JP3149152B2 - Non-crosslinked linear low density polyethylene resin pre-expanded particles and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-crosslinked linear low density polyethylene resin pre-expanded particle and a method for producing the same.

[0002]

2. Description of the Related Art Molded foams obtained by fusing a pre-expanded particle of a polyethylene resin in a mold by steam heating in a mold are well known. It has excellent low-temperature properties and chemical resistance, and is used in various markets, such as cushioning materials for packaging, mailing of industrial parts such as automobiles, and sheet cushion core materials for vehicles and furniture.

[0003] As this type of molded article, a molded article made of crosslinked high-pressure low-density polyethylene foam particles has been known. However, this crosslinked high-pressure low-density polyethylene foam molded article has good flexibility. However, impact cracking resistance and durability against repeated compression strain cannot be said to be sufficient, and improvements have been desired. Further, there is an economically disadvantageous problem that an extra step for cross-linking is required, and even if the cross-linked foam molded article becomes unnecessary, it cannot be returned to the original resin and regenerated. In an attempt to solve such a problem, many molded articles made of expanded particles using a non-crosslinked linear polyethylene resin having better mechanical strength than high-pressure low-density polyethylene have been developed. That is, JP-A-58-7643
No. 3 discloses a polymer density of 0.915 to 0.950 g.
/ A non-crosslinked linear low density polyethylene cm ³ is pre-expanded particles as a base resin, in JP-A-59-187035, a polymer with a molecular weight distribution of 15 or more - Density 0. 920 g
/ Cm ³ or more of the non-crosslinked linear polyethylene is pre-expanded particles as a base resin, in JP-A-63-117044, a polymer -. Density 0.920 to 0 differential scanning calorimetry at 940 g / cm ³ Pre-expanded particles using a non-crosslinked linear low-density polyethylene having two endothermic peaks in a DSC curve obtained by measurement as a base resin have been proposed.

[0004]

However, these non-crosslinked linear low-density polyethylene foamed particles have a non-crosslinked linear polyethylene having a polymer density of 0.915 g / cm ³ or more. The foamed particles obtained by in-mold fusion molding of these pre-expanded particles did not yet have satisfactory levels of impact cracking resistance and repeated compressive strain durability. Also, in these techniques, the polymer density of 0.915 g in a place having high toughness is used.
/ Cm ^{3 or} less, it is difficult to efficiently obtain pre-expanded particles having a high closed-cell structure and a high expansion ratio in a non-crosslinked state, and There remains a problem that the molded product obtained upon molding has a large sink mark, and a molded product having good impact cracking resistance and good durability against repeated compression strain cannot be obtained. As a measure for solving this problem, a cross-linked linear low-density polyethylene resin has been proposed in JP-A-61-51008, but there is a waste problem that such a resin cannot be recycled.

[0005] The object of the present invention is to solve the above-mentioned drawbacks, and the molded article obtained by fusion-molding the pre-expanded particles in the mold has the impact cracking resistance and the repeated compressive strain durability, which are conventionally known. It can be supplied as a molded foam superior to non-crosslinked linear low-density polyethylene resin molded foam, and has a high expansion ability of expanded particles during in-mold molding, and a small sink in molded products, and has excellent moldability. It is an object of the present invention to provide non-crosslinked linear low density polyethylene resin pre-expanded particles.

Another object of the present invention is to provide a method for producing non-crosslinked linear low-density polyethylene resin pre-expanded particles which achieves the above objects.

[0007]

That is, the pre-expanded particles of the present invention have a density of 0.990 to 0.930 g / cm ³ , and the polymer component obtained by fractionation by the temperature-elution method is 13C.
-The ratio Cw / Cn between the weight average distribution (Cw) and the number average distribution (Cn) measured by NMR is 1.1 to 2.5.
Pre-expanded particles comprising a non-crosslinked linear low-density polyethylene resin having an expansion ratio of 8 to 60 cm ³ /
g, and 90% or more of the cells have a closed cell structure, and are non-crosslinked linear low-density polyethylene resin pre-expanded particles.

Further, in the production method of the present invention, the ratio Cw / weight average distribution (Cw) and number average distribution (Cn) of the polymer components obtained by fractionation by the temperature rising elution method as measured by 13C-NMR. A non-crosslinked linear low-density polyethylene resin particle having a Cn of 1.1 to 2.5 is contacted with a foaming agent in a closed container in an airtight container, and the obtained foamable resin particle is heated to a temperature lower than the softening temperature of the resin particle by 5%. A method for producing non-crosslinked linear low-density polyethylene-based resin pre-expanded particles, characterized in that after heating and foaming at a high heating temperature of up to 15 ° C., a refrigerant is blown and cooled to a softening temperature or lower within 15 seconds. .

