JP4791018B2 - Polyolefin resin expanded particles and in-mold molded product thereof - Google Patents

Description

  The present invention relates to a polyolefin resin foamed particle having antistatic performance and an in-mold molded product thereof.

2. Description of the Related Art In recent years, electronic and electrical equipment, particularly personal computers and peripheral devices such as liquid crystal display devices and storage devices have been growing rapidly with the development of information culture represented by the Internet. Since these devices incorporate semiconductor products such as LSIs and are susceptible to electrostatic breakdown, these transport cushioning packaging materials contain cushioning for polyolefin resin-in-mold foam moldings that have antistatic properties. The current situation is that materials are needed and their importance is increasing.
In Patent Document 1 and Patent Document 2, the conductive performance is expressed by adding conductive carbon black to the polyolefin resin foamed particles and the in-mold molded product thereof. However, when conductive carbon black is used, it is difficult to find an electrical failure or dirt on the package due to the removal of the conductive carbon black, and control at an antistatic performance level of 10 ¹⁰ to 10 ¹² Ω is possible. There are problems such as difficulties. Moreover, in patent document 2, electroconductive performance is expressed by adding surfactant. However, when a surfactant type antistatic agent is used, there is no problem of dropping off, but the surfactant may be transferred to the package. Further, the surfactant type antistatic agent deteriorates in performance under a high temperature environment, or the performance greatly changes depending on humidity.
Japanese Patent Laid-Open No. 4-118224 JP 2002-3634 A

The present invention does not cause a transfer (contamination) phenomenon to a packaged object, does not cause an electrical failure to the packaged product due to dropping, has a stable antistatic performance level of 10 ¹⁰ to 10 ¹² Ω, and is permanent. An object of the present invention is to provide foamed polyolefin resin particles.

As a result of intensive studies in order to solve the above-mentioned problems, the present inventor has found that the object can be achieved by blending a specific conductive zinc oxide and a resin, and has reached the present invention.
That is, the present invention is as follows.
(1) The entire surface is covered with an adhesive resin layer containing an adhesive resin composed of conductive zinc oxide having a particle diameter of 0.01 to 0.1 μm and linear low-density polyethylene. Polyolefin resin foam particles.
(2) The polyolefin resin expanded particles according to (1), wherein the mass ratio of the conductive zinc oxide to the adhesive resin is 20:80 to 80:20.
(3) An in-mold foam molded article obtained by using the polyolefin resin foamed particles according to (1) or (2).

The polyolefin-based resin foamed particles and the in-mold molded product of the present invention have no transfer (contamination) phenomenon to the package, no electrical obstacles to the package due to dropping, and a surface resistivity of 10 ¹⁰ to 10 ¹² Ω. The antistatic performance level is stable and permanent.

Hereinafter, each configuration of the present invention will be described in detail.
"Polyolefin resin foamed particles"
The polyolefin resin expanded particles are a general term for crosslinked and non-crosslinked polyolefin resin expanded particles.
Polyolefin resins include low, medium and high density polyethylene, linear low density polyethylene, ultra high density polyethylene, metallocene-catalyzed polyethylene, ethylene resin represented by ethylene-vinyl acetate copolymer, polypropylene, and copolymer. Examples thereof include random or block copolymer resins of one or more components selected from ethylene, butene-1,4-methylpentene, and the like, and propylene, or a mixed resin in which two or more of these components are blended.
The average size of the polyolefin-based resin average particle before foaming is preferably 0.2 to 3.0 mm in diameter. When the foamed polyolefin resin particles before foaming have a diameter of 0.2 mm or more, the foaming is normally difficult to escape during foaming, and when the diameter is 3.0 mm or less, foaming occurs when the foam is highly foamed. The particle size is reduced, and a finely shaped molded product is obtained.
Expansion ratio of the polyolefin resin expanded particles is ^preferably from 2cm ³ / g~40cm 3 / g, more preferably ^{2cm 3} / ^g~30cm 3 / g. If the expansion ratio is 2 cm ³ / g or more, the sequential high foaming operation for use in in-mold molding (high magnification) is facilitated, and the foam molding production process is economical. On the other hand, when the expansion ratio is 40 cm ³ / g or less, the amount of the adhesive resin containing conductive zinc oxide is small, which is economical and has good processability.
The polyolefin resin foamed particles are preferably those obtained by impregnating a polyolefin resin with a volatile foaming agent and then heating and foaming at an appropriate foaming temperature.

