JPH0768401B2 - Linear low-density polyethylene resin colored particles for foaming and pre-expanded colored particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a linear low-density polyethylene resin for foaming (hereinafter simply referred to as LLDPE) colored particles and pre-expanded colored particles obtained from the particles, and more specifically, Evenly colored,
LLDP that has uniform coloring and high coloring density during the production of pre-expanded particles and in-mold foam molding, and that has a uniform cell diameter
E Pre-expanded particles and foamed LLDPE colored particles and pre-expanded colored particles capable of giving expanded molded articles.

(Prior Art) Conventionally, LLDPE foam molded articles have been widely used as materials for various cushioning materials, containers, and the like. These foamed molded articles are foamed by impregnating LLDPE particles with a volatile foaming agent at high temperature and high pressure and discharging under low pressure, and molding this into a desired shape by the so-called in-mold foam molding method of foamed particles. ing.

In addition, although many of these LLDPE foam-molded articles are non-colored, colored foam-molded articles have been widely demanded.

There are two methods for coloring the LLDPE foamed molded product: a method of coloring the surface of the foamed molded product with a paint or the like, and two methods of preliminarily coloring the raw material LLDPE, but the latter method is industrially and cost-effective. Is.

(Problems to be Solved by the Invention) In the above LLDPE foam molding coloring method, L
As a method of coloring the LDPE, a method of melt-kneading a colorant such as a dye or a pigment into the LLDPE and pelletizing the LLDPE particles when manufacturing the LLDPE particles as a raw material is performed.

In the above coloring, for coloring and uniform coloring of the colorant, the colorant is required to be uniformly and finely dispersed in the LLDPE resin, and thus the colorant is uniformly and finely dispersed in the LLDPE resin. The following problems occur when pre-expanded particles are produced using colored particles or in-mold expanded molded articles are formed using these expanded particles.

(1) Since the pigment particles act as nuclei of the foaming agent during the production of the pre-expanded particles, the bubbles generated are extremely fine. In particular, when the resin to be the foamed particles is non-crosslinked, further miniaturization of bubbles is promoted. The reason for this is as follows.

That is, in the case of non-crosslinked, unlike the case of crosslinked, the temperature range suitable for foaming is very narrow and crystals are present at that temperature. In other words, with the non-crosslinked resin particles, expanded particles having a high closed cell ratio cannot be obtained unless the temperature is in a slight temperature range where crystals exist. Therefore, when the foamed particles are produced in the state where the colorant is present in the resin particles, not only do they act as mere foaming nuclei but also act as crystal nuclei, and the crystal nuclei become foaming nuclei.

In the expanded colored particles thus obtained, secondary foaming tends to be poor during molding even if pressure aging is performed before in-mold foam molding. Even if good secondary foaming is performed, the foamed molded product obtained will undergo significant shrinkage. In any case, a good molded product cannot be obtained.

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

(3) If the dispersion of the coloring agent is insufficient, the problem of the above (1) does not occur, but the coloring of the coloring agent is poor and vivid coloring cannot be performed.

Therefore, an object of the present invention is to provide relatively large and uniform cells during the production of expanded particles, eliminate the need for a pressure aging step during in-mold molding, and to prevent shrinkage of the molded body after in-mold foam molding and Foaming LL that can give a colored foam that is uniformly colored without unevenness or whitening and has excellent color luster and density.
It is to provide DPE colored particles and pre-expanded colored particles.

(Means for Solving Problems) That is, the present invention relates to LLDPE, a coloring agent and the above LLD.
The LLDPE colored particles for foaming are characterized by containing a thermoplastic resin having a melting point lower than PE, and LLDPE pre-expanded colored particles obtained by heat-foaming by adding a volatile foaming agent to the particles.

(Function) When coloring LLDPE with a colorant, by mixing a thermoplastic resin having a lower melting point than LLDPE, dispersion and coloration of the colorant are sufficient, and the size of bubbles during the production of pre-expanded particles is compared. The LLDPE foamed molded product, which is uniform in size and does not require foaming ability when it is used as an in-mold foamed molded product, is a beautiful colored foamed molded product that does not shrink and has excellent sharpness and concentration. .

