JPH01240540A - Straight chain low-density polyethylene resin colored granule and preliminarily expanded colored granule - Google Patents

Abstract

PURPOSE:To obtain the present granules capable of giving foams of uniform air bubble size with uniform coloring and high coloring concentration, without the need for pressurized aging when expanded, by incorporating a straight chain low-density polyethylene resin with a thermoplastic resin of melting point lower than that of said polyethylene resin and a coloring agent. CONSTITUTION:A blend comprising (A) a straight chain low-density polyethylene resin, (B) a coloring agent (e.g., carbon black), and (C) a thermoplastic resin with its melting point lower than that of the component A by 10-50 deg.C (e.g., ethylene-vinyl acetate copolymer) is put to melt blending at 250 deg.C using an extruder to carry out extrusion followed by granulation in a pelletizer, thus obtaining the objective colored granules. These granules are left to stand at normal temperature and pressure and packed in a mold followed by molding on heating with a pressurized water vapor, thus obtaining a colored foam.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to colored particles of foamable linear low-density polyethylene resin (hereinafter simply referred to as LLDPE) and pre-foamed colored particles obtained from the particles. Uniformly colored, during production of pre-expanded particles and in-mold foam molding,
The present invention relates to LLDPE colored particles for foaming and pre-foamed colored particles that have uniform coloring, high color density, and can provide LLDPE pre-foamed particles and foamed molded articles with uniform cell diameters.

(Prior art) Conventionally, LLDPE foam molded products have been used for various cushioning materials,
Widely used as a material for containers, etc. These foam molded products are made by impregnating LLDPE particles with a volatile foaming agent under high temperature and high pressure, and then releasing the foam under low pressure to form the foam into the desired shape using the so-called in-mold foam molding method for foamed particles. are doing.

Furthermore, although many of these LLDPE foam molded products are uncolored, colored foam molded products are also becoming widely demanded.

There are two methods for coloring the LLDPE foam molded product: one is to color the surface of the foam molded product using paint, etc.
There are two methods for pre-coloring DPE, and the latter method is advantageous in terms of industrial and cost considerations.

(Problem to be solved by the invention) The above LLDPE
In the method for coloring foam molded products, the raw material LLDPE
The method for coloring is to melt and knead coloring agents such as dyes and pigments to LLDPE to form pellets when producing LLDPE particles as a raw material.

In the above coloring, it is required that the colorant be uniformly and finely dispersed in the LLDPE resin in order to develop and uniformly color the colorant. When pre-expanded particles are manufactured using the LLDPE colored particles, or when these expanded particles are used to form an in-mold foam molded article, the following problems occur.

(1) Since the pigment particles act as the core of the blowing agent during the production of pre-expanded particles, the bubbles produced become extremely fine. In particular, when the resin forming the expanded particles is non-crosslinked, the miniaturization of the cells is further promoted. The reason for this is as follows.

That is, in the case of a non-crosslinked material, unlike a crosslinked material, the temperature range suitable for foaming is very narrow, and at that temperature, crystals are present. In other words, with non-crosslinked resin particles, expanded particles with a high closed cell ratio cannot be obtained unless the temperature range is within a narrow range where crystals exist. Therefore, when foamed particles are manufactured with colorants present in the resin particles, a single gfJD force acts on them, and these crystal nuclei become foaming nuclei. It depends.

The foamed colored particles obtained in this manner tend to have poor secondary foaming during molding, even if pressure ripening is performed before in-mold foam molding. Even if good secondary foaming is achieved, the resulting foamed molded product will shrink significantly. In either case, a good molded product cannot be obtained.

(2) Color unevenness occurs in the colored appearance of the molded product, and even if a relatively large amount of coloring agent is used, the molded product has a whitish appearance with low gloss and density.

(3) If the dispersion of the colorant is insufficient, the above problem (1) will not occur, but the coloring of the colorant will be poor and clear coloring will not be possible.

