JP2002146082A - Polyethylene-based resin pre-expanded bead having antistaticity and its foamed-in-place molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyethylene-based resin foamed-in-place molded product having good antistaticity (surface resistivity of <1×1012 Ω/(square)) without polluting a half mirror, etc., in optical system components. SOLUTION: This foamed-in-place molded product is obtained from a polyethylene-based resin pre-expanded bead containing 0.3-3 wt.% of a fatty acid glyceryl ester having >=3 and <4 HLB (hydrophilic-lipophilic balance) value and 35-75 deg.C melting point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-expanded polyethylene resin particle having antistatic properties and an in-mold foam molded article thereof.

[0002]

2. Description of the Related Art A foamed molded article in a polyethylene resin mold (hereinafter referred to as a foamed molded article) is widely used as a cushioning packaging material for electric equipment parts such as home appliances and general equipment parts. In recent years, among electrical appliances, demand as cushioning packaging materials for electronics-related products such as liquid crystals, personal computers, and semiconductor parts has been increasing. In general, electronics-related products dislike dust and static electricity, but polyethylene-based resin itself is an insulator and is easily charged by heat and friction, so that it may adsorb dust and damage electronic-related products by static electricity. Attempts have been made to impart antistatic performance to foamed molded articles.

[0003] In order to solve this problem, a method of forming a foamed article using polyethylene resin pre-expanded particles (hereinafter referred to as pre-expanded particles) coated with an antistatic agent such as a surfactant, or an A method of applying an antistatic agent such as an activator, a method of forming a foamed molded article using pre-expanded particles impregnated with an antistatic agent, and a method of preventing the static electricity by reducing the surface specific resistance of the foamed molded article. Has been adopted. However, in these methods, the durability of the antistatic effect is poor due to peeling during use or the like, or the antistatic effect does not appear at all or is significantly reduced in the fractured surface of the foamed molded article. Also,
There is a problem that the process becomes complicated and the manufacturing cost increases. On the other hand, there is also known a method of producing pre-expanded particles and expanded molded articles from resin particles into which an antistatic agent has been kneaded in advance. For example, JP-A-3-28239 discloses a nonionic surfactant having an average molecular weight of 250 to 1000 and an HLB value of 4 to 8 having an antistatic ability of 0.1 to 5% by weight.
It has been proposed to knead and use it.

JP-A-8-113667 discloses that an ester of a higher fatty acid having 15 to 23 carbon atoms and a polyhydric alcohol having 3 to 7 hydroxyl groups is contained in an amount of 0.2 to 5.0% by weight. A linear low-density polyethylene-based resin foam molded article characterized by having been disclosed, but the purpose thereof is to reduce the shrinkage of the linear low-density polyethylene-based resin foam molded article, to obtain dimensional accuracy, No mention is made of the provision of a polyethylene resin-in-foam molded article having improved anti-static properties without contaminating optical components, which is an object of the present invention, which is an object of the present invention described below.

[0005]

The above-mentioned JP-A-3-28.
If the antistatic agent described in JP-A-239-239 is used, a foamed molded article having good antistatic performance cannot always be obtained, and in fact, there is a difference in the antistatic performance depending on the antistatic agent used. Also, depending on the type of antistatic agent used, when the foamed molded article is used as a cushioning wrapping material for optical components used for compact discs, etc. Contamination of polygon motor reflectors and the like (many white spots are generated on the surface) may significantly reduce the functions of products to be transported, and thus improvements are required. Such contamination occurs in spite of non-contact with the foam molded article.

[0006] Thus the invention without contaminating the like half mirror in the optical system component, a polyethylene resin-mold foam molding having good antistatic performance (surface resistivity 1 × 10 ¹² Ω / □ under) The purpose is to provide the body.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in view of such circumstances, and as a result, have found that the above-mentioned problems can be solved by using a specific fatty acid glycerin ester, thereby completing the present invention. Was.

That is, according to the present invention, the HLB value is 3 or more and 4 or more.
Pre-expanded polyethylene resin particles containing a fatty acid glycerin ester having a melting point of less than 35 ° C and not more than 75 ° C and not less than 0.3% by weight and not more than 3% by weight, and an in-mold expanded molded article thereof (Claim 1) The pre-expanded polyethylene resin particles according to claim 1, wherein the fatty acid glycerin ester is a mixture of glyceryl monostearate and glyceryl distearate, and an in-mold expanded molded article thereof (claim 2).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an antistatic agent having an HLB value of 3 to less than 4 and a melting point of 35 ° C. to 75
Use a fatty acid glycerin ester having a temperature of not more than ℃. Fatty acid glycerin esters are esters of fatty acids and glycerin. Examples of such fatty acids include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, succinic acid, citric acid and the like. Fatty acid glycerin esters are esters of one or more of these fatty acids with glycerin, and include monoesters,
They are diesters, triesters or mixtures thereof. Among them, glyceryl stearate which is industrially produced and easily available from monoester to triester is preferred.

