JPH0254764B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing foamed products of thermoplastic and thermoset compounds. Synthetic polymers are generally classified into two categories: One is that it changes from solid to liquid by heating,
One is a thermoplastic polymer that can recover its original physical properties by cooling without changing its chemical composition. It is a thermosetting polymer with physical changes. Virtually every polymer ever made has been foam-molded at one time or another. Foam molding is carried out by dispersing gas into the viscous material, either directly or from a chemical blowing agent.
As the plastic material solidifies, the gas may either become completely encapsulated within the closed cells in the material, or alternatively the gas may travel through passageways within the plastic material without being completely encapsulated. These two foam structures are known as closed cell and open cell, respectively. Foamed materials are widely used for insulation, packaging, structural decoration parts, flotation machines, etc. Since foamed materials can increase volume per unit weight, material costs may be reduced. Soft foams can be used in cushions, filters, packaging, clothing, and other applications. The density of foamed plastics has a wide range. Typical density ranges from 1.6 to 960Kg/m ³
It is. The twist-resistant foam can be used as is. Foaming foamed plastic material 1
One method is to produce the foam during processing by mixing or injecting the compound with a volatile liquid or gas. By performing a blending step, the compound mixture can be uniformly distributed before processing. Another method of foaming plastics is by thoroughly mixing the chemical blowing agent and the polymer. The blowing agent generates gas at a predetermined trigger temperature and foams within the viscous polymer. However, in the case of known foaming methods, there are always disadvantages in one of the steps. One disadvantage is that foamed products usually have to be formed under high pressure. Another disadvantage of molding foamed plastic products is that the compound must be maintained at the trigger temperature of the blowing agent throughout most of the process, and the compound must not be charged into the mold or other molding equipment. Afterwards, the compound must be heated further to generate gas from the blowing agent. One method for forming flexible foams is to disperse PVC compounds in liquid plasticizers.
Foam molding is then accomplished by chemical blowing agents or mechanical frosting. However, both methods are expensive because they require high pressure in the final stage of molding and a long cycle time.
The soft expanded PVC compound is made of special grade
It can also be made in an extruder from PVC compound. Applications of soft foam include door seals, gaskets, cable insulation, etc. The best known methods for producing foam materials include the following four steps. The mixing process involves mixing the compound with a blowing agent and, for PVC, milling to uniformly mix the mixture. Next, in the step of charging the mixture into the mold, the mixture is charged into the mold and then heated and cooled in a press under high pressure, generally for 30 minutes or more. The final process of foaming takes place in the mold.
This is done by holding this state for 60 minutes. Thus, for example, it takes more than two hours to produce a foamed PVC material. The present invention provides a method by which thermoplastic and thermoset foam products can be produced simply and quickly. Use of the method of the present invention reduces the number of steps required by most of the prior art, eliminates the high pressure normally required in molds or other shaping means, and eliminates the need for thermosetting materials. and the time required to foam the thermoplastic can be reduced. By using a high intensity mixer, the plastic compound and blowing agent are mixed and melted in a very short cycle time and then immediately formed into molds or other shapes at lower temperatures and pressures than previously possible. It has been found that it can be formed within the means. The present invention provides a method for producing a thermoplastic foam molded article from a granular thermoplastic resin. heating and generating gas at the trigger temperature of the blowing agent to produce a foam, the mixing and heating being carried out by mixing the particulate composition in a closed mixing chamber, the mixing chamber containing: A plurality of blades are attached to an arm, which has a length of about 18 m/s at the tip of the blade.
It rotates around an axis in a chamber at a speed of more than a second, and continues to mix the granular composition in a sealed container, heating the granular composition to a mixing temperature above the trigger temperature of the blowing agent, and mixing it. At a temperature sufficient to melt the particulate composition, the molten composition has a viscosity that allows it to contain the gas evolved from the blowing agent, and the molten composition reaches the mixing temperature and the blowing agent forms a foam. Before starting production, the molten composition is discharged from the mixing chamber, the discharged molten composition is supplied to a mold, the composition is confined in the mold, and the composition is molded while foaming the composition, It consists of the process of forming a plastic molded article in a mold. In other embodiments of the invention, the compound and blowing agent are fed into the mixing chamber at the same time, but the compound may be added to the mixing chamber after the compound has begun mixing. When the plastic compound is a rigid or flexible polyvinyl chloride or low density polyethylene resin, preferred blowing agents include azodicarbonamide or para, para-oxybis(benzenesulfonyl hydrazide). The blade tip speed in the mixing chamber is approximately 31−38
The desired temperature is within the meter/second range, and the set temperature is approx.
