JPH011741A - Non-crosslinked linear low density polyethylene pre-expanded particles - 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 [Industrial Field of Application] The present invention relates to non-crosslinked linear low density polyethylene pre-expanded particles.

[Problems to be solved by the prior art and the invention] A so-called bead foam molded product (in-mold molded product) obtained by filling pre-expanded particles under pressure inside a mold, heating and foaming it.It has excellent Fi buffering properties, heat insulation properties, etc. It is used in a wide range of applications such as cushioning materials, packaging materials, insulation materials, and construction materials, and the demand for it has increased greatly in recent years.

Conventionally, molded bodies made of polystyrene foam beads have been known as this type of molded body, but polystyrene bead foam molded bodies have the fatal disadvantage of being brittle and have the disadvantage of being inferior in chemical resistance. , improvements have been desired for a long time. A molded product made of polyethylene foam particles has been proposed as a solution to these drawbacks, but since the viscosity of polyethylene resin Fi drops significantly near the melting point, crosslinked products are usually used. In some cases, it is difficult to obtain a molded product with a low density (high foaming) by in-mold molding, and if you try to obtain a molded product with a low density, the product shrinks significantly, has high water absorption, and has poor physical properties. Only a molded body could be obtained, and a practically usable low-density polyethylene molded body could not be obtained at all. Furthermore, high-pressure low-density polyethylene is mainly used as a raw material for cross-linked polyethylene due to its good crosslinking properties, but high-pressure low-density polyethylene has poor heat resistance and lacks rigidity, so it is unavoidable. Therefore, the foaming ratio had to be relatively low.

As a way to solve these problems,
Publication No. 047 proposes a method of molding using pre-expanded particles made of non-crosslinked linear low-density polyethylene, but pre-expanded particles made of non-crosslinked polyethylene have a narrow heating temperature range during molding. Due to the inability to heat sufficiently and the crystal structure of non-crosslinked linear low-density polyethylene, sufficient secondary foaming will not occur unless foaming ability is imparted, and a good molded product will not be obtained. For this reason, when molding non-crosslinked linear low-density polyethylene pre-expanded particles, a method is adopted in which a blowing agent gas or an inorganic gas such as air is heated to an appropriate temperature and internal pressure is applied to the pre-expanded particles prior to molding. However, heating the foaming gas or inorganic gas to the pre-expanded particles at an appropriate temperature requires a large amount of equipment and expense, and there is a problem in that the manufacturing cost of the molded body is high. Moreover, in general, pre-expanded polyolefin resin particles have difficulty maintaining foaming ability for a long time because the gas inside the particles is easily released, even if they are given foaming ability by increasing the internal pressure with inorganic gas at an appropriate temperature. However, in order to obtain an excellent molded product using these conventional methods, the pre-expanded particles must be consumed in a short time after applying internal pressure, and the molding company receives the supply of pre-expanded particles from the pre-expanded particle manufacturer. However, it was not possible to easily produce a molded body just by using the method described above.

On the other hand, Japanese Patent Publication No. 55-7816 discloses that cross-linked polyethylene resin pre-expanded particles are molded without pretreatment of applying an internal pressure by injecting an inorganic gas at an appropriate temperature, and then cooling from the softening temperature of the resin to room temperature. After that, below the softening temperature of the resin ~
A method is disclosed in which the temperature is raised to a temperature 40°C lower than the softening temperature and then slowly cooled to obtain a molded body. As mentioned above, there is a problem in that it is difficult to obtain a molded product with a low density, and none of the methods are fully satisfactory.

[Means for solving problems]

As a result of intensive research in view of the above points, the present inventors found that two endothermic peaks appeared in the DSC curve obtained by differential scanning calorimetry, and based on the energy of the endothermic peak on the high temperature side, it was found that a crystal structure with a crystal structure of 5119 or higher was found. It was discovered that cross-linked linear low-density polyethylene pre-expanded particles can be molded without pretreatment to apply internal pressure, and that low-density molded products with excellent physical properties such as low water absorption and no shrinkage can be easily provided. The invention was completed.

That is, the present invention provides non-crosslinked linear low-density polyethylene pre-expanded particles, which have a DS obtained by differential scanning calorimetry.
Two endothermic peaks appear in C411M (the DSC curve obtained when 1 to 5 mg of pre-expanded particles are heated to 220°C at a temperature increase rate of 10°C/min using a differential scanning calorimeter), and two endothermic peaks appear on the high temperature side. The energy of the endothermic peak is 5
The gist of the present invention is non-crosslinked linear low-density polyethylene pre-expanded particles characterized by having a crystal structure of J/77 or higher.