Therefore, the object of the present invention is to provide relatively large and uniform bubbles during the production of expanded particles, eliminate the need for a pressure aging step during in-mold molding, eliminate shrinkage of the molded product after in-mold foam molding, and further improve color. L for foaming that can provide a colored foam that is uniformly colored without unevenness or whitening, and has excellent color gloss and density.
An object of the present invention is to provide LDPE colored particles and pre-expanded colored particles.

(Means for Solving the Problems) That is, the present invention provides LLDPE colored particles for foaming, characterized in that LLDPE contains a colorant and a thermoplastic resin having a lower melting point than the LLDPE, and the particles. L made by adding a volatile foaming agent to the mixture and foaming it by heating.
LDPE pre-expanded colored particles.

(Function) When coloring LLDPE with a coloring agent, 1. LDPE
By mixing a thermoplastic resin with a lower melting point than the pre-expanded particles, the dispersion and color development of the colorant are sufficient, and the size of the bubbles during the production of pre-expanded particles is relatively uniform, allowing the in-mold foam molding to be carried out. The resulting LDPE all-PE shape does not require any foaming ability, and is a beautiful colored foamed molded product with no shrinkage and excellent clarity and density.

(Preferred Embodiments) Next, the present invention will be described in more detail by citing preferred embodiments.

The LLDPE used in the present invention is non-crosslinked LL with a density of 0.915 to 0.940 g/crn2, a melt index of 0.1 to 5.0 g/710 min, and a melting point of 115°C or higher.
DPE is preferred. A particularly preferable melting point range is 118°C.
Above, a particularly preferable range of density is 0.920 to 0.940 g/crn'.

The LLDPE used in the present invention is a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms, and examples of the α-olefin include propylene, butene-1, pentene-1
, hexene-1, heptene-1, octene-1,4-methylpentene-1, etc., with propylene and butene-1 being particularly preferred. The composition of α-olefin is 10 mol%
Below, it is preferably 0.5 to 5 mol%.

The coloring agent used for coloring the above LLDPH may be any conventionally known pigments such as organic pigments, inorganic pigments, and extender pigments, or dyes, but pigments may be used in consideration of heat resistance, light resistance, color migration, etc. It is desirable to do so.

For example, organic pigments include phthalocyanine, azo, condensed azo, anthraquinone, perinone/perylene, indigo/thioindigo, isoindolinone,
Azomethine azo series, dioxazine series, quinacridone series,
These include aniline black, triphenylmethane, and carbon black, and inorganic pigments include titanium oxide, iron oxide, iron hydroxide, chromium oxide, spinel fired pigments, lead chromate, and chromic acid. Vermilion series,
Examples of extender pigments include navy blue, aluminum powder, bronze powder, etc., and extender pigments include calcium carbonate, barium sulfate, silicon oxide, and aluminum hydroxide.

Among these pigments, organic pigments and carbon black in particular tend to act as nucleating agents for foaming during the production of pre-expanded particles, and therefore these pigments are particularly useful as colorants in the present invention.

The above coloring agents are generally used in an amount of 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, per 100 parts by weight of the LLDPE.

The thermoplastic resin used in the present invention is the above-mentioned LLD
It is a thermoplastic resin with a melting point lower than that of PH, such as low density polyethylene (■p, -105°C), ethylene-vinyl acetate copolymer (+np, =95°C), ethylene-ethyl acrylate copolymer (mp, =90℃
), and any of these thermoplastic resins can be used alone or as a mixture.

Among the above thermoplastic resins, especially the above-mentioned LLDPH
Since the melting point of
Those having melting points as low as 0 to 50°C are preferred, and the most preferred are low density polyethylene and ethylene-vinyl acetate copolymers.

These thermoplastic resins are generally used in an amount of 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per 100 parts by weight of the LLDPE.

The essential components of the LLDPE colored particles of the present invention are as described above, but in addition, antistatic agents, antioxidants,
Light stabilizers, lubricants, dispersants, etc. can also be mixed in arbitrary proportions.

