JPS6026503B2 - Molded body made of cross-linked polyethylene foam particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a molded article made of crosslinked polyethylene foam particles and excellent in thermal dimensional stability over time and heat insulation properties.

Polyethylene foam moldings have attracted attention as a material that can replace polystyrene foam moldings, and in recent years have come to be used as cushioning materials, heat insulating materials, etc. in various fields.

However, polyethylene foam moldings have low dimensional stability over time and shrinkage when used for long periods of time under conditions exposed to high temperatures, which limits their use as insulation materials in high-temperature areas. The reality is that there are. For example, when applied to the interior ceiling material of a car, in the summer or in the tropics, 80 to 9500
When exposed to such high heat, the ceiling material shrinks and deforms significantly within a few days, not only making the ceiling ugly and distorted, but also causing the ceiling material to fall out of the panel's grooves. In addition, polyethylene foam formed into a flat plate is laid on top of concrete to insulate rooftops of apartments and other buildings.
Furthermore, even if the top surface is treated with waterproof resin, it will shrink and deform in a short period of time due to direct sunlight, causing distortion in the molded plate and damaging the waterproof membrane, creating voids in the joints, and affecting the appearance. Not only will this damage the insulation, but it will also act as a reservoir for rainwater, absorbing water, and significantly deteriorating its insulation performance. The present inventors have overcome the drawbacks of conventional polyethylene foam moldings, and have developed a cross-linked polyethylene that maintains good dimensional stability for a long period of time even under conditions of exposure to high heat and exhibits excellent heat insulation properties. As a result of extensive research to develop foamed molded products, approximately 90 foamed products have the property of being able to re-expand beyond a predetermined rate after being made into a molded product.
The inventors have found that the shrinkage rate is 2% by volume or less even after use for about 10 hours or more at a temperature of 100°C, showing good dimensional stability.Based on this finding, the present invention was developed.

That is, the present invention consists of a fused aggregate of foamed particles including a large number of cell structures formed of cross-linked polyethylene with a melting temperature of 107 to 124 qo, and when heated with steam at 110°C for 5 seconds, The present invention provides a crosslinked polyethylene foamed particle molded article characterized by having the ability to expand as described above.

In the present invention, the crosslinked tapolyethylene constituting the cell structure is preferably an ethylene homopolymer, but as long as the properties of polyethylene are maintained,
It may also be a copolymer containing other monomers.

In the present invention, it is necessary that the crosslinked polyethylene in such a cell structure has a melting temperature within the range of 107 to 124°C. Those with melting temperatures outside this range will not be able to achieve the objectives of the present invention, even if other conditions are met. Next, in the present invention, when the molded body is heated with steam for 5 seconds at 110° C., it is necessary that the molded body has the ability to expand by IZ volume % or more.

Figure 1 is a graph showing the relationship between expansion ability and shrinkage rate when various molded bodies are left at 90°C for 9 hours. According to this, each molded body belongs to solid line A and solid line B, respectively. It is divided into two groups, and changes significantly at the intersection of these two solid lines, that is, the point where the expansion chamber is 12% by volume and the shrinkage rate is 1% by volume, and it can be seen that the shrinkage rate of the group belonging to solid line B is extremely low. I understand.

In other words, if conditions are selected such that the expansion coefficient of the molded product measured as described above is 12% by volume or more, and a molded product made of polyethylene foam particles is manufactured, the dimensions under thermal ant strain will be This means that a molded article with good stability can be obtained. In general, when forming a cross-linked polyethylene foam particle, almost all of the foaming ability imparted to the foam particle during in-mold molding is utilized, and even if some blowing agent gas or Even if pressure remains in the foamed particles, it is thought that it will completely disappear if the molded product is left under atmospheric pressure. Nevertheless, it is completely unexpected that the molded product of the present invention has a high expansion capacity of 12% by volume or more, and it is completely unexpected that the molded product of the present invention has a high expansion capacity of 12% by volume or more.
Among the polyethylene foam molded products disclosed in known literature (for example, Japanese Patent Publication No. 51-22951, Japanese Patent Publication No. 53-33996, etc.), no one having such an expansion hole was known at all. The reason why the molded article of the present invention maintains a large expansion ability and thereby exhibits good dimensional stability over time can be explained as follows.

