JPH08198972A - Production of foaming resin composition - Google Patents

Abstract

PURPOSE: To obtain a smooth-surfaced thermoplastic resin foam with low variation in expansion magnification owing to homogeneous dispersion fo a foaming agent in the resin melt by using a solid thermal decomposition type foaming agent. CONSTITUTION: A thermoplastic resin 7 is fed from a feedstock hopper 2 into an extruder 1 having a vent port 3 and melted; and a solution 6 prepared by dissolving a solid thermal decomposition type foaming agent having a decomposition temperature higher than the melting point of the resin in an organic solvent having a boiling point lower than the above decomposition temperature is pressed, at an intermediate point of the extruder 1, into, using a relevant machine 5, the resin melt, and the organic solvent is expelled by a vacuum pump 4 through the vent port 3 while kneading the resin in a melt state, and the resin is extruded from the extruder 1 to produce the objective foaming resin composition in the form of a sheet 8, which is, in turn, heated to thermally decompose the foaming agent to effect foaming the resin, thus obtaining the other objective resin foam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a foamable resin composition using a solid pyrolytic foaming agent as a foaming agent.

[0002]

2. Description of the Related Art Pyrolysis type foaming agents which are solid at room temperature, such as azodicarbonamide, are widely used in the production of foamable resin compositions.

As a method for producing a foamable resin composition of this kind, a thermoplastic resin and a solid pyrolytic foaming agent such as azodicarbonamide are mixed in a ribbon blender or the like, and the mixture is extruded from a raw material hopper. It is widely practiced to supply the powder to the melt-kneaded product, melt-knead it, and extrude it from an extruder (for example, the plastic foam handbook 99-119, published by Nikkan Kogyo Shimbun, February 28, 1973, first edition).
See page).

[0004]

In the above conventional method for producing a foamable resin composition, both the thermoplastic resin and the solid pyrolyzable foaming agent are generally in powder form. However, when supplying a mixture of such a resin and a foaming agent from the raw material hopper to the extruder, since the specific gravity and particle size of the two are different, the dispersion state of the foaming agent powder in the raw material hopper is biased. Further, the foaming agent powder adheres to the inner wall of the raw material hopper.

As a result, there is a problem in that the thermal decomposition type foaming agent cannot be uniformly dispersed in the molten resin, resulting in a large variation in expansion ratio. In order to improve such a problem, the inventor tried a method of stirring the mixture in the raw material hopper and a method of vibrating the raw material hopper, but the effect was not so great.

The present invention is intended to solve the above problems. An object of the present invention is to use a solid pyrolyzable foaming agent, in which the pyrolyzable foaming agent is uniformly dispersed in a molten resin to form a foam. It is an object of the present invention to provide a method for producing a foamable resin composition capable of obtaining a thermoplastic resin foam having a small variation in magnification and a smooth surface.

[0007]

The method for producing a foamable resin composition according to the present invention is to supply a thermoplastic resin to an extruder having a vent port to melt the thermoplastic resin, and to melt the thermoplastic resin from the middle of the extruder. , A solid pyrolyzable foaming agent having a decomposition temperature higher than the melting point of the thermoplastic resin is dissolved in an organic solvent having a boiling point lower than the decomposition temperature of the foaming agent, and the solution is press-fitted to melt the resin. It is characterized in that the organic solvent is removed from the vent port while kneading and extruded from the extruder, whereby the above object can be achieved.

The thermoplastic resin used in the present invention is not particularly limited. For example, low density polyethylene, high density polyethylene, polypropylene, polybutene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer. Olefin resin such as polymer, polyvinyl chloride, vinyl chloride copolymer such as vinyl chloride-vinyl acetate copolymer, polyacrylic acid,
An acrylic resin such as polymethylmethacrylate may be used.

These thermoplastic resins are used in the form of pellets or powder, supplied from a raw material hopper to an extruder, and melted by heating by an extrusion cylinder and rotation of an extrusion screw. The extruder may be either a single screw or a twin screw as long as it has a vent port. The number of vent ports is not particularly limited, but a large number is preferable for complete removal of the organic solvent, and more preferably 3
It is preferable to have one or more.

From the foaming agent injection port provided in the middle of the extrusion cylinder of the extruder or the foaming agent injection hole provided so as to pass through the inside of the extrusion screw and open in the middle thereof, solid thermal decomposition is performed. A solution obtained by dissolving the mold blowing agent in a specific organic solvent is pressed into the molten resin.

The solid pyrolytic foaming agent is not particularly limited as long as it is a solid one in a normal use state and has a decomposition temperature higher than the melting point of the thermoplastic resin. Examples thereof include azodicarbonamide, N, N′-dinitrosopentamethylenetetramine, p, p′-oxybis (benzenesulfonylhydrazide), p-toluenesulfonylhydrazide and p-toluenesulfonylsemicarbazide.

