JPH0275636A - Electrically conductive foamed polyethylene particle and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain a foamed particle having excellent fusion and secondary foaming characteristics when it is molded in a mold and high conductivity by using a base resin contg. an uncrosslinked linear low-density polyethylene and carbon black at a specified ratio. CONSTITUTION:This electrically conductive foamed polyethylene particle is formed by using a resin consisting of 95-70wt.% uncrosslinked linear low-density polyethylene (hereinbelow described as LLDPE) and 5-30wt.% carbon black as a base material. It is pref. that LLDPE has an MFR of 0.5-2g/10min. It is pref. That said polyethylene particle has a foam diameter of 0.07mm or larger and an inner pressure decreasing rate coefficient (K) of smaller than 0.35. Said polyethylene particle is obtd. by the following method. Namely, the base resin particles at said compounding ratio are dispersed in a pressure container in the presence of water and a foaming agent and heated to impregnate the resin particles with the foaming agent. Then, the particles are kept in a temp. of the m.p. to m.p. minus 15 deg.C of the resin particles to take out the resin particles and water from the container in an atmosphere of a reduced pressure to foam the resin particles.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to conductive polyethylene foam particles and a method for producing the same.

[Conventional technology and Problems that the invention attempts to solve]

A lot of research has been done on polyolefin resin conductive foams. However, in the case of crosslinked foams, good foams have not been obtained because adding a large amount of carbon black inhibits crosslinking of the resin. Therefore, conventionally available highly foamed materials are somewhat open-celled and have a volume resistivity of 105 Ω·cfflO.

In addition, in the case of non-crosslinked foam, fluidity deteriorates, so
There are problems in that the viscosity of the resin increases and the elongation rate of the resin decreases, making it difficult to determine foaming conditions. To solve this problem, we developed a polyolefin resin with a specific surface area of 90 Or+?95 to 70% by weight. A method for producing a low-density polyolefin foam having a closed cell structure and conductivity has been proposed by foaming a composition containing 5 to 30% by weight of a conductive furnace blank of 5 to 30% by weight or more to a ratio of 5 times or more. Publication No. 51-25815).

However, with the foam obtained by the above method, the volume resistivity value is limited to about 1ObΩ・can, and even if the amount of carbon black added is increased to 30% by weight or more, the volume resistivity value does not increase dramatically. The problem is that a significant decline cannot be expected. In addition, although there is not much of a problem in the case of extruded foam as in the above method, when the amount of carbon black added is large in the case of foamed particles that are filled into a mold and molded, the foamed particles become difficult to mold in the mold. Problems arise with fusion properties and secondary foamability, and to date no good conductive foam has been obtained by the bead method.

[Means to solve the problem]

The present invention was made as a result of intensive research to solve the above-mentioned drawbacks of the conventional technology, and it uses linear low-density polyethylene as the base resin, and foamed particles obtained by non-crosslinking foaming have never been produced before. We have completed the present invention by discovering that it has excellent fusion properties and secondary foaming properties, and can also provide high electrical conductivity with a volume resistivity value of 102 Ω·cm.

That is, the present invention provides: (1) Non-crosslinked linear low density polyethylene 95-70
Conductive polyethylene foam particles characterized in that the base material is a resin consisting of 5% by weight and 5 to 30% by weight of carbon black.

(2) MFR of non-crosslinked linear low density polyethylene is 0.
The conductive polyethylene foam particles according to claim 1, characterized in that the amount is 5 to 2 g/10 minutes.

(3) Internal pressure reduction rate coefficient (K) within expanded particles is 0.35
The conductive polyethylene foam particles according to claim 1, characterized in that the conductive polyethylene foam particles are less than 10%.

(4) The conductive polyethylene foam particles according to claim 1, characterized in that the cell diameter is 0.07 am or more.