Non-crosslinked linear low density polyethylene (hereinafter abbreviated as LLDPI), which is the base resin of the pre-expanded particles of the present invention, includes a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms. Examples of α-olefins having numbers 4 to 10 include 1-butene, 1-pentene, 1-hexene, 3.3
-') Methyl-1-butene, 4-methyl-1-pentene, 4.4-dimethyl-1-pentene, ni-octene, etc., but 1-butene is particularly preferred. Also these α
- The content of olefin in LLDPE is usually 3 to 12% by weight, preferably 6 to 9% by weight.

The pre-expanded particles of the present invention exhibit two endothermic peaks in the DSC curve obtained by differential scanning calorimetry f fill determination,
And it has a crystal structure in which the energy of the endothermic peak on the high temperature side is 5J/11 or more. The temperature of the valley between the high-temperature peak and the low-temperature peak is preferably on the higher Al side than the temperature of the endothermic peak appearing in the DSC curve of the raw material used.

The above DSC curve refers to pre-expanded particles 1 to 5 and 119 measured by a differential scanning calorimeter at a heating rate of 1007 minutes to 220.
This is the DSC curve obtained when the sample is heated to 220°C and measured at a rate of 10°C/min. It is.

The endothermic peak on the low temperature side is considered to be due to endotherm during so-called melting of non-crosslinked linear low-density polyethylene, which is the base resin of the pre-expanded particles. On the other hand, the endothermic peak on the high temperature side is thought to be due to the existence of a crystal structure different from the structure that appears as the endothermic peak on the low temperature side. Then, only one possible endothermic peak appears, and two endothermic peaks do not appear. Therefore, the endothermic peak on the high temperature side is not due to the crystal structure of the base resin itself, but is considered to be due to the crystal structure of the pre-expanded particles (Figure 1 shows the DSC curve of the pre-expanded particles. is shown by a solid line, and the DSC curve of the raw resin particles is shown by a dotted line).

The energy of the endothermic peak on the high temperature side is calculated by dividing the high temperature side peak (b) and the low temperature side peak (c) at the valley part (a) between the high temperature side peak and the low temperature side peak (c) in Figure 1, and calculating the energy of the endothermic peak on the high temperature side (
The area of the peak on the higher temperature side than aJ is taken as the area of the higher temperature side peak (b), and this value is calculated based on this area.

9. The area of the endothermic peak on the far side on the chart -, the energy of the endothermic peak on the high temperature side can be determined by the following formula.

Energy of endothermic peak on high temperature side (J/11) = [
Surface on the chart of the endothermic peak on the high temperature side @R (cIl)
]x [Char) 1c! I hit the heat t (J/cd)] ÷
[Amount of measurement sample Ii (,9)] It is particularly preferable that the above energy is 5 to 25 J/i.

The pre-expanded particles of the present invention are prepared by dispersing resin particles and a volatile blowing agent in a dispersion medium such as water in a container, heating and holding the mixture, and then
When the resin particles and dispersion medium are discharged under low pressure inside the container to cause foaming, the resin particles are melted in the container at a temperature of T:
It can be obtained by setting the foaming temperature (temperature at the time of release) to a range of -20°C or more to the melting point of the resin and less than -10°C, without heating above m (°C). The melting end temperature of the resin: Tm is the melting end temperature in DSCIllM obtained when the resin particles used for foaming are heated at 10° C./min, and is measured using a sample amount of about 2 to 5 mg. The melting point is the temperature at the apex of the peak of the DSC curve obtained by the above measurement.Also, the resin particles used for producing pre-expanded particles are heated above the melting point and then heated to a crystallization temperature of −40°C.
Preferably, the material is rapidly cooled in an atmosphere of .degree. C. or lower. still,
The crystallization temperature refers to the temperature at the top of the peak of the DSC1lIl line obtained when the temperature is raised to 200°C at a rate of 10°C/min and then lowered at a cooling rate of 10°C/min.

Volatile blowing agents used in the production of the pre-expanded particles of the present invention include hydrocarbons or halogenated hydrocarbons having a boiling point of 150 to 120°C, such as propane, butane, pentane, hexane, hegetane, cyclohentane, cyclohexane, monochrome Lomethane, Tsuku 00 Methane, Monoku ClC
Examples include 2ethane, trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, and the like. These may be used alone, or 2
More than one species may be used in combination. These volatile foaming agents are impregnated in an amount of 5 to 40 parts with respect to 7100 parts (parts by weight, hereinafter the same) of non-crosslinked linear low-density polyethylene and used for foaming.

The amount of non-crosslinked linear low density polyethylene particles to be dispersed in water is preferably 10 to 100 parts per 100 parts of water to improve productivity and dispersion stability and to reduce utility costs. In addition, the amount of the volatile blowing agent to be dispersed in water together with the resin particles is determined by considering the type of blowing agent, the desired expansion ratio, the ratio of the amount of resin in the container to the space inside the container, etc. The content is determined to be within the above range.