Hereinafter, the present invention will be described in detail. The density of the base resin constituting the linear low-density polyethylene resin pre-expanded particles of the present invention is from 0.900 to 0.930 g / cm.
It is important that it is ³ , preferably 0.905 to 0.5.
920 g / cm ³ . If the density is too large exceeding 0.930 g / cm ³ , the obtained foamed molded article will have remarkably inferior impact cracking resistance and repetitive compression set durability, and the target product will not be obtained, and will be less than 0.900 g / cm ³ . If it is too small, it will be too flexible, and it will be necessary to use a low-magnification foam molded article when used in a buffer container for carrying heavy goods, for example, which is disadvantageous economically. In the present invention, the resin density is ASTM
It is a value measured according to D-1505.

The weight average distribution (C) of the base resin constituting the expanded particles of the linear low-density polyethylene resin of the present invention.
It is important that the ratio Cw / Cn (branch degree composition distribution) between w) and the number average distribution (Cn) is 1.1 to 2.5,
Preferably it is 1.1-2.0. Cw / Cn is a parameter indicating the distribution of the composition of the polymer irrespective of the molecular weight.
This is an important characteristic that specifies the structure of the base resin of the present invention. When Cw / Cn is too large, exceeding 2.5, the distribution of branching degree is too wide, the expansion ability of the expanded particles during in-mold molding is small, and only molded articles with large sink marks are obtained even in in-mold molding. The resulting molded foam is inferior in impact cracking resistance and durability against repeated compression strain. If the branching degree distribution is too narrow at less than 1.1, there is no suitable temperature range for foam molding processing, the moldability is poor, and the physical properties of the molded foam obtained are not good. This phenomenon is particularly remarkable in the case of pre-expanded particles composed of a resin having a density of less than 0.920 g / cm ³ .

In the present invention, the weight average branching degree Cw and the number average branching degree Cn are values measured by the following methods. In order to fractionate the composition of the linear low-density polyethylene resin constituting the pre-expanded particles, the pre-expanded resin particles were added to a mixed solvent of p-xylene and butyl cellosolve (volume ratio: 80/20), a heat stabilizer 2, 5-di-t
After dissolving in the presence of tert-butyl-4-methylphenol, diatomaceous earth (trade name: Celite 560, manufactured by John Manville Co., USA) was filled into a cylindrical column, and the mixture was mixed. While the solvent having the same composition as the solvent is phased and flown out into the column, the temperature inside the column is increased stepwise from 30 ° C. to 130 ° C. in steps of 5 ° C. to separate the coated linear low-density polyethylene resin. Thereafter, the precipitate is reprecipitated in methanol, separated by a furnace, and dried to obtain a separated product (heating and elution separation method). Next, the number of branches C per 1000 carbon atoms of each fraction was determined by the 13C-NMR method, and assuming that the number of branches C and the cumulative weight fraction I (w) of each fractionation section follow a lognormal distribution of the following equation, Cw and Cn are obtained by the square method.

[0012]

(Equation 1)

Further, the base resin constituting the pre-expanded particles of the linear low-density polyethylene resin of the present invention has a main chain carbon of 100%.
Molding obtained when the number of branches per 0 or less is 2 or less is 10% by weight or less in the amount of the composition component in the resin, and when the n-hexane extractables is 2.0% or less. Excellent impact cracking resistance and repeated compression strain durability of foam,
preferable.

The specific substrate of the linear low density polyethylene resin pre-expanded particles of the present invention is preferably one synthesized with a metallocene catalyst. Specifically, an organic transition metal catalyst component of Group IV of the periodic table of the metallocene compound;
Al-OA obtained by the reaction between an organic compound and water
and a modified aluminum organic compound containing an l-bond (eg, (n-BuCp) _z ZrCl ₂ / M
AO), or metallocene cation complex catalyst (e.g. _{CpSiNRTiMe · B (C 6 F 5} ) 4 -) with, are those prepared by copolymerizing ethylene and α- olefin so as to have a predetermined density .