The production particles of the LLDPER color particles for foaming of the present invention are produced by mixing the above-mentioned essential components and required components using a high-speed mixer, Henschel mixer, tumbler, etc., melt-kneading the mixture using an extruder, extruding it into a strand shape, and then extruding it into a strand shape using a pelletizer. For example, the diameter (D) is 0.5 to 3, the length (L) is 0.5 to 3, and L/D is granulated by
It can be obtained by granulation into particles having a particle size of about 1.0 to 21. These kneading and granulation methods themselves may be based on conventionally known methods.

In a particularly preferred manufacturing method in the present invention, the colorant and thermoplastic resin are first mixed at a colorant concentration of 20 to 70%.
Mix in a proportion of % by weight, mix the molecules at a temperature of about 100 to 250°C using a three-roll, kneader-1 extruder, etc. to pre-disperse the colorant to create a master patch. This masterbatch is mixed with uncolored LLDPH in a proportion to achieve a desired concentration, and granulated as described above, thereby achieving more sufficient colorant dispersion and color development.

The pre-foamed colored particles of the present invention are the LL for foaming of the present invention.
It is obtained by impregnating DPE colored particles with a volatile foaming agent and foaming them.

Examples of volatile blowing agents used in the present invention include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane, and cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane. and halogenated hydrocarbons exemplified by chlorodifluoromethane, trichlorofluoromethane, dichlorodifluoromethane, trifluorodichloroethane, tetrafluoroethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride, etc. . The amount of the foaming agent added varies depending on the type of the foaming agent and the desired degree of foaming, but is usually 5 to 50 parts by weight per 100 parts by weight of the LLDPE colored particles.

In the method for producing LLDP E pre-expanded colored particles of the present invention, the colored particles are impregnated with the volatile blowing agent, but this timing is not particularly limited. Colored particles impregnated with the agent may be placed in a closed container and dispersed in a dispersion medium within the closed container,
Alternatively, the colored particles and the foaming agent may be placed in a closed container, and the colored particles may be impregnated with the foaming agent while being dispersed in a dispersion medium within the closed container.

Also, in the process of heating the colored particles together with a dispersion medium to a predetermined temperature in a sealed container, a blowing agent is placed in the sealed container to disperse the colored particles and the foaming agent, and the colored particles are impregnated with the foaming agent. You may let them. Note that the temperature at which the colored particles are impregnated with the foaming agent is also arbitrary and is not particularly limited.

In the present invention, colored particles and a volatile blowing agent are used separately or after impregnating colored particles with a volatile blowing agent, they are dispersed in a dispersion medium. Inorganic substances such as basic magnesium carbonate, basic zinc carbonate, and calcium carbonate can be used. The amount of the dispersant added is usually 0.00 parts by weight per 100 parts by weight of the colored particles.
The amount is from 1 to 10 parts by weight.

In addition, when dispersing colored particles, the melting point is 20°C or higher, H
An organic compound having an LB value of 1 to 10, such as stearamide, may be added in an amount of 5 parts by weight or less per 100 parts by weight of the colored particles. Further, the dispersion medium may be any solvent that does not dissolve the colored particles, and examples thereof include one of water, ethylene glycol, glycerin, methanol, ethanol, etc., or a mixture of two or more thereof, but usually Water is preferred.

In the above method, one end of the container is opened and the colored particles and dispersion medium are simultaneously released into an atmosphere at normal pressure than inside the container.
The temperature at this time ranges from 15° C. lower than the melting point of the colored particles to 5° C. higher than the melting point. 15 from the melting point
If the temperature is lower than 0.degree. C., there will be little foaming, and if the temperature exceeds 5.degree. C. higher than the melting point, the number of closed cells will be significantly reduced and the foam will become open cells, resulting in a decrease in mechanical strength.

