JPH0328239A - Expansible olefin resin particle and preexpanded olefin resin particle - Google Patents

Abstract

PURPOSE:To obtain expansible olefin resin particles excellent is secondary expansibility and fusibility by adding a nonionic surfactant of a specified average-mol.wt. and a specified antistatic property to olefin resin particles. CONSTITUTION:Olefin resin particles containing 0.1-5wt.% antistatic nonionic surfactant having an average-mol.wt. of 250-1000 and an HLB of 4-8. Preexpanded olefin resin particles can be obtained by keeping the above olefin resin particles under high temperature and high pressure conditions and expanding the particles by releasing them into a lower pressure atmosphere. A molding obtained from these preexpanded particles acquires an excellent antistatic property at even a cut surface as well as a skin layer in 1-2 weeks. A desirable olefin resin is a low density polyethylene of a density of 0.915-0.935g/cm<3> and a melt index of 0.1-5.0g/10min.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to olefin resin particles for foaming and pre-expanded olefin resin particles. [Prior art and problems to be solved by the invention] In recent years, Kai-shaped bodies made of pre-expanded olefin resin particles have been widely used as cushioning materials, packaging materials, etc. However, this type of Kai-shaped bodies are not electrically charged. However, for products used for packaging electronic components that are sensitive to dust and static electricity, a pre-shaped body with antistatic properties and a surface resistivity of IXIO''Ω/C or less is required. .

In order to impart antistatic properties to this type of molded product, it is possible to use pre-expanded particles impregnated with an antistatic agent to produce the molded product, or to spray an antistatic agent onto the pre-expanded particles. Methods are also known, but the molded bodies obtained by molding pre-expanded particles impregnated with an antistatic agent or applied by spraying have poor sustainability of antistatic ability, and the pre-expanded particles The drawback was that it required complicated work to impregnate or spray the antistatic agent on the surface of the material. On the other hand, a method is also known in which an antistatic agent is kneaded into resin particles used for producing pre-expanded particles. In this method, the antistatic agent can be added to the resin at the same time during the manufacturing process of the resin particles, so there is no risk of complicating the work process, and it also has the advantage of excellent sustainability of antistatic performance. On the other hand, ■The surface specific resistance value is IXIO1! It is difficult to obtain pre-expanded particles with excellent antistatic properties of Ω or less.■ Especially in the case of non-crosslinked olefin resins, it is difficult to obtain pre-expanded particles with excellent fusion properties, resulting in poor fusion in the pre-shaped body. Although the surface resistivity value on the skin surface of the ■kai type body is excellent, it may not be possible to obtain a sufficient surface resistivity value on the cut surface, or it may take an extremely long time to obtain it (tc type body). (Many times, products are stored in recesses that have been cut into the body.)

[Means to solve the problem]

As a result of intensive research in view of the above points, the inventors of the present invention have found that by incorporating a specific surfactant into the foaming olefin resin particles, pre-foamed particles with excellent secondary foamability and fusion properties can be obtained. The inventors have also found that the pre-expanded particles obtained from the pre-expanded particles can exhibit excellent antistatic properties not only in the skin layer but also on the cut surface within 1 to 2 weeks, and have brought the present invention to fruition.

That is, the present invention provides: (1) an average molecular weight of 250 to 1000, H・LB
is a nonionic surfactant having an antistatic ability of 4 to 8. Olefin resin particles containing 1 to 5% by weight.

(2) Pre-expanded olefin resin particles, which are obtained by holding the olefin resin particles according to claim 1 containing a blowing agent under high temperature and high pressure, and then releasing them under low pressure to foam them.

The main points are as follows.

Examples of the olefin resin containing the olefin resin particles of the present invention include high density polyethylene (HDPE), medium density polyethylene (MDPE), and low density polyethylene (L
DPE), linear low density polyethylene (LLDPE),
Polypropylene, polybutene, ethylene-propylene copolymer, ethylene-hinyl acetate co-M polymer (EVA),
Examples include ethylene-vinyl chloride copolymer, ethylene-vinyl acetate vinyl alcohol copolymer, propylene-1-butene copolymer, low molecular weight polyethylene, low molecular weight polypropylene, etc., and these may be used alone or in a mixture of two or more types. Can be done. Among these resins, LLDP
E is preferable, especially when the density is 0. 9 1 5 ~0.
9 3 5 g/cd, melt index (M +
) is 0. 1-5. 0 g/10 min LLDP
E is preferred.

