JPH035407B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polychloroprene latex which has excellent stability and exhibits high initial adhesive strength when used as an adhesive. Chloroprene polymers are widely used in adhesives either in the form of solutions dissolved in organic solvents or as latex systems in water. However, a disadvantage of latex-based adhesives is that their initial adhesive strength is lower than that of solution-based adhesives. As a result of intensive research to improve this drawback, the present invention has been achieved. That is, the present invention uses 1 to 30% by weight of a polymerizable unsaturated carboxylic acid, 0.01 to 30% by weight of a water-soluble monomer, and 5 to 90% of a monomer that provides a soft component whose homopolymer glass transition temperature is 0°C or lower. % by weight, and 5 to 70% by weight of a monomer that provides a hard component with a homopolymer glass transition temperature of 0°C or higher;
The glass transition temperature of the copolymer obtained by copolymerizing a 100% monomer mixture is (T-10) °C or lower, preferably (T-60) to (T-20) °C (where T is the polymerization of chloroprene). Polymerization is performed by adding 30 to 99 parts by weight of chloroprene to a copolymer emulsion containing 1 to 70 parts by weight of a monomer mixture selected as shown in the polymerization temperature expressed in degrees Celsius. A method for producing chloroprene latex, which provides polychloroprene latex with excellent stability and exhibiting high initial adhesive strength when used as an adhesive. The production of the polychloroprene latex of the present invention is carried out in two stages. Each stage of polymerization can be carried out separately or sequentially. Examples of the polymerizable unsaturated carboxylic acid used in the first step include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. These monomers are used to maintain the stability of the latex and are used in amounts ranging from 1 to 30% by weight of the monomer mixture used in the first stage. If it is less than 1% by weight, the stability of the latex will be poor, and if it exceeds 30% by weight, the amount of precipitates during polymerization will increase. Similarly, the water-soluble monomer used in the first step may be any monomer that has a solubility in 100 g of water of 1 g or more at 20°C, excluding the above-mentioned polymerizable unsaturated carboxylic acids, such as methyl acrylate, Examples include acrylonitrile, vinyl acetate, sodium styrene sulfonate, and acrylamide. In these monomers, the polymerizable unsaturated carboxylic acid is soluble in water, while the monomers that provide the soft component and hard component described below are sparingly soluble or insoluble in water, so their copolymerizability is limited. used to enhance Although it is known that a stable latex can be obtained using a polymerizable unsaturated carboxylic acid, its stability has been insufficient due to poor copolymerizability with other monomers that are poorly soluble or insoluble in water.
The present inventors have discovered that a water-soluble monomer can be used to enhance this copolymerizability. This water-soluble monomer is compatible with monomers that are poorly soluble or insoluble in water, and is therefore considered to enhance copolymerizability with the water-soluble polymerizable unsaturated carboxylic acid. The water-soluble monomer is used in an amount of 0.01 to 30% by weight of the monomer mixture used in the first stage, but if it is less than 0.01% by weight, the stability of the latex will be poor, and if it exceeds 30% by weight, the viscosity of the latex will decrease. becomes extremely high. Furthermore, in the first step, monomers providing the soft component and the hard component are copolymerized. These form the core of the emulsion particles that are copolymerized in the first stage. As described below, the glass transition temperature (hereinafter abbreviated as Tg) of the copolymer is (T-10)℃ or lower (hereinafter Tg).
indicates the polymerization temperature expressed in degrees Celsius during the polymerization of chloroprene, and will be expressed as T from here on). A monomer that provides a hard component with a temperature of 0°C or higher is used in combination. Monomers that provide soft components include hexyl methacrylate (-5℃) and lauryl methacrylate (-65℃).
℃), butyl acrylate (-55℃), acrylic acid 2
-ethylhexyl (-60°C), etc.
In addition, monomers that provide hard components include methyl methacrylate (105℃) and ethyl methacrylate (55℃).
℃), vinyl chloride (81℃), and styrene (100℃). The Tg of the homopolymer of the monomer is shown in parentheses. The above monomers are copolymerized in the first step, and the Tg of the copolymer in this first step is (T-10)℃.
Hereinafter, the monomer components are preferably selected so that the temperature is between (T-60) and (T-20)C. As the polymerization temperature of chloroprene decreases, the crystallinity of polychloroprene itself increases. Therefore, when the polymerization temperature of chloroprene is lowered, the polychloroprene itself becomes harder. Therefore, in this case, it is preferable that the copolymer in the first stage is softer, that is, the copolymer has a lower Tg. Therefore, the Tg of the copolymer in the first stage of the present invention depends on the polymerization temperature T (°C) of chloroprene, and in order to obtain high initial adhesion, it should be below (T-10)°C, preferably (T -60) to (T-20)°C. Tg of copolymer is (T-10)
