BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view showing a molding apparatus for producing a molded foamed resin product according to an embodiment of the present invention.
FIGS. 2A-2D are shows cross-sectional views stepwise illustrating states of a mold from the end of charging of an expandable resin to the completion of a molded foamed resin product.
FIG. 3 is a graph showing changes in core-backing speed with time in Example 1.
FIG. 4 is a graph showing changes in the amount of backward movement (the core-backing distance) of the mold with time in Example 1.
FIG. 5 is a cross-sectional view showing a state of an expandable resin just after it is charged into the mold in Example 1.
FIG. 6 is a cross-sectional view showing a state of the expandable resin when a delay time has passed after the charging into the mold in Example 1.
FIG. 7 is a cross-sectional view showing a state of the expandable resin at the end of a previous core-backing term in Example 1.
FIG. 8 is a cross-sectional view showing a state of the expandable resin at the end of a latter core-backing term in Example 1.
FIG. 9 is a graph showing the relation between the foaming pressure of an expandable resin in the mold and the core-backing distance.
FIG. 10 is a graph showing changes in core-backing speed with time in Example 2.
FIG. 11 is a graph showing changes in core-backing speed with time in Example 3.
FIG. 12 is a graph showing changes in core-backing speed with time in Example 4.
FIG. 13 is a graph showing changes in core-backing speed with time in Example 5.
FIG. 14 is a graph showing changes in core-backing speed with time in Example 6.
FIG. 15 is a graph showing changes in core-backing speed with time in Example 7.
FIG. 16 is a graph showing changes in foaming speed with time when an expandable resin is allowed to freely expand.
DETAILED DESCRIPTION OF THE INVENTION
A description is given below of an embodiment of the present invention with reference to the drawings. Note that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the scope, applications and use of the invention.
FIG. 1 shows a molding apparatus for producing a molded foamed resin product, wherein reference numeral 1 denotes a mold and reference numeral 2 denotes an injector for charging an expandable resin into the cavity of the mold 1.
Referring to FIG. 2, the mold 1 is composed of a stationary mold half 3 and a movable mold half 4 movable towards and away from the stationary mold half 3. The stationary mold half 3 has a sprue 5 formed therein. Referring again to FIG. 1, the mold 1 is connected to a movable mold half actuator 6 for sliding the movable mold half 4 towards and away from the stationary mold half 3. The movable mold half actuator 6 is composed of a piston/cylinder assembly 7 and a guide 8 for guiding the forward and backward movement of the movable mold half 4 actuated by the piston/cylinder assembly 7. The movement of the piston/cylinder assembly 7 is controlled by a controller 9 using a microcomputer.
The injector 2 includes a cylinder 11 having a screw rotatably inserted therein and a heater disposed on the outer periphery thereof. The cylinder 11 is provided at the tip with a nozzle 12. The nozzle 12 is connected to the sprue 5 in the stationary mold half 3. The cylinder 11 is also provided at the root end with a hopper 13 for feeding an expandable resin or a resin material and a screw actuator 14 for rotating and reciprocating the screw.
In molding an expandable resin containing a chemical foaming agent, the expandable resin is loaded through the hopper 13 into the cylinder 11. In molding an expandable resin containing a physical foaming agent, a resin material is loaded through the hopper 13 into the cylinder 11 and the physical foaming agent is fed in the form of supercritical fluid from a supercritical fluid generator 15 partway into the cylinder 11. In producing a fiber-reinforced molded foamed resin product, reinforcing fibers are mixed in advance into a resin material.
Reinforcing fibers preferably used are those having an average fiber length smaller than the thickness of a molded foamed resin product to be produced in a direction of sliding of the movable mold half (a core-backing direction). In other words, molded foamed resin products preferably molded are those having a larger thickness in the core-backing direction than the average fiber length of reinforcing fibers used, particularly those having a thickness twice larger than the average fiber length. This is advantageous in utilizing the spring-back effect of reinforcing fibers to promote foaming of the expandable resin. The type of reinforcing fibers used is not particularly limited. For example, glass fibers or carbon fibers may be used.
