JP2683669B2 - Method for producing polyolefin foam - Google Patents

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 foam, and more specifically, it has a cell diameter of 250 to 250.
It is relatively large with about 450 μm and rich in compressive stress,
The present invention relates to a method for efficiently producing a polyolefin foam that is foamed 10 times or more.

[0002]

2. Description of the Related Art As a method for producing a polyolefin block foam, generally, a mixture of a polyolefin resin, a cross-linking agent and a foaming agent is filled in a mold and the cross-linking agent and the foaming agent are heated and pressurized. A method in which the mixture is completely decomposed and then depressurized to expand the mixture at one time to a desired density (hereinafter referred to as one-stage foaming), and JP-B-52-834.
No. 8, Japanese Patent Publication No. 2-42649, etc., the mixture is filled in a primary mold and heated under pressure to cause primary expansion, and then the foam is heated at normal pressure for secondary expansion. A method of obtaining a foam having a desired density (hereinafter referred to as two-stage foaming) is known.

[0003]

However, in the above-mentioned one-step foaming, when a foam having a volume of 10 times or more is obtained, since the final foam having a desired density is expanded at a time, the final foam obtained may be deformed. In addition, there is a problem in that when the product is taken out of the mold, the foam is cracked, resulting in a very low commercialization rate. On the other hand, in the two-stage foaming, the cross-linking of the foam progresses considerably during the secondary foaming, so that the cell diameter becomes small, and as a result, a foam having high compressive stress cannot be obtained.

The present invention overcomes the above-mentioned drawbacks, and efficiently and quality-improves a final foam that has been foamed 10 times or more, especially one having a relatively (reasonably) large cell diameter and high compressive stress. It is an object of the present invention to provide a method for manufacturing without variation.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have found that a specific foaming agent, that is, a decomposition in which the initial decomposition rate at the decomposition temperature is a slow decomposition in the range of 1/20 to 1/41 with respect to the main decomposition rate. Pattern and the initial decomposition rate is 4-9
ml / g-min, the main decomposition rate is 100-180 ml /
The present invention has been completed by finding a method for obtaining a foam having a high commercialization efficiency, a relatively large cell diameter, and a high compressive stress by using a foaming agent having g · min.
That is, the present invention is a method for producing a final foam that is foamed 10 times or more using a mixture of a polyolefin, a cross-linking agent and a foaming agent, and the average foam diameter of the final foam is 250 to 450 μm. And 25 of the final foam
The% compressive stress is 0.5 to 0.8 kg / cm ² , and the foaming agent is decomposed such that the initial decomposition rate at the decomposition temperature is low decomposition in the range of 1/20 to 1/41 with respect to the main decomposition rate. It has a pattern, and the initial decomposition rate is 4 to 9 m.
1 / g · min, the main decomposition rate is 100-180 ml / g
And 5 minutes to 30% of the foaming agent is decomposed by filling the mixture into a primary mold and heating the primary mold under a pressure of 50 kg / cm ² or more. The primary expansion is produced by decompressing and primary expansion to produce a primary foam having a volume expansion coefficient of 10 times or less, and then the primary foam is placed in a secondary mold and heated at normal pressure to produce the foaming agent. Is completely decomposed and secondarily expanded at a volume expansion coefficient of 10 times or less with respect to the primary foam to produce the final foam.

The "foaming agent" referred to in the present invention has a decomposition temperature which is equal to or higher than the flow initiation temperature of the above-mentioned polyolefin, and is, for example, azodicarbonamide, dinitrosopentamethylenetetramine, 4,4'-oxybisbenzenesulfonyl. Hydrazide or the like can be used. Further among these, have a decomposition pattern initial degradation rate at the decomposition temperature of the slow degradation in the range of 1/20 to 1/41 to the main degradation rate, and the rate of initial degradation is 4~9m
1 / g · min, the main decomposition rate is 100 to 180 ml / g
-You have to select the foaming agent that is the minute . The "decomposition temperature" referred to here is a temperature at which 50% or more of the decomposition rapidly occurs in the decomposition curve indicated by the amount of gas generated by the decomposition of the foaming agent when the temperature of the foaming agent is increased by heating. This is the temperature specified by the blowing agent manufacturer as the decomposition temperature of the blowing agent. Also, "decomposition rate" means 1 g
The amount of the foaming agent per unit is shown by the amount of gas decomposed and generated per minute. Further, the "initial decomposition rate" means that at the decomposition temperature, the decomposition rate of the foaming agent gradually increases,
It means the average speed until it reaches a substantially constant speed state, and it is usually shown by a value obtained by dividing the gas generation amount from the start of decomposition to the time when 10 to 30% of the foaming agent is decomposed by the time period therebetween. Also,
The "main decomposition rate" means the speed when the decomposition rate becomes substantially constant.