[0015] The polymerization reaction is carried out in the presence of the above catalyst in the presence of a slurry.
Any of polymerization, solution polymerization, or gas phase polymerization may be used, and particularly, slurry polymerization or gas phase polymerization is preferable. In such polymerization, a copolymer of ethylene and an α-olefin having 4 to 20 carbon atoms is polymerized in a state where oxygen, moisture and the like are substantially cut off. Here, the α-olefin component unit is preferably an α-olefin having 4 to 12 carbon atoms,
One or a mixture of two or more of these components may be used. As such an α-olefin component unit, specifically, 1-butene, 1-pentene, 1-hexene,
4-methyl-1-pentene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-octadecene, etc., and the content of the α-olefin component unit is determined by the specified polymer density and branching degree composition. It is optional within a range that satisfies the distribution, but is usually in the range of 0.5 to 10 mol%.

The polymerization conditions at this time are optional, but usually 2
0 to 300 ° C, normal pressure to 70 kg / cm
The pressure range is ² G, and the polymerization time is 5 minutes to 10 hours. Of course, it can be adjusted to some extent by changing the polymerization temperature, the type and amount of the catalyst, but the molecular weight can be effectively adjusted by adding hydrogen to the polymerization reaction system. In addition, a multi-stage polymerization method in which the hydrogen concentration and the polymerization temperature are different from each other in two or more stages can be applied, and the pre-expanded particles composed of this resin are preferable because of excellent in-mold fusion molding processability.

By applying the manufacturing method exemplified above, the specific linear low-density polyethylene resin constituting the pre-expanded particles of the present invention can be obtained. It is important that the pre-expanded particles of the present invention have an expansion ratio of 8 to 60 cm ³ / g and a closed cell ratio of 90% or more. When the expansion ratio is less than 8 cm ³ / g, the fusion property between particles during in-mold molding is inferior, and when it exceeds 60 cm ³ / g, in-mold moldability is inferior and the physical properties of the obtained molded foam are reduced. . A particularly preferred range of the expansion ratio is 15 to 50 cm ³ / g. If the closed cell ratio is less than 90%, the in-mold moldability is poor,
The physical properties of the obtained molded foam are reduced. The average cell diameter of the pre-expanded particles is preferably 0.03 to 3 mm in view of moldability in the mold and appearance of the molded foam itself. Here, the average cell diameter refers to the number of cells per arbitrary length L (1 mm or more) on each of three-dimensional axes obtained by cutting the expanded particles at three surfaces orthogonal to each other. Reading, L (m
m) divided by the number of bubbles.

As described above, by using the pre-expanded particles of the present invention, a foam molded article having high physical properties can be obtained. Next, a method for producing the non-crosslinked linear low density polyethylene resin pre-expanded particles of the present invention will be described. The linear low-density polyethylene-based resin particles used in the production method of the present invention are obtained by separating a polymer component obtained by fractionation by a temperature rising elution method into 13C.
-The ratio Cw / Cn between the weight average distribution (Cw) and the number average distribution (Cn) measured by NMR is 1.1 to 2.5.
It is. If Cw / Cn is more than 2.5 and too large, the distribution of branching degree is too wide and the secondary expansion ability is low. In particular, when the resin density is less than 0.920 g / cm ³ , it becomes remarkable and does not foam. If it is less than 1.1 and the distribution of branching degree is too narrow, extrusion processability is poor and productivity is lowered, which is not preferable. As another resin physical property, the molecular weight distribution (Mw / Mn) is 2
-40, preferably 15-40, and MI of 0.1-15 g / 10 min.
Preferably, those having 0.1 to 5 g / 10 minutes are excellent in foam molding processability.

As the base material used for the non-crosslinked linear low-density polyethylene resin pre-expanded particles of the present invention, resins having different densities of the specific linear low-density polyethylene resin obtained by the above-mentioned method are blended with each other. You can also. In addition, conventional linear low-density polyethylene, high-pressure low-density polyethylene, medium-density polyethylene, and high-density polyethylene may be mixed in a range that does not impair the essential characteristics, that is, in an amount of 40 parts by weight or less. . Further, another thermoplastic resin, for example, an olefin resin having 3 or more carbon atoms such as polypropylene, or various rubbers such as ethylene propylene rubber is used.
It can be mixed and used in an amount of 0 part by weight or less. Of course, various fillers such as antioxidants, light stabilizers, antistatic agents, flame retardants, lubricants, nucleating agents, pigments, dyes, and the like can be used in the resin of the present invention.

