JPH07300536A - Foamed electric conductive polypropylene resin particle, in-mold molded item formed from same, and production of in-mold molded item - Google Patents

Abstract

PURPOSE:To easily obtain a molded polypropylene resin foam with excellent electric conductivity and fusibililty and a low shrinkage. CONSTITUTION:Foamed electric conductive polypropylene resin particles are produced by foaming polypropylene resin particles comprising less than 90wt.% polypropylene random copolymer, 10-20wt.% furnace black, and 5wt.% or lower (except 0wt.%) metal salt and/or amide of a higher fatty acid under such conditions that the resulting foam particles contain secondary crystals having a heat of fusion (by differential scanning calorimetry) of 1-15J/g. The foamed particles are bonded to each other in a mold to give an in-mold molded item.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive polypropylene-based resin expanded particle, a conductive polypropylene-based in-mold foam molded article formed from the expanded particle, and the above-described conductive polypropylene-based resin. The present invention relates to a method for producing an in-mold molded body using expanded particles.

[0002]

2. Description of the Related Art Conventionally, as a polyolefin resin foamed particle having conductivity, for example, the applicant of the present application has a density of 0.
920 to 0.928 g / cm ³ , and MFR 0.5 to
1.5 g / 10 min non-crosslinked linear low density polyethylene 9
5-80% by weight and furnace black 5-20% by weight
The base material is a resin composed of
Conductive polyethylene expanded particles having a size of μm (Japanese Patent Laid-Open No. 3-223)
No. 0) is proposed. However, there has been almost no research or invention relating to expanded polypropylene resin particles having conductivity and an in-mold molded article using the expanded particles.

The expanded polypropylene resin particles are the same kind of resin as the expanded polyethylene resin particles in that they are polyolefin resins, but the chemical structure of the resin itself is different, and the polypropylene resin is a polyethylene resin in terms of physical properties. Because of its higher crystallinity than that of resin, the production conditions of polyethylene-based resin foamed particles, the molding conditions of in-mold molding, etc. cannot be directly applied to the expanded particles of polypropylene-based resin and the in-mold molding.

In particular, according to the research conducted by the inventors of the present invention, since polypropylene resin has high crystallinity when furnace black is added in order to impart conductivity to the expanded polypropylene resin particles, the polypropylene resin has a high crystallinity. It was very difficult to uniformly disperse the furnace black in it, and a good conductive polypropylene resin foam could not be obtained by simply adding the furnace black. That is, as in the case of the expanded polyethylene resin particles, by simply specifying the density and MFR of the resin and the mixing amount of the resin and furnace black, a good conductive polypropylene resin is also excellent in conductive polypropylene. It means that it is not possible to obtain an in-mold molded product.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned conventional drawbacks, and a first object thereof is a novel polypropylene resin-based foam which is excellent in conductivity and fusion property and has small shrinkage. Is to obtain an in-mold molded body consisting of.
A second object of the present invention is to provide conductive polypropylene resin expanded particles for producing the above-mentioned in-mold molded article. Further, the third object of the present invention is to
It is an object of the present invention to provide a method for producing an in-mold molded article that allows an electrically conductive polypropylene resin in-mold expanded molded article to be easily obtained from conductive polypropylene resin-based expanded particles.

As a result of intensive studies to solve the above problems, the present inventors have found that metal salts of higher fatty acids and / or amides of high fatty acids are used to improve the dispersibility of furnace black in polypropylene resins. In addition to finding that it is very effective to add a compound, in order to achieve the above-mentioned object, it is not only to improve the dispersibility of the furnace black, but also to the furnace black and a metal salt of a higher fatty acid or / By setting the content of the high fatty acid amide compound within a specific range and having a secondary crystal with a specific heat of fusion in the expanded particles, all the physical properties of the in-mold molded product can be sufficiently satisfied. The inventors have found that expanded particles can be obtained, and have completed the expanded particles of the present invention. In addition, the inventors of the present application specify the heat of fusion of the pre-expanded particles in the range of 4 to 11 J / g, so that the pre-expanded particles can be formed in a mold made of a conductive polypropylene-based resin without pretreatment of internal pressure. It is possible to manufacture a foamed molded product, and by a manufacturing method excellent in terms of productivity and production cost, it is found that a conductive polypropylene resin in-mold foamed molded product can be obtained, and the manufacturing method and mold of the present invention. We came to complete the inner molding.