In the present invention, the melting point of the thermoplastic resin means the endothermic peak temperature measured by DSC (differential scanning calorimeter), and the decomposition temperature of the thermal decomposition type foaming agent has a half-life of 1 minute. Is the temperature at which

The solution of the solid pyrolyzable foaming agent is prepared by dissolving the above foaming agent in an organic solvent. As the organic solvent, generally, an organic solvent having a boiling point lower than the decomposition temperature of the solid thermal decomposition type foaming agent used is used, and the concentration of the foaming agent is 3% by weight or more, and the foaming agent is completely dissolved. It is preferable to adjust the concentration. In the present invention, the boiling point means the boiling point under reduced pressure at the vent port.

If the concentration of the heat-decomposable foaming agent is too low, the amount of the organic solvent will increase, and this organic solvent will remain in the foamable resin composition or the foam and become soft and easily deformed.
Further, the higher the temperature, the higher the solubility of the pyrolytic foaming agent, so it is preferable to prepare and use the solid solution of the pyrolytic foaming agent at a high temperature.

When azodicarbonamide (decomposition temperature of 210 ° C.) is used as the thermal decomposition type foaming agent, dimethyl sulfoxide (boiling point at a reduced pressure of 30 mmHg of 7) is used as the organic solvent.
5 ° C.) is preferably used. By the way, about 3.9 g of azodicarbonamide is dissolved in 100 g of dimethyl sulfoxide at 20 ° C., and about 30 g is dissolved at 100 ° C.

When N, N'-dinitrosopentamethylenetetramine (decomposition temperature 205 ° C.) is used as the thermal decomposition type foaming agent, dimethylsulfoxide or dimethylformamide (boiling point 60 at a reduced pressure of 30 mmHg as an organic solvent is used.
(° C.) is preferably used. Incidentally, N, N′-dinitrosopentamethylenetetramine is dissolved in about 15.2 g in 100 g of dimethyl sulfoxide at 20 ° C. and about 9.3 g in 100 g of dimethylformamide at 20 ° C.

When p-toluenesulfonyl hydrazide (decomposition temperature: 111 ° C.) is used as the thermal decomposition type foaming agent,
Methanol (boiling point −15 ° C. at reduced pressure of 30 mmHg) is preferably used as the organic solvent. By the way, p-toluenesulfonyl hydrazide is 100 g of methanol at 20 ° C.
Dissolve about 8.42 g.

The amount of the solid pyrolyzable foaming agent solution to be pressed in varies depending on the kind of the thermoplastic resin and the desired expansion ratio, but in general, the solid pyrolysis is based on 100 parts by weight of the thermoplastic resin. The solution is pressed in such that the mold blowing agent is contained in the range of 5 to 30 parts by weight.

In the present invention, the molten resin in which the solution obtained by dissolving the above solid pyrolytic foaming agent in an organic solvent is pressed is further melt-kneaded and the organic solvent is removed from the vent port. A foamable resin composition is produced by extrusion from a sushi extruder. If necessary, the resin constituting this expandable resin composition is crosslinked, and then the heat-decomposable foaming agent is pyrolyzed by heating to foam the resin, and the expansion ratio is small and the surface is smooth. Is obtained.

The organic solvent is removed under reduced pressure from the vent port of the extruder. To improve the accuracy of removing the organic solvent,
The degree of reduced pressure is preferably 60 mmHg or less.

As a method of crosslinking the resin constituting the foamable resin composition, a method of irradiating the foamable resin composition with ionizing radiation such as an electron beam to crosslink the resin is preferably adopted. In this case, a crosslinking aid composed of a polyfunctional monomer such as divinylbenzene is used if necessary. Other,
A method of crosslinking the resin with a crosslinking agent such as an organic peroxide is also adopted. Such a crosslinking method is widely known.

[0022]

When a foamable resin composition is produced by using a solid pyrolyzable foaming agent, solid pyrolyzed foam is formed in the molten thermoplastic resin from the middle of the extruder as in the present invention. When the solution of the agent is pressed in, the solid pyrolyzable foaming agent is in a solution state, so that the foaming agent is uniformly dispersed in the molten resin, and as a result, the resin is uniformly foamed.

[0023]

EXAMPLES Examples and comparative examples of the present invention will be shown below. Example 1 FIG. 1 is a flow sheet showing an example of a method for producing a foamable resin composition of the present invention. In FIG. 1, propylene-
Resin mixture (7) prepared by mixing 100 parts by weight of ethylene block copolymer resin (MS630: manufactured by Tokuyama Soda Co., Ltd., melting point: 163 ° C.) with 2 parts by weight of divinylbenzene as a crosslinking aid,
The first half is maintained at 200 ℃, and the solution inlet is 190 ℃
Was fed to the raw material supply port of the extruder (1) from the raw material hopper (2) of the single-screw extruder (1) having five vent ports (3) held in the extruder, and the resin was melt-kneaded in the extruder. .

From the solution inlet of the extruder (1),
A solution of azodicarbonamide (decomposition temperature 210 ° C.) in dimethyl sulfoxide (boiling point 75 ° C. at a reduced pressure of 30 mmHg) (concentration 20% by weight) (6) was added at a ratio of 50 parts by weight to 100 parts by weight of the resin (5 ) By using a vacuum pump (4) to remove dimethylsulfoxide from five vent ports (3) at a pressure reduction degree of 30 mmHg while extruding from an extruder (1) while further press-fitting into molten resin and further kneading. The thickness is 2 by continuously extruding in sheet form at the amount of 100 kg / hr.
mm foamable resin composition sheet (8) was produced.

