JPS6149102B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a foamed resin molded article used as a cushioning material for foods, luxury goods, machines, appliances, etc.

Conventionally, this type of molded product was manufactured by first heating the material using a pair of male and female molds, and then cooling it as it was within the same mold, but recently, compared to this conventional method, energy consumption has increased. , a method was proposed that could save both manufacturing time. The device used in this method consists of two parallel plates and a quadrilateral frame between the plates.
It has two types. The two molds share the same frame, in which the molded product remains while being transferred from the heating mold to the cooling mold. The frame moves between the two molds, holding the molding between two parallel plates or between rolls juxtaposed next to each other to prevent deformation or expansion of the molding or termination of foaming, especially during transport. do. Therefore, with this production method, only plate-shaped molded products can be produced.
If it is desired to process the molded product into another shape, it is necessary to further press the molded plate after taking it out from the cooling mold.

Another method is also known in which a molded product is transferred from a first mold to a second mold similarly to this method.
However, in this method, only the foaming of the synthetic resin globules occurs in the first mold, and the entire molding process is performed in the second mold by heating and then cooling for each molding cycle.

Another known method is to apply heat treatment to the foamable resin before supplying it to the mold to bring it to a state close to the completion of foaming, and then place the hot resin into a press mold to simultaneously advance compression and bonding to form a molded product. There is also a method in which the molded product is cooled in the press mold. However, even in this method, the press mold must be heated and cooled during each production cycle while the molded product remains in the mold, resulting in a considerable waste of energy and time. Moreover, the molded product also has non-uniform bubbles.

An object of the present invention is to provide a method for producing a molded article made of foamed resin, which saves both energy and time, and allows the production of products of any desired shape with excellent quality.

The method according to the invention generally proceeds as follows.

(a) The pre-foamed synthetic resin small spheres are maintained and controlled at a predetermined heating temperature, and the pre-foamed synthetic resin small spheres are fed into a closed mold made of a material with a relatively low coefficient of thermal expansion. When the spheres are fed into this heated mold, they have approximately the same density as the finished mold.

(b) The synthetic resin pellets are heated and plasticized in this heated mold by a heating means such as steam. The globules are expanded with steam by a foaming or promoting medium (e.g. methane)
Contains. The globules are held together by the pressure created during expansion.

(c) The semi-finished product thus formed is removed from the heated mold and foaming is completed outside the mold. This may be in a free atmosphere or in a controlled atmosphere. As a result, an adiabatic relaxation state occurs inside the globule and the promoting medium and vapor condense. At this point, the semi-finished product has not yet been sufficiently cooled, so it is ready for plastic molding. On the other hand, the mold from which the semi-finished product has been removed and whose inner wall surface is exposed is cooled using air or a refrigerant (for example, water).

(d) The semi-finished product, still in a plastic state, is then inserted into a cooled mold and stabilized in the desired finished shape by hardening at least of the surfaces in contact with the walls of the mold.

In this invention, the synthetic resin spherules are not bonded together by the action of external pressure but by the internal pressure generated by gas expansion within the spherules, so the manufactured molded product has remarkable homogeneity. . The molded product also conforms to the shape and dimensions of the cooled mold, and is elastic and not brittle.
On the other hand, molds are repeatedly heated and cooled, but the material of the mold is made of a material with low thermal conductivity, such as inorganic materials such as thermosetting resins and ceramics. Since the hole surface can be cooled by applying refrigerant directly to it, only the surface area of the mold hole can be heated in a short time.
On the other hand, the time per production cycle is shortened and the energy consumption is reduced, since the semi-finished product is immediately removed from the mold, the outer surface is at least partially exposed to the atmosphere, and the inner part is adiabatic and relaxed. is also saved.

In addition, in this invention, the mold is maintained at 90 to 130 °C, preferably 120 °C during the heating cycle,
During the cooling cycle, the temperature is maintained below 90°C.

As mentioned above, in the apparatus used in this method, a single mold consisting of a male mold and a female mold is formed of a material with low thermal conductivity, and each means for heating and cooling the surface of the mold cavity is provided. is provided.

Note that the entire mold that is repeatedly heated and cooled may be made of a material with low thermal conductivity, but there are also other molds that have a structure that allows only the inner surface of the mold cavity to be repeatedly heated and cooled, such as a material with low thermal conductivity. The structure may be one in which the surface of the cavity of a mold made of a substance is coated with a metal coating layer. In addition, as means for heating and cooling the surface of the mold cavity, there is a method of using a mold with a medium passage for heating and cooling near the surface of the mold cavity, and a method of applying a medium consisting of gas or liquid to the mold cavity from outside the mold. You can use any method you like, such as contacting them.

The present invention will be described below with reference to illustrated embodiments.