The olefin resin particles of the present invention have an average molecular weight of 2
O is a nonionic surfactant having an antistatic ability of 50 to 1000 and an HLB of 4 to 8. It is contained in an amount of 1 to 5% by weight, preferably 0.3 to 3.0% by weight. Nonionic surfactants with antistatic properties have superior thermal stability compared to cationic and amphoteric surfactants, so they can be used to melt and knead resins at high temperatures of 150 to 200°C, or to pre-expand particles. It does not deteriorate its antistatic ability or cause coloring of the resin due to the heat generated during heating or molding in the mold, and it has superior antistatic ability compared to anionic surfactants. , cationic, and amphoteric surfactants, the dissolution into water is lower than that of cationic and amphoteric surfactants. Therefore, during granulation, the active agent in the resin is easily extruded into strands and cooled in water. There is little risk of elution and deterioration of antistatic ability. Examples of the nonionic surfactant having an antistatic ability with an average molecular weight of 250 to 1,000 and an HLB of 4 to 8 include the following compounds.

(R is an alkyl group consisting of at least one methyl group and 12 to 67 methylene groups and/or methine groups.) O 11 (R' is at least one methyl group and 6 to 52 methylene groups and/or an alkyl group consisting of a methine group.) or OH blind (R' is an alkyl group consisting of at least one methyl group and 6 to 60 methylene groups and/or a methine group.) (R'' is an alkyl group consisting of at least one methyl group and 8 to 62 methylene groups and/or methine groups.) Among the surfactants represented by the above general formulas (1) to (4), HLB5 to 7 In the general formula (1), N having 13 to 29 carbon atoms in the alkyl group R, N(2
-Hydroxyethyl)alkylamine, in general formula (2), diglycerin fatty acid ester with alkyl group R' having 6 to 20 carbon atoms; in general formula (3), alkyl group R# having 12 to 28 carbon atoms; In the sorbitan fatty acid ester of general formula (4), an alkyldiethanolamide in which the alkyl group R# has 10 to 26 carbon atoms is particularly preferred. It is also possible to use a combination of these surfactants.

HLB of nonionic surfactant contained in resin particles
If it is less than 4, it will be difficult to obtain a surface resistivity value of less than IXI012Ω/d within 1 to 2 weeks, resulting in poor antistatic properties. In addition, if the HLB exceeds 8, it is difficult to obtain a molded body with good fusion properties of foamed particles, and even if it is obtained, the molded body may be colored or come into contact with the molded body, such as a bottle for electronic parts. This causes the problem that the metals that are covered with the metal are likely to corrode. Furthermore, if the average molecular weight of the nonionic surfactant is less than 250, the antistatic ability will not last long, and if the average molecular weight exceeds 1000, the time required to develop the antistatic ability will be longer than two weeks. Undesirable. Furthermore, the amount of surfactant added is 0.1% by weight.
If it is less than 5% by weight, sufficient antistatic ability will not be imparted.
If it exceeds this value, the fusion between the expanded particles becomes insufficient, and a good molded body cannot be obtained in many cases.

The resin particles of the present invention have a diameter (D) of 0.5 to 3011I1,
Length (L) 0.5 to 3ffiI, and L/D = 1 to 2
It is preferable that the degree of

A method for producing the resin particles of the present invention includes a method in which a resin and a surfactant are melt-kneaded in an extruder, extruded from the extruder into a strand, and after cooling, the strand is cut into particles. A preferred method is to first mix 2 to 20% by weight of a nonionic surfactant with antistatic properties to the resin, and melt-knead the mixture at 100 to 250°C using a triple roll, kneader, extruder, etc. to form a master. The batch is cured and then the final content of surfactant is 0. This is a method of mixing the above masterbatch with a resin that does not contain a surfactant and granulating it as described above so that the concentration is 1 to 5% by weight. According to this method, the surfactant is uniformly mixed. It can be dispersed in resin particles. Incidentally, if necessary, a coloring agent such as a pigment may be added together with a surfactant in the above granulation step.

The pre-expanded particles of the present invention are obtained by impregnating the resin particles with a blowing agent, holding the impregnated resin particles at high temperature and pressure, and then releasing the impregnated particles under low pressure to cause foaming.

Foaming agents used for foaming include aliphatic hydrocarbons such as propane, butane, isobutane, pentane, isobentane, hexane, and hebutane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; and trichlorofluoromethane. , dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, etc., and/or volatile blowing agents such as halogenated hydrocarbons and/or Co! ,N. , an inorganic gas such as air can be used. The amount of the blowing agent added varies depending on the expansion ratio of the foamed particles, but is generally 3 to 40 parts by weight per 100 parts by weight of the resin particles. A preferred method for producing the pre-expanded particles of the present invention is to disperse the resin particles and a blowing agent in a dispersion medium such as water in a closed container, heat the resin particles with stirring to impregnate the blowing agent into the resin particles, and then heat the resin particles at a high temperature. An example of this method is to hold the resin particles under high pressure and then release the resin particles and the dispersion medium simultaneously to atmospheric pressure to foam the resin particles. The impregnation of the foaming agent into the resin particles for foaming may be carried out simultaneously with the step of dispersing the resin particles in a dispersion medium in a closed container and heating to the foaming temperature as described above, or may be carried out in a separate step. .