The non-crosslinked linear low-density polyethylene resin particles of the present invention may be somewhat crosslinked to the extent that they can be repelleted. In this case, the degree of crosslinking is 10% or less in terms of gel fraction. The non-crosslinked linear low-density polyethylene-based resin particles used as a substrate in the present invention are obtained by molding into particles according to a conventionally known method, for example, extruded into a strand by melt-kneading with an extruder. Is 0.5 to 3 mm in diameter and 0.5 to 3 m in length by a pelletizer.
m can be obtained by granulation.

In order to produce the pre-expanded particles of the present invention using the above-mentioned linear low-density polyethylene resin particles, the resin particles are contact-contained with a foaming agent in a closed container, and the obtained foamable resin is obtained. The particles are heated at a temperature 5 to 15 below the softening temperature of the resin particles.
After heating and foaming at a high heating temperature of ° C., a method of obtaining pre-expanded particles by spraying a refrigerant and cooling to a softening temperature or less within 15 seconds or less is adopted.

As the foaming process, conventionally known methods,
That is, a method in which the resin particles are put into a pressurized and heated container, contacted with a foaming agent to form foamable resin particles containing the foaming agent in the resin, and then heated and foamed to form foamed particles,
Alternatively, resin particles dispersed and maintained in an aqueous suspension state in a pressure-resistant container are contact-impregnated with a foaming agent under pressure and heat to form foamable resin particles, and the particles are formed together with the suspension in a lower pressure atmosphere than in the container. To form foamed particles, and a method in which these foamed particles are again mixed with a foaming agent gas and heated and expanded to obtain highly foamed foamed particles.

The blowing agents used in the present invention include carbon dioxide, nitrogen, air, propane, butane, pentane,
-1-1-2 tetrafluoroethane (F-134a),
1-1 difluoroethane (F-152a), methylene chloride, ethylene chloride and the like. Among them, carbon dioxide, which satisfies CFC regulations and is nonflammable, is a desirable blowing agent. The content of the foaming agent varies depending on the type of the foaming agent and the desired degree of the expansion ratio, but is usually 0.1%.
1 to 2.0 mol / kg. The temperature and pressure when the particles contain a foaming agent are arbitrary, and the method for impregnating the foaming agent may be either a gas phase or a liquid phase, and is not particularly limited.

The main point of the production method of the present invention is that the expandable resin particles are heated and foamed at a heating temperature 5 to 15 ° C. higher than the softening temperature of the resin particles. Heating of the system at the time of foaming is mainly performed by heated hot water and heated steam, and the foamable resin particles are heated to a temperature lower than the Vicat softening temperature by 5%.
~ 15 ° C higher temperature, preferably 5 ° C
-10 ° C higher temperature. If this temperature is less than the Vicat softening temperature of the resin particles, foaming is slow,
Low foaming efficiency due to superior external dissipation of the foaming agent, and narrower foaming suitability at temperatures higher than the Vicat softening temperature of the resin particles by 15 ° C or more, and the particles are fused together or have a low closed cell rate. And normal foamed particles cannot be obtained.

The particles thus foamed by heating are
Then it is cooled. Another important point of the production method of the present invention is that a refrigerant is sprayed and cooled to a temperature lower than the softening temperature within 15 seconds. This cooling is performed by a cool air of 50 ° C. or less,
By blowing a refrigerant such as cold water onto the foamed resin to forcibly cool the foamed resin, the pre-expanded particles are obtained by cooling from the foaming temperature to the Vicat softening temperature within 15 seconds, preferably 10 seconds or less. In other words, if the foamed particles are above the softening temperature more than necessary after foaming, the gas in the foamed particles escapes to the outside,
When the foamed and stretched resin undergoes thermal shrinkage, and it takes more than 15 seconds to cool from the foaming temperature to the Vicat softening temperature, it becomes difficult to efficiently produce uniform highly foamed particles. Molded foams made of pre-expanded particles obtained for more than 15 seconds to cool from the foaming temperature to the Vicat softening temperature or less have poor durability against repeated compression strain. Although this phenomenon is not clear, it is presumed that the resin molecule orientation of the foam film constituting the foamed particles is relaxed. In the present invention, the softening temperature is ASTM D
-A value measured according to 1525-65T.

