JP2646245B2 - Conductive polyethylene foam particles - Google Patents

Description

The present invention relates to conductive polyethylene foam particles and a method for producing the same.

[Problems to be Solved by Conventional Techniques and Inventions] There have been many studies on polyolefin resin conductive foams. However, in the case of a crosslinked foam, a favorable foam has not been obtained because addition of a large amount of carbon black inhibits crosslinking of the resin. Therefore, the conventionally obtained high-foamed product is somewhat open-celled and has a specific volume resistivity of 10 ⁵ Ω · cm. Further, in the case of a non-crosslinked foam, there is a problem that since the fluidity deteriorates, the viscosity of the resin increases, and the elongation rate of the resin decreases, so that it is difficult to determine the foaming conditions. In order to solve such a problem, a composition containing 5 to 30% by weight of a conductive furnace black having a drawing surface area of 900 m ² / g or more with respect to a polyolefin resin of 95 to 70% by weight has a magnification of 5 times or more. A method for producing a polyolefin low-density foam having a closed-cell structure and conductivity by foaming has been proposed (Japanese Patent Publication No. 59-25 / 1984).
No. 815).

However, the foam obtained by the above-described method has a limit of obtaining a volume resistivity of about 10 ⁶ Ω · cm, and even if the amount of carbon black added is increased to 30% by weight or more, the volume resistivity of the foam cannot be reduced. There is a problem that a dramatic decrease cannot be expected. In the case of extruded foam as in the above method, although there is not much problem, in the case of expanded particles to be filled in a mold and molded, when the added amount of carbon black increases, the fusion of the expanded particles in the mold The properties and the secondary foaming properties become problems, and a good conductive foam by the bead method has not been obtained until now.

[Means for solving the problem]

The present invention has been made as a result of intensive studies to solve the above-mentioned drawbacks of the prior art, using a linear low-density polyethylene as a base resin, and there is no foamed particle obtained by non-crosslinking foaming. The present inventors have found that they have excellent fusing property and secondary foaming property, and can obtain conductivity as high as 10 ² Ω · cm in volume specific resistance, and have completed the present invention.

That is, the present invention provides: (1) 95 to 70% by weight of a non-crosslinked linear low density polyethylene
And a resin comprising 5 to 30% by weight of carbon black, and an internal pressure reduction rate coefficient (K) of less than 0.35.

(2) Non-crosslinked linear low-density polyethylene having an MFR of 0.5 to
2. The foamed conductive polyethylene particles according to claim 1, wherein the weight is 2 g / 10 minutes.

(3) The conductive polyethylene foam particles according to claim 1, wherein the cell diameter is 0.07 mm or more.

It is the gist.

The linear low-density polyethylene (hereinafter abbreviated as LLDPE) used in the present invention is a low-pressure polymerized polyethylene having 4 carbon atoms.
Α-olefins of 1 to 10-butene, 1-pentene,
1-hexene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1
-Octene and the like. LL of these α-olefins
The content in DPE is usually 0.5 to 20% by weight,
15% by weight is preferred. The above LLDPE preferably has an MFR of 0.5 to 2 g / 10 minutes.

Antioxidants, light stabilizers, lubricants as additives in LLDPE,
Neutralizing agents and the like can be mentioned, and these are appropriately used depending on the purpose within a range that does not affect the bubble diameter and the conductivity. Of these, the stearic acid salt used as a neutralizing agent particularly affects the bubble diameter, and is therefore preferably 250 ppm or less. The extractable amount of n-hexane present in the resin is preferably 0.4% by weight or more and 1.5% by weight or less, particularly preferably 0.5% by weight or more.
1.2% by weight or less.

When such a low-density LLDPE is used, foamed particles having closed cells and high conductivity can be easily obtained even if the amount of added carbon is increased. In addition, foamed particles which can be satisfactorily secondary-foamed and fused by filling in a mold can be obtained.

In addition, within the range which does not hinder the intended purpose of the present invention.
Less than 50% by weight of low-density polyethylene (hereinafter abbreviated as LDPE) or / and linear ultra-low-density polyethylene (hereinafter referred to as LDPE)
Abbreviated as VLDPE. ) Can also be mixed.