Core-Backing Control
With the cavity 16 between the fixed and movable mold halves 3 and 4 charged with an expandable resin 21 as shown in FIG. 2A, the controller 9 controls the movable mold half actuator 6 to perform core-backing, i.e., set the movable mold half 4 back from the stationary mold half 3. Thus, the cavity 16 is extended to a volume corresponding to the size of a molded article. FIGS. 2B, 2C and 2D schematically show a state of the mold 1 when the delay time from the end of charging of the expandable resin to the start of core-backing terminates, a state of the mold 1 in process of core-backing and a state of the mold 1 at the end of core-backing, respectively. In FIGS. 2B to 2D, the bold border line in the cavity 16 denotes a skin layer 22 at the surface of the expandable resin, reference numeral 23 denotes an expanding foam of the expandable resin and reference numeral 24 denotes a molded foamed resin product after the end of foaming (after the end of core-backing).
Hereinafter, core-baking controls according to the present invention will be described with reference to a plurality of examples.
EXAMPLE 1
FIG. 3 is a time chart showing a core-backing control according to Example 1. The controller 9 receives a signal indicating the end of charging of an expandable resin (the end of injection) from the injector 2 and then starts core-backing at an interval of a predetermined delay time. The core-backing term is divided into a previous core-backing term Tf in which core-backing is performed at a low speed and a latter core-backing term Ts in which core-backing is performed at a higher speed than in the previous core-backing term Tf. In this example, the controller 9 controls core-backing so that, in the previous core-backing term Tf, the movable mold half 4 is accelerated from a speed of zero up to a first speed V1 and held at the first speed V1 for a predetermined time and, in the latter core-backing term Ts, the movable mold half 4 is accelerated from the first speed V1 up to a second speed V2, then held at the second speed V2 for a predetermined time and then decelerated down to a speed of zero. In this example, the second speed V2 is higher than the first speed V1 and the first and second speeds V1 and V2 are set to be equal to or lower than the expansion speed of the expandable resin in free expansion and, preferably, to be lower than the expansion speed.
The lengths of the delay time, the previous core-backing term Tf and the latter core-backing term Ts vary depending upon the type and the injection temperature of expandable resin used and the mold temperature. For example, the delay time can be set within the range of 5 to 25 seconds and the previous core-backing term Tf and the latter core-backing term Ts can be set within the range of 1 to 10 seconds. For the amount of extension of the cavity 16 by core-backing, the cavity 16 can be extended in the previous core-backing term Tf, for example, so that its thickness in the core-backing direction becomes 1.3 times to 1.7 times larger than that at the end of charging of the expandable resin, and can be extended in the latter core-backing term Ts, for example, so that its thickness in the core-backing direction becomes 2.1 times to 2.6 times larger than that at the end of charging of the expandable resin.
FIG. 4 shows changes in the amount of backward movement (the core-backing distance) of the movable mold half 4 due to the core-backing control with time. After a delay time has passed from the end of charging, the previous core-backing term Tf is reached. The amount of backward movement of the movable mold half 4 gradually increases during the previous core-backing term Tf and then gradually increases at a higher speed during the latter core-backing term Ts.
FIGS. 5 to 8 stepwise illustrates how a molded foamed resin product 24 is molded by the core-backing control. In this example, with the use of a supercritical fluid of carbon dioxide gas as a foaming agent and glass fibers as reinforcing fibers 25, the molded article 24 was obtained that has a thickness in the core-backing direction twice or more times larger than the average fiber length (1.0 to 1.8 mm) of the reinforcing fibers 25.