A particularly preferred range of this foaming temperature is from 13° C. below the melting point to a temperature below the melting point. Further, the pressure at this time may be either higher than or lower than the vapor pressure of the volatile blowing agent, and the atmosphere to be discharged is usually selected to be an atmosphere at normal pressure.

The pre-expanded colored particles of the present invention obtained by the above method usually have a bulk density of 0. Ol~0.3 g/crn',
Closed cell ratio 60% or more, average number of bubbles (hereinafter simply referred to as the number of bubbles) 1,000/mrr? It is as follows. If the bulk density is less than 0.0 Ig/crn', the shape of the pre-foamed colored particles tends to become distorted, and if it exceeds 0.3 g/crn', the shape of the colored particles not only tends to become distorted, but also The foaming state becomes uneven. A particularly preferred range of bulk density is 0.015 to 0.15 g/crn''. If the closed cell ratio is less than 60%, the expanded colored particles tend to become distorted and the compressive elasticity decreases. A particularly preferable range of the cell ratio is less than 80%.The cell number is 1.00.
If it exceeds 0 particles/mrn, the shape of the expanded colored particles becomes distorted and the mechanical strength decreases.

A particularly preferred range of the number of bubbles is 0.3 to 10097 mbar. Further, the particle size of the pre-foamed colored particles is not particularly limited, but from the viewpoint of fluidity, it is preferably from 0.5 to 20 mm.

The pre-expanded colored particles of the present invention as described above are usually aged at room temperature and pressure for a predetermined time, and then, if necessary, pressurized with an inorganic gas or a mixed gas of an inorganic gas and a volatile blowing agent at a predetermined pressure and a predetermined time. Matured (imbued with foaming ability). The pre-expanded colored particles, which have been given an internal pressure as necessary as described above, are filled into a mold, and are usually heated to a water vapor pressure of 0.5 to 2.0 g/cr.
n'' (G) to obtain the desired colored foamed molded product.

The colored foamed molded product obtained as described above can be used, for example, as packaging materials, cushioning materials, building materials, heat insulating materials, food containers, flotation materials, and the like.

(Effects) According to the present invention as described above, when coloring LLDPE with a colorant, by using a thermoplastic resin having a melting point lower than that of LLDPE, the colorant can be sufficiently dispersed and developed.

Further, according to the present invention, even if the colorant is uniformly and finely dispersed in this way, a predetermined amount of thermoplastic resin is mixed in the obtained LLDPE colored particles, and as a result, the nucleating agent of the colorant during foaming. The bubbles that are generated are relatively large and uniform in size, rather than becoming fine.
There is little tendency for the colored tone to become whitish pastel, and the color tone is uniform without unevenness.

In addition, since the bubbles generated as described above are relatively large, the process of pressurizing and ripening the pre-foamed colored particles during in-mold foam molding becomes unnecessary, resulting in colored foam molding with excellent color tone with little shrinkage and no color unevenness. The body is provided.

(Example) Next, the present invention will be described in more detail with reference to reference examples, examples, and comparative examples. In the text, parts or percentages are based on weight unless otherwise specified.

Reference Examples 1 to 4 The following thermoplastic resins and pigments were mixed in a predetermined ratio, and 1
After thorough kneading on three rolls heated to 20 to 130°C, the mixture was extruded into strands with an extruder at a temperature of 100 to 130°C, and granulated with a pelletizer to prepare a granular masterbatch.

Gloss Example 1 Thermoplastic resin; Low density polyethylene 70 parts Pigment: Carbon black 30 parts Gloss Thermoplastic resin; Ethylene-vinyl acetate copolymer 60 parts Pigment; Phthalocyanine green 40 parts Powder Calcium nistearate 5 parts Moxibustion Separate l Thermoplastic resin: 25 parts of low-density polyethylene 25 parts of ethylene-vinyl acetate copolymer Pigment: 50 parts of Quinacridone Red Reference Example 4 Same as Reference Example 1 using 60 parts of LLDPE (mp, =122) and 40 parts of carbon black. A masterbatch was created.