Examples of the carbon black used in the present invention include furnace black and acetylene black. Examples of such carbon blacks include Vulcan XC-72, Black Pearl (manufactured by Cabot), Conductec 975 (manufactured by Colombian), Talka Black 5500, Talka Black 7550 (manufactured by Tokai Carbon Co., Ltd.), and Denka Black. (Electrical Chemical Industry Co., Ltd.
Ketchen Black EC, Ketjen Black EC-
600 (all manufactured by Akzo), # 3250, # 3750, # 3600, # 3
950 (all manufactured by Mitsubishi Kasei Corporation) and the like. The carbon black used in the present invention has a BET specific surface area of 50 m.
It is preferably ² g / g or more. Among the above carbon blacks, particularly preferred are Ketjen Black EC, Ketjen Black EC-600, Black Pearl 2000, # 3750, # 3
BET specific surface areas such as 600 and # 3950 are 500 m ² / g or more. Two or more different types of carbon black may be used as a mixture, or may be used alone.

If the content of carbon black in the conductive foamed 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 used as the raw material of the foamed particles will be insufficient. In addition, the obtained foamed particles tend to be open cells, and the fusion of the foamed particles during molding is also poor.

The conductive polyethylene foam particles of the present invention have a cell diameter of 0.07 mm.
It is preferable that the thickness be less than 0.07 mm. In addition, as an index of the closed cell property and gas permeability of the expanded particles, the internal pressure reduction rate coefficient (K) in the particles is used.
Is used. Conductive polyethylene foam particles have K> 0.35
In this case, a molded article according to the mold can be easily obtained by in-mold molding.

The internal pressure reduction rate coefficient: K is [However, in the above formula, P ₁ is the initial internal pressure of the expanded particles (kg / cm ² ·
G), P ₂ is the internal pressure (kg / cm ² ·
G) and t indicate time (hr). ], And can be determined by measuring the initial internal pressure (P ₁ ) at 25 ° C. and the internal pressure (P ₂ ) at the lapse of one hour (t = 1).

Further, the conductive polyethylene foamed particles of the present invention may have a crystal structure in which two endothermic peaks appear in a DSC curve obtained by differential scanning calorimetry or a crystalline structure in which only one endothermic peak appears. It doesn't matter,
For those having a low carbon black content, particularly 5 to 10% by weight, those having a crystal structure having an endothermic peak on the high temperature side are preferred. In this case, the energy of the endothermic peak on the high temperature side is preferably 15 J / g or less. The above DSC curve means that 1 to 5 mg of expanded particles was measured by a differential scanning calorimeter.
4 is a DSC curve obtained when the temperature is increased to 220 ° C. at a temperature increasing rate of ° C./min and measured. The endothermic peak on the lower temperature side of the two endothermic peaks in the DSC curve is considered to be due to the endothermic so-called melting of LLDPE, which is the base resin of the expanded particles. On the other hand, it is considered that the endothermic peak on the high temperature side is caused by the existence of a crystal structure different from the structure appearing as the endothermic peak on the low temperature side.

In FIG. 1, the energy of the endothermic peak on the high temperature side is divided into the high temperature side peak b and the low temperature side peak c at the valley part a of the high temperature side peak and the low temperature side peak, and the area of the peak on the high temperature side from the valley part a is calculated. It is the area of the peak on the high temperature side, and is a value obtained from this area.

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

Energy of high-temperature endothermic peak (J / g) = [Area of high-temperature endothermic peak on chart (cm ² ) × [caloric value per cm ^{2 of} chart (J / cm ² )]] ÷ [weight of measurement sample (g) The foamed particles of the present invention have a mixed composition of LLDPE 95 to 70% by weight and carbon black 5 to 30% by weight as described above,
If necessary, an inorganic filler may be further added.

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 magnesium carbonate.

The expanded particles of the present invention are prepared by adding LLDPE to carbon black 5-2.
0% by weight and the particles of the resin composition mixed with a volatile foaming agent are dispersed in water in a closed container and heated to impregnate the resin particles with the foaming agent. When the resin particles are foamed by being released under a low-pressure atmosphere, the foaming temperature (release temperature) is determined from the melting point of the resin particles to the melting point−
It is obtained by setting the temperature range to 10 ° C. The melting point of the resin is the temperature at the top of the endothermic peak in the DSC curve obtained by raising the temperature of 1 to 5 mg of the resin particles used for firing by a differential scanning calorimeter at a rate of 10 ° C./min.

