JPS58145739A - Expanded polypropylene particle - Google Patents

Abstract

PURPOSE:To provide the titled pre-expanded particle which can be easily molded and composed of a particulate foam of a first polypropylene resin having a specified high melting point and a foam of a second polypropylene resin having a lower m.p. than that of the first resin and deposited on the surface of the first resin. CONSTITUTION:The titled particle is composed of a particulate foam of a first polypropylene resin having an m.p. of 140 deg.C or above, pref. 145-165 deg.C, such as propylene homopolymer or an olefin copolymer having a propylene unit content of 80wt% or higher and a foam of a second propylene resin (including the above copolymer) deposited on the surface of said first resin foam. The m.p. of the second resin is 2-10 deg.C lower than that of the first resin, and is pref. 140-150 deg.C. The surface area of the second resin is at least 30% of the entire surface area of the expanded particle. In the figure showing a cross-section of the particle, numerals 1, 3 represent the first resin, and numerals 2, 4 represent the second resin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to polypropylene foam particles that are a molding material for producing polypropylene resin foam moldings by in-mold molding.

Currently, polystyrene-based and polyethylene-based products are representative of thermoplastic synthetic resin foam moldings that are widely used for heat insulating materials, cushioning materials, packaging materials, etc. Each of these has characteristics in physical properties and is used depending on the application, but there are many fields where foamed molded products with higher performance are desired. An example of a foamed molded product that can meet such demands is a foamed molded product made of polypropylene or an ethylene-propylene copolymer. In other words, these foam molded products of polypropylene resin exhibit a rigidity similar to that of polystyrene, which is much greater than those made from polyethylene, which is the same polyolefin resin, and are also stronger than those made of polystyrene. It has the advantage of having a high heat distortion temperature. On the other hand, due to its high melting point, polypropylene resins have the problem that when pre-expanded resin particles (beads) are heated and molded in a mold, they tend to cause poor fusion between the particles. The only way to do this was to mold the product from foaming using the melt extrusion method. However, with the second method, it is difficult to produce a product with a high expansion ratio, and the shape of the molded product is also limited.

As a result of repeated research into improving the method of in-mold molding of polypropylene resin via pre-expanded particles, the inventors of the present invention have developed a method for pre-foaming polypropylene resin that is easy to mold, as detailed below. He completed the invention of particles.

That is, the present invention provides a first polypropylene resin 11 (fatty granular foam and a second polypropylene resin foam that adheres to the surface of the first polypropylene resin foam having a melting point (according to ASTM-D2117) of 40°C or higher). The melting point of the second polypropylene resin is 2 to 10°C lower than the melting point of the first polypropylene resin, and the surface area of the second polypropylene resin is 30% or more of the surface area of the entire expanded particle.
The object of the present invention is to provide polypropylene foamed particles characterized by being

Here, polypropylene resins include propylene homopolymers as well as olefin copolymers with a propylene unit content of 80% by weight or more, such as copolymers of ethylene, butene-1, pentene, etc., and propylene. means a polymer.

In addition, as the first polypropylene resin (hereinafter referred to as high melting point resin), a resin with as high a melting point as possible, which is intended to be used as a foam molded product, is used for at least 50% of the total, but from the viewpoint of moldability, in the present invention, Particularly preferred is a melting point of 145
~165°C. On the other hand, as the second polypropylene type O (hereinafter referred to as low melting point resin), one is selected from among the olefin copolymers listed in "-" that satisfies the requirements regarding the melting point in "-I", and its melting point is 13 - Desirably, the temperature is about 40 to 155°C.

FIG. 1 is a cross-sectional view showing the structure of an example of the foamed particles of the present invention as described in -1-, in which the entire surface of the spherical part made of foam 1 made of high melting point resin is foam made of low melting point resin. 2.

Further, FIG. 2 is a sectional view showing another example of the foamed particles of the present invention, in which a portion (however, 70% or more) of the foamed body 3 made of high melting point resin is shown.
1-) is covered with a foam 4 of low melting point resin.

Other than having the above-mentioned structure, the foamed particles of the present invention are not particularly different from conventional polyethylene-based or polystyrene-based pre-expanded particles. That is, the particle diameter is usually about 2 to 1.0 + nm, and the density of the entire particle is about 0.0, (11 to 0.3 g,/cm3, but is not limited to this range.

Since the foamed particles of the present invention have a surface with a lower melting point than the core, when the particles are filled into a mold and heated by blowing steam to re-foam, the particles are fused together and molded. Since the particle surface is more easily deformed and sticky than the core (that is, a state suitable for molding), the entire particle is in a state suitable for molding, and can be molded without intense heating. can. Therefore, polypropylene or ethylene-propylene copolymer with a high propylene content, which is difficult to soften to the extent necessary for molding when made into single foamed particles due to their high melting point, can also be used as foamed particles with a composite structure according to the present invention. By doing so, molding can be easily and reliably performed with a force of 1. However, 2
If the melting point difference between different types of resins is too large, the physical properties of the molded article will deteriorate.The melting point difference should be kept within the above range. Furthermore, the molded article obtained using the foamed particles of the present invention has a structure in which high-melting point foamed particles that have not been significantly deformed are dispersed in a continuous phase consisting of a low-melting point and therefore relatively flexible foam. Moreover, since the continuous phase and the dispersed phase are made of the same type of resin, there is no possibility of interphase separation, so the surface feels soft, the overall structure is strong, and the mechanical strength such as tensile strength and compressive strength is high. It exhibits excellent physical properties, such as high strength and durability against repeated compression.