[0007]

Means for Solving the Problems That is, the conductive polypropylene-based resin expanded particles of the present invention are (1) a polypropylene-based random copolymer (A), furnace black (B), and a metal salt of a higher fatty acid, or A conductive polypropylene-based resin foamed particle obtained by foaming a polypropylene-based resin particle composed of an amide compound (C) of a higher fatty acid, characterized in that both of the following are satisfied. The components (A) to (C) have the following blending ratios. (A): Less than 90% by weight (B): 10 to 20% by weight (C): 5% by weight or less (excluding 0) The secondary crystal is present in the conductive polypropylene resin foamed particles, and the secondary crystal is present. The heat of fusion based on the differential scanning calorimetry of the crystal is 1 to 15 J / g.

(2) In the expanded conductive polypropylene resin particles according to (1), the heat of fusion of the secondary crystal in the expanded conductive polypropylene resin particles is preferably 4 to 11 J / g.

(3) The in-mold molded article of the present invention is formed by integrally fusing a plurality of conductive polypropylene resin expanded particles described in (1) and (2) above in a mold. Characterize.

(4) The method for producing an in-mold molded article of the present invention is
The conductive polypropylene resin foamed particles according to the above (2) are filled in a mold without performing pretreatment of applying internal pressure, and then the foamed particles in the mold are heated and cooled, and then the mold The feature is that the inner molded body is taken out from the mold and cured in a heating atmosphere.

The conductive polypropylene resin expanded particles of the present invention (hereinafter sometimes simply referred to as expanded particles) contain less than 90% by weight of the polypropylene random copolymer (A) as a base resin. The polypropylene random copolymer used for the expanded particles of the present invention includes, for example, propylene-ethylene random copolymer, propylene-ethylene block copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer. Coalescence and the like are preferable. The content of the monomer component other than the propylene component in the above copolymer is preferably 0.5 to 10.0% by weight, and the MFR of the copolymer component is 0.1 to 25 g / 10.
Minutes are preferable (however, this MFR is a numerical value of the copolymer itself, and when furnace black is contained in the copolymer, it shifts to a smaller numerical value). A particularly preferable polypropylene random copolymer is a random copolymer of propylene and ethylene or / and butene-1.

Polypropylene random copolymer (A)
Can contain other additives. In that case, the additive is used so that the total amount of the polypropylene random copolymer and the additive is less than 90% by weight.

In the expanded beads of the present invention, the content of furnace black (B) is 10% by weight to 20% by weight. If the furnace black content is less than 10% by weight, sufficient conductivity cannot be imparted to the in-mold molded product formed from the expanded particles. On the other hand, if the content exceeds 20% by weight, in the in-mold molding formed from expanded particles, the fusion property between particles becomes poor. The content of furnace black is preferably 12.5 to 16.5% by weight. Within this range, the in-mold molded article exhibits strong fusion between the expanded particles and extremely excellent conductivity.

The furnace black contained in the polypropylene resin constituting the expanded particles of the present invention has a dibutyl phthalate oil absorption of 300 ml / 100 g or more and BE.
Those having a T specific surface area of 700 m ² / g or more are desirable because they show high conductivity even with a small amount of compounding. As such furnace black, for example, Black Pearl 2000
(Manufactured by Cabot), Ketjen Black EC (manufactured by Ketjen Black International), # 395
0 (manufactured by Mitsubishi Kasei) and the like are exemplified. These are used alone or in combination of two or more.

