JPS6333782B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vinylidene chloride resin foam, and more specifically, it can be used as a heat insulating board, for example, as it is.
This invention relates to a novel vinylidene chloride resin foam having a wide cross section and free shape that can be used as a buffer molded container.

In recent years, research into technology for foaming synthetic resins has been active, and as a result, many synthetic resins can now be foamed.
Each type of resin has its own technical field.

Among them, vinylidene chloride resin has a wide cross-sectional shape and a high-quality foam that has not yet been developed. There is no actual foam molded product having a plate area.

The reasons for this are generally that for vinylidene chloride resins: 1. The processing temperature at which the resin is melt-processed is too close to the decomposition temperature at which decomposition proceeds, so thermal decomposition of the resin occurs during the extrusion processing process.

2. When resin comes into contact with metals such as iron and copper at temperatures near the resin's melting point, the decomposition of the resin is significantly accelerated.

3. The barrier properties of the resin are high, making it difficult to impregnate the resin with a foaming agent.

4. It is difficult to adjust the foaming conditions because the viscoelasticity of the resin is highly dependent on temperature near the foaming temperature.

It is considered extremely difficult to obtain a highly foamed, well-homogeneous foam without causing thermal decomposition, and the current state of the art is that sufficient technology has not been developed.

In fact, vinylidene chloride resin foams and their manufacturing methods that have been introduced in literature are disclosed in, for example, Japanese Patent Publication No. 39-3968, Japanese Patent Publication No. 16419-1982, and US Patent No. 2948048. The technology used involves selecting a special chemical foaming agent and extrusion foaming.The resulting foam has a low expansion ratio of about 2 to 3 times, and its cross section is similar to that of artificial rattan, artificial rattan core, or decoration. It is nothing more than a small cross-sectional shape such as thread. Furthermore, the purpose of foaming is limited to adjusting surface gloss and imparting flexibility.

Further, a technique for achieving high foaming using a physical foaming agent is disclosed in US Pat. No. 3,983,080.
In this description, finely ground vinylidene chloride resin is mixed with a physical blowing agent, and then the mixture is heated at a low temperature (approximately 120
When extruded and foamed at ~150℃), the density is approximately 240Kg/
It is said that a foam ^with a cell diameter of about 0.1 to 1 mm can be obtained.

However, according to additional tests conducted by the present inventors, this method can only produce a string-like extruded foam with an uneven surface and significantly irregular cell diameters for a short period of time.
In reality, it is difficult to stably control thermal decomposition, and the thermal decomposition of the resin progresses, making it impossible to continue extrusion foaming.

Furthermore, on the other hand, Japanese Patent Publication No. 42-26524 and Japanese Patent Application Laid-open No. 49-59168 disclose a device with a diameter of approximately
We propose unicellular spherical particles of ~50 μm.
In this description, the definition of thermoplastic resin copolymer includes a copolymer of vinylidene chloride and acrylonitrile or butyl acrylate,
Further, in some of the examples, there is a description that a foam-like material is formed when the particles are thermally expanded and fused. However, the above-mentioned foam and the foam of the present invention are different in terms of foaming principle, foam structure, performance, and therefore usage.Here, we will first touch on the technical differences and clarify the distinction between the two. I'll keep it.

First of all, the biggest technical difference is that the foam of the present invention is made by impregnating (dissolving) a foaming agent into the resin, as described below.
As a result of this, we can obtain an aggregate foam made up of multicellular units with high resilience and repulsion, and further, as a result of achieving the aggregate formation using in-mold molding technology, it has a high closed cell ratio and is mechanically resistant. They have succeeded in imparting the advantage of superior strength to the foam. On the other hand, the one described in the above publication has a structure in which a liquid foaming agent is contained within a small balloon made of resin (a so-called microballoon), so even if it were to be heated and expanded and fused, it would still be possible to obtain The molded foam is an aggregate of balloon-shaped single cell particles, and has a low closed cell ratio and poor mechanical properties.

Furthermore, microballoons are used exclusively by mixing with ink, paint, etc. to create three-dimensional patterns on wallpaper, etc., and their particle size is 1 to 50 μm as mentioned above.
Because it is extremely small, even if you try to mold it in a mold, you will not be able to fill it uniformly in the mold, and there will be problems such as steam not passing through to the inside of the molded product. They differ fundamentally in that they are particles that cannot be aggregated.