The pre-expanded particles of the present invention obtained by the above method are used as materials for obtaining molded articles of various shapes by being subjected to in-mold molding by a known method. According to the production method of the present invention, it provides a molded foam having excellent specific compression strength, impact cracking resistance, and repeated compression strain durability, which could not be achieved by conventional non-crosslinked polyethylene resin pre-expanded particles, and The non-crosslinked linear low-density polyethylene-based resin pre-expanded particles of the present invention, which provide pre-expanded particles excellent in moldability, having a small expansion capacity during molding in the mold and a small sink in the molded product, can be naturally produced. I can do it.

[0027]

EXAMPLES The characteristics of the linear low-density polyethylene resin used in each example are shown in Table 1. The evaluation methods and evaluation scales of the characteristic values used in each of the examples and comparative examples are as shown below. (1) Expansion ratio of expanded particles (cm ³ / g) Weight (Wg) This is a value obtained by measuring the volume (Vcm ³ ) of a known expanded particle by a submersion method and dividing the volume by the weight. (2) Closed cell rate (%) It is an average of the values measured by the air-pycnometer method (manufactured by BECMAN, model 930) described in ASTM D-2856 (n = 10). (3) Internal pressure of foaming particles Approximately 10 g of secondary foaming particles taken out from a pressurized atmosphere are quickly dispensed into five containers, and the weight (w) is accurately weighed, and one end is placed under atmospheric pressure. respectively open two water tubes which are connected, the amount gas escapes from the secondary foaming particles (V _O) measured over time, with the average value calculated for each value according to the following equation pressure And

Internal pressure of foamed particles (kg / cm ² G) = V _O
/ (V _S -W / D), however, D is the density of the linear low density polyethylene used, V _S is determined the conversion factor Weight and volume by mass obtained samples from the same population were measured It is the volume of the foaming particles calculated from the weight of the foaming particles. In this case, the end point of the measurement is that the difference between the internal pressures in the preceding and following one hour is 0.01 k
g / cm ² . (4) Degree of fusion About 300 x 300 x 50
mm plate-shaped molded product, 100 × 1 from this molded product
A 00 mm square test piece was cut out, a 2 mm deep cut was made in the center of the test piece, and the formed product was cut open along the cut, and the material was fractured for all the particles present in the cut cross section. The percentage of the number of particles used was determined.

Evaluation scale: Classification symbol Remarks When the material fracture rate is 90% or more ○ Excellent 80% or more and less than 90% △ Good 80% or less × Bad (5) Mold shrinkage Molding at the above molding temperature The molded foam thus obtained was evaluated as follows by the dimensional shrinkage ratio with respect to a molding die.

Evaluation scale: Category symbol Remark 2.5% or less ○ Excellent 2.5% or more and 3.3% or less △ Good 3.3% or more × Bad (6) Appearance of molded foam Density (g / cm ³ ) This is a value obtained by accurately cutting out a test piece to a size of 10 × 10 cm square, measuring its weight and thickness, and dividing the weight by the volume to represent the weight per unit volume. (7) Compressive strength It is a compressive stress value when a 25% strain is generated, measured according to JIS K-6767. (8) Specific compressive strength A value obtained by dividing the value of the compressive strength by the value of the apparent density and evaluated as follows.

Evaluation scale: Classification symbol Remarks: 20 or more ○ Excellent: Less than 20: 18 or more △ Good: Less than 18 × Bad (9) Repeated compression set: Measured in accordance with JIS K-6767;
% Compression, repeated 80,000 times. And it evaluated as follows.

Evaluation scale: Classification symbol Remark 15% or less ○ Excellent Exceeding more than 15% and 25% or less △ Good Exceeding 25% × Bad (10) Shear impact resistance Thickness 30 mm, inner dimensions 70 × 70 × A 70 mm corner pad is formed and mounted on a 4 kg triangular pyramid-shaped drop dummy, and tested five times from the drop height at which the instantaneous maximum strain at the first drop is 60%, which is obtained by pre-testing each test piece. The sample was dropped at an angle, and the crack generated in the corner pad test piece was measured as a dimension parallel to the drop direction, and the crack depth was determined and evaluated as follows.

Evaluation scale: Classification symbol Remark: When the value is 5 mm or less ○ Excellent When the value is more than 5 mm and 10 mm or less △ Good When the value is more than 10 mm × Bad The present invention will be described below with reference to Examples.