"Conductive zinc oxide"
Conductive zinc oxide is a white powder made conductive by doping a different metal in the crystal lattice of zinc oxide.
The conductive zinc oxide preferably has a particle size of 0.01 to 0.2 μm, more preferably 0.01 to 0.1 μm. From the viewpoint of melt kneading processability with an adhesive resin using an extruder, a kneader, or the like, the particle diameter is preferably 0.01 μm or more. The amount of conductive zinc oxide added is uneconomical, and the particle size is preferably 0.2 μm or less from the viewpoint of workability.

"Adhesive resin"
The adhesive resin serves as a binder to firmly adhere the conductive zinc oxide to the surface of the primary expanded particles. Adhesive resins include low, medium and high density polyethylene, linear low density polyethylene, ultra high density polyethylene, metallocene-catalyzed polyethylene, ethylene resin represented by ethylene-vinyl acetate copolymer, polypropylene, and copolymer. Examples thereof include random or block copolymer resins of one or more components selected from ethylene, butene-1,4-methylpentene, and the like, and propylene, or a mixed resin in which two or more of these components are blended.
The adhesive resin needs to extend following the expansion of the polyolefin resin foamed particles, and as a resin having the necessary properties for that purpose, it is preferably linear low density polyethylene, more preferably MFR 2-50 g / 10 min, It is a linear low-density polyethylene having a density of 0.930 g / cm ³ or less.

"Adhesive resin layer"
The adhesive resin layer is preferably uniformly coated with a thickness of 1 to 400 μm.
1-15 mass% is preferable with respect to the mass of an expanded particle, and, as for an adhesive resin layer, More preferably, it is 1.5-10 mass%. When the content is 1% by mass or more with respect to the mass of the expanded particles, the entire surface of the expanded particles can be coated uniformly.

The mass ratio between the conductive zinc oxide and the adhesive resin is preferably 20:80 to 80:20, more preferably 30:70 to 70:30. When the mass ratio is 20:80 or more, antistatic performance is easily exhibited, and when the mass ratio is 80:20 or less, the fixing property to the surface is good.
The conductive zinc oxide is preferably melt kneaded with an adhesive resin in advance using an extruder, a kneader, or the like, whereby the effects described below can be expected.
1) The dispersion is high and uniform.
2) The effect can be easily and stably obtained.
3) The fixing process to the expanded particles is completed in one stage.
In order to form an adhesive resin layer, it is economical and preferable to use a high-speed shear mixer because the mixing time is short and the productivity is high.

Hereinafter, the contents of the present invention will be described in detail using examples.
The physical property values and evaluation methods used in the present invention are shown below.
1) Foaming ratio: Mass (g) The volume (cm ³ ) of a known foamed particle is measured by a submersion method, and the value obtained by dividing the volume by the mass is taken as the foaming ratio (cm ³ / g).
2) Molded body magnification: Mass (g) The volume (cm ³ ) of a known molded body is measured by a submersion method, and the value obtained by dividing the volume by the mass is the molding body magnification (cm ³ / g). ).
3) Surface resistivity: The surface of an in-mold molded product that has been conditioned for 24 hours in a room controlled at a temperature of 20 ° C. and a relative humidity of 65% is defined in JIS K6911 test method 5.13. Set between electrodes, measure the surface resistance of the molded skin surface with a resistance meter (trade name: SME-8220, manufactured by Toa Denpa Kogyo Co., Ltd., applied voltage: 500 V), and calculate the surface resistivity from the formula specified in JIS. And evaluate.
4) Evaluation of transfer (contamination) property; a clean glass substrate is placed on the surface of the molded body in the mold in a room controlled at a temperature of 20 ° C. and a relative humidity of 65%, and after standing for 24 hours, the surface of the glass substrate is observed and evaluated. .
5) Forced transfer (contamination) evaluation: Place a clean glass substrate on the surface of the molded body in the mold in a constant temperature and humidity chamber controlled at a temperature of 70 ° C. and a relative humidity of 90%. Observe and evaluate.
6) Temperature dependence; after fixing the humidity to 65%, storing it in an environment of temperature 20, 50, 70 ° C for 30 days, leaving it in a room controlled at 65% humidity, temperature 20 ° C for 24 hours, Measure resistivity and evaluate temperature dependence.
7) Humidity dependence: The temperature is fixed at 20 ° C., and the surface resistivity is measured in an environment of humidity of 20, 65, 90% to evaluate the humidity dependence.
8) Possibility of electrical failure; those with low volume resistivity cause a short circuit between the liquid crystal circuits when dropped. The possibility of electrical failure was evaluated from the volume resistivity.
9) Measurement of conductive zinc oxide particle diameter; obtained by measuring the specific surface area of the powder by the BET method using a rapid surface measuring device (trade name; SA-1000, manufactured by Shibata Chemical Instruments Co., Ltd.) From the specific surface area, assuming that the powder was spherical, the converted particle size was calculated by the following formula.
d = 6 / (ρ · S)
d: particle diameter (μm), S: specific surface area (m ² / g), ρ: sample density (g / cm ³ )
10) Measurement of polyolefin resin particle diameter before foaming; Measured with calipers and calculated an average value of n = 5.
11) Measurement of thickness of adhesive resin film layer; cross section of expanded particle was measured with optical microscope (trade name; PCS-81X, manufactured by Inabata Sangyo Co., Ltd.) and electron microscope (trade name; JSM-5600LV, JEOL Ltd.) The thickness of the adhesive resin layer was measured visually.