The present invention was made under such circumstances,
The first purpose is to produce foams that take advantage of the properties of vinylidene chloride resin (e.g., flame retardancy, oil/chemical resistance, gas barrier properties, mechanical strength, etc.) as they are, for example, as insulation boards. It is to provide a cross section and shape that can be used as a body,
The second purpose is to provide a product that has a wide degree of freedom in designing its shape and structure and is in line with target dimensions, and the third purpose is to satisfy the above first purpose. 1. The second objective is to provide a foam that has the characteristic of maintaining low thermal conductivity (excellent heat insulation properties) over a long period of time.

The vinylidene chloride foam that satisfies the above objectives is a completely new foam that has been long awaited but has never actually existed.

The above-mentioned object of the present invention is to achieve the gist of the present invention, that is, a large number of porous foamed particles made of substantially amorphous vinylidene chloride resin are brought into close contact with each other and fused together, resulting in foaming. This can be easily achieved by employing an in-mold foam molded product of vinylidene chloride resin, which is characterized by forming a polyurethane resin.

Hereinafter, in detailing the content of the present invention, we will first describe the main points of the manufacturing method since it is a new foam, and explain how we were able to accomplish what was previously impossible. Clarify the relationships that lead to the constituent requirements of the foam.

The key points in the manufacturing method that completed the foam of the present invention are: (a) The use of a substantially amorphous vinylidene chloride resin as the base resin; (b) The selection of a volatile organic blowing agent as the blowing agent, and the use of the resin. For example, the inclusion of the foam is based on the use of a contact impregnation method with a foaming agent that takes advantage of the large specific surface area of fine resin particles such as those obtained by suspension polymerization. It can be summarized as a combination of the above-mentioned (a), (b) and (c), which enables the adoption of a known molding method as an in-mold foam molding method using resin particles (typically expandable polystyrene particles).

For convenience of explanation, the reason will be explained in the order of categories a), b), and c).

First of all, the necessity of (a) is that the surface condition of the resin (including the internal structure) is such that the foaming agent impregnated in the resin can be extracted as a foaming ability that becomes multifoamed foam particles, and that This is to make the flow viscoelastic properties of the resin suitable for foaming. Figures 1A and 1B are shown to clearly illustrate the current situation. That is, FIGS. 1A and 1B are diagrams showing the surface state of vinylidene chloride resin particles corresponding to the base resin, where A is a substantially amorphous resin according to the present invention and B is a comparative crystalline resin. It is. Both are enlarged views taken using an electron microscope.

As is clear from the comparison between A and B in Figure 1, amorphous A has no gaps or cracks on its surface and is relatively smooth, whereas crystalline B has an accumulation of string-like materials. The block-like shapes come together to form an uneven surface as a whole, and voids and cracks appear to occur. It is assumed that the internal structure of the particle is probably the same in both states. The formation of this block is thought to be due to the crystalline nature of the resin.

If both A and B particles contain apparently the same amount of foaming agent and are heated and foamed, the A side will become highly foamed porous particles, whereas the B side will become highly foamed porous particles. This difference manifests itself in the fact that the change is only to the extent that it cannot be said that it has foamed.

The difference in the above phenomenon is probably that the inclusion of the blowing agent in the resin on the A side is due to the impregnation of the blowing agent in the form of the blowing agent dissolved in the resin, whereas on the B side, the blowing agent is introduced through the void cracks. On the A side, a large number of bubble nuclei are formed and they grow to make use of the expansion ability of the blowing agent, whereas on the B side, the expansion ability of the blowing agent is utilized. Because the foaming agent dissipates so much, it is difficult to utilize the foaming ability of the foaming agent, and in addition, on the B side, crystals generated during the cooling process of the molten resin impede the fluid expansion of the resin, causing air bubbles to form. It is presumed that this is a phenomenon that makes the formation and growth of the amorphous resin difficult, and this phenomenon is attracting attention as it indicates the role of the amorphous resin in the present invention.

Next, FIG. 2 is an experimental diagram showing the relationship between the particle size of the resin used in the present invention and the maximum expansion ratio. The meaning shown in FIG. 2 is that, in addition to the use of an amorphous resin as described in (a) above, it is also necessary to use the contact impregnation method as described in (b), that is, small particle size particles.

In other words, vinylidene chloride-based resins generally have a high barrier property against volatile blowing agents, especially freon-based organic blowing agents, and it is difficult to impregnate them with a blowing agent to obtain a homogeneous porous structure. It was thought that However, in the present invention, this is made possible by adopting a combination of the above selection of resin and a small particle size resin, and as shown in Figure 2, by selecting a particle size within an appropriate size range, highly This shows the fact that impregnation with a foaming agent can now be easily achieved under industrial conditions.

FIG. 3 is a diagram showing an example of the retention (sustainability) of the foaming agent (foaming ability) of the resin referred to in the present invention impregnated with the foaming agent. Figure 3 shows that if the blowing agent is impregnated into the resin in the present invention by simply utilizing the size of the specific surface area of the particles, the amount of blowing agent dissipated will be large in proportion to the specific surface area. This is a remarkable phenomenon that strongly refutes the assumption that the foaming ability cannot be sustained.

Further, FIG. 4 is an experimental diagram showing the cumulative expansion ratio at each stage when the foamable resin particles impregnated with the foaming agent referred to in the present invention are foamed and expanded in three stages. . The meaning shown in FIG. 4 is that the blowing agent impregnated into the resin as used in the present invention indicates that the unconsumed blowing agent during the initial heat foaming can remain in the pre-expanded particle resin, and This shows that the resin has viscoelastic properties that can withstand multiple stages of expansion and foaming. 3rd and 4th above
The retention of foaming ability shown in the figure is presumed to be a phenomenon based on the gas barrier properties of the resin.

In addition to the above phenomenon, FIG. 5 shows an even more surprising phenomenon. FIG. 5 is an experimental diagram illustrating the change over time in the re-expansion ability of the pre-expanded resin foam particles according to the present invention upon reheating when the particles are kept in the atmosphere. The phenomenon shown in Fig. 5 is thought to be a phenomenon in which the internal pressure of the blowing agent inside the bubbles, which was originally used for foaming, becomes higher than the original pressure due to the attraction of the atmosphere. This is a remarkable phenomenon that was first investigated by.

Next, the need for c) is to uniformly and efficiently heat vinylidene chloride resin, which is easily thermally decomposed, at a lower temperature and in a shorter time without having a wide residence time distribution, and to foam-form it. It is meant for the body.

The in-mold molding used here involves filling a mold with a wall with many small holes with foamable resin particles or pre-foamed particles, and heating the mold with a fluid such as steam through the small holes from outside the mold wall. As a result, foaming is caused to expand, the interparticle voids are filled and fused, and then this is rapidly cooled to form a molded product.

Furthermore, in this case, the use of amorphous resin according to (a) above shows a Vikato softening point 50 to 60°C lower than that of conventional crystalline resins. This makes it possible to fully perform the following heat foaming molding with water vapor, and the foaming temperature can be set to a temperature that is well below the decomposition temperature of the resin.

In addition, when fine-grained resin obtained by suspension polymerization is directly impregnated with a foaming agent to make a foamable resin, there is no need for heat melting or mechanical shearing that would otherwise be required in extrusion granulation, for example. In terms of making it a
This completely eliminates the deterioration and thermal decomposition of the resin that occurs, and also eliminates the need for the addition of plasticizers and heat stabilizers that are used to prevent this. This also leads to the utilization of the properties (e.g., fire resistance, flame retardance, etc.) as they are.

As described above, the foam of the present invention is a novel foam that has been completed for the first time by a manufacturing method that skillfully applies the characteristics summarized in (a), (b), and (c) above. Since it varies in various ways, it can be selected appropriately depending on the target foam.

Next, the foam of the present invention will be described.

FIG. 6 is an enlarged cross-sectional view of the foam of the present invention,
To make the structure easier to understand, a cross-section of the structure is shown using an electron microscope.

As shown in FIG. 6, the foam of the present invention is an aggregate of a large number of porous particles made of a substantially amorphous vinylidene chloride resin as a base resin.
The particles have a structure in which the outer surfaces of adjacent particles are closely contacted and fused together to form an integral foamed molded product. This structure accurately expresses the characteristics of the in-mold molding method that completed the foam of the present invention as detailed above.

Figures 7, 8, and 9 are representative examples of the beneficial attributes exhibited by the foams of the present invention; Figure 7 shows foam density and 5%
An example diagram showing the relationship with the compressive stress required when compressing. Figure 8 is an example diagram showing the sustainability of the heat insulation performance exhibited by the foam of the present invention. Figure 9 is a diagram showing the flame retardant performance exhibited by the base resin of the present invention. (Oxygen index) is an example diagram.

