JPS6020943A - Non-crosslinked polyethylene resin expanded particle - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to non-crosslinked polyethylene resin foam particles that can be used for in-mold foam molding, and more specifically, the present invention relates to non-crosslinked foamed polyethylene resin particles that can be used for in-mold foam molding, and more specifically, the present invention relates to non-crosslinked foamed polyethylene resin particles that are pre-foamed in a non-crosslinked state using a specific polyethylene resin as a base material. The present invention relates to non-crosslinked polyethylene resin foam particles that can be foam-molded in a mold by imparting secondary foaming ability to the foam particles.

In recent years, the technology in the field of polyethylene in-mold foam molding, which manufactures foam molded products by heating and expanding polyethylene resin-based foam particles in a mold, has made remarkable progress, and the technology used in conventional in-mold foam molding has significantly improved. It has come to be used in a wide range of industrial fields because it has excellent properties such as toughness, weather resistance, chemical resistance, and oil resistance that polystyrene resin foams do not have.

However, in these conventional polyethylene in-mold foam moldings, it is necessary to crosslink the base resin and foam it.
The base resin was chemically crosslinked by adding a crosslinking agent, or crosslinked by radiation irradiation, and then foam molded. The reason for this is
Compared to polystyrene resin, the temperature dependence of the viscoelastic properties of polyethylene resin when heated is extremely poor, and the appropriate heating conditions for foam molding are extremely narrow, making it industrially impossible or difficult to mold even if possible. This is because only products with inferior dimensional accuracy, surface appearance, and mechanical properties can be produced. These foam molded products based on cross-linked polyethylene resin are cross-linked, so even if you try to recycle the molded products after use, they have no heat fluidity and cannot be recycled, and must be incinerated. Polystyrene resin foams have not become widespread because they require an extra process for crosslinking, a crosslinking agent, etc., and are expensive compared to general-purpose foams.

In addition, attempts have been made to extrude foam non-crosslinked polyethylene resin and use granular foam obtained by crushing the resin to mold the resin in a mold (%Ko 46-29036, U.S. Pat. No. 3,504,068). Compared to foamed molded products that use resin as the base resin, products with inferior appearance can be obtained, and because they are crushed after extrusion foaming, the air bubbles on the cut surface may be destroyed, and the air bubbles inside the particles may also be damaged, resulting in inferior lamination. Only molded products have been obtained. In addition, in order to solve these problems, a method of manufacturing pre-expanded particles using a specific foaming method (Japanese Unexamined Patent Publication No. 5
No. 0-151269) has been proposed, but the ink that can be directly applied to non-crosslinked polyethylene resin is not specified, and the inventors' additional tests revealed that the apparent density was 0.
Only low foam particles of 5,9/c+++" or more were obtained.

The present inventors have solved the drawbacks of these crosslinked polyethylene resin foam molded products, provided a molded product with mechanical strength and dimensional stability equal to or greater than the foam molded products, and achieved excellent moldability. As a result of intensive research to develop non-crosslinked polyethylene resin foam particles with
It was discovered that ζ foamed particles are suitable for achieving the purpose, and based on this knowledge, the present invention was completed.

That is, in the present invention, the base resin is made of a non-crosslinked polyethylene resin having a melt index of 0.7 g/10 minutes or less, a melt index ratio of 40 or more, and a crystal melting point of 116° C. or more, and has an apparent density of 0.3 g/10 min. The present invention relates to polyethylene resin foam particles having a size of Cm3 or less.

The polyethylene resin in the present invention has a melt index of 0.71'710 minutes or less and a melt index of 0.71'710 minutes or less.
7 g/1 (When polyethylene resin 1 resin thicker than 3 minutes is made into foamed particles, the size of the air bubbles that make up the particles becomes uneven, and in some cases, the air bubbles are easily destroyed and voids are generated. Also, the dimensional shrinkage rate is extremely large and only molded products with poor appearance can be obtained, which is not preferable.

The polyethylene resin used in the present invention has a melt index ratio of 40 or more, and polyethylene resins smaller than 40 have a narrow range of suitable molding time during in-mold molding, and can be used for complex molded products with different wall thicknesses. When molding, it is difficult to set molding conditions to produce a molded product with excellent physical properties such as appearance and tear strength for both thick and thin parts, which limits what can be molded, and the tear strength of the molded product is also poor, which is undesirable. .