(5) Resin particles consisting of 95-70% by weight of non-crosslinked linear low-density polyethylene and 5-30% by weight of carbon black are dispersed in a pressure container in the presence of water and a blowing agent and heated to create a resin. The particles are impregnated with a foaming agent, and then the resin particles are foamed by maintaining the temperature in the range of from the melting point of the resin particles to -15°C, and releasing the resin particles and water into a low-pressure atmosphere from inside the container. A method for producing characteristically conductive polyethylene foam particles.

(6) In the manufacturing method according to claim 5, foamed particles having a bulk ratio of 10 times or less are obtained, and then the foamed particles are heated to 1 to 10 kg/c with an inorganic gas containing nitrogen gas as a main component.
A method for producing conductive polyethylene foam particles, which comprises applying an internal particle pressure of tA-G and then heating the particles to expand the particles to a bulk ratio of 10 times or more.

The main points are as follows.

The linear low-density polyethylene (hereinafter abbreviated as LLDPE) used in the present invention is a low-pressure polymerized polyethylene copolymerized with an α-olefin having 4 to 10 carbon atoms,
The above α-olefins include 1-butene, 1-pentene, ■-hexene, 3,3-dimethyl-1-butene, 4
-Methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-octene and the like. The content of these α-olefins in LLDPE is usually 0.5 to 20% by weight.
However, 1 to 15% by weight is particularly preferred.

The above LLDPE preferably has a VFR of 0.5 to 2 g/10 minutes.

Additives in LLDPE include antioxidants, light stabilizers, lubricants, neutralizing agents, and the like, and these are used as appropriate depending on the purpose as long as they do not affect the cell diameter and conductivity. Among these, stearate, which is used as a neutralizing agent, affects the bubble diameter, so it is preferably kept at 250 ppm or less. In addition, the n-hexane extract present in the resin is 0.4% by weight.
Above, it is preferably 1.5% by weight or less, particularly preferably 0
．． It is 5% by weight or more and 1.2% by weight or less.

When such low-density LLDPE is used, it is possible to easily obtain foamed particles that are closed cells and have high conductivity even if the amount of carbon added is increased. In addition, it is possible to obtain foamed particles that can be filled into a mold and undergo secondary foaming and fusing well.

Incidentally, within the range that does not impede the intended purpose of the present invention, 5
Low density polyethylene (hereinafter referred to as LDP) in the range of less than 0% by weight
It is abbreviated as E. ) or/and linear ultra-low density polyethylene (
Hereinafter abbreviated as VLDPE. ) can also be mixed.

Examples of the carbon black used in the present invention include those called furnace black and acetylene black. Such carbon blacks include, for example, Palkan XC-72, Bra 7 Kbal (manufactured by Cabot), Conductor Tesoku 975 (manufactured by Colombian), Toka Black 5500, and Toka Black 7550.
(more than bundles) made by Carbon A Kiku), Denka Black (manufactured by Denki Kagaku Kogyo), Ketchen Black EC, Ketchen Bra, Ri EC-60'0 (manufactured by Akzo), #32
50, #3750, #3600, #3950 (manufactured by Mitsubishi Kasei 01), and the like. The carbon black used in the present invention preferably has a BET specific surface area of 50 m/g or more. Among the above carbon blacks, particularly preferred are Ketchen Black EC, Ketchen Black EC-600, Black Pearl 2000, and #375.
0, #3600, #3950 etc. BET specific surface area is 50
It is 0 m/g or more. Carbon black may be used in combination of two or more different types, or may be used alone.

If the content of carbon black in the conductive expanded particles of the present invention is less than 5% by weight, sufficient conductivity cannot be imparted, and if it exceeds 30% by weight, the kneadability with the resin particles that are the raw material of the expanded particles will deteriorate. The resulting foamed particles tend to become open cells, and the fusion between the foamed particles during molding also deteriorates.

