JPH06322167A - Production of polyolefinic resin foam - Google Patents

Abstract

PURPOSE:To obtain a polyolefinic resin foam having uniform and fine cells and a high ratio of closed cells expanded in high magnification by using an inexpensive inorganic gas free from environmental problems as a blowing agent. CONSTITUTION:100 pts.wt. of a polyolefinic resin (polyethylene or polypropylene) is mixed with an inorganic foam nucleus forming agent (talc) subjected to surface treatment with a coupling agent (silane-based coupling agent) to prepare a resin composition. The resin composition is fed to a vented extruder, melted and kneaded, an inorganic gas (carbon dioxide gas) is introduced under pressure as a blowing agent from the vent part of the extruder and the melted material is extruded and expanded from an extrusion spinneret to give the objective polyolefinic 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 polyolefin resin foam using an inorganic gas as a foaming agent.

[0002]

2. Description of the Related Art A foaming agent is usually used for producing a polyolefin resin foam. As the foaming agent, a thermal decomposition type organic foaming agent such as azodicarbonamide, a low boiling point organic solvent foaming agent such as pentane or dichlorodifluoroethane, and an inorganic gas foaming agent such as carbon dioxide and nitrogen are used.

When a thermal decomposition type organic foaming agent is used, since the foaming agent contains decomposition residues of the foaming agent, discoloration or odor occurs in the foam and the quality deteriorates. When using a low boiling organic solvent blowing agent, there are environmental problems such as explosion risk and ozone layer depletion. The use of an inorganic gas foaming agent is preferable because it does not cause the above problems and is inexpensive.

However, in the case of extruding and foaming a polyolefin resin using an inorganic gas as a foaming agent, the compatibility of the inorganic gas with the resin is poor and the inorganic gas is quickly separated from the resin during foaming,
Therefore, it is difficult to have uniform and fine air bubbles and to foam at a high magnification (for example, 10 times or more).

In order to generate uniform and fine bubbles, bubble nucleating agents such as calcium carbonate and talc are usually used. Of course, the viscoelasticity of the resin and the press-fit amount of the inorganic gas are also adjusted (for example, see Japanese Patent Publication No. 60-41818).

[0006]

[Problems to be Solved by the Invention]

However, the inorganic gas does not act to remove the latent heat of vaporization from the resin during the foaming of the resin to fix the bubbles. Further, if a large amount of the bubble nucleating agent is used, the elongation of the resin will deteriorate. Therefore, if the inorganic gas is injected into the resin at a high pressure to obtain a high magnification, the bubbles tend to break,
The expansion ratio is at most about 8 times, and it is not easy to expand to a higher expansion ratio.

The present invention is intended to solve the above problems. An object of the present invention is to use an inorganic gas such as carbon dioxide gas as a foaming agent and to make a polyolefin resin have uniform and fine cells and independent cells. It is intended to provide a method for producing a polyolefin resin foam, which has a high rate and can be easily foamed at a high magnification.

[0009]

The polyolefin resin used in the present invention includes polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate. Examples thereof include copolymers, ethylene-propylene-diene copolymers, chlorinated polyethylene, polybutene, polymethylpentene and the like.

These polyolefin resins are JIS
Melt Idex (MI) by K 7210
It is preferably 0.05 to 20. If the MI of the resin is too low, the melt viscosity becomes too high to obtain a high-magnification foam, and the load on the extruder increases, making extrusion difficult. On the other hand, if the MI is too high, the viscosity against the elongation of the resin at the time of foaming is low and the cells are easily broken, so that a foam having a high magnification cannot be obtained.

Among these polyolefin resins,
In particular, polypropylene resins (polypropylene and propylene copolymer) are preferable because they have excellent heat resistance and mechanical strength. Among them, polypropylene resin having long chain branch is preferable.