In the expanded beads of the present invention, the metal salt of higher fatty acid or / and the amide compound (C) of higher fatty acid is 5
It is used with a content of less than or equal to wt% (excluding 0 wt%). By using the metal salt of higher fatty acid and / or the amide compound of higher fatty acid in the above range, the fluidity inside the extruder is improved, the kneading property is improved, and the furnace black can be uniformly dispersed in the resin. it can. Furthermore,
The addition of the metal salt of higher fatty acid or / and the amide compound (C) of higher fatty acid improves the fluidity of the resin, and reduces the adhesion of the carbon-containing resin to the wall surface when mixing in the extruder, which results in different types. Cleaning of the extruder becomes extremely easy when producing the resin particles. When the content of the metal salt of higher fatty acid or / and the amide compound of higher fatty acid in the expanded particles of the present invention is 0% by weight, the kneadability of the furnace black is lowered and the furnace black is contained in the above specific range. However, good conductivity cannot be obtained because the particles are not uniformly dispersed in the expanded particles. Further, when the content of the metal salt of higher fatty acid and / or the amide compound of higher fatty acid exceeds 5% by weight, the fusion property between the foamed particles in the in-mold molded article formed from the foamed particles deteriorates. The content of the metal salt of higher fatty acid and / or the amide compound of higher fatty acid is preferably 0.1 to 2.0% by weight.

Metal salts of higher fatty acids include caproic acid (C ₆ ), capric acid (C ₁₀ ), lauric acid (C ₁₂ ), mistyric acid (C ₁₄ ), palmitic acid (C ₁₆ ), stearin as higher fatty acids. A straight chain saturated fatty acid such as an acid (C ₁₈ ),
2 side chain acids such as ethylhexoic acid (C ₈ ), those having a double bond with a hydroxyl group such as ricinoleic acid (C ₁₈ ), those having a polymethylene ring such as naphthenic acid (C _{13 15} ) and the like,
Li, M as a metal in fatty acids having 6 to 22 carbon atoms
g, Ca, Sr, Ba, Zn, Cd, Al, Sn, P
It is a metal salt to which b, Cu, etc. are bound. Preferred metal salts of higher fatty acids include lead stearate (PbSt), cadmium stearate (CdSt), barium stearate (BaSt), calcium stearate (CaSt),
Zinc stearate (ZnSt), magnesium stearate (MgSt), and the like are preferable from the viewpoint of high dispersibility of furnace black in polypropylene resin and, in turn, high conductivity. A particularly preferable metal salt of higher fatty acid is zinc stearate.

Specific examples of the amide compound of higher fatty acid include stearic acid amide, palmitic acid amide, oleic acid amide, and alkene bis fatty acid amides such as methylenebisstearamide and ethylenebisstearamide. In particular, from the viewpoint of high dispersibility of furnace black in polypropylene resin, and further high conductivity, alkene bis higher fatty acid amide such as ethylene bis stearamide is desirable.

To obtain the expanded beads of the present invention, for example, the above-mentioned polypropylene random copolymer (A), furnace black (B), and a metal salt of a higher fatty acid or / and an amide compound (C) of a higher fatty acid are used. To obtain a polypropylene-based resin particles, and to make the polypropylene-based resin particles a foaming agent by containing a foaming agent, to disperse the resin particles in a dispersion medium in a closed container, the softening temperature of the resin particles At the above temperature, the resin particles and the dispersion medium are discharged under an atmosphere of a pressure lower than that in the container to foam the polypropylene resin particles, whereby the polypropylene resin resin expanded particles having conductivity are obtained. The components (A) to (C) are mixed by, for example, supplying each component into a mixer such as a mixer and melt-kneading.

The weight per particle of the polypropylene resin particles used for foaming is arbitrarily adjusted. For example,
Each of the components (A) to (C) is fed into a mixer such as a mixer and melt-kneaded to form a compound having an appropriate size, and then the compound is melt-kneaded with an extruder and extruded into a strand. After passing through water, the strand is cut and pelletized to an appropriate size to obtain an arbitrary weight of polypropylene resin particles.

The weight per particle of polypropylene resin particles (the above-mentioned pellets) used for foaming is generally 0.2 to 10 mg, and particularly when formed to 0.5 to 4 mg, the particles at the time of pelletizing. The effect is that the weight uniformity is excellent, the obtained expanded particles have an appropriate average cell diameter (not too fine), and the expanded particles have excellent foaming power during in-mold molding.

