JPS6017385B2 - Ethylene-vinyl acetate copolymer resin compound for foam processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a highly concentrated composition (hereinafter abbreviated as masterbatch) of a powdery compounding material for foam processing based on low molecular weight polyisoprene rubber.

) and an ethylene monovinyl acetate copolymer resin (hereinafter abbreviated as EVA). the current,
Ethylene-vinyl acetate copolymer resin (hereinafter abbreviated as EVA).

) is used for foam molding by blending powdered compounding materials such as foaming agents, and is used for various purposes. However, E
When mixing powdered ingredients into VA, loss of powdered ingredients due to scattering during measuring, mixing, kneading, and molding processes, contamination of intermediate products or final products due to falling and adhesion of scattered particles, This caused problems such as deterioration and contamination of the working environment and equipment. In order to solve such problems, a method has been considered in which a powdered compounding material is mixed in advance with a polymer (hereinafter abbreviated as a masterbatch) and is blended into EVA. It is strongly desired that the performance of these masterbatches is as follows: 1) Workability and moldability in measuring, mixing, kneading, and molding processes are not impaired; 2) Product properties are not impaired; 3) They can be combined more economically. .

Therefore, in order to retain the function as a masterbatch, selection of the base polymer is extremely important.

For example, in order to satisfy item 1, it is inevitable that the fluidity of the masterbatch will decrease due to the addition of powdery compounding materials, and as a result, it is inevitable that the moldability will deteriorate.
To compensate for this, it is necessary to keep the masterbatch concentration as low as possible, or to use a material with better fluidity than the main raw material polymer as a base.

Regarding item 2, it is necessary to select and use a material that has good compatibility between the main raw material polymer and the masterbatch base.

Optimally, a masterbatch based on the same material as the main raw material is desirable. Regarding item 3, since the cost of manufacturing the masterbatch itself is added,
Since it is inevitable that the compounding unit price will increase, it is desirable that the masterbatch concentration be high so that the amount of masterbatch used can be reduced as much as possible.

As described above, quality, moldability, and cost are desired to conflict with each other as required characteristics for a masterbatch, so the reality is that it is necessary to compromise on appropriate points when using masterbatches.

From this point of view, the present inventors have developed a highly concentrated powder composition of one or more of powder compound A and polyisoprene rubber B having a molecular weight of 10,000 to 80,000 and a vinyl bond content of 25% or less. The present invention has been completed based on the discovery that the above-mentioned contradictory points can be overcome by blending an ethylene-vinyl acetate copolymer resin with one or more of the high-concentration powder compositions. I came to the conclusion. Foam molding requires a wide variety of powdered ingredients such as blowing agents, crosslinking agents, pigments, fillers, solvents, foaming aids, etc., and when compared to other types of molding, the proportions of these ingredients are It is characterized by an extremely large number of them.

Therefore, the masterbatch concentration in this field has to be quite high to provide little economic benefit, which has been a major obstacle to the use of masterbatches. When attempting to increase the concentration of conventionally known masterbatches, the drop in fluidity may cause accidents such as prolongation of the weeping time or non-uniform dispersion during the molding process, so the masterbatch concentration is Usually 30-40% is common. In contrast, masterbatches based on low-molecular-weight polyisoprene rubber, which is the subject of the present invention, can have a high concentration of up to 95%, retain flexibility, and are compatible with EVA. It has excellent properties and can be uniformly dispersed. Therefore, abnormalities in the cell structure (so-called pinholes) due to non-uniform dispersion of the powdered compound can be prevented. Furthermore, it has the characteristic that it can be easily crosslinked with organic peroxides such as dicumyl peroxide, and it is based on the fact that it has been found to be extremely effective against foaming of EVA. . E that can be used in the present invention
VA has a pinyl acetate content of 3 to 45% by weight,
Preferably, the amount is 5 to 3%.

The low molecular weight polyisoprene rubber that can be used in the present invention is
One with a molecular weight of 10,000 to 80,000, preferably 4
0000 to 60000.

If the molecular weight is higher than this, it will be difficult to increase the concentration of the powdered compound, and if the molecular weight is lower than this, the physical properties of EVA will deteriorate, so it cannot be used. In addition, the molecular weight here means the viscosity average molecular weight (Mv), [ri]=1.
21×10-4MVo. 77 (However, [ri] is 30:00
Intrinsic viscosity measured in toluene. ). Further, the vinyl bond amount is 25% or less. If the amount of vinyl bonds exceeds 25%, the masterbatch becomes hard, which is not preferable. Furthermore, considering these points, the amount of bonds other than vinyl bonds, especially the cis-1
．． It is desirable that the total amount of relief is 70% or more. In addition, the powdered compounding materials that can be used as masterbatches include, in addition to blowing agents, crosslinking agents, and blowing aids, pigments, fillers, stabilizers, solvents, antistatic agents, and antistatic agents used during the foaming process of EVA. Fuel, nucleating agents, etc. are thrown.

The preferred amount of powdered compounding material in the masterbatch is 60-95% by weight for the reasons described above. Each of the powdery compounding materials can be used as a masterbatch, or a plurality of powdery compounding materials can be used in one masterbatch. The method for producing a masterbatch according to the present invention involves weighing the above-mentioned powdered compounding materials and the polyisoprene rubber, and then uniformly kneading them using a conventional kneading machine such as a roll or a bath ball mixer or a kneader. Cut into sheets, cut into pellets using cutting equipment,
It can be easily obtained by forming it into flakes, plates, or pastes.

In the kneading process, it is efficient to knead at a temperature of about 80 to 120°C.

Foam molding of EVA involves simply injecting the foam into a mold through an injection molding machine or an extruder, and further,
Molding to obtain a crosslinked foam through a series of steps of forming a sheet after making it into a sheet using a hawking machine such as a roll, Banbury mixer, powder, or Henschel mixer, compressing it with a heated press, and then removing the pressure. Forming to obtain a low density crosslinked foam by heating to decompose the residual powder decomposed foaming agent, refers to a sheet that has undergone the above mixed twilling process,
This is the same method as conventional methods, such as forming a crosslinked foam into a pellet shape, injecting it into a heated mold using an injection molding machine, and then opening the mold to obtain a crosslinked foam. Even if this masterbatch is used, there is no need to change the equipment.

This masterbatch can be used in the usual way, and the crosslinking speed of low molecular weight polyisoprene rubber and EVA is similar, so it has very little effect on the physical properties of the product and can suitably achieve the originally intended performance of the masterbatch. be satisfied. Hereinafter, this will be described in detail with reference to Examples.

Example 1 When producing a crosslinked foam of EVA (melt index 1.5 minutes/10 minutes, vinyl acetate content 15% by weight), a masterbatch of filler (calcium carbonate average particle size 1.4 degrees Fahrenheit) was used. Therefore, we used the same EVA as the main raw material EVA and polyisoprene rubber (molecular weight 47,000, vinyl bond amount 1).
An attempt was made to manufacture a masterbatch based on 3%).

The above base polymer was wound around an 8-inch strawberry roll kept at about 90%, and fillers were sequentially added to increase the concentration (see Table 1).
is the limit, whereas polyisoprene rubber still had flexibility even at a cloud cover of 9%. This had an extremely high concentration and fully satisfied one of its functions as a masterbatch.

Table 1 Change in kneading state due to addition of filler ○ Extremely easy ○ △ Slightly difficult to mix △ Difficult to mix ○ ) is shown.

0 The filler masterbatch produced in this way (
Calcium carbonate content: 9% by weight) and a blowing agent masterbatch separately produced in the same manner (content: 9% by weight)
), and using a masterbatch pellet made into a pellet shape with an elevation angle of about 3 using a cutting machine, cross-linked EVA (melt index 1.5 minutes/10 minutes, vinyl acetate content 15% by weight) crosslinked foam. It was manufactured according to the formulation shown in Table 2.

The foam was prepared by first measuring a predetermined amount of filler masterbatch and blowing agent masterbatch, and then maintaining the temperature at approximately 90°C.
After kneading with EVA using an inch diameter roll to form a sheet with a thickness of about 3 ribs, it was inserted into a mold attached to a compression molding machine kept at 170°C and compressed for 15 minutes, after which the pressure was removed and the mold was opened. obtained by doing.

For comparison, cross-linked foams were produced without using a filler or blowing agent as a masterbatch, but with the same contest. Note that no pigment was used to observe changes in appearance color. As a result, the roll kneading performance, when using masterbatch and when not using it,
It was found that the masterbatch of the present invention was superior as there was a significant difference in scattering properties. Furthermore, the results showed that there was almost no difference in the physical properties of the products, and that the influence of this masterbatch on the products was extremely small. Table 2 Comparison of crosslinked foam molding Compound unit: parts by weight, contents of foaming agent and filler in parentheses (Note) The foaming agent used was Celmic CAP manufactured by Sankyo Kasei.

*1 Masterbatch content is 90% by weight, so foaming agent is 8.9 parts by weight x 0.9 = 8 parts by weight *2 Masterbatch content is 90% by weight, so calcium carbonate is 55.5 parts by weight x 0.9 = 49.95 parts by weight Example 2 Using polyisoprene rubber with a molecular weight of 47,000 and a vinyl bond content of 13% and a polyisoprene rubber with a molecular weight of 7,000 and a vinyl bond content of 15%, polyisoprene rubber was prepared. In order to examine the influence of molecular weight on EVA, crosslinking foam molding was attempted under the compounding conditions shown in Table 3.

The molding conditions in this case were the same as those described in Example 1.

As a result, those with a low molecular weight had a much greater influence on the product than those with a higher molecular weight, making it impossible to obtain a good product.

Table 3 Comparison of polyisoprene rubbers with different molecular weights (Note) Pinifoli AK-2 manufactured by Eiwa Kasei was used as the blowing agent.

Claims (1)

[Claims] 1 Powder compounding material A used during foaming processing of ethylene-vinyl acetate copolymer resin 30 to 95% by weight and molecular weight 10
A foaming process consisting of one or more of the high-concentration compositions of a powder compound consisting of 70 to 5% by weight of polyisoprene rubber B having a molecular weight of 000 to 80,000 and a vinyl bond content of 25% or less, and an ethylene-vinyl acetate copolymer resin C. Ethylene-vinyl acetate copolymer resin blend for use.