If the temperature is higher than 0.degree. C., the particle surface will be too hard, resulting in poor cohesive force, and the initial adhesive strength will decrease, making it impossible to obtain the effects of the present invention. Here, the Tg of the copolymer in the present invention is
I ₆ E ₆ Calculated using the method described in "Mechanical Properties of Polymers" by Nielsen, translated by Nobuharu Onogi, pages 26-27. The polymerization temperature in the first stage is not particularly limited, and can be freely selected from 0°C to 100°C depending on the catalyst system used, but preferably from 50 to 80°C. Polymerization time varies depending on polymerization conditions, so
Although not required, it is preferred that the polymerization be carried out until essentially complete. Although not necessarily required in the first stage polymerization, for the purpose of further improving polymerization stability, emulsifiers used in normal emulsion polymerization, such as alkyl sulfates, alkylbenzene sulfonates, fatty acid salts, polyoxy There is no problem in using ethylene alkyl ether or the like in a small amount of about 0 to 1% by weight based on water. Furthermore, a chain transfer agent such as an alkyl mercaptan may be added to the system to control the molecular weight of the copolymer. The polymerization initiator used in the present invention may be any initiator used in radical polymerization, such as persulfates and alkyl hydroperoxides, but in particular potassium persulfate and ammonium persulfate initiators having persulfate ions are used. extremely effective;
This further contributes to the stabilization of the latex particles. Further, these can be used alone or in combination with reducing substances such as thiosulfates, thiosulfites, organic amines, etc. In the present invention, as a second step, chloroprene is added to the emulsion produced as described above, and the polymerization of chloroprene is continued to obtain a polychloroprene latex. At this time, it is effective to first adjust the pH of the emulsion to 7 or higher, preferably 9 to 11, by adding a base to the emulsion. This is because the carboxyl groups on the surface of the emulsion particles are ionized and have anions on the surface of the particles, thereby further increasing the stability of the latex. At this time, examples of the base used include sodium hydroxide, potassium hydroxide, aqueous ammonia, and the like. In the polymerization of chloroprene, chloroprene can be added either all at once or continuously. When adding chloroprene continuously, the time for adding chloroprene can be freely selected, but it is desirable to prevent a large amount of monomer oil droplets from appearing in the polymerization system, and it is preferable to add chloroprene over 100 minutes or more. The polymerization temperature of chloroprene can be set in the range of 0 to 60°C, as in the case of ordinary emulsion polymerization of chloroprene. Polymerization of chloroprene may be carried out until all the monomers are substantially polymerized, but in order to develop better initial adhesive strength, the polymerization conversion rate should be 40 to 40%.
When reaching 85%, preferably 60-80%, it is desirable to stop the polymerization by adding a commonly used polymerization terminator. In this case, the residual monomer can be removed by a conventional method to obtain a latex. When the polymerization conversion rate is less than 40%, adhesive strength is low and productivity is also poor. On the other hand, if it exceeds 85%, chloroprene will gel and the initial adhesive strength will decrease. In the polymerization of chloroprene, the molecular weight is controlled by adding a chain transfer agent such as an alkyl mercaptan to chloroprene, as is done in the production of ordinary chloroprene polymers. Furthermore, other vinyl monomers copolymerizable with chloroprene,
For example, methacrylic esters, acrylic esters, styrene, etc., diene monomers such as butadiene, isoprene, 2,3-dichlorobutadiene, etc., or crosslinking monomers such as divinylbenzene, ethylene glycol dimethacrylate, etc., in an amount of up to 20% by weight. Polychloroprene latex can be modified by adding a small amount and copolymerizing with chloroprene. Such modification is not particularly limited as long as it does not impair the essence of the present invention. The amount of chloroprene added and polymerized in the second step is 1 to 70% of the monomer mixture used in the first step.
It is used in an amount of 99 to 30 parts by weight. If it exceeds 99 parts by weight, the stability of the latex will be poor and precipitates will be generated during polymerization. If the amount is less than 30 parts by weight, the properties as a polychloroprene latex will be lacking.
