JP3218333B2 - Expanded polyolefin resin 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 expanded polyolefin resin particles and a method for producing the same, and more particularly to expanded polyolefin resin particles having a high expansion ratio and small shrinkage, and a method for producing the same.

[0002]

2. Description of the Related Art There is known a method for producing expanded particles by adding an inorganic gas-based blowing agent to polyolefin-based resin particles and releasing them under a high pressure and a low pressure under a low pressure (JP-B-62-61227). JP-A-60-229
No. 936, JP-A-60-245650). On the other hand, a method of obtaining expanded particles having a higher expansion ratio by using polyolefin resin particles containing an inorganic powder or a crystal nucleating agent is also known (Japanese Patent Application Laid-Open Nos. 61-4736 and 61-3838).
No. 2741). In these known methods, expanded particles can be obtained with a high expansion ratio.However, in the examples disclosed in the above-mentioned known documents, only examples using a very small-scale apparatus on a laboratory scale have been found, and the present inventors have found that When a supplementary test was conducted using a large-scale apparatus, the cause was not clear, but expanded particles having a high expansion ratio could not be obtained. Therefore, the present inventors have intensively studied a method for obtaining expanded particles having a high expansion ratio with good reproducibility even when using a large-scale apparatus, and using a polyolefin resin containing a water-soluble inorganic substance such as borax. We found that good results could be obtained and filed a patent application (Japanese Patent Application No.
-202238). The main feature of this method is that polyolefin-based resin particles containing a water-soluble inorganic substance such as borax are used. In this method, foamed particles having a high expansion ratio can be stably obtained even when a large-scale apparatus is used. Can be However, since the obtained expanded particles have large shrinkage, a shrinkage removing step such as holding the expanded particles under a high pressure for a long time is indispensable. In the above-described method of adding a nucleating agent (same as the nucleating agent) (Japanese Patent Application Laid-Open No. 61-2741), only dibenzylidene sorbitol and aluminum pt-butyl benzoate are disclosed as nucleating agents. There is no disclosure or suggestion of the organic phosphorus nucleating agent. Further, the present inventors have studied, when carbon dioxide is used as a blowing agent, when comparing these known nucleating agents and those of the present application, as is clear from the examples and comparative examples of the present application, those known nucleating agents, It was clear that the nucleating agent was significantly less efficient than that of the present application.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide expanded particles having a small shrinkage and containing inorganic gas, which have many advantages in terms of environment and safety, and a method for producing the same.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and have completed the present invention. That is, according to the present invention, in the expanded polyolefin resin particles containing an inorganic gas therein, the resin is
2,2-methylenebis (4,6-di-tert-phosphate)
The present invention provides foamed polyolefin-based resin particles containing a nucleating agent consisting of (butylphenyl) sodium . Further, according to the present invention, a mixture of an inorganic gas-based blowing agent , a polyolefin-based resin particle, and an aqueous medium that does not dissolve the resin, at a temperature equal to or higher than the softening point of the resin particle, is discharged into a low pressure region. A method for obtaining expanded particles, wherein the polyolefin-based resin particles include 2,2-methylenebisphosphate phosphate.
(4,6-di-tert-butylphenyl) sodium
Consisting nucleating agent is process for producing a polyolefin resin foam particles characterized that you have been contained is provided.

The resin for the polyolefin resin particles used for the resin particles as the base material in the present invention includes propylene homopolymer, propylene-ethylene random copolymer, propylene-ethylene block copolymer, and propylene-butene random copolymer. Propylene-based polymer such as propylene-ethylene-butene random copolymer, or high-density polyethylene, or a straight-chain copolymer of ethylene and a small amount of α-olefin (carbon number of 4, 6, 8, etc.) And ethylene-based copolymers such as linear low-density polyethylene. Among these, use of propylene-based random copolymer resin particles such as a propylene-ethylene random copolymer, a propylene-butene random copolymer, and a propylene-ethylene-butene random copolymer is particularly preferable.
These polymers may be cross-linked, but non-cross-linked ones are particularly preferable, and the use of non-cross-linked propylene random copolymers is particularly preferable.