The blowing agent used in the present invention has an initial decomposition rate / main decomposition rate in the range of 1/20 to 1/41.
Slow decomposition and initial decomposition rate of 4-9 ml / g
Minutes, the main decomposition rate is 100-180 ml / g.min.
It is. This is because the above ratio exceeds 1/20
The reason is that when the initial decomposition rate exceeds 9 ml / g · minute, the average cell diameter of the final foam becomes too small and the cell uniformity becomes poor. On the other hand, the initial decomposition rate is 4 ml / g
If less than a minute, the formation of cell nuclei in primary foaming
If the average bubble size becomes too large, the number will be insufficient.
In addition, the bubble diameters are also nonuniform, which is not preferable.
As a foaming agent having such a decomposition pattern, for example, "Vinihol AC # 3" (manufactured by Eiwa Kasei, decomposition temperature:
200 ° C, initial decomposition rate: 9 ml / g-min, main decomposition rate: 180 ml / g-min, both speed ratio = 1/20) "Vinihol AC # R" (manufactured by the same company, decomposition temperature: 200 ° C, initial decomposition rate) 5 ml / g-min, main decomposition rate; 140 ml /
g · min, both speed ratio = 1/28), “Cellular D” (manufactured by Eiwa Kasei Co., decomposition temperature: 205 ° C., initial decomposition rate: 4 ml)
/ G · min, main decomposition rate: 165 ml / g · min, both speed ratio = 1/41), “Neocerbon N # 1000S” (manufactured by Eiwa Kasei Co., decomposition temperature: 159 ° C., initial decomposition rate: 4 ml)
/ G · min, main decomposition rate; 100 ml / g · min, both speed ratio = 1/25).

In the present invention, the decomposition of the foaming agent in the primary mold is 5 to 30%. If it is less than 5%, the number of cell nuclei formed is extremely small, the average cell diameter becomes too large, and the cell diameter becomes non-uniform, so that a desired foam cannot be obtained. On the contrary, if this exceeds 30%, the average bubble diameter becomes too small and the compressive stress decreases. The means for decomposing 5 to 30% is not particularly limited, but the heating temperature of primary foaming is 120 to 150 ° C, preferably 130 to 145 ° C.
The easiest and most reliable method is to adjust the expansion coefficient of the primary foaming by controlling a predetermined heating time with the temperature set to a relatively low temperature, thereby controlling the decomposition amount of the foaming agent. The time can be arbitrarily selected depending on the intended primary expansion ratio, that is, the amount of decomposition of the foaming agent.

In the secondary foaming, "completely decompose the rest of the foaming agent" is meant to include a case where the foaming agent is almost completely decomposed, that is, substantially completely decomposed. The heating temperature and the heating time are not particularly limited either, but it is important to completely decompose and foam the foaming agent, and it is preferable to set it within a range that does not adversely affect the polyolefin resin, and usually about 160 to 190 ° C. The heating time is usually about 20 to 60 minutes.

In the present invention, the pressure in the primary expansion step is
It is 50 kg / cm ² or more. If the pressure is less than this, depending on the expansion ratio, under the condition of expanding to about 10 times, the foam leaks from the mold and causes the deformation of the primary expanded product, resulting in a decrease in the commercialization rate. Because. Also, the secondary expansion is performed under normal pressure, usually 20 k
It will be processed under a pressure of g / cm ² or less. Further, in the present invention, both the primary expansion ratio and the secondary expansion ratio have a volume expansion coefficient of 10 times or less. If the primary expansion ratio exceeds 10 times, the primary foam will be deformed or cracked. Also, if the secondary expansion ratio exceeds 10 times, the average cell diameter becomes too large and the secondary foam is deformed or cracked.

In the present invention, "polyolefin" means
For example, polyethylene, an ethylene-propylene copolymer, an ethylene-butene copolymer, an ethylene-vinyl acetate copolymer, ethylene and methyl, ethyl, propyl which are usually produced by a high pressure method, a medium pressure method or a low pressure method which are commercially available Or a copolymer of butyl with each acrylate (the content of this ester; within 45 mol%), or those chlorinated to a chlorine content of 60% by weight,
Further, a mixture of two or more of these, or a mixture of these with isotactic polypropylene or atactic polypropylene, and the like.

The "crosslinking agent" referred to in the present invention has a decomposition temperature of at least the flow initiation temperature of the polyolefin in the above-mentioned polyolefin, and is decomposed by heating to generate free radicals to cause intermolecular formation. Examples thereof include organic peroxides, which are radical generators that cause cross-linking. For example, dicumyl peroxide, 2,5-dimethyl-2,5-bis-tert-butylperoxyhexane, 1,3-bis-tert-peroxy-isopropylbenzene, and the like.