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

Examples 1 to 3, Comparative Examples 1 to 5 Ml is 1.0 g/10 min, density is 0.9 2 5 g/
A nonionic surfactant having an antistatic ability shown in Table 1 was added to the LLDPE of cj, and the mixture was sufficiently kneaded on a three-roll roller heated to 155-165°C.
The mixture was extruded into strands using an extruder at 0°C, and then granulated using a pelletizer to produce a granular masterbatch. Next, this masterbatch and LLD containing no surfactant
PE (Ml and density are the same as the above LLDPE) are mixed so that the amount of masterbatch added is the value shown in Table 1,
After melt-kneading at 250"C in an extruder, extrusion into strands, then granulation with a pelletizer, diameter (D)
LLDPE particles for foaming with a length (L) of 2 m and 2 mm were obtained. Next, per 10 parts by weight of the resin particles, 30 parts by weight of a blowing agent (a foaming agent made by mixing trichlorofluoromethane and dichlorodifluoromethane in a weight ratio of 7:3) and 1.0 parts by weight of basic magnesium carbonate (dispersing agent). and water 30
0 parts by weight was placed in an autoclave, and the temperature was raised to a temperature of -10'C, the melting point of LLDPE particles for foaming, while stirring.
While maintaining the pressure inside the autoclave at 15 to 50 kg/cd, one end of the container was opened, and the resin particles and water were released under atmospheric pressure to foam the resin particles.

Table 2 shows the properties of the obtained pre-expanded particles.

The obtained pre-expanded particles were left to mature for 48 hours at room temperature and under normal pressure, and then filled into a mold and heated with steam to form a mold. The properties of the obtained Kai-type body are also shown in Table 2.

w4l Table n: Oxyethylene group loss Table 2 *l The condition of the particles was determined as follows by observing the quality of the spherical shape of the pre-expanded particles, the presence or absence of shrinkage, the size of the air bubbles in the particles, etc. ○: No deformation of the spherical shape, no shrinkage, and no miniaturization of air bubbles in the particles.

Δ: Some particles are deformed, shrunk, or have microscopic bubbles.

×: An extremely large number of particles are deformed, shrunk, and have microscopic bubbles.

*2 Observe the surface (epidermal surface) of a certain mold, O...Surface is smooth with small irregularities and wrinkles.

×: Poor surface smoothness, large unevenness and wrinkles.

It was evaluated as

*3 The fusion properties are as follows: The length of the Kai type body is 150 mm, the width is 50 mm,
A test piece cut to a thickness of Ion was tested using a tensile tester.
0 nvm/min. Pull it at a high speed to break it, observe the state of the cross section, and find that: O: Breakage occurs between materials, and there is no breakage between particles. ×...Cut between particles.

It was evaluated as *4ti. The surface specific resistance value of the skin layer of the mold is 2 after the Kai mold.
0'C. Measurements were taken after one day of curing at a relative humidity of 65%.

*5 rfi. The surface specific resistance value of the cut surface of the mold is 20°C after cutting. Measurements were taken after curing for 10 days at a relative humidity of 65%.

〔Effect of the invention〕

The foamable olefin resin particles of the present invention contain 0.1 to 5% by weight of a nonionic surfactant having an antistatic ability with an average molecular weight of 250 to 1000 and an HLB of 4 to 8. The pre-expanded particles obtained from resin particles have excellent secondary foaming properties and fusion properties, and can be shaped into shapes without applying pressure treatment to the pre-expanded particles to impart foaming ability, and the particles have excellent fusion properties. You can obtain a new Kai-type body. Moreover, the molded product obtained has excellent antistatic properties of IXIO''Ω/C or less.Furthermore, the molded product not only has excellent antistatic properties on the epidermis surface, but also has excellent antistatic properties on the cut surface. However, after processing such as cutting, 1-2
In order to exhibit excellent antistatic properties, the molded body is cut by punching, cutting, etc., and even when electronic components are stored in these processed areas, the electronic components are protected from dust and static electricity. Can be done.

Claims (2)

[Claims] (1) Average molecular weight is 250-1000, HLB is 4-4
Nonionic surfactant with antistatic ability of 0.1
Olefin resin particles characterized by containing ~5% by weight. (2) Pre-expanded olefin resin particles, which are obtained by holding the olefin resin particles according to claim 1 containing a blowing agent under high temperature and high pressure, and then releasing them under low pressure to foam them.