The conductive polyethylene foam particles of the present invention have cell diameters of 0 and 07.
It is preferable that it is more than am, and if it is less than 0.07 m, the secondary foamability tends to decrease. In addition, the internal pressure reduction rate coefficient (K) within the particles is used as an index of the closed cell property and gas permeability of the expanded particles. Preferably.

In addition, the internal pressure reduction rate coefficient: is expressed by the following formula [in the above formula, Pl is the initial internal pressure of the expanded particles (kg/c
t-G), Pz is the internal pressure of the expanded particles after 1 hour (k
g/cffl-G), t indicates time (hr). ], the initial internal pressure at 25°C (
PI) and the internal pressure (P2) after one hour has passed (t=1).

Furthermore, the conductive polyethylene foam particles of the present invention may have a crystal structure in which two endothermic peaks appear in the DSC curve obtained in differential scanning calorimetry, or may have a crystal structure in which only one endothermic peak appears. I don't mind, but
Those with a low carbon black content, especially 5 to 10
Among the weight% ones, those with a crystalline structure that also has an endothermic peak on the high temperature side are preferable. In this case, the energy of the endothermic peak on the high temperature side is preferably 15 J/g or less. The above-mentioned DSC curve is a DSC curve obtained when expanded particles 1 to 5 cm were heated to 220° C. at a heating rate of 10° C./minute using a differential scanning calorimeter. Of the two endothermic peaks in the DSC curve, the endothermic peak on the low-temperature side is considered to be due to endothermic heat generated during so-called melting of LLDPE, which is the base resin of the expanded particles. On the other hand, the endothermic peak on the high temperature side is considered to be due to the existence of a crystal structure different from the structure that appears as the endothermic peak on the low temperature side.

In Figure 1, the energy of the endothermic peak on the high temperature side is the valley part a between the high temperature side peak and the low temperature side peak, and the high temperature side peak b
The area of the peak on the higher temperature side than the valley part a is taken as the area of the high temperature side peak, and the value is calculated from this area.

That is, the energy of the endothermic peak on the high temperature side can be determined from the area of the endothermic peak on the high temperature side using the following equation.

Energy of the endothermic peak on the high temperature side (J/g) - [Area of the endothermic peak on the high temperature side on Char 1 (cn x [Heat i per ctA (J/cut))] C [Weight of measurement sample (g)] The foamed particles of the present invention have a mixed composition of 95 to 70% by weight of LLDPE and 5 to 30% by weight of carbon black as described above, but an inorganic filler may be further added as required.

Examples of the inorganic filler include metal oxides such as zinc oxide, titanium oxide, magnesium oxide, and silicon oxide, and carbonates such as calcium carbonate and magsium carbonate.

The foamed particles of the present invention are produced by dispersing particles of a resin composition containing LLDP E and 5 to 20% by weight of carbon black together with a volatile foaming agent in water in a closed container, and heating the mixture to form inside the resin particles. When foaming the resin particles by impregnating them with a foaming agent and then releasing the resin particles and water into a low-pressure atmosphere from inside the container, the foaming temperature (release temperature) is set at a temperature between the melting point of the resin particles and the melting point -10°C. Obtained by setting the range. The melting point of the above resin refers to the resin particles used for foaming.
This is the temperature at the top of the endothermic peak in the DSC curve obtained by heating 5 mg at a rate of 10° C./min in a differential scanning calorimeter.

The foaming agent used in the production of the foamed particles of the present invention may be an inorganic gas such as carbon dioxide, air, or nitrogen, or a gas with a boiling point of 150
Examples include organic blowing agents such as hydrocarbons or halogenated hydrocarbons having a temperature of ~120°C, and specific examples of organic blowing agents include propane, butane, pentane, hexane, heptane, cyclobencune, cyclohexane, monochloromethane, dichloromethane, and monochlorodifluoro. Examples include methane, monochloroethane, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, and the like.

