JPH0815746B2 - Method and apparatus for manufacturing olefin resin foam molded article - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an olefin-based resin foam-molded article, and more specifically, it compresses and fills olefin-based resin pre-expanded particles into a mold to produce an automobile bumper. The present invention relates to a method for producing an olefin-based resin foamed article, in which the weight of the foamed body is made constant and a foamed product with less variation is obtained when foaming an energy absorber such as a core material or a cushioning packaging material.

(Prior Art) In an in-mold foam molding method using pre-expanded particles of olefinic resin such as polypropylene or polyethylene, the pre-expanded particles are filled in a mold in a compressed state, and heat-sealed with steam or the like, A molding method for cooling to obtain a molded body as a mold has been widely known.

By the way, as a known conventional technique relating to such a molding method, there are methods described in Japanese Patent Publication No. 53-33996, US Pat. No. 3,504,168, and Japanese Patent Laid-Open No. 62-179929. In all of these methods, the pre-expanded particles are compressed by using compressed air or the like, and the pre-expanded particles are expanded in the heating of the next step by filling the mold in a compressed state. The purpose of the present invention is to obtain a good molded product which has a much smaller shrinkage than that when molded by heat fusion and filling in a non-compressed state.
However, in any of the methods, it is almost impossible to make the weight of the pre-expanded particles compressed and filled in the mold (the same meaning as making the expansion ratio of the molded product after foam molding constant). It is not explicitly stated, but it can only be estimated that the expansion ratio of the obtained molded article should be constant to some extent if the compression filling pressure of the pre-expanded particles is made constant.

However, when this is done industrially under normal conditions,
Even if only the set value of the compression filling pressure is made constant, the weight of the pre-expanded particles filled in the mold is not constant, and there is a drawback that the expansion ratio of the obtained foamed molded product greatly varies. In order to adjust the weight of the molded body, the information on the weight of the molded body immediately after molding and the weight after drying is obtained and the compression filling pressure control valve of the molding machine is manually operated according to the skill of the site worker. However, it is almost impossible to make such an adjustment for each molding shot, and therefore, there is a limit to the adjustment of the variation of the product weight, which has a great adverse effect on the yield and quality. In particular, in applications where foam plays a role of absorbing energy at the time of collision, such as automobile bumper core material, a large variation in foaming ratio causes a large difference in its function, which in turn results in Excessive safety design is required for safety.

(Problems to be Solved by the Invention) As described above, in the production method by the compression filling method of the foamed molded article made of the olefin resin pre-expanded particles, there is little variation in the expansion ratio when industrially produced, and more than the current situation. Even if the product expansion ratio specification width is narrowed, a foam molding method with a high product yield has not been found.

Therefore, in view of the above-mentioned problems of the prior art, the present inventors have earnestly conducted research on a compression filling molding method capable of solving the above problems, and as a result, the temperature and apparent density of the pre-expanded particles before the start of compression filling. It has been found that there is an important relationship between the pressure and the compression filling pressure, and the present invention capable of solving all the above problems has been completed.

That is, the inventors of the present invention have diligently studied the cause of the expansion ratio of the molded product to solve the above problems, and as a result, when the temperature of the pre-expanded particles changes, the mold may be compressed under the same pressure. It was found that the weights of the pre-expanded particles packed inside were significantly different.

In addition, it is difficult to expand each pre-expanded particle to exactly the same expansion ratio because of restrictions on the production of pre-expanded particles. Generally, it is a mixture, and such pre-expanded particles must be allowed to have a certain allowable range of apparent density at the stage of being used for foam molding.

Furthermore, since such pre-expanded particles are classified when they are discharged to a stock silo or transferred from the silo to a pressure filling container, when the pre-expanded particles on the verge of being compressed in a mold are sampled in a certain volume. , It turned out that the weight is not always constant.

The present invention has been discovered based on the above findings of the present inventors, whereby the weight of pre-expanded particles to be filled in a mold is made constant, and an olefin resin foam molded article with less weight variation is produced. The purpose is to do.