FIG. 1 shows an example of a mold used in the present invention.
This mold consists of a male mold 41 and a female mold 42, and a mold cavity 43 filled with thermoplastic resin is formed between the two molds.
The male mold 41 is equipped with a steam supply path 44 that connects to an internal channel 45 , allowing steam to enter the mold cavity 43 via a nozzle 46 at the internal end of the channel 45 . The female mold 42 is equipped with a conical inlet 47 for the thermoplastic resin and a diversion nozzle 48 for excess steam, which is connected to a steam outlet 49 and a condensate outlet 50 .

At the start of operation of the device described above, the male mold 41 of the mold is inserted by means of a piston into the female mold 42 of the mold, forming a mold cavity 43 of a shape corresponding to the molding to be produced.
is formed. The mold is heated by a known device (not shown). When the mold is ready for loading, pre-expanded polystyrene pellets in a storage container (not shown) are fed into the mold cavity 43. Steam entering the mold through nozzle 46 causes expansion and bonding of the thermoplastic globules. After this process is completed, the male mold 41 fixed to the transfer member is pulled out to the left in FIG. 1 by the piston. The semi-finished product formed in the mold cavity remains attached to the male mold 41 and becomes freely relaxed by being released from mechanical restraint.

After a predetermined period of time, the completely relaxed semi-finished product is reinserted into the female mold 42 whose cavity surface has been cooled, and a molded product conforming to the shape and dimensions to be manufactured is formed. The piston is then moved again to the left in FIG. 1, and the finished molded part corresponding to the mold cavity is ejected by a mechanically or pneumatically actuated ejector and falls into the container.

FIG. 2 shows another embodiment for use with the present invention. The mold shown in this figure is in the closed state, with female mold 6
1. A male mold 62, a mold cavity 63, and an opening 6 into which pre-foamed synthetic resin beads are supplied from a device 65.
4. It has a heating element 66 and channels 67, 68 for supplying and discharging steam.

Furthermore, one possible modification is to apply negative pressure to the mold that has been cooled for a predetermined period of time. In this case, the relative pressure inside the sphere of foamed thermoplastic resin can be increased considerably, and it is therefore possible to reduce the density and therefore the weight of the molded product.

Both male and female types may be provided on the same base, or may be provided on separate bases. Also, one heated mold and a number of cooled molds may work together, or vice versa.

The device for transferring the semi-finished product from the heated mold to the cooled mold can be driven by various methods such as mechanical or pneumatic.

Heat can be supplied to the mold and the thermoplastic resin within the mold by any known means, such as heating wire, steam or hot oil.

As described in detail above, according to the present invention, the mold is first heated and the semi-finished product is formed in the mold as described above, and then the semi-finished product is removed from the mold in order to be relaxed outside the mold. During this time, the walls of the mold cavity are cooled,
Thereafter, the semi-finished product is inserted into the mold again. Such operations facilitate cooling and shorten the manufacturing cycle. Since the material used for the mold has a low thermal conductivity, cooling the surface of the mold cavity for a short period of time does not cool the entire mold, so energy loss can be kept to a minimum. can.

The method of the present invention can produce molded products with greater flexibility than those produced by conventional methods even though they have a higher density. Since this molded product is elastic and has low brittleness, it exhibits remarkable effects when used as a cushioning material, especially as a packaging material.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic sectional views showing an apparatus used in the method of the present invention. 41...male mold, 42...female mold, 43...mold hole,
44... Steam supply path, 45... Channel, 46...
...Nozzle, 61...Female type, 62...Male type, 63...
...Mold hole, 66...Heating body.

Claims (1)

[Claims] 1. Forming a pre-foamed thermoplastic resin in the form of small lumps into a mold hole corresponding to the shape of the final molded product to be manufactured;
The required amount is poured into a heated closed mold consisting of a male mold and a female mold made of a material with a relatively low coefficient of thermal expansion, and the thermal energy necessary for foaming is applied, and the expansion internal pressure inside the small lump The nodules are at least partially bonded and formed into a semi-finished product which is still in a plasticized state but has a shape corresponding to the final molding to be produced, after which the mold is opened and the surroundings of the semi-finished product are formed. At least one of the entire surfaces is exposed to the atmosphere and the inner surface of at least one mold cavity of the mold is cooled, and then the semi-finished product is reinserted into the cooled mold, and both the male and female parts of the mold are cooled. 1. A method for producing a foamed resin molded product, characterized in that the final molded product is obtained by closing with a mold and cooling. 2. The manufacturing method according to claim 1, characterized in that foaming of the semi-finished product is completed in a free atmosphere. 3. The manufacturing method according to claim 1, characterized in that foaming of the semi-finished product is completed in a controlled atmosphere. 4. The manufacturing method according to any one of claims 1 to 3, characterized in that a negative pressure is generated in the mold cavity during cooling in the cooled mold. 5. The method according to claim 1, characterized in that the semi-finished product is moved for removal from the mold and reinsertion into the mold using at least a part of either the male mold or the female mold. Production method.