JPS61113627A - Foamed particle of high-density polyethylene resin and production thereof - Google Patents

Abstract

PURPOSE:To provide the titled foamed particle having controlled foam diameter and foam structure, and having high closed cell ratio, by using an alcohol or water as the foam regulator, and cutting the extruded and foamed strand immediately after the extrusion through a die. CONSTITUTION:(A) 100pts.(wt.) of a non-crosslinked high-density polyethylene having a melt index of <=0.7g/10min, a melt index ratio of >=40, and a density of >=0.94g/cm<3> is mixed with (B) a volatile organic foaming agent and (C) 0.05-5pts. of a foam regulator selected from a lower aliphatic alcohol and water. The mixture is melted and kneaded at high temperature and pressure, extruded through the die to a low temperature and pressure atmosphere, and cut before the expansion of the foamed strand completes. The obtained foamed particle has a heterogeneous foam structure wherein the foam diameter at the skin part is <=1/3 of that of the core part of the particle, a foam diameter of 0.2-1mm at the core part, a closed cell ratio of >=80%, a density of 0.1-0.015g/cm<3> and particle diameter of 2-10mm.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to foamed particles of high-density polyethylene resin and a method for producing the same, in which alcohol or water is used as a cell regulator to control the cell diameter and cell structure of the foamed particles. The present invention relates to foamed particles with high closed-cell properties obtained by adjusting the foamed particles, and a method for producing the same.

(Prior Art) Foams obtained by steam-molding crosslinked polyolefin resin foam particles in a mold are well known.
It has excellent flexibility, toughness, low-temperature properties, and chemical resistance, and is used in various markets such as packaging cushioning materials, insulation materials, and industrial materials.

However, these conventional in-mold polyethylene foam molded products are foam-molded by subjecting the base resin to a crosslinking treatment and foaming, or by treating the foamed particles with radiation or the like to introduce a crosslinked structure.

This is true for non-crosslinked polyethylene, which is a crystalline resin.
At present, the viscoelastic properties when heated have a large temperature dependence, and the temperature range suitable for foam molding is narrow, making it impractical, so it has not yet been put into practical use.

These foam molded products based on cross-linked polyethylene resin cannot be recycled because the base resin is cross-linked, and must be incinerated, and a process of cross-linking the base resin is required. Productivity is also poor, resulting in relatively high prices.
It is not as widely used as polystyrene foam.

In addition, attempts have been made to extrude and foam non-crosslinked polyethylene resin and then mold it in a mold using pulverized foamed particles (Japanese Patent Publication No. 46-29036, U.S. Patent No. 35
04068), within a few minutes after foaming, the pressure inside the bubbles is reduced due to the diffusion and outflow of the blowing agent gas, causing the bubbles to contract, and the initial bulk density that they had immediately after foaming is not reached, and after extrusion foaming, pulverization occurs. As a result, the air bubbles on the cut surface are destroyed and the air bubbles inside the particles are also damaged, resulting in a disadvantage that only molded products of inferior quality can be obtained.

The present inventors solved the drawbacks of these crosslinked polyethylene resin foam molded products, and created a molded product that has physical properties equivalent to or better than the excellent properties such as flexibility, toughness, and chemical resistance that the foam molded products have. As a result of intensive research to develop non-crosslinked polyethylene resin foam particles that provide the same properties and have excellent expansion ability and fusion properties between particles during in-mold molding, we have developed a polyethylene foam based on a specific polyethylene resin. We found that it was possible to achieve the objective by selecting the material resin, and completed the application first (Patent application No. 58-615).
82). In this application, as the base resin, the ratio of weight average molecular weight (M w ) to number average molecular weight (Mn) M W
/Mn is 15 or more, the weight average molecular weight is 2X10' or more, and the density is 0.920 g/cc or more using a linear ethylene resin that has a manufacturing method based on known conventional technology to reduce expansion upon heating. This makes it possible to obtain non-crosslinked linear ethylene resin foam particles with excellent performance. This patented technology is an epoch-making technology that eliminates the need for a crosslinking process, which has been strongly desired in the past, and makes it possible to industrially implement in-mold foam molding of recyclable, energy-saving, and resource-saving polyethylene. However, there is still room for improvement in the flexibility of the resulting foam molded product and its elastic recovery properties upon compression.

