JPH0768400B2 - 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,
When pre-expanded particles are produced or when in-mold expansion molding is performed using these expanded particles, LLDPE pre-expanded colored particles having uniform coloring and a high coloring density and a uniform cell diameter and a colored expanded molded article are provided. The present invention relates to expandable LLDPE colored particles for foaming and pre-expanded colored particles.

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

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

As a method for coloring the LLDPE foam-molded article, a method of coloring from the surface with a paint or the like after foam-molding and LLDPE which is a raw material
There are two methods of preliminarily coloring, but the latter method is industrially and cost-effective.

(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. When pre-expanded particles are produced by using colored particles or in-mold foam molding is performed using these expanded particles, the following problems occur depending on the LLDPE used.

(1) Since the colorant acts as a foaming nucleus during the production of pre-expanded particles, the bubbles produced 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 a non-crosslinked resin, unlike the crosslinked resin, the temperature range suitable for foaming is very narrow, and crystals are present at that temperature. In other words, in the non-crosslinked resin particles, expanded particles having a high closed cell rate 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, these not only act as mere foaming nuclei,
This is because it also acts as a crystal nucleus, and this crystal nucleus becomes a foaming nucleus.

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 favorable 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 pre-expanded particles, to eliminate the need for a pressure aging step during in-mold molding, and to prevent the molded body from shrinking after in-mold 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 comprises LLDPE and a colorant, and
The n-hexane extract X of LDPE is 0.3 to 1.5% by weight, and the relationship between the colorant concentration Y and the n-hexane extract X is Y.
LLDPE colored particles for foaming, characterized in that ≦ 7.5X, and the particles containing a volatile foaming agent under high temperature and high pressure,
LLDPE pre-expanded colored particles that are foamed by discharging under low pressure.

(Function) In coloring LLDPE with a colorant, by making the concentration of the n-hexane extract and the colorant in LLDPE have a specific relationship, dispersion and coloration of the colorant become sufficient, and The size of the bubbles during production is relatively uniform and does not require pressure aging for in-mold foam molding, and the obtained LLDPE foam molded body has no shrinkage and is excellent in sharpness and density. It becomes a colored foamed molded article.

That is, according to a detailed study by the present inventor, the concentration of n-hexane extract of LLDPE varies depending on its type, grade, or manufacturing method, and the dispersibility and color developability of the colorant depend on the concentration of this n-hexane extract. As the colorability of the pre-expanded particles is changed, the diameter of the cells is changed during the production of the pre-expanded particles, and the coloring and physical properties of the pre-expanded particles are changed,
It has been found that the object of the invention is achieved by having a specific relationship between the colorant and the n-hexane extract.

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

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 LLDPE used in the present invention has the n-hexane extract content of 0.3 to 1.5 of the above LLDPE. If the n-hexane extract content is less than the above range, the dispersibility of the colorant is poor and the LLDPE content is insufficient. However, various bubbles as described above occur because the bubbles generated during the production of the pre-expanded particles become too fine. On the other hand, if the n-hexane extract content exceeds the above range, the bubbles generated during the production of the pre-expanded particles are liable to form communicating holes, the proportion of the closed bubbles is reduced, and various problems occur during molding, which is not preferable. The LLDPE having the n-hexane extract as described above is the n-hexane of LLDPE available from the market.
It is sufficient to measure the hexane extract and select an appropriate n-hexane extract, and the n-hexane extract is low.
An n-hexane extract may be added to LLDPE at the time of coloring. The n-hexane extract in the present invention is a numerical value determined by the following measuring method.

n-Hexane extractable content measurement method Set a constant temperature water bath at 50 ° C ± 0.5 ° C, put n-hexane in a 600 ml wide mouth sample bottle, and put this wide mouth sample bottle in the constant temperature water tank.

