JP2012224751A - Method for producing crosslinked polyolefin resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a crosslinked polyolefin resin foam which is reduced in odor and free from shrinkage after expansion.SOLUTION: The method for producing the crosslinked polyolefin foam which is reduced in odor and free from shrinkage after expansion comprises: a first step of adding a foaming agent, a cross-linking agent and the like to a polyolefin resin followed by kneading and heating the resulting crosslinkable foaming composition under pressurization to generate an intermediate foam; and a second step of heating the intermediate foam to decompose the foaming agent which is left without decomposition. In the method, 5-20 pts.wt of sodium hydrogen carbonate is added to 100 pts.wt. of the polyolefin resin, the pressing pressure is 5-30 kg/cmand the temperature is 150-170°C in the first step, and the temperature in the second step is lower by 20°C or more than that in the first step.

Description

    The present invention relates to a method for producing a crosslinked polyolefin foam having low odor and no shrinkage after foaming.

    Polyolefin foams are excellent in physical properties such as heat insulating properties, buffer properties, weather resistance, chemical resistance, etc., and are widely used in various applications such as buffer materials, joint materials, and miscellaneous goods.

Conventionally, when producing a polyolefin-based foam, a thermally decomposable foaming agent is used as a foaming agent, and a polyolefin-based resin is foamed with the decomposition gas to obtain a foam. Azodicarbonamide is generally used as a foaming agent, but a small amount of ammonia is contained in the decomposition gas, causing odor. The decomposition gas is only carbon dioxide and water vapor, and sodium hydrogen carbonate is known as a foaming agent that does not contain ammonia, but it is known that shrinkage occurs after foaming. In order to prevent shrinkage, a method of adding an alkali metal or alkaline earth metal oxide (JP 2007-217505 A) or a method of adding a water absorbent resin (JP 2007-217639 A) has been proposed. ing.

JP 2007-217505 A JP 2007-217639 A

However, since the alkali metal or alkaline earth metal oxide used in the production method described in Patent Document 1 has high hygroscopicity, it is difficult to preserve and pinholes are easily generated in the foam. The water-absorbent resin used in the production method described in Patent Document 2 is difficult to obtain a high-magnification foam by inhibiting crosslinking.

    The present inventors have developed a crosslinked polyolefin foam having a low odor and no shrinkage after foaming by heating and foaming the polyolefin resin without adding anything other than a foaming agent, a crosslinking agent and a foaming aid. .

In order to achieve the above object, the first method of the present invention is to obtain a crosslinkable foamable composition obtained by adding and kneading 5 to 20 parts by weight of sodium hydrogen carbonate as a foaming agent to 100 parts by weight of a polyolefin-based resin and a crosslinking agent. This is a method for producing a crosslinked polyolefin-based foam, wherein the product is heated at 150-170 ° C. under a press pressure of 5-30 kg / cm ² and then depressurized to produce a foam.

In the second method of the present invention, 5 to 20 parts by weight of sodium hydrogen carbonate as a foaming agent and a crosslinking agent are added and kneaded to 100 parts by weight of a polyolefin resin, and the resulting crosslinkable foamable composition is pressed at a pressure of 5 to 30 kg. / Cm < ² > at 150-170 [deg.] C. to remove pressure in a partially decomposed state of the foaming agent in the composition to form an intermediate foam, and then the intermediate foam It is a method for producing a crosslinked polyolefin-based foam characterized by comprising a second step in which the foaming agent remaining undecomposed is heated by heating at a temperature 20 ° C. or more lower than that in the first step.

    In the production method of the present invention, the amount of foaming agent added is preferably 5 to 20 parts by weight. When the addition amount of the foaming agent is less than 5 parts by weight, the foam is hard and is inferior in buffering properties to the conventional crosslinked polyolefin foam. When the amount exceeds 20 parts by weight, the shape of the foam becomes distorted and the bubble diameter varies, and a satisfactory foam cannot be obtained.

    In the manufacturing method of this invention, it is preferable that the particle size of sodium hydrogencarbonate is 20 micrometers or more. When the particle diameter is less than 20 μm, the retention of bubbles is low and shrinkage occurs after foaming.

  In the second method of the present invention, the heating temperature in the second step is preferably 20 ° C. or more lower than the heating temperature in the first step. When the heating temperature in the second step is high or the same, shrinkage occurs after foaming.

    According to the method of the present invention, a crosslinked polyolefin-based foam having low odor and no shrinkage after foaming can be obtained.

    The polyolefin referred to in the present invention is, for example, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polytetrafluoroethylene, ethylene-propylene copolymer, poly-4-methyl-1-pentene, polyvinyl chloride, polyvinylidene chloride. , Polyvinylidene fluoride, tetrafluoroethylene, and ethylene copolymer.

The foaming agent in the present invention refers to a compound that decomposes upon heating to generate carbon dioxide gas and water vapor, and sodium hydrogen carbonate is particularly preferable.