Thereafter, both sides of the foamable resin composition sheet (8) are irradiated with an electron beam of 6 Mrad (accelerating voltage 600 KV) to crosslink the resin, and the crosslinked foamable resin composition sheet is heated at 230 ° C. The resin was foamed by heating to a temperature to produce a foam.

The surface of this foam was smooth and beautiful.
Further, when the expansion ratio of this foam was measured every 10 m in the length direction, the average expansion ratio was 20.2 times and the standard deviation was 0.80, and the dispersion of the expansion ratio was very small.

Example 2 In FIG. 1, a resin (7) made of polyethylene (YK-60: manufactured by Mitsubishi Petrochemical Co., Ltd., melting point 114 ° C.) was used as a unit having five vent ports (3) held at 180 ° C. The resin was supplied from the raw material hopper (2) of the axial extruder (1) to the raw material supply port of the extruder (1), and the resin was melt-kneaded in the extruder.

From the solution inlet of the extruder (1),
N, N'-dinitrosopentamethylenetetramine (decomposition temperature 205 ° C) dimethylformamide (pressure reduction degree 30 mm
Boiling point in Hg 60 ° C) Solution (concentration 11.1% by weight)
(6) was supplied at a ratio of 67.5 parts by weight with respect to 100 parts by weight of the resin using the press-fitting machine (5), and was pressed into the molten resin for further melt-kneading, and the degree of pressure reduction by the vacuum pump (4). Extrusion amount 100 k from extruder (1) while removing dimethylformamide from 5 vent ports (3) at 30 mmHg
A foamable resin composition sheet 8 having a thickness of 2 mm was formed by continuously extruding in a sheet form at g / hr.

Then, an electron beam of 6 Mrad (acceleration voltage 600 K) was applied to both surfaces of the foamable resin composition sheet 8.
V) was irradiated to crosslink the resin, and the crosslinked expandable resin composition sheet was heated to a temperature of 230 ° C. to foam the resin to produce a foam.

The surface of this foam was smooth and beautiful.
Further, when the expansion ratio of this foam was measured every 10 m in the length direction, the average expansion ratio was 15.1 times and the standard deviation was 0.84, and the dispersion of the expansion ratio was very small.

Comparative Example 1 In FIG. 1, 100 parts by weight of a propylene-ethylene block copolymer (MS630: manufactured by Tokuyama Soda Co., Ltd.), 2 parts by weight of divinylbenzene as a crosslinking aid, and azodicarbonamide powder (Uniform AZ-HM: Otsuka). 10 parts by weight of a chemical composition) was uniformly mixed with a tumbler for 20 minutes to supply a resin mixture (7) from a raw material hopper of the extruder (1) to a raw material supply port of the extruder (1), and then the extruder. No solution of the foaming agent was press-fitted from the solution inlet of (1). Other than that was performed like Example 1.

In this case, the dispersion state of the foaming agent powder was uneven in the raw material hopper, and the foaming agent powder adhered to the inner wall of the raw material hopper. Further, when the expansion ratio of the obtained foam was measured every 10 m in the length direction, the average expansion ratio was 20.1 times and the standard deviation was 3.9, and the dispersion of the expansion ratio was very large. .

In order to improve the uneven distribution of the foaming agent powder and to improve the adhesion to the inner wall of the raw material hopper,
The mixture in the raw material hopper was stirred, and the raw material hopper was further vibrated, but the variation in the expansion ratio was the same as above, and there was not much effect.

[0034]

As described above, according to the present invention, a thermoplastic resin is supplied to an extruder having a vent port and melted, and the melting point of the thermoplastic resin is higher than the melting point of the thermoplastic resin from the middle of the extruder. A solid pyrolyzable foaming agent having a decomposition temperature is dissolved in an organic solvent having a boiling point lower than the decomposition temperature of the foaming agent to obtain a solution, which is press-fitted, and an organic solvent is melted and kneaded from the vent port while the resin is melted and kneaded. A foaming resin composition is produced by removing and extruding from an extruder, whereby a foaming agent is uniformly dispersed in a molten resin, and there is little variation in expansion ratio, and a foam with a smooth surface can be obtained. it can.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of a method for producing a foamable resin composition of the present invention.

[Explanation of symbols]

 1 Extruder 2 Raw Material Hopper 3 Vent Port 4 Vacuum Pump 5 Pressing Machine 6 Foaming Agent Solution 7 Resin or Resin Blend Resin 8 Foaming Resin Composition Sheet

Claims (1)

[Claims] 1. A thermoplastic resin is supplied to an extruder having a vent and melted, and a solid heat having a decomposition temperature higher than the melting point of the thermoplastic resin is contained in the molten resin from the middle of the extruder. Dissolving the decomposing type foaming agent in an organic solvent having a boiling point lower than the decomposition temperature of this foaming agent, press-fitting the solution, extruding from the extruder by removing the organic solvent from the vent while melting and kneading the resin. A method for producing a foamable resin composition, comprising: