOO.).

This is because an initiator that generates a tertiary alkoxy radical does not cause polymerization delay or incomplete polymerization, whereas an initiator that generates only a carboxy radical causes polymerization delay or incomplete polymerization.

Examples of the initiator for generating a tertiary alkoxy radical used in the present invention include t-butylperoxybenzoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyhexahydroterephthalate, and n-butylperoxyhexahydroterephthalate. Butyl-4,4-bis (t-butylperoxy) valerate, 1,1-bis (t-butylperoxy)
-3,3,5-Trimethylcyclohexane, dicumyl peroxide, di-t-butylperoxybutane, t-butylperoxyisopropyl carbonate and the like.

Among these initiators, dicumyl peroxide,
n-butyl-4,4-bis (t-butylperoxy) valerate, 1,1-bis (t-butylperoxy) -3,3,5-
Trimethylcyclohexane and t-butylperoxyisopropyl carbonate are particularly preferred because they do not generate carboxy radicals.

Examples of the polymerization initiator include an initiator mainly generating a carboxy radical such as benzoyl peroxide and lauroyl peroxide. As described above, an initiator mainly generating such a carboxy radical causes the polymerization reaction to proceed. It is not preferred as an initiator for use in the present invention, because it retards and increases the amount of unreacted vinyl monomer. However, such a carboxy radical-generating initiator or an azo-based initiator such as azobisisobutyronitrile, if used in a relatively small amount, can be used to start the tertiary alkoxy radical used in the present invention. It can be used in combination with the agent.

In an embodiment of the present invention, the olefin resin has a melting point.
Low-density polyethylene at 100-123 ° C, ethylene-vinyl acetate copolymer, ethylene-acrylic acid alkyl ester copolymer when the ethylene resin, as a polymerization initiator
Polymerization initiator mainly used for styrene polymerization with a decomposition temperature of 50 to 105 ° C to obtain a half-life of 10 hours, and crosslinking of an ethylene resin having a decomposition temperature of 105 ° C to 140 ° C to obtain a half-life of 10 hours Polymerization initiators such as dicumyl peroxide, di-t-butyl peroxide, t
When -butylcumyl peroxide or the like is used in combination, the obtained styrene-modified foamable ethylene-based resin particles are crosslinked, so that the steam foaming moldability is further improved.

The amount of the polymerization initiator used in the present invention is 0.1 to 4 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the styrene-containing vinyl monomer. When a polymerization initiator that mainly generates a carboxy radical is used in combination, the amount of the polymerization initiator is preferably 1% by weight or less based on the styrene-containing vinyl monomer.
If the amount of the polymerization initiator is too small, the polymerization is not completed, and the amount of the unreacted vinyl monomer increases. If the amount is too large, resin particles giving a brittle foam are obtained.

The polymerization temperature in the present invention is determined in consideration of the decomposition temperature of the polymerization initiator used, the degree of polymerization of the polymer to be produced, and the absorption rate of the vinyl monomer, and is usually 50 to 150 ° C.
Is appropriately selected from the range.

In the present invention, the polymerization initiator may be added to the polymerization system before adding the styrene-containing vinyl monomer, or may be added after being dissolved in the vinyl monomer.

Vinyl monomers include plasticizers such as toluene, xylene, cyclohexane, ethyl acetate, dioctyl phthalate, and tetrachloroethylene; small amounts of oil-soluble polymerization inhibitors; chain transfer agents such as mercaptans and α-methylstyrene monomers. ,
Flame retardants, dyes and the like can be added.

(Water-soluble polymerization inhibitor) Examples of the water-soluble polymerization inhibitor include nitrites such as sodium nitrite, potassium nitrite and ammonium nitrite.

For example, the required addition amount of sodium nitrite depends on the required blackness, conductivity and the amount of polymerization initiator to be added, the size of the carbon-containing olefin-based resin particles, and the like,
It is preferably from several tens of ppm to several thousand ppm with respect to water, and if added in a large amount, a good in-mold bead molded foam may not be obtained due to a decrease in the molecular weight of polystyrene or an increase in residual vinyl monomers.

In addition, even if an oil-soluble inhibitor such as para-t-butylcatechol, hydroquinone, or benzoquinone is dissolved in styrene, the effect of the present invention is not exhibited. A good foam molded article cannot be obtained due to an increase in body.

