JPS5861128A - Foamed molded propylene resin article and its preparation - Google Patents

Abstract

PURPOSE:To obtain the titled molded article having improved dynamic buffering characteristics, permanent compression set resistance, etc., by foaming a specific propylene resin under specific conditions, foaming the resultant uncrosslinked foamed particles in a mold, and fusing and integrating the surfaces of the particles together. CONSTITUTION:(B) A volatile organic foaming agent having -50-+110 deg.C boiling point in the surface parts of foamable resin particles containing (A) propylene-ethylene random copolymer, consisting of 90wt% or more propylene component and 10wt% or less ethylenic component, and having <=0.7 randomness factor (R), <40% stereoregularity (II) and 50-35 deg.C Vicat softening point under 5kg/cm<2> load and (B) the volatile organic foaming agent is preferentially volatilized, and the whole particles are then foamed to give foamed particles having a thick-wall skin. The foaming ability is then given to the foamed particles, which are in an uncrosslinked state foamed under heating in a mold to fuse and integrate the surfaces of the particles together so that the thickness of the fused film may be 8 times or more that of the cellular wall of the particles in the molded article. Thus, the aimed molded article is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a propylene resin foam molded article that is foam-molded in a substantially non-crosslinked state and a method for producing the same. A foamed molded article made of improved propylene-based resin foam particles and a method for producing the same, which has a cushioning property that is durable over 5 cycles while making full use of its oil resistance, etc. Regarding.

BACKGROUND ART With the development of in-mold molding methods for polyethylene foam particles, expanded propylene resin particles and methods for producing molded articles made from the particles have been introduced in many documents. For example, Japanese Patent Publication No. 51-22951, Japanese Patent Publication No. 53
33996 and JP-A-56-467.35, in short, a) a step of crosslinking a resin and incorporating a volatile foaming agent therein to form expandable resin particles.

Mouth) A step of expanding the shell foamable resin particles to form one foamed particle.

c) A step of imparting foaming ability to the foamed particles in the mold (increasing the internal pressure of the particles, compressing one particle and reducing its volume), 2) Using the foaming ability to produce the foaming ability in the mold. A process in which foam particles are foamed and heat-fused to each other to form a foam molded product.

A method for in-mold molding of foamed particles of crosslinked polyolefin (actually crosslinked polyethylene) is described, which comprises a combination of the above steps (a) to (e), e) removing the foamed molded product while cooling it. The book also introduces the idea that, if applied directly, propylene-based resins, which are a subordinate concept of polyolefins, can be made into excellent foam molded products.

On the other hand, 1, for example, Japanese Patent Publication No. 49-2183, Japanese Patent Publication No. 56
JP-A-1344 discloses a method for producing expanded propylene resin particles in which the steps up to (a) 90) are foamed in a non-crosslinked state. Therefore, if you combine the above two,
According to the literature, the in-mold molding method Fi using non-crosslinked propylene resin foam particles is extremely easy to complete.

However, in reality, it is not so simple, and it is not possible to produce a foam molded product that can be put to practical use.

One of the proofs is that there are reports of the completion of virtually non-crosslinked propylene resin foam moldings in newspapers and other publications; When transferring the shape to the production process, problems such as communication of air bubbles, unresponsiveness of air bubbles, sinkage, and poor adhesion occurred frequently, resulting in failure to maintain the properties as designed in the catalog, especially the characteristics of propylene resin. Because it is not possible to stably supply a molded body that fills the pillars with the foam, it is still not possible to list it as a commercially available foam.

The reason for this is that propylene resin has a higher degree of crystallinity and a higher melting point than, for example, polyethylene, and its fluid viscoelastic properties when melted have a greater temperature dependence. The foaming ability should be sufficiently maintained up to the temperature.

Foaming is carried out by controlling the temperature within a very narrow foaming temperature range.
The heat of crystallization generated when the molten resin solidifies must be carefully balanced, and in history, the particles filled in the mold are heated directly with steam or the like to foam, and then When trying to achieve a molded product using an in-mold molding method that uses external cooling with water or the like to form a molded product, for example, if the water vapor source is increased because the internal temperature is insufficient, the melting of particles on the surface will be reduced. This is because the deposition progresses first, obstructing the circulation of water vapor, and the troublesome phenomenon that the internal temperature becomes insufficient is added, making it even more difficult to maintain this balance.

On the other hand, as means for modifying the above propylene resin, methods of crosslinking and methods of copolymerizing and mixing other monomers and other polymers have been known for a long time. The content of the above-mentioned monomers and polymers is sufficient to sufficiently modify the melt-foaming applicability of the resin, but this results in the disadvantage that the resulting foam loses its properties as a propylene resin. On the other hand, reducing the wrinkle content has the disadvantage that it does not lead to improvement in the applicability of melt foaming, and a middle ground cannot be found.