All of these demonstrate the characteristics of the manufacturing method of the foam of the present invention, which is devised to exhibit the characteristics of vinylidene chloride-based resin without thermal decomposition or alteration, and the foam of the present invention This makes it useful to industry.

That is, FIG. 7 shows the fact that the foam of the present invention can be provided as a foam with a wide range of densities, and shows the possibility of meeting the compressive strength requirements of various foams depending on the application. This excellent compressive strength per density property is also achieved because the foam of the present invention is an aggregate of porous particles.

Figure 8 shows an example of the benefits of using the foam of the present invention as a heat insulating board. This shows that the heat insulating board of the present invention can maintain excellent heat insulating properties over a long period of time. This insulation performance is
The absolute level can be changed depending on the density of the foam, the diameter of the bubbles that make up the foam, the type of gas retained within the foam, etc.
According to experiments conducted by the present inventors, it has been confirmed that a thermal conductivity of up to 0.018 [Kcal/mhr°C] at 24°C can be obtained.

FIG. 9 suggests the advantage that a flame-retardant foam can be provided without intentionally using a flame retardant or the like in producing the foam of the present invention. This is one advantage in that the properties of the base resin itself can be effectively utilized.

Furthermore, one of the advantages of the foam production method of the present invention is that the thickness, dimensions, cross-sectional area, and shape of the foam can be freely set. According to experiments conducted by the present inventors, Foams can be freely manufactured within the range that can be effectively created by molds, for example, foams with dimensions of approximately 3 mm or more and cross-sectional areas of 9 mm ^{or more} , and within the scope of the experiment, the wall thickness is 100 mm, the width is 900 mm, and the length is 900 mm. A block of 1800 mm was easily molded, demonstrating the possibility of creating products of any size and shape depending on the mold design.

The vinylidene chloride resin in the present invention is a general term for copolymer resins of vinylidene chloride and one or more comonomer components copolymerizable with vinylidene chloride.
The above copolymerizable comonomer components include, for example,
Vinyl chloride, vinyl bromide, vinyl acetate, acrylonitrile, methacrylonitrile, styrene, chlorostyrene, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl acrylate, acrylic acid, methacrylic acid, etc. This can be done and these are known. In addition, it is common knowledge that the term vinylidene chloride-based refers to products containing 50% by weight or more of vinylidene chloride, and the reason for this is that the characteristics of the main vinylidene chloride component are similar to the characteristics of the copolymer resin itself. It is said that this is because it is dominant. In this sense, the vinylidene chloride resin that can be used in the foam of the present invention also has a vinylidene chloride component of 50%.
When the multi-component content is on the above-mentioned side, the foam is in the region where it effectively exhibits special effects such as heat insulation performance and flame retardancy, and it is still a desirable resin. However, in the case of the foam of the present invention, the difference is whether or not the vinylidene chloride component is present, specifically, the vinylidene chloride component is 10% by weight (preferably 30% by weight).
The general term for vinylidene chloride resins in the present invention is based on the fact that even the presence of only a certain amount (weight% or more) significantly improves flame retardancy and heat insulation performance compared to resins that do not contain vinylidene chloride resins. It is defined to extend beyond common sense.

The vinylidene chloride resin referred to in the present invention is substantially amorphous. The term "amorphous" is the opposite of the usual crystalline state. For example, DSC (Differential Scanning) measures the crystal melting temperature of the resin.
It can be defined as a resin that does not exhibit a temperature peak value that indicates crystal melting or crystal formation when measured using a dynamic scanning calorimetry method.

However, when the amorphous resin referred to in the present invention contains a small amount of crystalline component for other purposes, such as controlling fusion between foamed particles, or contains additives, Unless it changes the technical idea of ``utilizing the characteristics of an amorphous resin to complete a foam'' of the present invention, it is included in the substantially amorphous resin of the present invention.

The above-mentioned amorphous vinylidene chloride resin can be produced by the known bulk polymerization method, emulsion polymerization method, or suspension polymerization method, but it is difficult to avoid thermal decomposition and to easily obtain a particle size suitable for foamed particles. From this point of view, as mentioned above, it is desirable to employ the suspension method. In addition, in order to obtain amorphous vinylidene chloride resin, increasing the component ratio of the comonomer causes a transition from crystalline to amorphous, but it is difficult to determine at what percentage of the comonomer component the transition occurs. Since the amount differs depending on the type of comonomer, the amount of the comonomer component is usually 5 to 10% by weight or more, and 30% by weight in high cases.
It may be at least % by weight.

Furthermore, if the goal of the foam to be obtained is to achieve a high foaming level while also having high rigidity and heat resistance, methyl methacrylate should be selected as a comonomer that can be copolymerized with vinylidene chloride, and its component amount It is desirable to use a resin copolymerized with 30 to 90% by weight.

Further, as a crosslinking component, for example, divinylbenzene or polyethylene glycol esterified at both ends with acrylic acid, or a crosslinked non-containing material obtained by including glycidyl methacrylate and methacrylic acid as part of the monomer. When crystalline vinylidene chloride resin particles are used, moldability in the mold is good, the resulting foam is rich in closed cells, and has improved compressive strength and thermal conductivity.

The size of the resin particles must be selected based on the relationship between the impregnation rate of the blowing agent, the sustainability of the foaming ability of the expandable resin particles, the internal dimensions and shape of the mold, and the heating efficiency in the mold. Particles with an average diameter of 0.01 mm or more and 5 mm or less can be used, but in order to balance the above relationship as a whole, it is recommended to select particles with an average diameter of 0.1 to 1.0 mm and as uniform in diameter as possible. desirable.

Furthermore, from the viewpoint of selecting a resin suitable for in-mold steam foaming from the obtained substantially amorphous resins, it is recommended to use the Vikato softening point of the resin as an index. This generally shows a value of about 120℃ or less, but among them
When selecting a temperature in the range of 60 to 100°C, it is preferable because the particles inside the molded body are tightly fused and a molded body with excellent surface smoothness can be obtained.

The blowing agent that can be used to create the foam of the present invention is a volatile organic blowing agent that has a boiling point lower than the softening temperature of the resin used, and specifically includes aliphatic blowing agents such as propane, butane, pentane, and hexane. Hydrocarbons, chlorinated hydrocarbons such as methyl chloride, methylene chloride, ethyl chloride, chlorofluorocarbons such as trichloromonofluoromethane, dichlorodifluoromethane, monochlorodifluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, Ethers such as dimethyl ether and methyl ethyl ether are mentioned, and selected from these.

It is desirable to select these blowing agents carefully based on the relationship between compatibility with the resin, vapor pressure at foaming temperature, blowing agent boiling point, etc. When the above target conditions are not satisfied with one type of blowing agent, It is desirable to mix two or more types of blowing agents to create a blowing agent suitable for foaming resin.

FIG. 10 is a typical example of mixing two or more types of foaming agents to create a foaming agent suitable for foaming.

Figure 10 shows an example when a certain amount of a mixed blowing agent of Freon 11 (trichloromonofluoromethane) and Freon 12 (dichlorodifluoromethane) is used as a blowing agent, and the horizontal axis shows the mixture of both blowing agents ( weight) ratio,
The vertical axis shows the maximum expansion ratio of the expandable resin particles when the foaming agent is used.

According to Figure 10, the blowing agent is (Freon 11/Freon
An example is shown in which a good foam cannot be obtained unless the weight ratio of 12) is in the range of (20/80) to (70/30). That is, when selecting a blowing agent, there is a possibility that the optimum composition may be overlooked unless sufficient care is taken. In this sense, it is thought that the selection of the blowing agent also played an important role in the completion of the foam of the present invention.

Furthermore, when a fluorocarbon-based mixed foaming agent as shown in Figure 10 is used, the foaming ability of the foamable resin particles is greatly retained due to the gas barrier properties of the resin, and furthermore, the foaming ability of the foamable resin particles is improved. One of its advantages is its body's excellent thermal insulation properties. This phenomenon is thought to be due to the heat insulating effect of the fluorocarbon gas itself held within the bubbles.

Methods for incorporating the blowing agent into the resin include a gas phase or liquid phase impregnation method in which resin particles are impregnated with the blowing agent in gaseous or liquid form under heating and pressure if necessary in an autoclave, and resin particles are impregnated in water. There is a suspension impregnation method in water, which involves suspending and impregnating a foaming agent. It is also possible to carry out the polymerization in the presence of a blowing agent to directly obtain expandable polymer particles.

The foaming agent used in the present invention can be generally used in an amount of 1 to 40 parts by weight per 100 parts by weight of the resin particles, and the amount used is adjusted depending on the target density of the foam. It is known that the lower the density, the smaller the cell diameter, and the higher the closed cell ratio, the better the insulation performance of the foam when the same blowing agent is used. When a suitable mixed blowing agent as shown in Figure 10 is used, it is possible to freely obtain a molded article with a high closed cell ratio and well-uniformed cell diameters in the range of about 0.005 mm to 1 mm.

The evaluation method used in this specification is as follows.

Γ Foam density: Based on JISK6767.

Γ Foaming ratio: Base resin density divided by foam density.

Γ Closed cell ratio: Based on ASTM D2856.

Γ Thermal conductivity: Based on ASTMC518.

Γ 5% compressive strength: Based on ASTM D1621, the amount of compressive strain is 5%.

Γ Combustion test: According to JISA9511, the test piece is held horizontally.

Γ Vikatsu Softening Point: Based on ASTMD1525.

Γ Oxygen index: Based on ASTMD2863.

Example 1 Copolymer resin particles obtained by a suspension polymerization method and having an average particle diameter of 0.25 mm and a weight composition ratio of vinylidene chloride and methyl methacrylate of 60/40 were subjected to an experiment.

This resin has a specific gravity of approximately 1.49 and does not show any peaks in DSC.The solution viscosity of a 1% THF solution at 30℃ is
It is an amorphous resin with a density of 1.4 centipoise. An electron micrograph of this resin particle is shown in Figure 1A.
It is observed that the surface is smooth.

First, the resin particles are placed in an autoclave, and after the autoclave is sealed, the inside of the autoclave is evacuated and degassed. Next, a liquid mixed blowing agent consisting of an equal weight of Freon 11 and Freon 12 is introduced to the extent that the sample particles are located below the liquid surface. After leaving it at 70°C for about 4 hours, it is cooled to 20°C and returned to normal pressure, after which the particles inside are taken out. Calculating from the weight measurements before and after impregnation with the blowing agent, the particles were impregnated with 22 parts (based on 100 parts of resin; the same applies hereinafter) of the blowing agent.

The foaming agent-impregnated particles were left open in a room and the retention of the foaming agent was evaluated by tracking the change in weight. The results are shown in FIG. For comparison, the results of expandable polystyrene beads with a diameter of 1 mm impregnated with 11 parts of butane gas under the same storage conditions are also shown.
As is clear from the figure, it can be seen that the vinylidene chloride resin particles exhibit extremely excellent blowing agent retention (absolute value and retention rate).

Immediately after impregnation with the blowing agent, the particles were loosened from slight adhesion between particles, and then placed in a steam foaming machine and heated and foamed. At this time, using steam at 0 kg/cm ² (gauge pressure; the same applies hereinafter), foaming expansion was performed in three successive stages, with primary foaming in the first stage for 20 seconds, secondary foaming in the second stage for 20 seconds, and Figure 4 shows the cumulative expansion ratio of the particles when tertiary foaming was performed for 20 seconds. As is clear from the figure, it can be seen that even the pre-expanded particles that have been foamed once maintain their strong foaming ability.

Next, after impregnating the blowing agent particles with the blowing agent, the particles were left open in a room for two weeks, and then heated with 0 kg/cm ² steam.
The particles were heated and foamed for 34 seconds to produce pre-expanded particles with an expansion ratio of 30 times, and then left in a room and heated and re-foamed with the same steam for 30 seconds over time to track the secondary expansion ability. FIG. 5 shows the results of the secondary expansion ratio obtained by dividing the secondary expansion ratio by the pre-expansion ratio. For comparison, the results for the aforementioned expandable polystyrene beads are also shown in the same figure. As is clear from the figure, it is clear that the pre-expanded particles according to the present invention have a higher secondary expansion ability than polystyrene foam particles, which are said to have excellent secondary expansion ability. Ru.

Next, these pre-expanded particles with an expansion ratio of 30 times were aged indoors for one day and then molded using an in-mold steam molding machine for expandable polystyrene to form a foamed flat plate molded product with a thickness of 25 mm, 300 mm square, and a density of 30 kg/m ^3. I got it.

This molded body has a smooth surface and faithfully reproduces the mold, and is attached to the mold surface with a width of 3 mm, depth of 3 mm, and length of 10 mm.
The rectangular depression was also beautifully reproduced.

FIG. 6 shows an enlarged view of the cracked cross section when this foamed molded product is broken by hand. From the same figure, it is observed that a large number of porous foamed particles are in close contact with each other and fused together, forming a cross section of the foam.