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments.

The LLDPE used in the present invention has a density of 0.915 to 0.940 g / c.
m ³ , melt index 0.1 to 5.0 g / 10 min and melting point 115
Non-crosslinked LLDPE having a temperature of ℃ or above is preferable. A particularly preferable range of the melting point is 118 ° C. or higher, and a particularly preferable range of the density is 0.9
20 to 0.940 g / cm ³ .

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

The colorant used for coloring the above LLDPE may be any of conventionally known organic pigments, pigments such as inorganic pigments and extender pigments, or dyes, but when considering heat resistance, light resistance and color migration, a pigment is used. It is desirable to do.

For example, organic pigments include phthalocyanine-based, azo-based, condensed azo-based, anthraquinone-based, perinone-perylene-based, indigo-thioindigo-based, isoindolinone-based, azomethineazo-based, dioxazine-based, quinacridone-based, aniline black-based, tri-based Phenylmethane-based and carbon black, etc.Inorganic pigment-based, titanium oxide-based, iron oxide-based, iron hydroxide-based, chromium oxide-based, spinel-type calcined pigment, lead chromate-based, vermilion chromate-based, dark blue Examples of extender pigments such as powders, aluminum powders, bronze powders, and the like include calcium carbonate-based, barium sulfate-based, silicon oxide-based, aluminum hydroxide-based and the like.

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

The colorant as described above is usually 0.5 part with respect to 100 parts by weight of the LLDPE.
It is used in an amount of 1 to 10 parts by weight, preferably 1 to 5 parts by weight.

The thermoplastic resin used in the present invention is the LLDPE described above.
Is a thermoplastic resin having a melting point lower than that of, for example,
Low density polyethylene (mp. = 105 ° C.), ethylene-vinyl acetate copolymer (mp. = 95 ° C.), ethylene-ethyl acrylate copolymer (mp. = 90 ° C.), etc. Any of these can be used alone or as a mixture.

Among the above-mentioned thermoplastic resins, the melting point of LLDPE is 115 ° C. or higher, so that the melting point of LLDPE is about 10 to 50.
Those having a melting point lower by 0 ° C. are preferable, and most preferable are low density polyethylene and ethylene-vinyl acetate copolymer.

These thermoplastic resins are usually used in an amount of about 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, based on 100 parts by weight of the LLDPE.

The essential components of the LLDPE colored particles of the present invention are as described above, but if necessary, an antistatic agent, an antioxidant, a light stabilizer, a lubricant, a dispersant and the like can be mixed in any proportion. .

The method for producing LLDPE colored particles for foaming of the present invention, the essential components and necessary components as described above are mixed with a high-speed mixer, a Henschel mixer, a tumbler, etc., and melt-kneaded with an extruder to be extruded into a strand, which is then pelletized. Granulate, for example, diameter (D) 0.5 to 3 mm, length (L)
It can be obtained by granulating particles having a diameter of 0.5 to 3 mm and an L / D of about 1.0 to 2 mm. Any of these kneading and granulation methods may be based on conventionally known methods.

Particularly preferred production method in the present invention is to first mix the colorant and the thermoplastic resin in a proportion that the colorant concentration is 20 to 70% by weight, and this is a three-roll, kneader,
A masterbatch is prepared by thoroughly kneading the colorant with an extruder or the like at a temperature of about 100 to 250 ° C. to prepare a masterbatch, and the masterbatch is mixed with uncolored LLDPE at a ratio of a desired concentration, As described above, it is possible to achieve more sufficient dispersion and color development of the colorant.

The pre-expanded colored particles of the present invention are the above-mentioned LLDP for foaming of the present invention.
It is obtained by impregnating E-colored particles with a volatile foaming agent and foaming them.

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

In the method for producing LLDPE pre-expanded colored particles of the present invention,
The colored particles are impregnated with the volatile foaming agent, but this time is not particularly limited, and the colored particles are impregnated with the foaming agent in advance, and the colored particles impregnated with the foaming agent are put in a closed container to The colored particles and the foaming agent may be dispersed in a dispersion medium in a closed container, or the colored particles may be impregnated with a foaming agent while dispersing them in a dispersion medium in the closed container. .