Desirably within the range of 190-240℃. Batches made within this desired range will reach set point temperature in about 7-20 seconds. In other embodiments, the forming means includes a molding means, a shaping means, an extrusion molding machine, about 550-2200
A press operating at pressures in the kilopascal range is included, and the time the composition is confined within the mold is about 5 minutes or less. High-intensity mixers can be used to melt thermoplastic and thermoset materials. One high-power mixer is disclosed in U.S. Pat. No. 3,266,738, issued to Gussel et al. This patent describes a high-power mixer that is commercially available today under the trade name Drais-Gelimat. The mixer includes a plurality of blades that rotate about an axis within a closed container.
U.S. Pat. No. 4,230,615, issued to Krotzker et al. on October 28, 1980, discloses that the temperature of the batch in the high-intensity mixer is monitored separately from the mixer temperature, and that when the batch reaches the final set temperature, the temperature of the batch is removed from the mixer. An apparatus for discharging batches is disclosed. In column 5, line 34 of this patent, it is stated that the blowing agent is added at the end of the mixing process so that foaming does not occur too quickly in the mixer, and that the batch temperature is just below the foaming temperature. Discharge of batches is described in . However, in the present invention,
It has been found that the blowing agent does not necessarily need to be added at the end of the mixing process, but can be added at the beginning of the mixing process. Furthermore, in the present invention, the batch of thermoplastic resin particles and blowing agent is heated to a temperature above the trigger temperature at which gas is generated. Another way to control the amount of mixture is described in US Patent No. 6, issued March 6, 1979 to Mr.
Disclosed in No. 4142804. This patent discloses a method for controlling the state of a batch melt produced in a high-power mixer by monitoring vibrations within the mixer, and ejecting the batch from the mixer when the vibrations reach a set point indicative of a predetermined melt state. are doing. In a series of tests, batches of thermoset or thermoplastic compounds were processed in an intensive mixer with a blowing agent. The mixer used was a high-powered mixer made by Drais Gerimat, with a blade tip speed of 18 meters/second or higher. The blowing agent is added at the same time as the compound, or the compound is fed into the mixing chamber by the screw conveyor of the Gerimat mixer, and the blowing agent is added via the screw conveyor after the mixing process has started. There is. The weight of the batch fed into the mixer varied from 100 grams to 300 grams depending on the batch size required, but the total time in the mixer did not exceed 30 seconds. FIG. 1 shows a schematic diagram of an apparatus suitable for the method of the invention. Powerful Mixer 10 has US Patent No.
No. 3,266,788, the mixer comprises a closed mixing chamber 11 in which a rotating blade 12 mounted on an arm 13 of a shaft 14 is provided. The batches are loaded through the inlet port 15 and fed into the mixing chamber 11 by a screw conveyor 16. When the batch reaches a predetermined temperature, the hydraulic cylinder 17 is actuated to open the discharge flap 18 and the material is dropped from the funnel 19 directly into the mold 20. The mold 20 is moved from below the mixer and the lid 21 is placed over the mold 20 to trap the material inside the mold. In a preferred embodiment, batch temperature within the mixer was determined by measuring infrared radiation from the batch. It is based on the apparatus and method disclosed in U.S. Pat. No. 4,230,615, which includes:
Batch temperature was measured separately from mixer and mixer blade temperatures. The purpose of setting the batch temperature is to control when the batch is discharged. The batch temperature is selected at a temperature at which the plastic compound discharged from the high-intensity mixer melts, becomes viscous, and is fed into a mold or other shaping means to form the final product. Since the discharge temperature of the batch is higher than the trigger temperature of the blowing agent, foaming or gas evolution from the blowing agent has already begun in the mixer before the batch is discharged from the mixer. However, since the time until discharge from the mixer is short, the progress of foaming is not large. When the blowing agent reaches the trigger temperature, foaming begins already in the mixer and the batch has sufficient viscosity to be able to contain the gas generated by the blowing agent. Therefore, as soon as the batch is discharged from the mixer, it is placed into a mold without undue delay and kept in the mold until foaming is complete and the product is cooled. The trigger temperature must be high enough so that gas begins to evolve from the blowing agent at about the same time as or after the molten compound reaches a viscous state in which it can contain the evolved gas. If the trigger temperature is too low, the gases generated will disperse into the atmosphere and cannot be included in the compound. The batch discharged from the mixer may be submitted to a mold, extruder or other shaping means. If the foam product to be made is a plate or sheet, the molten batch is placed between two flat surfaces and compressed. The pressure between the flat surfaces does not need to exceed 2200 kilopascals, and the high temperature of the molten material allows it to continue foaming without heating the press. By continuing to foam, the material fills the mold and begins to harden. Since the material is foamed in an unheated mold and does not require any external heat, there are no restrictions on the thickness of the material being molded.