(Problems to be Solved by the Invention) Generally, the cell diameter of expanded particles has a large effect on the mechanical strength, flexibility, and elastic recovery of the in-mold foam molded product, as well as the external visual appearance of the molded product. In order to achieve this, various bubble control agents have been devised to control the bubble diameter and its distribution. For these materials, inorganic fine powders, organic metal salts of higher fatty acids, esters, amides, etc. of higher fatty acids have been used with the aim of uniformly reducing the cell diameter.

However, when the above-mentioned cell regulators are applied to extruded foams made of high-density polyethylene resin as the base resin, the cell diameter becomes extremely fine, often resulting in a decrease in the closed cell ratio or, conversely, a coarse cell size. The amount of the cell regulator added must be controlled with a high degree of precision that is not industrially possible, and it has been difficult to control the cell size and closed cell ratio within appropriate ranges.

(Means for Solving the Problems) In view of the above-mentioned circumstances, the inventors of the present invention have made extensive studies and found that the above-mentioned problems can be solved by using at least one kind of lower aliphatic alcohol or water as a bubble regulator. By solving this problem and cutting the extruded foam with a rotary blade after exiting the die and before the expansion is completed, high-density polyethylene with excellent closed-cell properties and a fine cell structure in the outer shell can be produced. It has been found that foamed resin particles can be obtained.

That is, the present invention provides (1) a melt index of 0.7 g/10 minutes or less, a melt index ratio of 40 or more, and a density of 0.940 g/10 min.
- Foamed particles made of non-crosslinked high-density polyethylene as described above, which have a non-uniform cell structure in which the cell diameter in the outer skin portion of the particle is 1/3 or less of the cell diameter in the center of the particle. and the bubble diameter at the center of the particle is 0.2
to 1.0, the closed cell ratio is 80% or more, and the density is 0.
100-0.015g/crA, particle diameter 2-10m
High-density polyethylene resin foam particles characterized by:

(2) Melt index 0.7g/10 minutes or less, melt index ratio 40 or more, density 0.940g/
The foamed particles are made of non-crosslinked high-density polyethylene with a particle size of d or more, and have a non-uniform cell structure in which the cell diameter in the outer skin portion of the particle is 1/3 times or less of the cell diameter in the center of the particle. , and the bubble diameter at the center of the particle is 0.2
to 1.0 fi, closed cell ratio of 80% or more, density of o, too to 0.015 g/all, particle diameter of 2 to t
In the method for producing foamed high-density polyethylene resin particles that are OW, a volatile organic blowing agent and a lower aliphatic alcohol as a cell regulator are added to the base resin. or at least one kind of water at 0.0 parts by weight per 100 parts by weight of the resin.
After adding and mixing 5 to 5 parts by weight, melting and kneading under high temperature and high pressure, and extruding from a die under low temperature and low pressure, the foamed strand is cut before expansion is completed to form fine bubbles in the outer shell. A method for producing foamed particles of a high-density polyethylene resin, the method comprising forming foamed particles with a high closed cell ratio.

Our goal is to provide the following.

According to the present invention, it has both high closed cell properties and a fine cell structure, and has a cell diameter of 17
It is possible to provide foamed particles having a non-uniform cell structure I in which a part of the fine cell size of 3 times or less is introduced into a part of the skin layer of the particle.

In-mold foam molded products obtained using foamed particles having such a cellular structure have particularly excellent flexibility, and when used as cushioning materials for packaging, they improve the scratch resistance of the surface of the packaged object. It also exhibits excellent properties such as excellent compressive elastic recovery rate, and can be used as a useful packaging material.

Figure 1 is an example showing the distribution of the bubble diameter in a cross section of the spherical or cylindrical foamed particles of the present invention taken along a cross section that includes the central axis and is parallel to the extrusion direction. It is clear that the bubble diameters in the periphery have an asymmetric distribution, and that fine bubble diameters are formed in the outer shell of the foamed particles, especially when cutting shear is applied with a cutting blade when obtaining the foamed particles. be.