Therefore, at present, we are relying on a modification method that involves crosslinking, even though we are aware that it is uneconomical. In the technique of 46-38716, a specific propylene-ethylene copolymer is used in combination with a bridge, and further,
When making this into a foam, efforts have been made to use chemical blowing agents with low volatility (see examples).

The present invention has been made in view of the current situation, and its first purpose is to provide a substantially non-crosslinked propylene resin foam molded product with improved thermal stability (thermal dimensional stability), oil resistance, rigidity, etc. The purpose is to provide a foam molded product that has the characteristics of a propylene resin and also has high-level cushioning properties and repeated durability.The second purpose is to make the above-mentioned foam even more durable. An object of the present invention is to provide a foam molding method using foamed propylene resin particles that can be economically stably supplied.

The first object of the present invention is to provide a foam molded article constituted by a large number of propylene-based resin foam particles having a fine cell structure, the surfaces of which are in contact with each other and fused and aggregated. System resin Fi, propylene with a propylene component of 90% by weight or more and an ethylene component of 10% by weight or less
An ethylene random copolymer having a random coefficient (R
) is 0.7 or less, the stereoregularity of the propylene segment (
II) is less than 40 ratio.

The copolymer has a Vicat softening point of about 50 to 35°C under a load of 51 cf.

(a) The resin foam is substantially non-crosslinked.

c) The fused film produced by the above-mentioned fusion aggregation is about 8 times or more thicker than the cell film inside the core particle.

The second object of the present invention is to form a propylene-ethylene random product having a propylene component of 90% by weight or more and an ethylene component of 10% by weight or less. A copolymer with a random coefficient (R) of 0.7 or less and a stereoregularity (II) of propylene segments of 4 (less than 1%,
5 Kg/cs” load Vicat softening point is approximately 50-35
℃, is impregnated with a volatile organic blowing agent having a boiling point of 150 to 110℃ to form foamable resin particles 1
Next, after the foaming agent present on the surface of the foamable resin particles is preferentially volatilized, the entire particle is foamed to form foamed particles having a thick skin, and then the foamed resin particles are foamed. The particles are heated and foamed in a non-crosslinked state in a mold to fuse the surfaces of the particles to form an integrated molded body. The fused film formed in the method is characterized in that the size of the fused film formed in the method is about 8 times or more. Both of these can be easily achieved by employing a method for producing a molded body made of expanded propylene resin particles.

Hereinafter, the content of the present invention will be explained first using the drawings etc.
The invention will be explained in detail starting from the invention (manufacturing method). However, this explanation is merely a convenient means for deepening the understanding of the content of the present invention.

According to this explanation, the first invention (molded object) is not subject to the restrictions of the second invention.

If so, the explanation as to why the present invention enables in-mold foaming of non-crosslinked propylene-based resin and why the molded product has characteristics that have not been recognized in the past is as follows. It would be better to explain in order the structure of the foamed particles brought about by the production method of the present invention, the role played by the particles of that structure in the method, and the structure and function that it has when it becomes a foamed molded product. This is because I understood these relationships and thought that this would lead to a true understanding of the technical idea of the present invention. On the other hand, once the technical idea of the present invention is deeply understood, it will be easier to accomplish the present invention in other ways.

FIG. 1 is a representative photomicrograph of the foamed particles used in the present invention, and FIG. 2 is a representative photomicrograph of the foamed particles used for comparison (conventional).

In addition, the comparison in Figure 192 shows that the requirement of "foaming the entire particle after preferentially volatilizing the foaming agent present on the surface of the foamable resin particles" corresponds to the second invention part. While using the same resin as shown in Figure 1, the above requirements, especially "
It also means a comparison with FIG. 2, which is a conventional process for manufacturing expanded particles that does not involve the step of "preferentially volatilizing the blowing agent present on the surface of the particles."

This difference can be seen in Figure 1 compared to Figure 2.
It is important to look objectively at the fact that the one in Figure 1 has an independent cell structure with finer cells and has a thicker skin part 1 than the average cell membrane 2 inside. I can do it.

That is, it is thought that the thick skin part in FIG. 1 is formed by slight foaming failure in the skin part caused by the volatile organic foaming agent that is preferentially volatilized. This thick skin portion first imparts expansion ability (this is called self-expansion ability) to the foamed particles themselves. Self-expansion ability can be confirmed by leaving the foamed particles in the air for several days to fully volatilize the foaming agent inside them, then heating them with steam at 143°C for 5 seconds, and heating them at room temperature at 90°C. After 15 hours below, add 2 more
This can be discussed by evaluating the value obtained by dividing the volume of the particles left at 5° C. for 24 hours by the volume of the foamed particles.