These may be used alone or in combination of two or more. The amount of these blowing agents varies depending on the type of blowing agent, desired expansion ratio, cell diameter, etc., but for example, the expansion ratio is 5 to 50 times (bulk ratio, hereinafter the expansion ratio of foamed particles refers to bulk ratio). In order to do this, the amount is usually 5 to 40 parts by weight per 100 parts by weight of the resin particles, but when an inorganic foaming agent is used as the foaming agent, the expansion ratio of the foamed particles usually obtained is 10 times or less. . In order to make such foamed particles even more highly foamed, - after foaming them to 10 times or less,
1 to 10 kg/inorganic gas mainly composed of nitrogen gas
Conductive polyethylene foam particles having a desired high expansion ratio can be obtained by repeating the operation of applying a particle internal pressure of c+a-G and then heating and foaming the particles several times as necessary. This method of achieving a high expansion ratio without using a fluorocarbon foaming agent is particularly preferable as a solution to the current ozone layer depletion problem caused by fluorocarbons.

This method can also be applied to foamed particles produced using fluorocarbon gas. In this case, the amount of Freon used can be extremely small.

The amount of resin particles to be dispersed in water when producing the expanded particles of the present invention is preferably 10 to 100 parts by weight per 100 parts by weight of water to improve productivity and dispersion stability and to reduce utility costs.

In addition, the amount of blowing agent to be dispersed in water together with the above-mentioned resin particles is determined by taking into account the type of blowing agent, the desired expansion ratio, the ratio of the amount of resin particles in the container to the space inside the container, etc. The ratio is determined so that it falls within the above range.

A dispersant can also be used if necessary when dispersing the resin particles in water. Dispersants are used to prevent resin particles from coagulating and fusing together when heated, and include fine powders of poorly water-soluble inorganic substances such as calcium phosphate, magnesium birophosphate, zinc carbonate, titanium oxide, and aluminum oxide. is used. When using the above inorganic substances, use a small amount of a surfactant such as sodium alkyl hanzene sulfonate, sodium α-olefin sulfonate, or sodium alkyl sulfonate as a dispersion aid to reduce the amount of inorganic substance used. It is preferable to reduce the amount in order to improve the mutual adhesion of the foamed particles during molding. In this case, for 100 parts by weight of resin particles, 0.1 to 3 parts by weight of fine powder of inorganic substance and 0.001 to 0 parts by weight of surfactant.
．． It is preferable to use about 5 parts by weight. Further, when a water-soluble polymer is used as a dispersant, it is preferable to use about 0.1 to 5 parts by weight of the water-soluble polymer per 100 parts by weight of the resin particles.

In the method of the present invention, the resin particles and the blowing agent are dispersed in water and heated to impregnate the resin particles with the blowing agent. It is necessary to set the temperature at between the melting point of the resin particles and the melting point -15°C.

If the temperature at the time of discharge is outside this range, good expanded particles cannot be obtained. In particular, foamed particles with two endothermic peaks appearing in the DSC curve are difficult to obtain when the amount of carbon black added is large.However, this problem can be solved by sufficiently maintaining the resin particles containing carbon black at a temperature close to the foaming temperature. In addition, even if the expanded particles have a crystal structure in which only one endothermic peak appears in the DSC curve, if the amount of carbon black added is 10% by weight or more, good expanded particles can be obtained due to the pseudo-crosslinking effect. Can be done.

The foamed particles obtained as described above are molded into various shapes in a mold. Examples of the in-mold molding method include the following methods.

■ Fill the expanded particles directly into a mold and mold them using steam.

■ The foam particles are placed in a closed chamber, and then an inorganic gas such as air or nitrogen gas is forced into the chamber to increase the pressure inside the cells of the foam particles and give them secondary foamability. Fill a mold with the foam particles and steam mold them.

(2) The foam particles are pre-impregnated with a volatile expansion agent to impart secondary foamability to the foam particles, which are then filled into a mold and steam-molded.