The use of these fatty acid glycerin esters can prevent contamination of half mirrors and the like in optical components.

The present inventors have found that when a nitrogen-containing compound such as alkyldiethanolamine or the like is used as an antistatic agent, contamination of optical parts is often observed. This is because optical components are often surface-treated with titanium, chromium, nickel or a compound thereof, and in the case of a nitrogen-containing antistatic agent having an unpaired electron pair, it is easy to coordinate with the metal or metal compound. It seems that there is much pollution in the area. That is, in the case of the fatty acid glycerin ester, it is considered that the coordination tendency to the metal or the metal compound is low, so that the optical system component is hardly contaminated.

The HLB value of the antistatic agent used in the present invention is 3 or more and less than 4. Here, the HLB value is defined as Gri
According to the method of fin, the saponification value of the fatty acid glycerin ester is S and the neutralization value A of the fatty acid constituting the fatty acid glycerin ester is HLB value = 20 (1-S /
It is calculated from A). When the fatty acid glycerin ester is composed of the same fatty acid, the HLB value decreases when the number of fatty acid bonds to glycerin increases, and when the number of fatty acid bonds is the same, the HLB value increases when the alkyl chain length of the fatty acid increases.
The LB value decreases. That is, even when the fatty acid glycerin ester is composed of the same fatty acid, HL is determined by the mixing ratio of monoester, diester, and triester.
The B value changes, and when the number of bonded fatty acids is the same, the HLB value changes depending on the type of fatty acid and its composition ratio.

[0013] When the HLB value is less than 3, the bleed-out antistatic agent does not have sufficient hydrophilicity and does not exhibit good antistatic performance. When the HLB value is 4 or more, there is no problem in the antistatic performance, but a problem occurs in that the amount of the attached dispersant on the surface of the pre-expanded particles increases. Generally, polyethylene-based resin pre-expanded particles are obtained by dispersing the resin particles in an aqueous dispersion medium in a closed container, impregnating the blowing agent by heating while stirring and mixing, and then releasing the mixture under a pressure lower than the internal pressure of the closed container. (Preliminary foaming step) It is manufactured by the method.
In the aqueous dispersion medium, a sparingly water-soluble inorganic compound such as tertiary calcium phosphate, basic magnesium carbonate, or calcium carbonate is added as a dispersant to prevent fusion between the resin particles. If a large amount adheres to the surface, problems such as poor fusion will occur in the subsequent molding process.

The HLB value of the fatty acid glycerin ester is calculated by the Griffin method as described above. In many cases, the HLB value is about 4 to 7 for the monoester, 1 to 4 for the diester, and about 0.5 to 2 for the triester. Take a value. By mixing these, it can be used after adjusting to a desired HLB value.

The antistatic agent used has an HLB value of 3
It is not enough even if it is less than 4 and its melting point is 35 ° C.
It is necessary that the temperature is not less than 75 ° C and more preferably not less than 40 ° C and not more than 70 ° C. When the melting point is 35 ° C. or less, stickiness is liable to occur during use, dust and the like may adhere to the surface of the foamed molded article and impair the appearance, and may also degrade the antistatic performance. If the melting point exceeds 75 ° C., the antistatic performance may be significantly reduced, or it may take a long time to exhibit the antistatic performance. This is because the foamed molded body is cured to recover shrinkage after molding and for drying, but when the curing temperature is lower than 70 ° C., it takes a long time to recover shrinkage, and when the temperature exceeds 80 ° C., the shrinkage conversely occurs. Is usually cured at 70 ° C. to 80 ° C., and it is considered that the antistatic agent bleeds out in the curing step to exhibit antistatic performance. That is, it is considered that if the melting point of the antistatic agent is higher than the curing temperature, the antistatic agent required for exhibiting the antistatic performance cannot sufficiently bleed out.

Here, the melting point of the antistatic agent is determined by measuring 5 to 10 mg of the antistatic agent from 0 ° C. to 120 ° C. by a differential scanning calorimeter.
Up to 10 ° C / min.
In the SC curve, it is measured as the peak temperature of the endothermic peak.