The polypropylene resin having a long chain branch has a higher melt tension (elongation viscosity) than a conventional polypropylene resin having no long chain branch. Therefore, when a polypropylene resin having such a long-chain branch is used, the viscosity, tension, and elongation at the time of melting are suitable for foaming, and the suitable foaming temperature range is widened.

Particularly, in a polypropylene resin having a long chain branch, the elongation strain rate is 0.01 to 1.0 (s ^-1 ).
Amount of elongation strain A at any two points that can be measured within the range of
Melt elongation viscosity η _A (Pa ·
s), the maximum value of the ratio of η _B (Pa · s) is η _B / η _A =
3.0-100, and B / A = 10, A = 0.1-1.
Those of 0 are preferred.

Incidentally, η _B / η _A of a conventional polypropylene resin having no long-chain branch is generally 2.0 or less.
The melt elongational viscosity of the resin can be easily measured by using a commercially available melt elongational viscometer (for example, a melten rheometer manufactured by Toyo Seiki Co., Ltd.).

In the present invention, first, a resin composition is prepared by mixing the above polyolefin resin with an inorganic cell nucleating agent surface-treated with a coupling agent. Here, as the inorganic cell nucleating agent, an inorganic cell nucleating agent which has been conventionally used for producing a foam is used.

Examples of these cell nucleating agents include talc,
Calcium carbonate, clay, kaolin, mica, magnesium oxide, zinc oxide, carbon black, glass, quartz,
Examples thereof include silica, alumina, novaculite, hydrated alumina, wollastonite, iron, iron oxide, silicon dioxide and titanium oxide.

The average particle size of these cell nucleating agents is preferably 0.1 to 500 μm, more preferably 1 to 500 μm.
It is 100 μm. If the average particle size is too large, the foam size of the resulting foam will be coarse, and the surface smoothness and heat insulating properties will decrease. Conversely, if the average particle size is too small, it will be difficult to uniformly disperse the resin in the resin. A foam having uniform fine cells cannot be obtained.

As the coupling agent for treating the surface of the bubble nucleation agent, a silane coupling agent or a titanate titanium coupling agent is mainly used. In addition, an aluminum coupling agent or a zirconia coupling agent is used. Agents and the like can also be used.

These coupling agents have a group having a reactivity or affinity with an inorganic substance and a group having a reactivity or affinity with an organic substance in the molecule. In particular, the group having reactivity or affinity with an inorganic substance is preferably an alkoxy group or a hydroxyl group, and the group having reactivity or affinity with an organic substance is a vinyl group, a phenyl group, an alkyl group or (meth) acryl. A group is preferable, and a glycidyl group, an amino group, a mercapto group and the like may be further present in these groups.

Examples of silane coupling agents include 3-
[N-allyl-N (2-aminoethyl)] aminopropyltrimethoxysilane, 3- [N-allyl-N-glycidyl) aminopropyltrimethoxysilane, 3- [N-
Allyl-N-methacryl) aminopropyltrimethoxysilane, p- [N- (2-aminoethyl) aminomethyl] phenethyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, 3
-Aminopropyltriethoxysilane, N, N-bis [(methyldimethoxysilyl) propyl] amine, N,
N-bis [3- (methyldimethoxysilyl) propyl]
Ethylenediamine, N, N-bis [(methyldimethoxysilyl) propyl] methacrylamide, N, N-bis [3- (trimethoxysilyl) propyl] amine, N,
N-bis [3- (trimethoxysilyl) propyl] ethylenediamine, N, N-bis [3- (trimethoxysilyl) propyl] methacrylamide, cyclohexylmethyldimethoxysilane, 3- (N, N-diglycidyl) aminopropyltri Methoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, dimethylethoxysilane, dimethylvinylethoxysilane, dimethylvinylmethoxysilane, diphenyldiethoxysilane, diphenyldimethoxysilane, diphenylsilanediol,
N-glycidyl-N, N-bis [3- (methyldimethoxysilyl) propyl] amine, N-glycidyl-N, N
-Bis [3- (trimethoxysilyl) propyl] amine, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, hexyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-methacryl Roxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, methyltrimethoxysilane, methyldiethoxysilane, methyldimethoxysilane, methyltris (dimethylsiloxy) silane, methylvinyldiethoxysilane, methylvinyldimethoxysilane, octadecylmethyldimethoxy Silane, octadecyltriethoxysilane, octadecyltrimethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, N-
[(3-Trimethoxysilyl) propyl] diethylenetriamine, N-[(3-trimethoxysilyl) propyl] triethylenetetramine, N-3-trimethoxysilylpropyl-m-phenylenediamine, trimethylsilylvinylbicyclo [2.2. 1] Heplan, trimethylmethoxysilane, triphenylethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, vinyltrimethoxysilane, β-
Examples include (3,4-epoxycyclohexyl) ethyltrimethoxysilane.

