JPH0388813A - Production of emulsion for adhesive - Google Patents

Abstract

PURPOSE:To easily obtain the subject emulsion having excellent cohesivity and adhesivity by polymerizing a specific (meth)acrylic acid ester and a comonomer in an aqueous medium in the presence of a redox polymerization initiator consisting of a peroxide and a reducing agent under specific condition. CONSTITUTION:The objective emulsion can be produced by the emulsion polymerization of (A) 50-95wt.% of a (meth)acrylic acid ester having >=4C alkyl group and (B) 5-50wt.% of other polymerizable monomer copolymerizable with the component A in the presence of (C) a redox polymerization initiator consisting of 0.1-5wt.% (based on the monomer component) of a peroxide and 0.5-5mol (based on 1mol of the peroxide) of a reducing agent. The molar ratio of the reducing agent to the peroxide supplied to the aqueous medium is adjusted to >=5 at an arbitrary stage between the time immediately before the supply of the monomer component to the aqueous medium and the time when the amount of supplied monomer reaches <20wt.% and the molar ratio is successively decreased until the amount of supplied monomer component reaches 80wt.%.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for producing an emulsion for adhesives that has excellent cohesive strength and adhesive strength.

[Prior art J] Water-based emulsion adhesives are highly safe, have no risk of air pollution, and are advantageous in terms of resource conservation, so they have a wider range of applications than organic solvent solution adhesives. is being expanded. In particular, acrylic emulsions have excellent physical properties such as water resistance and weather resistance, and are often used as pressure-sensitive adhesives. In addition, compositions with improved adhesion to polyolefin films and foams by incorporating tackifiers and the like have been developed for use in civil engineering and construction, light electrical appliances, and the like. The basic properties of these adhesives are generally evaluated based on adhesive strength, which is an index of wettability to the substrate, adhesive strength, which indicates resistance when peeled from the substrate, and cohesive strength, which indicates durability and heat resistance. being done. Normally, adhesive strength/adhesive strength and cohesive strength have contradictory tendencies; improving adhesive strength will decrease cohesive strength, and conversely, improving cohesive strength will decrease adhesive strength, so it is necessary to improve both at the same time. It is very difficult to do so. This process includes the introduction of functional monomers, cross-linking agents,
Improvements are being investigated by combining chain transfer agents, etc. On the other hand, in emulsion polymerization using monomers mainly composed of acrylic esters, thermal decomposition reactions such as ammonium persulfate, hydrogen peroxide, azobisamidinopropane hydrochloride, etc. are used as polymerization initiators, or peroxides are used as polymerization initiators. Conventionally, a method using a redox polymerization initiator in combination with a reducing agent such as sodium bisulfite, ascorbic acid, and ferric sulfate has been common. Among these polymerization initiators, especially when using a redox polymerization initiator, there are two methods: adding an aqueous solution of peroxide and reducing agent separately or continuously in accordance with the dropwise addition of the monomer mixture; Add the oxide to the reaction pot in advance,
Although a method of polymerizing while adding a reducing agent together with other components at a relatively low temperature is generally used, studies are also being conducted to improve the physical properties by using a specific polymerization initiator. JP-A No. 58-25378 proposes a method in which a balance between adhesive force and cohesive force can be obtained by combining a specific amount of a water-soluble azo compound polymerization initiator and a chain transfer agent. Furthermore, Japanese Patent Publication No. 54-15076 discloses a method using a specific polymerization initiator and a chain transfer agent under specific polymerization conditions. In general, adding a chain transfer agent in a very small amount can greatly change the cohesive force and adhesive strength, so it is necessary to measure it strictly during manufacturing, and there are problems such as lingering odors. In applications, it is used as a means to improve adhesive strength at the expense of a slight decrease in cohesive strength. [Problems to be Solved by the Invention] The present invention was created in view of these circumstances. Therefore, an object of the present invention is to provide a new method for producing an emulsion for adhesives.As a result of extensive research, the present inventors have found that peroxides constituting a redox polymerization initiator We have discovered that by controlling the ratio of the reducing agent within a specific range, it is possible to improve adhesive strength without using chain transfer agents or special initiators, and without reducing cohesive strength. , the present invention is completed. [Means and effects for solving the problem] That is, the present invention provides 50 to 95% by weight of (meth)acrylic acid ester (a) having an alkyl group having 4 or more carbon atoms and other copolymerizable polymerizable monomers. A polymerizable monomer component consisting of 5 to 50% of polymerizable monomer component (b) (however, the total of (a) and (b) above is 100% by weight) is added in an amount of 0.0% to the polymerizable monomer component. 1