Next, the measurement sample is cut to a size of about 2.5 ± 0.3 g (30 cm width × 2.1 cm dimensions), the sample is accurately weighed, and the sample is placed in the sample bottle. In this way, extraction is performed for 120 minutes in the constant temperature water tank, the sample bottle is taken out from the constant temperature water tank, and separated into a sample and a waste liquid by a Buchner funnel. The sample is assembled with a ring and vacuum dried in a dessicator for 30 minutes.

The sample taken out is weighed, and the n-hexane extract is obtained by the following formula.

However, A: weight before extraction (g) B: weight after extraction (g) Further, the LLDPE is preferably a non-crosslinked LLDPE having a density of 0.915 to 0.935 g / cm ³ , a melt index of 0.1 to 5.0 and a melting point of 115 ° C. or higher. . A particularly preferable range of the melting point is 118 ° C or higher.

The colorant used for coloring the above LLDPE may be any colorant such as conventionally known organic pigments, pigments such as inorganic pigments and extender pigments, dyes, etc., but considering heat resistance, light resistance and color migration property, etc. In some cases it is desirable to use pigments.

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.

Further, according to the research by the present inventor, when the concentration of the n-hexane extract is X and the addition amount of the colorant is Y, the relation between X and Y is Y ≦ 7.5X. It has been found that the objects of the invention are best achieved in the range. Y is
If it is larger than 7.5X, the bubbles become too fine during the production of pre-expanded particles, and the coloring of the colorant is not sufficient. X and Y
The range of the preferable relationship with is shown in FIG. In FIG. 1, the shaded area shows the range of the preferable relationship between X and Y in the present invention.

The essential components and preferred 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 pigment dispersant, etc. are mixed in any proportion. You can also do it.

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. Any of these kneading and granulation methods may be based on conventionally known methods.

In the present invention, a particularly preferred production method is to first mix the colorant and a suitable simple substance resin in a ratio such that the colorant concentration is 20 to 70% by weight, and use a three-roll mill, a kneader, an extruder or the like. A masterbatch is prepared by sufficiently kneading at a temperature of about 100 to 250 ° C to preliminarily disperse the colorant, and the masterbatch is mixed with uncolored LLDPE at a ratio of a desired concentration and granulated as described above. Is the way
More satisfactory colorant dispersion and color development can be achieved.

As the carrier resin, in addition to the same LLDPE as the resin to be colored, low density polyethylene, polyvinyl acetate, ethylene-
Vinyl acetate copolymer, ethylene-vinyl chloride copolymer,
Vinyl acetate-vinyl chloride copolymers, ethylene-vinyl acetate-vinyl alcohol copolymers, low molecular weight polyethylene, low molecular weight polypropylene, various synthetic or natural wax, and other thermoplastic resins, and these thermoplastic resins are all It can be used alone or as a mixture.

When a carrier resin other than the LLDPE of the present invention is used among the above carrier resins, the LLDPE of the present invention must be blended so as to be 50% by weight or more. Also, in such a case, the colorant concentration X
Is defined as follows.

Further, in the present invention, it is also preferable to use the colorant in a dry color form in which the colorant is preliminarily and uniformly mixed with a dispersant such as a higher fatty acid metal soap.

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 trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride and the like. The amount of the foaming agent added depends on the type of the foaming agent and the desired degree of foaming, but LLDPE
It is usually 5 to 50 parts by weight with respect to 100 parts by weight of colored particles.

In the method for producing LLDPE pre-expanded colored particles of the present invention,
Although the colored particles are impregnated with the volatile foaming agent, the timing is not particularly limited, and the coloring particles are preliminarily contained with the foaming agent, and the coloring particles impregnated with the foaming agent are put in a closed container to remove the foaming agent. 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. At a temperature lower than the melting point by 15 ° C., almost no foaming occurs, and when the temperature exceeds 5 ° C. higher than the melting point, the number of closed cells is remarkably reduced, resulting in open cells and lower mechanical strength.