(Means for Solving the Problems) That is, according to the production method of the present invention which meets the above-mentioned object, first, the olefin resin pre-expanded particles are compression-filled in a mold and foam-molded to produce a foam-molded article. At this time, the temperature of the pre-compressed pre-expanded particles to be compressed is measured, and the compression filling pressure adapted to the temperature is determined. The second method is to make the temperature of the pre-expanded particles to be compressed constant. The third method of the present invention is a filling method of measuring the apparent density of the pre-compressed pre-expanded particles before starting the compression filling to determine the compression filling pressure adapted to the apparent density, and the fourth method of the present invention. Is a filling method in which the temperature and apparent density of the pre-compressed particles to be compressed are measured before the compression filling is started, and the compression filling pressure adapted to the temperature and the apparent specific gravity is determined. By adopting these methods, Filling into the mold respectively It is characterized in that the weight of the pre-expanded particles is made constant and the variation in the obtained foam weight is reduced.

In addition, the present invention comprises, as an apparatus configuration for carrying out the above method, a raw material silo, a sub hopper, a pressure filling container, and a mold device, and compresses pre-expanded particles from the raw material silo and the sub hopper via the pressure filling container. In a device for compression-filling in a mold and producing a foam-molded body by foam-molding, a temperature sensor is installed in the raw material silo or sub hopper,
On the other hand, a bypass system is provided between the sub hopper and the pressure filling container, an apparent density measuring device is arranged in the bypass system, and the mold is compressed into the pressure filling container and the mold communicating therewith. A pressure relief valve is attached to keep the filling pressure constant,
The temperature information by the temperature sensor and the weight information by the apparent density measuring device are input to the pressure relief valve, and the depressurization pressure value of the pressure relief valve is calculated based on this, and a computer and pressure control device for automatic setting are also combined. It is characterized by being provided.

Examples of the olefin resin used in the present invention include polypropylene, a random or block copolymer of propylene and polyethylene, a three-group copolymer of propylene, ethylene and butene, low density polyethylene, linear low density polyethylene, medium density polyethylene. , High density polyethylene, ethylene-vinyl acetate copolymer, copolymer of ethylene and acrylic acid or a metal salt of acrylic acid, polybutene-1, poly-4-methylpentene-1 and the like, but are not limited thereto. Not something.

These resins may be used alone or in combination of two or more. Further, a mixture of the resin and an inorganic or organic filler may be used.

Among the polyolefin resins, crosslinked or non-crosslinked propylene-ethylene copolymer and polyethylene resin are particularly preferable.

The method for producing the pre-expanded olefin resin particles used in the present invention is not particularly limited and may be obtained by any method.

For example, the volatile foaming agent, the olefin resin particles and the dispersant are dispersed and suspended together with water in a pressure tight container, and then the temperature is raised to a predetermined temperature and pressure, and then the olefin resin particles and water are reduced in low pressure. Pre-expanded particles obtained by discharging into a pressure-resistant container, olefin-based resin particles impregnated with a volatile foaming agent or an inorganic gas, pre-expanded particles obtained by heating with steam or the like in the container, After heating and kneading the olefin resin and the foaming agent with an extruder or the like, cooling and extruding as an extruded foam strand from a porous die provided at the tip of the extruder, the foam strand is cut into a suitable length with a cutter or the like. Examples include pre-expanded particles obtained by cutting into pieces, and any method obtained by any method can be used. For bumper core materials and cushioning packaging materials, etc., first determine the expansion ratio of the molded body according to the application, and select pre-expanded particles with an apparent density that suits this, depending on the method for producing pre-expanded particles described above. Unless the specially prepared pre-expanded particles are prepared, each pre-expanded particle is not a uniform expansion ratio but a mixture of particles having an expansion ratio distribution. Obtaining particles is difficult. Therefore, as a raw material for foam molding, it is usual to allow some deformation of the apparent density.

The pre-expanded olefin resin particles used in the present invention are also pre-expanded particles having a distribution of expansion ratio and an allowable range of apparent density.

Further, the temperature of the pre-expanded particles as referred to in the present invention is most preferably the temperature of the resin that is the base material of the pre-expanded particles, but since it is difficult to measure in practice, the pre-expanded particles are retained relatively long. It was assumed that the temperature of the atmosphere inside the pre-expanded particle group at a position considered to be the closest to the temperature of the base material was taken as the temperature of the pre-expanded particles.

Specifically, it is the temperature of the constant temperature laboratory or the temperature of the lower part of the raw material silo described later.

(Function) When the foamed molded article is manufactured by the above-described manufacturing method, when the temperature or apparent density of the compressed pre-expanded particles and the compression filling pressure are matched and the temperature or the apparent density of the pre-expanded particles is high. The compression filling pressure is low, and conversely, when they are low, the compression filling pressure is low, and the compression filling pressure is appropriately adjusted according to the temperature or the apparent density to make the expansion ratio of the foam molded article constant.