For example, the foamed particles shown in FIG. 1 exhibit a self-expansion capacity of 1.3 to 1.6 times, while those shown in FIG. 2 exhibit a value of less than 1.1 times at most. '-Next, in the second invention, in order to make the expanded particles more complete in foaming in the mold, the nests are "imbued with foaming ability." This foaming ability is added to the above-mentioned self-expanding ability, and specifically Fi, the internal pressure of the foamed particles is 0.
．． 5-3? /is” (gauge pressure), fill with inorganic gas such as air (foaming agent gas), or fill one foamed particle with a volume of 95 to 50% of the bulk volume of the circle. This can be achieved by performing one or a combination of operations such as compressing to a volume.However, in the present invention,
There is no need to choose a high value granting condition, at most 0.5 to 2
14/m'' (gauge pressure), a range of 95 to 70X is sufficient.

At this time, the thick skin part, in cooperation with the fine cells held inside, has the function of maintaining the applied internal pressure for a long time, or the function of increasing the repulsion force per unit compression generated in the compression. Doru. Also, this effect is caused by factors such as temporal fluctuations that occur during the process of heating and expanding one foamed particle in the mold, or temperature fluctuations caused by the difficulty of uniform heating in the mold, etc. To prevent the foaming ability from becoming locally insufficient, and to facilitate the management of expandable foam particles and the setting of molding conditions.

Regarding foaming in the mold as mentioned above.

In the method of the present invention using foamed particles modified in accordance with No. 81, even if the particles are heated and foamed in an uncrosslinked state in an L-shape, the surfaces of the particles are fused together and integrated. The result is a complete and unrivaled internal fusion that has never been achieved by anyone before.

A molded article with a beautiful surface is completed without crosslinking.

The light latitude of E is due to the fact that the thick skin of the foamed particles described above is synergistic with the thermal properties of the specific resin of the present invention, which will be described later.
For example, conventional resins could not be used because the particles on the inner surface of the mold would melt and flow first. This allows for a relative range of molding conditions such as the availability of (i.e. high pressure) fill water vapor, which also passes through the interparticle spacing.

In addition to increasing the temperature raising ability of the steam that heats even the foamed particles located inside the mold, it is possible to uniformly heat the inside of the mold in an extremely short period of time.

In addition, the foamed particles heated in the mold retain the foaming ability imparted to them as described above in a state where they are easy to exhibit, and furthermore, they also have self-expansion ability, which is a stage unprecedented in the past. It is presumed that foaming occurs with a certain behavior, filling the nooks and crannies between particles with sufficient foaming force, and completing dense interparticle fusion.

Figure 3 shows the foamed particles of the present invention (Figure 1) K.

FIG. 4 is a microscopic photograph illustrating a cross section of a molded product obtained by molding the expanded particles of comparison (FIG. 2).

In comparing Fig. 324, the one in Fig. 3 (invention) is 1
The common constituent features of the present invention are that [the fused W4 produced by the fused aggregation becomes #, the film thickness of the cell inside the particle [about 8 times or more of 1-1 compared to 3], and is formed. You can directly see how the body meets the requirements.

This fused film 4 is, needless to say, formed by the thick skin portion l of the foamed particles referred to in this application being deformed and fused by expansion.

However, as mentioned above, the thick skin of the foamed particles is effective because the method of the present invention adopts the operation of "preferentially volatilizing the foaming agent present on the surface of the foamable resin particles." However, not all propylene resins can be used for in-mold foam molding. According to the findings of the present inventors, the majority of these are those that cause 1 foaming spots 5 insufficient foaming phenomena, those that are difficult to form foamed particles with a thick skin, and those that are difficult to form in the mold in a non-crosslinked state. Care must be taken when selecting resins, as there are causes of defects that can be classified as those that cannot be subjected to foam molding, or those that cannot exhibit the expected characteristics even if they become -74+ foam molded products. be.

The propylene resin used in the present invention was finally extracted through repeated modifications and careful selection of propylene resins. The outline of the process is that, for example, it is difficult to form a 2-wall thick skin part with propylene homopolymer or a copolymer with other single caps, and when foaming it in a non-crosslinked state, foaming It has the disadvantage that spots occur and it is difficult to obtain a foam of the desired quality.

Furthermore, even when using the same propylene-ethylene copolymer, it is difficult to uniformly foam the block copolymer. On the other hand, according to books on random copolymerization, when the ethylene component is as large as 10% by weight, there is a marked tendency for ethylene to copolymerize in block form, and the softening temperature of the copolymer decreases, causing propylene to It is undesirable because the properties as a system polymer are lost, and conversely, if the amount is less than 1% of 21E, no modification effect can be obtained. In addition, even when using a propylene ethylene random copolymer whose ethylene component is within the range of the present invention, those with random & (R) exceeding 0.7 (that is, those close to block copolymers) Homogeneous foaming is difficult to achieve and the foaming ratio cannot be increased.

