JP2002012692A - Foaming rubber-modified styrene-based resin particle, method for producing the same and foamed molded material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide foaming rubber-modified styrene-based resin particles capable of obtaining a foamed molded material having excellent characteristics in its resiliency and decompression property. SOLUTION: The foaming rubber-modified styrene-based resin particles consist of a rubber-modified styrene-based resin obtained by mixing for reforming (I) 40-80 wt.% matrix component containing a polystyrene resin as a main component with (II) 20-50 wt.% high impact polystyrene resin and (III) 5-15 wt.% styrene-butadiene-styrene block copolymer resin, and contain 3-12 wt.% volatile blowing agent containing butane as a main component. The method for producing the same particles and the foamed molded material obtained by using the same are also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to expandable rubber-modified styrenic resin particles, a method for producing the same, and a foam molded article. More specifically, a foamed molded article having excellent elasticity, resilience, and impact resistance, which is suitably used mainly as a cushioning packaging material, a heat insulating material, and the like, and a foamed rubber modified material used in the production of the molded article. The present invention relates to styrene resin particles and a method for producing the same.

The use of the foamed molded article of the present invention is not particularly limited, but it is characterized by its excellent repetitive resilience and impact resistance, and is used as a cushioning packaging material for various OA equipment, audio equipment, home electric appliances and the like, a heat insulating material. It is particularly preferably used as a form.

[0003]

2. Description of the Related Art Expandable styrenic resin particles containing a volatile foaming agent are heated with steam to form pre-expanded particles.
This is filled in a mold and heated again to obtain a foamed styrene-based resin article having the foamed particles heated and fused. Foams made of polystyrene resin have excellent cushioning properties and heat insulation properties, and are easy to mold.
Although it is often used as a heat insulating material, it has the disadvantages of insufficient impact resistance and flexibility, being easily chipped by impact, and having a tendency for distortion to remain.

[0004] Polyolefin resin foam molded articles such as EPE and EPP generally have excellent impact resistance and flexibility. However, since the expandable polyolefin-based resin particles used in the production of the expanded molded article have extremely poor retention of the impregnated blowing agent, it is necessary to rapidly pre-expand them to form expanded particles. Since it has to be transported from the manufacturer to the molding manufacturer in the form of particles, there is a problem that the manufacturing cost increases. Further, for such foaming and molding, general-purpose polystyrene foam production equipment cannot be used, and special auxiliary equipment is required.

Therefore, a high-impact polystyrene resin obtained by modifying a polystyrene resin with butadiene rubber (hereinafter referred to as H
The use of IPS resin) to improve the impact resistance has been proposed in Japanese Patent Publication Nos. 47-18428 and 51-46536, and the like. HIP, although improved
When the S resin was a foam, the degree of improvement in impact resistance and flexibility was insufficient.

In order to further improve impact resistance and flexibility, Japanese Patent Application Laid-Open No. 54-154471 and Japanese Patent Publication No.
JP-A-4-158467 discloses a resin composition obtained by mechanically mixing a block copolymer of styrene and butadiene with a styrene resin, and JP-A-3-182529 discloses a resin composition obtained by hydrogenating a HIPS resin. A description is given of expandable resin particles obtained by impregnating a resin composition obtained by mechanically mixing a block copolymer of styrene and butadiene with a blowing agent. It is recognized that the foamed molded article using this has improved impact resistance to some extent as compared with the conventional HIPS foamed molded article, but using a large amount of the HIPS resin or the block copolymer increases the cost, It is considered difficult to mass produce.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve such problems, and as a result, have found that polystyrene resins, HIPS resins and styrene-butadiene-styrene block copolymer resins (hereinafter referred to as SBS resins). A) a modified rubber-modified styrenic resin obtained by mixing with a specific compounding agent to form a foamed resin having excellent elasticity and resilience by butaneing the main component of a volatile foaming agent. The present inventors have found that foamable rubber-modified styrene resin particles for obtaining particles can be obtained, and have reached the present invention.

That is, according to the present invention, a high impact polystyrene resin (II) is added to a matrix component (I) of 40 to 80% by weight and a high impact polystyrene resin (II) of 20 to 50% by weight.
And a styrene-butadiene-styrene block copolymer resin (III) mixed with 5 to 15% by weight of a modified rubber-modified styrene resin, and a volatile foaming agent containing butane as a main component in the resin. The present invention relates to expandable rubber-modified styrenic resin particles containing 3 to 12% by weight of the resin.

