JPH09202837A - Foamed particle of electrically conductive polypropylene resin and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain foamed particles of electrically conductive polypropylene resin capable of giving a molded article having excellent properties in spite of high content (>=10wt.%) of electrically conductive carbon. SOLUTION: This foamed particle of an electrically conductive polypropylene resin is produced by impregnating a foaming agent into a polypropylene resin particle containing a carboxyl-containing polypropylene resin as a base and further containing >=10wt.% of electrically conductive carbon and nucleus bubbles and foaming the impregnated product or by impregnating a foaming agent into a polypropylene resin particle containing >=10wt.% of electrically conductive carbon and 0.01-5wt.% of a water-soluble inorganic substance and foaming the impregnated product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to conductive polypropylene resin expanded particles and a method for producing the same.

[0002]

2. Description of the Related Art Foamed polyolefin resin particles are widely used as a raw material for manufacturing various molded products such as packaging materials and cushioning materials, but in recent years, they have been used as conductive materials for packaging electronic parts such as ICs. There is a demand for molded bodies having. As one of the methods for imparting conductivity to the molded body, there is a method in which a conductive agent is contained in the foamed particles that are the raw material for producing the molded body, and as such conductive polyolefin resin foamed particles, conductive carbon is dispersed. The conductive expanded polyethylene resin particles are known (Japanese Patent Application Laid-Open No. 3-2230).
issue). However, even if it is the same polyolefin resin as the polyethylene resin, the polypropylene resin has high crystallinity, so even if a large amount of conductive carbon is dispersed in the resin, it achieves a dispersed state in which it exhibits good conductivity. It was difficult to obtain, and it was difficult to obtain expanded polypropylene resin particles having excellent conductivity.

The applicant of the present invention blended a higher fatty acid amide and / or a higher fatty acid metal salt with a conductive carbon in a specific proportion in a polypropylene resin to obtain expanded polypropylene resin particles and a foamed polypropylene resin having excellent conductivity. It was found that (Japanese Patent Application No. 6-117698).
issue).

[0004]

However, the expanded polypropylene resin particles obtained by adding the higher fatty acid amide and / or the higher fatty acid metal salt together with the conductive carbon are
Although it is excellent in conductivity, there is a problem that it is difficult to obtain a molded article having excellent physical properties because the bubbles in the particles become fine. In addition, the polypropylene resin expanded particles to which conductive carbon is added are likely to have a decrease in the internal pressure of the particles applied by the pressure treatment prior to the molding of the expanded particles. It is difficult to stably obtain an excellent molded product with a high expansion ratio by applying an internal pressure of particles, and the dimensional stability of the resulting molded product,
The compression recovery property was not sufficiently satisfactory.

[0005] The present invention has been made in view of the above points,
It is an object of the present invention to provide a conductive polypropylene-based resin expanded particle capable of providing a molded product having excellent conductivity and excellent physical properties, and a method for producing the same.

[0006]

That is, the expanded conductive polypropylene resin particles of the present invention are characterized by containing conductive carbon in an amount of 10% by weight or more and having an internal pressure attenuation coefficient of less than 0.3.

The method for producing expanded beads of conductive polypropylene resin of the present invention is based on polypropylene resin having a carboxyl group as a base material and contains 10% by weight or more of conductive carbon and nuclear bubbles. It is characterized in that foamable resin particles obtained by impregnating resin particles with a foaming agent are foamed. Alternatively, the method for producing expanded particles of conductive polypropylene resin according to the present invention comprises impregnating a polypropylene resin particle containing 10% by weight or more of conductive carbon and 0.01 to 5% by weight of a water-soluble inorganic substance with a foaming agent. It is characterized in that the expandable resin particles thus foamed.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The conductive polypropylene resin foamed particles of the present invention exhibit excellent conductivity by containing 10% by weight or more of conductive carbon, and the higher the content of conductive carbon is, the more conductive it is. However, if the expanded particles contain conductive carbon in an amount of 10 to 16% by weight, a molded product having a volume resistivity value of 10 ⁰ to 10 ⁴ Ωcm and excellent conductivity can be obtained. If the conductive carbon content exceeds 100, a cost disadvantage arises, and the fluidity of the expandable resin particles impregnated with the foaming agent at the time of melting decreases, resulting in poor foamability and a large expansion ratio. It becomes difficult to obtain a good molded product. Therefore, the content of conductive carbon is preferably 10% by weight.
As described above, the amount is 16% by weight or less, particularly preferably 12 to 14% by weight.

