JPH0686087B2 - Manufacturing method of polypropylene foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polypropylene foam.

(Prior art and its problems) Conventionally, polypropylene, a gas such as nitrogen and carbon dioxide, a hydrocarbon such as propane and butane, and a foaming agent of a volatile liquid such as fluorocarbon are pressed into an extruder and kneaded. Techniques for extrusion foaming are known. However, using these foaming agents, advanced technology is required to produce highly expanded polypropylene having uniform fine cells with a foaming degree of several times to several tens of times and an appearance, and particularly temperature and viscosity during extrusion foaming. Since it is extremely difficult to control, it has not been industrially successful.

Polypropylene has a larger viscosity change with temperature than polyethylene and the like, and it is difficult to maintain the viscosity within an appropriate range for obtaining a foam having closed cells. It is possible to improve the properties of this polypropylene by mixing other resins, but in this case, the excellent properties of polypropylene itself,
For example, heat resistance is deteriorated.

Japanese Unexamined Patent Publication (Kokai) No. 57-24221 discloses a method in which polypropylene is lightly cross-linked (gel fraction 60% or less) and extruded. In this case, the presence of the gel component causes a large heat generation in the extruder. Therefore, there is a drawback that the foaming suitable temperature cannot be obtained and a good foam cannot be obtained, or the extrusion rate is extremely limited. In order to avoid this even a little, it was necessary to add a cooling device such as a large separate extruder designed to have a very large cooling capacity to the above-mentioned extruder. It was also inconvenient to make a thin film-shaped product or a modified product having a narrow nozzle. There is also a drawback that extrudates are liable to have lumps and melt fractures.

(Object of the Invention) The present invention is a polypropylene foam without the above-mentioned drawbacks,
In particular, it provides a method for producing a polypropylene foam having an expansion ratio of 1.5 to 60 times.

(Structure / Effect of Invention) That is, the present invention has an MFI (melt flow index) of 0.5 to
A polypropylene resin containing 10 parts by weight of 0.005 to 2.0 parts by weight of a main chain scission inhibitor which is a quinone dioxime compound is mixed and supplied to the extruder, and 0.025 to 0.5 parts by weight of peroxide is added from the middle of the extruder. A method for producing a polypropylene extruded foam, which comprises extruding and foaming with a foaming agent having a gel fraction of substantially 0%.

The polypropylene used in the present invention has an MFI (melt flow index) of 0.5 to 10, preferably 1 to 5. When the MFI exceeds 10, the addition of peroxide in an amount substantially suppressed to 0% gel content is still insufficient in improving the foamability, and excess peroxide is added to detect the gel content. If it becomes so much, the extrudate will appear as spots and streaky unevenness, and a satisfactory foam cannot be obtained. If the MFI is less than 0.5, the intrinsic melt viscosity of the resin is large, it is difficult to carry out uniform kneading and reaction with the press-in peroxide, and it is difficult to cool to the proper foaming temperature. Expensive equipment is required.

As mentioned above, polypropylene is difficult to adjust to a viscosity suitable for forming a foam. In the present invention, a main chain scission inhibitor is used to keep the gel fraction at substantially 0% to facilitate viscosity adjustment.

Usually, when a radical is generated by adding a peroxide to plastics, there are two types of plastics that crosslink and ones that collapse, and polypropylene belongs to a type that disintegrates. Therefore, even if a peroxide is added and reacted without adding the main chain scission inhibitor, the main chain scission of polypropylene occurs, resulting in a low molecular weight and a starch syrup shape. The main chain scission inhibitor of the present invention means one that suppresses the main chain scission reaction and enhances the crosslinking efficiency.

Examples of the main chain cleavage inhibitor premixed with the polypropylene resin include polyfunctional monomers such as triallyl cyanurate, triallyl isocyanurate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene and diallyl phthalate. Can monofunctional monomers such as vinyltoluene, ethylvinylbenzene and the like; oxime compounds and nitrone compounds such as quinonedioxime and benzoquinonedioxime; maleimide compounds such as N, Nm-phenylene bismaleimide and the like be used? Among them, quinone dioxime compounds such as quinone dioxime, benzoquinone dioxime and p, p'-dibenzoylquinone dioxime can be used particularly effectively. Also, hydroquinone diacrylate, p, p'-bis (methacryloyloxy) phenyl ether, p, p'-bis (acryloyloxy) benzophenone, 1,4-bis (methacryloyloxy) cyclohexane, p, p'-bis (allyloxy) )
Phenyl ether, diallyl butene tricarboxylate, triallyl trimellitate, bis (β-acryloyloxyethyl) adipate and the like can also be preferably used.