In the present invention, the added amount of the antistatic agent is 0.1.
The content is 3% by weight or more and 3% by weight or less, preferably 0.5% by weight or more and 2% by weight or less. If it is less than 0.3% by weight, sufficient antistatic performance is not exhibited. If the content exceeds 3% by weight, it is not preferable since dispersion failure may occur in the preliminary foaming step and the amount of the attached dispersant may increase.

As the polyethylene resin used in the present invention, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene-
Examples thereof include vinyl acetate copolymers, and these can be used alone or in combination of two or more. Among these resins, linear low-density polyethylene is preferable, and particularly, the density is 0.920 to 0.935 g / cm ³ , the melt index is 0.5 to ³ g / 10 minutes, and the comonomer is hexene, 4-methylpentene or Octene, a linear low-density polyethylene, is preferred for obtaining good moldability. These polyethylene resins include color pigments, cell nucleating agents,
Antioxidants, weathering agents, lubricants, nucleating agents, and the like can be added. The addition amount is preferably 3% by weight or less, more preferably 1% by weight or less so that the cell diameter of the pre-expanded particles does not become fine and non-uniform.

These polyethylene resins are melted in advance using an extruder, a kneader, a Banbury mixer, a roll, or the like, and have a desired particle shape such as a columnar shape, an elliptical columnar shape, a spherical shape, a cubic shape, a rectangular parallelepiped shape, or the like. The particles are processed into resin particles having a particle weight of 0.2 to 10 mg, preferably 0.5 to 6 mg. At this time, an antistatic agent is added,
Usually, a master batch having an antistatic agent concentration of 5 to 20% by weight is added so that the antistatic agent has a desired concentration.

In the present invention, a conventionally known method comprises:
That is, in an airtight container, charged with an aqueous dispersion medium containing a resin particle, a dispersant and a dispersant and a volatile foaming agent,
The pre-expanded particles are produced by a method in which the resin particles are impregnated with a foaming agent at a constant pressure and a constant temperature by raising the temperature while stirring, and then the resin particles are discharged under a pressure lower than the internal pressure of the closed vessel (pre-expansion step). The closed container used is not particularly limited as long as it can withstand the pressure and temperature in the preliminary foaming step, and examples thereof include an autoclave-type pressure-resistant container.

Examples of dispersants include poorly water-soluble inorganic compounds such as tribasic calcium phosphate, basic magnesium carbonate and calcium carbonate, and examples of dispersants include sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonic acid, and α-olefinsulfonic acid. An anionic surfactant such as soda is used. Among them, the use of tricalcium phosphate and sodium n-paraffin sulfonate is preferable in obtaining good dispersibility. The amount of the dispersant and the dispersing aid used varies depending on the type thereof, the type and the amount of the polyethylene resin used, and the like. Usually, 0.2 to 3 parts by weight of the inorganic dispersant per 100 parts by weight of water, Agent 0.0
005 to 0.1 part by weight.

Examples of the volatile foaming agent include, for example, isobutane, normal butane, normal pentane, propane, carbon dioxide, nitrogen and the like, but are not limited thereto. ,
It is 5 to 50 parts by weight based on 100 parts by weight of the resin.

The temperature and pressure in the pre-foaming step vary depending on the type of polyethylene resin used and the desired expansion ratio, but usually at a temperature equal to or higher than the softening point of the polyethylene resin used, and usually at 100 to 130 ° C. , The pressure is about 1 to 3 MPa, and the preliminary expansion ratio is 5 to 5 MPa.
It is about 40 times.

To form the pre-expanded particles obtained as described above into an in-mold foam molded article, for example, (a) press-treating the pre-expanded particles with an inorganic gas to impregnate the pre-expanded particles with the inorganic gas, After applying the internal pressure, filling the mold and heat-sealing it with steam, etc., (b) compressing the pre-expanded particles by gas pressure, filling the mold and utilizing the recovery force of the pre-expanded particles ,
A method of heating and fusing with steam or the like, (c) a method of filling a mold without pretreatment, and fusing with heat or the like can be used, but no special equipment is required (c). Is preferred.

