JP4963602B2 - Method for producing methacrylic resin plate - Google Patents

Description

  The present invention relates to a method for producing a methacrylic resin plate using a stainless steel plate as a mold.

As a method for producing a plate-like polymer by cast polymerization, a polymerizable unsaturated simple substance mainly composed of methyl methacrylate is formed on a mold made of a pair of inorganic glass or metal plate whose four sides are sealed with a gasket such as polyvinyl chloride. A cell casting method in which a syrup as a polymer is injected and polymerized in a mold to obtain a plate polymer, two mirror-polished stainless steel steel endless belts arranged opposite to each other and both sides thereof There is a continuous plate making method in which a methacrylic resin plate is obtained by continuously injecting and polymerizing a syrup into a mold that is sealed with a gasket sandwiched between belts at the sides. Compared with the cell casting method of batch operation, the cost can be reduced by rationalization, and the thickness of the plate can be easily made constant. Therefore, many products except special applications are manufactured by the continuous plate method. ing.
In these plates, when peeling the molded plate after polymerization from the mold, there is a case where adhesion is too strong and it may not be peeled easily, so a release agent is mixed with the raw material for the purpose of promoting peeling. The peelability is improved (see Patent Document 1).

  However, when a large amount of release agent is mixed, the release agent adheres to the mold surface and causes mold contamination, or the release agent attached to the surface of the mold accumulates, resulting in irregularities on the mold surface. Concavities and convexities may be transferred to the outermost layer of the resin, leading to a decrease in transparency, which is a characteristic of methacrylic resin. When such a problem occurs, a mirror polishing process is performed on the mold surface, but the mirror polishing process requires a long time.

Furthermore, in the continuous plate manufacturing method using a stainless steel plate endless belt as a mold, the peeling between the stainless steel plate and the methacrylic resin plate is very poor in the initial production after the mirror polishing process, and the methacrylic resin plate is deformed or cracked. As a result, defective products frequently occur and a lot of waste is generated. For this reason, a large amount of release agent must be added at the initial stage of production, resulting in a vicious circle in which the release agent contaminates the stainless steel plate surface. Under these circumstances, production by continuous plate making has been carried out for many years, and a method for improving the peelability has also been desired from the viewpoint of stabilizing quality and reducing waste (waste materials). It was. The deterioration of peelability occurs not only after mirror polishing of the surface of the stainless steel plate but also during production using a new (unused) stainless steel plate.
Japanese Patent Publication No. 47-13147

  The object of the present invention is to improve the releasability between the mold and the methacrylic resin plate when using a stainless steel plate as a mold, to avoid the trouble of peeling failure that occurs in the initial stage of production after mirror polishing, and to reduce waste materials and The present invention provides a method for producing a stable and excellent methacrylic resin plate.

  As a result of diligent research to achieve the above-mentioned object, the present inventors have analyzed the surface of the stainless steel plate after mirror polishing by XPS (X-ray photoelectron spectrometer) and a passive film on the surface of a new stainless steel plate. It was found that the Fe content in the steel was higher than the Fe content in the passive film on the surface of the stainless steel plate when the peelability was stable. That is, in the initial stage of production, a part of Fe in the passive film of stainless steel dissolves in the unsaturated monomer mixture mainly composed of methyl methacrylate, but as the polymerization is repeated using the stainless steel sheet, the Fe content increases. It was estimated that dissolution would stop. The reason why the dissolution of Fe deteriorates the releasability is not clearly clarified, but it is presumed that the molecular weight of the methacrylic resin plate in contact with the stainless steel plate is lowered due to the influence of this Fe on the polymerization behavior. .

  Therefore, as a result of studies to reduce the Fe content on the surface of a new stainless steel plate after mirror polishing to the Fe content in the passive film on the surface of the stainless steel plate when the peelability is stable, the stainless steel plate was etched. It has been found that the releasability is improved by immersing in a liquid to perform a cleaning treatment and lowering the Fe content, resulting in the present invention.

  That is, the present invention uses a stainless steel plate having a Fe / Cr ratio in the surface passive film of 0.4 or more and 1.2 or less as a mold by etching treatment, and methyl methacrylate monomer alone in the mold, Alternatively, it is a method for producing a methacrylic resin plate obtained by polymerizing a monomer mixture of methyl methacrylate and another vinyl monomer copolymerizable therewith to form a plate-like molded product.

  The peelability between the stainless steel plate and the methacrylic resin plate can be improved by etching the surface of the stainless steel plate serving as a mold. That is, it is possible to avoid the trouble of peeling failure occurring in the initial stage of production after the mirror polishing process, and it is possible to produce a methacrylic resin plate which is reduced in waste material and stable and excellent in quality.

  In the present invention, a mold made of a stainless steel plate whose sides are sealed with a gasket or the like, a methyl methacrylate monomer alone, or a monomer mixture of methyl methacrylate and another vinyl monomer copolymerizable therewith. And polymerized in the mold to obtain a methacrylic resin plate as a plate.

  Examples of the material of the stainless steel plate used as a mold in the present invention include austenite (SUS304, SUS316, etc.), ferrite (SUS430, etc.), and martensite (SUS403, etc.). Among these, an austenitic system is preferable from the viewpoint of corrosion resistance.

  The method for reducing the Fe content in the passive film on the surface of the stainless steel plate that has been mirror-polished is, for example, a method of etching with an acidic solution, or reducing the Fe content by promoting the oxidation of Cr in the passive film. Examples of the method include a known method such as a method of immersing in a non-oxidizing aqueous solution in which ozone is dissolved, or a method of heating a stainless steel plate to 300 ° C. or higher, but the present invention does not require large-scale equipment. An etching method is used. The etching solution used for the etching treatment is preferably an acidic solution described later. Incidentally, the mirror polishing of the surface of the stainless steel plate is preferably performed by mirror polishing by mechanical polishing using a polishing cloth and an abrasive and buffing.

  As described above, the Fe content in the passive film on the stainless steel plate surface can be reduced by etching the stainless steel plate surface, but the Fe / Cr ratio in the passive film on the stainless steel plate surface is 0.4 or more. It is necessary to make it 1.2 or less. If it exceeds 1.2, the effect of improving the peelability intended by the present invention cannot be obtained, and if it is less than 0.4, the mechanical strength of the stainless steel may be lowered.

  The Fe / Cr ratio can be obtained by a known method such as analysis using XPS which is one of surface analyzers.

  Examples of the etching solution used for the etching treatment in the present invention include nitric acid, sulfuric acid, perchloric acid, and hydrogen peroxide. Among them, nitric acid has a function as an acid for eluting Fe and a function as an oxidizing agent. Therefore, it is particularly preferable from the viewpoint of easy handling of the solution.

  As for the etching solution, the pH value may be controlled by changing the concentration as an aqueous solution. Specifically, it is preferably adjusted to a pH value of 1 to 4, more preferably adjusted to a pH value of 2 to 3. When the pH value is 1 or more, only Fe in the passive film is eluted and Fe in the substrate is not eluted. On the other hand, when the pH value is 4 or less, the elution of Fe in the passive film is sufficiently performed.

Further, for the purpose of effectively reducing the Fe content in the passive film, a fluoride can be added to the etching solution to obtain an aqueous nitric acid solution containing fluoride.
Examples of the fluoride include hydrogen fluoride, lithium fluoride, sodium fluoride, and potassium fluoride. Among them, sodium fluoride and potassium fluoride are preferable from the viewpoint of easy handling.

The concentration of fluoride is preferably 1 × 10 ⁻² mol or less, and more preferably 1 × 10 ⁻³ mol to 8 × 10 ⁻³ mol so as not to impair the surface state of the substrate.

  The etching solution containing fluoride is preferably adjusted to a pH value of 1 or less (0.1 molar concentration or more).

  Furthermore, for the purpose of forming a dense passive film on the surface of the stainless steel plate, the Fe content in the passive film can be lowered and then immersed in an aqueous nitric acid solution. In this case, the concentration of the nitric acid aqueous solution is preferably 6 to 8 molar.

  The temperature of the etching solution is not particularly limited. However, since elution of Fe in the passive film can be promoted at a high temperature, it is preferably 35 ° C. or more and 90 ° C. or less, and 50 ° C. or more and 90 ° C. or less More preferably, it is more preferably 60 ° C. or higher and 70 ° C. or lower. The temperature of the etching solution containing fluoride is preferably 35 ° C. or higher and 70 ° C. or lower.

  The immersion time of the etching solution is preferably at least 30 minutes, more preferably 1 to 2 hours.

  By doing in this way, the content rate of Fe in a passive film falls, and the elution can be suppressed as a result.

  The monomer used as a raw material in the present invention is a methyl methacrylate monomer alone or a monomer mixture of methyl methacrylate and another vinyl monomer copolymerizable therewith.