The cross-linking agent as used in the present invention has a decomposition temperature at least equal to or higher than the flow start temperature of the polyethylene resin in the polyethylene-based resin, and is decomposed by heating to generate free radicals between the molecules or within the molecules. Organic peroxides that are radical generators that cause cross-linking, such as dicumyl peroxide, 1,1-ditertiary butyl peroxide, 1,1-ditertiary butyl peroxy-3,3,5-trimethylcyclohexane 2,5-dimethyl-2,5-ditertiary butyl peroxyhexane, 2,5-dimethyl-2,5-ditertiary butyl peroxyhexyne, α, α-ditertiary butyl peroxyisopropylbenzene, tertiary butyl per Oxyketone, tertiary butyl peroxy There are benzoates, etc., and the optimum organic peroxide must be selected according to the resin used at that time.

In the present invention, a foaming aid can be added depending on the type of foaming agent. Examples of the foaming aid include compounds mainly composed of urea, metal oxides such as zinc oxide and lead oxide, compounds mainly composed of salicylic acid and stearic acid, that is, higher fatty acids or higher fatty acid metal compounds.

In the present invention, for the purpose of improving the physical properties of the composition to be used or reducing the price, a compounding agent (filler) that does not significantly adversely affect the cross-linking, such as zinc oxide, titanium oxide, calcium oxide, magnesium oxide, oxidation Metal oxides such as silicon, carbonates such as magnesium carbonate and calcium carbonate, fiber materials such as pulp, various dyes, pigments, fluorescent materials, and other commonly used compounding agents can be added as necessary.

Next, a method for producing a crosslinked polyolefin-based foam having low odor and no shrinkage after foaming according to the present invention will be described.

In the first method of the invention, 5 to 20 parts by weight of sodium bicarbonate having a particle size of 20 μm or more, a crosslinking agent, and a foaming aid are added to 100 parts by weight of a polyolefin resin, and this is mixed with a mixing roll, a pressure kneader, and an extruder. Knead by etc. Next, the obtained foamable crosslinkable composition is filled in a mold during pressing, heated at a pressure of 5 to 30 kg / cm ² for a certain time at 150 to 170 ° C., and then depressurized to generate a foam. It is.

In the second method of the invention, 5 to 20 parts by weight of sodium bicarbonate having a particle size of 20 μm or more, a crosslinking agent, and a foaming aid are added to 100 parts by weight of a polyolefin resin, and this is mixed with a mixing roll, a pressure kneader, and an extruder. The foamable crosslinkable composition obtained by kneading is filled into a mold during pressing, and heated at 150 to 170 ° C. under a pressure of 5 to 30 kg / cm ² for a certain period of time to partially expand the foaming agent. Then, the pressure is released to obtain an intermediate foam.

Next, the intermediate foam is put into a mold having a desired shape such as a rectangular parallelepiped mold which is not a closed system, heated at a temperature lower by 20 ° C. or more than the temperature of the press for a predetermined time, and then taken out to generate a foam.

Evaluation of Shrinkage The shrinkage of the foam obtained in the present invention was measured by measuring the size immediately after taking out (L0) and the size after leaving it at room temperature for 1 hour (L1), and calculating the shrinkage rate by the following formula. -5% or less, it was determined that there was no contraction.
Shrinkage rate = (L1-L0) × 100 / L0

Evaluation of Odor (Ammonia Concentration) The ammonia concentration of the foam obtained in the present invention was measured by the following method.
0.2 g of the foam was placed in a 200 cc flask, left in an oven at 80 ° C. for 2 hours, then taken out and allowed to cool, and measured with an ammonia detector tube (manufactured by Gastec Co., Ltd.). An ammonia concentration of 10 ppm or less was judged as low odor.

Hereinafter, the embodiment will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.
(Examples 1-18 and Comparative Examples 1-15)
First, the raw material of the crosslinked polyolefin-based foam used in each example and comparative example is shown below.

Low density polyethylene (trade name: Novatec LF441, density 0.924 g / cm ³ , melt flow rate 2.0 g / 10 min, manufactured by Mitsubishi Chemical Corporation)
Foaming agent 1: sodium hydrogen carbonate (trade name: Cerbon FE-507R, particle size 25-30 μm, manufactured by Eiwa Kasei Kogyo Co., Ltd.)
Foaming agent 2: Sodium hydrogen carbonate (trade name: Cellbon FE-507, particle size 10 to 15 μm, manufactured by Eiwa Kasei Kogyo Co., Ltd.)
Crosslinking agent 1: Dicumyl peroxide (trade name: Park Mill D, manufactured by NOF Corporation)
Cross-linking agent 2: n-butyl-4,4-di (t-butylperoxy) valerate (trade name: Perhexa V-40, manufactured by NOF Corporation)

    In Tables 1 to 7, the composition of the cross-linked polyolefin foam and the foaming conditions are shown.

