JPS5815539A - Production of foam - Google Patents

Abstract

PURPOSE:To produce a foam at an expansion ratio of 3 or above with a chemical blowing agent, by using polyolefin pellets contg. a chemical blowing agent and polyolefin powder in a specified ratio. CONSTITUTION:A chemical blowing agent (B) having a particle size of 10mu, such as azodicarbonamide or sodium bicarbonate, and polyolefine powder (C) having a particle size of 1mm. or below are blended with rectangular or round polyolefin pellets of 2-5mm. in length or diameter in such a proportion that the sum of components B and C amounts to 1.1-10wt% with the proviso that the amount of the chemical blowing agent is at least 1wt% and that of the polyolefin powder is at least 0.1wt% based on that of the blowing agent. The resulting mixture is expansion-molded by a convertional method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyolefin foam having an expansion ratio of 3 times or more using a chemical blowing agent.

Polyolefin foams have traditionally been used as thermoplastic resins, while retaining the unique properties of plastics, and are also given insulation, cushioning, and sound-absorbing properties, making them ideal for use in building materials, packaging materials, etc. It is widely used in various fields such as insulation materials. In order to produce a polyolefin foam, it is usual to add a blowing agent to the polyolefin, and the blowing agent may be a liquid blowing agent such as a fluorocarbon type, or pentane, or a gas blowing agent such as N2 or CO2.
and chemical blowing agents such as azodicarbonamide. Among these, liquid and gas blowing agents are usually added to the polyolefin by directly pressurizing them into a molding machine such as an extruder.
Ruh: In this case, in addition to the general-purpose molding machine, new equipment for injection of the blowing agent is required, which increases the equipment cost (2), and solvents such as pentane are harmful to the human body, and [There is a risk of a large explosion, which is unfavorable for health and safety.

On the other hand, chemical blowing agents have the advantage that they are safe because they are inert, and can be used with ordinary extruders without requiring any special equipment.

However, with the conventional chemical foaming method, it is impossible to easily produce a foam of high quality that can be put to practical use with a foaming ratio of 5 times or more.

The inventors of the present invention have conducted extensive research with the aim of providing a method for easily producing polyolefin foam with a foaming ratio of 3 times or more using a chemical blowing agent that has the advantages described below. As a result, uniform dispersion of polyolefin and chemical blowing agent,
It was discovered that it is necessary to increase the outflow rate in the molding machine and stabilize the extrusion rate.

In other words, there are two methods for adding a chemical blowing agent to polyolefin: the tri-blend method, in which the blowing agent powder is added to the polyolefin pellets through Tα contact, and the method, in which the blowing agent and polyolefin pellets are heated and mixed, and the blowing agent is kneaded into the polyolefin. There are two types of 9゛I.

The tri-blend method has the advantage of being lower in cost than the kneading method because it does not require a kneading process, but because the powder is directly added to solid polyolefin such as pellets, the blowing agent is less uniformly dispersed, and it is difficult to extrude. The kneading method is generally used because the foam gets stuck in the screw of a molding machine, making the extrusion rate unstable and making it impossible to obtain a foam of uniform quality.

However, in order to produce foams with a foaming ratio of 6 times or more, the amount of blowing agent used is considerably increased compared to when the normal foaming ratio is 2 times or less, and 10 In this case, even in the kneading method, problems arise in terms of uniform dispersion of the blowing agent during kneading, and loss due to thermal decomposition of the blowing agent. O In view of these problems, the present invention @ etc. has conducted repeated tests to solve the drawbacks of the dry blend method, and as a result, it is possible to add a powdered chemical blowing agent and powdered polyolefin to polyolefin pellets. The method of blending has been found to be suitable for the purpose described in Item 111.The blending method of powdered chemical blowing agent and powdered polyolefin to polyolefin pellets is 11 to 100% by weight in terms of the total amount of rain sound, and powder 1ffi of powder polyolefin per 1 weight/1 volume of blowing agent: 774 parts or more, more preferably 1.0 parts
In order to obtain a foaming ratio of 6 times or more, the blowing agent is added in an amount of 1.0% by weight or less, as described above.

The polyolefin pellets used in the present invention are rectangular or round in length and diameter within the range of 2 to 5 muφ, and the powder polyolefin has a length and diameter of 1 mm. The following are preferred. The foaming agent is approximately 1
It is a fine powder of around 101 tons.

The reason why the blending of powdered polyolefin is effective in the present invention is mainly because it improves the compatibility between the powdered blowing agent and the polyolefin pellets (5). This is to speed up the outflow rate.

Generally, polyolefin powder has poor fluidity than polyolefin pellets, and since pellets and powder have different particle sizes and bulk specific gravity, it was thought that blending the two would reduce fluidity and result in poor dispersion. However, when chemical blowing agent powder is blended with polyolefin pellets as in the present invention, unexpectedly, the combined use of powdered polyolefin increases the fluidity of the blend and makes poor dispersion less likely to occur. The reason for this is thought to be that polyolefin powder has better fluidity than chemical blowing agent powder and that the powdered polyolefin has a larger surface area. Even if it is directly supplied to the machine, there will be no bomber ringing or changes in the blending ratio over time, allowing stable operation over long periods of time.