■ After filling the foam particles into the mold, the foam particles are compressed to reduce their volume by 15 to 50%, and then compressed to 1 to 5 kg/kg.
Steam of c+flG is introduced to fuse the foam particles together, and then the mold is cooled to obtain a product.

■ A combination of two or more of the above ■ to ■.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 7, Comparative Examples 1 to 4 Using resin particles containing LLDPE and carbon black in the amounts shown in Table 1, 100 parts by weight of the resin particles and a blowing agent in the amounts shown in Table 1 were placed in a closed container. The resin particles were dispersed in water and heated to impregnate the resin particles with the foaming agent, and then the resin particles and water were discharged under atmospheric pressure at the foaming temperature shown in the same table to foam the resin particles. Table 2 shows the expansion ratio (bulk ratio), cell diameter, internal pressure reduction rate coefficient, and results of differential scanning calorimetry of the expanded resin particles.

Example 8.9 Using a resin containing LL'DPE and carbon black in the amounts shown in Table 1, 100 parts by weight of the resin particles and carbon dioxide in the amounts shown in Table 1 were dispersed in water in a closed container. After heating to impregnate the resin particles with a foaming agent, the resin particles and water were discharged under atmospheric pressure at the foaming temperature shown in the same table to foam the resin particles. The expansion ratio (bulk ratio), cell diameter, internal pressure reduction rate coefficient, and differential scanning calorimetry results of the obtained expanded particles are also shown in Table 2. Next, these foamed particles were pressurized with air to give the internal pressure shown in Table 2,
It was further foamed by heating in a steam unit containing 1.2 kg/Cl11-G. The expansion ratio (bulk ratio), cell diameter, internal pressure reduction rate coefficient, and differential scanning calorimetry results of the obtained expanded particles (expanded particles after two-stage foaming) are also shown in Table 2.

Among the expanded particles obtained in Examples 1 to 9 and Comparative Examples 1 to 4, the expanded particles of Example 3, in which two endothermic peaks appeared in the DSC curve in differential scanning calorimetry, had a weight of 2 kg/ctA.
After being pressurized with -G air for one day, it was subjected to molding. The other expanded particles were used for molding as they were. Molding is 300m
(2) It was filled into a molding die of size X3QQmmX5Qmm and heated and foamed with steam.

After the obtained molded body was cured at 80° C. for 24 hours, the physical properties of this molded body were measured. The results are shown in Table 3. Further, the DSC curve (dotted line) of the foamable resin particles used in Example 3 and the DSC curve (solid line) of the foamed particles obtained using the same are shown in FIG.

Table 3 *I Fll indicates trichlorofluoromethane, F12 indicates dichlorofluoromethane, and the mixing ratio of both is a weight ratio.

*2 The measuring device is Loresta A manufactured by Mitsubishi Yuka.
PMCP-T400 was used.

*3 Closed cell ratio: Measured with Toshiba Tsukuman air comparison type hydrometer, W,
'J, Remington and R, Pari
Judgment was made based on the closed cell ratio calculated using the method of ser.

85% or more...○ Less than 85% to 65976 or more...6 Less than 65%...×4 Tensile strength test according to JIS-6767A method and below. Judgment was made.

Only material destruction of the molded body occurs...○ Material destruction and interparticle destruction occur...△ Only interparticle destruction of I occurs...×*5 Secondary foamability JIS-6767B method The water absorption rate of the molded body was determined below the measurement.

Water absorption rate is less than 0.003 g/c++・・・○
〃Less than 0.003-0.03 g/cnt...△o
O, 03 g/ad or more...× [Effects of the Invention] As explained above, the conductive polyethylene foam particles of the present invention have a conductive carbon content of at least Has excellent conductivity. Further, the foamed particles of the present invention have a closed cell structure, which makes it possible to provide an excellent molded article with good fusion properties between the foamed particles. Also, among LLDPE, MFR=0.5~
When using 2 g/10 min, it is possible to obtain particularly excellent closed cell properties and easily impart high conductivity. Further, if the internal pressure reduction rate coefficient of the foamed particles is less than 0.35, the foamed particles will have an excellent expansion effect when heated with steam in a mold, and a molded product that is faithful to the mold can be obtained. Furthermore, the bubble diameter of the expanded particles is 0.
．． When the temperature is 0.07 am or more, the above-mentioned expansion effect is even better, and a molded product that is even more faithful to the mold can be obtained.