Such a non-uniform cell structure means that when the cell diameter at the center of the foam particle exceeds 1.0 mm, the above-mentioned characteristics will no longer be exhibited when the cell is formed into an in-mold product, and the external visual appearance will be affected. However, the shape of the bubbles is clearly discernible, and the product value is inferior. Furthermore, if the cell diameter at the center of the foamed particles is less than 0.2w, the closed cell ratio of the expanded particles will decrease, and a closed cell ratio of 80% or more cannot be maintained, resulting in shrinkage and Significant sink marks will result.

The non-uniform structure of the present invention depends on the size of the central cell diameter of the foamed particles and the timing at which the foamed strands are cut during the expansion process during extrusion and foaming.

If the diameter of the bubbles in the center of the foam particle exceeds 1.0■■, the expansion speed after exiting the extrusion nozzle will decrease, so the effect of making the bubbles finer by the cutting blade will be reduced, and the fine bubbles around the cut surface will be reduced. It becomes difficult to form. When the diameter of the bubbles at the center of the particle is reduced, the diameter of the bubbles around the cut surface tends to become finer. If this is significant, a phenomenon occurs in which the cells around the cut surface become open cells, and the product cannot be subjected to in-mold molding. Therefore, the diameter of the bubbles in the outer shell of the spherical or cylindrical expanded particles is 1/3 times or less of the diameter of the bubbles in the center of the particle, and the diameter of the bubbles in the center of the particle is in the range of 0.2 to 1.0 vm. There is a need to. Preferably, the bubble diameter at the center of the particle is 0.2 to 0.
．． With eight fins, it is desirable that the outer skin cell diameter be in the range of 1/3 to 1/10.

The high-density polyethylene resin that can be provided by the present invention includes:
The melt index must be 0.7 g/10 minutes or less, and the melt index ratio must be 40 or higher.

If the melt index exceeds 0.7 g/10 minutes, the size of the bubbles within the particles tends to be non-uniform when obtaining expanded particles, and in some cases, the bubbles may be destroyed, making it impossible to obtain expanded particles with a closed cell structure. Furthermore, even when in-mold foam molding is performed, problems arise such as the occurrence of sink marks and large dimensional shrinkage, resulting in molded products with poor appearance.

In addition, for those with a melt index ratio of less than 40, flow breakage is likely to occur when the base resin itself is melted,
The temperature range suitable for thermal expansion is narrow and the expansion ability is substantially reduced, making it unsuitable for industrially obtaining foamed molded products.

For the above reasons, the base resin is more preferably one having a melt index of 0.3 to 0.02 g/10 minutes and a melt index ratio of 70 to 250.

The base resin of the present invention is a non-crosslinked high-density polyethylene resin that simultaneously satisfies the above requirements, and this high-density polyethylene resin has a resin density of 0.940 g/
A homopolymer of ethylene with cra or more, a copolymer with an ethylene monomer substituted with an α-alkyl group within 10 mol% to the extent that its mechanical and thermal properties are not impaired, and
Mixtures of these can be used. Examples of these high-density polyethylene resins include high-density polyethylene produced by a low-pressure method or a medium-pressure method. Alternatively, a substantially non-crosslinked high-density polyethylene resin with slight crosslinking (gel fraction of 10% or less) may be used.

In the base resin of the present invention, other thermoplastic resins may be mixed with the above-mentioned non-crosslinked high-density polyethylene resin within a range of 20 weight or less. In addition, antistatic agents, nucleating agents, coloring agents,
Known additives such as lubricants can also be mixed.

In order to achieve the foamed particles of the present invention, in a method of manufacturing foamed particles by melt-kneading a volatile organic blowing agent into a base resin under high temperature and high pressure, and cutting the obtained foamed strands by extruding from a die, (a) A lower aliphatic alcohol or a small amount of water as a foam regulator (in both cases, at least one kind is added to the base resin
Add and mix 0.05 to 5 parts by weight to 0 parts by weight.

(b) Cutting the foam strand after extrusion from the die but before completion of expansion.

This can be achieved by satisfying the following conditions.

