Patent Application
20090140454
The present invention relates to an apparatus for continuous plate formation using belts to produce a plate-form product (a plate-form polymer) by continuously polymerizing a polymerizable raw material, and a method of continuous plate formation using belts by using the apparatus.
As a method of continuously producing a plate-form polymer, using methyl methacrylate as a main raw material, there is a continuous casting method using an apparatus for continuous plate formation using belts. This apparatus for continuous plate formation using belts is the apparatus in which a polymerizable raw material is fed to one end of a space between two endless belts facing each other, disposed up and down and provided to run in the horizontal direction at the same speed, and polymerized by a method such as heating along with a movement of the endless belts, and the plate-form polymer is obtained from the other end of the space (for example, refer to Japanese Patent Publication No. Sho 47-33,496).
In a zone where the greater part of a polymerization is carried out in this apparatus for continuous plate formation using belts, the polymerization is carried out while heating and cooling, or heating or cooling running belts being conducted. As a method of heating or cooling, for example, a method of blowing hot air to belt surfaces, a method of scattering warm water on belt surfaces, a method of making belts run in a water bath, and a method of using an infrared heater can be listed. The temperature of heating or cooling may be a fixed ambient temperature throughout the whole zone where the polymerization is carried out or may be changed stepwise or continuously. The temperature of a heating medium should be selected in accordance with a polymerization initiator to be used, however, it needs to be a boiling point of a raw material or below till the greater part of polymerization is carried out. In this step, the method of scattering warm water on the belt surfaces has been frequently used because handling of warm water is easy and heat-transfer coefficient is relatively high in the case of warm water. Further, in a zone after warm water is scattered, generally, the polymerization is completed by raising temperature to a depolymerization temperature of a polymer or below using hot air or an infrared heater.
In the above-mentioned steps, the raw material is heated or cooled to a temperature of a boiling point of the raw material or below in a zone where the greater part of the polymerization is carried out (for example, the foregoing zone where warm water is scattered) because rate of polymerization of the raw material is low, and in a succeeding zone (for example, the foregoing zone where hot air or an infrared heater is used), temperature is raised to fall within a range of from boiling point of the liquid raw material to a depolymerization temperature of the polymer to promptly complete the polymerization. In the following explanation, the latter zone is expressed as a “high-temperature heating zone”, for convenience. Now, in the case that the polymerization initiator is not added or the concentration of the polymerization initiator is lowered for some reason, the polymerization does not occur or retardation of the polymerization occurs. Subsequently, when the raw material enters into the high-temperature heating zone while being in a state of liquid owing to nonoccurrence of the polymerization or retardation of the polymerization, boiling of the liquid raw material occurs, nonreacted monomer and the like are gasified to cause internal pressure of a space sealed with two belts and gaskets to rise, and finally, leakage of gas and a part of the liquid raw material occurs from gaps between the belts and the gaskets. The liquid raw material existing in the space sealed with two belts and gaskets after the leakage forms a foam caused by boiling of the nonreacted monomer.
Such a foaming considerably deteriorates the appearance of plate-form products. Further, the foam strongly adheres to the belts, and it is so difficult to peel the foam from the belts that the time loss becomes large because it is necessary to cautiously operate to peel it so as not to damage the belts. Further, there is a possibility that the leaked gas forms an explosive mixed gas or a flammable mixed gas, and there is a danger of causing explosion or fire in the case that a heat source such as a far infrared heater, which can have a temperature of the ignition point of the gas or above, is used in the zone or in the case that there is a ignition source such as static electricity in the zone.
The present invention has been made to solve the problems of the above-mentioned conventional technology. Namely, it is an object of the present invention to provide an apparatus for continuous plate formation using belts and a method of continuous plate formation using belts, which can stably produce an excellent plate-form product (a plate-form polymer) without causing boiling or foaming of a raw material.