Here, the combination ratio of the blowing agent and the powder polyolefin (6) is limited, but if the powder polyolefin F5J is 1 part by weight or more than 1 part by weight per 1 part by weight of the blowing agent, +41 part by weight. If it becomes...-1, the foaming effect of the foaming agent may be adversely affected. Specifically, the bubble diameter of the foam becomes 11 mm, and the smoothness of the outer surface 1 is lost. (This is because the blending effect will be lost if the powder blowing agent and polyolefin are combined. If the total amount of the powdered blowing agent and polyolefin exceeds 10% by weight, the polyolefin powder will be blended and the polyolefin effect will be lost. Further, if the chemical blowing agent is less than 14% by weight, a foaming ratio tI'i of 3 times or more id cannot be obtained.

Furthermore, when the polyolefin is composed of polyolefin or several types of polyolefins, it is effective to use polyolefin powder with the highest blending type (1), while powders of polyolefins with a blending type - and with a lower FTk are less effective.

Chemical blowing agents used in the present invention include blowing agents that decompose upon heating and generate gases such as nitrogen gas, and organic blowing agents such as abdicarbonamide, PSP+-oxybishenzenesulfonylhydrazide, and dinitrosopentamethylenetetramine. and inorganic foaming agents such as bicarbonate of soda and ammonium carbonate.

Example 1 Pellet-shaped low density polyethylene (MI=4 density opening 92
) was mixed with blowing agent abdicarbonamide powder (variable) and low density polyethylene powder (variable), and the outflow rate and particle size segregation of each mixture were measured.

The outflow rate is measured by placing 500 samples into the hopper (unit: mm) shown in the attached figure and measuring outflow rate <9 times.

A nl/kotsuper was used to measure particle size segregation and outflow rate, and the sample was poured into the mpeller and then allowed to flow out. During the outflow, the effluent was collected in four parts, and the powder and Vereso I. Measure the content.

From the results shown in Table 1, it can be seen that when the mixture of powdered low-density foam IJ or blowing agent is 1 part or more, the flow rate of the mixture becomes faster and Particle size segregation is also common. In Experiment 10, particle size segregation appeared, and the total amount of outside the powder was 10 weight φ.
This is because the effectiveness of powdered low-density polyethylene has diminished as the amount of powdered low-density polyethylene has increased.

Example 2 Low density polyethylene (M = 4
, density 092) and high density polyethylene (M = 0.4,
Using a blend with a density of 095), the outflow rate and particle size segregation of the mixture were measured when the blowing agent azodicarbonamide was blended.

(10) Table 2 From Table 2, when the polyolefin pellets are a blend of several types of polyolefins, it is effective to use powdered polyolefin in combination with a large amount of polyolefin powder. When the amounts of different types of polyolefins are the same as in Experiment 15.14, the effect is observed with any polyolefin powder.

Example 5 A foaming resin mixture using 4.41-oxybisbenzenesulfonyl hydrazide as a foaming agent was injected into a 43 mmφ copper tube using a (11) 7.5 mm screw extruder at an extrusion temperature of about 140°C. Cover it thickly,
We made a foam insulated hand cope. Table 6 shows the characteristics of the obtained prototype.

Table 6】O 1゜O 17 Ryodai Note 1) Low density polyethylene MI=4.0 Density=
[1,92 High-density polyolefin MI = 0.40 Density = 095 Note 5) All resin mixtures for foaming were prepared using the triblend (12) method. From these examples, polyolefin pellets were mixed with a powdered chemical blowing agent. It can be seen that a foam with good properties can be easily obtained by adding powdered polyolefin.

The method of the present invention has the effect of reducing foaming agent loss during mixing of foaming resins compared to the conventional blowing agent kneading method, and can produce a foamed one-stroke resin composition that is cheaper than the conventional method. It is.

[Brief explanation of drawings]

The attached drawings show the flow rate of the resin mixture used in the present invention;
FIG. 2 is a schematic diagram of a hopper used to measure particle size segregation. Agents 1) Akira Agent Ryo Hagiwara - (15)

Claims (1)

[Claims] 1. In a method for producing a polyolefin foam using a chemical blowing agent, a total amount of chemical blowing agent powder and polyolefin powder is added to a polyolefin pellet in a total amount of 1.
1 to 10.0 parts by weight (7 t% blended, and 1"l of chemical blowing agent powder: 1.0 parts by weight or less"). 2. A method for producing a foam with an expansion ratio of 3 times or more, characterized in that the amount of polyolefin powder is blended in an amount of 10 parts by weight or less per 1 part by weight of chemical blowing agent powder. A method for producing a foam according to claim 1, wherein the foaming method according to claim 1 or 2, wherein the chemical blowing agent powder and the powdered polyolefin are blended by a tri-blend method in which the powdered chemical blowing agent and the powdered polyolefin are directly added to polyolefin pellets. Body manufacturing (1) Method.