As the blowing agent used for producing the expanded particles of the present invention,
Inorganic gas such as carbon dioxide, air, nitrogen or boiling point is -50
Organic blowing agents such as hydrocarbons or halogenated hydrocarbons at temperatures of up to 120 ° C. may be mentioned. Specific examples of the organic blowing agents include propane, butane, pentane, hexane, heptane, cyclopuntane, cyclohexane, monochloromethane, dichloromethane, and monochlorofluorofluorocarbon. Methane, monochloroethane, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluorofluoroethane, dichlorotetrafluoroethane and the like can be mentioned. These may be used alone or as a mixture of two or more. The amount of the foaming agent varies depending on the type of the foaming agent, the desired expansion ratio, the cell diameter, and the like. For example, the expansion ratio is 5 to 50 times (bulk ratio; hereinafter, the expansion ratio of expanded particles indicates the bulk ratio). To do so, it is usually 5 to 40 parts by weight, based on 100 parts by weight of the resin particles, but when an inorganic blowing agent is used as the blowing agent, the expansion ratio of the normally obtained expanded particles is 10 times or less. . In order to further expand such expanded particles, once expanded to 10 times or less, then apply an internal pressure of 1 to 10 kg / cm ² G with an inorganic gas containing nitrogen gas as a main component, Thereafter, the operation of heating and foaming is repeated several times as necessary, whereby conductive polyethylene foam particles having a desired high foaming ratio can be obtained. The method of increasing the expansion ratio without using a chlorofluorocarbon-based blowing agent is particularly preferable for solving the current problem of destruction of the ozone layer of chlorofluorocarbons. This method can also be adopted for foamed particles produced using Freon gas. In this case, the amount of CFC used is extremely small.

The amount of the resin particles to be dispersed in water at the time of producing the expanded particles of the present invention is preferably from 10 to 100 parts by weight per 100 parts by weight of water from the viewpoints of improving productivity and dispersion stability, reducing utility costs, and the like. The amount of the foaming agent to be dispersed in water together with the resin particles, the type of the foaming agent, the desired expansion ratio, the ratio of the amount of the resin particles in the container to the space in the container, etc. The ratio is determined so as to be within the above range.

In dispersing the resin particles in water, a dispersant may be used as necessary. The dispersant is used to prevent agglomeration and fusion of resin particles during heating,
For example, fine powder of a poorly water-soluble inorganic substance such as calcium phosphate, magnesium pyrophosphate, zinc carbonate, titanium oxide, and aluminum oxide is used. When the above-mentioned inorganic substance is used, a small amount of a surfactant such as sodium alkylbenzene sulfonate, sodium α-olefin sulfonate, and sodium alkyl sulfonate may be used in combination as a dispersing aid to reduce the amount of the inorganic substance used. ,
It is preferable to improve the fusion property between the foamed particles during molding. In this case, it is preferable to use about 0.1 to 3 parts by weight of a fine powder of an inorganic substance and about 0.001 to 0.5 parts by weight of a surfactant based on 100 parts by weight of the resin particles. When a water-soluble polymer is used as a dispersant, it is preferable to use about 0.1 to 5 parts by weight of a water-soluble polymer per 100 parts by weight of resin particles.

In the method of the present invention, after dispersing the resin particles and the foaming agent in water and heating to impregnate the resin particles with the foaming agent, the resin particles and water are released under a low-pressure atmosphere from the container. It is necessary that the temperature at this time be between the melting point of the resin particles and the melting point −15 ° C. If the temperature at the time of release is out of this range, good expanded particles cannot be obtained. Especially for DSC curve 2
Expanded particles having two endothermic peaks become difficult to obtain as the amount of carbon black added increases. However, this problem can be solved by sufficiently holding the resin particles containing carbon black at a temperature near the foaming temperature. Even in the case of expanded particles having a crystal structure in which only one endothermic peak appears in the DSC curve, the amount of added carbon black is
When the content is 10% by weight or more, favorable expanded particles can be obtained by a pseudo-crosslinking effect.

The foamed particles obtained as described above are molded into various shapes in a mold. As an in-mold molding method, the following method is exemplified.

The foamed particles are directly filled in a mold and molded by steam.

The foam 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 pressure in the cells of the foam particles to impart secondary foaming properties. The provided foam particles are filled in a mold and steam-molded.

The foam particles are impregnated with a volatile expanding agent in advance to impart secondary expandability to the foam particles, and the foam particles are filled in a mold and steam-molded.