Further, the present invention provides a method for preparing a matrix component (I)
The components (II) and (III) are dispersed by an extruder, and the rubber-modified styrene-based resin obtained by hot-cutting into spherical particles having a diameter of 0.5 to 3.0 mm is dispersed in a dispersant. The method for producing expandable rubber-modified resin particles described above, wherein the particles are suspended in an aqueous medium containing, and in the presence of a blowing agent containing butane as a main component, a volatile blowing agent is impregnated at a temperature equal to or higher than the softening point of the resin. About. The present invention also relates to a foam molded article obtained from the foamable rubber-modified styrene resin particles.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The rubber-modified styrenic resin particles of the present invention are prepared by mixing 40 to 80% by weight of a matrix component (I) containing a polystyrene resin as a main component with a HIPS resin (II) 2.
0 to 50% by weight and 5 to 15% by weight of SBS resin (III)
And a modified rubber-modified styrenic resin obtained by mixing

The styrene resin used in the present invention is not particularly limited, and the weight average molecular weight usually used for expandable polystyrene resin particles is 150,000 to 35.
000 is preferred.

The HIPS resin is not particularly limited, but preferably has a generally used polybutadiene rubber content of 5 to 20% by weight based on the total HIPS resin content.

The SBS resin contains 20 to 40% by weight of the polystyrene resin based on the total amount of the SBS resin because of its homogeneous mixing property.
The amount of the polybutadiene rubber is preferably from 60 to 80% by weight.

In the present invention, the content of the butadiene rubber component in the total rubber-modified styrenic resin mixed is preferably 3 to 15% by weight, more preferably 5 to 1% by weight.
2% by weight. If too small, sufficient elasticity and resilience cannot be obtained, and if too large, on the other hand, the strength is reduced and when a foam molded article is obtained using the obtained foamed particles,
Shrinkage easily occurs, and the appearance of the molded product deteriorates.

The styrene-based resin in the rubber-modified styrene-based resin can be dissolved in, for example, tetrahydrofuran (THF) and filtered to remove the rubber component, and the weight-average molecular weight of the resin contained in the solution can be measured. . The weight average molecular weight is preferably 150,000 or more, more preferably 200,000 or more.
When the weight average molecular weight is smaller than 150,000, the strength and moldability of the obtained foam tend to be inferior.

The foamable rubber-modified styrenic resin particles of the present invention contain the volatile foaming agent described below in an amount of 3 to 12% by weight, preferably 5 to 10%, based on the rubber-modified styrenic resin.
% By weight.

The volatile foaming agent contains butane such as n-butane and i-butane as a main component, and this component accounts for at least 50% by weight or more of the total volatile foaming agent. Industrially, mixtures having an i-butane / n-butane ratio of 40/60% by weight are available and available. In addition, as a volatile foaming agent other than mixed butane, a volatile organic compound having a boiling point of 80 ° C. or less such as propane, n-pentane, i-pentane, n-hexane, i-hexane, and cyclopentane is mixed with butane. Can be used as a foaming agent.

The volatile foaming agent is contained in the rubber-modified styrenic resin in an amount of 3 to 12% by weight, preferably 5 to 10% by weight. When the content of the foaming agent is less than 3% by weight, when the material is heated to form pre-expanded particles, it cannot be foamed to a desired magnification, and when it exceeds 12% by weight, the cell diameter of the obtained pre-expanded particles is reduced. It becomes large and causes a decrease in strength.

The impregnation of the volatile blowing agent is from 100 to 130
C., preferably at a temperature of 100 to 120C. When the impregnation temperature is lower than 100 ° C., the shape of the obtained rubber-modified styrene resin particles does not become spherical. When a core (unimpregnated portion) is formed at the center of the rubber-modified styrene-based resin particles and pre-expanded particles are formed, an expanded portion and an unexpanded portion are formed within the expanded particles. The body cannot obtain the desired physical properties. If the temperature exceeds 130 ° C., the dispersion becomes unstable, and the particles tend to unite.

The impregnation time of the volatile foaming agent varies depending on the size of the rubber-modified styrene resin particles, but is not particularly limited. If the size per rubber-modified styrene resin particle is about 1 mm, it is at least 3 hours, preferably at least 6 hours. When the impregnation time is less than 3 hours, a core (unimpregnated portion) is formed at the center of the obtained rubber-modified styrene resin particles.

Additives usually used for dispersing rubber-modified styrene resin particles and impregnating a foaming agent, such as dispersants, surfactants, nonvolatile plasticizers, and solvents, can be added. Examples of the solvent shown here include cyclohexane, toluene, ethylbenzene, and the like. These are usually added in an amount of 3.0% by weight or less, preferably 1.0% by weight or less, based on the rubber-modified styrenic resin.

Furthermore, the rubber-modified styrene resin particles include:
If necessary, various additives, antioxidants, ultraviolet absorbers,
Lubricants, flame retardants, flame retardant aids, antistatic agents, inorganic fillers, carbon black, pigments and the like can be added. For example, lubricants include metal soaps, fatty acid esters, paraffin wax, and inorganic fillers include talc, calcium carbonate, magnesium carbonate and the like.

As the surface coating agent for the rubber-modified styrenic resin particles impregnated with a foaming agent, those generally used for foamable styrenic resins can be used. For example, metal soaps such as zinc stearate and calcium stearate used for preventing agglomeration in prefoaming, and higher fatty acid amides such as ethylenebisamide and stearamide can be mentioned. These agglomeration inhibitors are
0.05 to foamable rubber-modified styrenic resin particles
~ 0.5% by weight is added.

In the molding step, an additive having an effect of accelerating the fusion of the expanded rubber-modified styrene resin particles can also be used. Conventionally known additives can be used as such additives. For example, higher fatty acid triesters such as glyceride stearate and glyceride oleate, diesters, monoesters, and sucrose esters can be used.
Nonionic surfactants such as polyhydric alcohols such as glycerin, sorbitol, polyethylene glycol, and polypropylene glycol, sorbitan esters, and ethylene glycol adducts of higher fatty acids, which are used as antistatic agents for rubber-modified styrene resin foam particles; It is added in combination with the agent. These fusion promoters and antistatic agents are used in an amount of 0.005 to 0.005 to the foamable rubber-modified styrene resin particles.
0.2% by weight is added.

The coating of these coating agents is not particularly limited.
Conventionally known means can be used. For example, a mixer such as a ribo blender, a V-type blender, a Henschel mixer, a Loedige mixer or the like can be used.

The method for obtaining the foamable rubber-modified resin of the present invention includes the above-mentioned components (I), (II) and (II).
I) is melt-kneaded with an extruder, and a rubber-modified styrene resin granulated to a diameter of 0.5 to 3.0 mm by hot cutting is suspended and dispersed in an aqueous medium in a pressure-resistant closed container. And a method for producing foamable rubber-modified resin particles by impregnating with a foaming agent.

The foamable rubber-modified styrene resin particles impregnated with a foaming agent containing butane as a main component can be made into a product after aging for a certain period. The foamable rubber-modified styrene-based resin particles are heated by steam to form rubber-modified styrene-based resin foamed particles, filled into a mold having a predetermined shape, and then heated and fused by steam to obtain a foam molded article. be able to.

Prefoaming can be performed by charging foamable rubber-modified styrenic resin particles into a prefoaming tank and injecting steam of about 0.03 MPa.
After being foamed by steam, it is dried by warm air or compressed air. The discharged pre-expanded particles are usually left at room temperature for about one day before being subjected to molding.

The molding is carried out after filling the pre-expanded particles into a mold that has the desired shape and can be closed but cannot be sealed.
The foamed particles are heated and fused together by introducing steam of about 08 MPa. After cooling for a predetermined time by cooling water or evaporation latent heat in a vacuum state, the foamed particles are taken out of the mold to form a foamed molded article. These can be molded using molding equipment usually used for producing a polystyrene foam molded article.

The average cell diameter of the obtained foamed molded product is 150
If it is less than μm, individual bubbles are likely to be deformed by stress or the like, and the restoring property is reduced. Restorability improves as the average cell diameter increases. If the thickness exceeds 600 μm, the resilience is good, but the strength and impact resistance are reduced.

The average cell diameter of the foamed molded article can be adjusted by a known technique which is generally used when producing expandable styrene resin particles. For the bubble size adjusting agent,
Usually, amide compounds, sulfur compounds, inorganic substances (such as talc)
Is used. These foam control agents are kneaded into the resin by an extruder when producing rubber-modified styrene resin particles, or added to an aqueous medium when impregnating the foaming agent into the rubber-modified styrene resin particles. Is raised.

[0032]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited by these examples.