In the present invention, in order to control the foaming state, a compound containing urea as a main component, a metal oxide such as zinc oxide or lead oxide, a lower or higher fatty acid or a metal salt of a lower or higher fatty acid, etc. A foaming aid and the like can be added. Further, carbon black, zinc white, titanium oxide, and other commonly used compounding agents can be added to improve physical properties.

[0014]

In the present invention, since the foaming agent having an initial decomposition rate of low decomposition rate is decomposed by 30% or less in the primary mold, the decomposition of the foaming agent in the foam in the primary mold is mainly Only the low decomposition rate region is stimulated, and the number of bubble nuclei formed thereby can be suppressed.
Furthermore, as a result, the decomposition of the foaming agent in the secondary mold is
A main decomposition rate, in other words, a high decomposition rate region is mainly caused, and the gas generated thereby flows into the bubble nuclei already formed in the primary foaming in a short time. Therefore, by growing a bubble by the inflow, 250-450
have a relatively large uniform bubbles of [mu] m, and the 25
% Compressive stress is not relatively high and 0.5~0.8kg / cm ²
A final foam can be obtained .

The reason why the decomposition of the foaming agent under high pressure mainly contributes to the formation of cell nuclei and the number of the cell nuclei formed depends on the decomposition rate of the foaming agent is unknown. Is estimated to be: That is, under high pressure, the gas generated by the decomposition of the foaming agent is in a high pressure state, so it is difficult to contribute to the formation of bubbles and is highly dissolved in the resin, and the dissolution reaches a saturated state. At this point, it is considered that some of the nuclei bubbles are vaporized and remain in the resin. Therefore, when the decomposition rate of the foaming agent is high, the gas concentration in the vicinity of the foaming agent fine particles in the resin reaches the saturation solubility before gas diffusion and easily forms a cell nucleus. On the contrary, if the decomposition rate of the foaming agent is slow, it is presumed that the gas diffuses before the saturated solubility is reached and it becomes difficult to form a bubble nucleus. For these reasons, it is considered that the number of bubble nuclei formed by mainly decomposing the foaming agent in the low-decomposition rate region in the primary mold is remarkably suppressed and becomes an appropriate number.

On the other hand, since the secondary foam is in a low pressure state under normal pressure, the primary foam is in a microstructurally loose state, and the foaming agent gas decomposed and generated in the secondary foam is already formed. It is presumed that it easily flows into the existing bubble nucleus and promotes bubble growth. At this time, if the decomposition rate is slow, the fine structure of the primary foam is loose, so the generated gas easily flows into the looser part,
As a result, cell spots may be caused. Therefore, in the decomposition of the foaming agent in the second order, it is preferable to generate a large amount of gas at a time at a decomposition rate as high as possible from the viewpoint of uniform cell growth and uniform cell size.

Further, since both the primary expansion ratio and the secondary expansion ratio are 10 times or less, the average foam diameter of the final foam can be made not too large and not too small. Deformation and cracking of the secondary foam can also be prevented. Furthermore, the pressure in the primary expansion step is 50 kg / c
Since it is m ² or more, leakage of the foam from the mold does not occur and it does not cause deformation of the primary expansion product, and therefore the productization rate is excellent. From the above, in the present invention, by using a predetermined foaming agent, the foaming in the high pressure state in the primary is suppressed to a certain level or less, and in the normal pressure state in the secondary, by foaming as much as possible, it is possible to obtain a proper foam in the final foam. It is possible to secure a desired bubble diameter of a large size, secure an excellent compressive stress, and prevent deformation and cracks.

[0018]

The present invention will be described below in detail with reference to examples. A composition comprising 100 parts by weight of polyethylene having a melt index of 1.0 (hereinafter referred to as "parts"), 2 parts of dicumyl peroxide (purity 40%) , 0.5 part of zinc oxide and 1.0 part of stearic acid, A mixture (two kinds of "composition A" according to the present invention and "composition B" according to a comparative example) in which 10 parts of the following two kinds of foaming agents are added is prepared. Here, as the foaming agent in "composition A", azodicarbonamide "Vinihol AC # 3" (manufactured by Eiwa Chemical Co., Ltd., decomposition temperature: 200 ° C, initial decomposition rate: 5 ml / g · min, main decomposition rate: 140 ml / g · min, both speed ratio = 1/28)
Was used. As the foaming agent in "Composition B", azodicarbonamide "Vinihol SW # 5" (manufactured by Eiwa Kasei, decomposition temperature: 200 ° C, initial decomposition rate: 27 ml / g)
・ Min, main decomposition rate; 27 ml / g ・ min, both speed ratio = 1 /
1) was used.

