JPS61283633A - Production of polyolefin foam - Google Patents

Abstract

PURPOSE:To produce the titled foam of a high expansion ratio, by placing and expanding a polyolefin-containing expandable composition in the primary mol and placing and expanding (secondary expansion) the obtained intermediate product in the secondary mold. CONSTITUTION:An expandable composition (A) is obtained by mixing and kneading a polyolefin (a) with a blowing agent (b) having decomposition temperature >= the melting temperature of component (a), a blowing aid (c) and a crosslinking agent having a decomposition temperature >= the flow initiation temperature of component (a) and/or a filler. This composition A is placed in a primary mold 1 comprising pressurized sealed container placed within a press 2 and its primary expansion to an expansion ratio of 2-7 is performed by heating for a definite time at an applied pressure while releasing the pressure to obtain an intermediate product B. This intermediate product B is placed in a secondary mold 3 comprising a heating container, heated for a definite time at normal pressure to decomposed the blowing agent remaining undecomposed and to effect its secondary expansion. The expanded product is heat-aged and cooled to obtain polyolefin foam C of a high expansion ratio >=40.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention particularly relates to a method for producing a polyolefin foam suitable for producing a foam with a high expansion ratio of 40 times or more.

(Prior art) Conventionally, as a method for obtaining polyolefin foam, a foaming mixture obtained by adding and kneading a blowing agent, a blowing aid, and a crosslinking agent to polyolefin is filled into a mold, and the mixture is sealed and held under constant pressure. The intermediate foam is molded by heating for a period of time, and the pressure is removed during high-temperature heating to leave 40 to 85% of the undecomposed blowing agent remaining, and then the intermediate foam is heated under normal pressure to foam the undecomposed blowing agent. A method for manufacturing a foam as a final product (Japanese Patent Publication No. 45-29381) has been proposed.

(Problems to be Solved by the Invention) In the above conventional manufacturing method, the blowing agent is
This method decomposes 60% of the foam and decomposes the undecomposed foaming agent in the secondary foaming process, but the decomposition rate of the foaming agent in the primary foaming of this method is 9 to 12 times when converted to a foaming ratio of 8. Become.

This method can produce a polyolefin foam with relatively uniform and fine cells when producing a polyolefin foam with a final expansion ratio of up to 30 times, but for example, when producing a foam with a final expansion ratio of 40 times or more, When the foaming agent is heated to a secondary foaming ratio of around 10 times, the internal heat storage of the decomposition heat of the blowing agent increases, and even after heating is stopped, the remaining foaming agent remains due to the internal heat storage. Due to the so-called runaway decomposition phenomenon, in which the decomposition of This has the disadvantage that the quality of the final product is unstable due to variations in the quality of the final product.

In addition, as in the conventional method described above, the foaming ratio (primary) is 10.
When the foaming internal pressure increases, the foaming composition filled in the mold leaks out in an extremely large amount.
Raw materials are wasted, which is uneconomical, and the foaming ratio may also be affected.

This invention was made in view of the above-mentioned points, and in particular,
Even when producing foam with a high expansion ratio of about 60 times,
- It is difficult for the blowing agent to decompose and run away after the next heating, making it easy and accurate to control the primary foaming ratio, with almost no leakage of the foaming composition outside the mold, and foaming with uniform and fine closed cells. The aim is to provide a manufacturing method that provides stable results.

(Means for Solving the Problems) The basic structure of the manufacturing method of the present invention is to suppress the primary foaming ratio to a range of 2 to 7 times (selected arbitrarily depending on the ratio of the final product and the cell diameter). The main points are as follows.

(Actions and Effects) According to the method for producing a polyolefin foam of the present invention,
The foaming agent is decomposed under pressure and heat in the primary foaming process, but because the pressure is applied, the decomposed gas is uniformly dispersed, and this becomes the cell nucleus of the final foam. In the process, the foaming ratio was suppressed to a range of 2 to 7 times, making the foaming ratio smaller than that in the conventional method, so leakage of the foamable composition as a raw material from the pressure-sealed mold was prevented, and In this step, the accumulation of heat of decomposition of the blowing agent and the uncontrollable runaway decomposition of the blowing agent (runaway decomposition phenomenon) are reliably prevented, and as shown in Examples 1 to 5 below, uniform decomposition is achieved. In addition, it has become possible to produce a foam that is 40 to 60 times larger and has fine cells.

In addition, in the above conventional method, the product thickness of the foam was 80 m.
However, according to the method of this invention, as shown in Example 6 below, the product thickness can be reduced to 12
It was possible to produce a foam product of 0fl. this is,
This increases the product thickness by 50% compared to the conventional method. Although this effect is not evident in the production of small thin samples of about 10 mm thickness at the experimental stage, it can be used in practical applications, for example, 10 mm thick.
This is noticeable when manufacturing a product with a size of 1 m x 2 m and a thickness of about 0.00 m. The reason why the product can be made so thick is that the primary expansion ratio, which is set to 2 to 7 times according to the present invention, is a very large factor.

On the other hand, as shown in Comparative Example 1 below, when trying to manufacture a foam product with a final magnification of 45 times, in the first step
When the foam is expanded to 1 times its original size, the blowing agent starts to decompose runaway immediately after the secondary foaming intermediate product is removed from the mold, making it virtually difficult to proceed to the secondary foaming process. Ta.

In addition, FIG. 1 shows a comparison diagram of the foaming process (a) according to the method of the present invention and the foaming process (b) according to the conventional method,
The diagram of the present invention (al is created based on Example 1 in which a foam with a final expansion ratio of 42 times is produced with the primary expansion ratio of 5 times, and in the diagram of the conventional method) is - It was created based on the expected expansion ratio when a foam with a final expansion ratio of 46 times is to be produced with the subsequent expansion ratio of 9.4 times, and the dotted line portion represents the decomposition runaway phenomenon.

In addition, in order to facilitate comparison with the conventional method described above, if the primary foaming ratio is converted to the decomposition rate of the blowing agent based on the relational expression below, Examples 1 to 6 described later are as shown in the table below. become.

(Relational expression〕 (Example) Examples of the manufacturing method of the present invention will be described in detail below.

First, FIGS. 2(a) to 2(e) are cross-sectional views schematically showing the manufacturing process. This is a secondary foaming process.

In the figure, 1 is a primary mold consisting of a pressurized airtight container in a press 2, and 3 is a secondary mold as a heating container. A steam pipe (not shown) for heating is installed. In addition, A is a foamable composition as a raw material, B is an intermediate product as a primary foam,
C indicates a product as a foam, and the foamable composition is obtained by kneading a polyolefin with a blowing agent, a foaming aid, a crosslinking agent, or a filler in addition to these.

Next, the polyolefin referred to in the present invention includes, for example, polyethylene produced by a commonly commercially available high-, medium-, or low-pressure method;
Ethylene-propylene copolymers, ethylene-propylene copolymers, ethylene and vinyl acetate, or ethylene and methyl, ethyl, propyl, and butyl acrylates containing up to 45%, or each of these (chlorine A crosslinking agent referred to in the present invention refers to a chlorinated product (up to a content of 60% by weight), a mixture of two or more of these, or a mixture of these and polypropylene. Organic peroxides that have a decomposition temperature higher than the flow initiation temperature, are decomposed by heating, generate free radicals, and are radical generators that create crosslinks between the molecules, such as organic peroxides. , alpha dicumyl peroxide, 2.
5. Biesterary butyl peroxide, 5. dimethyl hexane, ditertiary butyl perterephthalate, others 2.5 bisterary butyl, peroxy, 2.5 dimethyhexine, dibenzoyl peroxide, ditertiary butyl perterephthalate. Depending on the type of polyolefin used,
Since the optimal organic peroxide differs, it is necessary to select the optimal one each time.

The blowing agent referred to in the present invention is one having a decomposition temperature at least higher than the melting temperature of the polyolefin among commercially available normally solid blowing agents, such as dinitroso pentamethylene tetramine, a nitroso compound, Refers to sulfonyl semicarbazide compounds, pp' oxybisbenzene sulfonyl semicarbazide, P toluenesulfonyl semicarbazide, azo dicarbonamide of azo compounds, barium azo dicarboxylate, etc. .

The foaming aids used in the present invention include, depending on the type of foaming agent, for example, commercially available metal oxides such as zinc oxide and lead oxide, higher fatty acids such as stearic acid and salicylic acid, odonium stearate, and stearic acid. It refers to metal salts of higher fatty acids such as zinc, or compounds whose main component is urea. By selecting an appropriate foaming aid from among these and combining it with a foaming agent in an appropriate ratio, its decomposition temperature can be adjusted. can be adjusted arbitrarily. In addition, zinc oxide is preferable as a foaming aid when azodicarbonamide is used as a foaming agent. This is because it is difficult to control the decomposition rate of the blowing agent with a urea-based blowing aid.

For the purpose of improving the physical properties or lowering the price of the composition used in the present invention, fillers that do not have a significant adverse effect on crosslinking, such as carbonates such as magnesium carbonate and calcium carbonate, fibrous substances such as pulp, and various Scraping material, pigments, flame retardants such as antimony trioxide, chlorinated paraffin, bromine compounds, and other rubber compounding materials for passenger vehicles can be added as necessary.

Next, the manufacturing method of the present invention will be described with reference to specific examples, but the present invention is not limited to these examples.

Example 1 High pressure polyethylene (Yukalon YF-30, MFR: 1
．． 0 density: 0.92 + Mitsubishi Yuka Co., Ltd.) 100 parts by weight, and azodicarbonamide (ADCA) as a blowing agent.
22 parts by weight, 0.3 parts by weight of zinc oxide (ZnO) as a foaming aid
Part by weight, dicumyl peroxide (DCP) as a crosslinking agent
) 0.5 part by weight of the foamable composition is heated on a mixing roll at a temperature (100 to 105%) that does not decompose the ingredients.
After kneading and uniformly dispersing the foamable composition A at 150°C, the mold 1 (28mm x 34 (hn x 620 crane)) in the press 2 heated to 150°C was filled with 50 kg. After heating for 30 minutes under pressure of /cat or more, the pressure was removed and intermediate product B as a primary foam was taken out. The obtained intermediate product B had a volume expansion coefficient of 5°0. , this intermediate product B was used as a heating container heated to 160°C, and a secondary mold 3 (inner size 95 cranes x 1
050 Tsuru x 2100 m), heated for 30 minutes, stopped heating and allowed to mature, and was cooled with cooling water at room temperature to obtain a foam C as a final product. The obtained foam has uniform, fine closed cells, has a thickness of 93 mm, a density of 0.022 g/cc (expansion ratio of approximately 42 times), and has no defective phenomena both externally and internally. Ta.

Example 2 The same foamable composition A as in Example 1 was kneaded in the same manner as in Example 1, filled into mold 1 in press 2 heated to 153°C, and heated for 35 minutes under pressure of 50 kg/- or more. After that, the pressure was reduced, and intermediate product B as a primary foam was taken out. The obtained intermediate product B had a volume expansion coefficient of 6.5 times. Next, the product B was placed in a secondary mold 3 as a heating container heated to 160°C for 25 minutes, heated for 25 minutes, stopped heating and aged for 5 minutes, and then heated with cooling water at room temperature. After cooling for 40 minutes, foam C was obtained as the final product.

The obtained foam C had a density of 0.022 g/cc (expansion ratio of about 42 times), and as with the foam obtained in Example 1, no defects were observed.

Example 3 Ethylene-vinyl acetate conjugate (Evaflex P-14
03, MFR: 1.4. Vinyl acetate content 14w5%)
A foamable composition A consisting of 100 parts by weight, 22 parts of APCA, 0.15 parts by weight of zinc oxide, and 0.8 parts by weight of dicumyl peroxide was kneaded in the same manner as in Example 1, and heated to 145°C in a press 2. The mixture was filled into the mold 1 and heated under pressure for 35 minutes to obtain a primary foamed intermediate product B whose volume expanded 5.5 times. Next, in the same manner as in Example 1, it was heated to obtain a foam C having uniform, fine, and flexible closed cells. Note that the density was 0.023 g/cc (expansion ratio approximately 40 times).

Example 4 High pressure polyethylene (Yukalon HE-30, MFR: O
35, density: 0.92 manufactured by Mitsubishi Yuka Co., Ltd.) 100 parts by weight, azodicarbonamide 15 parts by weight, zinc oxide 0.1
After kneading foamable composition A consisting of parts by weight and 0.5 parts by weight of dicumyl peroxide in the same manner as in Example 1,
Mold 1 in press 2 at °C (inner size 28tm x 360
m x 720 m) and 10 kg/co! Heating was performed under the above pressure for 35 minutes to obtain a primary foamed intermediate product B with a volumetric expansion rate of 2.5 times. Next, it was placed in a second mold 3 heated to 165° C. and heated for 60 minutes, then aged and cooled, and a foam C as a final product was taken out. The obtained foam had an apparent density of 0.0318/cc (expansion ratio of about 30 times) and uniform fine closed cells.

Example 5 To 100 parts by weight of the same resin as in Example 1, 1 part of foamable composition A consisting of 35 parts by weight of azodicarbonamide, 0.15 parts by weight of zinc oxide, and 0.5 parts by weight of dicumyl peroxide was added.
Mold 1 in press 2 (25 m x 152 cranes x 152 mm) was kneaded with rolls at 10°C and heated to 148°C.
An intermediate product B was obtained as a primary foam which expanded in volume by 4° and 8 times by heating for 40 minutes. Then 155℃
The final foam C was placed in a heated secondary mold 3 (inner size: 85 mm x 600 mm x 600 mm) and heated for 40 minutes, and after aging and cooling, the final foam C was taken out. The resulting foam has a density of 0.0
It was 16 g/cc (expansion ratio of about 57°, 5 times) and thickness was 82 mm.

Example 6 A foamable composition A consisting of 100 parts by weight of the same resin as in Example 1, 16 parts by weight of azodicarbonamide, 0.2 parts by weight of zinc oxide, and 0.5 parts by weight of dicumyl peroxide was prepared as in Example 1. It was kneaded in the same way and filled into the mold 1 (inner size 32 m1 x 350 mm x 700 mm) in the press 2 heated to 153°C, and the mixture was mixed at 50 kg/cn! Heating was performed under the above pressure for 45 minutes to obtain an intermediate product B as a primary foam having a volume expansion coefficient of 6.0 times. Next, a jacket type heating mold 3 heated to 160°C (inner size 123 vs.
After heating for 40 minutes and aging and cooling,
The final foam C was removed. The resulting foam has a density of 0
．． 025 g/cc (expansion ratio of approximately 3γ times), uniform fine cells, and a thickness of 120 mm.

(Comparative Example) Comparative Example 1 100 parts by weight of the same resin as in Example 1, 22 parts by weight of azodicarbonamide, 3 parts by weight of a urea-based compound as a foaming aid,
A foamable composition consisting of 85 parts by weight of dicumyl peroxide O was kneaded in the same manner as in Example 1, and foam-molded under the same heating conditions.

After press pressure release, the obtained intermediate foam B has a volumetric expansion coefficient of 11
In this case, a cavity was formed inside the intermediate foam B by the time the blowing agent went to the next step due to runaway decomposition of the blowing agent.

Comparative Example 2 The amount of foaming aid (zinc oxide) added in Example 1 was reduced to 0.
A primary foam B was obtained under the same conditions as in Example 1 except that 6 parts by weight and the press temperature were 155°C.

The intermediate foam B obtained in this primary foaming process had a volumetric expansion rate of 9 times, had chipping around the foam, and was also significantly deformed due to its non-conformity to press molding. Ta.

Subsequently, under the same conditions as in Example 1, a final foam C was obtained. The thickness and cell diameter of this final foam C were not much different from those of the foam obtained in Example 1, but the quality was extremely low, with cracks and wrinkles appearing in the peripheral area.

Comparative Example 3 A foam was obtained under the same conditions as in Example 4, except that the amount of foaming aid added in Example 3 was changed to 0.05 parts by weight. Since the volumetric expansion coefficient of the primary intermediate foam B was 1.2 times,
The cell diameter inside the final foam C was generally large, and there was a large difference in the cell diameter between the central part and the part near the skin layer, and the quality of the product was low.

[Brief explanation of drawings]

Figure 1 is a comparison diagram of the foaming process (a) according to the method of the present invention and the foaming process (b) according to the conventional method, and Figure 2 (a)
-(e) are cross-sectional views schematically showing the manufacturing process. 1...-molding mold, 2... press, 3... secondary mold, A... foamable composition, B... intermediate product, C...
Final foam product.

Claims (1)

[Claims] A foamed product with a high expansion ratio is produced by foaming a foamable composition obtained by mixing and kneading a foaming agent, a foaming aid, a crosslinking agent, or a filler in addition to the polyolefin in two stages. The foaming composition is filled into a primary mold, heated under pressure for a certain period of time, and then depressurized to cause primary foaming so that the foaming ratio is 2 to 7 times. A first step in which an intermediate product is obtained by taking it out from a primary mold; Next, the intermediate product is placed in a second mold and heated under normal pressure for a certain period of time to decompose the undecomposed foaming agent; A method for producing a polyolefin foam, which comprises a second step of foaming, then aging and cooling, and removing from a second mold to obtain a final product.