As mentioned above, the condition (a) greatly influences the cell size distribution and closed cell ratio of the expanded particles. That is, the presence of lower alcohol or water influences the cell diameter of the expanded particles, and if these compounds or mixtures are less than 0.05 parts by weight based on 100 parts by weight of the base resin, the closed cell ratio of the expanded particles will decrease. is less than 80% and cannot be subjected to in-mold foam molding. Moreover, if it exceeds 5 parts by weight, the cell diameter of the foamed particles becomes large, and the foamed particles having a non-uniform cell structure as defined in the present invention cannot be obtained. The amount is preferably 0.1 to 2 parts by weight.

The lower aliphatic alcohol is preferably a linear or branched aliphatic monoalcohol having 1 to 5 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, or n-butyl alcohol. , isobutyl alcohol, 5ec-butyl alcohol, tert-butyl alcohol, n-amyl alcohol, isoamyl alcohol, tert-amyl alcohol, etc. can be used.

(Concerning the conditions for bl, when cutting the foamed strand in the expansion process to obtain foamed particles, there is an open area on the cut surface.
This is an essential requirement for not forming cells, and it is necessary to make the cutting blade act substantially along the die surface. If the gap between the die surface and the cutting blade is large, the foamed particles may become cracked, or in severe cases, the foamed pieces may become abnormally deformed.

The volatile organic compounds used by Suizenmeisha include ASTM
, D-1133 has a quasi-9 KB value of 12 to 150
Preferred are organic compounds within the range of, for example, aliphatic hydrocarbons such as propane, propylene, butane, butene, pentane, pentene, hexane, hexene, heptane, and alicyclic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane. , trichlorofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, monochlorodifluoromethane, methyl chloride, methylene chloride, ethyl chloride, ethylene chloride, etc., and the KB value is 12. One type or a mixture of two or more types within the range of 140 to 140 can be used.

Any known method can be used to mix the foam control agent with the resin, but since it is volatile, it is preferable to impregnate the foaming agent with the necessary amount of volatile organic foaming agent in advance and mix it with the resin melted in an extruder. It is desirable to use a method of mixing, or a method of press-fitting the resin alone into the molten resin and mixing.

The temperature at which the cell control agent and volatile blowing agent are mixed with the base resin is usually in the range of 170 to 250"C. If the temperature is too low, the load on the extruder motor will increase, and if it is too high, the temperature of the base resin will increase. There are problems such as deterioration of quality.The pressure is appropriately selected depending on the equipment used, die shape, extrusion amount, blowing agent concentration, temperature, etc., but it is usually 100 to 4 (10 kg
This is done within the range of /-.

The above-mentioned foamable molten resin mixture is passed through a cooler connected to the extruder and passed through a porous die attached to the tip of the extruder at a temperature below the melting point of the base resin and under a pressure below the vapor pressure of the volatile blowing agent. However, it is usually economically preferable to extrude and foam in an atmosphere at room temperature and pressure.

The expanded particles of the present invention can be formed into an in-mold body by a known method. In other words, it is given foaming ability to ensure complete foaming in the mold and good fusion between foamed particles, and is filled into a mold that can be closed but cannot be sealed and heated and melted with a heating medium. wear it. This foaming ability is imparted to the foamed particles by inorganic gases such as air, organic volatile blowing agents, and mixed gases thereof such that the internal pressure of the foamed particles is in the range of 0.5 to 3 kg/cd (gauge pressure). or pressurize the expanded particles to 95-50% of their original bulk volume.
This can be achieved by performing either one of these operations, such as shrinking, or a combination of both.

The obtained foamed molded product has excellent compressive elastic recovery properties and flexibility, and is useful as a packaging material and a heat-resistant heat insulating material with good external appearance.

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

(1) Melt index of base resin Measured according to ASTM D-1238. condition is,
Measurement was performed at 190° C. and a load of 2.16 kg.

(2) Melt index ratio of base resin ASTM D
-1238, high road melt index (H, M, 1.) measured at 190°C and a load of 21.6 kg and melt index CM, I at a load of 2.16 kg.
, ).

(3) Density of base resin Measured according to ASTM-D-1505.

(4) Appearance of foamed particles: Density For foamed particles that have been pre-foamed for one day or more,
The weight was accurately weighed, the sample was immersed in water, and the volume was measured.