In this way, the variation in the expansion ratio of the obtained foamed molded article is reduced, and the quality as a product is improved.

(Examples) Examples of the present invention will be further described below.

FIG. 1 shows an example of an apparatus for carrying out the manufacturing method of the present invention. In the figure, (1) is a raw material silo, (2) is a sub hopper, (3) is a pressure filling container, and (4) is a male and female pair. The above-mentioned devices form a basic part of the device for producing a foamed molded article of the present invention, and the pre-compressed pre-compressed particles are added through the raw material silo (1) and the sub hopper (2). After being sent to the pressure filling container (3) and stored therein, it is compression-filled into the mold (4) by known supply means through the supply part (3a) and compression-molded. In the process, a device for measuring the temperature and apparent density of the compressed pre-expanded particles before the start of compression and filling, and the compression and filling pressure in the pressure filling container and the mold communicating therewith from the measured values are kept constant. Pressure relief valve (9)
Also, a computer / pressure control device (10) for calculating and automatically setting the depressurization pressure value of the pressure relief valve (9) is attached.

Incidentally, (5) is a temperature sensor for measuring the temperature of the pre-compressed particles to be compressed, which is attached to the raw material silo (1) in the figure, but may be attached to the sub hopper (2) as a matter of course.

Further, (6), (7) and (8) are devices for measuring the apparent density of the pre-expanded particles to be compressed, (6) is a constant volume sampling device, (7) is a weigher, and (8) is a receiving tank. Then, these measured preliminary particles are merged with the preliminary foaming fed from the sub hopper (2) to the pressure filling container (3).

In the figure, (11) is a steam pipe, which is designed to pass through the pressurizing and filling container (3) and ascend to be sent into each of the male and female molds, and set in the pressure relief valve (9). The compression filling pressure in the mold is kept constant by the restraining pressure value.
Hereinafter, experimental examples of the present invention will be listed.

Experimental Example 1 A thermostatic pre-foaming consisting of 1800 cc of ethylene propylene random copolymer was placed in a graduated 2000 cc pressure resistant glass container in a laboratory where the temperature could be controlled at -15 ℃ to 60 ℃. When the particles were put in and compressed under pressure using compressed air so that the volume was always constant, the pressurizing pressure adapted to the temperature was obtained, and the data shown in Table 1 were obtained.

When this was plotted, the temperature range adopted was a straight line as shown in FIG.

Also, when the pre-expanded particles having different apparent densities at a constant temperature are taken into a 2,000 cc pressure resistant glass container by 1800 cc and compressed with compressed air to a predetermined apparent density, the apparent density is adapted. As a result of obtaining the pressurizing pressure, the data shown in Table 2 was obtained. When this was plotted, the apparent density width adopted was a straight line as shown in FIG.

However, it was found that the pressurizing compression pressure changes with the number of pressurizations, and the data adopted here is the pressure value after three pressurizations that seems to have stabilized. However, linearity was recognized.

From the results of Tables 1 and 2 above, it was found that if the temperature and apparent density of the pre-expanded particles are known, the pressurizing pressure for pressurizing and compressing to a certain apparent density can be set. .

Experimental Example 2 Using the apparatus shown in FIG. 3, 20 times as many square pieces were compression-filled and molded.

The pre-expanded particles used in this experimental example were expanded particles of ethylene propylene random copolymer having a substrate density of 0.9 g / cc, and the apparent density (apparent expansion ratio) was 24.5 g / (36.7
The value varied from 2 times) to 28.5 g / (31.6 times).

The square metal mold (here, the shape and volume of the portion to be filled) in this experimental example had a rectangular parallelepiped shape with a length of 1000 mm, a width and a thickness of 160 mm, and a volume of 25.6.

If this square timber is used as a product, the magnification standard is 20 ± 2
When doubled, When calculated by the formula, those in the following weight range in a dried state after molding are passed.

Product weight standard (20 times ± 2 times) = 1047 (minimum value) ~ 1152 (median value) ~ 1280 (maximum value) If the magnification standard is 20 times ± 1 times, the product weight standard (20 times ± 1 times) ) = 1097 (minimum value) to 1152 (median value) to 1213 (maximum value) Table 3 shows the results of molding evaluation under various conditions.

Each level in Table 3 above is the result of molding for a full day (2 "hours"), except for Experimental Example 2-2, the pre-expanded particles (beads) used were affected by the environmental temperature of the molding factory. From Table 3 above, the experiment of the present invention was clearly better than the comparative example of ordinary molding.

From the viewpoint of the comparative example, it is appropriate to set the product standard to 20 ± 2 times, but in the case of the present Experimental Examples 2-1 and 2-4, even if the product standard is changed to 20 ± 1 times, the product yield is increased. Was over 95%, and the product yield was such that practical production was possible.

(Results of the Invention) As described above, in the present invention, in the production of olefin resin foam by compression molding, the temperature or apparent density of the specific compression pre-expanded particles is measured before the start of compression filling, and the control is performed in accordance therewith. It is a method of foaming and molding by determining the compression filling pressure that adapts to the temperature or apparent density, and making the weight of the pre-expanded particles filled in the mold constant, and conventionally, it is simply the set value of the compression filling pressure. Even if only constant, the weight of the specific compression pre-expanded particles filled in the mold is not necessarily constant due to the temperature and apparent density of the specific compression pre-expanded particles. There was a problem that the variation of the molded body was relatively large, but the temperature or apparent density of the specific compression pre-expanded particles before the start of compression filling was measured, and the compression filling pressure was determined by adapting to this. Is largely eliminated As a result, it is possible to obtain a foamed molded product having a small variation in foaming ratio and a uniform product weight, which has a remarkable effect in improving product quality and yield.

According to the second aspect of the present invention, the temperature of the pre-expanded particles is kept constant in advance, so that the compression filling pressure is maintained at a pressure adapted thereto, and the same effect as described above is exhibited.

The apparatus according to claim 5 is suitable for industrially carrying out the method, and can advantageously produce a foamed molded product by the method.

[Brief description of drawings]

FIG. 1 is a chart showing the relationship between the pre-expanded particle temperature and the pressurizing compression pressure in Experimental Example 1, and FIG. 2 is a chart showing the relationship between the pre-expanded particle apparent density and the pressurizing compressing pressure in Experimental Example 1 as well. FIG. 3 is a schematic diagram showing an example of a compression filling device used for carrying out the method of the present invention. (1) …… Material silo, (2) …… Sub hopper, (3) …… Pressurized filling container, (4) …… Mold, (5) …… Temperature sensor, (6) …… Constant volume sampling , (7) …… Weigher, (8) …… Batch tank, (9) …… Pressure relief valve, (10) …… Computer / pressure control device,

Claims (5)

[Claims] 1. A method for producing a foam of an olefin resin in which a pre-expanded olefin resin particle is compression-filled in a mold and foam-molded, the temperature of the pre-expanded particle to be compressed is measured before the start of compression filling. A method for producing an olefin-based resin foam-molded article having a small weight variation, characterized in that a compression filling pressure adapted to the temperature is determined. 2. A method for producing a foam of an olefin resin in which pre-expanded olefin-based particles are compression-filled in a mold and foam-molded, wherein the temperature of the pre-expanded particles is kept constant in advance. A method for producing an olefin-based resin foamed molded product having less variation in weight. 3. A method for producing a foamed product of an olefinic resin, which comprises compression-filling olefinic resin pre-expanded particles in a mold and foam-molding the olefin-based resin pre-expanded particles. A method for producing an olefin-based resin foam-molded article having a small weight variation, which comprises measuring and determining a compression filling pressure adapted to the apparent density. 4. A method for producing a foam of an olefinic resin, which comprises compression-filling an olefinic resin pre-expanded particle in a mold, and foam-molding the olefin-based resin pre-expanded particle. A method for producing an olefin-based resin foam-molded article having a small weight variation, which comprises measuring a density and determining a compression filling pressure adapted to the temperature and the apparent density. 5. A raw material silo, a sub hopper, a pressure filling container, and a mold device are provided, and the pre-compressed pre-expanded particles are compressed and filled into the mold from the raw material silo and sub hopper through the pressure filling container, and foam molding is performed. In the apparatus for producing a foamed molded article, a temperature sensor is installed in the raw material silo or sub hopper, while a bypass system is provided between the sub hopper and the pressure filling container to measure the apparent density in the bypass system. A device is provided, and a pressure relief valve for maintaining a constant compression and filling pressure in the pressure filling container and the mold communicating with the device is attached to the mold, and the pressure relief valve has temperature information by the temperature sensor and It is characterized in that a weight information by an apparent density measuring device is inputted, and based on this, a restraining pressure value of the pressure relief valve is calculated, and a computer and a pressure control device for automatically setting are provided together. Apparatus for producing olefin resin expansion molding.