To contain a blowing agent in the polypropylene resin particles, the above polypropylene resin particles are dispersed in a dispersion medium together with the blowing agent in a closed container and heated to a temperature higher than the softening temperature of the resin particles. The blowing agent is impregnated in the polypropylene resin particles. As the above-mentioned foaming agent, either a volatile foaming agent or an inorganic gas-based foaming agent may be used, but the inorganic gas is generally cheaper and has a higher safety than the volatile foaming agent, and an inorganic gas that is less likely to cause a problem of environmental destruction or the like. A foaming agent is preferred.

Examples of the inorganic gas type foaming agent include air, carbon dioxide, oxygen, nitrogen, etc., but especially carbon dioxide,
Air is preferable because it is inexpensive, highly safe, and has no problem of environmental destruction. As the volatile foaming agent, aliphatic hydrocarbons such as propane, butane and pentane, cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane, halogenated hydrocarbons such as trichlorofluoromethane and dichlorodifluoromethane And the like.

When a volatile foaming agent is used as the foaming agent,
It is preferable to add 2 to 40 parts by weight of the foaming agent to 100 parts by weight of the resin particles. When an inorganic gas type foaming agent is used as the foaming agent, it is preferable to add 5 to 50 parts by weight of the foaming agent per 100 parts by weight of the resin particles. The foaming agent may be added in either a gaseous state or a liquid state, and in the case of carbon dioxide or the like, it may be added in a solid state such as dry ice.

The dispersion medium in which the polypropylene resin particles are dispersed may be any dispersion medium which does not dissolve the resin particles, such as water, ethylene glycol, glycerin,
Methanol, ethanol and the like can be mentioned, but water is usually used.

An anti-fusion agent may be added to the dispersion medium for the purpose of preventing the fusion of polypropylene resin particles with each other. As the anti-fusing agent, either an inorganic type or an organic type can be used as long as it does not dissolve in the dispersion medium and does not melt by heating, but an inorganic type is generally preferable. Examples of the inorganic anti-fusing agent include tricalcium phosphate, magnesium pyrophosphate and the like, and it is preferable to add these in combination with a surfactant. As the above surfactant, anionic surfactants such as sodium dodecylbenzene sulfonate and sodium oleate are suitable. The above fusion preventing agent has a particle size of 0.001 to 100
μ, particularly 0.001 to 30 μ is preferable because a small amount can exhibit a sufficient anti-fusion effect. The amount of the anti-fusing agent added was 100 parts by weight based on 100 parts by weight of the polypropylene resin particles.
01 to 10 parts by weight is preferable. The surfactant is 0.001 to 5 per 100 parts by weight of the polypropylene resin particles.
It is preferable to add parts by weight.

Further, as a fusion preventing agent, talc, kaolin,
Mica or the like can also be used. The use of carbon dioxide as a blowing agent causes the aqueous medium to become acidic. In this case, for example, if tricalcium phosphate is used, the foaming agent will be dissolved in an acidic aqueous medium, and the fusion preventing effect will be reduced.
However, the above three types of anti-fusing agents do not dissolve in the aqueous medium even when carbon dioxide is used as the blowing agent and the aqueous medium is inclined to be acidic, so that when carbon dioxide is used as the blowing agent, it is very effective. Target. When carbon dioxide is used as a foaming agent, the amount of talc, kaolin, mica, etc. used is
0.05 to 1.0 part by weight is sufficient per 100 parts by weight of the resin particles, and in this case, the amount of the surfactant used is 0 to 0.02 parts by weight per 100 parts by weight of the resin particles. As described above, when the amount of the fusion inhibitor and the surfactant used is extremely small, the cost for treating the wastewater after the production of the expanded particles can be reduced. In the case of a foaming agent other than carbon dioxide, the fusion preventing agent may be any of those exemplified above.