Further, the solid content concentration of the polychloroprene latex finally produced is selected to be 5 to 70% by weight, which is the same as the concentration of latex produced by ordinary emulsion polymerization. The polychloroprene latex thus obtained is essentially free of emulsifiers, exhibits excellent stability, has high initial adhesive strength, and has many properties similar to conventional polychloroprene latex. It can be used for various purposes. In addition, as with conventional polychloroprene latex,
Various types of vulcanizing agents, anti-aging agents, thickeners, tackifiers, etc. can also be added. In particular, the polychloroprene latex of the present invention has carboxyl groups on the particle surface, and when mixed with multifunctional compounds such as diols, diepoxy, isocyanates, etc., it forms a crosslinked structure and increases strength and strength.
Various adhesive properties such as water resistance can be improved. Furthermore, when resins conventionally known as tackifying resins, such as rosin resins, rosin derivatives, terpene resins, and petroleum resins, are blended, the tackiness can be further improved than when blended with conventional polychloroprene latex. This makes it possible to further increase the high initial adhesive strength that is characteristic of the polychloroprene latex of the present invention. In order to make the present invention easier to understand, the present invention will be explained below using some examples, but the present invention is not limited to these examples. In the text, unless otherwise specified, parts represent parts by weight. The initial adhesive strength was measured by applying latex to each of two No. 9 canvases cut to 25 mm diameter, repeating drying at 80°C (10 minutes), and after the third application, during the specified open time (except for Example 18). After leaving to dry for 120 minutes, they were laminated together and pressed 5 times with a 5Kg roller, and the peel strength was immediately determined using an Instron tensile tester, which was taken as the initial adhesive strength. To measure the adhesive strength, do the same thing as before.
After the second application, they were bonded together with an open time of 60 minutes, pressed 5 times with a 5Kg roller, left at 25℃ for 1 day, and dried at 100℃ for 1 hour. After being left at 25°C for one day, the peel strength was determined. Further, a test piece prepared in the same manner was immersed in hot water at 30°C for 24 hours, and then the peel strength was measured to evaluate water resistance. Explanation of symbols used below VAC Vinyl acetate MA Methyl acrylate AAm Acrylamide NaSS Sodium styrene sulfonate St Styrene MMA Methyl methacrylate BA n-Butyl acrylate Examples 1 to 4 0.4 part of sodium laurate was dissolved in a nitrogen stream. Pour 400 parts of water into a polymerization vessel, heat it to 70°C, add 3 parts of ammonium persulfate, and then add 24 parts of styrene, 24 parts of methyl methacrylate, 57 parts of n-butyl acrylate, 5.4 parts of acrylic acid,
- A monomer mixture consisting of 0.15 parts of octyl mercaptan and 2 parts of the monomers shown in Table 1 was polymerized while being added dropwise over 120 minutes. After the dropwise addition was completed, stirring was continued at 70°C for 1 hour to complete the polymerization. At this time, substantially no coagulum was observed in any case, and the stability of the emulsion was excellent. Furthermore, chloroprene was subsequently polymerized. First, the temperature of the emulsion obtained above is
After lowering the temperature to 40°C, a 10% by weight aqueous sodium hydroxide solution was added to adjust the pH to 10.0. Next, chloroprene to which 0.64 parts of n-octyl mercaptan was added
Polymerization was carried out while dropping 320 parts over 100 minutes. After completion of the dropwise addition, the temperature was maintained at 40°C, and polymerization was continued until substantially all of the chloroprene had been polymerized. At this time, substantially no coagulation was observed, and the solid content of the obtained latex was 50% by weight, and the stability of the latex was excellent. Furthermore, when the initial adhesive strength was measured, as shown in Table 1, all of the products of the present invention were superior to commercially available polychloroprene latexes. Examples 5 to 8 and Comparative Example 1 In a nitrogen stream, 400 parts of water in which 0.4 parts of sodium laurate was dissolved was charged into a polymerization container, heated to 70°C, and then 3 parts of ammonium persulfate was added, and then the mixture shown in Table 2 was added. Composition (expressed in parts by weight used) of monomers and 3 parts vinyl acetate, 5.4 parts acrylic acid
Polymerization was carried out by dropping a monomer mixture containing 0.15 parts of n-octyl mercaptan and 0.15 parts of n-octyl mercaptan over 120 minutes.
After the dropwise addition was completed, stirring was continued for 1 hour at 70°C to complete the polymerization. At this time, substantially no coagulum was observed in any case, and the stability of the emulsion was excellent. Next, chloroprene was polymerized in the same manner as in Example 1. At this time, substantially no coagulation was observed in any case, and the stability of the latex was excellent. Furthermore, when we measured the initial adhesive strength, Table 2
As shown, the superiority of the product of the present invention was clear.

【table】

[Table] Example 9 A copolymer emulsion with the same composition as that used in Example 1 was synthesized, and the temperature of the emulsion was then adjusted.
After lowering the temperature to 40°C, a 10% by weight aqueous sodium hydroxide solution was added to adjust the pH to 10.2. Next, chloroprene 450 with 0.9 parts of n-octyl mercaptan added.
Polymerization was carried out by dropping a portion over 100 minutes. After the dropwise addition, the temperature is maintained at 40℃ to maintain the polymerization conversion rate of chloroprene.
When reaching 70%, add 0.1 part of phenothiazine,
Polymerization was stopped. Subsequently, unreacted chloroprene was removed by stripping to obtain a polychloroprene latex with a solid content of 45% by weight. At this time, no coagulum was observed and the stability of the latex was excellent. Furthermore, compared to Example 1, the initial adhesive strength was
Increased to 7.0Kg/25mm. Example 10 A polychloroprene latex was obtained in the same manner as in Example 9, except that 3 parts of vinyl acetate in Example 7 was replaced with 5 parts of methyl acrylate. At this time,
A latex with a solid content of 44% by weight was obtained, with no coagulation and excellent stability. The initial adhesive strength showed a value of 7.3Kg/25mm. Examples 11 to 13 and Comparative Examples 2 and 3 First-stage emulsions were synthesized in the same manner as in Example 5 using the monomer compositions shown in Table 3 (expressed in parts by weight used). Next, polymerization of chloroprene was carried out in the same manner as Polymer 9 except that the temperature was changed to 15°C to obtain a latex. At this time, substantially no coagulation was observed in any case, and the stability of the latex was excellent. Furthermore, the initial adhesive strength showed excellent values in different Tg regions from Examples 5 to 8.

【table】

[Table] Example 14 Using Examples 9 and 10 and commercially available polychloroprene latex, polymer 100 in the latex was
part, 5 parts of zinc white, 5 parts of ethylene glycol
and 30 parts of a rosin resin as a tackifier resin to prepare an adhesive composition. The adhesive properties are shown in Table 4, and the product of the present invention has a high initial adhesive strength, and even if the open time is changed, a high initial adhesive strength is always obtained, and the adhesive strength develops quickly, and it is usable. It had excellent performance as a water-based contact adhesive that lasted for a long time. Furthermore, the water resistance after adhesion was also excellent.

【table】

Claims (1)

[Claims] 1 1 to 30% by weight of a polymerizable unsaturated carboxylic acid, 0.01 to 30% by weight of a water-soluble monomer, 5 to 90% by weight of a monomer that provides a soft component with a homopolymer glass transition temperature of 0°C or lower, and individual Monomer 5 that provides a hard component with a polymer glass transition temperature of 0°C or higher
The glass transition temperature of the copolymer obtained by copolymerizing a monomer mixture consisting of ~70% by weight is (T-10)
30 to 99 parts by weight of chloroprene in a copolymer emulsion of 1 to 70 parts by weight of a monomer mixture selected such that T indicates the polymerization temperature in degrees Celsius during the polymerization of chloroprene. A method for producing polychloroprene latex, which comprises adding and polymerizing.