A particularly preferred range of this foaming temperature is from 10 ° 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 cell number (hereinafter, simply referred to as cell number) of 200 cells / mm.
² or less.

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. To be done. As described above, the pre-expanded colored particles to which the internal pressure is applied as necessary are filled in the mold,
Normally, it is heated and foamed at a steam pressure of 0.5 to 2.0 kg / cm ² (G),
The desired colored foamed molded product is obtained.

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.

(Effect) According to the present invention as described above, when coloring LLDPE with a colorant, by making the n-hexane extract of LLDPE and the colorant concentration have a specific relationship, the colorant can be dispersed and colored. Will be enough.

Further, according to the present invention, even if the colorant is uniformly and finely dispersed as described above, a predetermined amount of the n-hexane extract is mixed in the obtained LLDPE colored particles. As a result, the colorant at the time of foaming is obtained. Since the action as a nucleating agent is suppressed and the bubbles generated do not become fine and become relatively large and uniform in size, there is little tendency for the color tone to become a whitish pastel tone, and a uniform color tone without color unevenness. Becomes

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.

Examples 1 to 8 and Comparative Examples 1 to 8 As shown in Table 1, 100 parts of LLDPE and carbon black were mixed in the mixing ratio shown in Table 1, and thoroughly kneaded on a three-roll heated to 120 to 130 ° C. Then, it was extruded in a strand shape by an extruder at a temperature of 100 to 130 ° C., and granulated with a pelletizer to obtain colored particles.

Subsequently, 100 parts of these colored particles, 34 parts of dichlorodifluoromethane, 1.0 part of basic magnesium carbonate and 300 parts of water were placed in an autoclave and heated to 90 to 150 ° C. under stirring,
While maintaining the pressure in the autoclave at 10 to 50 kg / cm ² , one end of the container was opened, and the container was discharged into the atmosphere and foamed to obtain the colored pre-expanded particles of the present invention shown in Table 1 below.

The obtained colored pre-expanded particles are left at room temperature and atmospheric pressure for 48 hours, then filled in a mold, and the melting point of LLDPE is -5 ° C, 0.5 to 2.
It was heat-molded with 0 kg / cm ² (G) of steam to obtain a colored foam molded article. Then, the molded body was left to stand in an oven at 80 ° C. for 24 hours to be dried and cured.

Table 1 shows the results of various evaluation tests carried out on the colored pre-expanded particles and the colored expanded molded article thus obtained.

Evaluation criteria Colorability; ◯; High density and gloss.

Δ: High density but no gloss, pastel-like whitish appearance.

X: Low density and whitish appearance.

Secondary foamability; O: There are few voids in the molded product, and there is no problem as a product.

Δ: Molded body has a few voids and can be used depending on the application.

X: Many voids are present in the molded product, which is not possible as a product.

Molded product shrinkage; Good; Shrinkage ratio in the surface direction is within 4%.

Δ: Shrinkage in the plane direction is 4 to 6%.

X: Shrinkage ratio in the plane direction is 6% or more.

Comprehensive evaluation: ○: Can be used as a foam.

Δ: Partly usable as foam.

X: Cannot be used as a foam.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the colorant and the n-hexane extract in the present invention. The vertical axis represents the colorant concentration (% by weight),
The abscissa represents the n-hexane extract (% by weight).

Claims (4)

[Claims] 1. A linear low-density polyethylene resin and a colorant, wherein the linear low-density polyethylene resin has an n-hexane extract X of 0.3 to 1.5% by weight, and a colorant concentration Y and n-. A linear low-density polyethylene resin colored particle for foaming, characterized in that the relationship with the hexane extract X is Y ≦ 7.5X. 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 has a density of 0.91.
The expandable linear low-density polyethylene resin colored particles and pre-expanded colored particles according to claim 1 or 2, which have a melt index of 5 to 0.935 and a melt index of 0.1 to 5.0. 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.