After filling the foam particles into the mold, the foam particles are compressed to reduce the volume by 15 to 50%, and then steam of 1 to 5 kg / cm ² G is guided to fuse the foam particles together. ,
Cool the mold and get the product.

 Combinations of two or more of the above.

〔Example〕

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

Examples 1 to 7 and 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 these resin particles and a foaming agent in the amount shown in Table 1 were used in a closed container. After the resin particles were dispersed in water and heated to impregnate the resin particles with the foaming agent, the resin particles and water were released 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 of the obtained resin particles, and the results of differential scanning calorimetry of the expanded particles.

Examples 8 and 9 Using a resin containing LLDPE 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. Heating,
After impregnating the resin particles with the foaming agent, the resin particles and water were released under atmospheric pressure at the foaming temperatures shown in the table to foam the resin particles. Expanding ratio of the obtained expanded particles (bulk ratio),
Table 2 shows the bubble diameter, the internal pressure reduction rate coefficient, and the results of differential scanning calorimetry. Next, these foamed particles were subjected to a pressure treatment with air to give an internal pressure shown in Table 2, and then 1.2 kg /
The foam was further foamed by heating with steam of cm ² · G. Table 2 shows the expansion ratio (bulk ratio), cell diameter, internal pressure reduction rate coefficient, and differential scanning calorimetry results of the obtained expanded particles (reported particles after two-stage expansion).

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 on the DSC curve in the differential scanning calorimetry were 2 kg / cm ² · G air. And subjected to molding for 1 day. The other expanded particles were directly used for molding. Molding is 300mm x 300mm x 60
The mixture was filled in a molding die of mm and heated and foamed with steam.

After the obtained molded body was trained at 80 ° C. for 24 hours, the physical properties of the molded body were measured. The results are shown in Table 3. Example 3
FIG. 1 shows the DSC curve (dotted line) of the foaming resin particles used in the above and the DSC curve (solid line) of the foaming particles obtained using the same.

* 1 F11 indicates trichlorofluoromethane, F12 indicates dichlorofluoromethane, and the mixing ratio of both is a weight ratio.

* 2 Loresta AP MCP manufactured by Mitsubishi Yuka Co., Ltd.
-T400 was used.

* 3 Closed cell rate Measured with a Toshiba Beckman air-comparison hydrometer.
Judgment was made based on the closed cell rate calculated by the method of J. Remington and R. Pariser.

85% or more ○ 未 満 Less than 85% to 65% or more △ 未 満 Less than 65% × × * 4 Tensile strength test according to the JIS-K6767A method was performed and judged as follows.

Only material destruction of the molded body occurs .... ○ Material destruction of the molded body and interparticle destruction occur ........ △ Only interparticle destruction of the molded body occurs .... × * 5 Secondary foamability Molded product by JIS-K6767B method Was determined below the measurement.

The present invention as water absorption is 0.003 g / cm ³ less than ...... ○ Water absorption 0.003~0.03g / cm ³ less than ...... △ water absorption has been described [Effect of the Invention] ...... × 0.03g / cm ³ or more The conductive polyethylene foam particles of (1) have conductivity in which the amount of conductive carbon added is at least superior to that of conventional conductive foams. Further, the expanded particles of the present invention have a closed cell structure and have an internal pressure reduction rate coefficient (K).
Is less than 0.35, so that the particles are excellent in the fusion property between the particles during in-mold molding, and the expanded particles have excellent expandability, so that a molded article faithful to the mold can be easily obtained. Also LLDPE
Among them, when MFR = 0.5 to 2 g / 10 min is used, it is possible to obtain particularly excellent closed-cell properties and easily impart high conductivity. Furthermore, when the cell diameter of the foamed particles is 0.07 mm or more, the above-mentioned expansion action is more excellent, and a molded article more faithful to the mold can be obtained.

[Brief description of the drawings]

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 the foaming.

Claims (3)

(57) [Claims] A resin comprising 95 to 70% by weight of a non-crosslinked linear low-density polyethylene and 5 to 30% by weight of carbon black as a base material, and having an internal pressure reduction rate coefficient (K) of less than 0.35. Characterized conductive polyethylene foam particles. 2. The non-crosslinked linear low-density polyethylene has an MFR of
2. The conductive polyethylene foam particles according to claim 1, wherein the amount is 0.5 to 2 g / 10 minutes. 3. The foamed conductive polyethylene particles according to claim 1, wherein the cell diameter is 0.07 mm or more.