The polyethylene resin in the present invention has a crystal melting point of 1
Polyethylene resins having a temperature of 13° C. or higher and lower than 116° C. can no longer be formed into foamed particles without crosslinking. Furthermore, even if the melt viscoelasticity is improved by increasing the molecular weight, a long cooling time is required during in-mold foam molding, and the dimensional shrinkage ratio is large, resulting in molded products with poor appearance.

The base resin used in the present invention is a non-crosslinked polyethylene resin that simultaneously satisfies the above six conditions.

As this polyethylene resin, a homopolymer of tr ethylene containing 50 molar or more ethylene units, a crystalline copolymer of a monomer copolymerizable with ethylene, and a mixture thereof can be used. Examples of these polyethylene resins include low-pressure or medium-pressure-produced low-density polyethylene, hemispherical low-density polyethylene, medium-density polyethylene, and low-density polyethylene.

The base resin of the present invention can also be mixed with the above-mentioned non-crosslinked polyethylene resin. In addition, banding prevention agents, nucleating agents, coloring agents,
It is also possible to mix known additives with the number ratio inhibitor, anti-fusing agent, and lubricant.

The polyethylene resin foam particles in the present invention have an apparent density of 0.3, j9/cyn'' or less, and sometimes are commercial foam particles with an apparent density of 0.033 g/Cm3 or less.

The polyethylene resin foam particles of the present invention are mainly used for in-mold foam molding, and the apparent density of the foam particles is 0.39.
When molding larger /cyn3, the mold clamping pressure will be greater, and higher temperatures will be required to eliminate the fusion between particles, which will likely cause shrinkage wrinkles and blisters due to delayed claws on the surface of the molded product. I don't like it. Furthermore, when the foamed polyethylene resin particles of the present invention are used as they are as a P filter material for an upward flow raster to adsorb and over-separate heavy metal sludge in plating waste liquid, the appearance of the foamed particles is If the density is greater than 0.3 g/♂, the sorption/passage efficiency will decrease, which is not preferable.

Furthermore, since the polyethylene resin foam particles of the present invention are in a non-crosslinked state, foam particles with an apparent density of more than 0.39/crn3 have non-uniform cells, with large poi-P-shaped cavities particularly in the center. Even if in-mold molding is performed, only molded products of inferior quality can be obtained.

The polyethylene resin foam particles of the present invention can be produced by a conventionally known pre-foaming method. for example.

A base resin is supplied into the extruder, and a volatile organic compound with a low boiling point (foaming agent) is injected into the molten base resin to uniformly contain it, and this foamable resin is stranded under atmospheric pressure. A method in which polyethylene resin particles are extruded through a mold to form a shape, and simultaneously cut on the mold surface and pre-foamed. Polyethylene resin particles are placed in a sealed container, brought into contact with a low boiling point volatile organic compound, and heated under pressure to form the inside of the resin. In particular, the method involves impregnating resin particles dispersed in an aqueous suspension state in a pressure-resistant container with a volatile organic compound under pressure and heating, and then foaming the Ibi suspension by heating. A method of foaming by discharging the foam into a low-temperature, low-pressure atmosphere is preferred because foamed particles with a wide range of apparent densities can be produced.

The volatile compound used in 1 is fi-8TM.
Organic compounds having a KB value in the range of 12 to 80 according to D-1133 are preferable, such as aliphatic hydrocarbons such as fluoropane, propylene, butane, butene, (methane, pentene, hexane, hexene, heptane, etc.). aliphatic hydrocarbons such as cyclobutane, cyclo(methane, cyclohexane), trichlorofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, monochlorodifluoromethane, methyl chloride, methylene chloride, ethyl chloride, ethylene One or a mixture of two or more selected from 710 denated hydrocarbons such as loride having a KB value in the range of 12 to 80 can be used.

The foamed polyethylene 4m resin particles of the present invention can be used as cushioning materials, cushioning containers, rain ventilation, and heat insulating materials by foaming (expansion) molding using the conventionally known bead molding method.

Used as floating material, etc. In addition, the foamed particles as they are can be used as fillers for cushions, fillers for composites, fillers, filtration materials, etc.