The conductive polypropylene resin expanded particles of the present invention have secondary crystals. FIG. 1 shows an example of a DSC curve obtained by differential scanning calorimetry of expanded particles having secondary crystals of the present invention. Whether or not secondary crystals are present in the expanded beads can be determined by performing differential scanning calorimetry twice on the same sample. As shown in FIG. 1, in the DSC curve of the expanded beads, there are endothermic peaks P1 and P2 associated with the melting of the resin component of the expanded particles, which are called specific peaks, and the first measurement (P1) shows the endothermic peaks P1 and P2. Measurement (P
2), but when secondary crystals are present in the expanded particles, only in the first DSC curve, an endothermic peak (H1) called a high temperature peak on the higher temperature side than the specific peak.
Appears. The temperatures at the vertices of the characteristic peaks P1 and P2 of the first DSC curve and the second DSC curve may be slightly different between the first and second times, but the difference is usually 5
It is less than ℃.

The conductive polypropylene expanded resin particles of the present invention have a heat of fusion of 1 to 15 J / g of the secondary crystal based on the above-mentioned differential scanning calorimetry. If the heat of fusion of the expanded particles is less than 1 J / g, the in-mold molded product obtained therefrom shows a large shrinkage, while if it exceeds 15 J / g, the fusion property between the expanded particles of the obtained in-mold molded product is low. Will be. In particular, the heat of fusion is more preferably 4 to 11 J / g. Usually, when the foamed particles are molded in a mold, the foamed particles are previously placed in a pressure chamber of an atmosphere (air) of ² to 10 kg / cm ² G for 1 to 2 days to increase the internal pressure within the foamed particles [general 2 to 4 atm (absolute pressure)] is applied to the molded product, and then the molded product is dried in a drying chamber having an atmosphere of 40 to 80 ° C. to recover a slightly contracted dimension, and then shipped. Take the process of
However, in the case of the expanded beads of the present invention, by setting the heat of fusion of the secondary crystal to 4 to 11 J / g, the in-mold molded article obtained from the secondary crystal has extremely small shrinkage without performing the step of applying internal pressure, and It is possible that the in-molded article has a high fusion bond between the foamed particles. The fact that the pretreatment for applying the internal pressure is not required means that a pressurizing device is not required and that the in-mold molding can be performed immediately after the production of the expanded particles, which is a great advantage in terms of equipment and processes.

In the present invention, the measurement conditions for the differential scanning calorimetry of expanded particles are as follows. As a sample, 1 to 5 mg of expanded particles whose fusion heat is to be measured were measured by a differential scanning calorimeter at a temperature rising rate of 10 ° C./min to 220 ° C. to obtain a first DSC curve, and then from 220 ° C. After lowering the temperature to around 40 ° C at a rate of 10 ° C / min, repeat 1
Second DSC by measuring the temperature up to 220 ℃ at 0 ℃ / minute
Get the curve. The calorific value of the high temperature peak is measured from the DSC curve obtained by the first measurement to obtain the heat of fusion (J / g). The heat quantity of the high temperature peak (H1) is
1) and the characteristic peak (P1) are divided by the valley portion V, and it can be obtained from the area of the peak on the high temperature side from the valley portion V.

Also, in the above two DSC curves, the second
It is desirable that the difference between the temperature at the apex of the unique peak P2 appearing in the DSC curve for the first time and the temperature at the apex of the high temperature peak H1 appearing in the first DSC curve is large. It is preferable that the temperature is not lower than 0 ° C from the viewpoint of ease of in-mold molding.

The expanded particles of the present invention in which secondary crystals are present and have a heat of fusion within a specific range can be obtained by heat-treating the polypropylene resin particles at a secondary crystallization accelerating temperature for a sufficient period of time before foaming. can get. Specifically, this heat treatment is performed, for example, in a pressure vessel without raising the temperature of the polypropylene-based resin particles to a temperature above the melting end temperature of the polypropylene-based random copolymer of the particles.
20 [deg.] C. or higher and lower than the melting end temperature (secondary crystallization acceleration temperature), it may be maintained for a sufficient time (usually about 5 to 90 minutes) so that the heat of fusion falls within the above range. It is desirable that the heat treatment for forming the secondary crystal be divided into a plurality of times in order to facilitate temperature control. In this case, it is desirable that the heating be performed so that the holding temperature after that becomes higher than the holding temperature, and the final holding temperature is the foaming temperature.