Emulsion polymerization in an aqueous medium using a redox polymerization initiator consisting of a peroxide in an amount of ~5% by weight and a reducing agent in an amount of 0.5 to 5 moles per mole of the peroxide. In this case, the reducing agent and peroxide supplied into the aqueous medium at any time from immediately before the supply of the polymerizable monomer component into the aqueous medium until the supply amount reaches 20% by weight without swirling. The molar ratio is set to 5 or more, and polymerization is performed while successively decreasing the molar ratio of the supplied reducing agent and peroxide until the amount of the polymerizable monomer component supplied reaches at least 80% by weight. The present invention relates to a method for producing an emulsion for adhesives. According to the present invention, it is possible to obtain an adhesive emulsion having excellent adhesive strength and cohesive strength. In the present invention, the (meth)acrylic ester (a) having an alkyl group having 4 or more carbon atoms includes acrylic acid n
Examples include acrylic esters such as -butyl, 2-ethylhexyl acrylate, inoctyl acrylate, and isononyl acrylate, and alkyl methacrylates such as butyl methacrylate, 2-ethylhexyl methacrylate, and dodecyl methacrylate. One type or two or more types can be used. (Meth)acrylic acid ester (a) is used to impart tackiness and initial adhesiveness to the adhesive formed using the adhesive emulsion according to the present invention, and is used in an amount of 50 to 95% by weight in the monomer components. used in range. (meth)acrylic acid ester (a)
If the ratio is less than 50% by weight, the polymer becomes hard and the adhesiveness decreases, which is not preferable. Other copolymerizable monomers (b) used in the present invention are not particularly limited as long as they can be copolymerized with (meth)acrylic acid ester (a), such as acrylonitrile, methacrylate, etc. Unsaturated nitriles such as lyl; hydroxy (meth)acrylates such as hydroxyethyl (meth)acrylate and hydroxypropyl acrylate; vinyl aromatics such as styrene, α-methylstyrene, and vinyltoluene; glycidyl acrylate,
Epoxy group-containing monomers such as allyl glycidyl ether;
Furthermore, carboxyl group-containing monomers such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, or half ester compounds thereof; crosslinking monomers such as divinylbenzene, ethylene glycol diacrylate, methacrylate, and diallyl phthalate: N -Methylol acrylamide, N-methylolmethacrylamide, (meth)acrylamide, etc., and one or two of these can be mentioned.
More than one species can be used. The redox polymerization initiator used in the present invention may be a combination of known peroxides and reducing agents, such as potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, cumene hydroperoxide, One or more peroxides exemplified by lauroyl peroxide, acetyl peroxide, benzoyl peroxide, hydrogen peroxide, etc., and sodium metabisulfite, sodium or potassium birophosphate, sodium formaldehyde sulfoxylate, and ascorbic acid. , tartaric acid, ersorbic acid or its sodium salt, etc., or a combination of two or more thereof can be used. Further, if necessary, heavy metals such as iron, nickel, copper, cobalt, chromium, molybdenum, or cerium in the form of sulfate or chloride can also be used as an activator for the redox polymerization initiator. In the production method of the present invention, the peroxide is used in a proportion of 0.1 to 5% by weight based on the polymerizable monomer component. If the amount used is less than 0.1, the emulsion polymerization reaction will be difficult to proceed, and if it exceeds 5% by weight, the resulting adhesive emulsion will have poor cohesive strength. The amount is preferably 0.2 to 1.0% by weight based on the polymerizable monomer component. The reducing agent is used in a ratio of 0.5 to 5 moles per mole of peroxide. If the amount used is less than 0.5, the effect of using the reducing agent will hardly be recognized, and if it exceeds 5 mol, the emulsion polymerization reaction will be difficult to proceed and the polymerization will become unstable. Preferably 0.5 to 1 mole of peroxide
The ratio is 2.0 moles. The production method of the present invention is characterized by emulsion polymerization of polymerizable monomer components under the following two conditions. That is, (a) a supply amount of less than 20% by weight immediately before supplying the polymerizable monomer component into the aqueous medium, preferably 10% by weight immediately before supplying the polymerizable monomer component into the aqueous medium;
The molar ratio of the reducing agent and peroxide supplied into the aqueous medium at any time during which the supply amount is less than % by weight is 5 or more, and (b) thereafter the supply amount of the polymerizable monomer component is is at least 80
It is an essential requirement that the polymerization be carried out while successively reducing the molar ratio of the reducing agent and peroxide supplied until it reaches % by weight, preferably at least 95% by weight. To describe a specific embodiment of the present invention, an amount equivalent to 50 to 100% by weight of the total amount of reducing agent used in the emulsion polymerization reaction is supplied to the aqueous medium, and if necessary, peroxide is added. A method of supplying the reducing agent in an amount such that the molar ratio of the reducing agent to the peroxide is 5 or more, and then carrying out emulsion polymerization while sequentially supplying the polymerizable monomer component together with the remaining amount of the peroxide and the reducing agent into an aqueous medium. can be mentioned. At this time, the condition is satisfied that the molar ratio of the supplied reducing agent and peroxide is successively reduced until the amount of the polymerizable monomer component supplied reaches at least 80% by weight, preferably at least 95% by weight. The supply rates of the reducing agent and the peroxide can be arbitrarily controlled within the range. In addition, it is preferable that the ratio of peroxide and reducing agent changes during the entire process of polymerization, and even if the molar ratio is adjusted to 5 or more from the middle of the polymerization process, the effect will be reduced and the polymerization stability will decrease. Easy to cause. The feature of the present invention is that the molar ratio between the total amount of reducing agent used in emulsion polymerization and the total amount of peroxide is reduced from immediately before the supply of the polymerizable monomer component until the supply amount is less than 20% by weight. The problem becomes more pronounced as the molar ratio between the reducing agent and peroxide supplied at any given time increases. Therefore, the most typical operating procedure for carrying out the manufacturing method of the present invention is accomplished as follows. The entire amount of water and a reducing agent used in the emulsion polymerization reaction are supplied to a reaction vessel, and the mixture is heated and dissolved. After nitrogen gas is sent to remove dissolved oxygen in the water, emulsion polymerization is performed while continuously or intermittently supplying the polymerizable monomer component and peroxide. The amount of peroxide used in the redox polymerization initiator used in the present invention may be within a range that does not reduce adhesive properties, polymerization rate, etc., and ranges from 0.1 to 100 parts by weight of the monomer mixture. The range is 5 parts by weight. Further, the amount of the reducing agent is 0.5 to 5 mol per mol of peroxide. Any conventionally known emulsion polymerization method can be used except for the method of adding the redox polymerization initiator. At this time, the emulsifier that can be used if necessary is not particularly limited, and includes, for example, anionic emulsifiers such as sodium lauryl sulfate and sodium dodecylbenzenesulfonate, and nonionic emulsifiers such as polyethylene glycol nonylphenyl ether. and cationic emulsifiers typified by dodecyltrimethylammonium chloride and the like. The adhesive emulsion thus obtained can be used as an adhesive as it is, but if necessary, it may be used by blending chroman resin, phenol resin, terpene with a tackifier such as enol resin or rosin resin. .

【Effect of the invention】

According to the method of the present invention, without using special raw materials,
An adhesive emulsion with excellent cohesive force and adhesive force can be obtained. [Examples] The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples. All parts and percentages in the Examples are by weight. Example 1 One part water was added to a one-part reaction vessel equipped with a stirrer, a thermometer, and a cooling tube.
32 parts, Lebenol WZ (manufactured by Kao ■) 20 as an emulsifier
% aqueous solution, 3.5 parts of sodium formaldehyde sulfoxylate as a reducing agent, and kept the internal temperature at 70°C.
After purging the inside of the reaction vessel with nitrogen, 303 parts of butyl acrylate and 19 parts of di-tylhexyl acrylate, which had been prepared in advance, were added.
5 parts, 90 parts of styrene, 6 parts of acrylic acid, 6 parts of glycidyl methacrylate and 140 parts of water, Levenol W220
An amount equivalent to 10% by weight of a pre-emulsion of polymerizable monomer components consisting of 57 parts of an aqueous solution was used as peroxide, and an amount of 10% by weight of an aqueous initiator solution consisting of 2.8 parts of t-butyl hydroperoxide and 90 parts of water was added. %wt% to start the reaction. The molar ratio of reducing agent and peroxide at this time is 9
, 5/1.0. remaining monomer pre-emulsion,
The initiator aqueous solution was uniformly dropped over 3 hours, and the molar ratio of the reducing agent and peroxide at the end of the 0 drop was 0.
．． It is 95/1.0. After further reaction at 80° C. for 1 hour, the mixture was cooled and neutralized with ammonia to obtain an emulsion (1) for adhesives having a pH of 8.0. This adhesive emulsion (1) has a solid content of 56.9%,
The viscosity was 1600 cps. Example 2 An adhesive emulsion (2) was obtained in the same manner as in Example 1, except that the aqueous initiator solution was added dropwise at 10 minute intervals over a period of 3 hours. Therefore, the change in the molar ratio of reducing agent and peroxide is the same as in Example 1. This adhesive emulsion (2) has a solid content of 56.5%,
viscosity? It was 20 cps. Example 3 The amount of sodium formaldehyde sulfoxylate was adjusted to 4.
7 parts, the amount of t-butyl hydroperoxide was 3.7
Emulsion for adhesives (3) was obtained by the same operation as in Example 1, except that m was changed to 1. Therefore, the molar ratio of reducing agent and peroxide at the start of the reaction is 10. O/1. O, and 1.0/1.0 at the end of dropping. It is O. This adhesive emulsion (3) has a solid content of 56.6% and a viscosity of 140.
It was 0 cps. Example 4 In a reaction vessel similar to Example 1, 132 parts of water and Lebenol WZ were added.
(manufactured by Kao ■), 2.1 parts of sodium formaldehyde sulfoxylate as a reducing agent were added, the inside temperature was maintained at 70°C, and the interior of the reaction vessel was replaced with nitrogen. 10% of an initiator aqueous solution consisting of 2.8 parts of t-butyl hydroperoxide and 45 parts of water was used as peroxide in an amount equivalent to 10% by weight of 797 parts of a pre-emulsion of polymerizable monomer components with the same composition. Add wt%,
Start the reaction. The molar ratio of reducing agent and peroxide at this time is 5.7/1
．． It is 0. An aqueous solution consisting of 1.4 parts of the remaining monomer breemulsion sodium formaldehyde sulfoxylate and 45 parts of water, and an aqueous initiator solution were uniformly added dropwise over 3 hours. The molar ratio of reducing agent and peroxide at the end of dropping is 0.
95/1. It is O. After further reaction at 80° C. for 1 hour, the mixture was cooled and neutralized with ammonia to obtain an adhesive emulsion (4). This adhesive emulsion (4) has a solid content of 56.
8%, and the viscosity was 2400 cps. Comparative Example 1 One part water was added to a one-part reaction vessel equipped with a stirrer, a thermometer, and a cooling tube.
32 parts, Lebenol WZ (manufactured by Kao ■) 20 as an emulsifier
Add 3 parts of % aqueous solution and keep the internal temperature at 70°C. After replacing the inside of the reaction vessel with nitrogen, add 303 parts of butyl acrylate and 19 parts of 2-functional methylhexyl acrylate that had been prepared in advance.
5 parts, 90 parts of styrene, 6 parts of acrylic acid, 6 parts of glycidyl methacrylate and 140 parts of water, Levenol W220
An amount corresponding to 10% by weight of a pre-emulsion of polymerizable monomer components consisting of 57 parts aqueous solution and an aqueous peroxide solution consisting of 2.8 parts of t-butyl hydroperoxide and 45 parts of water as peroxides. The reaction is started by adding 10% by weight of an aqueous reducing agent solution consisting of 3.5 parts of sodium formaldehyde sulfoxylate and 45 parts of water as a reducing agent. The molar ratio of the reducing agent and peroxide at this time is 0.95/1.0. The remaining monomer pre-emulsion and initiator aqueous solution were uniformly dropped over a period of 3 hours, and at the end of the zero drop, the existing molar ratio of reducing agent and peroxide was 0.95/1. It is O. After further reaction at 80° C. for 1 hour, the mixture was cooled and neutralized with ammonia to obtain a comparative emulsion (1) with a pH of 8.0. Comparative Example 2 In Example 1, the amount of sodium formaldehyde sulfoxylate added before addition of the polymerizable monomer component was 0.5 parts, and the remaining 3.0 parts of sodium formaldehyde sulfoxylate was added after starting polymerization. A comparative emulsion (2°) was obtained in the same manner as in Example 1 except that the mixture was added all at once after 2 hours. The molar ratio of the reducing agent and peroxide before the addition of the polymerizable monomer component was 1.09/1.0, and the ratio after 2 hours was 1.09/1.0.
The existing molar ratio of the reducing agent and peroxide at the end of the zero drop, which is 1.0, is 0.95/l. It is O. This comparative emulsion (2°) had a solid content of 56.4%,
The viscosity was 4900 cps. Example 5 Adhesive emulsions (1) to (4) obtained in Examples 1 to 4 and Comparative Examples 1 to 2 and comparative emulsion (l
Apply o) to (2') uniformly to a thickness of 250μ on one side of a 20μ thick polyester film, evaporate water by drying, cover the adhesive side with release paper, cut into 201gm width and evaluate adhesive properties. tapes (1) to (6) were obtained. Table 1 shows the results of evaluating these physical properties using the following methods. Table note 1: The adhesive strength in the table above is calculated by placing a stainless steel plate with a length of about 1250 mm and a width of about 251 mm vertically with No. 280 water-resistant abrasive paper specified in JISR6253, and applying a sample adhesive tape with a width of 2011 Il in the vertical direction. Paste, 1 day later, at a 180 degree angle 2
It shows the strength when peeled at a speed of 00 m/min. Note 2: For the tack shown in the table above, place the adhesive tape of the sample on a 30-degree slope with the adhesive side facing upward, leave a 10 cm adhesive surface in the middle, cover the top and bottom with cellophane, and then apply a tape from 1/32 inch to this. A steel ball with a diameter of 1/32 inch to 1 inch in 1/32 inch increments is rolled starting from a position 10 centimeters away from the top of the sticky surface and stops on the sticky surface. Indicates the diameter of the steel ball with the largest diameter. Note 3: The cohesive force in the table above is based on a stainless steel plate with a length of approximately 1250 mm and a width of approximately 25 mm, treated in the same manner as in Note 1, and then pasted so that the dimensions of the surface are 20 am width + 20 am length. After fixing the upper end of the stainless steel plate and leaving it at 40°C for 30 minutes, a load of 1 kg was applied to the lower end of the adhesive tape. Thereafter, the temperature was increased at a rate of 0.5° C./win, and the temperature at which the adhesive tape dropped together with the load due to cohesive failure is shown. The performance measurements and sample preparations described in Notes 1 to 3 above were all carried out at a constant temperature of 20° C. and 65% humidity.

Claims (1)

[Scope of Claims] 1. (meth)acrylic acid ester having an alkyl group having 4 or more carbon atoms (a) 50 to 95% by weight and other copolymerizable polymerizable monomers (b) 5 to 50% by weight % (however, the total of (a) and (b) above is 100% by weight) is 0.1 to 5% by weight based on the polymerizable monomer component. When performing emulsion polymerization in an aqueous medium using a redox polymerization initiator consisting of an amount of peroxide and a reducing agent in an amount of 0.5 to 5 mol per mol of the peroxide, the aqueous medium The molar ratio of the reducing agent and peroxide supplied into the aqueous medium at any time from immediately before the supply of the polymerizable monomer component to the supply amount of less than 20% by weight is 5 or more. An emulsion for adhesives, characterized in that polymerization is carried out by successively decreasing the molar ratio of the supplied reducing agent and peroxide until the amount of the polymerizable monomer component supplied reaches at least 80% by weight. manufacturing method. 2. 50 to 100% by weight of the reducing agent used in the polymerization reaction,
2. The production method according to claim 1, wherein the polymerizable monomer component is supplied into an aqueous medium before being supplied, and thereafter the remaining amount of the reducing agent and the peroxide are supplied as the polymerization reaction progresses. 3. The molar ratio of the reducing agent and peroxide supplied from immediately before the supply of the polymerizable monomer component to the supply amount of less than 20% by weight is the same as the total amount of the reducing agent used in the polymerization reaction and the peroxide. The manufacturing method according to claim 1, wherein the molar ratio is 5 times or more with respect to the total amount of the product.