The polyolefin resin particles used as the base resin particles for foaming in the present invention can be obtained by molding a polyolefin resin into particles according to a conventionally known method. Add nucleating agent. In this case, the method for adding the nucleating agent is as follows.
It is generally added as a powder having a size of from 150 to 150 μm, preferably from 1 to 100 μm, but it may be added in the form of a larger particle. In short, a nucleating agent may be added to the resin in an arbitrary shape. In order to obtain the raw material resin particles used in the present invention, the resin and the nucleating agent may be melt-kneaded and then formed into granules, or do not include the resin nucleating agent containing a large amount of the nucleating agent in advance and the nucleating agent. The resin pellets may be melt-kneaded before molding. The nucleating agent used in the present invention,
When melt molding is added to the port Li olefin resin improves the crystallinity of the polyolefin resin. For example <br/> words, non-crosslinked ethylene - in the case of using the propylene random copolymer (ethylene component 2.3% by weight, melting point 146.5 ° C., the melting end temperature 165 ° C.), this nucleating agent And the mixture is brought to a temperature of 170-30 in the extruder.
The mixture is melted and kneaded at 0 ° C.
From the end of the extruder die into a cylindrical shape in extrusion, molding temperature 70 ° C. obtained less, preferably rapidly cooled by introducing into water of 50 ° C. or less, by cutting the appropriate length, a nucleating agent The resulting resin particles can be obtained. The above temperature is of a nature that can be appropriately selected depending on the resin used.
You. The addition amount of the nucleating agent, as weight percent based on the polyolefin resin, 0.01 to 2.0 wt%, preferably 0.0
2 to 1.0% by weight. If the amount is too large, the obtained expanded particles tend to shrink, and if the amount is too small, the expansion ratio decreases. When a foam is obtained in the present invention, the particle size of the resin particles containing the nucleating agent is set to 0.3 to 5.0 mm, preferably 0.5 to 5.0 mm.
When the thickness is 3.0 mm, a foam having particularly good foaming properties can be obtained.

In the present invention, in order to prevent fusion of the resin particles during the heating and foaming of the polyolefin resin,
Resin particle fusion inhibitor can be used. This resin particle anti-fusing agent can be used regardless of organic or inorganic type as long as it is substantially water-insoluble and is non-melting at the time of heating. preferable. Illustrative examples of typical anti-fusing agents include, for example, aluminum oxide, titanium oxide, aluminum hydroxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate,
Tricalcium phosphate, magnesium pyrophosphate and the like. Such an anti-fusion agent usually has a particle size of 0.00
It is used in the form of fine particles of 1 to 100 µm, preferably 0.001 to 30 µm. The amount of the anti-fusing agent is usually about 0.01 to 10 parts by weight based on 100 parts by weight of the resin particles. When the anti-fusing agent is used, it is desirable to use an emulsifier in combination. As the emulsifier, an anionic surfactant such as sodium dodecylbenzenesulfonate or sodium oleate is suitable. The amount of the emulsifier added may be about 0.001 to 5.0 parts by weight per 100 parts by weight of the resin particles.

In the present invention, it is preferable that the expandable resin particles contained in the contents when the contents of the container are discharged from the high-pressure zone to the low-pressure zone contain secondary crystals. The expandable resin particles in which the secondary crystals are present give expanded particles having good moldability. When a non-crosslinked polypropylene-based resin or a non-crosslinked linear polyethylene-based resin is used as a raw material resin, it is particularly advantageous that secondary crystals are present in the expandable resin particles.