The above melting point is the second DSC curve when measured under exactly the same conditions as in the differential scanning calorimetry of the above expanded particles except that 6 mg of polypropylene random copolymer is used as the sample. Is the temperature at the apex of the peculiar peak P2 of. The melting end temperature is the second DS
It is the temperature at the end of the endothermic peak P2 of the C curve.

The expanded particles of the present invention can be obtained by discharging polypropylene-based resin particles in an atmosphere at a pressure lower than that in the container to cause foaming. The temperature at the time of discharging (foaming temperature) is usually Within the range of the melting point of −15 ° C. or more of the polypropylene random copolymer used for the polypropylene resin particles to the temperature of the apex of the high temperature peak H1 of the foamed particles or less, foamed particles having good moldability are obtained. be able to. The suitable foaming temperature range varies depending on the type of resin used and the type and amount of the foaming agent used, but as a guide, it is 5 as a polypropylene-based random copolymer.
If a polypropylene random copolymer containing up to wt% of a comonomer other than propylene is used and carbon dioxide is used for foaming (there is almost no effect of the amount of carbon dioxide used on the suitable foaming temperature), polypropylene random The melting point of the copolymer is not lower than [melting point +15 [deg.] C.], especially [melting point + 3 [deg.] C.] to [melting point + 10 [deg.] C. In addition, the softening temperature of polypropylene-based resin particles refers to a load of 4. in ASTM-D-648 method.
It is the softening temperature obtained under the condition of 6 kg / cm ² .

The expandable resin particles before being foamed in the above container are generally kept under pressure in a closed container at a pressure of 5 kg / cm ² G or more so as not to foam in the container. In the method of the present invention, in order to apply a back pressure at the time of foaming, nitrogen, air, argon, an inorganic gas such as carbon dioxide can be supplied into the container in the same manner as in the conventional method. It is preferred to use / and air.

The in-mold molded article of the present invention can be obtained by using a plurality of the above-mentioned expanded polypropylene resin particles having conductivity and bonding them in a mold for molding. The following methods (1) to (4) are used to combine the foamed particles in the mold to obtain a molded product. The foamed particles are directly filled in a mold and heated by steam to mold. The expanded particles are placed in a closed chamber, and then an inorganic gas such as air or nitrogen gas is pressed into the chamber to increase the internal pressure of the expanded particles to give secondary expandability, and then heated by steam to mold. To do. The foamed particles are impregnated with a volatile foaming agent in advance to impart secondary foamability, and after being filled in a mold, they are heated with steam to be molded. The foamed particles are compressed by gas pressure or the like so as to be reduced in volume by 15 to 50%, and in that state, the foamed particles are filled in a mold and then heated with steam to be molded. A method of combining two or more of the above methods. The vapor pressure of steam during heating is usually 2 to 5 Kg / cm.
It is ² G.

According to the method for producing an in-mold molded article of the present invention, a plurality of conductive polypropylene-based foamed particles having a heat of fusion of foamed particles of 4 to 11 J / g are subjected to a predetermined shape without performing a pretreatment of applying internal pressure. The method is to fill the molding die in (1), heat the foamed particles in the die, and cool them, and then take out the in-mold molded body from the die and perform curing in a heating atmosphere. The heating atmosphere at the time of curing is about 40 to 80 ° C. The purpose of the heating atmosphere is to keep the water vapor used for heating during molding remaining in the molded body, so that it can be dried, and after the molded body is taken out of the mold, the molded body will shrink. Is to do. This also requires the same curing step when the internal pressure is applied and in-molding is performed.

The in-mold molded product of the present invention has good conductivity, and also has the buffering property of the polypropylene resin foam,
A half set such as a printed circuit board equipped with integrated circuits such as IC and LSI, which has characteristics such as waist strength, replacement parts, computers, radios, audio products, VTRs, calculators,
Storage of products that use electronic components such as watches, various measuring devices, and medical devices that require protection from static electricity,
It can be optimally used as an antistatic packaging material that also serves as a cushioning material during transportation, an electromagnetic wave shielding material, a heating element, and the like.

[0040]

EXAMPLES The present invention will be described in more detail with reference to examples. [Examples 1 to 7, Comparative Examples 1 to 6] Ethylene-propylene random copolymer (2.3% by weight of ethylene, MI = 10)
g / 10 minutes, density 0.9 g / cm ³ , melting point 146.5
℃, melting end temperature 163 ℃, furnace black (Ketjen Black International Co., Ltd. product name "Ketjen Black EC", dibutyl phthalate oil absorption: 360 ml / 100 g, BET specific surface area: 800 m
² / g) and a metal salt of a higher fatty acid or / and an amide compound of a higher fatty acid with the composition shown in Table 1 by heating and mixing with a Banbury mixer, and then pelletized, and then the pellets are put into an extruder. The mixture was melt-kneaded, then extruded into a strand, and rapidly cooled in water to obtain polypropylene random copolymer resin particles for foaming (average weight per particle is about 2 mg). To 100 parts by weight of these particles, 300 parts by weight of water, 0.3 part by weight of a dispersant (kaolin), 0.004 part by weight of a surfactant (sodium dodecylbenzenesulfonate), and a blowing agent (carbon dioxide) are shown in Table 1. The amount shown in (1) was mixed in a closed container, the temperature in the container was raised to the temperature shown in Table 1 with stirring, and the temperature was maintained for 15 minutes. After this temperature was maintained, the valve at the bottom of the container was opened to release the contents of the container to the outside of the container (under atmospheric pressure) to obtain conductive polypropylene-based resin expanded particles.
During this discharge, high-pressure carbon dioxide was continuously supplied into the container from the upper part of the container to maintain the pressure in the container. After drying the obtained expanded particles, DSC measurement was performed on the expanded particles to measure the heat of fusion of the high temperature peak.

Further, the dried expanded particles (internal pressure is as shown in Table 2) are filled in a mold of 300 mm × 300 mm × 40 mm (internal dimensions) and heated with 3.0 to 4.2 kg / cm ² G of steam. And molded. The obtained molded product was dried in an oven at 60 ° C. for 24 hours, and the results of measuring the conductivity, fusion property and shrinkability of the molded product are shown in Table 2 together with the heat of fusion of the high temperature peak.

[0042]

[Table 1]

[0043]

[Table 2]

As shown in Tables 1 and 2, Examples 1 to 1
7 was excellent in electroconductivity and fusion property, and a small shrinkage was obtained, but Comparative Examples 1 to 6 in which any of the constituent requirements of the present application were missing were electroconductivity, fusion property, and However, a defect was found in either the shrinkability or the shrinkability, and a molded product satisfying all the above properties could not be obtained. In addition, the evaluation method of the molded body in Table 2 is as follows.

[Evaluation of Shrinkability] 2 in an oven at 60 ° C.
The length (Amm) of the side corresponding to the in-mold dimension of 300 mm of the molded body after being dried and cured for 4 hours was measured and substituted into the following formula (1) to obtain the shrinkage rate, and evaluated according to the following criteria. ○ ・ ・ ・ ・ Shrinkage rate is less than 3% △ ・ ・ ・ ・ 〃 3% or more and less than 4% × ・ ・ ・ ・ 〃 4% or more Shrinkage rate (%) = (300-A) / 300 × 100 ・ ・(1)

[Evaluation of Fusing Property] Similarly to the above, the molded body after curing was sliced into a piece having a thickness of 10 mm and a width of 50 mm (the length was 300 mm), and this sample was pulled in the longitudinal direction to break the sample. The fracture surface was observed and evaluated according to the following criteria. ○ ・ ・ ・ ・ Ratio (number) of rupture (number) at the fused part of expanded particles is 40% or less △ ・ ・ ・ 〃 more than 40%, 60% or less × ・ ・ ・ ・

[0047]

As described above, the conductive polypropylene resin foamed particles of the present invention include the polypropylene random copolymer (A), furnace black (B), and metal salts of higher fatty acids and / or higher fatty acids. Amide compound (C), (A): less than 90 wt%, (B): 10
20% by weight, (C): 5% by weight or less (excluding 0) of a polypropylene-based resin particle having a specific composition, and secondary crystals are present in the conductive polypropylene-based resin expanded particle. Then, by adopting a constitution in which the amount of heat of fusion of the secondary crystal based on the differential scanning calorimetry is set to 1 to 15 J / g, the conductive polypropylene resin foam in which the furnace black is well dispersed in the polypropylene resin is adopted. Particles are obtained, and by subjecting the expanded particles to in-mold molding, a polypropylene resin foam-molded article having excellent conductivity and fusion properties and low shrinkability can be obtained. Furthermore, since the conductive polypropylene resin foamed particles of the present invention are added with a metal salt of a higher fatty acid or / and an amide compound (C) of a higher fatty acid, a composition of furnace black and a polypropylene random copolymer is prepared. When melt-kneading, the fluidity of the composition is improved, and there is no risk of the composition containing carbon adhering to the inside of the kneading device, and it is intended to produce expanded particles containing no carbon using the kneading device. In addition, the effect of facilitating the cleaning of the kneading device and improving the work efficiency of the foamed particle production is achieved.

The heat of fusion of the expanded beads of the present invention is 4 to 11 J.
In the case of / g, when performing in-mold molding using the expanded beads, it becomes possible to perform in-mold molding without subjecting the expanded particles to pretreatment for applying internal pressure. Pretreatment for applying internal pressure is 2-10 kg / cm ² G
This is an operation in which the expanded particles are left under pressurized air for 1 to 2 days and an increased pressure is applied to the expanded particles. The fact that this pretreatment operation is unnecessary eliminates the need for a pressurizing device, and the foamed particles after production can be immediately subjected to in-mold molding, which is a great advantage in terms of equipment and processes.

The in-mold molded article of the present invention comprises a plurality of the expanded particles according to claim 1 or claim 2 integrally fused within the mold, and thus has a novel conductivity and fusion property which have never existed before. It is a polypropylene resin molded product with excellent shrinkage and small shrinkage.

In the method for producing an in-mold foam molded article of the present invention, a plurality of conductive polypropylene-based foamed particles having a heat of fusion of 4 to 11 J / g as described in claim 2 are used to perform a pretreatment for applying an internal pressure. By adopting a method of filling, heating, cooling, and curing in the mold without using it, it is not necessary to apply an internal pressure to the expanded particles and a pressurizing device is not required, and the expanded particles can be immediately molded in the mold immediately after manufacturing. The process is shortened, the productivity of the molded product is excellent, and the manufacturing cost can be low.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a DSC curve obtained by differential scanning calorimetry of conductive polypropylene resin expanded particles having secondary crystals of the present invention.

[Explanation of symbols]

 P1 Unique peak of first DSC curve P2 Unique peak of second DSC curve H1 High temperature peak of first DSC curve

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Claims (4)

[Claims] 1. A conductive material obtained by foaming polypropylene resin particles comprising a polypropylene random copolymer (A), furnace black (B), and a metal salt of a higher fatty acid or / and an amide compound (C) of a higher fatty acid. Expanded conductive polypropylene resin particles, which are expanded polypropylene resin particles satisfying both of the following requirements. The components (A) to (C) have the following blending ratios. (A): Less than 90% by weight (B): 10 to 20% by weight (C): 5% by weight or less (excluding 0) The secondary crystal is present in the conductive polypropylene resin foamed particles, and the secondary crystal is present. The heat of fusion based on the differential scanning calorimetry of the crystal is 1 to 15 J / g. 2. The expanded conductive polypropylene resin particles according to claim 1, wherein the heat of fusion of the secondary crystal in the expanded particles is 4 to 11 J / g. 3. An in-mold molded article, which is obtained by integrally fusing a plurality of conductive polypropylene resin expanded particles according to claim 1 or 2 in a mold. 4. A plurality of the conductive polypropylene resin expanded particles according to claim 2 are filled in a mold without performing a pretreatment of applying internal pressure, and then the expanded particles in the mold are heated.
After cooling, the in-mold molded product is taken out of the mold and cured in a heating atmosphere, which is a method for producing an in-mold molded product.