Even if the degree of randomness (R) is 0.7 or more), in the present invention, it is necessary to select one with low stereoregularity (II). That is, if the stereoregularity (0) is large, for example, a ratio of 40 or more, it is difficult to make it into a foam in a non-crosslinked state and utilize the characteristics of the resin in the foam. In addition, in the present invention, a material having a Vicat softening point under a 5q load of 50 to 35°C is selected. This necessity is to adjust the delicate balance of the flow deformation of the resin that occurs during heat foaming when foamed particles with a thick skin are molded in a mold.

If the temperature is lower than 35°C, the flow deformation of the resin on the inner surface of the mold will progress easily, while if the temperature exceeds 50°C, the flow deformation will be slow overall, and the resin will be easily deformed between the particles on the surface of the molded product. It tends to leave dark spots and cause poor adhesion.

In either case, it is necessary to narrow the applicable molding temperature range, and it is impossible to produce a molded product of high quality.

In this way, the carefully selected propylene-ethylene random copolymer Fi has a melting point of about 140 to 120°C, which facilitates the formation of a thick skin when forming foamed particles, and By foaming without crosslinking, it is possible to set the molding condition of a molded product with unprecedented homogeneous foaming and a smooth surface with good fusion even on the inside.

However, in reality, the random coefficient (R) is 0.7. As the stereoregularity (II) increases to 40%, uniform foaming tends to become more difficult. Therefore, for products with a large stereoregularity (II) of 40%, mild crosslinking, which accounts for several percent of the total, such as surface crosslinking, is applied. This will result in a higher quality foam.

In order to stably supply a completely non-crosslinked product, it is desirable to use a resin with a random coefficient (R) of 0.
4. It is better to carefully select those with stereoregularity (II) of 15% or less.

In addition, if the skin of the foamed particles becomes too thick, the particles may crack during one foaming process, resulting in poor foaming, or may give abnormal hardness to the molded product. It is advantageous to form a fusion layer that is about 15 times as thick as the cell membrane inside the foamed particles when they are made into a body.

Next, the first invention (molded body) of the present invention will be explained.

The propylene ethylene random copolymer specified in the first invention has, in addition to the above-mentioned advantages in terms of the manufacturing method, when formed into a foam, it has, for example, oil resistance, heat resistance (dimensional stability over time), etc. This advantage is that the essential properties of propylene resin can be utilized as they are in the copolymer foam.

In addition to the economic efficiency of foams due to the simplification of the manufacturing process, the non-crosslinked material also makes it possible to reuse the foams as propylene resin, reducing pollution problems caused by disposal. There is a starting point that can contribute to countermeasures against resource problems.

Next, the advantages of the first invention include dynamic buffering properties, pressure dynamic permanent set resistance, and repeated compression set resistance.

The degree of particle fusion of the molded body is to be on par with the standard.

This advantage Fi, for example, when applying the molded article of the present invention to a buffer molded container that is used repeatedly as a returnable container,
It has the effect of being a robust container that can maintain sufficient buffering capacity and is less likely to be damaged.

This advantage is due to the fact that in addition to selecting the specific copolymer of the present invention, propylene-based resins were conventionally considered to be too rigid and easy to break into brittle foams. As shown in FIG. 3, it is foamed into a relatively homogeneous fine cell structure, and a thick fused film 3 is formed on top of it. ! It is presumed that they were able to arrive because they were stereoregularly arranged in large numbers inside the molded body and were tightly and tightly bonded.

By the way, Figure 5 A)90) is a diagram showing the Fi buffer characteristics, and A) shows the relationship between 1 large deceleration 1t (G) and static stress.
Figure 3) shows the relationship between the maximum strain and the commercially available foam.

Other characteristics of the molded product of the present invention shown in FIG. 5 are shown in Example 4, and it is well proven that it is a high quality foam.

Fi, volatile organic foaming, is a typical method of "foaming the entire particle after preferentially volatilizing the foaming agent present on the surface of the foamable resin particles" in the present invention (method). Expandable resin particles containing a predetermined amount of the agent are placed in a foaming pot, and a heating medium (for example, water vapor) is blown thereto to raise the temperature and foam the particles. At this time, normally, in order to increase the foaming efficiency, one tries to shorten the heating time to the foaming temperature, but in the single method, on the contrary, the heating time to the foaming temperature is shortened. It is practical to adopt a method in which the temperature is increased for a long time, during which time the foaming agent present on the surface of the particles is preferentially volatilized, and then the entire particle is foamed at the foaming temperature reached.

At this time, the foaming temperature and heating time should be set appropriately depending on the blowing agent used, but if the heating time is too long, the foaming agent inside the particles will also volatilize, resulting in Since the phenomenon of insufficient foaming may occur, it is necessary to conduct preliminary experiments in advance to find conditions suitable for the foaming pot and foaming agent.

In short, in this method Fi, the blowing agent on the surface of the expandable resin particles that is closer to the blowing agent-containing state is removed prior to the entire particle foaming under an OA degree that is somewhat lower than the foaming temperature or at a pressure that is somewhat lower than the equilibrium pressure. Since it is completed by volatilization under certain conditions, it can be manifested in a variety of ways, whether in gas or in the form of nine substances.

In describing the manufacturing method of the second invention, a method for manufacturing expandable particles, a method for foaming the expanded particles, a method for imparting foaming ability generated in a mold, a method for filling the mold and molding in the mold, and measurement of internal pressure. The basic contents of the methods, etc. are also described in the publications cited in the main text, and these are well known as the manufacturing process conditions for olefins and crosslinked olefins. Since it is only necessary to adopt a book suitable for the process, we have omitted its description.

The propylene resin used in the present invention uses a halogenated titanium compound represented by the general formula TiXn (where X represents chlorine, bromine or iodine, and n is 2 or 3) as a catalyst as the first component, and periodically Metals in group 1A of the Table of Contents or compounds of the organic class of metals of groups iA to mA of the periodic table are
Ingredients, depending on the case, organic compounds containing electron-donating N9P*Ot8, etc. or inorganic salts such as alkali metal halides, oxyacids of all alkali classes, etc. as 3rd #:%
By using two-component or three-component yarn, continuously supplying ethylene and propylene at a ratio of one foot to the other, and adjusting the ethylene content in the gas phase, it is possible to produce a lantum copolymer with a desired ethylene content. It is produced by cultivating one field at 40 to 90 degrees Celsius.

Catalysts to be used, summer mixture, 1% polymerization method, and post-treatment of the product, as long as a copolymer with appropriate randomness, intacticity, and softening temperature can be obtained for use in the present invention. There are no particular limitations on the method.

The random coefficient (R) referred to in the present invention is a tl calculated value based on the side legs of an infrared absorption spectrum, and is a tl value according to JIS K6758 Kl.
f of 250 to 300μ is obtained using the α-based test piece adjustment method.
Infrared spectrometer (e.g. Perkin Elmer model 521) on the #J resin film made by carefully pressing c.
was used to absorb the 7223-'' part corresponding to the ethylene component co-united blockwise, and to absorb the 733ct of ethylene.
The scanning speed was adjusted so that the absorption waveform corresponding to the n-' portion was accurately aligned with the edge 1 side, and the measurement was performed at a room temperature of 25° C., and the transmittance was determined using the baseline method.

? Absorbance at 22cIR-' IIC (Aytt)
The absorbance (Ayns) at and 733ay+' is calculated, and the ratio R% (R=A72t/Ayss) is used as a random coefficient.

■ The principle of the calculation formula is A = -Log - Therefore, ■0 Ru.

Stereoregularity (II) of the propylene segment in the present invention
) Fi, resin, or foam was molded into a sheet with a thickness of about 100 μm by heating at 7°C, and this sheet was cut into 3-square pieces to prepare samples. Molding conditions, post-processing conditions FiJIS
The test was carried out according to the test piece preparation method described in K6758.

Precisely weigh the sample using a Kumagawa extractor.

Extracted at the boiling point of n-hebutane for 8 hours and dried in a vacuum dryer for 2 m
The residue was dried under reduced pressure of Hg at 80° C. for 98 hours, and the residue was accurately weighed. The ratio of the weight of the extracted residue to the original weight was expressed as ~, and this was taken as the stereoregularity of the propylene segment (1).

The Vicat softening point referred to in the present invention is based on ASTM D 1525.
This is the value when #1 is added under the condition of load 11[5~.

The evaluation method and evaluation criteria for the characteristics evaluated in the present invention will be described below.

The thickness of the skin part of the foamed particles and the bubble film inside the particles is determined by 0.25Rν0 from the center of the cut surface of each of the 20 sample cut pieces cut at the center cross section of 20 roughly spherical foamed particle samples. , 7S R and 0.9R (R is the average radius of the cut surface), and the length of the cut bubble film was 0.34D (D The film thickness at the center of the cut surface of each cell membrane was measured by randomly selecting 2*18r 26 points from the inner part of each particle and 32 points from the skin part. .

For the cell membrane within the foamed particles, the thickness was determined by Mitsuki's average value, and for the skin portion, the arithmetic average value was determined as the thickness.

In addition, the average film thickness of one skin part/average bubble film thickness was determined by calculating the ratio of one skin film thickness.

Foamed particle fusion film thickness ratio of molded product For 20 particles cut at the center cross section of #t foamed particles within the cut surface of the molded product, the maximum inscribed circle of each particle cross section (the radius of the circle Take microscopic photographs of the inside of the container and the particle-fused film using the same method as above, find the average thickness of the bubble film and the average thickness of the particle-fused film, and calculate the ratio.

Uniformity of Cells Approximately 20 foamed particle samples were visually observed using sample fragments cut at their central cross-sections and magnified 50 times.

Various properties of molded products 1) Degree of fusion Cut a 100 x 100 square test piece from a part of the molded product with a thickness of 20 or more, make a 2 m cut in the center, and bend it along the cut. The article was cleaved and the percentage of the number of particles breaking and cutting the material relative to the total number of particles present in the cut cross section was determined.

Evaluation criteria 2) Density Measured according to JIS K6767.

3) Dynamic buffer properties Measured according to JIS Z0234. The measurement conditions were a buffering material thickness of 50 cm and a drop height of 60 mouths, and the measured value of the first drop was L7.

4) Heating size cost: 200 ■ A molded sample cut into squares was heated to 25°C for 24 hours.
Draw a 100x100 square and a central cross in the center of the time frame, measure the length of each line segment, and measure the length to 100℃±1℃.
The sample was placed in a constant temperature bath for 96 hours, taken out, and left to cool at 25℃ for 1 hour. The dimensions of the marked lines were refined, and the percent change from the original dimensions was determined, and the average value was determined. .

Evaluation Criteria: Less than 4%: No practical problem 4% or more: Not usable 5) Compression set: Measured according to JI8 K6767. The test conditions are 25
% constant compression.

6) Repeated compression set Measured according to JI8 K6767. Test conditions are %2
It was subjected to constant compression of 5% and repeated 80,000 times.

7) Sink Place a straight ruler in the direction of the force on the upper surface of a plate-shaped test piece of a molded product measuring 300 m in length and width and 20 cm in thickness, and calculate the maximum pressure lI# in the gap created between the test piece and the ruler. It was evaluated as a percentage of the length of the diagonal.

Evaluation 8) Water absorption rate Cut 3 test pieces of 5oxsox thickness from the molded product b',
After accurately measuring its volume and weight.

After being immersed in a 25°C water tank for 24 hours, one surface was quickly wiped off to accurately measure Nii.

The change in weight before and after immersion is determined and calculated using a quintic equation.

Evaluation was made using the average value of the obtained measurement results.

Example 1 Propylene ethylene random copolymer C-r-tv component 6% by weight, random coefficient (R) 0.35. Stereoregularity of propylene segment (II) 7.5%, 5-X
- The Vicat softening point of the load is 48°C, the melting point is 135°C] is made into granules by extrusion and shredding, and in a pressure-resistant container, a volatile organic blowing agent (dichlorodifluoromethane, B, P, -29,
8° C.) was contained in a predetermined amount with respect to the amount of resin to obtain expandable resin particles.

When these particles are foamed in a foaming pot at a foaming temperature of 135°C, the foamable resin particles are prepared in advance at a pressure equal to or lower than the equilibrium pressure of the foaming agent at the foaming temperature as shown below.

Pressure atmosphere higher than the pressure at which foaming occurs (40-30Q/cs
n'' gauge) for several tens of seconds, and then the pressure was released to a low pressure region where foaming completely occurred to cause foaming.

When the cross section of the expanded particles (hereinafter referred to as particles A) obtained under the conditions of Experiment A1 was observed with a microscope (X450), a thick skin was formed on the surface, and the inside was relatively uniform. It was formed of a large number of small-diameter closed cells (as shown in FIG. 1).

Next, these foamed particles were heated at 90°C s 1 (IK
When pressurized with an air pressure of 4/ex'', the internal pressure within one particle bubble is 2
Kf/m", fill it into a box-shaped mold with a cavity of 300 x 300 The molded product was heated to form a molded product, taken out from the mold, and then aged in a room at 90° C. for 8 hours.

Regarding the obtained molded body A11t12t13t14.

Various properties were evaluated using the evaluation method described in the text, and the results are summarized in Table 1. Further, a cross-sectional microscopic photograph of the molded body All is shown in FIG.

Comparative Example-1 In Example-1, using expandable resin particles containing 25% by weight of a volatile organic blowing agent, only the residence time below the equilibrium pressure of the blowing agent in the foaming pot was changed to 10 seconds and 5 seconds. (
Experiments A5 and 6) The evaluation results for molding rest 15y16 obtained by repeating the experiment of Example-1 except that the surface foaming agent was not volatilized preferentially were summarized in the first article. . The cross section at* (X450) of the expanded particles (hereinafter referred to as particles B) obtained in Experiment A5 is shown in the second figure.
In the figure, that of the same molded body A15 is shown in FIG.

From Table 1 in the margin below, molded products in which the foam particle fusion film thickness is 8 times or more than the bubble film thickness inside the particles have excellent interparticle fusion degree, and the optimum stress in terms of dynamic cushioning properties is on the high stress side. It is clear that the maximum deceleration at that time is small and the maximum strain is small.

In addition, dimensional changes due to heating are small and dimensional stability when exposed to high temperatures is excellent.

The reason for this is that, as shown in FIG. 3, in a molded body using particles A with a thick skin film, thick-film particle fusion parts are formed three-dimensionally in the shape of a mesh inside the molded body, resulting in mechanical deformation and This is thought to be because it exhibits a structural reinforcement effect against thermal deformation.

Furthermore, even when the expansion ratio is small, a molded product having a thick particle fusion portion exhibits excellent performance.

Example 2v Comparative Example 2 Expanded particles of Example IAI (particles A) and Comparative Example IJE5
For both expanded particles (particles B), the following 1) t2)
Two experiments were conducted.

1) After leaving this in a room under natural conditions for 3 days and 7 days, it was heated with steam at 143°C for 5 seconds, and then kept in a room at 90°C for 15 hours and taken out.
The expansion of the bulk volume of the foamed particles caused by the heat treatment after being left at ℃ for 24 hours is shown in terms of volume ratio.

2) Pressure inject (impregnate) air into each of the expanded particle groups of both the original AνB so that the internal pressure of each particle is approximately 1. , 5 Kg/CM
&'' (gauge pressure) K.Then, the particles are left indoors under natural conditions.

(b) After leaving it for about 3 days, take out some of the expanded particles of both A>B and use the particles for each.

The same procedure as in Example 1 was carried out to obtain a molded article.

(b) After discharging for about 7 days, the remaining foamed particles of both AvB are used to perform in-mold molding in the same manner as above to obtain a molded article.

These are: 1) s 2) t (a) 9 (b) Evaluate the results of the experiment.

The results are summarized in Tables 2 and 3.

Margin below Table 2 Table 3 From Table 2, it can be seen that the expanded particles of the present invention last for a long period of time.

It is clear that the expansion ratio is kept high and the expansion ability is excellent. As shown in Table 3, this unique performance of expanded particles is also evident when molded into molded products, resulting in excellent molded products with excellent fusion, few sink marks, and low water absorption. This is the cause of the excellent buffering performance as shown in Example 1.

Example 3? Comparative Example 3 Each of the 15 propylene-based resin particles shown in Table 4-1 was placed in a pressure-resistant container, and a volatile blowing agent (dichlorodifluoromethane) was pressurized into the container. The foaming resin particles are made into foamable resin particles containing 25% of the blowing agent based on the amount of the foaming agent.

When heating and foaming each of the obtained expandable resin particles to the respective foaming temperature in a foaming pot, the atmospheric pressure was set at 40 to 3
5K17cm" and then post-foamed the particles in an effort to obtain foamed particles with a thick skin. At this time, for particles for which a skin cannot be obtained or resin particles in a poor foamed state,
The atmospheric pressure and residence time were varied, and the particles that were found to be the best were selected as the particles to be tested.

Each of the obtained expanded particles was evaluated for 1 expansion ratio, 1 skin film ratio, and bubble uniformity using the method described in the text, and the results are shown in Table 4-2.

Table 4-1 Polymer used Table 4-2 shows that when the random coefficient (R) is larger than 0.7, the bubbles in the foamed particles become non-uniform, and the thickness of the skin layer becomes approximately equal to the bubble layer thickness. It is clear that foaming does not occur when the random coefficient increases and the block copolymer becomes a block copolymer. In addition, even if the random coefficient (R) is 0.7 or less, foaming will not occur if the stereoregularity (II) is 405A or more, and even if the random coefficient (R) is 0.7 or less and the stereoregularity (II) is less than 40%, foaming will not occur. It is clear that if the softening point is higher than 50°C or lower than 35°C, even if foaming occurs, the foaming efficiency will be low, the uniformity of the bubbles will be poor, and the surface film thickness will become thin.

Example 4 ν Comparative Example 4 Using the expanded particles shown in Table 4-2 and having the experimental symbol Mui t/・+f+wa, the internal pressure of each particle was 1.0 to /3″ (
Air was press-injected (impregnated) to give a pressure (gauge pressure), and the particles were immediately filled into a mold (the same mold as in Example-1) and heated and foamed in the mold to obtain a molded article. In this case, water vapor of ii2 Ky/cm'' was used for preheating for about 15 seconds and color heating for 15 seconds at 3.2 Kf/cm'', and then cooled and taken out.

The molded product taken out was aged in a room at 90° C. for 8 hours.