A dispersant can also be used if necessary when dispersing the resin particles in water. Dispersants are used to prevent resin particles from clumping together during heating, and include water-soluble polymers such as polyvinyl alcohol, methylcellulose, and N-polyvinylpyrrolidone, calcium phosphate, magmotosium pyrophosphate, and carbonic acid. Fine powder of poorly water-soluble inorganic substances such as zinc, titanium oxide, and aluminum oxide is used. When using the above inorganic substance, a small amount of sodium alkylbenzenesulfonate as a dispersion aid,
It is preferable to use a surfactant such as α-olefin sodium sulfonate or alkyl sodium sulfonate in combination to reduce the amount of inorganic substance used, in order to improve the fusion of the pre-expanded particles during molding. In this case, approximately 0.1 to 3 parts of poorly water-soluble inorganic substance fine powder and 0.001 to 0.5 parts of anionic surfactant are used per 100 parts of resin particles. In addition, when water-soluble polymer is used, resin particles 100
It is used about 0.1 to 5 parts per part.

The pre-expanded particles of the present invention are used for producing bead-foamed molded products, and the pre-expanded particles of the present invention can be used to produce excellent molded products with low density without shrinkage even when used without pretreatment of applying internal pressure prior to molding. can be obtained.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1 to 3, Comparative Examples 1 to 2 LLDPE made by copolymerizing ethylene and 1-butene and having the density and melt flow rate (MFR) melting point shown in Table 1 was melted in an extruder, Thereafter, it was extruded into a strand from a die, rapidly cooled in water, and granulated into pellets of about 4 ny/piece. After that, the above Veleno was placed in a 400t autoclave for 100 to 9. Water 2001 and 0.3 kg of finely divided aluminum oxide as a dispersant were charged, and 35 kg of dichlorodifluoromethane was added while stirring, and the temperature was raised to the foaming temperature shown in Table 1 without raising the temperature above the melting end temperature of the particles. It was kept warm for 10 minutes. The internal pressure of the autoclave at this time was 229/d·G. Next, at the same temperature, the discharge pulp at the bottom end of the container was opened, and the resin particles and water were discharged under atmospheric pressure to foam the resin particles. During the release,
Inject air into the container to increase the container internal pressure to 3okg/cd-
I kept it in G. Table 1 shows the average expansion ratio and differential scanning calorimetry results of the obtained pre-expanded particles. The pre-expanded particles were aged at room temperature and under atmospheric pressure for 24 hours.
A mold measuring 0 m x 300 mm x 60 m was filled, and after the air in the metal was evacuated, it was heated with steam at 1.2 kg/d-G to perform molding. After cooling with water, the molded product was taken out from the mold and cured at 80° C. for 20 hours, after which various physical properties were measured. The results are shown in Table 2.

Table 2 *I Measured according to ASTM D3576K.

*2 Measured in accordance with JIS K6767B method, 0
．． Less than 005Ii/cj・・・・・・・・・・・・・・・
・OO,005,9/- or more・・・・・・・・・・・・
...It was determined as ×.

*3 Molding vapor pressure 1.2 ky/ad -c ~ 1.6
k! We observed the stability of molding when molding was performed by changing the temperature of il/cffl/G, and found that molding could be performed in the same way at any vapor pressure.
・・・・・・○ There is no stability in molding due to the difference in vapor pressure ・・・・・・・・It was judged as ×.

*4 According to JIS K6767K.

〔Effect of the invention〕

As explained above, in the non-crosslinked linear low density polyethylene pre-expanded particles of the present invention, two endothermic peaks appear in the DSC curve obtained by differential scanning calorimetry, and the energy of the endothermic peak on the high temperature side is 5 J/1 or more. Due to its crystal structure, although it is a non-crosslinked linear low-density polyethylene pre-expanded particle, it can be heated over a wide temperature range during molding, and a good molded product can be obtained even after pre-treatment to apply internal pressure. , Equipment for applying internal pressure and internal pressure applying process K
Such expenses can be reduced. Further, the pre-expanded particles of the present invention have excellent physical properties such as low shrinkage and low water absorption, and also have the effect that a low-density molded product can be easily obtained.

[Brief explanation of drawings]

FIG. 1 is a DSC1ill line obtained by differential scanning calorimetry of raw resin particles and pre-expanded particles of the present invention.
The solid line is the DSC curve of the pre-expanded particles of the present invention, and the broken line is the DSC curve of the raw resin particles used for producing the pre-expanded particles of the present invention.

Claims (1)

[Claims] Non-crosslinked linear low-density polyethylene pre-expanded particles, DSC curve obtained by differential scanning calorimetry (however, 1 to 5 mg of pre-expanded particles are measured by differential scanning calorimetry).
It must have a crystal structure in which two endothermic peaks appear in the DSC curve obtained when the temperature is raised to 220°C at a heating rate of 0°C/min, and the energy of the endothermic peak on the high temperature side is 5 J/g or more. Non-crosslinked linear low-density polyethylene pre-expanded particles characterized by: