JPH02194037A - Open-cell polyethylene resin foam and its production - Google Patents

Abstract

PURPOSE:To obtain a resin foam having a high open cell rate and excellent compressive characteristics comprising a crosslinkable PE resin and a PP resin and prepared by cross-linking the PE resin so as to give a specified open cell rate thereto. CONSTITUTION:A resin foam containing a crosslinkable polyethylene resin (a) and a polypropylene resin (b) having an m.p. higher that that of the crosslinkable polyethylene resin by at least 20 deg.C and is lower than 190 deg.C in a range of (a)/[(a)+(b)]=40-90wt.% and (b)/[(a)+(b)]=10-60wt.% and prepared by crosslinking the crosslinkable polyethylene resin so as to give thereto an open cell rate of 60-90%. As the crosslinkable polyethylene resin used, a low- density polyethylene or an ethylene/vinyl acetate copolymer is particularly desirable. As the polypropylene resin, a crystalline homopolymer of propylene is particularly desirable.

Description

[Detailed Description of the Invention] The present invention, which is produced using clay, has a high open cell ratio and excellent sound absorption properties.
Moreover, the present invention relates to a polyethylene resin foam having good compression properties and a method for producing the same.

In recent years, with the rapid spread of wooden flooring in housing complexes, there has been a strong demand for the development of sound-insulating flooring.

In such sound insulating flooring materials, it is preferable to use foam with a high open cell ratio as the flooring material.
However, conventional open-celled polyolefin foams have extremely low compression hardness, making them impractical for use as flooring materials. In addition, there are many other fields in which foams having a high open cell ratio and excellent compression properties are desired.

For example, in Japanese Patent Publication No. 47-31695, a closed-cell crosslinked polyolefin foam having a compression rate of 5% or more and a compression recovery rate of 85% or more is first prepared, and this foam is heated to a temperature below the glass transition temperature. It has been proposed that the closed cell structure be destroyed by compression after cooling to open cells.

However, the foam obtained by this method undergoes a severe compression process that exceeds its elastic limit, resulting in an extremely low compression hardness.Furthermore, since the process is a two-step process, equipment costs and It was undeniable that the processing costs would also be high.

Furthermore, Japanese Patent Publication No. 55-42100 discloses that 20 to 60% by weight of an amorphous polypropylene resin, which is a by-product during the production of general-purpose polypropylene, and a blowing agent and a crosslinking agent are added to a crosslinkable polyolefin resin at a temperature at which the blowing agent does not decompose. It has been proposed to produce an open-cell foam by blending them into a foamable composition and foaming this by a step-processing or hot pressing method.

However, the foam obtained by this method.

Since it contains a large amount of amorphous polypropylene resin with low compression hardness, the foam itself also has extremely low compression hardness, which limits its uses.

Furthermore, since polyolefin resin and non-crosslinkable amorphous polypropylene resin are melt-mixed during sheet molding in the pre-foaming process, crosslinking, which is particularly important in the cell formation process at the foaming stage, is adversely affected, and uniform open cells are not formed. It has been difficult to manufacture foams with

The present invention aims to provide a polyethylene resin foam having a high open cell ratio and excellent compression properties.

The polyethylene resin foam of the present invention includes (a) a crosslinkable polyethylene resin and (b) a polypropylene resin whose melting point is 20°C or more higher than the crosslinkable polyethylene resin and 190°C or lower. , (a)/[(a) + (
b)] = 40-90% by weight (b)/[(a) +
(b)]=contains in the range of 10 to 60% by weight, and
The crosslinkable polyethylene resin is crosslinked and has an open cell ratio of 60 to 90% by weight.

Furthermore, the method for producing the polyethylene resin foam of the present invention includes:
The melted (a) crosslinkable polyethylene resin, the thermally decomposable blowing agent, and the organic peroxide;
Powdered polypropylene resin having a temperature of 90°C or less (a)/[(a) + (b)] = 40 to 90% by weight (b)/[(a) + (b)] 10 to 60% by weight
(b) to uniformly disperse the powdered polypropylene resin in an unmolten state;
It is characterized in that a) a crosslinkable polyethylene resin is crosslinked and foamed, and (b) a powdered polypropylene resin is melted.