The presence of secondary crystals in the resin particles can be determined by a DSC curve obtained by differential scanning calorimetry of the expanded resin particles. in this case,
DS obtained by differential scanning calorimetry of resin expanded particles
The C curve refers to expanded polyolefin resin particles 1 to 3 mg.
Was measured at a heating rate of 10 ° C./min by a differential scanning calorimeter.
The DSC curve obtained when the temperature was raised to 0 ° C., for example, the DSC curve obtained when the sample was heated from room temperature to 220 ° C. at a temperature rising rate of 10 ° C./min is the first DSC
Then, the temperature was lowered from 220 ° C. to a temperature of about 40 ° C. at a rate of 10 ° C./min, and again at a rate of 10 ° C./min.
The DSC curve obtained when the temperature was raised to 20 ° C. was used as the second DSC curve, and a unique peak,
High temperature peaks can be determined. In this case, the intrinsic peak is considered to be due to the so-called endothermic during melting of the polyolefin-based resin constituting the expanded particles. This unique peak is also used in the first DSC curve for the second time.
In the second DSC curve, the peak apex temperature is 1st.
There may be a slight difference between the second and the second round, but the difference is 5
Less than 2 ° C, usually less than 2 ° C. On the other hand, a high-temperature peak is an endothermic peak that appears on the higher temperature side than the above-mentioned intrinsic peak in the first DSC curve. The presence of secondary crystals in the resin particles is determined by whether or not this high-temperature peak appears on the DSC curve. If no substantial high-temperature peak appears, the secondary crystals are present in the resin. It is determined that it does not exist. In the case of the present invention, it is desirable that the difference between the temperature of the intrinsic peak appearing in the second DSC curve and the temperature of the high-temperature peak appearing in the first DSC curve is large, and the second DSC curve The difference between the temperature at the top of the intrinsic peak and the temperature at the top of the high temperature peak is 5 ° C. or more, preferably 10 ° C.
That is all.

Next, the DSC curve of the expanded particles obtained by differential scanning calorimetry is shown in the drawing. FIG. 1 relates to expanded particles containing secondary crystals, and FIG. 2 relates to expanded particles containing no secondary crystals. FIG.
In FIG. 2 and FIG. 2, curves 1 and 2 show the DSC curves obtained by measuring the expanded particles as a sample (first measurement), and curves 1 'and 2' show the first measurement. The DSC curve obtained by measuring the sample after the measurement again (the second measurement) is shown. As can be seen by comparing FIGS. 1 and 2, in the case of expanded particles containing secondary crystals, curve 1 showing the first measurement results shows that in addition to intrinsic peak B, high-temperature peak A appears and this high-temperature peak
It is confirmed that secondary crystals are present in the foamed particles by the presence of kuA. On the other hand, in the case of the expanded particles containing no secondary crystal, the curve 2 showing the first measurement result shows only the intrinsic peak b but no high-temperature peak.
It is confirmed that the expanded particles do not contain secondary crystals.
The reason why secondary particles are not present in the expanded particles in FIG. 2 is that the raw material unexpanded resin particles are not subjected to heat treatment for a sufficient time at the secondary crystallization accelerating temperature (from the melting point to a temperature lower than the melting end temperature). Due to foaming at temperature. In the second measurement, high-temperature peaks do not appear in the expanded particles shown in FIGS. 1 and 2, but only intrinsic peaks B 'and b' appear.

In the present invention, in order to obtain expandable resin particles containing secondary crystals, in the case of a non-crosslinked polypropylene resin, the resin particles are heated to a melting point in a pressure vessel without being heated to the melting end temperature or higher. The temperature may be maintained at a temperature about 20 ° C. lower than the melting point (−20 ° C.) or higher and lower than the melting end temperature for a sufficient time, usually 5 to 90 minutes, preferably about 15 to 60 minutes. When the secondary crystallized foamable resin particles are foamed in this way, the foaming temperature is not less than the melting end temperature of the intrinsic peak, but is not higher than the high temperature peak. Can be obtained. In the case of non-crosslinked linear low density polyethylene,
Foamable resin particles containing secondary crystals can be obtained in the same manner as in the case of the non-crosslinked polypropylene resin,
The heat treatment temperature in this case is a temperature not less than about 15 ° C. lower than the melting point and less than the melting end temperature, and the time is 5 to 5.
90 minutes, preferably 5 to 30 minutes.