Because heat is supplied from within the molten material and not from the exterior surface, products of almost any thickness can be foam molded. The external surfaces of the mold or other shaping device may also be preheated to prevent the material from becoming too cold when it contacts the two external surfaces. Foaming is done by decomposition of chemical blowing agents,
Since gases are released during chemical reactions, several thousand steps are required to drain the batches during foaming and feed the batches during foaming to the shaping equipment in order to reduce the loss of gas that could contribute to foam molding. It is strictly controlled within a fraction of a second. The method according to the invention was tested using two types of blowing agents. One is azodicarbonamide, sold under the trade name Ficel-AC/4, with a trigger temperature range of
The temperature is 190 to 220°C. This trigger temperature is soft
With the metal salt stabilizers often present in PVC compounds, temperatures can be lowered to 170°C. The second blowing agent is para-oxybis (para-oxybis), sold under the trade name Celogen OT.
oxybis) (benzenesulfonyl hydrazide)
(benzenesulfonylhydrazide). The trigger temperature of this blowing agent was within the range of 130 to 160°C, and the most efficient trigger temperature was 150°C or higher. This blowing agent is suitable for injection molding and compression molding of PVC and low density polyethylene. This is particularly useful for obtaining cellular structures with non-cellular thin or thick skins. The compound used in the test was a blowing agent
Ficel-trade name CTR- containing 0.5% AC/4
They were 12D hard PVC powder, a hard PVC compound called CGP-1100 used for thin film manufacturing, BPVS, a hard vinyl compound for plates, and a hard PVC compound for pipes. In addition, hard pipe
PVC compound is 300 parts of 366 resin, TM692
It contains 1.8 parts of CAST6, 1.2 parts of CAST6, 3.0 parts of K1.25, and 6.0 parts of Atomite. Another plastic compound is
It was a plastic PVC product known as R7203A. Low density polyethylene with code number EXPY134-175 has a melt index of 4.4 and was also foam molded.

[Table] Pre-mix 5 R7203A 150 Ficel AC/
4 0.7 1.0 36
Premix 6 PE 140 Celogen O
T 0.6 0.84 31
pre-mixing

[Table] Example 1 As shown in Table 1, 300 grams of a rigid PVC compound designated CTR-12D was pressurized in a high-power mixer. Foaming agent is in the compound
It was present at 0.5% by weight. The blade tip speed of the powerful mixer is 38 m/s, and the mixer is not equipped with a cooling mechanism. In this first preliminary test, when the compound was added to the mixer, although not necessarily in an optimal amount, the blowing agent was already premixed with the compound and the discharge temperature was 215°C. After draining from the mixer, approx.
Approximately one-half of the batch was molded in a press at a temperature of 180°C and a pressure of 2200 kilopascals. The resulting foamed product had a specific gravity of 1.29, indicating some foaming when compared to the unfoamed product's specific gravity of 1.35. In a second test, an additional 1.5 grams of blowing agent was added to 300 grams of compound after the batch temperature in the mixer reached 220°C. The discharge temperature was 240°C, and the molded product had a specific gravity of less than 1 and floated in water. Example 2 The specific gravity of a product made by foam molding by adding Ficel AC/4 foaming agent to CGP-1100 compound is approximately 0.7.
It was hot. The blowing agent is added to the compound by weight%.
Added 0.3-1.2%. In other examples, carbon black and titanium dioxide were added to the compound without affecting the foaming properties. When the press pressure was 550 kilopascals, the foamed product obtained was satisfactory. In one particularly simple test, 1 gram of blowing agent was added to 170 grams of the compound in a slightly preheated shoe sole mold.
A density of less than 1 was obtained by molding in a mold.