The present invention will be explained in more detail below.

Examples of the crosslinkable polyethylene resin (a) used in the present invention include low density polyethylene, linear low density polyethylene, high density polyethylene, ethylene copolymers such as ethylene-vinyl acetate copolymer, etc. These may be used alone or in combination of two or more. Among these,
Particularly preferred are low density polyethylene and ethylene-vinyl acetate copolymer.

(b) As the polypropylene resin, one whose melting point is 20°C or more higher than the crosslinkable polyethylene resin used above and 190°C or lower is used. Specific examples include crystalline homopolymer of propylene, Examples include random copolymers, block copolymers, and graft copolymers containing propylene, and among these, crystalline homopolymers of propylene are particularly preferred.

In the present invention, (a) the crosslinkable polyethylene resin is
It is used in an amount of 40 to 90% by weight, preferably 60 to 80% by weight based on the total amount of (a) crosslinkable polyethylene resin and (b) polypropylene resin. If this amount is less than 40% by weight, the cells of the foam will be non-uniform and coarse, resulting in significantly poor compression hardness of the foam. On the other hand, 9
If it exceeds 0% by weight, the open cell ratio will be too low, which is not preferable.

The (b) polypropylene resin used in the present invention is used in powder form, and is required to remain in powder form and not melt during the uniform dispersion process into the molten (a) crosslinkable polyethylene resin before foaming. For this purpose, it is necessary to have a melting point that is 20°C or more higher than (a) the crosslinkable polyethylene resin, preferably 30°C or more.

In addition, in the foam molding process, it is necessary to melt the (b) polypropylene resin, and for that purpose, (b)
) It is necessary that the melting point of the polypropylene resin is 190°C or lower. The average particle size of the powdered polypropylene resin is preferably 300 to 600 μm, more preferably 450 to 550 μm. When the average particle size is less than 300 μm, it becomes difficult to obtain a foam with a high open cell ratio. On the other hand, if the average particle size exceeds 600 μm, the cells tend to be non-uniform and coarse, making it difficult to obtain a foam having good compression hardness.

The polyethylene resin foam of the present invention has an open cell ratio of 60 to 90%, and preferably has a compression hardness of 1.2 kg/aJ or more. By having this, not only excellent performance such as sound absorption properties can be obtained, but also satisfactory strength can be obtained.

In the foam of the present invention, a pyrolytic foaming agent is used during foam molding, and an organic peroxide is used for crosslinking the crosslinkable polyethylene resin. As a thermally decomposable blowing agent, azosicabonamide is used.

diphenylsulfone-3,3'-disulfohydrazide,
Benzylsulfonic acid diphenylhydrazide and the like are preferred. As an organic peroxide, l.

3-bis(tert-butylperoxyisopropyl)
Benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, dicumyl peroxide and the like are preferred.

Furthermore, the open-celled foam contains calcium carbonate,
Various additives such as inorganic powders such as talc and carbon black, antioxidants, colorants, foaming aids, crosslinking aids, lubricants, and flame retardants may be added as necessary.

Next, a method for producing a polyethylene resin foam according to the present invention will be described.

First, polyethylene-based Hatsumode, powdered polypropylene-based resin, pyrolytic foaming agent, organic peroxide, and various additives as necessary are uniformly mixed in a device such as an internal mixer, Banbury mixer 1 pressure kneader, etc. The mixture is melt-kneaded and then formed into a desired shape such as a sheet using a device such as a roll or an extruder. In this melt-kneading-forming process, which is preferably formed into a sheet shape, it is necessary to uniformly disperse the powdered polypropylene resin in its powder form without melting it, and specifically,
For example, it is preferable that the melt-kneading step is carried out at a temperature of 100 to 140°C, and the forming process such as forming into a sheet is carried out at a temperature of 90 to 130°C. Moreover, this condition is a temperature condition in which the blowing agent and the crosslinking agent are substantially not decomposed.

Next, the mixed composition prepared in the above step is crosslinked and foamed at a temperature of 160 to 190° C. and a pressure of 150 to 200 kg/aJ, for example, by a one-stage pressurization and heat foaming method using a pressure press device or the like. This - stage pressurization.

By heating and foaming, the crosslinkable polyethylene resin is foamed and crosslinked in the -stage treatment step, and the polypropylene resin is melted and integrated to obtain the polyethylene resin foam of the present invention. If the crosslinking and foaming temperature is less than 160°C,
Powdered polypropylene resin does not melt, making it difficult to form continuous bubbles. Furthermore, if the temperature exceeds 190°C, the formation of bubbles in the polyethylene resin and the melting of the powdered polypropylene resin rapidly proceed.

It becomes difficult to form uniform open cells, and the cells in the resulting foam become uneven and coarse.

The polyethylene resin foam produced in this way has an open cell ratio of 60 to 90% and a compression hardness of 1.
At 2 kg/ff1 or more, the foam has excellent sound absorption properties and compression properties.

Powdered polypropylene resin has a melting point 20°C higher than polyethylene resin, so by setting the processing temperature in the sheet forming process to an appropriate temperature, only the polyethylene resin melts and the powdered polypropylene resin melts. is uniformly dispersed as a powder without being melt-mixed. In the next one-stage pressurization and heat foaming process, the foaming agent and crosslinking agent first decompose rapidly from around 150°C under elevated temperature, and the polyethylene resin is crosslinked and first closed cells are formed. .

Then, at 160° C. or higher, the powdered polypropylene resin melts on the membrane walls of these closed cells. Since this polypropylene resin is non-crosslinkable, it is presumed that it cannot resist the gas pressure of the bubbles that have already been formed, and the bubbles are destroyed to form open cells.

In addition, the reason why the foam has excellent compression properties even when the cells are made open is that the polypropylene resin itself does not foam, and because the polypropylene resin has excellent rigidity, it acts as a reinforcing agent for the cells. It is estimated that

As described above, the present invention has extremely superior compression properties compared to conventional foams with open cells, so it is extremely useful for sound-insulating flooring materials that require sound absorption properties. In addition, its uses are extremely wide, including water absorbing materials, heat insulating materials, filtration materials, and even packaging materials that require compressive hardness.

The present invention will be explained in more detail with reference to Examples below, but prior to that, the test methods employed in the Examples will be described.

(Left below) (1) Apparent density: Determined using a linear equation according to JIS K-6767 polyethylene foam test method.

D=-W- ■ D: Apparent density (g/al) W: Mass of test piece (g) V: Volume of test piece (an) (2) Compression characteristics (compression hardness) JIS K-6767 polyethylene foam test It was calculated using a linear equation according to the method.

H=-l- L H: Compression hardness (kg/a#) P: 25% compression, load after 20 seconds (kg) W: Width of test piece (CI) L: Length of test piece (cm ) (Hereinafter, blank) (3) Open cell rate It was determined by the following formula according to the ASTM-D-2856 air pycnometer method.

■=-Eko-Ken"-X100 SV: Open cell rate (%) vs: Apparent volume of test piece (cc) ΔV: True volume of test piece (cc) Example 1 Ethylene-vinyl acetate co- As a polymer, Evatate H-2020 (melting point = 91°C, density: 0.9, manufactured by Sumima Kagaku ■) was used.
3g/cd, melt index: 1.5g/10min, vinyl acetate content 215% by weight), 74.2 parts by weight,
Noblen H1t-100 (homopolymer) manufactured by Sumitomo Chemical ■ (particle size: 500μ) is used as a powdered polypropylene resin.
31.8 parts by weight of foam, melting point 170°C, density: 0.91 g/aJ, melt index: 7 g/10 min), and Azocicabonamide AZ- manufactured by Otsuka Chemical ■ as a blowing agent.
5 parts by weight of L, 1 part of Kayaku Nuso mum as a crosslinking agent,
1 part by weight of 3-bis(tert-butylperoxyisopropyl)benzene [Berriki Dox 14/40] was melted in an internal mixer, mixed, and then formed into a sheet with two rolls at a foaming temperature of 175°C. One stage pressurization,
A foam was obtained using a heating foaming method. The resulting foam was excellent in both compression hardness and open cell ratio, as shown in Table 1 below.

Examples 2 to 4 Foams were obtained in the same manner as in Example 1 by changing the blending ratio of the same ethylene-vinyl acetate copolymer and powdered polypropylene resin as shown in Table 1. Ta. The obtained foam had a compression hardness superior to that of ordinary closed-cell foams used in sound-insulating flooring materials, and was sufficiently durable for practical use. Furthermore, as the amount of powdered polypropylene resin increased, the open cell rate was high and the open cell foam was good.

Comparative Example 1 As shown in Table 1, a foam was obtained in the same manner as in Example 1 using 106 parts by weight of the ethylene-vinyl acetate copolymer used in Example 1. As shown in Table 1, the resulting foam had a significantly low open cell ratio and was mostly a closed cell foam.

Comparative Examples 2 to J A foam was obtained in the same manner as in Example 1 using the ethylene-vinyl acetate copolymer and powdered polypropylene resin used in Example 1 and having the composition shown in Table 1. The obtained foam has a powdery polypropylene resin of 74.2
If the amount of powdered polypropylene resin is 5.3 parts by weight, the open cell rate is high, but the compression hardness is significantly reduced and it cannot be used as a floor sub-material, etc. On the other hand, if the powdered polypropylene resin is 5.3 parts by weight, the compression hardness is excellent. However, since the open cell ratio is extremely low and the sound absorption properties are extremely poor, it is not suitable for use as a floor subfloor material, as mentioned above.

Examples 5 to 6 F-216 manufactured by Juumin Chemical Co., Ltd. as a low-density polyethylene
1 (melting point: 115°C, density: 0.92 g/aI, melt index 1.2 g/10 min), a foam was obtained in the same manner as in Example 1 with the composition shown in Table 1. .

The obtained foam ensured an open cell ratio of 60% or more to satisfy sound insulation properties, and had extremely excellent compression hardness.

Example 7 Heavy calcium carbonate [Niscallon #800] manufactured by Sankyo Seifun ■ (average particle size 1.6 μm) was used as the inorganic powder, and foamed in the same manner as in Example 1 with the composition shown in Table 1. I got a body. The obtained foam was a good foam as in Example 1.

Example 8 The powdered polypropylene resin used in Example 1 was ground to a size of 300 μm using a grinder, and a foam was obtained in the same manner as in Example 1 using the blending composition shown in Table 1. The obtained foam had the same good quality as Example 1.

Example 9 J-650H (manufactured by Idemitsu Petrochemical Co., Ltd.) was used as a pelleted polypropylene resin (propylene-ethylene copolymer).
block copolymer) (melting point: 168°C, density: 0.9
0 g/d, melt index: 5 g/10 min) was ground into 600 microns using a grinder, and a foam was obtained in the same manner as in Example 1 with the composition shown in Table 1. Although the compression hardness of the obtained foam was slightly lower than that of Example 1, there was no practical problem at all, and a foam with a high open cell ratio was obtained.

The above results are summarized in Table 1.

(Margin below)

Claims (1)

[Scope of Claims] 1. (a) a crosslinkable polyethylene resin and (b) a polypropylene resin whose melting point is 20°C or more higher than the crosslinkable polyethylene resin and 190°C or lower, (a)/[ (a) + (b)] = 40-90% by weight (b)
/[(a)+(b)]=10 to 60% by weight, and the polyethylene is crosslinked with the crosslinkable polyethylene resin, and has an open cell ratio of 60 to 90%. system resin foam. 2. Melted (a) crosslinkable polyethylene resin, a thermally decomposable blowing agent and an organic peroxide, and (b) a melting point that is 20°C or more higher than the crosslinkable polyethylene resin and 190°C or less Powdered polypropylene resin (a)/[(a)+(b)]=40 to 90% by weight (b)
/[(a)+(b)]=10 to 60% by weight, (b) powdered polypropylene resin is uniformly dispersed in an unmolten state, and then heated to (a) crosslink In addition to crosslinking and foaming polyethylene resin,
b) A method for producing a polyethylene resin foam, which comprises melting a powdered polypropylene resin.