Examples of titanate coupling agents are isopropyl triisostearoyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, isopropyl tri (N-aminoethyl-aminoethyl) titanate, tetraoctyl bis (ditridecyl phosphite) titanate. , Bis (dioctyl pyrophosphate) oxyacetate titanate, bis (dioctyl pyrophosphate) ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryl isostearoyl titanate, isopropyl tridodecyl benzene sulfonyl titanate, isopropyl isostearoyl diacrylic titanate, isopropyl tri ( Dioctyl phosphate) titanate, isopropyl tricumyl Eniruchitaneto, tetraisopropyl bis (dioctyl phosphite) titanate.

Examples of aluminum-based coupling agents include acetoalkoxyaluminum diisopropylate and the like.

To treat the surface of the bubble nucleation agent with a coupling agent, for example, the coupling agent is dissolved in water or an organic solvent such as alcohol, hexane or toluene, and the coupling agent solution and bubble nucleation are formed. A method of removing water or an organic solvent by mixing and stirring the agent with a Henschel mixer or a super mixer and then heating and drying is employed.

In addition, while the cell nucleating agent is forcibly stirred by a V blender, the coupling agent solution is sprayed with dry air or nitrogen gas, or when the cell nucleating agent is heated and coupled at a high temperature. A method of spraying the agent solution can also be adopted.

In this case, it is preferable that the surface treatment is carried out at a ratio of 0.1 to 10 parts by weight of the coupling agent to 100 parts by weight of the cell nucleating agent. If the surface treatment amount of the coupling agent is too small, the surface of the cell nucleating agent will be incompletely treated,
The affinity between the resin and the cell nucleating agent is inferior, and gas is often released during extrusion foaming, making it difficult to foam at a high ratio. On the contrary, if the surface treatment amount of the coupling agent is too large,
This is wasteful because the effect proportional to the amount of surface treatment does not increase.

It is preferable that the inorganic cell nucleating agent surface-treated with the above coupling agent is contained in an amount of 0.01 to 10 parts by weight with respect to 100 parts by weight of the polyolefin resin. When the content of the surface treated cell nucleating agent is too small, the cells of the resulting foam become coarse,
On the other hand, if the content of the surface-treated bubble nucleating agent is too large, the elongation of the resin at the time of foaming will be poor and the cells will be easily broken,
It becomes difficult to foam at a high magnification.

Next, a resin composition containing a surface-treated cell nucleus forming agent in a polyolefin resin is extruded and foamed by using an inorganic gas as a foaming agent. A vent type extruder is generally used for extrusion foaming of a resin composition, and an inorganic gas is press-fitted as a foaming agent into the melt-kneaded resin composition in the extruder from a vent portion of the extruder.

In addition, a method in which the raw material supply port of the extruder is closed and the inorganic gas is pressed into the resin through the raw material supply port, or an extrusion screw having a hole is used, and the inorganic gas is pressed into the resin through the hole. It is also possible to adopt a method of doing so.

As the inorganic gas as a foaming agent, a single gas such as carbon dioxide gas, nitrogen, air, oxygen, neon, argon or a mixed gas is used. In particular, since carbon dioxide has a high solubility in polyolefin resin, carbon dioxide or an inorganic gas containing carbon dioxide is suitable as the foaming agent.