The properties of each of the obtained molded bodies 421922g23*24 were evaluated using the method described in the text, and the results are shown in Table 5.
I stopped it.

Further, the relationship between the maximum deceleration & (G) and the static stress for the molded body height 21 is shown in 5th rgU (a), and the relationship with the instantaneous maximum strain is shown in Figure 5 (b).

Margin below From Table 5, the foam of the present invention has dynamic relaxation properties.

It is clear that the foam has excellent compression properties and dimensional stability under heating.

If a polymer other than the ethylene propylene random copolymer specified in the present invention is used, the skin thickness of the expanded particles will become smaller, resulting in poor foam molding performance during in-mold molding and a decrease in fusion bond strength. , the density of the molded product obtained is also high,
Only foams with inferior properties such as compression set, repeated compression set, and heating dimensional change can be obtained.

Comparative Example 5 A commercially available highly foamed polyolefin foam was evaluated for mechanical properties by the method described in the text, and the results are shown in Table 5.

The foam used was It is.

Furthermore, the relationship between the maximum deceleration 1 (G) and the static stress is shown in FIG. 5 (a), and the relationship with the maximum strain at the same time is shown in FIG.

As is clear from Table 5, the foam Fi of the present invention has dynamic buffering properties with a larger optimal stress, smaller maximum deceleration, and smaller maximum strain than the commercially available highly expanded polyolefin foam of four-dimensional density. It has excellent performance as a packaging material. In particular, the small maximum strain means that the phenomenon of bottoming out is unlikely to occur when packaged items with convex portions are cushioned, and exhibits excellent performance with a small amount of cushioning material, resulting in great economic effects.

In addition, the small dimensional change due to heating indicates that the material is a highly reliable cushioning material, as it does not cause cargo to collapse due to temperature rises in the cargo hold during export, nor does it suffer from deterioration in cushioning performance due to sagging of the cushioning material. Furthermore, it has the advantage that it can be used in high-temperature atmospheres, which conventional foams cannot be used with.

From Figure 5, it is clear that the foam of the present invention has a lower maximum strain on the high stress side than the polyethylene foam with the same density, and that the foam of the present invention has a lower maximum strain on the high stress side than the polyethylene foam with the same density. It is clear that the instantaneous maximum strain is smaller than that of thread foam, and that it has excellent performance and is economical because the density of the foam can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional micrograph of foamed particles with a thick skin film according to the present invention, FIG. 2 #'i is a cross-sectional microphotograph of foamed particles with a thin skin film for comparison, and FIG. Figure 4 is a cross-sectional microscopic photograph showing the particle fused film of a molded article obtained from the expanded particles shown in Figure 2, and Figure 4 shows the particle fused membrane of a molded article obtained from the expanded particles shown in Figure 2 for comparison. Cross-sectional micrograph,
5th plJ Kt (b) is a molded article of the present invention (curve l) and a commercially available high-foam polyethylene foam (curve IN2).
FIG. 4 is a diagram showing the dynamic cushioning characteristics (a) impact characteristics, and (b) instantaneous maximum strain) of ~4).

Claims (1)

[Claims] 1. A foamed molded article constituted by a large number of foamed propylene resin particles having a fine cell structure, which are fused and aggregated with the surfaces of adjacent particles in contact with each other. b) The propylene resin has a propylene component of 90% by weight.
The above is a propylene-ethylene random copolymer having an ethylene component of 10 g% or less, and having a random coefficient (R)
is 0.7 or more1. Stereoregularity of propylene segments (I
I) is less than 40%, Vicat softening point at initial load of 5 is approximately 50
It should be a comonomer showing a value of ~35°C. (1) The resin foam is substantially non-crosslinked; (3) The fused film formed by the above-mentioned fusion aggregation has a thickness that is approximately 8 times or more thicker than the cell membrane inside the particles. A foam molded article 2 made of expanded polypropylene resin particles whose percentage image is a propylene-ethylene random copolymer with a propylene component of 90% by weight or more and an ethylene component of 10% by weight or less, which has a random coefficient ( R) is 0.7 or less, the stereoregularity (II) of the propylene segment is less than 40%, 5
A copolymer having a Vicat softening point of about 50 to 35°C under edge/cII load is mixed with a volatile organic blowing agent having a boiling point of 150 to 110°C to form expandable resin particles, and then After the foaming agent present on the surface of the foamable resin particles is preferentially volatilized, the entire particles are foamed to form foamed particles having a thick skin, and then foaming ability is imparted to the foamed particles. The particles are applied and heated and foamed in a non-crosslinked state in a mold to fuse the surfaces of the particles to each other to form an integrated molded body.
A method for producing a molded body made of expanded propylene resin particles, characterized in that the size of the fused film formed by the above fusion is about 8 times or more as compared to the cell group constituting the particles inside the molded body.