The water-soluble polymerization inhibitor such as nitrite hardly impregnates the olefin resin particles and dissolves in the aqueous medium.
Therefore, the polymerization of the vinyl monomer containing styrene impregnated in the carbon-containing olefin-based resin particles of the seed particles is performed, but in the aqueous medium not absorbed by the carbon-containing olefin-based resin particles of the seed particles. Suppression of polymerization of styrene-containing vinyl monomer near the particle surface being absorbed by styrene-containing vinyl monomer micro oil droplets and carbon-containing olefin resin particles, resulting in styrene modification The surface portion of the expandable olefin-based resin particles has a smaller amount of polystyrene than the central portion of the particles, in other words, the surface portion has a larger amount of conductive carbon. Olefin resin particles are obtained.

(Suspension polymerization) The polymerization reaction of the present invention is performed in an aqueous medium. In the aqueous medium, as a dispersion stabilizer, for example, polyvinyl alcohol, water-soluble polymer such as polyvinylpyrrolidone, tricalcium phosphate, magnesium pyrophosphate,
A poorly water-soluble inorganic dispersant such as calcium carbonate can be added. When adding the inorganic dispersant, it is desirable to use a surfactant such as sodium dodecylbenzenesulfonate in combination. The amount of the dispersant used is preferably 0.1% by weight or more based on water. However, the use of a large amount of 4% by weight or more is not inconvenient, but is not economically disadvantageous because the effect corresponding to the large amount cannot be expected.

In the present invention, during or after the polymerization reaction step of the suspension polymerization, an organic foaming agent is added according to a conventional technique, and the resulting carbon-containing styrene-modified foamable olefin resin particles are added to the organic foaming agent. Impregnated. As the organic blowing agent, those having a boiling point lower than the glass transition temperature of a styrene resin which is a polymer of a styrene monomer, for example, hexane, normal pentane, isopentane, neopentane, normal butane, isobutane, propane, Trichloromonofluoromethane, dichlorodifluoromethane, etc., alone or in a mixture are used.

In the present invention, when the organic foaming agent is added during the polymerization step, it is preferable that 70% by weight of the monomer is added after polymerization, and when the polymerization is completed at least 99%, Subsequently, impregnation with a foaming agent may be performed. Further, an aqueous medium is newly added and dispersed in the carbon-containing styrene-modified foamable olefin-based resin particles obtained by terminating the polymerization reaction, and a foaming agent is added thereto, and the foaming agent is impregnated. Is also good.

(Examples, etc.) Hereinafter, examples and comparative examples will be described in more detail.

Example 1 In a polymerization reactor having an internal volume of 20 m ³ , 9,000 kg of pure, 270 kg of tribasic calcium phosphate and 0.9 kg of sodium dodecylbenzenesulfonate as dispersants, and 9 kg of sodium nitrite as a water-soluble polymerization inhibitor were added, and an aqueous medium was added. And

Next, 18 parts by weight of Ketjen Black EC (manufactured by Akzo, The Netherlands) and 82 parts by weight of low-density polyethylene “Mitsubishi Polyethylene HE-60” (trade name of Diapolymer Co., Ltd.) having a melting point of 105 ° C. One part by weight of bis-stearic acid amide “Kao Wax EB-F” (manufactured by Kao Corporation) is kneaded with an extruder, and 2200 kg of carbon-containing polyethylene particles granulated to a size of 0.6 mg / piece with an underwater cut, and tertiary Butyl peroxy 2-ethylhexanoate 33k
g, tertiary butyl peroxyisopropyl carbonate 20 kg and dicumyl peroxide 5 kg, xylene 7
A solution obtained by dissolving 0 kg in styrene (3300 kg) was suspended in the aqueous medium, and the air in the gas phase in the polymerization reactor was sufficiently replaced with nitrogen gas, and then sealed with nitrogen gas at 1 kg / cm ² G under pressure. .

Thereafter, the temperature was raised to 76 ° C. in 1 hour, and maintained at the same temperature for 6 hours. Then, the temperature was raised to 80 ° C., and maintained for 4 hours to polymerize styrene. Then, the temperature was raised to 125 ° C. for 2 hours. After 2 hours, the polymerization was completed and cross-linked.

Then, after cooling to 76 ° C., 750 kg of butane was added to the aqueous medium, and kept for 3 hours to impregnate butane into the resin particles.

After the suspension was cooled to room temperature, the content was separated and taken out of water, and tribasic calcium phosphate was dissolved and removed with nitric acid, followed by washing with water to produce styrene-modified foamable modified polyethylene particles containing carbon particles.

The expandable resin particles were heated to 97 to 100 ° C. by steam using a 30-patch pre-expansion machine to obtain 25 g / pre-expanded particles.

After aging this pre-expanded particle for 1 day, 400mm long, 400mm wide,
Filling into a mold having a 50 mm thick mold cavity and having a vapor permeable hole, the steam pressure was 0.8 kg / cm ² · G.
After heating for 2 seconds, the pre-expanded particles were expanded and mutually fused, and then cooled to obtain an in-mold bead expanded molded product. This molded product had good appearance, fusion, blackness, and conductivity as shown in Table 1.

The method for measuring the surface polystyrene content of the modified resin particles was as follows: 1 g of the pre-expanded carbon-containing expanded styrene modified resin particles was immersed in 100 ml of toluene at 23 ° C. for 20 minutes, and the toluene was removed by filtration. Immerse in 50 ml of fresh toluene for 10 minutes and filter the toluene. The first extracted toluene and the second extracted toluene are combined, and the toluene is dissipated by an infrared lamp or the like, and the amount of the extracted polystyrene is determined.
Polyethylene content is high. ).

Examples 2 to 8 Same as Example 1 except that the weight per one of sodium nitrite, t-butyl peroxy-2-ethylhexanoate and carbon-containing polyethylene particles was changed as shown in Table 1. This was performed to obtain an in-mold bead foam molded product.
As shown in Table 1, these molded products had good appearance, fusion, blackness, and conductivity.

Example 9 The same procedure as in Example 1 was carried out except that potassium nitrite was added instead of sodium nitrite, to obtain an in-mold bead foam molded article. This molded product had good appearance, fusion, blackness and conductivity as shown in Table 1.

Comparative Examples 1, 2, and 3 Using the flask of No. 3 as a polymerization reactor, adding no sodium nitrite, performing no air replacement of the gas phase with nitrogen gas, and changing the supply amount of each sample to 3/20. Was carried out in the same manner as in Examples 1, 2 and 3 to obtain an in-mold bead foam molded article. The obtained molded product had good appearance, fusion, blackness, and conductivity as shown in Table 1.

Comparative Examples 4, 5, and 6 Except that sodium nitrite was not added, an in-mold bead foam molded product was obtained in the same manner as in Examples 1, 2 and 3. The resulting moldings had the appearance, fusion, blackness,
It was poor in conductivity.

Comparative Example 7 An in-mold bead foam molded product was obtained in the same manner as in Example 3, except that sodium nitrite was not added and that the polymerization inhibitor para-t-butylcatechol, which was oil-soluble in styrene, was added at 5000 ppm. The obtained molded product was poor in appearance and conductivity as shown in Table 1.

[Effect of the Invention] By using a water-soluble polymerization inhibitor at the time of suspension polymerization, foamable, highly conductive styrene-modified olefin-based resin particles containing carbon uniformly can be easily obtained, and the resin particles are formed in a mold. The moldability during bead foam molding is excellent. The foam molded article obtained by using the same is uniformly colored black to the inside, has excellent conductivity and antistatic properties, and has a good surface appearance.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification code FI C08F 255/00 C08F 255/00 (58) Field surveyed (Int.Cl. ⁶ , DB name) C08F 255/00 C08F 2/18 C08F 2/44 C08F 2/40 C08J 9/20

Claims (2)

(57) [Claims] 1. A styrene monomer is supplied to an aqueous medium in which olefin resin particles containing carbon particles are dispersed in water in a polymerization reactor, and the styrene monomer is supplied in the presence of a polymerization initiator and a polymerization inhibitor. Suspension polymerization of the styrene-based monomer, during or after the styrene-based monomer polymerization reaction step, an organic substance having a boiling point lower than the glass transition temperature of the styrene-based resin which is a polymer of the styrene-based monomer formed. In a method for producing carbon-containing styrene-modified foamable olefin-based resin particles by impregnating particles with a volatile expanding agent comprising a solvent or a gas, (i) a water-soluble polymerization inhibitor is used as a polymerization inhibitor. (Ii) An organic peroxide that generates a tertiary alkoxy radical is used as a polymerization initiator. A method for producing carbon-containing styrene-modified foamable olefin-based resin particles, comprising: 2. The method according to claim 1, wherein the water-soluble polymerization inhibitor is nitrite.