JPH0365834B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to acrylic emulsions for use as water-based strippable paints. Strippable paint is a removable coating used to temporarily protect the surface of an article. In recent years, metal plates such as steel plates, galvanized steel plates, aluminum plated steel plates, stainless steel plates, and aluminum plates, pre-coated surface-treated metal plates, other metal products, wood products, plastic products, glass products, rubber products, etc. For temporary surface protection of various products, for example, prevention of damage, contamination, or corrosion during transportation or storage, protection of processed and unprocessed surfaces during press processing, and shielding of non-painted surfaces during surface painting ( The demand for strippable paint is increasing because of masking). PVC organosol has been the most common conventional strippable paint, but PVC organosol has the following problems: (a) It is solvent-based, so there are concerns about pollution, poisoning, and ignition; (b) PVC sol contains Large amounts of plasticizers and solvents may cause discoloration and stains on coated steel plates (so-called pre-coated steel plates, etc.); (c) On base materials such as unpainted steel plates and stainless steel plates, PVC may decompose. The disadvantages were that the generated hydrochloric acid gas caused rust and the film could not be peeled off. Therefore, when masking these metal plates and surface-treated metal plates, a water-based strippable paint that covers these defects is desired. However, the line speed of the coating process is generally very fast (approximately 50 ~
200 m/min), the drying time is extremely short (generally 30 to 90 seconds), and therefore the drying temperature has to be high (1800°C to 300°C). When coating with conventional emulsion paints, bumping of water occurs in the drying oven, causing foaming and holes on the surface of the formed film, making it impractical. In addition, from the viewpoint of secondary workability of steel sheets, PVC has been widely used because its film is stronger and has a suitable elongation, making it easier to process than acrylic. In the present invention, the temperature is 100℃ or higher (generally 150℃~
Even when immediately passed through a drying oven at 250℃),
It is excellent as a strippable paint because it produces a clean film with no bubbles or holes after drying, has film strength and elongation comparable to PVC film, and has adhesion properties that allow it to be easily peeled off from various materials. The purpose of this invention is to provide an acrylic emulsion with a high quality. That is, the present invention provides: (1) a) Tg of an acrylic resin containing 35 to 50% by weight of AN (acrylonitrile) in the total copolymerized monomers;
Acrylic emulsion () whose temperature is -25℃ to +10℃ and (b) AN are copolymerized at 15 to 15% of all monomers.
Tg of acrylic resin containing less than 35% by weight is -
It must be an acrylic emulsion obtained by blending acrylic emulsion () with a temperature of 15°C to +20°C, (2) The blend of acrylic emulsion () and acrylic emulsion () is based on the weight ratio (in terms of resin content). ) is 90:10 to 30:70, and the Tg of the acrylic resin () after blending is -10°C to +10°C, and (3) the acrylic emulsion () and (2) is an acrylic emulsion characterized in that when it is produced by emulsion polymerization, a water-soluble polymer is used in an amount of 0.01 to 5% by weight based on the total monomers during polymerization. The details of the present invention will be explained below. The acrylic resin, which is a mixed component constituting the paint of the present invention, is an acrylic copolymer resin containing acrylonitrile as an essential component.
35 to 50 wt% in acrylic resin (), and less than 15 to 35 wt% in acrylic resin (). If the content of acrylonitrile is too small, the adhesion will be too strong, the peelability will deteriorate, and the film will not have sufficient strength. or,
If the amount is too high, the film becomes too hard and easily breaks, resulting in poor workability. If the amount exceeds 50%, film forming properties will deteriorate and it will be difficult to obtain a uniform film simply by drying. If acrylonitrile is not used, adhesion that allows easy peeling cannot be obtained even if the Tg is the same. In addition, the Tg (glass transition temperature) of acrylic resin is
The temperature is preferably -25°C to +10°C for acrylic resin (), and -15°C to +20°C for acrylic resin (2). When Tg is low, the film becomes soft and peelability deteriorates. Also, as the Tg increases, the film becomes harder and more likely to tear, resulting in poor removability.
Furthermore, parts of the paint may peel off or tear during press processing, and may be scratched by the press mold, making it unsuitable as a strippable paint. Tg can be adjusted by combining copolymerizable monomers. These copolymerizable monomers other than acrylonitrile include, in the case of acrylic resin (), based on 35 to 50 parts by weight of acrylonitrile,
One or more types of copolymerizable non-functional monomers (A) such as acrylic esters or methacrylic esters
64 to 40 parts by weight, capable of copolymerizing acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic anhydride, acrylamide, methacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, hydroxyacrylate, hydroxymethacrylate, etc. Functional group monomer (B) 1
~10 parts by weight can be used. In addition, in the case of acrylic resin (), 15 to less than 35 parts by weight of acrylonitrile, 84 to 55 parts by weight of the above-mentioned copolymerizable non-functional monomer (A), 1 part by weight of the above-mentioned copolymerizable functional group monomer (B) ~10 parts by weight can be used. Note that styrene may be included as a part of the non-functional monomer (A). Although it is not necessary to use the functional group monomer (B), by using it,
The storage or mechanical stability of the emulsion is improved. Acrylic resin () and acrylic resin () are each manufactured by an emulsion polymerization method, but during polymerization, 0.01 to 5 parts by weight of a water-soluble polymer is used as a protective colloid based on 100 parts by weight of the total copolymerized monomer. , it is necessary to carry out the polymerization. In this case, if emulsion polymerization is carried out using only a normal emulsifier without using a water-soluble polymer, a clean film without foaming or holes cannot be obtained when dried. The water-soluble polymer is preferably used in the early stage of polymerization, and a common emulsifier (surfactant) may be used in the latter stage of polymerization. As the water-soluble polymer, high-molecular polysaccharides and polyvinyl alcohol are preferred. Examples of high-molecular polysaccharides include hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, and carboxymethylcellulose. If the amount of the water-soluble polymer is less than 0.01 parts by weight, the protective colloid properties will be poor, and if it exceeds 5 parts by weight, gelation will occur easily during polymerization and the water resistance of the film will deteriorate. The nonvolatile content (resin content) of the acrylic emulsion to be polymerized is not particularly limited, and may be at a general concentration. Generally, the resin content when polymerizing acrylic emulsion is 30 to 55% by weight as the final product.
There are many types, and in the present invention, polymerization may be carried out within these ranges, but there is no particular limitation. The lower the concentration during polymerization, the better the polymerization stability.
Polymerization can be carried out even at a concentration of 20%, but drying properties become worse due to the increased moisture content. On the other hand, there is a method of increasing the resin content by concentrating after polymerization, but this is not common because it increases the manufacturing cost. However, there is no problem in polymerizing the acrylic emulsion of the present invention by these methods, and products with good polymerization stability can be obtained. However, if the effects of the present invention are to be expected, the resin content of acrylic emulsion (2) and acrylic emulsion (2) may be different as long as they are blended in terms of resin content. The weight ratio (resin content equivalent) of the acrylic resins () and () obtained in this way is ()/()=
They may be mixed in a ratio of 90/10 to 30/70, and the resulting acrylic emulsion may be used as the strippable paint of the present invention. When only acrylic emulsion (2) is used, the film is hard and has poor workability, while when only acrylic emulsion (2) is used, the adhesion is so good that there is a risk that it will not peel off later. More preferable results can be obtained when the acrylonitrile contents of the acrylic resins () and () to be mixed are different from each other by 5% by weight or more. The acrylic resin () constituting the acrylic emulsion after blending must have a Tg of -10°C to +0°C. Tg is −10
If the temperature is below +10°C, the peelability will be poor, and if it exceeds +10°C, the processability will deteriorate. As described above, the present invention provides suitable limitation by mixing an acrylic emulsion (2) with a high acrylonitrile content and a relatively low Tg and an acrylic emulsion (2) with a low acrylonitrile content and a relatively high Tg. Within this range, an acrylic emulsion with a good balance of film strength and elongation, releasability and adhesion can be obtained, and by using a water-soluble polymer as a protective colloid in the early stage of polymerization, it can be used even in high-temperature, short-time drying lines. A practical and excellent water-based strippable paint that does not cause water bumping, foaming on the surface, or pinholes was obtained. The appropriate range of acrylonitrile content and Tg of acrylic resins (), () and () is shown in FIG. The shaded area indicates the compositional constituent parts of the acrylic resin ( ) obtained after blending. . It should be noted that commonly used additives such as thickeners, film-forming aids, antifoaming agents, etc. may be added to the paint. Furthermore, although the present invention was manufactured with the aim of drying emulsion paints for a short time at 100°C or higher, which was previously impossible, it is possible to form a film from emulsion even at a drying temperature of 100°C or lower. If it is dried at 70°C for 5 minutes, it can fully fulfill its role as a strippable paint. Therefore, it can be used without any problem even under such conditions. This will be explained in more detail below with reference to Examples. Parts in the examples are parts by weight. Example 1 600 parts of water and 1 part of hydroxyethylcellulose were placed in a flask No. 2 equipped with a thermometer, reflux condenser, stirrer, and monomer charger, and the temperature was raised to 80°C. After adding 5 parts of potassium persulfate, about 1/10 of a mixture of 400 parts of acrylonitrile, 580 parts of butyl acrylate, and 20 parts of methacrylic acid was fed into the flask and polymerized for 30 minutes. Add 2 parts of DBS (sodium dodecylbenzene sulfonate) to the remaining monomer and further add 400 parts of water to emulsify. The emulsified monomer was continuously added dropwise into the flask over a period of 3 hours, and the reaction was then continued for an additional 3 hours at the same temperature to complete polymerization, yielding an acrylic emulsion (). Separately, in the same manner, the monomer composition was changed to 240 parts of acrylonitrile, 240 parts of methyl methacrylate,
An acrylic emulsion () containing 500 parts of butyl acrylate and 20 parts of methacrylic acid was obtained. A mixture was obtained by mixing 500 parts of acrylic emulsion (2) with 500 parts of acrylic emulsion (2), and adding a small amount of antifoaming agent. Apply this resin to a polyester-coated steel plate using a #60 bar coater, 180℃×1 minute, 200℃×40℃.
The drying properties were tested under three conditions: 2 seconds, and 250°C x 20 seconds. In addition, for film strength and elongation, after coating in the same manner as above, dry at 180℃ x 1 minute,
This was peeled off to obtain a test film. Separately, apply it to stainless steel plate (SUS304), acrylic coated steel plate, polyester coated steel plate, and heat it at 180℃.
After drying for several minutes, a test piece whose surface was coated with the acrylic film of the present invention was obtained. Various tests were conducted on this test piece. These results are shown in Table 1. The film strength and elongation rate are both higher than that of the vinyl chloride organosol (Comparative Example 5), and the drying properties are also good, with no foaming or pinholes. Compared to conventional PVC organosol, it has extremely good weather resistance, has little change in adhesion, and does not rust on stainless steel. The test method is as follows. Drying property: The presence or absence of foaming and pinholes was visually determined under the three conditions listed. Film strength and film elongation: The film obtained by drying at 180° C. for 1 minute was measured using a Tensilon tensile tester. Adhesion: Measured by a peeling test at 180°C at a peeling rate of 100 mm/min. Peelability after drawing: of an actual stainless steel sink

【table】

[Table] Processing was performed and peelability was observed. Weather meter: Measured the adhesion strength after being left for 100 hours. Ultraviolet irradiation: Irradiate with a germicidal lamp 30cm apart for 3 days.
The adhesion force was measured. Further, the symbols in the copolymer composition are as follows. AN: Acrylonitrile MMA: Methyl methacrylate BA: Butyl acrylate MAC: Methacrylic acid HEC: Hydroxyethyl cellulose DBS: Sodium dodecylbenzenesulfonate EA: Ethyl acrylate PVA: Polyvinyl alcohol DOP: Dioctyl phthalate MEK: Methyl ethyl ketone Ethyl acetate: Ethyl acetate Example 2 Polyvinyl alcohol is used as the water-soluble polymer. The same procedure as in Example 1 was conducted except that the copolymerization composition and blend ratio were changed. Comparative Example 1 Only the acrylic emulsion () of Example 1 was used as an aqueous strippable paint. The film peels off more easily than necessary, and the film is hard and has poor workability, so it cannot be used alone as a strippable paint. Comparative Example 2 Only the acrylic emulsion () of Example 1 was used as an aqueous strippable paint. It has strong adhesion and cannot be peeled off, so it cannot be used alone as a strippable paint. Comparative Example 3 Acrylic emulsion () Instead of mixing () and (), the monomers constituting () and () were combined and emulsion polymerized in a single product type. The adhesion strength changes significantly before and after the drawing process, making it difficult to peel and having low strength, making it impossible to use as a strippable paint. Comparative Example 4 Emulsion polymerization was carried out without using a water-soluble polymer, and the copolymer composition was the same as in Example 1, but foamed over the entire surface during drying, making it unsuitable for high-temperature, short-time drying. Comparative Example 5 This is a conventional vinyl chloride organosol type strippable paint. There are deficiencies in weather resistance. As detailed above, the strippable paint of the present invention is water-based and does not cause pollution, poisoning, flammability, discoloration, staining, rust, etc. due to the presence of solvents or plasticizers, and is especially suitable for use at high line speeds. It is a strippable paint with extremely good paintability, with no foaming or pinholes during the coating process.

[Brief explanation of drawings]

FIG. 1 is a graph showing the compositions of acrylic resins (), () and blended acrylic resins ().

Claims (1)

[Claims] 1 Acrylonitrile copolymerized from 35 to 35% of all monomers
50% by weight, the Tg of the acrylic resin () obtained by copolymerization is -25℃ to +10℃, and when copolymerization is carried out by emulsion polymerization, a water-soluble polymer is added to all monomers as a protective colloid. Acrylic emulsion () containing 90 to 30 parts by weight (resin content equivalent) containing 0.01 to 5% by weight of acrylonitrile and 15 to less than 35 parts by weight of the total monomers to be copolymerized. The Tg of the acrylic resin () is -15℃ to +20℃, and when copolymerization is carried out by emulsion polymerization, 0.01 to 5% by weight of water-soluble polymer is used as a protective colloid based on the total monomers. A certain acrylic emulsion () 10~
Acrylic emulsion () obtained by mixing 70 parts by weight (resin content equivalent) to a total of 100 parts by weight (acrylic resin solid content), which contains acrylonitrile in all copolymerized monomers of the acrylic emulsion (). The content is 5 to 35% by weight higher than the acrylonitrile content in all the copolymerized monomers of the acrylic emulsion (), and the Tg of the acrylic resin () constituting the acrylic emulsion () is -10.
Water-based strippable paint with temperatures between ℃ and +10℃.