Furthermore, the method of the present invention ensures the production of conductive polyethylene foam particles that have the above-mentioned excellent closed cell structure, have good interparticle fusion properties when molded, and can provide a molded product with excellent conductivity. can be manufactured. In addition, when obtaining highly expanded particles with an expansion ratio of 10 times or more, after first foaming the particles to a ratio of 10 times or less, applying internal pressure with an inorganic gas containing nitrogen gas as a main component, and then foaming again to obtain the desired 10 times or less. By adopting the method of making foamed particles more than double the size, it is possible to use an inorganic blowing agent that does not pose a risk of ozone layer depletion in the first stage of foaming, and fluorocarbon-based blowing agents are not used at all, or even if they are used. However, since only a small amount is required, environmental problems such as ozone layer depletion can be prevented as much as possible.

[Brief explanation of the drawing]

The drawing is a graph showing DSC curves of the foamed particles of Example 3 of the present invention and the resin particles used for foaming them. Procedural amendment cap button 1, Indication of the case Patent Application No. 229251 of 1988 2, Name of the invention Conductive polyethylene foam particles and method for manufacturing the same 3, Person making the amendment Relationship to the case Patent applicant address Chiyoda-ku, Tokyo 2-1-1 Uchisaiwai-cho Name: Japan Styrene Paper Co., Ltd. Representative: Masayo Uchiyama 4, Agent: 101 Address: 2-10-25 Iwamoto-cho, Chiyoda-ku, Tokyo Date of amendment order Voluntary amendment (1) Page 20 of the specification In Table 1, Example 1 and Example 8
, r950J in the surface area term of Ketchen Black EC in Comparative Examples 3 and 4 is corrected to "800". (2) In the same table, Ketchen Black EC of Example 4 = 6
Correct r950J of the surface area term of 00 to [1270J. that's all

Claims (6)

[Claims] (1) Conductive foamed polyethylene particles characterized by having a base material of a resin consisting of 95 to 70% by weight of non-crosslinked linear low-density polyethylene and 5 to 30% by weight of carbon black. (2) MFR of non-crosslinked linear low density polyethylene is 0.
The conductive polyethylene foam particles according to claim 1, characterized in that the rate is 5 to 2 g/10 minutes. (3) Internal pressure reduction rate coefficient (K) within expanded particles is 0.35
The conductive polyethylene foam particles according to claim 1, characterized in that the conductive polyethylene foam particles are less than 10%. (4) The conductive polyethylene foam particles according to claim 1, characterized in that the cell diameter is 0.07 mm or more. (5) Resin particles consisting of 95-70% by weight of non-crosslinked linear low-density polyethylene and 5-30% by weight of carbon black are dispersed in a pressure container in the presence of water and a blowing agent and heated to create a resin. The resin particles are foamed by impregnating the particles with a foaming agent, then maintaining the temperature within the temperature range from the melting point of the resin particles to -15°C below the melting point, and releasing the resin particles and water into a low-pressure atmosphere from inside the container. A method for producing conductive polyethylene foam particles. (6) In the manufacturing method according to claim 5, expanded particles having a bulk ratio of 10 times or less are obtained, and then the particles are heated with an inorganic gas containing nitrogen gas as a main component at 1 to 10 kg/cm^2.
A method for producing conductive polyethylene foam particles, which comprises applying an internal pressure of G to the particles, and then heating the particles to expand the particles to a bulk ratio of 10 times or more.