The use amount (press-fit amount) of these inorganic gases is
It depends on the type of inorganic gas, the type of polyolefin resin, and the desired expansion ratio, but generally, the reading of the pressure gauge attached to the injection part of the extruder shows that the press-fitting pressure is 25 to 150 k.
It is press-fitted in the range of g / cm ² .

When the amount of the inorganic gas used is too small, the gas expansion pressure at the time of foaming is small and a foam having uniform and fine bubbles cannot be obtained. On the other hand, if the amount of the inorganic gas used is too large, the expansion pressure of the gas at the time of foaming increases, the bubble film ruptures, the surface property deteriorates, and a high-magnification foam cannot be obtained.

The molten resin composition into which the inorganic gas is pressed is continuously extruded into a desired shape from the die of the extrusion die attached to the tip of the extruder, and the pressure is released to release the resin composition. Foaming takes place. The shape of the die of the extrusion die is generally similar to the shape of the target foam.

The temperature of the resin composition extruded from the die die is preferably adjusted within the range of the melting point of the resin ± 10 ° C. If the temperature of the resin composition is too low, it is difficult to extrude the resin viscosity is too high, conversely, if the temperature of the resin composition is too high, the viscoelasticity of the resin becomes low and foam breakage easily occurs, It becomes difficult to foam at a high magnification.

In this way, the resin composition extruded from the extrusion die satisfactorily foams, and a closed-cell polyolefin resin having uniform and fine cells and having a high expansion ratio is produced. The foam of the resin composition extruded from the extrusion die is preferably cooled with water, cold air, or the like in order to maintain its shape in good condition.

If necessary, additives such as flame retardants, fillers, antioxidants, flame retardants, pigments, etc. may be added to the polyolefin resin as long as the effects of the present invention are not impaired. Good. Such additives are widely known.

For example, as the flame retardant, a brominated flame retardant such as hexabromobiphenol ether or decabromodiphenyl ether, a phosphorus-containing flame retardant such as ammonium polyphosphate, trimethyl phosphate, triethyl phosphate, a melamine derivative, an inorganic flame retardant, etc. There is.

[0037]

[Function] When the polyolefin-based resin, the inorganic cell nucleating agent surface-treated with the coupling agent, and the inorganic gas are supplied to the extruder and foamed, the affinity between the resin and the coupling agent increases, and the inorganic gas Fast separation from resin is suppressed.

Therefore, even if the bubble nucleating agent is used to generate uniform and fine bubbles, the proportion of the inorganic gas escaping from the resin before contributing to the foaming is small, and a small amount of the bubble nucleating agent is used. As a result, uniform and fine bubbles are generated, and the inorganic gas is efficiently used for foaming the resin, so that the resin is foamed at a high magnification.

[0039]

EXAMPLES Examples and comparative examples of the present invention will be shown below. Example 1 1 part by weight of 3-methacryloxypropyltrimethoxysilane was added to 3 parts by weight of a mixed solution of ethanol and water (containing 80% by weight of ethanol) and mixed to prepare a silane coupling agent solution.

100 parts by weight of talc having an average particle size of 9 μm (MS: manufactured by Nippon Talc Co., Ltd.) was put into a super mixer and stirred, and 4 parts by weight of the above-mentioned silane coupling agent solution was divided into several parts for several minutes. , And stir in the super mixer for another 7 minutes, then remove to a tray for 150
It dried at 1 degreeC for 1 hour, and produced the coupling agent processing talc A.

Low-density polyethylene A (MI2.8, melting point 112.5 ° C.) (Yukaron ZH51: manufactured by Mitsubishi Petrochemical Co., Ltd.) 1
A resin composition was prepared by mixing 0.6 part by weight of coupling agent-treated talc A with 100 parts by weight of the resin composition.
The resin composition was melt-kneaded in the extruder from a hopper of a vent type extruder (diameter 65 mm, L / D = 35) set at a temperature of 30 ° C., to the raw material supply port of the extruder.