[Example 1]
High-speed fluid mixer (trade name: Supermixer SMV? 500, manufactured by Kawata Co., Ltd., rotation speed: inverter-controlled non-transmission 100-900 rpm, temperature detection end: J-type φ1 mm attached to the lower part of the guide plate, jacket: 30 ° C water In the tank of the circulating water) (trade name; Mef LD, manufactured by Asahi Kasei Life & Living Co., Ltd., melting point 117 ° C., magnification 2.7 cm ³ / g, polyethylene resin average particle 1 before foaming) .2 mm) in a bulk volume of 0.4 m ³ , the rotation speed was set to 900 rpm, and the mixing was continued until the surface temperature of the foamed particles reached 110 ° C. due to fluid frictional heat between the high speed rotating mixing blade and the foamed particles. Thereafter, the rotational speed was immediately reduced to 400 rpm, and at the same time, the pulverized powder of the adhesive resin obtained by melting and kneading the conductive zinc oxide described below was reduced to 4 with respect to the mass of the expanded particles. Fed portionwise over the amount% of 4 minutes, the pulverized powder of the adhesive resin was melt coated on the surface of the mixture to foam particles from the start of the supply 7 minutes. During mixing, the temperature of the foamed particles was controlled from the air outlet provided in the lid of the mixer main body so that the surface temperature of the foamed particles did not exceed 110 ° C.

Thereafter, the number of rotations was reduced to 200 rpm, and continuously blown from the lid part air outlet under intermittent mixing, and cooled until the surface temperature of the foamed particles decreased to 100 ° C., and taken out foamed particles were obtained. . As a result of observing the surface state of the obtained expanded particles with an optical microscope and an electron microscope, the expanded particles were obtained by melt-coating a powder having a mass ratio of the conductive zinc oxide and the adhesive resin of the present invention of 50:50 (implemented) In Example 1), the adhesive resin was uniformly coated over the entire particle surface (adhesive resin layer thickness 100 μm).
(Preparation of ground powder of adhesive resin in which conductive zinc oxide is melt-kneaded)
Using a resin pellet manufacturing apparatus with a twin screw extruder, the adhesive resin is linear low density polyethylene (trade name; Nipolon-Z, 8P06A, manufactured by Tosoh Corporation), and conductive polyethylene oxide is added to this polyethylene. (Product name: Pasette-CK, manufactured by Hakusuitec Co., Ltd., volume resistivity of 10 ⁴ Ω · cm, particle size of 0.03 μm) was prepared in a mass ratio of 50:50 pellets. In addition, a red pigment (trade name; Fastogen Super Magenta RE-03, manufactured by Dainippon Ink & Chemicals, Inc., 0.06% by mass) was simultaneously added as a colorant. The pellets were pulverized by a room temperature pulverizer to obtain a 60 mesh sieve (pass) powder.