That is, it is thought that the expansion ability of the molded article of the present invention is mainly derived from the thermal expansion of the gas existing in the cells of the expanded particles constituting the molded article, but the expansion ability actually expressed is
It depends on the cell structure and the material used to form it.

For example, in order to exhibit sufficient expansion capacity, the cell membrane needs to have gas permeability that is at least low enough to exhibit an effect of thermal expansion of gas when the molded body is heated. On the other hand, when this molded body is cooled, it has the strength to maintain the cell dimensions against the pressure reduction caused by the cooling contraction of the gas, and then draws in outside air to balance the cell internal pressure and external pressure. It is necessary to have such rigidity and gas permeability that it can be used. 0 In this way, a molded product with a cell structure that can exhibit sufficient expansion ability and the characteristics of the resin that forms it will maintain sufficient resistance to shrinkage even when exposed to high heat for a long period of time, and will retain its flexibility. As a result, it does not exhibit the disadvantages of polyethylene foam molded products.

In other words, in the molded article of the present invention, the cell structure and the material forming it have an important meaning, but even if the same material is used, the thickness of the cell membrane, damage, wrinkles, orientation, etc. The properties of the molded article vary depending on the cell shape, homogeneity, etc., and are inevitably influenced by method factors such as the degree of crosslinking, crosslinking means, foaming conditions, and operating conditions.

However, it is virtually impossible to combine these factors individually, examine their effects, and specify configuration requirements, but fortunately in the present invention, comprehensive management of these factors is possible. The above-described expansion chamber can be used as a factor. Therefore, in the present invention, 'a) the polyethylene forming the cell structure of the expanded particles constituting the molded product has a melting temperature in the range of 107 to 124°C, and It is essential that the material expands by 12% or more of its original volume when heated with water vapor for 5 seconds.

The molded article of the present invention can be produced by preparing foamed polyethylene particles from polyethylene resin, subjecting them to a foaming treatment as necessary, filling them into a mold, and heating and foaming them. .

In this case, the foamed particles can be prepared by adding 0.2 to 2.5% by weight of a crosslinking agent to a polyethylene resin having a predetermined melting temperature, and heating the mixture to a temperature of 100 to 13 mm to form crosslinked polyethylene particles. Thereafter, a blowing agent such as dichlorodifluoromethane is added at 70 to 90°C for 0.5 to 1. Impregnated with insect terama, 0.
The sand is heated for 10 to 3 degrees with water vapor of 3 to 0.9 kg/gauge pressure for primary foaming, and then treated with air of 1 to 20 k9/gauge pressure at 80 to 90°C for 4 to 6 hours. Further, secondary foaming is carried out by heating the rat sand for 5 to 2 minutes with water vapor of 0.3 to 1.0 k9/ground (gauge pressure).

The foamed particles obtained in this way are left under atmospheric pressure for several days to more than ten days to bring the internal pressure of the particles to substantially OK9/gauge pressure, and then, if necessary, stored at room temperature in a pressure-resistant container. Air of 0.3 to 0.7 kg/ground (gauge pressure) is injected and compressed to a compression rate of 2 to 18%, and this is directly filled into a mold of a predetermined shape, and the air is compressed to a compression ratio of 1.0 to 1. 7k9/ground (
The desired molded product can be obtained by heating with water vapor (gauge pressure) and then cooling.

This molded body is further heated in a heating room at 60 to 90o0.
It is best to dry for about 0 hours. The melting temperature of the polyethylene that forms the cell structure of the molded product of the present invention is measured using a differential thermometer (manufactured by Perkin-Elmer, differential scanning calorimeter, model 11B).
It is determined by measuring under the conditions of a sample amount of 0.005 m/min and a heating rate of 10 m/min.