The in-mold bead molding method involves pressure-injecting air, an inorganic gas such as nitrogen gas, or an organic gas such as a volatile compound gas into the foamed particles to give them secondary foaming ability, then filling them into a mold and heating them. There are methods such as compressing the foamed particles to a volume smaller than the original bulk volume by a predetermined amount, filling them in a mold as it is, giving expansion ability and heating molding, and methods that combine these methods. Can be used.

Measurement and evaluation of characteristics in the present invention were performed as follows.

(1) Sample for measuring characteristics of base resin: Compress and heat the shaped foam particles into a sheet of about 0.5 mm in a heated press controlled at 200°C, hold for 5 minutes, release the pressure, and prepare the sample. The sample was taken out and left to cool.

(2) Melt index of base resin Measured according to ASTM Ll-1238. The condition is 19
0℃, load 2.16 to 1? It was measured with

;3) Melt index ratio of base resin A8TM L
According to l-1238, 190℃ load is 21.6! ? It is determined by the ratio of the melt index (H, M, 1.) measured at No. 1 load and the melt index (M, I, ) at a load of 2.117.

M.I.

(4) Using a crystal melting point differential thermometer (Model DBC1-B, manufactured by Parkin and Nilmer) of the base resin, the heating rate was 10°C/min, and the sample i0.
The peak position of the endothermic peak measured under the conditions of 01# was defined as the crystal melting point.

(5) Density of profiteering resin Measured according to l~sT+x-D-1505.

+61 Appearance of foamed particles: Density For foamed particles that have been pre-foamed for one day or more,
Weigh the weight, immerse the sample in water, and measure its volume.

(7) Characteristic evaluation of in-mold foam molded products The apparent density is approximately 0. The pre-foamed polyethylene particles were pre-foamed into Oro3 Fi/an3 at 80°C for 10 minutes.
In pressurized air with a cage pressure of 0n2, the internal pressure of the particles is approximately 1kg/
cm2 dage pressure, and then molded it into a closed mold with small holes (same dimensions 300 x 30 o x 50 m).
m), heated with water vapor to a temperature near the crystalline melting point of the base resin, foamed and fused, and then cooled with water at about 20°C, after which the mold was opened and the molded product was taken out. The molded product was left in a constant temperature bath at 70° C. for 8 hours to dry.

■ Appropriate molding time range Molding is performed using steam at a temperature equivalent to the crystalline melting point of the base resin + 5°C, and the heating time is changed every second, and heating is performed so that the dimensional shrinkage of the molded product is 10 factors or less. The time is shown in the IWI range.

The larger the time range, the greater the degree of control of the molding conditions, and even molded products with different wall thicknesses can be uniformly foam-molded.

■ Minimum cooling time The shortest cooling time is shown as the shortest cooling time in which the molded product does not develop or become deformed when it is cooled with water at about 20°C after steam heating and taken out.

In in-mold molding, this cooling time 181 occupies most of one cycle of molding, so shortening this cooling time shortens the cycle time and is the key to improving the quality of the molded product.

(2) Dimensional Shrinkage Rate After the dried molded product is left at 26°C for 24 hours, the vertical, horizontal, and thickness dimensions of the molded product are measured at 6 points each, and the difference from the mold dimension is shown.

The evaluation was performed based on the average value of the shrinkage percentage of each part.

The molding was carried out under the conditions of the median value of the suitable ri time range and the shortest cooling time.

(H) Tear strength Early measurements were made according to JIS K 6767.

Example 1 In an autoclave equipped with a heating jacket equipped with a stirrer, a nitrogen gas pressure inlet, a pressure elbow and a discharge valve at the bottom, linear polyethylene (density 0.953 ji/cm3, melt index 0.5.9/10) was placed. minutes, melt index ratio 74, crystal melting point 124°C) non-crosslinked particles 100,
, 'T4f 3ij part, n-butane 25 N'Di,
and 2 parts by weight of basic magnesium carbonate in 400 parts of water.
The dispersed core/colloid dispersion was placed in a heavy-ht section, heated to a temperature 5°C higher than the crystalline point of the first finger of the tree while stirring, and held for 45 minutes to convert n-butane into polyethylene resin particles. After impregnating, pressurize with nitrogen gas to a pressure that is 5 to 6 kg/cm24 higher than the vapor ratio of n-butane at that temperature, and while maintaining the pressure at that pressure, the relationship between the resin particles and water is discharged from the bottom outlet 5P. The turbidity was released under atmospheric pressure to obtain foamed particles. After the pre-expanded particles were left for one day and night, the apparent weight was 0.032! ? It was 76m3. These pre-expanded particles were molded by the method described above, and their properties were evaluated. The results are shown in Table 1, Experiment F; 1.