The above mixture was kneaded on rolls each having a surface temperature of 100 ° C. to obtain each mixture. Then, each of the blends was processed under various conditions shown in Table 1 to produce 30 times the final foam. Further, the above-mentioned blending amount of the foaming agent is 10
A mixture similar to the above was prepared, except that the parts were changed to 5 parts, and this was processed under the various conditions shown in Table 2 to give 15
Double final foam was similarly prepared. Incidentally, Examples 1 to 4,
Composition A was used in Comparative Examples 1 to 4 and 6, 7 and Composition B was used in the other cases (Comparative Examples 5, 8, and 9). When this composition B was used, in the table, the mark * was added after the number of this comparative example. Incidentally, in the table, the numbers marked with * are out of the scope of the present invention.

[0020]

[Table 1]

[0021]

[Table 2]

In order to evaluate the performance of each of the above final foams, the items shown in Tables 1 and 2 were measured, and the results are shown in the same table. In the same table, the units of the numbers in the "leakage of foam in the primary mold" column and the "deformation and cracking of primary and secondary foams" are numbers. "Amount of foaming agent decomposed in the primary mold" is%
Is shown. The "average cell size" is 10 for each foam.
The diameter of 0 bubbles is measured, and the average value is shown. "25% compressive stress" is measured according to JIS K676
The method of 7 was used. The evaluation method of "bubble uniformity" is
The evaluation was made by visual judgment, and the evaluation was made as follows.
◯: Good uniformity, Δ: Slightly non-uniform, ×: Non-uniform.

According to these results, the primary pressure is 40 k
When it was as low as g / cm ² (Comparative Example 4), the foam leaked in the primary mold, and the primary and secondary foams were deformed and cracked. Also, when the primary expansion ratio was as large as 11 times (Comparative Example 1), the primary and secondary foams were deformed and cracked. Further, when the primary expansion ratio is as large as 11 times (Comparative Example 1) and the decomposition amount of the foaming agent is as large as about 36% (Comparative Example 6), the average cell diameter is 105 to 115.
As small as μm, and compressive stress is 0.30, 0.47 kg
As small as / cm ² . Further, when the secondary expansion ratios were as large as 11 and 15 times (Comparative Examples 3 and 2), the average cell diameter was 635 and 750 μm, which were extremely large, and the secondary foam was deformed and cracked. Furthermore, the amount of decomposition is 3.4,
When it was as small as 3.6% (Comparative Examples 2 and 7), the average bubble diameter was 750 and 580 μm, which were extremely large, and the bubbles were non-uniform. Further, when the initial / main decomposition rate ratio was as large as 1/1 (Comparative Examples 5, 8, and 9), the average bubble diameter was as small as 105 to 125 μm and the compressive stress (0.3
^{2 to} 0.49 kg / cm ² ) was not excellent.

On the other hand, in Examples 1 to 6, in both the 15-fold and 30-fold foams, there were none of the above problems, and the desired average cell diameter (265-450 μm) was obtained.
m), excellent uniformity of cells, and excellent compressive stress (0.57 to 0.79 kg / cm ² ) can be produced, and the foam leaks from the mold. Since it does not exist, the productization rate is also very good. It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention according to the purpose and application.

[0025]

According to the production method of the present invention, a final foam that is foamed 10 times or more, particularly a foam having a reasonably large cell size (that is, not too large and not too small) and a high compressive stress, It can be manufactured efficiently and without variation in quality.

Claims (1)

(57) [Claims] 1. A method for producing a final foam which is foamed 10 times or more using a mixture of a polyolefin, a crosslinking agent and a foaming agent, wherein the final foam has an average cell diameter of 250 to 450 μm. Yes, the 25% compressive stress of the final foam is 0.5-0.8 kg
/ Cm ² , the foaming agent has a decomposition pattern in which the initial decomposition rate at the decomposition temperature is a slow decomposition in the range of 1/20 to 1/41 with respect to the main decomposition rate, and the initial decomposition rate is 4-
9 ml / g-min, the main decomposition rate is 100-180 ml
/G.min., The above mixture is filled in a primary mold, and the primary mold is heated to 50 k
By heating in a pressurized state of g / cm ² or more, 5 to 30% of the foaming agent is decomposed and then depressurized to be primary expanded, and the primary expansion has a volume expansion coefficient of 10 times or less. Then, the primary foam is put into a secondary mold and heated at normal pressure to completely decompose the rest of the foaming agent, and at a volume expansion coefficient of 10 times or less with respect to the primary foam. A method for producing a polyolefin foam, which comprises secondary expansion to produce the final foam.