In addition, the expansion ability of a molded product can be determined by determining the density (D, volume/unit) before heating of a sample cut out as a cube with 5 skins on each side from its weight and true volume, and then heating the sample at 110°C. After heating with water vapor for 5 seconds, it is aged in a constant temperature room at 70 qo, and the density D2 (ground/tan) is determined in the same manner as described above, and can be calculated using the following formula.

Expansion ability (%) = 3 x 3 × blood Furthermore, the thermal stability over time was determined by cutting out a sample as a cube with 5 sides on each side and leaving it in a heated greenhouse for 9 minutes. Thereafter, the sample was taken out and allowed to cool for 1 hour, and the dimensional change rate with respect to the initial size was determined, and the maximum value is shown.

The molded article of the present invention has excellent dimensional stability over time and heat insulation properties, and is therefore particularly suitable as a heat insulating material used in contact with high temperatures, such as pipe covers for supply and damage, and tile base materials.

Next, the present invention will be explained in more detail with reference to Examples. In addition, the measurement and evaluation method of the characteristics in each example is shown below. '1} Volume reduction rate of the pipe cover: The temperature in the constant temperature chamber 1 of the apparatus shown in Fig. 2 was maintained at 80q0, and the length of the pipe was 50 m2 so that the pipe cover attachment part 2 could cover the entire circumference of the pipe. Three sets of covers made from the sample were installed in series, and 1
Over 50 grants were made.

After leaving it in this state for one year, the sample was removed, its bulk volume (V2) was measured, and the volume reduction rate was calculated from the pre-measured bulk volume (V,) before installation according to the following formula. , evaluated according to the following criteria. Volume reduction rate (
%): Sanyunjun X.o.

{2' Volume reduction rate and insulation performance sustainability of tile base material: The tile base material is used under roof tiles of ordinary houses that are particularly exposed to high temperature and humidity conditions (in this experiment, a residential insulation experimental building in Okinawa was used). Approximately one year after it was installed, it was removed and the following evaluations were performed.

i Bulk volume (V2) of molded body subjected to volume reduction rate test
The volume (V) has been measured in advance before installation.
, ), the volume reduction rate was calculated using the above formula, and evaluated based on the following criteria.

(5) 200 vertically and 20 horizontally from the same part of the molded body subjected to the insulation performance sustainability test.
Cut out a sample piece with a thickness of 5 mm and the size of the ship's side. Wipe the surface lightly with gauze and measure the thermal conductivity of this material using the method specified in ASTM C 518. The state of change in thermal conductivity ^ determined from a sample piece cut out from the molded body was calculated for input/input', and evaluated according to the following criteria.

Example 1 Molded articles were obtained by the following method using polyethylene resins A to E shown in Table 1 as base resins.

Table 1 shows that 18 parts by weight of water containing 0.25 parts by weight of calcium phosphate prepared from an aqueous solution of sodium IJ phosphate and an aqueous solution of calcium chloride were placed in a pressure-resistant container, and while stirring, water 2 parts by weight containing 0.1 part by weight of Neoverex was placed. After adding a predetermined amount of dicumyl peroxide finely dispersed while stirring under heating to parts by weight of , 100 parts by weight of polyethylene resin was added, and the inside of the container was replaced with nitrogen to reduce
When the contents were taken out after treatment for 2 hours at 135qo and 7 hours at 135qo, the particle size was 1.2 ribs and the gel fraction was 30-80%.
crosslinked polyethylene particles were obtained.

The amount of dicumyl peroxide was selected from 0.2 parts to 2.5 parts by weight depending on the desired degree of crosslinking. The crosslinked particles were placed in a pressure-resistant container, impregnated with dichlorodifluoromethane, and then heated and foamed to obtain primary foamed particles with an apparent bulk volume of about 17 square meters. The primary foamed particles were placed in a pressure-resistant container, impregnated with air, and then heated and foamed to obtain secondary foamed particles with an apparent bulk volume of about 41/cm. For the above foaming method, the optimum value among the following conditions was used.