FIG. 5 shows an expandable resin 21 at the end of charging into the mold. The expandable resin 21 flows through the sprue 5 in the stationary mold half 3 shown in FIG. 2 into the cavity 16 towards its surrounding region. Therefore, by the effect of the flow in the cavity 16, the reinforcing fibers 25 are oriented along the opposed molding surfaces of the fixed and movable mold halves 3 and 4 (in a direction substantially orthogonal to the core-backing direction (the thickness direction of the molded article)).
FIG. 6 shows the expandable resin 21 when the delay time has passed. During the delay time, the expandable resin 21 gives heat at a part thereof in contact with the molding surfaces of the mold 1 (at its surrounding surface) to the mold 1 and thereby starts curing to gradually form a skin layer 22 around it.
FIG. 7 shows the expandable resin 21 at the end of the previous core-backing term Tf. Since core-backing starts and reduces the in-mold pressure, the expandable resin 21 develops expansion and gradually becomes a foam 23. During the previous core-backing term Tf, the expandable resin 21 has high foaming pressures as shown in FIG. 9 and the spring-back effect of the reinforcing fibers 25 causes an expansion force inside the expandable resin 21. However, since the core-backing speed is restricted to the first speed V1, this avoids an abrupt foaming of the foaming agent and prevents foaming from progressing to such an extent as to cause a breakage of the skin layer 2. Also during the previous core-backing term Tf, the foam 23 gives heat to the mold 1 to gradually form the skin layer 22 and gradually increase the strength of the skin layer 22.
FIG. 8 shows the expandable resin 21 at the end of the latter core-backing term Ts. In the latter core-backing term Ts, the core-backing speed is set at the second speed V2 higher than the first speed V1 in the previous core-backing term Tf. Therefore, by a combination of in-mold pressure reduction due to core-backing at the higher speed and the spring-back effect of the reinforcing fibers 25, the foaming agent in the foam 23 rapidly expands so that the entire foam 23 uniformly expands and foams. Since the high-strength skin layer 22 has yet been formed at the start of the latter core-backing term Ts, this prevents the skin layer 22 from breaking owing to the foaming during the latter core-backing term Ts. As a result, a good appearance molded foamed resin product 24 can be obtained that has a homogeneous foam structure under the skin layer 22.
EXAMPLE 2
FIG. 10 shows a core-backing control according to Example 2. In this example, in the previous core-backing term Tf after the elapse of the delay time, the core-backing speed is stepwise increased so as to be first increased to a first A speed V1a, held at the first A speed V1a for a certain period of time, then increased to a first B speed V1b and then held at the first B speed V1b for a certain period of time. In the latter core-backing term Ts, like Example 1, the core-backing speed is increased to the second speed V2 higher than in the previous core-backing term Tf and held at the second speed V2 for a certain period of time. Then, the core-backing is terminated.
Also in this example, the core-backing speed is restricted to relatively low speeds V1a and V1b in the previous core-backing term Tf and increased to a relatively high second speed V2 in the latter core-backing term Ts. Therefore, like Example 1, the entire foam can be uniformly expanded without breaking through the skin layer. As a result, a good appearance molded foamed resin product can be obtained that has a homogeneous foam structure under the skin layer.
Furthermore, since the core-backing speed is stepwise increased in the previous core-backing term Tf, this is advantageous in promoting a smooth expandable resin foaming towards the latter core-backing term Ts while preventing the skin layer from being broken through by abrupt foaming of the foaming agent.
Instead of stepwise increasing the core-backing speed in the previous core-backing term Tf, the core-backing speed may be continuously increased during the previous core-backing term Tf until the cavity volume of the mold extends up to 1.3 to 1.7 times larger than its original volume, and then may reach the second speed V2 in the latter core-backing term Ts.
EXAMPLE 3
FIG. 11 shows a core-backing control according to Example 3. In this example, in the previous core-backing term Tf after the elapse of the delay time, the core-backing speed is increased to the first speed V1, held at the first speed V1 for a certain period of time and then reduced to zero to stop the core-backing. Thereafter, when the latter core-backing term Ts is reached, the core-backing speed is increased to the second speed V2.