Note that the pressure was simply keeping a person standing on the lid of the mold. The mold was slightly preheated, which was necessary to eliminate the effects of heat drop on the fairly heavy metal mold. The foam molded rigid PVC material could be conveniently processed by most common wood processing and joining techniques. The material can be drilled, sawed, planed, sanded, routed, or otherwise shaped. This material also has a retention of
This is evidenced by the ability to reposition large and small screws many times without loss of retention strength. Example 3 A rigid PVC material for vinyl board was fully foamed by adding 0.6% blowing agent 12 seconds after starting the intensive mixing cycle. The specific gravity of the foamed sheet was measured to be 1.17, which indicates that the specific gravity was significantly reduced since the specific gravity of the molten material without the addition of a foaming agent was 1.49. Example 4 A rigid PVC compound for pipes was sufficiently foamed under the conditions shown in the table. The specific gravity of the unfoamed compound was 1.38, while the specific gravity of the foamed compound was 1.0 or less. Example 5 The specific gravity of a soft PVC compound was 1.21 in an unfoamed state, and when foamed at a pressure of about 550 kilopascals, the specific gravity was 0.713. Example 6 Polyethylene was foamed using the blowing agent Celogen OT, which has a lower trigger temperature than the blowing agents used previously. The specific gravity of this foam was 0.65, and the specific gravity of a product produced by processing the same compound in a high-power mixer under the same conditions without adding a blowing agent was 0.90. The method of the invention is such that when the batch reaches a certain temperature,
Accurate temperature control is provided by means of which the batch can be discharged from the high-power mixer, at which temperature the blowing agent begins to foam even when the compound is at or near a molten state. . If the blowing agent is added just before the batch reaches its discharge temperature, the amount of foaming will be minimal in a high-power mixer, and as soon as the heated batch is discharged, most of the foam will be formed and formed into the desired shape. . The foaming process of the present invention can be applied to other known methods,
It can also be supplied to various shaping means, but in this case it is necessary to add a heating step and foam in the heating step. Various changes may be made to the method defined herein without departing from the scope of the invention as defined by the claims.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an intensive mixer and mold suitable for carrying out the method of the invention. 10...Powerful mixer, 11...Mixing chamber, 12
... blade, 13 ... arm, 14 ... shaft, 15 ... inlet port, 18 ... discharge flap, 20 ... mold, 21 ... lid.

Claims (1)

[Claims] 1. A method for producing a thermoplastic foam molded article from a granular thermoplastic resin, the method comprising: intensively mixing a granular composition consisting of a granular thermoplastic resin and a blowing agent, and then using thermal motion; heating and gas evolution at the trigger temperature of the blowing agent to produce a foam, the mixing and heating being carried out by mixing the particulate composition in a closed mixing chamber; has a plurality of blades attached to an arm, the arm rotating at a speed of about 18 meters per second or more at the tip of the blade, to continue mixing the particulate composition in the closed container, and the particulate composition The particulate composition is heated to a mixing temperature equal to or higher than the trigger temperature of the blowing agent, at which the granular composition is sufficiently melted, and the molten composition has sufficient viscosity to contain the gas generated by the blowing agent. and when the molten composition reaches the mixing temperature and the blowing agent begins to produce foam, the molten composition is discharged from the mixing chamber, the discharged molten composition is fed into a mold, and the mold is 1. A method for producing a foamed plastic product, comprising the steps of: trapping a composition in a mold; molding the composition while foaming; and forming a foamed plastic molded article in a mold. 2. A method according to claim 1, wherein the blowing agent and the granular resin are simultaneously charged into the mixing chamber. 3. The method of claim 1, wherein the blowing agent is present in the composition at about 0.5-1.2% by weight. 4. The method of claim 1, wherein the particulate resin is a resin selected from the group consisting of polyvinyl chloride and low density polyethylene. 5. The method of claim 4, wherein the blade tip speed is about 31-38 meters/second. 6. The method of claim 4, wherein the blowing agent is selected from the group consisting of azodicarbonamide and para-oxybis(benzenesulfonylhydrazide). 7. The method of claim 5, wherein the mixing temperature is about 190-240<0>C. 8. The method of claim 7, wherein the mixing and heating is carried out for about 7-20 seconds. 9. The method of claim 1, wherein the composition is confined in a mold to which a pressure of 550-2200 kilopascals is applied. 10. The method of claim 1, wherein the composition is confined in a mold for a maximum of 5 minutes under said pressure. 11. The method of claim 1, wherein the blowing agent is charged into the mixing chamber after charging the particulate resin.