The foaming agent in the present invention is an inorganic gas foaming agent such as nitrogen, carbon dioxide, argon, air, etc., and carbon dioxide is particularly preferred.
In general, the supply is made to be 0 kg / cm ² · G or less. In addition, volatile organic foaming agents such as propane, butane, pentane, hexane, cyclohexane, dichlorodifluoromethane, and trichlorofluoromethane were added at 50% by weight.
Although there is no particular problem even when used together to the extent, 25% of the total foaming agent is used.
It should be kept to less than 20% by weight, preferably less than 20% by weight. The pressurization with the inorganic gas is at least one.
5 kg / cm ² · G, preferably 20 kg / cm ² · G or more. The time of pressurization with the inorganic gas varies depending on the pressure to be applied, but is several seconds or more at or above the melting point of the resin.
It is about 1 hour, and usually about 5 to 30 minutes is sufficient. The pressurization of the contents of the container with the inorganic gas can be performed at any time, and can be performed immediately after filling the contents of the container, during the temperature rise, or when the foaming temperature is reached. In particular, when using carbon dioxide as a foaming agent, it can be introduced into the container in the form of dry ice, and in this case, it is supplied into the container together with the resin particles and the dispersion medium, and the container is sealed. Thereafter, a method of heating is adopted. The heating rate of the contents of the container by heating is usually
The temperature is 1 to 10C / min, preferably 2 to 5C / min.

The dispersing medium for dispersing the resin particles may be any one which does not dissolve the resin particles. Examples of such a dispersing medium include water, ethylene glycol, glycerin, methanol and ethanol. It is common to use

In the present invention, the step of impregnating the resin particles with the foaming agent is generally performed simultaneously with the step of dispersing the resin particles. Therefore, the foaming agent is once dissolved or dispersed in a dispersion medium and then impregnated into the resin particles. The foaming agent can be impregnated into the resin particles by a method such as heating and pressurizing while stirring the resin particles, the foaming agent and the dispersion medium in a closed container. Therefore, to implement the method of the present invention,
In a pressure vessel, the nucleating agent-containing polyolefin-based resin particles described above, an anti-fusing agent, and an aqueous medium (usually water) are blended and heated to a foaming temperature under the pressure of an inorganic foaming agent. The pressurized zone to the low pressure zone (usually atmospheric pressure)
And foaming the resin particles containing the foaming agent.

The foaming temperature in practicing the present invention is generally a temperature higher than the softening point of the resin, but the temperature around the melting point of the resin particles used is particularly preferred. The preferred foaming temperature range varies depending on the type of the resin. When a non-crosslinked polypropylene resin is used, the temperature ranges from 5 ° C lower than the melting point to 15 ° C higher than the melting point, particularly from 3 ° C lower than the melting temperature to 10 ° C higher The optimum temperature range is from 10 ° C. lower than the melting point to 5 ° C. higher than the melting point of the polyethylene resin. The heating rate when heating to the foaming temperature is 1 to 10 ° C / min, preferably 2 to 5 ° C.
/ Min. The melting point of the resin referred to in the present specification means that about 6 mg of a sample is heated to 220 ° C. at a rate of 10 ° C./min by a differential scanning calorimeter, and then about 50 mg at a rate of 10 ° C./min.
° C, and the temperature of the endothermic curve peak (intrinsic peak) obtained when the temperature is raised again to 220 ° C at a rate of 10 ° C / min. The melting end temperature of the resin is the second temperature.
It means the end temperature of the second endothermic curve.