Therefore, also according to this example, like Example 1, a good appearance molded foamed resin product can be obtained that has a homogeneous foam structure under the skin layer. Furthermore, since the core-backing speed is once reduced to zero during transition from the previous core-backing term Tf to the latter core-backing term Ts, this is advantageous in forming a high-strength skin layer to prevent the skin layer from being broken through by foaming.
EXAMPLE 4
FIG. 12 shows a core-backing control according to Example 4. In this example, in the previous core-backing term Tf after the elapse of the delay time, the core-backing speed is increased to the first speed V1, held at the first speed V1 for a certain period of time, then once reduced to zero to stop the core-backing, then increased again to the first speed V1, held at the first speed V1 for a certain period of time and then reduced again to zero. Thereafter, when the latter core-backing term Ts is reached, the core-backing speed is increased to the second speed V2.
Therefore, also according to this example, like Example 1, a good appearance molded foamed resin product can be obtained that has a homogeneous foam structure under the skin layer. Furthermore, since the core-backing speed is once reduced to zero midway in the previous core-backing term Tf, this is advantageous in forming a high-strength skin layer to prevent the skin layer from being broken through by foaming.
EXAMPLE 5
FIG. 13 shows a core-backing control according to Example 5. In this example, like Example 2, the core-backing speed is stepwise increased first to a first A speed V1a and then to a first B speed V1b in the previous core-backing term Tf after the elapse of the delay time, and then increased to the second speed V2 when the latter core-backing term Ts is reached. Unlike Example 2, however, the core-backing speed is reduced to zero between the first A and B speeds V1a and V1b and between the first B speed V1b and the second speed V2 in the latter core-backing term Ts.
Therefore, also according to this example, like Example 1, a good appearance molded foamed resin product can be obtained that has a homogeneous foam structure under the skin layer. Furthermore, since the core-backing speed is once reduced to zero midway in the previous core-backing term Tf, this is advantageous in forming a high-strength skin layer to prevent the skin layer from being broken through by foaming.
EXAMPLE 6
FIG. 14 shows a core-backing control according to Example 6. In this example, like Example 5, the core-backing speed is once reduced to zero midway in the previous core-backing term Tf after the elapse of the delay time. Unlike Example 5, however, the first B speed V1b is lower than the first A speed V1a. The rest of the core-backing control are the same as according to Example 5.
Therefore, also according to this example, like Example 1, a good appearance molded foamed resin product can be obtained that has a homogeneous foam structure under the skin layer. Furthermore, since the core-backing speed is once reduced to zero midway in the previous core-backing term Tf, this is advantageous in forming a high-strength skin layer to prevent the skin layer from being broken through by foaming. Furthermore, since the first B speed V1b is lower than the first A speed V1a, the core-backing can make the transition from the previous core-backing term Tf to the latter core-backing term Ts with bubble cells in the foam arrayed, which is advantageous in forming homogeneous bubble cells.
EXAMPLE 7
FIG. 15 shows a core-backing control according to Example 7. In this example, after the end of charging of an expandable resin, core-backing is immediately started without giving any delay time and the core-backing speed is stepwise increased as in Example 5. Since, however, no delay time is given after the end of charging unlike Example 5, the first A and B speeds V1a and V1b in the previous core-backing term Tf are restricted to lower levels.
Therefore, also according to this example, like Example 1, a good appearance molded foamed resin product can be obtained that has a homogeneous foam structure under the skin layer.
The molding method and apparatus for producing a molded foamed resin product according to the present invention can be applied to molding of automotive parts and other various kinds of molded foamed resin products. For example, applicable automotive parts include door module plates in which a speaker, a door latch assembly, a door lock actuating mechanism, a glass elevating mechanism and the like are incorporated, bumpers and other plate articles.
Patent Application
20080012166