[0034]

EXAMPLE 1 and COMPARATIVE EXAMPLE 1 This experiment is particularly intended to show the significance of the method for producing pre-expanded particles of the present invention.
In a pressure vessel, 100 parts by weight of particles of the non-crosslinked linear low-density polyethylene resin A, 8 parts by weight of carbon dioxide, and 2 parts by weight of basic magnesium carbonate are dispersed in 400 parts by weight of water, and while stirring, foaming shown in Table 2 is performed. After heating to a temperature and holding for 45 minutes to impregnate the foaming agent, the inner pressure of the container was 30 kg /
One end of the container is opened while maintaining the pressure at ² cm ² G, and the resin particles and hot water are simultaneously released under normal pressure to foam the resin particles. The resin particles were cooled until the temperature reached the softening temperature of the resin particles or lower as shown in No. 2 to obtain pre-expanded particles (primary expanded particles). Pre-expanded particles (primary expanded particles) were obtained in the same manner for other non-crosslinked linear low-density polyethylene resin C and G particles. Table 3 shows the temperature during foaming, the cooling time below the softening temperature, the presence or absence of fusion of the obtained foamed particles, the closed cell ratio, and the expansion ratio for each resin.

Next, after leaving each of the pre-expanded particles under atmospheric pressure for one week, the pre-expanded particles are placed in a pressure vessel,
After pressurizing to 9.5 kg / cm ² G with air and maintaining the temperature at 70 ° C. to adjust the internal pressure of the expanded particles to 3 kg / cm ² G, the particles are cooled and taken out. The expanded particles having this internal pressure were immediately placed in a steam chamber and heated at various temperatures to perform secondary expansion. The obtained foamed particles were left to stand under atmospheric pressure and aged, and then the closed cell ratio and the expansion ratio were measured. The results are shown in Table 3. The density and Cw / Cn of the obtained expanded particles were the same as those of the resin before firing.

According to the results shown in Tables 2 and 3, it can be seen that the production method of the present invention can provide expanded particles having high expansion efficiency and excellent secondary expansion ability.

[0037]

EXAMPLE 2 and COMPARATIVE EXAMPLE 2 The experiment here is to show the importance of the pre-expanded particles composed of the resin component in the present invention. Resins B, D, E, F, H, I in Table 3
The same procedure as in Example 1 was repeated except that the resin particles were heated and foamed at a heating temperature of 10 ° C. higher than the softening temperature of the resin particles, and that the resin particles were cooled to a temperature lower than the softening temperature by blowing cold water for 5 seconds. Expanded particles (primary expanded particles) were obtained (experiment
No. 11-13, 18-20).

The secondary expanded particles of Experiment Nos. 1 and 2 of Example 1 and Experiment No. 9 of Comparative Example 1 were subjected to tertiary expansion under the same conditions as the secondary expansion method of Example 1 and Comparative Example 1, and tertiary expansion was performed. Particles were obtained (Experiment No. 14, 21-22). Table 4 shows the measurement results of the resin properties, expansion ratio, and closed cell ratio of the pre-expanded particles. Table 4 shows the secondary expanded particles of Experiment No. 2 in Example 1 (Experiment No. 15), the primary expanded particles of Experiment No. 3 (Experiment No. 16), and the secondary expanded particles of Experiment No. 5 in Example 1. Next expanded particles (experiment
No. 17) and the results of measurement of the resin properties, expansion ratio, and closed cell ratio of each pre-expanded particle of the primary expanded particles of Experiment No. 6 of Comparative Example 1 (Experiment No. 23) are also shown.

Next, the pre-expanded particles of Experiment Nos. 11 to 23 were allowed to stand at room temperature and normal pressure for 48 hours, then stored in a pressure-resistant container, and 63% (compressibility) of the original bulk volume in air at room temperature. 37%), while maintaining the state, in an in-mold molding die having a water vapor hole (inner dimensions 300 × 300 × 5
0mm ^t plate type, 30mm ^t with inner dimensions 70x70x
Two 70 mm corner pad molds were filled and heated with steam to expand and fuse the foamed particles to each other, then cooled and taken out of the molding die. The molded body taken out is 60
After aging for 8 hours in a room at 23 ° C., the mixture was left at 23 ° C. for 3 days to obtain a molded foam. The molding performance and the physical properties of the obtained molded foam were evaluated by the methods described above.
Shown in

According to Table 5, the pre-expanded particles of the present invention are excellent in in-mold moldability (degree of fusion, shrinkage ratio to mold).
It can be seen that the physical properties of the specific compression strength, impact cracking resistance, and repeated compression strain durability of the molded foam obtained by in-mold molding exhibit high values with high quality. Also, as Experiment No. 24, it took more than 15 seconds to cool from the foaming temperature obtained in Comparative Example 1 to the Vicat softening temperature or lower, and the foaming ratio 1 obtained in a cooling time of 20 seconds.
When the pre-expanded particles of 7.2 cm ³ / g (No. 7 in Tables 2 and 3) were molded in a mold in the same manner as above, and the physical properties were evaluated.
The repetitive compression strain was 21%, which was inferior in durability.