As a preferred embodiment of the present invention, a linear low-density polyethylene containing an antioxidant and a cell nucleating agent, an HLB value of 3 to less than 4, and a melting point of 35 ° C. to 75
A master batch of fatty acid glycerin ester at a temperature of not more than 0 ° C. is mixed so that the final concentration of the fatty acid glycerin ester is 0.3% by weight or more and 3% by weight or less, extruded into a strand form from an extruder, and cooled, and the strand is cut. ~
5 mg of cylindrical resin particles. In an autoclave-type pressure-resistant container, 150 to 500 parts by weight of water, 0.08 to 2.5 parts by weight of tribasic calcium phosphate as a dispersing agent, and n as a dispersing aid with respect to 100 parts by weight of the resin particles (melting point Tm ° C.).
-Sodium paraffin sulfonate 0.0005 to 0.0
1 part by weight and 5 to 3 of isobutane as a volatile blowing agent
0 parts by weight, and heated to (Tm-10) to (Tm + 1).
0) The resin particles are impregnated with a foaming agent at a constant temperature and a constant pressure of 1 to 3 MPa at a temperature of 1 ° C., and then released under atmospheric pressure to obtain pre-expanded particles. The pre-expanded particles are filled in a mold, heated and fused with steam of 0.09 to 0.12 MPa to form a foamed molded product, and then dried in a drying chamber at 70 to 80 ° C. for 18 to 2 hours.
A method of curing for 4 hours may be used.

[0026]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. Examples 1 to 6 and Comparative Examples 1 to 9 have a melt flow index of 2 g / 10 min and a melting point of 12
The antistatic agent (mixture of glyceryl monostearate and glyceryl distearate) having an HLB value and a melting point shown in Table 1 for a linear low-density polyethylene having a comonomer of 4-methylpentene at 2.4 ° C. 1
The mixture was mixed in a master batch so as to have the concentration described, and kneaded with an extruder to prepare a pellet having a weight of 1.3 mg. In an autoclave having a capacity of about 0.2 m ³ , 100 parts by weight (50 kg) of the pellet, 300 parts by weight of water,
After charging 2 parts by weight of tribasic calcium phosphate, 0.001 part by weight of n-paraffin sodium sulfonate, and 20 parts by weight of isobutane, the temperature was raised to 114.0 ° C., and isobutane was injected to maintain the internal pressure of the autoclave at 1.82 MPa for 10 minutes. Thereafter, while maintaining the internal pressure of the autoclave with isobutane vapor, the autoclave was discharged through a 4.0 mm orifice under atmospheric pressure to obtain pre-expanded particles. Immediately after foaming, the obtained pre-expanded particles were washed with a 30 ppm aqueous solution of sodium metaphosphate (manufactured by Taihei Chemical Co., Ltd.) and dried with hot air at 60 ° C. The pre-expanded particles were filled in a plank mold of 300 × 300 × 60 mm, molded at a heating steam pressure of 0.1 MPa, and cured under an atmosphere of 75 ° C. for 24 hours. The properties of the pre-expanded particles and the expanded molded article were evaluated by the following methods. Table 1 shows the results. (Agglomerated particle amount) 5 L of the pre-expanded particles were sieved through a mesh having a mesh size of 4 mm, and the weight fraction of the pre-expanded particles remaining on the mesh was measured and evaluated based on the following criteria. ：: less than 0.2% Δ: 0.2% or more and less than 1.0% ×: 1.0% or more (adhering dispersant) ammonium metavanadate 0.022
50.0 mL of an aqueous solution (colorimetric liquid) containing 5% by weight, 0.54% by weight of ammonium molybdate and 3% by weight of nitric acid and W
The pre-expanded particles (g) (normally about 0.5 g) were placed in a conical beaker, stirred for 1 minute, and left for 10 minutes.
The obtained liquid phase was taken in a quartz cell having an optical path length of 1.0 cm, and the absorbance A at 410 nm was measured by a spectrophotometer.

For the same colorimetric liquid, the absorbance coefficient ε at 410 nm of tricalcium phosphate, which was measured in advance,
(G / L · cm) and the amount of the attached dispersant (p
pm) and evaluated according to the following criteria.

[0028]