Reference Example 5 Carbon black alone Examples 1 to 4 and Comparative Examples 1 to 4 100 parts of LLDPE were mixed with the masterbatch or pigment shown in Table 1 below at a predetermined ratio, and the mixture was heated at a resin temperature of 250°C using a 65φ extruder. The colored particles of the present invention were melt-kneaded and extruded, and granulated using a pelletizer to obtain colored particles of the present invention having a particle diameter of 2 mm and a length of 2 mm.

rj 1 to M, 1. (g/l0m1n,) 1. +0.
8 4.0 2.1 Saba, P, (”C)
120 122 120 122 Density (g/crn”) 0.925 0.925 0.
925 0.9307 Star batch (reference example) I
2 3 4” Pigment concentration (PIIR) 3 2 5 5M
, 1. (g/10o+in,) 1.1
0.8 4.0 1.1 Mackerel, P.
('C) 120 122
+20 +20 density (g/crn'
) 0.925 0.925 0.925 0.9
25 Pigment concentration (PIIR) 3 2 5
-*I: Furthermore, 10 ethylene-vinyl acetate copolymer
Added at the rate of PIIR (addition amount per 100 parts of resin) *2
, excluding LLDPE.

*3 Ni blank test Medium 4; Excludes LLDPE.

Example 5 100 parts by weight of the colored particles of Example 1, 235 parts by weight of dichlorotafluorometa, 1.0 parts by weight of basic magnesium carbonate, and 300 parts by weight of water were placed in an autoclave, and the temperature was raised to mp-10°C while stirring. and reduce the pressure inside the autoclave to 10
While maintaining the weight at 50 kg/crn', one end of the container was opened, and the mixture was discharged into the atmosphere to cause foaming, thereby obtaining colored pre-expanded particles of the present invention shown in Table 3 below.

The obtained colored pre-expanded particles were left at room temperature and pressure for 48 hours, and then filled into a mold and packed at 0.5 to 2.0 kg/
A colored foamed molded product was obtained by heating and molding with water vapor of c I (G).

Table 2 shows the results of various evaluation tests conducted on the colored pre-expanded particles and the obtained colored foamed molded articles.

Examples 6 to 8 and Comparative Examples 5 to 8 The results in Table 2 were obtained in the same manner as in Example 1 except that the colored particles of Examples 2 to 4 and Comparative Examples 1 to 4 (Comparative Example 4 was uncolored) were used. I got it.

γ2 is one! −゛suL knee ′ ]′5L mn ゝ5
30 0.25 None 0
6 30 0.22 None
07 30 0.22 None
08 30 0.23 None
○Comparative example 5 30 0.08 small
△6 30 0.10 Small
×7 30 0.18 large
×8 30 0.24-- O: High density and gloss.

△: High density but lack luster, giving a pastel-like, whitish appearance.

X: Low density and whitish appearance.

Claims (5)

[Claims] (1) A linear low-density polyethylene resin for foaming, characterized in that the linear low-density polyethylene resin contains a colorant and a thermoplastic resin having a lower melting point than the linear low-density polyethylene resin. colored particles. (2) Linear low-density polyethylene resin pre-foamed by impregnating the linear low-density polyethylene resin colored particles according to claim 1 with a volatile foaming agent under high temperature and high pressure, and foaming by releasing the particles under low pressure. colored particles. (3) Claims 1 and 2 in which the melting point of the thermoplastic resin is 10 to 50°C lower than the melting point of the linear low density polyethylene resin.
Linear low-density polyethylene resin colored particles for foaming and pre-foamed colored particles as described in . (4) The foamable linear low-density polyethylene resin colored particles and pre-foamed colored particles according to claims 1 and 2, wherein the colorant is an organic pigment or carbon black. (5) The foamable linear low-density polyethylene resin colored particles and pre-foamed colored particles according to claims 1 and 2, wherein the thermoplastic resin is low-density polyethylene and/or ethylene-vinyl acetate copolymer.