Therefore, according to the present invention, it is possible to manufacture a high-performance foam molded article using a material that has been difficult to mold in the past.

In addition, if the foamed particles of the composite structure according to the present invention are made of materials that can be molded alone, they can be molded with less heat consumption and can be molded using molding equipment with low pressure resistance.

Next, a typical method for producing expanded particles of the present invention will be explained.

The two types of raw resins are heated and melted at the same time, but using separate extruders, and the resulting melt flows are merged in the extrusion port so that the high melting point resin becomes the core and the low melting point resin becomes the sheath. It is extruded as a filament with a thickness of about 0.5 to 5+nKl. The obtained core-sheath type composite fiber is shredded into particles by any means. Alternatively, a melt of two types of resins is extruded into a laminated sheet in the order of low melting point resin/high melting point resin/low melting point resin by a coextrusion method, and then shredded into particles by any means. In the above method, the extrudate is shredded while it is still in a molten state, and the resulting composite resin particles are immediately poured into an inert liquid (e.g., hot water) heated to a temperature near the melting point of the low melting point resin. When passed through the medium, the entire surface becomes spherical due to surface tension and the low melting point resin flows, and most of the surface of the high melting point resin is covered with the low melting point resin (this can be the raw material for the example in Figure 1). ) is obtained.

The foamed particles of the present invention can be obtained by impregnating the obtained composite structure resin particles with a foaming agent and then foaming them. Since this can be done in the same manner as above, detailed explanation will be omitted.

The present invention will be explained below with reference to Examples.

Examples 1 with different ethylene copolymerization ratios as shown in Table 1
Five types of ethylene/propylene random copolymers were prepared.

Various combinations of two types of resins selected from these resins are used to obtain sheath-core type or side-pie-side type composite strands by coextrusion, which are then shredded into pieces with a diameter of 1. The pellets were made into pellets with a diameter of 5 + nm and a length of 2.5 mm. In this case, the low melting point resin was arranged on the surface of the high melting point resin particles, and a small amount of coloring agent was mixed with one of the resins so that the coverage of the foamed particles by the low melting point resin foam could be determined.

A mixture of 100 parts by weight of the obtained pellets, 300 parts by weight of water, 15 parts by weight of dichlorodifluoromethane, and 0.5 parts by weight of aluminum oxide fine particles was heated to 130 parts by weight in an autoclave.
The mixture was heated to ~165°C and discharged into the atmosphere under a pressure of 25 Kg/cm2 to cause foaming.

Table 2 summarizes the properties of the obtained expanded particles (density of about 0.03 g7 cm3) and the molded product thereof. The molding method and testing method are as follows.

a. Molding method 2. 2.2 Kg/cm2 (
G) After curing in pressurized air for 7-24 hours, 300a+mX 300mmX
It was filled into a 300 mm mold, molded by injecting steam, and after cooling to 60°C, the molded product was taken out and cured in air at 65°C for 24 hours.

11 Foaming state ◎ Closed cell 0 Low melting point part is like open cell × Low melting point part is open cell C6 coverage 2 Ratio d of surface area of low melting point resin foam part to surface area of foamed particles, moldable Minimum steam pressure P: The molded product obtained! ]() Minimum steam pressure required to fuse and form foamed particles to the extent that they do not break even when bent.

e. Heat resistance 2. Place the molded product in an oven at 110°C for 24 hours.
Time, processed according to JIS K 6767 and judged based on the following criteria.

◎ Shrinkage rate less than 5% ○ Shrinkage rate 5-10% × Shrinkage rate more than 10% 8- Table 1 (J Melting point (°C) A 165B
163C161 D 159E
157F
155G
153H151 1149 J 147K
145L
143M 1
41N 1390
137

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views showing the structure of specific examples of expanded particles according to the present invention. 1.3: Foam of high melting point resin (first polypropylene resin) 2.4: Foam of low melting point resin (second polypropylene resin) Agent Patent attorney Figure 243-

Claims (2)

[Claims] (1) A granular foam of a first polypropylene resin having a melting point of 140°C or higher, and a second foam of a polypropylene resin in close contact with its surface; 2 to 10°C lower than the melting point of the first polypropylene resin, and 30% of the surface area of the second polypropylene resin or the surface area of the entire expanded particle.
Polypropylene foam particles characterized by the above. (2) The expanded particles according to claim 1, wherein the polypropylene resin is an ethylene-propylene random copolymer.