[0016]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 3 Per 100 parts by weight of a non-crosslinked ethylene-propylene random copolymer (2.3% by weight of ethylene component, melting point: 146.5 ° C., melting end temperature: 165 ° C.) After adding 0.2 parts by weight of sodium methylenebis (4,6-di-tert-butylphenyl), melt kneading in an extruder, extruding it into a stride from a die at the tip of the extruder, quenching in water, and cutting. And granulated into pellets (length 2.4 mm, cross-sectional diameter 1.1 mm). This pellet 1
00 kg and 1 kg of finely divided tricalcium phosphate,
40 g of sodium dodecylbenzenesulfonate and water 2
20 liters and the amount of dry ice shown in Table 1 were blended, and the temperature was raised to the temperature shown in the same table without stirring to a temperature higher than the melting temperature while stirring in a closed container (capacity: 400 liters), and 10 minutes Held. Table 1 shows the pressure inside the container at this time.
It was shown to. Thereafter, high-pressure nitrogen gas is introduced into the container while maintaining the same temperature, and one end of the container is opened while maintaining the inside of the container at the pressure shown in Table 1 to release foamable resin particles and water under atmospheric pressure. And foamed. Table 1 shows the average bulk expansion ratio after leaving the obtained expanded particles at room temperature and pressure for one day.
In order to confirm the shrinkage of these foamed particles, these foamed particles were placed in a closed container, and the pressure in the container was increased to 0.3 kg / cm ² · G with air over 1 hour.
Pressurize to 2kg / cm ² · G over time and increase to 2kg / c
After holding at m ² · G for 1 hour, the sample was taken out, and the average bulk ratio was measured again. In addition, the contraction rate of Table 1 was calculated by the following formula.

Comparative Example 1 Expanded particles were obtained in the same manner as in Example 3, except that the nucleating agent was changed to dibenzylidene sorbitol. Table 1 shows the expansion conditions, expansion ratios, and shrinkage ratios at that time.

[0019] Except for using borax in place of nucleating agent in Comparative Example 2 Example 2 to obtain expanded beads in the same manner as in Example 2. Table 1 shows the expansion conditions, expansion ratio, and shrinkage ratio.

[0020]

[Table 1]

[0021]

According to the present invention, by adding a small amount of a specific nucleating agent to a raw material polyolefin resin, even when an inorganic gas-based foaming agent is used, the shrinkage ratio can be stably reduced when a large-sized foaming apparatus is used. Small foamed particles can be obtained. The expanded particles obtained by the present invention have an advantage that there is no problem in their handling and storage due to their small shrinkage, and they are used as a cushioning material by themselves. It is preferably used as particles, and a foamed molded article is obtained by filling a metal and heating and foaming.

[Brief description of the drawings]

FIG. 1 shows a DSC curve obtained by performing differential scanning calorimetry on expanded particles in which secondary crystals are present.
The first DSC curve is shown, and the curve 1 'is the second DSC curve.

FIG. 2 shows a DSC curve obtained by differential scanning calorimetry of expanded particles having no secondary crystals, curve 2 shows a first DSC curve, and curve 2 ′ shows a second DSC curve. ing.

[Explanation of symbols]

 A High temperature peak B, B ', b, b' Specific peak

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Shioya 1785-31 Tsukuse-cho, Utsunomiya City, Tochigi Prefecture Hara Nobo Kaikan 301 (72) Inventor Wataru Kikuchi 3186-2 Tsuruga-cho, Utsunomiya City, Tochigi Prefecture Takanari A202 (56) References JP-A-61-2741 (JP, A) JP-A-61-103944 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/00-9 / 42 C08K 5/523 C08L 23/00-23/36

Claims (5)

(57) [Claims] 1. A polyolefin resin foam particle containing an inorganic gas therein, wherein the resin is 2,2- medium phosphate.
Tylene bis (4,6-di-tert-butylphenyl)
Polyolefin resin foam particles containing a nucleating agent made of sodium . 2. A mixture of an inorganic gas-based blowing agent , polyolefin-based resin particles, and an aqueous medium that does not dissolve the resin is discharged into a low-pressure region at a temperature equal to or higher than the softening point of the resin particles to form expanded particles. a get method, the said polyolefin-based resin particles phosphate 2,2-methylenebis (4,6-di -
Nucleating agent consisting of tert-butylphenyl) sodium
Process for producing a polyolefin resin foam particles but characterized that you have been contained. 3. 50% by weight of the total weight of the inorganic gas-based blowing agent
% Or more is occupied by inorganic gas.
A method for producing expanded polyolefin-based resin particles as described above. 4. 75% by weight of the total weight of the inorganic gas blowing agent
% Or more is occupied by inorganic gas.
A method for producing expanded polyolefin-based resin particles as described above. 5. The method of manufacturing a polyolefin resin foamed particles according to claim 2, wherein the inorganic gas type foaming agent is characterized in that carbon dioxide.