To attain the above-mentioned object, the present inventors firstly have investigated a method of checking whether the polymerization of the raw material is sufficiently performed or not (namely, completion or incompletion of the polymerization) in a stage before the raw material enters into the high-temperature heating zone.
When the polymerization does not occur or retardation of the polymerization occurs, it becomes necessary to carry out an operation such as stopping the belts, causing a temperature of a heating medium in the high-temperature heating zone to become the boiling point of a liquid raw material or below, or lowering a transfer speed of the belts. However, if the completion or incompletion of the polymerization is not checked continuously, it is not possible to take prompt measures in case of an unusual situation. Further, it is possible, for example, to extend a zone where the greater part of the polymerization is carried out or to secure a sufficient residence time in the zone where the greater part of the polymerization is carried out by measures such as slowing down the transfer speed of the belts, on the assumption that the polymerization is retarded, however, it is not good in point of the cost of equipment or productivity. Consequently, it becomes necessary to investigate a method of continuously checking the completion or incompletion of the polymerization.
As a method of continuously checking the completion or incompletion of the polymerization, for example, a method of measuring a peak temperature caused by exothermic heat of polymerization or a method of measuring a volume change caused by polymerization-induced shrinkage can be thought of. However, the method of measuring the volume change is not a practical method because it easily becomes difficult to obtain measurement accuracy of the volume change or it easily becomes impossible to detect the volume change by a slight change of plate thickness of the product at the measuring part caused by very little unevenness in an amount of filling of the raw material. On the other hand, as the method of measuring a peak temperature caused by exothermic heat of polymerization, concretely, a method of measuring the peak temperature by bringing a thermometer into contact with surfaces of the belts can be thought of. However, this is not preferable in point of damages on the belts because it is not always the case, depending on an operational condition, that a polymerization peak position locates on a fixed place, so that many thermometers are needed along the advancing direction of the belts and all these thermometers contact with the belts, which may considerably damage the belts.
The present inventors have carried out the above-mentioned investigations and further have diligently carried out investigations to obtain a result that a plate-form product can be produced while the polymerization peak position is easily detected by using the warm water used to heat or cool the belts, and thus have completed the invention.
Namely, a first aspect of the present invention resides in an apparatus for continuous plate formation using belts, in which a polymerizable raw material is fed to one end of a space surrounded by opposed surfaces of two endless belts facing each other and provided to run in the same direction at the same speed and by continuous gaskets running with the belts in a state being disposed at side edges of these belt surfaces so as to be sandwiched between the surfaces, the polymerizable raw material is polymerized in a section where the belts are heated or cooled with warm water, and a plate-form polymer is taken out of the other end of the space, the apparatus comprising:
three or more recovery vessels for recovering the warm water used to heat or cool the belts; and
temperature sensing elements for measuring the temperature of the warm water recovered in every recovery vessel.
A second aspect of the present invention resides in a method of continuous plate formation using belts, which comprises the step of producing a plate-form polymer from a polymerizable raw material comprising methyl methacrylate while measuring temperature of warm water recovered in every recovery vessel with temperature sensing elements by using the foregoing apparatus for continuous plate formation using belts.
In the present invention, the warm water used to heat or cool the belts is recovered to three or more recovery vessels and a polymerization is carried out while the temperature of the warm water recovered is measured in order to continuously check completion or incompletion of the polymerization. As will be explained later, the polymerization peak in a zone where the greater part of the polymerization is carried out can be continuously and easily detected by using the temperature data. Consequently, for example, when the polymerization of a liquid raw material is ceased or retarded, it is possible to adjust a maximum belt speed so as to previously prevent the liquid raw material from entering into a high-temperature polymerizing zone and cause the polymerization peak to be disposed in the zone where the greater part of the polymerization is carried out, so that safety and productivity are improved and it becomes possible to stably produce a plate-form product (a plate-form polymer).