These results indicate that the base resin, which is a feature of the pre-expanded particles of the present invention, has a density in the range of 0.900 to 0.930 g / cm ³ synthesized with a metallocene catalyst. The polymer component obtained by fractionation by the temperature rising elution method was 13
Non-crosslinked linear low density having a ratio Cw / Cn (composition branching distribution) between the weight average distribution (Cw) and the number average distribution (Cn) measured by C-NMR of 1.1 to 2.5. It is made of polyethylene resin and has an expansion ratio of 8 to 60 cm ³ / g
And means that the closed cell rate is 90% or more,
From the comparison between Experiment No. 15 and Experiment No. 24, it can be seen that since the pre-expanded particles were obtained under the production conditions of the present invention, a molded foam having excellent physical properties was provided.

[0042]

Example 3 60 parts by weight of resin B in Table 1 and 4 parts of resin D
Using the mixed resin composition with 0 parts by weight, mixed resin particles were produced. The mixed resin particles had a polymer density of 0.913 g.
/ Cm ³ , composition branching degree distribution Cw / Cn 2.3, and softening temperature 101 ° C. 10 ° C. below the softening temperature of the resin particles
Pre-expanded particles were obtained by performing primary and secondary expansion in the same manner as in Example 1 except that the mixture was foamed by heating under a high heating temperature, and was cooled to a softening temperature or lower in 5 seconds by blowing cold water. The pre-expanded particles obtained had an expansion ratio of 32 cm ³ / g and a closed cell ratio of 99%. The pre-expanded particles were molded in a mold in the same manner as in Example 2 and had an apparent density of 0.033 g.
/ Cm ³ was obtained. The specific compression strength of this molded article is 22, the compressive strain is repeatedly 14%, and the resistance to shear impact cracking is 4 mm.
And it was excellent.

The results show that resins having different densities can be blended and used as the base resin of the present invention.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

[Table 5]

[0049]

According to the present invention having the above-described structure,
It has excellent in-mold fusion molding performance, and has excellent specific compression strength, repeated compression set, and crack resistance to withstand repeated drop impact (shear resistance compared to conventional non-crosslinked linear polyethylene resin molded foam) A molded foam that satisfies the practical properties of (impact) at a high level can be easily provided. The obtained molded foam is used, for example, for cushioning material for packaging,
Its commercial value is extremely high because it is widely used and useful as a cushion core material. And it is a non-crosslinked linear low density polyethylene resin pre-expanded particle which satisfies the waste problem of the cross-linked polyethylene resin pre-expanded particle, and satisfies the desire of the industry.

Claims (2)

(57) [Claims] (1) a density of 0.900 to 0.930 g / cm ^3;
And the polymer component obtained by fractionation by the temperature rising elution method was 13
The ratio Cw / Cn between the weight average distribution (Cw) and the number average distribution (Cn) measured by C-NMR is 1.1 to 2.
Pre-expanded particles made of a non-crosslinked linear low-density polyethylene resin having an expansion ratio of 8 to 60 cm ^3.
/ G and 90% or more of the cells have a closed cell structure. Pre-expanded particles of a non-crosslinked linear low density polyethylene resin. 2. A weight-average distribution (C) measured by 13 C-NMR for a polymer component obtained by fractionation by a temperature rising elution method.
w) and the ratio Cw / Cn of the number average distribution (Cn) are 1.1.
A non-crosslinked linear low-density polyethylene resin particle having a particle size of up to 2.5 is contacted with a blowing agent in a closed container, and the obtained expandable resin particle is heated to a temperature of 5 to 15 ° C. below the softening temperature of the resin particle.
A method for producing non-crosslinked linear low-density polyethylene-based resin pre-expanded particles, characterized in that a foam is heated and foamed at a high heating temperature and then cooled to a softening temperature or less within 15 seconds by blowing a refrigerant.