In the same manner, the properties of molded products were evaluated using the polyethylene resins listed in Table 1'5A Test Plan 2.6, and the results are shown in the first panel.

Comparative Example 1 Expanded particles were produced in the same manner as in Example 1, except that the polyethylene Q4 resin used was changed.

The characteristics of the molded product were evaluated. These results are shown in Table 1 for experimental cups 4 to 4.
9.

From Table 1, polyethylene tree 1i with a melt index greater than 0.7&/10 minutes! r Foamed particles (experimental cup 4.
8.9) has a narrow suitable molding time range, a small tear strength δ, a large dimensional shrinkage rate, and a melt index ratio of less than 40.
．． In case 9), the fusion between the foamed particles is insufficient, resulting in a low tear strength of the molded product and a narrow suitable time range, and polyethylene resin foamed particles with a crystal melting point lower than 115°C (experiment t5.7°). It is clear that 9) requires a long cooling time and has a large dimensional shrinkage rate.

On the other hand, foamed particles (Shokenban 1.2.6), which meet the above requirements within the scope of the present invention, have a wide suitable molding time range, a short cooling time, a small dimensional shrinkage rate of the molded product, and tear resistance. It is clear that the strength is unclear.
Expanded particles were produced in the same manner as in Example 1, except that the particles were changed to those shown in Example 1, and molded in the same manner as in Example 1. The results are shown in Table 2.

In addition, the results of Example 1 and Experiments 1 and 2 are also listed.

Table 2 shows that the foamed particles in which the polyethylene resin of the present invention has a melt index of 0.7 g/10 minutes or less, a melt index ratio of 70 or more, and a crystalline melting point of 116°C or more have excellent in-mold moldability, and the physical properties of the molded product are also good. It is clear that good is better than good.

One-Person Boarding Mill Example 6 In Example 1 (Experiment 1), the tht of n-butane was changed to produce foamed particles with apparently different densities. Using these expanded particles, molded articles were molded in the same manner as in Example 1, and the results were as shown in Table 6. From Table 6, it is clear that foamed particles with an apparent density of more than 0.5 g/cm3 have non-uniform cells and only inferior molded products can be obtained.

Table 6 Procedural Amendment (White Brother) January 7th, 1980 Kazuo Wakasugi, Commissioner of the Patent Office 1. Indication of the case 1981 Patent Application No. 126940 2. Name of the invention Non-crosslinked polyethylene resin foaming Relationship to the particle amendment case Patent applicant 1-2-6 Dojimahama, Kita-ku, Osaka-shi, Osaka Prefecture (oo3) Asahi Kasei Co., Ltd. Column 5 of "Detailed Description of the Invention" of the specification subject to the amendment, Amendment Contents (1) Page 5, line 17 of the specification, "As a resin, ethylene units" is corrected to "As a resin, an ethylene homopolymer, an ethylene unit."

(2) On page 6, line 4, insert the following sentence after "There is polyethylene."

"Among these, high-density polyethylene with a density of 0.940 or more is superior in terms of in-mold foaming, wide molding time range, and shortest cooling time of less than 1 minute." (3) Same, page 1O, No. 9 ~ Line 10 [Correct High Road Melt Index, Melt Index (H, M, 1.ll to "High Road Melt Index (u, M, 1.) J.

(4) Insert the following sentence on page 15, line 10.

[Among these, the one using high-density polyethylene with a density of 0.940 or more (Experiment N [L 1, 2 ) has a minimum cooling time of less than 1 minute and is particularly useful industrially. ” (5) Table 3, page 19, lowest mood column “1 to 2
Correct "1 to 2 coarse bubbles" to "1 to 2 coarse bubbles".

that's all

Claims (1)

[Claims] 1. The base resin has a melt index of 0.75'/I
Expanded polyethylene resin particles having an apparent density Q of 39/cm" or less and made of a non-crosslinked polyethylene resin having a melt index ratio of 40 or more and a crystalline melting point of 116° C. or more.