Next, of the three stages of foamed particles shown in Figure 4, the first
The foamed particles of the stage and third stage were molded in the same way, and the densities were 50Kg/m ³ (29 times) and 18Kg/m ³ respectively.
A foamed flat plate molded body having the above-mentioned dimensions (80 times) was obtained. The results of measuring these 5% compressive strengths are
As shown in the figure. From the figure, it can be seen that by appropriately adjusting the density of the foam, for example, by a method such as the present method, a foamed molded product having a desired compressive strength can be obtained.

Figure 8 shows the results of tracing the change in thermal conductivity of the flat plate with a density of 50 kg/m ³ over time. For comparison, we also show that of an extruded polystyrene foam board, which is said to have excellent thermal conductivity. As is clear from the figure, the foam of the present invention exhibits a much lower thermal conductivity than that of polystyrene, and it maintains its low thermal conductivity because it retains foaming gas well. I understand.

A combustion test was also conducted on these foams, and they all showed self-extinguishing properties.

Next, in this example, resin particles having average particle diameters of approximately 0.25 mm, 0.4 mm, and 0.9 mm were impregnated with a foaming agent under the same conditions as described above, and then 0 kg/cm ²
Figure 2 shows the results obtained by heating and foaming with steam, determining the maximum expansion ratio at this time, and plotting this against the particle diameter. As is clear from this figure, resin particles related to the foam of the present invention are highly foamed because smaller particle diameters are more quickly impregnated with the foaming agent and have better retention properties.

In addition, in this example, the composition ratio of the mixed blowing agent Freon 11/Freon 12 impregnated into the particles was 25/75, 40/
60, 50/50, 60/40, and 70/30, and in the same manner as before, particles with an average particle size of 0.25 mm were impregnated with a foaming agent, and then heated and foamed with 0 kg/cm ² of steam. The relationship between the maximum foaming ratio and the foaming agent composition is shown in FIG. 10. From this figure, it can be seen that if the selection of the blowing agent composition for obtaining the foam of the present invention is not done carefully, a suitable composition may be overlooked.

Comparative example: Vinylidene chloride 80% by weight, vinyl chloride 20% by weight
Vinylidene chloride resin with an average particle diameter of 0.15 mm was used in the experiment. This resin exhibited crystallinity with a peak at 160°C when melted by DSC. In addition, the Vikatsu softening point was 131°C. Furthermore, an enlarged photograph of the resin particles taken by an electron microscope is shown in FIG. 1B. It can be seen that the particle surface and interior are porous.

This particle was treated in exactly the same manner as in Example-1,
A mixed blowing agent of Freon 11/Freon 12 was impregnated with various composition ratios. Weight measurements before and after impregnation indicated that the particles were impregnated with up to about 8 parts blowing agent.

The blowing agent-containing particles are heated at a steam pressure of 0 to 1.5.
I tried foaming variously by changing the amount up to Kg/cm ² , but it did not foam at all. Furthermore, use silicone oil and raise the temperature to 120℃.
When the resin particles were placed in heated silicone oil at temperatures ranging from 170°C to 170°C, only bubbles were generated and the resin particles did not foam at all.

Example 2 Copolymer particles having an average particle diameter of approximately 0.25 mm consisting of 30% by weight of vinylidene chloride and 70% by weight of methyl methacrylate were prepared in the same manner as in Example-1, and a mixed foaming agent of 1/1 of Freon 11/Freon 12 was prepared. I tried foaming.

The base resin was amorphous, showing no peaks in DSC, and had a Vikato softening point of 89°C. The amount of impregnated foaming agent is 27 parts, and after leaving it indoors for 2 weeks, it becomes 0 kg/
46 times pre-expanded particles were obtained by heating with ^cm2 steam for 60 seconds. After aging this for one day, a flat plate foam molded product with an expansion ratio of 73 times was obtained by in-mold steam foam molding in the same manner as in Example-1. The cross section of this molded body was formed by a large number of adjacent multicellular particles being closely contacted and fused together. The foam molded article had a smooth surface and could be used as it is, for example, as a heat insulating plate or a cushioning material.

Example 3 60% by weight vinylidene chloride, methyl acrylate
Freon was added to vinylidene chloride resin particles containing 40% by weight and having an average particle diameter of 0.15mm in the same manner as in Example-1.
It was impregnated with a foaming agent mixture of 11/12 Freon and 1/1.
The base resin particles were amorphous, showing no peaks in DSC, and had a Vicat softening point of 52°C.

The amount of impregnated foaming agent was 24 parts, and after leaving the foamable particles open in a room for two weeks, they were evenly filled horizontally into a mold with the flat part held horizontally so that the apparent volume was 10%. When heated, foamed, and molded using a mixture of steam and air at a temperature of 65℃, a large number of porous particles with a density of 96Kg/ ^m3 come into close contact with each other and fuse together. A flat foam molded body was obtained which formed a cross section.

Example 4 60 parts of vinylidene chloride, methyl methacrylate
Polyvinylidene chloride resin particles with an average particle diameter of 0.25 mm were used in the experiment, and were composed of 40 parts of glycidyl methacrylate and 0.3 parts of methacrylic acid to give it a crosslinked structure. In the same manner as in Example-1, the composition ratio of the mixed foaming agent consisting of Freon 11 and Freon 12 was varied to find the optimum composition ratio, and Freon 11/Freon 12 showed the highest foaming ratio of 7/3. The amount of blowing agent impregnated at this time was 23 parts. After impregnation, the particles were left open in a room for two weeks and then heated and foamed with 0.3Kg/ ^cm2 steam for 30 seconds, resulting in a density of 62Kg/ ^m3.
Pre-expanded particles were obtained. After aging in an open room for one day, the product was molded in a steam mold in the same manner as in Example 1 to obtain a molded foam with a density of 40 kg/m ³ and a smooth surface. When the 5% compressive strength of this product was measured, it was 2.8 kg/cm ² . From Figure 7, the 5% compressive strength without a crosslinking element with a density of 40Kg/ ^m3 is 1.7
Since it is estimated to be Kg/cm ² , it can be seen that the compressive strength is greatly improved by providing crosslinking.

As explained above in detail and clarified, the present invention has the above-mentioned configuration, so that a foam that takes advantage of the characteristics of vinylidene chloride resin (i.e., flame retardancy, gas barrier properties, mechanical strength, etc.) can be produced. It is provided as it is in a shape and size that can be used as a heat insulating plate, a buffer container, a floating material, etc. Depending on the design of the mold, this in-mold foam molded product
From those with complex surface shapes to flat plates of various dimensions,
It plays a major role in industry because it can be supplied as a molded product of any shape and size with good dimensional accuracy and a smooth surface, and has excellent mechanical properties such as repulsion and compressive strength. It is a foam. In particular, when using this as a heat insulating material, it has excellent heat insulating performance and long-lasting performance.
This is a breakthrough invention that provides industry with a new foam material that is particularly beneficial in terms of its flame retardant properties.

[Brief explanation of drawings]

FIG. 1A shows an electron micrograph of amorphous vinylidene chloride resin particles according to the present invention. Figure 1B
shows an electron micrograph of crystalline vinylidene chloride resin particles. FIG. 2 is a diagram showing the relationship between the particle diameter of the amorphous vinylidene chloride resin and the maximum expansion ratio according to the present invention. FIG. 3 is a diagram showing the foaming agent retention properties of expandable amorphous vinylidene chloride resin particles according to the present invention and expandable polystyrene particles for comparison. FIG. 4 is a diagram showing the cumulative expansion ratio when the expandable amorphous vinylidene chloride resin particles according to the present invention are expanded in three stages. FIG. 5 is a diagram showing changes over time in the secondary expansion coefficient of amorphous vinylidene chloride resin pre-expanded particles according to the present invention and polystyrene pre-expanded particles for comparison. FIG. 6 shows an electron micrograph of a fractured surface of the foam particle structure of the foam of the present invention. FIG. 7 is a diagram showing the relationship between foam density and 5% compressive strength of the foam of the present invention. FIG. 8 is a diagram showing changes over time in thermal conductivity of a polystyrene extruded foam board for comparison with the vinylidene chloride resin foam molded board of the present invention. FIG. 9 is a diagram showing the relationship between the vinylidene chloride content in the resin and the oxygen index in a copolymer resin of vinylidene chloride and methyl methacrylate. FIG. 10 is a diagram showing the foaming agent composition ratio and maximum expansion ratio of Freon 11 and Freon 12.

Claims (1)

[Claims] 1. A foam is formed by a large number of polyvesicular foamed particles made of substantially amorphous vinylidene chloride resin, which are fused together with adjacent particles in close contact with each other. Polyvinylidene chloride resin in-mold foam molding.