(Equation 1) ：: less than 2000 ppm ×: 2,000 ppm or more (stickiness) After curing the planck-shaped molded body, 30
The sample was allowed to stand at room temperature for minutes, and evaluated according to the following criteria by touch. ：: No sticky feeling or slimy feeling ×: Sticky feeling or slimy feeling (fusibility) After leaving the planck-shaped molded body at room temperature for at least 24 hours after curing, a knife is formed on the surface of the foamed molded body. , A crack having a depth of about 5 mm was formed, the formed body was broken along the crack, the fracture surface was observed, and the evaluation was made according to the following criteria. ：: The rate at which particles are broken is 60% or more. ×: The rate at which particles are broken is less than 60%. (Surface resistivity) After curing the planck-shaped molded body,
After standing in a constant temperature and humidity room at a temperature of 23 ° C. and a humidity of 50% RH for 24 hours, a super insulation resistance meter (TR8 manufactured by Advantest Co., Ltd.) was used.
601), the surface resistivity was measured under the conditions of 500 V and 1 minute, and evaluated according to the following criteria. ： １: less than 1 × 10 ¹² Ω / □ △: 1 × 10 ¹² Ω / □ or more and less than 1 × 10 ¹³ Ω / □ ×: 1 × 10 ¹³ Ω / □ or more (contamination) Outer dimensions than the planck-shaped molded body 200mm ×
A 200 mm × 150 mm, 15 mm thick box and its lid were made. A half mirror coated with titanium oxide on one side is placed inside the box so that the coated surface does not contact the wall, and the lid is closed.
It was left in an atmosphere of 90% RH for 90 hours. The titanium oxide coated surface before and after the contamination test was observed under a microscope, and evaluated according to the following criteria. ：: No noticeable deposit is observed. Δ: Small patchy deposit is observed locally. ×: Large patchy deposit is observed on the entire surface. As shown in Examples 1 to 6, as an antistatic agent HLB
By containing a fatty acid glycerin ester having a value of 3 or more and less than 4 and a melting point of 35 ° C. or more and 75 ° C. or less, 0.3% by weight or more and 3% by weight or less, the agglomeration particles and the adhering dispersant in the pre-expanded particles are small, and foam molding is performed. There is no problem in stickiness and fusing property, surface resistivity, and contamination in the body. That is, good antistatic performance (surface resistivity is 1 × 10 ¹²⁾ without contaminating half mirrors and the like in optical system parts. Ω / □) can be obtained.

As in Comparative Examples 1 to 3, the nitrogen-containing antistatic agent tends to cause a problem in contamination.

From the comparison between Examples 1 to 4 and Comparative Examples 4 to 7, even if the fatty acid glycerin ester is the same, the HLB value is less than 3 (the diester or triester content is high).
Did not provide good antistatic performance (Comparative Example 4),
When the B value exceeds 4, problems occur in the adhesion dispersant and the fusibility (Comparative Example 5). Further, even when the HLB value is in the desired range, sufficient antistatic performance cannot be obtained if the addition amount is less than 0.3% by weight (Comparative Example 6). Agglomerate particles were generated (Comparative Example 7).

As shown in Comparative Examples 8 to 10, when the melting point of the antistatic agent is less than 35 ° C., the surface of the foamed molded product tends to be sticky, and when it exceeds 75 ° C., sufficient antistatic performance cannot be obtained.

[0032]

[Table 1]

[0033]

EFFECTS OF THE INVENTION Pre-expanded polyethylene resin particles containing 0.3 to 3% by weight of a fatty acid glycerin ester having an HLB value of 3 to less than 4 and a melting point of 35 to 75 ° C. as an antistatic agent. When used, it is possible to obtain a polyethylene-based resin molded foam having good antistatic performance (surface resistivity of less than 1 × 10 ¹² Ω / □) without contaminating a half mirror or the like in an optical system component. it can. When the above antistatic agent is used, the amount of agglomerate particles and the amount of the attached dispersant in the pre-expanded particles are small, and there is no problem in stickiness and fusing property in the expanded molded article. Therefore, an expanded molded article molded from the polyethylene resin pre-expanded particles having the antistatic performance of the present invention,
It can be suitably used as a cushioning packaging material for electronic components, particularly electronic components incorporating optical components. In particular, it can be suitably used as a buffer packaging material for an optical component having a metal compound layer such as titanium oxide or an electronic component incorporating the same by a vacuum processing method such as vapor deposition or sputtering. Of course, it can be used not only as a component such as a CD-ROM drive, a liquid crystal display device, and a personal computer but also as a buffer packaging material for a finished product.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kenichi Senda 5-1-1 Torikai Nishi, Settsu-shi, Osaka Kanebuchi Chemical Industry Co., Ltd. Osaka Plant F-term (reference) 4F074 AA17 AA20 AD11 BA32 BA33 BA35 BA36 BA38 BA39 CA38 CA49 CC03Z CC04Z CC22X CC25X CC42 DA47 4J002 BB031 DE017 EA017 EH046 EH056 FD106 FD327 GP00

Claims (2)

[Claims] An HLB value of 3 to less than 4 and a melting point of 35.
Fatty acid glycerin ester of not less than 75 ° C
Polyethylene resin pre-expanded particles and an in-mold expanded molded article thereof, characterized in that the content is not less than 3% by weight and not more than 3% by weight. 2. The pre-expanded polyethylene resin particles according to claim 1, wherein the fatty acid glycerin ester is a mixture of glyceryl monostearate and glyceryl distearate.