The amount of the main chain breaking inhibitor is usually polypropylene resin 10
0 to 0 parts by weight, 0.05 to 2.0 parts by weight, preferably 0.05 to 1.
0 parts by weight is suitable. If the amount exceeds 2 parts by weight, the amount exceeds the amount required for the reaction of the present invention, and the inhibitor does not have sufficient compatibility with the polypropylene resin, resulting in poor dispersion and appearing as fine lumps in the foam, impairing the appearance. Has drawbacks such as
If the amount is less than 0.05 parts by weight, the polypropylene resin will have a low molecular weight and will have a starch syrup shape.

As the foaming agent of the present invention, a gas such as nitrogen gas or helium,
A volatile liquid such as fluorocarbon or propanebutane and a foaming agent that generates a gas by thermal decomposition of strontium azodicarboxylate or hydrazodicarbonamide can be used. The liquid foaming agent is the most suitable for the present invention, because it has the advantages of cooling polypropylene at the same time as it is pressed into polypropylene, and having the effect of plasticizing polypropylene to reduce the viscosity and facilitate uniform dissolution. .

In the present invention, the peroxide is injected from the middle of the extruder, but preferably has the following characteristics.

Effective in crosslinking polypropylene.

To make a uniform dispersion with the volatile blowing agent or solvent to be diluted. Desirably, it should be compatible with the solvent to be diluted.

In order to carry out a stable and uniform reaction, the one-minute half-life temperature must not be lower than 15 ℃ below the melting point of polypropylene. Desirably, the temperature is equal to or higher than the melting point of polypropylene.

In particular, for the injection of peroxide as a crosslinking agent, in order to stably supply a small amount of peroxide necessary for the present invention from the middle of the extruder, and to make the reaction more gradual by dilution, It is necessary in order to make the mixing of the resin and the peroxide uniform, and of course the effect of stabilizing the unstable peroxide by dilution can be expected. Relates to dispersion of crosslinking points, which is an important condition in the present invention. That is, the peroxide is usually diluted and then injected under pressure in the middle of the extruder, but as a guide for the crosslinking reaction time by the peroxide, it is set to 5 to 10 times the half-life. The temperature of the polypropylene melt at the position where the peroxide is press-fitted in the middle of the extruder is higher than the melting point of polypropylene, and the reaction time is generally long because of dilution injection, but the peroxide with a low 1-minute half-life temperature is used. (Peroxide with low decomposition temperature)
Then, it reacts almost instantly, and the efficiency of crosslinking decreases, or mixing with the resin is insufficient and intensive crosslinking occurs. Therefore, the effect of the present invention cannot be obtained. Further, at the time of press-fitting, there is a possibility that a decomposition reaction has occurred before the press-fitting. By using a peroxide having a high one-minute half-life temperature, stable press-fitting and the time required for kneading are secured, and uniform dispersion of crosslinking points can be expected, so that the effects of the present invention can be obtained. is there.

Examples of the peroxide include various ones. For example, when the melting point of polypropylene is 165 ° C., dicumyl peroxide (DCP), t-butyl cumyl peroxide,
Di-t-butyl peroxide, 2,5-dimethyl-2,5-
(T-Butyl peroxide) hexane, 2,5-dimethyl-2,5-di (t-butyl peroxide) hexane, 1,3-
Di- (t-butyl peroxide isopropyl) benzene etc. are mentioned.

If the main chain scission inhibitor is a quinone dioxime compound, the amount of peroxide used is 0.1 to 1 times the amount used, and 0.005 to 2.0 per 100 parts by weight of polypropylene.
Weight part, preferably 0.025 to 0.5 weight part is preferable. 0.00
If it is less than 5 parts by weight, an appropriate crosslinking reaction does not occur. If the amount exceeds 2.0 parts by weight, the crosslinking reaction occurs beyond the limit necessary for the present invention to form a gel, appear as lumps in the foam, and have a drawback such as an extrusion obstacle such as a decrease in extrusion amount. Have.