(5) Measurement of bubble diameter of foamed particles Regarding the cut surfaces of 10 samples of foamed particles exhibiting a spherical or cylindrical shape, each of the 10 sample pieces were cut along a cross section that includes the central axis and is parallel to the extrusion direction. , 0.25R from the center of the surface (R is the average radius of the cut surface)
The average bubble diameter at the position was measured and taken as the bubble diameter at the center of the particle.

In addition, the bubble diameter around the outer skin of the foamed particles was determined by measuring the average bubble diameter at a position of 0.8R to IR on the surface where the rotary blade acted when obtaining the foamed particles. The smaller bubble diameter was adopted.

(6) Measurement of closed cell ratio: Manufactured by Beckman, according to ASTM D-2856.
Measurement and calculation were performed using an air comparison type hydrometer MODEL930.

(7) Measurement thickness of compressive strength and compressive elastic recovery rate: 50fl
Cut a 100 mm square test piece from the center of the molded product, compress it all over in the thickness direction at a compression speed of 10 m/lll1n, and take the compressive stress when the strain is 25% as the compressive strength of the molded product, and the strain is 80%. When the stress reaches l Q m/
The thickness X when removed at a speed of win is measured, and is taken as the compressive elastic recovery rate.

(8) Measurement of bending modulus A test piece with a thickness of 50 m, a length of 300 m, and a width of 120 m is cut from the center of the molded body, supported horizontally on two fulcrums with a span distance of 254 fins, and bent at the center between the fulcrums (span). 10m/
n+in in the thickness direction, the load per unit deflection in the straight portion of the load-deflection curve (P o/Y
o) The bending elastic modulus (kg
/crA). This value is used as a measure of the flexibility of the foam molded product.

4bh” Yo Here, 1. b and h are the distance between spans [Kushi],
These are the width [mouth] and thickness (cm 2 ) of the test piece.

Pa1Yo is load (kg) and displacement [ω] (effects of examples and inventions) Example/Comparative Example 1 An extruder with a foaming agent injection hole in the middle of the barrel and a 40φ foaming extrusion equipment equipped with cooling equipment. A multi-hole die with 8 circular holes of lφ width is installed at the tip, a cutter with a rotating blade is installed close to the die face, and equipment is used that allows fine adjustment of the clearance between the die face and the rotating blade. , high-density polyethylene (density 0.954 g/ad, melt index 0.03 g/10 min, melt index ratio 123) was fed from the hopper at a rate of about 2 kg/hour, and dichlorotetrafluoroethane and methylene were fed from the blowing agent injection hole. A blowing agent mixture with chloride having a molar composition of A was adjusted in an amount shown in Table 1 based on 100 parts by weight of the base resin, and was press-injected.

As shown in Table 1, the foam regulator was prepared by mixing alcohol or water into a foaming agent and melting and kneading it into the resin.

The strand extruded and foamed from the porous die was cut by a rotary blade rotating along the die face surface to obtain foamed particles.

Table 1 shows the properties of the foamed particles obtained.

In addition, about 1.1 kg of the obtained expanded particles was placed in a pressure vessel.
60% of the bulk volume of the original beads with compressed air at /cd cage pressure.
%, and filled in the compressed state into a closed mold with small holes (inner dimensions: 300 x 300 x 50), then released to atmospheric pressure and heated with water vapor at a temperature near the melting point of the base resin. After heating, foaming and fusing, cooling and taking out,
A foamed molded product was obtained by leaving it in a constant temperature bath at 80° C. for 6 hours.

The compressive strength, compressive elastic recovery rate, flexural modulus as a measure of flexibility, and appearance of the molded product obtained were evaluated, and the results are shown in Table 1.

The evaluation criteria for the appearance of the molded product are as follows.

◎-・Surface is uneven (air bubbles in foamed particles are difficult to identify.

O-: Surface irregularities are observed, but the bubbles in the foamed particles are difficult to identify and pose no practical problem.

× - Significant surface irregularities or visible bubbles in the foamed particles.