Primary blowing agent impregnation temperature 70-90CO Primary blowing agent impregnation time 0.5-1. Insect time - Total trace steaming 0.3~0.9k9/(gauge pressure) Primary foaming heating time 10~3 sand air chamber impregnation pressure 10k9/ground (gauge pressure) Elevation impregnation temperature 80~90pm 0 air Impregnation time: 4 to 6 hours Secondary foaming water vapor pressure: 0
．． 3 to 1.0k9/lump (gauge pressure) Secondary foaming heating time 5 to 2 nights The obtained foamed particles were left under atmospheric pressure for one week until the internal pressure of the particles was
After confirming that the pressure is k9/ground (gauge pressure), the particles are placed in a pressure-resistant container and heated to 0 at room temperature depending on the type of base resin used.
．． Treated with air at 3 to 0.7 k9/ground (gauge pressure) for about 5 seconds and compressed to 90% of the original bulk volume (compression ratio 10%),
This is placed as is in a mold with internal dimensions of 30 mm x 30 mm x 5 mm (thickness), heated with steam at 1.0 to 1.7 k9/cm (gauge pressure), and then cooled and molded. I got a body.

Regarding the molded body obtained here, the melting temperature of the cell membrane and 110
The expansion ability was measured when heated with water vapor at ℃ for 5 seconds.

The results are shown in Table 2. According to the results in Table 2, approximately 10
It has been found that it is necessary to select a group of cell membrane melting temperatures in the range of at least 107 to 124 DEG C. that can provide the molded article with an expansion ability of more than 10%.

The dimensional stability over time of heat was evaluated for each molded article within the above range by the evaluation method described above.

The results are also listed in Table 2 and shown in Figure 1 as the relationship between expansion ability and shrinkage rate. According to the results shown in Fig. 1, the dimensional stability over time of heat changes steeply below the 12% expansion chamber, and changes little in the range exceeding 12% by volume.

In other words, in order to obtain good quality dimensional stability over time, the expansion capacity must exceed at least 12% by volume. Table 2 Example 2 Using polyethylene resins B, C, and D in Table 1 as the base resin, dicumyl peroxide was added as a crosslinking agent, and the gel was crosslinked by heating together with other cell diameter adjusting agents and dispersants. crosslinking ratio 58-62%, average particle size 1.2 side. Retiren particles were prepared.

The particles were impregnated with a foaming agent and then heated and foamed to obtain primary foamed particles. Secondary foamed particles are obtained by impregnating the primary foamed particles with air and then heating and foaming them.Furthermore, the secondary foamed particles are impregnated with air and heated and foamed to give an apparent bulk volume of approximately 47 mm/mm. Tertiary expanded particles were prepared. For the foaming method, the optimum value among the following conditions was used.

Foaming agent dichlorodifluoromethane Foaming agent impregnation temperature 80-90qo Foaming agent immersion time 1-1. Insect time Primary foaming water vapor pressure 0.3-0.9k9/(gauge pressure) Primary foaming heating time 10-3 Current air impregnation pressure 10kg/(gauge pressure) Air impregnation temperature 80-90q0 Air impregnation time 4-6 Time: Secondary and tertiary foaming Steam pressure: 0.4 to 0.9 k9/ground (gauge pressure) Secondary and tertiary foaming: Heating time: 5 to 19 steps The obtained expanded particles were left under atmospheric pressure for one week until the internal pressure of the particles was OK.
After confirming that the pressure is 9/2 (gauge pressure), the particles are placed in a pressure-resistant container and kept at room temperature 0.0 or 0.0, depending on the type of base resin used.
It was treated with air at 3 to 0.7 k9/kg (gauge pressure) for about 5 seconds to compress it to 90% of the original cage volume (compression ratio 10%), and as it was, the molded product shown in Figure 3 1 and Row was obtained. The molded product is placed in a mold having the shape to be obtained, heated with steam at 1.0 to 1.7 kg/(gauge pressure), cooled, and taken out.
Furthermore, it was left in a drying room at 75° C. for 5 hours.