A composition comprising low-density polyethylene, foaming agents 1 and 2, and crosslinking agents 1 and 2 is kneaded with a roll at 100 ° C., and a mold (24 × 160 × 160 mm) in the press is filled with the kneaded product. After heating at the pressure and temperature for 60 minutes, the pressure was released to obtain a foam.
The obtained foam was allowed to cool and checked for shrinkage. The foam that did not shrink was measured for apparent density and ammonia concentration. The results are also shown in Table 1, Table 2 and Table 3.

    As shown in Tables 1 and 2, in Examples 1 to 9, no contraction was observed, the ammonia concentration was 10 ppm or less, and the concentration was low enough to be undetectable by the human nose.

    On the other hand, in Comparative Examples 1 to 7, Comparative Example 1 in which the addition amount of foaming agent 1 is 3 parts by weight is harder in foam and inferior in buffering properties than conventional crosslinked polyolefin foam, and the addition amount is 30 wt. In Comparative Example 2 of the part, the shape of the foam was irregular and the bubble diameters varied, and a satisfactory foam could not be obtained. Further, Comparative Example 5 in which the press temperature was changed to 140 ° C. had a low foaming ratio and was hard and inferior in buffering properties, and a satisfactory foam could not be obtained.

Foams of Comparative Example 6 was changed to Comparative Examples 4 and pressing temperature was changed pressing pressure to a comparative example 3,40kg / cm ² was changed to 3 kg / cm ² to 180 ° C. was contracted after cooling.

    In Comparative Example 7 in which the foaming agent 1 was changed to the foaming agent 2 having a particle diameter of 10 to 15 μm, the foam contracted after cooling.

    A composition comprising low-density polyethylene, foaming agents 1 and 2, and crosslinking agents 1 and 2 is kneaded with a roll at 100 ° C., and a mold (24 × 160 × 160 mm) in the press is filled with the kneaded product. The foamable crosslinked composition was molded in the first step of heating at the temperature and pressure.

Next, the intermediate foam is put into a mold (60 × 500 × 500 mm) in the press, heated at a predetermined temperature for 30 minutes, and then cooled after the second step of decomposing the remaining foaming agent and crosslinking agent. Got the body.
The obtained foam was left to check for shrinkage. The foam that did not shrink was measured for apparent density and ammonia concentration. The results are shown in Tables 4-7.

    As shown in Tables 4 and 5, in Examples 10 to 18, no contraction was observed, the ammonia concentration was 10 ppm or less, and the concentration was low enough to be undetectable by the human nose.

    On the other hand, in Comparative Examples 8 to 15, the foam of Comparative Example 8 in which the second process temperature was 10 ° C. lower than the first process contracted after cooling.

In Comparative Example 9 in which the amount of the foaming agent 1 added was 3 parts by weight, the foam was hard and inferior in buffering properties compared to the conventional cross-linked polyolefin foam, and in Comparative Example 10 in which the amount added was 30 parts by weight, The shape was irregular and the bubble diameters varied, and a satisfactory foam could not be obtained. Further, in Comparative Example 11 in which the first step press pressure was changed to 3 kg / cm ^2, there were many burrs from the press, and a foam was not obtained.

The foam of Comparative Example 12 in which the first step pressing pressure was changed to 40 kg / cm ² contracted after cooling.

The foam of Comparative Example 13 in which the first process temperature was changed to 140 ° C. had a low foaming ratio and was hard, had poor buffering properties, and a satisfactory foam could not be obtained.
The foam of Comparative Example 14 in which the first process temperature was changed to 180 ° C. contracted after cooling.

    The foam of Comparative Example 15 in which the foaming agent 1 was changed to the foaming agent 2 contracted after cooling.

As described above, according to the method of the present invention, it is possible to produce a crosslinked polyolefin-based foam having low odor and no shrinkage after foaming. The crosslinked polyolefin-based foam produced by the method of the present invention is excellent in physical properties such as heat insulating properties, buffer properties, weather resistance, chemical resistance, and can be widely applied to various uses such as buffer materials, joint materials, and miscellaneous goods.

Claims (3)

Sodium hydrogen carbonate 5 to 20 parts by weight as a foaming agent and a crosslinking agent are added and kneaded to 100 parts by weight of a polyolefin resin, and the obtained crosslinkable foamable composition is 150 to 170 under a press pressure of 5 to 30 kg / cm ² . A method for producing a crosslinked polyolefin-based foam, characterized in that the foam is formed by heating at 0 ° C. and then depressurizing. Sodium hydrogen carbonate 5 to 20 parts by weight as a foaming agent and a crosslinking agent are added and kneaded to 100 parts by weight of a polyolefin resin, and the obtained crosslinkable foamable composition is 150 to 170 under a press pressure of 5 to 30 kg / cm ² . A first step of heating at 0 ° C. and depressurizing the foaming agent in the composition in a partially decomposed state to form an intermediate foam, and then the intermediate foam is 20 ° C. or higher than the first step. A method for producing a crosslinked polyolefin-based foam, comprising a second step of heating at a low temperature to decompose a foaming agent remaining undecomposed. The method for producing a crosslinked polyolefin-based foam according to claim 1 or 2, wherein the particle size of sodium hydrogen carbonate is 20 µm or more.