As is clear from this example, if a lower aliphatic alcohol or water is not used as a cell regulator, foamed particles with very fine cell diameters can be obtained, but the closed cell ratio is low and the inside of the mold is The appearance and physical properties of the molded product also deteriorate. Also 5
If the amount exceeds 1 part by weight, a fine cell structure will not be formed around the outer shell of the foamed particles by the cutting blade during the production of the particles, and the in-mold molded product will have a poor appearance and give a poor product image with low flexibility.

The distribution of cell diameters in the direction of the cylinder axis was measured on a cut plane including the cylinder axis of the cylindrical expanded particles obtained in Experiment Na2, and is shown in FIG. It is clear that the bubble diameter becomes finer at the end of the cylinder axis. That is, it is shown that a fine cell structure is formed in the peripheral area where the foamed strand extruded from the die is cut by the rotary blade.

Example 2, Comparative Example 2 Experimental Example 10 in which polyethylene resin had the melt index, melt index ratio, and density shown in Table 2.
Using the same foaming equipment as in Example 1, replacing the high-density polyethylene of ~15 and the low-density polyethylene of Experimental Arashi 16, feeding the resin from a hopper at a rate of about 2 kg/hour, and dichlorotetrafluoroethane and methylene chloride. A foam regulator was blended with a foaming agent having an equimolar composition as shown in Table 2, and the mixture was press-injected through a foaming agent injection hole and extruded into foam to produce foamed particles.

The properties of the obtained expanded particles are shown in Table 2.

Furthermore, in-mold molded products were obtained using each expanded particle in the same manner as described in Example 1. The dimensional shrinkage rate of each molded article with respect to the mold dimensions was measured and shown in Table 2.

As is clear from the results in Table 2 below, the melt and
If the index exceeds 0.7 g/10 minutes, or if the melt
If the index ratio is less than 40, the closed cell ratio of the foamed particles obtained will be low, and the dimensional shrinkage of the obtained molded product will also be large, which poses a practical problem.

Furthermore, in low-density polyethylene whose base resin has a density of less than 0.940, foamed particles with a high closed cell ratio can be obtained without using the cell regulator of the present invention, but the heating during in-mold molding causes significant damage. Dimensional shrinkage occurs, making it unusable.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the bubble diameter within the foamed particles and the radius of the foamed particles. Patent Applicant: Asahi Kasei Kogyo Co., Ltd. Figure 1-1,0-0,500,51,0 Registration Request (7)

Claims (2)

[Claims] (1) Melt index 0.7g/10 minutes or less, melt index ratio 40 or more, density 0.940g/
Non-uniform cells, which are foamed particles made of non-crosslinked high-density polyethylene with a size of cm^3 or more, and have a portion in which the cell diameter in the outer skin portion of the particle is 1/3 or less of the cell diameter in the center of the particle. structure, and the cell diameter at the center of the particle is 0.2 to 1.0 mm, the closed cell ratio is 80% or more, the density is 0.100 to 0.015 g/cm^3, and the particle diameter is 2 to 1.0 mm. High-density polyethylene resin foam particles having a diameter of 10 mm. (2) Melt index 0.7g/10 minutes or less, melt index ratio 40 or more, density 0.940g/
It is a foamed particle made of non-crosslinked high-density polyethylene with a size of cm^3 or more, and has a non-uniform cell structure in which the cell diameter in the outer skin part of the particle is 1/3 times or less of the cell diameter in the center of the particle. and the cell diameter at the center of the particle is 0.2 to 1.0 mm, the closed cell ratio is 80% or more, the density is 0.100 to 0.015 g/cm^3, and the particle diameter is 2 to 10 mm. In a certain method for producing expanded high-density polyethylene resin particles, a volatile organic blowing agent is added to the base resin, and at least one of a lower aliphatic alcohol or water is added as a foam control agent to 100 parts by weight of the resin. After adding and mixing 0.05 to 5 parts by weight, melting and kneading under high temperature and high pressure, and extruding from a die under low temperature and low pressure, the foamed strand is cut before the expansion is completed to form fine bubbles in the outer shell. A method for producing foamed particles of a high-density polyethylene resin, the method comprising forming foamed particles having a large diameter and a high closed cell ratio.