The volume reduction rate of the supply moat pipe cover, the volume reduction rate of the tile base material, and the sustainability of the insulation performance were measured and evaluated for the obtained molded bodies using the evaluation methods described above.

The results are shown in Table 3.

As is clear from the results shown in Figure 3, the molded product of the present invention exhibits very little shrinkage deformation and deterioration in heat insulation performance over time compared to molded products produced by the conventional method, and is therefore extremely excellent as a heat insulating material. Ru.

Comparative Example 18 parts by weight of water containing 0.25 parts by weight of potassium phosphate prepared from an aqueous sodium phosphate solution and an aqueous potassium chloride solution were placed in a pressure-resistant container, and while stirring, 20 parts by weight of water containing 0.1 part by weight of Neoverex was added. Add 0.3 parts by weight of dicumyl peroxide to the mixture, and while stirring,
After adding the finely dispersed material, 10% of polyethylene with a particle size of 1.2 (trade name Mirason-9 manufactured by Mitsui Polychemicals) was added.
Add the low weight part, replace the inside of the container with nitrogen, and add 2 at 100qo.
When the contents were taken out after treatment at 135 oo for 7 hours, crosslinked polyethylene particles with a gel fraction of about 50% were obtained.

[A] The crosslinked particles are placed in a pressure container and impregnated with 12% dichlorodifluoromethane to form heat-foamed particles.The expanded particles are held under dichlorodifluoromethane gas at 18k9/cm (gauge pressure), and then removed. The mixture was pressed to obtain foamed particles having a volume of approximately 4 mm. The foamed particles were housed in a pressure-resistant container and pressurized with air at 1.2k9/gage pressure to compress the foamed particle volume to 72% of the original bulk volume, and then molded as shown in Figures 1 and 0'. The body was placed in a mold shaped to obtain the body. At this time, the filling amount was determined so that the volume of the foamed particles in the mold would be 80% of the original bulk volume. The foamed particles housed in the mold were heated with steam at 2.5k9/ground (gauge pressure) and then cooled to obtain a molded body. [
B] The above-mentioned crosslinked particles were placed in a pressure-resistant container and subjected to pressure impregnation treatment with dichlorodifluoromethane at 6 pi○ for 2 hours.
3.5% by weight impregnated beads were obtained.

Next, this material was heated with water vapor at a pressure of 1.2 k9/m (gauge pressure) to obtain foamed particles having an apparent volume of about 18 m/m. The particles were placed in a pressure container and kept in air at 75° C. (gauge pressure) for 20 minutes, and then removed to atmospheric pressure to form foamed particles with an apparent volume of about 27 g/m.
The average internal pressure within this particle is 0. The hammer was k9/ground (gauge pressure). The foamed particles were immediately placed in a mold having a shape to obtain the molded product shown in Fig. 3 and 1, and heated with sand for two nights with steam at 1.9 kQ/ (gauge pressure). After cooling, a molded body was obtained. The molded bodies obtained in this example were evaluated by measuring and evaluating the volume reduction rate of the pipe cover for the moat, the volume reduction rate of the tile base material, and the sustainability of the insulation performance using the evaluation method described above.

The results are shown in Table 3.

Table 3

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the expansion capacity of a molded body and the shrinkage rate of the molded body over heat, and Figure 2 is a graph used to measure the volume reduction rate of a pipe cover. FIG. 3 is a perspective view showing the shape of a molded body manufactured for a practical aging test. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 Consists of a fused aggregate of foamed particles containing a large number of cell structures formed of cross-linked polyethylene with a melting temperature of 107 to 124 °C, and when heated with steam at 110 °C for 5 seconds, 12
A crosslinked polyethylene foamed particle molded article characterized by having the ability to expand by more than % by volume.