In the apparatus shown in this figure, tension of two endless belts 1 and 1′ (stainless steel belts or the like) are given by main pulleys 2, 3, 2′, and 3′, respectively, and a lower belt 1′ is started by the main pulley 3′. A polymerizable liquid raw material containing a polymerizable compound is supplied from a raw material nozzle 5 onto a surface of the lower belt 1′.
Each width of the endless belts 1 and 1′ is preferably 500 mm to 5,000 mm, and each thickness thereof is preferably 0.1 mm to 3 mm. Further, it is preferable that the opposingly disposed endless belts 1 and 1′ be horizontally disposed each other.
An upper endless belt 1 runs in the same direction at the same speed as the lower endless belt 1′ does by frictional force through gaskets or a plate-form polymer which will be mentioned later. The running speed thereof is preferably 0.1 m/min to 10 m/min, and is properly changeable according to circumstances such as a plate thickness to be produced and a timing of changing a kind of the raw material. Further, as a retaining mechanism of the belt surfaces, a plurality of pairs of upper and lower rolls 4 and 4′ are provided along the running direction of the belts in such a way that each axis of the roll is set perpendicular to the running direction of the belts.
The polymerizable liquid raw material is transferred together with the running of the endless belts 1 and 1′, and heated or cooled to be polymerized and solidified. At this time, both side edges between the upper and lower belt surfaces are sealed with elastic gaskets 7.
In a zone where the greater part of the polymerization of the raw material is carried out, the endless belts 1 and 1′ are heated or cooled with warm water. The warm water is very advantageous as a heating medium because it is easy to handle and has a relatively high heat transfer coefficient. A method of heating or cooling with the warm water is not particularly limited as long as it can recover used warm water to three or more recovery vessels which will be explained in detail later. Concretely, a method in which the warm water is scattered on the surfaces of the endless belts 1 and 1′ (surfaces being located opposite side to the space containing the polymerizable raw material) is preferable. Further, it is preferable to use warm water sprays 6 and 6′ as shown in
In the apparatus shown in
After the greater part of the polymerization of the raw material is carried out, a zone where temperature is further raised to promptly complete the polymerization (high-temperature heating zone) is provided. This zone corresponds to a section where temperature is further raised by far infrared heaters 8 and 8′ in
In the next place, recovery vessel 13 for recovering the warm water used to heat or cool the belts will be explained.
In
In the present invention, the three or more recovery vessels 13 may be the ones in which each vessel can distinctively recover the warm water at different positions in a running direction of the belts. The recovery vessels 13 shown in
In
The positions where the recovery vessels 13 are disposed are not particularly limited either. For example, in the above-mentioned example, the recovery vessels 13 may also be disposed only on one side of the vicinity of the side edges in the transverse direction of the belts 1 and 1′ as shown in
Further, the three or more recovery vessels 13 may be disposed not only in the whole zone where the greater part of the polymerization is carried out (the section of the warm water sprays 6 and 6′ in
In the present invention, the polymerization is continuously carried out while the temperature of the warm water recovered in every recovery vessel is measured by using the apparatus having the structure explained above. Hereinafter, a method of detecting the polymerization peak will be explained.
The polymerizable raw material is heated, and progressively polymerized and solidified as the endless belts 1 and 1′ run, and a temperature peak caused by exothermic heat of polymerization, namely a polymerization peak, appears. Because the rate of polymerization at the time when the polymerization peak appears is usually 50 to 90% by mass, it is possible to conclude that the polymerization has advanced to a considerable extent if the polymerization peak has appeared. The zone where the polymerization peak appears has high temperature owing to the exothermic heat of polymerization. Therefore, the warm water to be supplied with the warm water sprays 6 and 6′ has a role to cool the belts at the zone. Further, in the zone where the polymerization is carried out, the temperature of the warm water recovered becomes higher than that of the warm water to be supplied owing to the heat transfer from the belts to the warm water. In the zone where the polymerization peak appears, a difference between the temperature of the warm water recovered and the temperature of the warm water to be supplied becomes large as compared with the difference of the temperatures in another zone. Consequently, for example, the polymerization peak position can be known by detecting the zone where the difference between the temperature of the warm water recovered and the temperature of the warm water to be supplied becomes the largest.