In the present invention, polypropylene foam is produced by the following method: MFI 0.5 to 10 polypropylene resin 100
Premixed with 0.05 to 2.0 parts by weight of main chain scission inhibitor (limited quinonedioxime type compound) per part by weight, and supplied to the extruder, and 0.1 to 1.0 culture amount of peroxide for the main chain scission inhibitor. A substance (having a one-minute half-life temperature higher than the melting point of polypropylene) is dissolved in an easily volatile foaming agent having a boiling point of 100 ° C. or lower, and injected from the middle of the extruder. Alternatively, if the easily volatile foaming agent used does not dissolve the existing peroxide, a part of the easily volatile foaming agent that already dissolves the peroxide is used together and injected into the extruder. After kneading, decomposition of peroxide, and reaction, the mixture was extruded from a mold attached to the end of the extruder, and the gel fraction (hot toluene method) was substantially 0.
% Polypropylene polypropylene is obtained.

In the present invention, the gelation rate of polypropylene (hot toluene method)
It is kept substantially at 0%. By reducing the gel fraction to substantially 0%, the amount of extrusion decreases little, and there are no other problems in extrusion.
Greatly improves foamability.

In the hot toluene method for measuring the gel fraction, specifically, a sample is dissolved in toluene in a Soxhlet extractor (or flask) at 110 ° C. for 5 hours, and this is filtered through a wire mesh of 80 mesh. The wire net to which the gel is attached is dried under reduced pressure at 110 ° C. for 2 hours. Next, the wire net is dried with a desiccator for 30 minutes, and then the weight is precisely measured. Next, put in the following formula and calculate.

(Example) The present invention will be described in more detail.

Example 1 As a polypropylene resin, Sumitomo Noblen H501 (MFI =
3.5) For 100 parts by weight, p, p'-
Dibenzoylquinone dioxime (Kawaguchi Chemical "Actor D
Q ") was added to 0.3 part by weight and 0.5 part of talc as a nucleating agent and well stirred (2) was fed to the hopper (1) of the single extruder (3) shown in FIG. 1 (see FIG. 1). The diameter of the cylinder of the extruder was 65 mm, and the length was 35 times the diameter.).

The temperature of the die (5) of the extruder (3) was set to 150 ° C. From the pressure inlet (4) into the melt where the resin and the additives are sufficiently kneaded through the melting part, 1.5 parts by weight of butane as a foaming agent and a one-minute half-life temperature of the composition is about 193 ° C.
1.0 parts by weight of a 10 wt% ethanol solution of 2,5-dimethyl-2,5-di (t-butylperoxy) hexin-3 (NOF Perhexin 25B) (0.1 parts by weight as a peroxide amount) from (6) Press-fit, further knead thoroughly, let the reaction proceed,
When the foamable melt was cooled and extruded through a die having a slit of 0.5t × 190w, a foam having a density of 0.14 g / cc and a closed cell ratio of 50% or more was obtained. The closed cell ratio is ASTM
D2856 (measured with an air pycnometer.

Comparative Example 1 When extruding under the same conditions without adding the main chain scission suppressor in Example, a foam having a density of 0.8 g / cc and having almost open cells was obtained.

When extruding under the same conditions without adding the composition, violent cell breakage occurred near the die, resulting in an open-cell foam having a density of 0.6 g / cc.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. The symbols in the figure are as follows: (1) …… Bopper, (2) …… Polypropylene, a main chain scission inhibitor and a nucleating agent such as talc, and other materials pre-blended, (3) …… Extrusion Machine, (4) ... foaming agent, peroxide pressurizing port, (5) ... die.

Claims (4)

[Claims] 1. MFI (melt flow index) 0.5-10
A polypropylene resin having 100 parts by weight of 0.005 to 2.0 parts by weight of a main chain scission inhibitor which is a quinone dioxime compound is mixed and supplied to the extruder, and 0.025 to 0.5 parts by weight of peroxide is added from the middle of the extruder. A method for producing a polypropylene extruded foam, which comprises extruding and foaming with a foaming agent having a gel fraction of substantially 0%. 2. The method according to claim 1, wherein the one-minute half-life temperature of the peroxide is higher than the melting point of polypropylene. 3. The method according to claim 1, wherein the foaming agent is a volatile foaming agent. 4. The method according to claim 1, wherein a peroxide diluted with a foaming agent is added.