  Other vinyl monomers copolymerizable with methyl methacrylate are, for example, ethyl methacrylate, isopropyl methacrylate, t-butyl methacrylate, s-butyl methacrylate, n-butyl methacrylate, amyl methacrylate, octyl methacrylate, Methacrylic acid esters other than methyl methacrylate such as 2-ethylhexyl methacrylate, lauryl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate; methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, acrylic Acrylic acid such as t-butyl acid, amyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, etc. Ters; vinyl aromatics such as styrene, α-methyl styrene, paramethyl styrene, isopropenyl styrene, vinyl toluene; unsaturated nitriles such as acrylonitrile, methacrylonitrile; methacrylic acid, acrylic acid, maleic anhydride, etc. Unsaturated carboxylic acids; polyunsaturated compounds such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and divinylbenzene. However, it is not limited to these, and these can be used alone or in combination of two or more. Here, “(meth) acrylate” means “methacrylate” or “acrylate”.

  The composition ratio of the monomer that is a raw material of the methacrylic resin plate of the present invention is 60 to 100% by mass of methyl methacrylate from the viewpoint of maintaining the original physical properties of the methacrylic resin obtained by polymerization, and other copolymerizable with this. The vinyl monomer is preferably 40 to 0% by mass, more preferably 95 to 100% by mass of methyl methacrylate and 5 to 0% by mass of another vinyl monomer copolymerizable therewith.

  In the present invention, the above-mentioned monomer or monomer mixture is used for cast polymerization, but instead of the monomer, a mixture of the monomer and its polymer (hereinafter referred to as “syrup”). There is no problem even if it is subjected to polymerization.

  Examples of the polymerization initiator that can be used for polymerization of the monomer or monomer mixture or syrup include azo polymerization initiators such as azobisisobutyronitrile and azobisdimethylvaleronitrile, benzoyl peroxide, and t-butyl. And organic peroxides such as peroxy 2-ethylhexanoate and t-hexyl peroxypivalate.

  In the polymerization, a molecular weight regulator is used as necessary. Examples of the molecular weight regulator include alkyl mercaptans such as n-butyl mercaptan, n-dodecyl mercaptan and octyl mercaptan.

  Although the polymerization temperature varies depending on the type of polymerization initiator used, it is preferably 40 to 140 ° C. from the viewpoint of ease of control of the polymerization reaction, productivity, etc. In that case, the first stage is 40 to 140 ° C. It is more preferable to perform polymerization at a two-stage polymerization temperature of 90 ° C. and the second stage of 100 to 140 ° C.

  In the polymerization, various additives used in producing a normal methacrylic resin or a modified product thereof can be added. Additives include dyes, pigments or antioxidants used for coloring, stabilizers such as ultraviolet absorbers or flame retardants, release agents that facilitate the release of molds from plasticizers or resin castings, chain transfer agents , A crosslinking agent, etc.

  After polymerization, a methacrylic resin plate can be obtained by peeling off the obtained plate-shaped molded product from the mold.

  Hereinafter, the present invention will be described specifically by way of examples.

  The method for obtaining the Fe / Cr ratio in the passive film on the surface of the stainless steel plate after the etching treatment with the aqueous nitric acid solution carried out in the Examples is 200 W monochrome X-ray source (AlKα), Pass Energy by XPS (ESCA LAB220iXL manufactured by VG). The measurement was performed under the condition of 200 eV (narrow scan), and the obtained Fe2p3 / 2 peak area (integrated) value was divided by the Cr2p3 / 2 peak area (integrated) value to obtain the Fe / Cr ratio. In the XPS measurement, ultrasonic cleaning was performed for about 30 minutes by dipping in an acetone solvent at 25 ° C. for the purpose of removing contaminants adhering to the surface of the stainless steel plate as a test piece.

[Production example]
Methyl methacrylate containing 1000 ppm of azobisdimethylvaleronitrile as a polymerization initiator and 650 ppm of n-dodecyl mercaptan as a molecular weight regulator is supplied to a glass container equipped with a stirrer and a reflux condenser. Holding for a minute, a syrup having a polymerization rate of about 22% by mass and a viscosity at 70 ° C. of 1500 mPa · s was obtained.

  A polymerizable composition was prepared by adding 0.22 g of t-hexyl peroxypivalate as a polymerization initiator and 0.005 g of sodium di (2-ethylhexyl) sulfosuccinate as a release agent to 100 g of this syrup.

[Example 1]
An unused stainless steel plate (material: SUS304) that was mirror-polished as a mold was immersed in an aqueous nitric acid solution adjusted to a pH value of 2.3, and etched with warm water at 60 ° C. for 2 hours. In addition, as the mirror polishing treatment, mirror polishing was performed by mechanical polishing using a polishing cloth and an abrasive and buff polishing.

  After the etching treatment, the nitric acid aqueous solution on the stainless steel plate surface was washed with distilled water and dried by blowing dry air.