To recognize the temperature of the warm water recovered as a peak, it is necessary to judge by comparing temperature data of the zone corresponding to the polymerization peak position with temperature data of zones other than that. Concretely, it is preferable to recognize each existence of the starting point, the peak point, and the end point of a temperature rise by at least three recovery vessels. This will be explained in the following by using figures.
a) is a graph in which a value obtained by subtracting the temperature of the warm water to be supplied from the temperature of the warm water to be recovered (temperature difference) is plotted for every recovery vessel in the case of using three intermittently disposed recovery vessels. In this example, the temperature difference with regard to the warm water recovered in the center recovery vessel is the largest, and hence, it is recognized that the polymerization peak is located around the position of the center recovery vessel.
b) is a graph showing another example in the case of using the same three recovery vessels as in the case of
c) is a graph showing another example in the case of using the same three recovery vessels as in the case of
As explained above, it is possible to recognize the polymerization peak position easily, to promptly cope with unusual situations, and to realize a stable production step, by disposing three or more recovery vessels for recovering the warm water used to heat or cool the belts along the running direction of the belts, and by measuring the temperature of the warm water recovered in every recovery vessel. In the above explanation, the example in the case of the three recovery vessels was explained, however, it is possible to detect the position of the polymerization peak more clearly if the number of the recovery vessels is increased. However, this is disadvantageous in the cost of equipment because the total number of the recovery vessels and temperature sensing elements equipped with them increases. From these respects, it is preferable that the number of the recovery vessels be about 5 to 20. Further, it is preferable that a length and an interval for disposition of each recovery vessel along the running direction of the belts in the case of intermittently disposing three or more recovery vessels along the running direction of the belts, or a length of each recovery vessel along the running direction of the belts in the case of continuously constructing three or more recovery vessels by dividing a long vessel (refer to
The raw material of a plate-form polymer can be properly selected in accordance with a target plate-form polymer. The apparatus for continuous plate formation of the present invention is particularly suitable for producing a methacrylic resin plate using methyl methacrylate as a main raw material. In the case of producing the methacrylic resin plate, it is preferable to use a polymerizable raw material containing 50% by mass or more of methyl methacrylate. As a representative polymerizable raw material, methyl methacrylate alone or a mixture of methyl methacrylate and another copolymerizable monomer can be listed; further, a syrup obtained by dissolving methyl methacrylate polymer in methyl methacrylate or its mixture, or a syrup in which part of methyl methacrylate or its mixture is previously polymerized can also be listed.
As the other copolymerizable monomer, for example, an acrylate such as methyl acrylate, ethyl acrylate, n-butyl acrylate, or 2-ethylhexyl acrylate; a methacrylate other than methyl methacrylate such as ethyl methacrylate, n-butyl methacrylate, or 2-ethylhexyl methacrylate; or vinyl acetate, acrylonitrile, methacrylonitrile, or styrene can be listed. In the case of syrup, it is preferable that the syrup be prepared to have polymer content of 50% by mass or less in consideration of the fluidity of the polymerizable raw material.
A chain transfer agent can also be added to the polymerizable raw material, when it is needed. As the chain transfer agent, for example, a primary, secondary, or tertiary mercaptan having an alkyl group or a substituted alkyl group can be used. As its concrete example, n-butyl mercaptan, i-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, s-butyl mercaptan, s-dodecyl mercaptan, or t-butyl mercaptan can be listed.
Further, a polymerization initiator is usually added to the polymerizable raw material. As its concrete example, an organic peroxide such as tert-hexyl peroxypivalate, tert-hexyl peroxy-2-ethylhexanoate, di-isopropyl peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, lauroyl peroxide, benzoyl peroxide, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxybenzoate, dicumyl peroxide, or di-tert-butyl peroxide; or an azo compound such as 2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis(1-cyclohexanecarbonitrile), or 2,2′-azobis(2,4,4-trimethylpentane) can be listed.