Further, in the process of heating the colored particles together with a dispersion medium to a predetermined temperature in a closed container, a foaming agent is placed in the closed container to disperse the colored particles and the foaming agent while impregnating the colored particles with the foaming agent. May be. 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, the colored particles and the volatile foaming agent are separately or dispersed in the dispersion medium after the colored particles are impregnated with the volatile foaming agent. At this time, if necessary, a dispersant, for example, tricalcium phosphate, a base. Inorganic substances such as basic magnesium carbonate, basic zinc carbonate and calcium carbonate can be used. The amount of the dispersant added is usually 0.01 to 10 parts by weight with respect to 100 parts by weight of the colored particles.

In addition, when dispersing colored particles, melting point 20 ℃ or more, HLB
It is also possible to add 5 parts by weight or less of an organic compound having a value of 1 to 10, such as stearic acid amide, to 100 parts by weight of the colored particles. The dispersion medium may be a solvent that does not dissolve the colored particles, and examples thereof include one of water, ethylene glycol, glycerin, methanol, ethanol and the like, or a mixture of two or more thereof. Water is preferred.

In the above method, one end of the container is opened to release the colored particles and the dispersion medium at the same time under an atmosphere of normal pressure than in the container,
The temperature at this time is in the range of 15 ° C. lower than the melting point of the colored particles to 5 ° C. higher than the melting point. Below 15 ° C. below the melting point, almost no foaming occurs, and above 5 ° C. above the melting point, the number of closed cells is remarkably reduced, resulting in open cells and reduced mechanical strength.

A particularly preferred range of this foaming temperature is from 13 ° C below the melting point to below the melting point. Further, the pressure at this time may be higher or lower than the vapor pressure of the volatile foaming agent,
The atmosphere to be released is usually an atmospheric pressure atmosphere.

The pre-expanded colored particles of the present invention obtained by the above method usually have a bulk density of 0.01 to 0.3 g / cm ³ , a closed cell ratio of 60% or more, and an average number of cells (hereinafter, simply referred to as the number of cells) of 1,000 /
It is less than or equal to mm ² . If the bulk density is less than 0.01 g / cm ³ , the shape of the pre-expanded colored particles tends to be distorted, and if the bulk density exceeds 0.3 g / cm ³ , not only the shape of the colored particles tends to be distorted, but also the foamed state is It becomes uneven. A particularly preferred range of bulk density is 0.
It is 015 to 0.15 g / cm ³ . When the closed cell ratio is less than 60%, the expanded colored particles are likely to be distorted and the compression elasticity is lowered. A particularly preferable range of the closed cell ratio is less than 80%. If the number of bubbles exceeds 1,000 / mm ² , the shape of the bubble-colored particles will be distorted and the mechanical strength will decrease. A particularly preferable range of the number of bubbles is 0.3 to 100 cells / mm ² . The particle size of the pre-expanded colored particles is not particularly limited, but is preferably 0.5 to 20 mm from the viewpoint of fluidity.

The pre-expanded colored particles of the present invention as described above are usually aged for a predetermined time at room temperature and normal pressure, and then, if necessary, aged under a predetermined pressure for a predetermined time with an inorganic gas or a mixed gas of an inorganic gas and a volatile foaming agent. (Giving foaming ability). The pre-expanded colored particles, to which the internal pressure is applied as necessary as described above, are filled in a mold and usually heat-foamed at a steam pressure of 0.5 to 2.0 Kg / cm ² (G) to obtain a desired colored expanded molded article. .

The colored foamed molded product obtained as described above can be used, for example, as a packaging material, a cushioning material, a building material, a heat insulating material, a food container, a floating material and the like.

(Effects) According to the present invention as described above, in coloring LLDPE with a coloring agent, the use of a thermoplastic resin having a melting point lower than that of LLDPE enables sufficient dispersion and coloring of the coloring agent.

Further, according to the present invention, even if the colorant is thus finely dispersed, as a result that a predetermined amount of the thermoplastic resin is mixed in the LLDPE colored particles to be obtained, a nucleating agent for the colorant during foaming. The effect of the above is suppressed, and the generated bubbles do not become fine and become relatively large and uniform in size. Therefore, the color tone is less likely to become a whitish pastel tone, and a uniform color tone without color unevenness is obtained.

In addition, since the bubbles generated as described above are relatively large, the step of aging the pre-expanded colored particles under pressure is not required for the in-mold foam molding, and the colored foam molding has excellent color tone with little shrinkage and no color unevenness. The body is provided.

(Examples) Next, the present invention will be described more specifically with reference to Reference Examples, Examples, and Comparative Examples. In the text, parts and% 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
After thoroughly kneading on a triple roll heated to 0 to 130 ℃,
It was extruded in a strand shape by an extruder at a temperature of 0 to 130 ° C., and granulated by a pelletizer to prepare a granular masterbatch.

Reference Example 1 Thermoplastic Resin; Low Density Polyethylene 70 Parts Pigment; Carbon Black 30 Parts Reference Example 2 Thermoplastic Resin; Ethylene-Vinyl Acetate Copolymer 60 Parts Pigment; Phthalocyanine Green 40 Parts Dispersant; Calcium Stearate 5 Parts Reference Example 3 Thermoplastic resin: Low density polyethylene 25 parts Ethylene-vinyl acetate copolymer 25 parts Pigment: Quinacridone red 50 parts Reference Example 4 LLDPE (mp. = 122) 60 parts and carbon black 40 parts In the same manner as in Reference Example 1 A masterbatch was created.

Reference Example 5 Carbon Black Alone Examples 1 to 4 and Comparative Examples 1 to 4 100 parts of LLDPE was mixed with a masterbatch or a pigment shown in Table 1 below at a predetermined ratio, and the mixture was heated at a resin temperature of 250 ° C. in an extruder of 65φ. Melt kneading, extrusion, and granulation with a pelletizer to obtain colored particles of the present invention having a particle size of about 2 mm and a length of 2 mm.

Example 5 100 parts by weight of the colored particles of Example 1, 35 parts by weight of dichlorodifluoromethane, 1.0 part by weight of basic magnesium carbonate and 3 parts of water.
Put 00 parts by weight into the autoclave, raise the temperature to mp-10 ° C with stirring, open one end of the container while maintaining the pressure in the autoclave at 10 to 50 kg / cm ² , and release into the atmosphere to foam. The colored pre-expanded particles of the present invention shown in Table 3 below were obtained.

The colored pre-expanded particles thus obtained were allowed to stand at room temperature and atmospheric pressure for 48 hours, then filled in a mold and heat-molded with steam of 0.5 to 2.0 kg / cm ² (G) to obtain a colored foam-molded product.

Table 2 shows the results of various evaluation tests carried out on the colored pre-expanded particles and the colored expanded molded article thus obtained.

Examples 6 to 8 and Comparative Examples 5 to 8 The results of 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 were used (Comparative Example 4 was uncolored). Got

Claims (5)

[Claims] 1. A linear low-density foaming product comprising a linear low-density polyethylene resin containing a colorant and a thermoplastic resin having a melting point lower than that of the linear low-density polyethylene resin. Polyethylene resin colored particles. 2. A linear low-density polyethylene resin obtained 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 discharging under low pressure for foaming. Pre-expanded colored particles. 3. The linear low-density polyethylene resin colored particles for foaming and pre-expansion according to claim 1, wherein the melting point of the thermoplastic resin is lower than that of the linear low-density polyethylene resin by 10 to 50 ° C. Colored particles. 4. The linear low-density polyethylene resin colored particles for foaming and pre-expanded colored particles according to claim 1, wherein the colorant is an organic pigment or carbon black. 5. The thermoplastic resin is low density polyethylene and / or
Alternatively, the linear low-density polyethylene resin colored particles for foaming and the pre-expanded colored particles according to claim 1 or 2, which are ethylene-vinyl acetate copolymers.