Examples 1-4 Polystyrene resin (trade name: Hibeads GP, manufactured by Hitachi Chemical Co., Ltd.), HIPS resin (trade name: HI polystyrene H430 825-21, manufactured by Nippon Polystyrene Co., Ltd.), S
BS resin (Clayton D-11 manufactured by Shell Japan Co., Ltd.)
02JS) in a composition ratio shown in Table 1 using a mixer, and then mixing and kneading the mixed resins separately using a 47 mm twin screw extruder (TEX-44, manufactured by Nippon Steel Works, Ltd.). By cutting, spherical particles of about 1.2 mm were obtained. In a pressure-resistant sealed container with an internal volume of 4 liters with a stirrer,
1850 g of ion-exchanged water and polyvinyl alcohol (Gohsenol KH-
20) 1.15 g, tricalcium phosphate 11.5 g, sodium dodecylbenzenesulfonate 0.1 g as activator.
12 g was added to obtain an aqueous medium. Next, 1150 g of the obtained rubber-modified styrenic resin was added, and the stirring speed was 300 rpm.
m. Thereafter, the temperature was constantly raised to 80 ° C., and after reaching 80 ° C., mixed butane (ratio of i-butane / n-butane = 4 /
6: weight ratio) 55 g each, press-fit with nitrogen twice
After the temperature was raised to 115 ° C. and maintained for 8 hours, it was cooled to 30 ° C. or lower to obtain expandable rubber-modified styrene resin particles.

The polybutadiene rubber content and the weight average molecular weight were measured by the following methods. (A) Polybutadiene rubber amount: 2% by weight of expandable rubber-modified styrene resin particles are dissolved in a solvent THF (tetrahydrofuran) (agitated with a magnetic stirrer for 15 hours or more).
This was divided into a soluble component and an insoluble rubber component, and the insoluble content was defined as the amount of polybutadiene rubber (% by weight). (B) Measurement of weight average molecular weight: 0.2% by weight of expandable rubber-modified styrenic resin particles were dissolved in a solvent THF (tetrahydrofuran), and the rubber component was removed by filtration.
It measured using C (gel permeation chromatograph). Table 1 shows the results.

The obtained expandable rubber-modified styrene resin particles are taken out, dehydrated, dried, and passed through 8.6 mesh.
Classification was performed with the mesh remaining, and 0.1% by weight of zinc stearate with respect to 100% by weight of the resin particles.
1% by weight was coated on the surface.

Next, the foamable rubber-modified styrene resin particles are put into a 35-liter batch foaming machine equipped with a stirrer, and steam having a pressure of 0.03 MPa is blown into the foamed rubber to form pre-foamed particles having a bulk density of 0.02 g / cm ^3. Obtained.

After the thus obtained pre-expanded particles are allowed to stand for 24 hours, the particles are filled in a mold that can be closed but cannot be hermetically sealed, and a foamed styrene resin molding machine (VS-500, manufactured by Daisen Industries). To obtain a foam molded article having a bulk density of 0.02 g / cm ³ by heating with steam. The molding conditions are shown below.・ Steam pressure 0.08MPa ・ Heating time (mold heating, one-side heating, both-side heating) 22 seconds ・ Water cooling time 5 seconds ・ Vacuum cooling Removal surface pressure 0.01MPa It had good wear and good appearance without shrinkage.

With respect to the obtained foamed molded product, the appearance of the molded product, the average cell diameter, the compression elastic modulus, the compression strength, and the compression restorability were evaluated by the following test methods and evaluation methods. Table 1 shows the results. Table 1 shows that the foamed rubber-modified styrenic resin according to the present invention has excellent elasticity and resilience.

1. Molded product appearance: The surface appearance of the foamed molded article was visually evaluated based on the following criteria. A: Almost no gap between particles and no shrinkage. ；: Interparticle gap and shrinkage are slightly observed. Δ: Interparticle gap and shrinkage are observed. X: remarkable interparticle gap and shrinkage are observed. 2. Average cell diameter: A part of the foam molded article was cut, and the cell diameter was measured with a transmission optical microscope. 3. Compressive modulus; JIS Z 02
34mm, length 50mm x width 50mm x thickness 50m
m, and the specimen was compressed at a rate of 10 mm / min in the thickness direction, and the stress value (in MPa) at which 25% of the initial thickness was subjected to compressive strain was defined as the compressive strength and the initial value of the stress-strain diagram. The compression modulus was determined by the gradient. 4. 4. Compressive strength ；: Compressive strength less than 0.12 MPa Δ: Compressive strength 0.12 to 0.14 MPa ×: Compressive strength exceeding 0.14 MPa Compression recovery rate: The obtained foam was subjected to JIS Z 02
34mm, length 50mm x width 50mm x thickness 50m
m, and the sample was compressed in the thickness direction at a speed of 10 mm / min to generate a compressive strain of 50%. Then, the sample was taken out and determined as follows. Restoration rate (%) = (T / 50) * 100 Here, T indicates a dimension after restoration in the compression direction. ；: Compression restoration ratio of over 85% △: Compression restoration ratio of 80 to 85% ×: Compression restoration ratio of less than 80% Cushioning property; the obtained foam is 50 mm thick;
1 at a falling distance of 60 cm and a static load of 0.07 kgf / cm ²
Dropping was repeated 0 times, and the change in the maximum acceleration (G) was measured.

Example 5 The procedure of Example 4 was repeated, except that the blowing agent was changed twice to 49 g of butane, and 11.5 g of cyclohexane was further used. Tables 1 and 2 show the evaluation results of the foam molded article. From Tables 1 and 2, it can be seen that the appearance of the molded product is good, and the molded product is excellent in elasticity, compression recovery, and buffer characteristics.

Example 6 The procedure of Example 5 was repeated except that the cell conditioner was changed to 0 g of talc. Table 1 shows the evaluation results of the foam molded article. Table 1
The results show that the average cell diameter was 440 μm, the molded article had good appearance, and was excellent in elasticity and resilience.

Comparative Examples 1 to 4 Polystyrene resin, HIPS resin and S
A foam molded article was obtained in the same manner as in Example 1 except that the composition of the BS resin was changed as shown in Table 1. Table 1 shows the evaluation results. It can be seen that the elasticity and the compression recovery were also poor. In the combination of polystyrene resin and HIPS resin, and the combination of polystyrene resin and SBS,
It was found that a foam molded article having excellent elasticity and compression restorability could not be obtained.

Comparative Example 5 A foam molded article was obtained in the same manner as in Example 5, except that the foam control agent was changed from 1% talc to 0.1% EBA (ethylenebisstearylamide). Table 1 shows the evaluation results. Molded product appearance is good, but average cell diameter is 140μ
m, which is inferior to the compression restoring property.

Comparative Example 6 Example 1 was repeated except that general expandable styrene resin particles (EPS) (expanded polystyrene beads manufactured by Hitachi Chemical Co., Ltd.) were used.
In the same manner as in the above, foaming and molding were performed to obtain a foam molded article. Tables 1 and 2 show the evaluation results. It can be seen that the elasticity, the compression restoring property, and the cushioning property were inferior.

Comparative Example 7 A foamed polypropylene molded article (E
PP) was obtained and the buffer properties were measured. Table 2 shows the results.
Shown in

The foamed molded article obtained from the foamable rubber-modified styrene resin particles of the present invention has excellent characteristics in elasticity and compression recovery. The foamed molded article of the present invention can be suitably used for applications such as buffer packaging materials and heat insulating materials that require elasticity and compression recovery.

[0047]

[Table 1]

[0048]

[Table 2]

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Claims (4)

[Claims] 1. A high-impact polystyrene resin (II), 20 to 50% by weight, and a styrene-butadiene-styrene block copolymer resin (III) in 40 to 80% by weight of a matrix component (I) containing a polystyrene resin as a main component.
5 to 15% by weight of a modified rubber-modified styrenic resin mixed with a volatile blowing agent containing butane as a main component in the resin in an amount of 3 to 12% by weight based on the resin. Rubber-modified styrene resin particles. 2. The expandable rubber-modified styrenic resin particles according to claim 1, wherein the sum of the butadiene rubber components contained in the components (II) and (III) is 3 to 15% by weight. 3. Component (II) to matrix component (I)
And (III) are dispersed by an extruder,
A rubber-modified styrene-based resin obtained by hot-cutting into spherical particles having a diameter of 3.0 mm is suspended in an aqueous medium containing a dispersant, and is suspended in the presence of a foaming agent containing butane as a main component. The method for producing expandable rubber-modified styrene resin particles according to claim 1, wherein a volatile foaming agent is impregnated at a temperature equal to or higher than the softening point of the resin. 4. A foamed rubber-modified styrene resin obtained from the expandable rubber-modified styrene resin particles according to claim 1.