Further, it is also possible to add various additives, for example, an ultraviolet light absorber, a light stabilizer, an antioxidant, a plasticizer, a dye, a pigment, a mold release agent, and a multilayered acrylic rubber to the raw material, when it is needed. Further, it is also possible to produce an artificial marble plate-form polymer by adding inorganic fillers to the polymerizable raw material.
The thickness of the plate-form polymer to be produced by the present invention is preferably about 0.3 to 20 mm. Hereinafter, the present invention will be explained in more detail by examples, however, the present invention is not limited to these examples. In the following description, “% by mass” is abbreviated to “%” and “part(s) by mass” is abbreviated to “part(s)”.
To 100 parts of methyl methacrylate syrup having a rate of polymerization of 20% (viscosity at 20° C. being 1 Pa·s), 0.1 part of tert-hexyl peroxypivalate (manufactured by NOF CORPORATION, trade name: PERHEXYL PV) as a polymerization initiator, and 0.005 part of dioctyl sodium sulfosuccinate as a mold release agent were added and mixed homogeneously to obtain a polymerizable liquid raw material. The polymerizable liquid raw material was degassed in a vacuum container, and a plate-form product (a plate-form polymer) of 5 mm in thickness and 1,800 mm in width was produced using the apparatus of
In the present example, this apparatus has a total length of 10 m, and two endless belts 1 and 1′ made of stainless steel have a thickness of 1.5 mm and a width of 2 m, and a tension of 30 Mpa is given to both of the upper and lower belts by oil pressure. Further, as gaskets 7, gaskets 7 made of polyvinyl chloride are provided.
Further, this apparatus has 5 m of a heating zone with warm water sprays 6 and 6′ as a zone where the greater part of the polymerization is carried out. Succeeding to the heating zone with the warm water sprays 6 and 6′, the apparatus has 2 m of a heating zone with far infrared heaters 8 and 8′ as a high-temperature heating zone to complete the polymerization. Further, as for recovery vessels, recovery vessels 13 (50 mm in width, 50 mm in length, and 60 mm in height) are disposed in a position of 3 to 5 m from a raw material feeding side and at intervals of 0.2 m in the heating zone with the warm water sprays 6 and 6′ as shown in
Using the apparatus as mentioned above, a plate-form product of 5 mm in thickness and 1,800 mm in width was produced by operating the endless belts 1 and 1′ with a running speed of 130 mm/min and scattering the warm water of 76° C. from the warm water sprays 6 and 6′ to the surfaces of the belts 1 and 1′. Further, at the same time, differences between the temperatures of the warm water to be recovered by ten recovery vessels 13 and the temperature of the warm water to be supplied were plotted to catch hold of a polymerization peak.
From the result shown in
Further, in the production step of the present example, a thermocouple was introduced with the raw material from the end of the belts at the raw material feeding side to measure temperature changes with time of inside liquid of the raw material near the thermocouple and to compare them with positions of the polymerization apparatus for confirmation. As a result, it was confirmed that the peak of exothermic heat of polymerization was located at 4.2 m from the raw material feeding side of the heating zone with the warm water sprays 6 and 6′ and this coincided well with the result shown in
The same procedure as in Example 1 was performed except that the amount of tert-hexyl peroxypivalate, which is a polymerization initiator in the polymerizable raw material, was reduced from 0.1 part to 0.07 part, and a plate-form product of 5 mm in thickness and 1,800 mm in width was produced by operating the endless belts 1 and 1′ with a running speed of 130 mm/min.
Subsequently, the running speed of the endless belts 1 and 1′ was changed to 110 mm/min, and operation was resumed.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2005/013577 | 7/25/2005 | WO | 00 | 4/22/2008 |