  A mold composed of one stainless steel plate obtained in this way, one tempered glass of the same size, and a gasket made of polyvinyl chloride disposed between the opposing surface sides. The polymerizable composition obtained in the production example was injected, polymerized for 30 minutes in an 80 ° C. water bath, and subsequently polymerized for 30 minutes in a 110 ° C. hot air thermostat.

  After taking out from the thermostat and peeling off the tempered glass quickly, the obtained plate-like molded product (molded plate) was peeled off from the stainless steel plate.

  Evaluation of peelability is ○, which can be done without requiring force when peeling the molded plate from the mold, △ which peels, but that which requires force, △, which does not peel or is difficult to peel and is molded in the middle of peeling The thing which the board broke was evaluated as x. The results are shown in Table 1.

[Example 2]
A stainless steel plate (material: SUS304) used for several years in cast polymerization was subjected to mirror polishing similar to that in Example 1 and immersed in an aqueous nitric acid solution having a pH value of 2.3 (0.005 molar concentration). Etching was performed for 2 hours with 60 ° C. warm water.

  After the etching treatment, the nitric acid aqueous solution on the stainless steel plate surface was washed with distilled water and dried by blowing dry air to obtain a stainless steel plate polymerization mold.

  Using the polymerizable composition obtained in the production example, a molded plate was obtained under the same conditions and techniques as in Example 1, and peeling evaluation was performed. The results are shown in Table 1.

Example 3
An unused stainless steel plate (material: SUS304, size: length 610 mm, width 460 mm, thickness 1 mm) that has been mirror-polished as a mold is added to a 1.5 mol concentration nitric acid aqueous solution with 5 × 10 ⁻³ mol of sodium fluoride. It was immersed in a nitric acid aqueous solution prepared so as to have a concentration and etched with warm water at 40 ° C. for 1 hour. Furthermore, it was immersed in the nitric acid aqueous solution prepared to 7.5 molar concentration, and was immersed in 50 degreeC warm water for 1 hour.

  After the etching treatment, the nitric acid aqueous solution on the stainless steel plate surface was washed with distilled water and dried by blowing dry air.

Using the polymerization composition obtained in the production example, a molded plate was obtained under the same conditions and techniques as in Example 1, and peel evaluation was performed. The results are shown in Table 1.
Example 4

A stainless steel plate (material: SUS304, size: length: 610 mm, width: 460 mm, thickness: 1 mm) used for several years in casting polymerization is mirror-polished, and 5 × 10 5 of sodium fluoride is added to a 1.5 molar nitric acid aqueous solution. ^It was immersed in a nitric acid aqueous solution prepared to have a ^-3 molar concentration and etched with warm water at 40 ° C. for 1 hour. Furthermore, it was immersed in the nitric acid aqueous solution prepared to 7.5 molar concentration, and was immersed in 50 degreeC warm water for 1 hour.

  After the etching treatment, the nitric acid aqueous solution on the stainless steel plate surface was washed with distilled water and dried by blowing dry air.

  Using the polymerization composition obtained in the production example, a molded plate was obtained under the same conditions and techniques as in Example 1, and peel evaluation was performed. The results are shown in Table 1.

[Comparative Example 1]
Except for not performing the etching treatment, a molded plate was obtained under the same conditions and method as in Example 1 and evaluated for peeling. The results are shown in Table 1.

[Comparative Example 2]
Except for not performing the etching treatment, a molded plate was obtained under the same conditions and method as in Example 2 and evaluated for peeling. The results are shown in Table 1.

  As shown in the results of the above examples, an unused stainless steel plate and a stainless steel plate that has been mirror-polished after being used for several years in casting polymerization are preliminarily etched with a nitric acid aqueous solution, thereby improving peeling defects. I was able to.

  The methacrylic resin plate obtained by the production method of the present invention has good peelability from a stainless steel plate as a mold and excellent quality, and is suitable for various applications.

Claims (3)

  A stainless steel plate having a Fe / Cr ratio of 0.4 to 1.2 in the passive film on the surface by etching is used as a mold, and the methyl methacrylate monomer alone or methyl methacrylate in the mold, A method for producing a methacrylic resin plate by polymerizing a monomer mixture with another vinyl monomer copolymerizable therewith to form a plate-like molded product.   The method for producing a methacrylic resin plate according to claim 1, wherein the etching solution used for the etching treatment is an aqueous nitric acid solution having a pH value of 1 to 4.   The method for producing a methacrylic resin plate according to claim 1, wherein the etching solution used for the etching treatment is an aqueous nitric acid solution containing fluoride.