Then, carbon dioxide gas was injected from the vent portion of the extruder at a pressure of 75 kg / cm ² , and this was melt-kneaded in the extruder, and subsequently 20 from the extrusion die with a diameter of 2 mm set at 108 ° C. Extrusion foaming was performed at an extrusion rate of kg / hr to continuously produce a rod-shaped foam.

The expansion ratio of the obtained foam is 22.5 cc /
g, closed cell ratio 79.5%, average cell diameter 400 μm
It was a foam having uniform fine cells and a high closed cell ratio, which was expanded at a high magnification. The closed cell ratio was measured using an air comparison type hydrometer 1000 (manufactured by Tokyo Science Co., Ltd.). The results are summarized in Table 1.

Example 2 In Example 1, low density polyethylene A (MI2.
8, melting point 112.5 ° C.) (Yukaron ZH51: manufactured by Mitsubishi Petrochemical Co., Ltd.) was changed to low density polyethylene B (MI 0.15, melting point 109 ° C.) (Yukaron ZC30: manufactured by Mitsubishi Petrochemical Co., Ltd.). Other than that was performed like Example 1. The results are summarized in Table 1.

Example 3 In Example 1, low density polyethylene A (MI2.
8, melting point 112.5 ° C) (Yukaron ZH51: manufactured by Mitsubishi Petrochemical Co., Ltd.) using polypropylene (MI4, melting point 169 ° C)
(Pro-fax PF814: manufactured by HIMONT, USA) was changed to 100 parts by weight. Other than that was performed like Example 1. The results are summarized in Table 1.

The above polypropylene has long-chain branching, and the measured values regarding the melt extensional viscosity were as follows. Elongation strain rate: 0.4 s ^-1 , Elongation strain amount A: 0.86,
Elongation strain amount B: 8.6, melt elongation viscosity η _A : 21544P
a · s, melt elongation viscosity η _B : 843190 Pa · s, η
_B / [eta] _A : 39.1. Here, the melt extensional viscosity was measured using a melten rheometer (manufactured by Toyo Seiki Co., Ltd.).

Example 4 Coupling agent-treated talc B was prepared by changing 3-methacryloxypropyltrimethoxysilane in Example 1 to vinyltris (2-methoxyethoxy) silane. Other than that was performed like Example 1. The results are summarized in Table 1.

Comparative Example 1 In Example 1, no talc A treated with a coupling agent was added. Other than that was performed like Example 1.
The results are summarized in Table 1.

Comparative Example 2 In Example 1, the talc A treated with the coupling agent was replaced with 0.6 part by weight of talc not surface-treated with the coupling agent (untreated talc). Other than that was performed like Example 1. The results are summarized in Table 1.

[0050]

[Table 1]

[0051]

As described above, according to the present invention, the polyolefin-based resin, the inorganic cell nucleating agent surface-treated with the coupling agent, and the inorganic gas are supplied to the extruder for foaming. The foamability of the resin due to the foaming agent is improved, and it is possible to easily obtain a polyolefin-based resin foam having uniform fine cells, high closed cell ratio, and high-foaming ratio.

Further, according to the present invention, since the inorganic gas is used as the foaming agent, it is inexpensive and does not cause the danger of explosion or environmental problems, and the obtained foam is free from discoloration or odor. The advantage is that there is no deterioration in quality.

According to the present invention, a long polyolefin resin foam having various shapes such as a film, a sheet, a board, a tube, and a rod can be obtained, and a heat insulating material, a cushioning material, a soundproofing material, a floating material, It can be used for a wide range of applications such as sealing materials.

Claims (1)

[Claims] 1. A method for producing a polyolefin resin foam, which comprises supplying an polyolefin-based resin, an inorganic cell nucleating agent surface-treated with a coupling agent, and an inorganic gas to an extruder for foaming.