As the conductive carbon, acetylene black, furnace black or the like can be used.
Furnace black, which can provide high conductivity with a small amount of addition, is preferred. Furnace black having a dibutyl phthalate oil absorption of 300 ml / 100 g or more and a BET specific surface area of 700 m ² / g or more is preferable because high conductivity can be imparted even with a small amount of the compound. As such furnace black, for example, black pearl 2
000 (made by Cabot), Ketjen Black EC
(Made by Ketjen Black International),
# 3950 (manufactured by Mitsubishi Kasei) and the like. These can be used alone or in combination of two or more.

The expanded particles of the present invention have an internal pressure attenuation coefficient of 0.3.
However, it is particularly preferably less than 0.2. When the internal pressure attenuation coefficient is 0.3 or more, the moldability is poor, and it is difficult to stably obtain an excellent molded article with a high expansion ratio, and the obtained molded article is poor in dimensional stability and surface smoothness. In addition, the physical properties such as compression residual strain tend to be inferior.

The expanded particles of the present invention have a DSC curve obtained by differential scanning calorimetry of the expanded particles, which has two peaks on the higher temperature side than the endothermic peak (referred to as an intrinsic peak) due to the melting of the base resin. It is preferable that the polymer has an endothermic peak (referred to as a high temperature peak) that is considered to be caused by the presence of a secondary crystal, and the heat of fusion of the high temperature peak is 9 to 30 J / g. Having such a high temperature peak of the heat of fusion is a necessary condition for obtaining a molded product having a high independent foaming rate. The heat of fusion of the high temperature peak corresponds to the area of the portion surrounded by the peak c of the high temperature peak b on the higher temperature side than the specific peak a and the baseline c in the DSC curve shown in FIG.

The conductive polypropylene resin foamed particles of the present invention contain, in addition to conductive carbon, additives such as an antistatic agent, an antioxidant, a light stabilizer, a lubricant, and a pigment, if desired. It may be contained. The expanded particles of the present invention,
Usually, the bulk density is 0.01 to 0.3 g / cm ³ , and the average cell diameter is 0.05 to 0.5 mm.

Containing 10% by weight or more of conductive carbon,
The conductive polypropylene-based resin expanded particles having an internal pressure attenuation coefficient of less than 0.3 can be manufactured as follows.

The first manufacturing method is a foaming resin in which particles having a carboxyl group-containing polypropylene resin as a base resin contain conductive carbon and nuclear bubbles, and the resin particles are impregnated with a foaming agent. This is a method of foaming particles. The impregnation of the foaming agent into the resin particles and the foaming process are, for example,
Resin particles are dispersed in a dispersion medium in a closed container and heated to a temperature equal to or higher than the softening point of the resin particles, and pressurized, and after impregnating the resin particles with a foaming agent, one end of the container is opened to expand the resin particles. A method in which the dispersion medium and the dispersion medium are discharged under a lower pressure atmosphere than the inside of the container to foam is preferably adopted.

As the polypropylene resin having a carboxyl group, for example, propylene homopolymer, ethylene-propylene block copolymer, ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene-butene. Ordinary propylene-based polymer such as random copolymer, maleic acid, fumaric acid, mesaconic acid, unsaturated dicarboxylic acid such as itaconic acid, maleic anhydride, citraconic acid anhydride, unsaturated dicarboxylic acid anhydride such as itaconic acid anhydride Or dimethyl maleate, monoethyl maleate, dibutyl fumarate, dimethyl citraconate, those graft-modified with a modifying agent such as unsaturated dicarboxylic acid lower ester such as dimethyl mesaconate, and those and ordinary carboxyl group-free polypropylene A mixture of resins. Particularly preferred as the modifier is maleic anhydride,
Graft modification is very easy, which is preferable.

Examples of the polypropylene resin having a carboxyl group used as the base resin of the polypropylene resin particles include, for example, those graft-modified with the above-mentioned modifying agent, the graft-modified polypropylene resin and the ordinary polypropylene resin. Both the mixture of, and the graft-modified polypropylene-based resin alone have a graft modification amount of 0.001 to 0.1 as the entire base resin.
It is preferable to set it to be mol%.

The nuclear bubbles contained in the polypropylene resin particles are fine bubbles which become the nuclei of the bubbles when the resin particles are impregnated with a foaming agent and foamed. The growth of bubbles when the expandable resin particles impregnated with the agent are expanded is promoted, and expanded particles having a large bubble diameter can be obtained. Moreover, the effect of increasing the expansion ratio of the expanded particles is also produced by containing the nuclear bubbles. The size of the nuclear bubble is 10 to 150 μ, preferably 40.
˜100 μ, which is confirmed by cutting the resin particles and observing the cross section with a microscope. It is essential that the base resin of the resin particles used in the first method of the present invention is a polypropylene resin having a carboxyl group,
When only a normal polypropylene resin not containing a carboxyl group is used, and when the graft modification amount of the base resin as a whole by the modifying agent is less than 0.001 mol%, nuclear bubbles are present in the resin particles. As a result, it becomes difficult to disperse the particles uniformly, and as a result, the expanded particles obtained by impregnating the resin particles with a foaming agent and expanded the bubbles have an increased bubble diameter due to the nucleus bubbles Since the variation will be large, the internal pressure damping property will be poor,
It is difficult to obtain a molded product having excellent dimensional stability and compression recovery. As a method of obtaining the nucleus bubbles, for example, a step of melting the polypropylene-based resin in an extruder, extruding it in a strand shape from the extruder, and cutting the strand to obtain resin particles (hereinafter referred to as a pelletizing step). In melting the resin in the extruder, a decomposing type foaming agent is added and the foaming agent is kneaded into the resin at a temperature equal to or higher than the decomposition temperature of the foaming agent to decompose at least a part of the foaming agent to form nuclear bubbles. A method of kneading a volatile foaming agent into a resin, forming a nuclear bubble by volatilizing the volatile foaming agent, a method of kneading a void-forming agent into the resin to form a void by the void-forming agent into a nuclear bubble. A method of melting and kneading foamed particles or a foamed molded product into a resin to make bubbles of the foamed particles or a foamed molded product into a nuclear bubble, or a method of kneading an inorganic gas into a molten resin to form a nuclear bubble. Thought But it is,
The method (2) is most preferable because the resin particles in which the nuclear bubbles are dispersed can be obtained most uniformly.

As the decomposition type foaming agent used in the above method, azodicarbonamide, monosodium citrate,
Examples thereof include dinitrosopentamethylenetetramine, p, p'-oxybisbenzenesulfonyl hydrazide, diazoaminobenzene, azobisisobutyronitrile, p-toluenesulfonyl semicarbazide, benzenesulfonyl hydrazide, sodium hydrogen carbonate and the like. When forming a nuclear bubble in the resin particle by the decomposing type foaming agent, the volume of the resin particle after the nuclear bubble is formed is 1.01 to 2.0 times, preferably 1 to the volume of the resin particle before the nuclear bubble is formed. .0
It is preferable to add the foaming agent so that the ratio is 1 to 1.5 times. The decomposition-type foaming agent is preferably used in an amount of 0.005 to 5% by weight, particularly 0.01 to 0.3% by weight, based on the resin.

In dispersing the additive such as conductive carbon in the resin particles, a raw material mixture in which the resin and the additive are predispersed by using a Banbury mixer or a pressure kneader is used before the pelletizing step of the resin particles. It is preferable to create it.

As a method for foaming the polypropylene resin particles containing 10% by weight or more of conductive carbon and nuclear bubbles formed as described above, the resin particles and the foaming agent are dispersed in a dispersion medium in a closed container. After heating and pressurizing to a temperature above the softening point of the resin particles to impregnate the resin particles with a foaming agent, one end of the container is opened and the expandable resin particles and the dispersion medium are at a lower pressure than in the container. In the case of using the method of releasing and foaming, the dispersion medium for dispersing the resin particles does not dissolve water, alcohols such as methanol and ethanol, glycols such as ethylene glycol, and resin particles such as glycerin. Although a solvent can be used, water is usually used.

As the foaming agent for foaming the resin particles, it is preferable to use a volatile foaming agent or an inorganic gas, and as the volatile foaming agent, aliphatic hydrocarbons such as propane, butane, hexane and cyclobutane are used. , Cyclohexane and other cycloaliphatic hydrocarbons, trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, halogenated hydrocarbons such as methylene chloride, and the like, the inorganic gas, Examples thereof include carbon dioxide, air, nitrogen, helium and argon. These foaming agents may be used alone, or two or more kinds may be mixed and used, or the volatile foaming agent and the inorganic gas may be mixed and used. When a volatile foaming agent is used as the foaming agent, the addition amount of the foaming agent is preferably 5 to 30 parts by weight with respect to 100 parts by weight of the resin particles, and when an inorganic gas is used, the equilibrium vapor pressure in the closed container. Is preferably 20 to 60 kgf / cm ² G.

When the resin particles are dispersed in the dispersion medium and heated, a fusion preventing agent may be added to the dispersion medium in order to prevent the resin particles from being fused to each other. As the anti-fusing agent, any inorganic or organic one can be used as long as it does not dissolve in the dispersion medium and does not melt by heating. In general, an inorganic anti-fusing agent is used. As the inorganic anti-fusing agent, powders of kaolin, mica, aluminum oxide, titanium oxide, aluminum hydroxide and the like are suitable. The anti-fusing agent preferably has an average particle size of 0.001 to 100 μm, particularly preferably 0.001 to 30 μm. When an anti-fusing agent is added, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate or sodium oleate as a dispersing aid. The anti-fusing agent is added in an amount of about 0.01 to 2 parts by weight per 100 parts by weight of the resin particles, and the surfactant is 0.00 per 100 parts by weight of the resin particles.
It is preferable to add about 1 to 1 part by weight.

After the resin particles containing the conductive carbon and the nuclear bubbles are impregnated with the foaming agent as described above, one end of the closed container is opened to remove the resin particles and the dispersion medium at a pressure lower than that in the container. The resin particles can be foamed to obtain expanded particles by discharging the resin particles under the atmosphere, usually under atmospheric pressure. At this time, the pressure in the container is at least 20 atm or higher, preferably 30 atm or higher, and the temperature in the container is preferably from −10 ° C. to + 15 ° C. of melting point of the resin.

A second method for obtaining the expanded beads of the present invention is to impregnate the resin particles with a polypropylene resin particle containing conductive carbon and a water-soluble inorganic substance in the same manner as the above-mentioned first method with a foaming agent. And foamed to obtain expanded particles.

As the base resin for the resin particles used in the second method, since the resin particles do not contain nuclear bubbles, the above-mentioned first resin is used.
It is not necessary to contain a polypropylene-based resin having a carboxyl group like the base resin in the method of 1., a usual polypropylene-based resin can be used, but a polypropylene-based resin having a carboxyl group can also be used. Of course.

Examples of the water-soluble inorganic substance include borax, zinc borate, sodium borate, magnesium borate, sodium chloride, magnesium chloride, calcium chloride and the like. Among them, when boric acid metal salt is used, the bubble diameter is large and It is preferable because expanded beads having excellent moldability can be obtained. The water-soluble inorganic substances can be used alone or in combination of two or more. These water-soluble inorganic substances are usually added to the resin in the pelletizing step of the polypropylene resin. The water-soluble inorganic substance is usually added as a powder, but the particle size is not particularly limited. However, it is preferable to use particles having a particle size of generally 0.1 to 150 μm, particularly 0.5 to 20 μm. The water-soluble inorganic substance is contained in the resin particles in an amount of 0.01 to 5% by weight, preferably 0.01 to 1% by weight. The content of the water-soluble inorganic substance in the resin particles is 0.
If it is less than 01% by weight, the expanded particles will be inferior in the internal pressure damping property, and if it exceeds 5% by weight, the cost will be high and the contraction rate of the expanded particles immediately after expansion will be high, which is not preferable. Even in this method, the conductive carbon is contained in the resin particles in the same manner as in the above method.

The polypropylene-based resin particles containing 10% by weight or more of conductive carbon and 0.01 to 5% by weight of water-soluble inorganic substance obtained as described above are prepared in the same manner as in the first method. The expanded particles of the present invention can be obtained by foaming.

The conductive polypropylene-based resin expanded particles obtained by the first and second methods of the present invention are aged under atmospheric pressure, and then subjected to a pressure treatment to give an internal pressure, and then in a mold. Then, the foamed particles are fused with each other to obtain a molded product having a desired shape.

[0029]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

Examples 1 to 4, Comparative Examples 1 to 3 Conductive carbon ("Ketjen Black EC" manufactured by Ketjen Black International, BET specific surface area 800 m ² / g), ethylene-propylene random copolymer (ethylene 4.5% by weight, melting point 135 ° C.,
MI = 8 g / 10 minutes), maleic anhydride modified polypropylene (“P371K” manufactured by Mitsubishi Chemical Corporation, maleic anhydride graft modification amount 0.11 mol%, melting point 139 ° C., M
FR = 6 g / 10 minutes) was mixed with a Banbury mixer to prepare a raw material mixture. Next, 0.1 part by weight of monosodium citrate was added to 100 parts by weight of this raw material mixture (only Comparative Example 1 was not added), and the mixture was melt-kneaded at 240 ° C. in an extruder, then extruded into a strand, and then the strand was cut. To obtain resin particles. Table 1 shows the amount of maleic anhydride modified and the conductive carbon content of the resin particles with respect to the entire base resin.

Next, 100 parts by weight of the above resin particles and 30 parts of water
0 parts by weight, carbon dioxide in the amounts shown in Table 1, kaolin 0.3
Parts by weight and 0.006 parts by weight of a surfactant (sodium dodecylbenzenesulfonate) were charged into a 400 liter autoclave, heated to the foaming temperature shown in Table 1 with stirring, and kept at the same temperature for 15 minutes, and then the autoclave. Nitrogen gas was introduced into the autoclave to maintain the equilibrium vapor pressure in the autoclave, one end of the autoclave was opened, and the contents were discharged under atmospheric pressure to foam the resin particles. Table 1 shows the physical properties of the obtained expanded beads. In addition, 2
After aging for 4 hours under atmospheric pressure, pressurizing with air 1.
After applying an internal pressure of 5 kgf / cm ² G and leaving it at 23 ° C. for 1 hour, it was filled in a mold of 300 mm × 300 mm × 60 mm and steam-heated to mold. The obtained molded body was cured at 60 ° C. under atmospheric pressure for 1 day. Various physical properties of the obtained molded product are also shown in Table 1.

[0032]

[Table 1]

The physical properties of the expanded beads and the physical properties of the molded product in Table 1 were evaluated as follows. Attenuation of internal pressure 23 ° C, 1atm, internal pressure 2kgf / cm ² G to 1k
The time (t: unit is time) for decreasing to gf / cm ² G is measured, and the internal pressure damping coefficient k is calculated by the following equation (1). The internal pressure damping coefficient k is less than 0.3 ... It was evaluated as k of 0.3 or more ... Further, the internal pressure of the foamed particles when the ambient temperature was T (° K) was obtained by the following formula (2).

[0034]

## EQU1 ## log (1/2) =-kt (1)

[0035]

[Equation 2]

Uniformity of Bubbles 20 foamed particles were cut at the center and observed with a cross section magnified 50 times, and there was almost no variation in bubbles within particles or between particles. There are variations in the air bubbles ...
It was evaluated as x.

Average Cell Diameter 20 foamed particles were cut at the center and the cross section was magnified 50 times to observe the average diameter of the cells, and the average cell diameter was 0.05 mm or more. The diameter was less than 0.05 mm ...

Presence or absence of nuclear bubbles The resin particles were cut, and the cut surface was observed with a microscope to confirm the presence or absence of nuclear bubbles.

Conductivity of Molded Body The volume resistivity of the molded body was measured with a resistance meter (Loresta AP) manufactured by Mitsubishi Chemical Corporation.

Dimensional stability of molded body Dimensional stability of molded body after curing at 60 ° C for 1 day (300 mm
X300 mm), the length of the line segment connecting the midpoints of the two opposite sides is measured for each of the four sides around one side, and the average length: A (mm) is calculated. Then
The shrinkage rate was calculated by substituting it in the following formula (3), and the shrinkage rate was evaluated as less than 2.7% ... ◯ Shrinkage rate is 2.7% or more ...

[0041]

## EQU00003 ## Shrinkage (%) = [(300-A) / 300] .times.100 (3)

Compressive recovery of molded body 50 minutes long by slicing the molded body aged at 60 ° C for 1 day
m, width 50 mm, thickness 25 mm rectangular parallelepiped test piece is created, and the test piece is compressed by 75% in the thickness direction at a speed of 10 mm / min using a universal testing machine, and immediately thereafter at a speed of 10 mm / min. The thickness: B (mm) of the molded product when the stress becomes zero is measured, and the residual strain is obtained by substituting it in the following formula (4). The residual strain is 30% or less ... ∘∘ The residual strain exceeded 30% and was evaluated as ×.

[0043]

## EQU00004 ## Residual strain (%) = [(25-B) / 25] .times.100 ... (4)

Examples 5 to 7 and Comparative Examples 4 to 6 The same conductive carbon and ethylene-propylene random copolymer as those used in Examples 1 to 4 (ethylene content 4.
5% by weight, melting point 135 ° C., MI = 8 g / 10 minutes) and a water-soluble inorganic substance were mixed with a Banbury mixer to prepare a raw material mixture. Next, this raw material mixture was melt-kneaded in an extruder, then extruded into a strand, and then this strand was cut to obtain resin particles. Table 2 shows the conductive carbon content of the resin particles in the base resin, the type and content of the water-soluble inorganic substance.

Next, 100 parts by weight of the above resin particles and 30 parts of water
0 parts by weight, carbon dioxide in the amounts shown in Table 2, kaolin 0.3
Parts by weight and 0.006 parts by weight of a surfactant (sodium dodecylbenzenesulfonate) were charged into a 400 liter autoclave, heated to the foaming temperature shown in Table 2 with stirring, and kept at the same temperature for 15 minutes, and then the autoclave. Nitrogen gas was introduced into the autoclave to maintain the equilibrium vapor pressure in the autoclave, one end of the autoclave was opened, and the contents were discharged under atmospheric pressure to foam the resin particles. Table 2 shows the physical properties of the obtained expanded beads. In addition, 2
After aging for 4 hours under atmospheric pressure, pressurizing with air 1.
After applying an internal pressure of 5 kgf / cm ² G and leaving it at 23 ° C. for 1 hour, it was molded with a mold having the same dimensions as in Examples 1 to 4 and cured at 60 ° C. under atmospheric pressure for 1 day. Various physical properties of the obtained molded product are also shown in Table 2.

[0046]

[Table 2]

[0047]

The expanded particles of the present invention contain 10% by weight or more of conductive carbon and have an internal pressure attenuation coefficient of 0.3.
Since it is less than the above, the polypropylene resin is used as the base resin, but the bubbles do not become fine as in the conventional polypropylene resin expanded particles to which conductive carbon is added, and the conductivity and dimensional stability are high at a high expansion ratio. It is possible to obtain a molded product having excellent properties such as properties and compression recovery properties.

Further, according to the method of the present invention, there is an effect that the above excellent expanded beads can be reliably produced.

[Brief description of drawings]

FIG. 1 is an example of a DSC curve of expanded particles having a high temperature peak.

Claims (3)

[Claims] 1. A conductive polypropylene-based resin foamed particle containing 10% by weight or more of conductive carbon and having an internal pressure attenuation coefficient of less than 0.3. 2. Foamable resin particles obtained by impregnating a polypropylene resin having a carboxyl group as a base material and containing 10% by weight or more of conductive carbon and nuclear bubbles with a foaming agent. A method for producing expanded particles of a conductive polypropylene resin, which comprises foaming. 3. Conductive carbon of 10% by weight or more,
A method for producing conductive polypropylene resin foamed particles, which comprises foaming expandable resin particles obtained by impregnating polypropylene resin particles containing 0.01 to 5% by weight of a water-soluble inorganic substance with a foaming agent.