[Example 2]
The expanded particles obtained in Example 1 were accommodated in an autoclave having a pressurizing (high pressure air) / heating device, and the pressure was increased over 1 hour at a temperature of 80 ° C., and the pressure was 1.0 MPa (gauge pressure). For 8 hours to increase the internal pressure of the expanded particles, and then accommodated in a foaming apparatus and heated and foamed with heated steam at a pressure of 0.06 MPa (gauge pressure) for 15 seconds. It was set as a secondary expanded particle of 0.7 cm ³ / g. Further, the secondary foamed particles were made into the tertiary foamed particles having a foaming ratio of 23 and 35 cm ³ / g while adjusting the heating steam pressure in the range of 0.04 to 0.065 MPa (gauge pressure) in the same manner as described above. The adhesive resin layer thickness of the secondary expanded particles was 20 ± 5 μm, and the adhesive resin layer thickness of the tertiary expanded particles was 3 ± 2 μm. The secondary and tertiary expanded particles are each filled in an in-mold mold (internal dimensions: 30 cm × 30 cm × 2.5 cmt) having water vapor holes (note) (mold open width: 8.3 to 14.7 mm) ), Heated with heated steam at a pressure of 0.11 MPa (gauge pressure), cooled, removed from the mold, and left in a drying room at room temperature of 80 ° C. for 12 hours to be molded at 20, ³⁰ cm ³ / g. Got the body. [(Note): Filling method in which the foamed particles are filled in the mold with the mold opened in an amount corresponding to the void volume between the foamed particles, and the mold is closed to the proper position after filling]

[ Comparative Example 3]
In Example 1 “Preparation of ground powder of adhesive resin in which conductive zinc oxide is melt-kneaded”, the adhesive resin is low-density polyethylene (trade name; Suntech-LD, M grade, Asahi Kasei Chemicals Corporation The foamed particles were obtained in the same manner as in Example 1 except that the product was manufactured in the same manner as in Example 2, and an in-mold molded product was obtained.

[ Comparative Example 4]
In Example 1 “Preparation of ground powder of adhesive resin in which conductive zinc oxide is melt-kneaded”, conductive zinc oxide is converted into conductive zinc oxide having a different particle diameter (trade name; 23K, Hakusuitec Co., Ltd.). The foamed particles were obtained in the same manner as in Example 1 except that the volume resistivity was 10 ² Ω · cm and the particle diameter was 0.18 μm.

[Comparative Example 1]
In Example 1 “Preparation of ground powder of adhesive resin in which conductive zinc oxide was melt-kneaded”, conductive zinc oxide was converted into a surfactant type antistatic agent (trade name; Electro Stripper TS-13B, Kao Co., Ltd.) is contained in an amount of 20% by mass, and the adhesive resin is low density polyethylene (trade name; Suntec-LD, M grade, Asahi Kasei Chemicals Co., Ltd.). After obtaining the expanded particles, an in-mold molded product was obtained in the same manner as in Example 2.

[Comparative Example 2]
In Example 1 “Preparation of ground powder of adhesive resin in which conductive zinc oxide is melt-kneaded”, conductive zinc oxide is mixed with conductive carbon black (trade name: Ketjen Black EC-600JD, Lion ( 8% by mass), and the adhesive resin is low density polyethylene (trade name: Suntech-LD, M grade, manufactured by Asahi Kasei Chemicals), and the amount of conductive carbon black added to the expanded particles The foamed particles were obtained in the same manner as in Example 1 except that the amount was 3% by mass.
About the obtained in-mold molded product (Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 1, Comparative Example 2), the coating antistatic performance and transferability were evaluated by the evaluation method described in the text, and the results were obtained. Tables 1 and 2 show.

  The foamed polyolefin resin particles having antistatic properties of the present invention and in-mold molded articles thereof can be suitably used as buffer packaging materials for electronic parts, particularly electronic parts incorporating optical parts.

Claims (3)

A polyolefin resin characterized in that the entire surface is covered with an adhesive resin layer containing an adhesive resin composed of conductive zinc oxide having a particle size of 0.01 to 0.1 μm and linear low-density polyethylene. Expanded particles. 2. The polyolefin-based resin expanded particles according to claim 1, wherein the mass ratio of the conductive zinc oxide to the adhesive resin is 20:80 to 80:20. An in-mold foam molded article obtained by using the polyolefin resin foamed particles according to claim 1 or 2.