JPS6412315B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing a pressure-sensitive adhesive, and in particular to a process for continuously producing a polymeric product that exhibits tackiness at room temperature and becomes the main component of the adhesive by bulk polymerization using polymerization raw materials mainly consisting of acrylic monomers. Regarding the manufacturing method. Conventionally, solution polymerization and emulsion polymerization have been known as methods for polymerizing the polymer component of acrylic pressure-sensitive adhesive compositions, but since the former method uses a solvent, the lower the monomer concentration during polymerization, the more the solvent is used. Because chain transfer tends to occur, it is difficult to achieve good adhesion and cohesive force, which are typical characteristics of pressure-sensitive adhesives.In order to suppress this chain transfer to some extent, benzene, ethyl acetate, etc. If such a solvent is selected, there are problems in terms of toxicity and cost. On the other hand, in the latter method, it is difficult to obtain a pure product due to residual additive components such as emulsifiers, and these residual components cause problems in properties such as water resistance. In contrast, polymerization in the absence of a solvent, that is, bulk polymerization, solves the above-mentioned problems, but this method has hitherto been inapplicable to acrylic polymers. Generally, in the bulk polymerization method, temperature control becomes difficult due to thickening due to rapid reaction progress depending on the type of monomer, and the reaction tends to run out of control. As a result, not only is the polymerization work dangerous, but it is also difficult to design the molecular weight of the polymer, gelled products and degraded products are likely to occur as by-products, it is difficult to obtain a homogeneous polymer, and it is difficult to obtain a homogeneous polymer in the next step. Processing problems may occur. Among ethylenically unsaturated monomers, styrene and the like are known to be able to control relatively high conversion rates, and their bulk polymerization has been studied and industrialized for a long time. Most of it is polymerized in a kettle-type prepolymerization vessel to a conversion rate of 30 to 70%, and the remainder is demonomerized to make the product.
Alternatively, the above-mentioned conversion rate is fed to an extruder and the reaction is carried out in a gentle manner up to a conversion rate of 95 to 96%. On the other hand, acrylic monomers generate a large amount of heat during polymerization, and even when using a pot-type polymerization method such as the above-mentioned styrene, it is difficult to control the temperature, making it impossible to avoid the aforementioned drawbacks due to runaway reactions. For this reason, the actual situation is that industrial bulk polymerization methods for acrylic monomers have not yet been put to practical use. The inventors have been conducting research on the bulk polymerization method of acrylic monomers for many years, but in the course of their research, they discovered that the large amount of heat generated during polymerization, which is an impediment to the application of the bulk polymerization method mentioned above, The inventors have investigated a method of continuously obtaining homogeneous bulk polymers by taking advantage of the accompanying rapid viscosity, and have accomplished this invention. That is, the present invention uses a reactor that can continuously transfer the contents while renewing the surface and is equipped with a temperature control mechanism over the entire transfer process. A polymerization raw material that does not contain a solvent used in ordinary solution polymerization is continuously supplied, and it is continuously polymerized using at least two types of polymerization initiators with different half-lives, and the tackiness is maintained at room temperature when a predetermined conversion rate is reached. The method for producing a pressure-sensitive adhesive is characterized in that a bulk polymer shown in the figure is continuously taken out from a reactor. This process is carried out in a continuous manner to obtain a polymer that exhibits tackiness at room temperature and is the main component of the pressure-sensitive adhesive. In the reactor used in the method of this invention, such as a single-screw or twin-screw extruder, which can continuously transport the contents while renewing the surface, it is extremely easy to stably transport a substance with a constant viscosity. However, in the case of materials with a large viscosity gradient in the transfer direction, the transfer force of the screw, etc. is not transmitted to the contents in the low viscosity region, and the contents rotate idly, causing stagnation or backflow of the contents, making stable transfer impossible. Therefore, it is necessary to make the viscosity gradient as long as possible in a state where the viscosity gradient is small. As mentioned above, acrylic monomers tend to thicken due to the rapid progress of the polymerization reaction, which has traditionally been an obstacle to the application of bulk polymerization, but the above properties are an advantage when using the above reactor. The viscosity required for stable transport can be achieved by rapid polymerization at least in the first half of the transport process. In addition, in the above method, the surface of the contents is renewed and transferred, and the contact surface between the contents and the reaction vessel is constantly renewed, so the efficiency of heat exchange between the two is good and the temperature distribution width of the contents is narrowed. Therefore, sufficient temperature control can be performed to prevent side reactions and runaway reactions from occurring. The drawing shows one example of a reactor used in this invention.
This shows the cross-sectional structure of an axial screw extruder.
The polymerization method of the present invention will be explained below with reference to this drawing. In the figure, reference numeral 1 denotes a barrel constituting the outer cylinder of the extruder, and one end thereof is provided with a supply port 2 for polymerization raw materials, and the other end is provided with a discharge port 3 for polymerization contents. Inside the barrel 1, a plurality of screws 5 are formed around a rotating shaft 4, and the polymerization raw materials supplied by the screws 5 are mixed and advanced by the rotation of the shaft 4. The distance between the screw 5 and the barrel 1 is appropriately set to improve miscibility. Generally, about 0.5 to 2 mm is appropriate. 6, 7, 8,
Reference numeral 9 denotes a heating controller provided at each part of the entire length of the barrel, and is configured to be able to control the temperature at an appropriate temperature for each part, but as shown in the example below, the heating is controlled evenly over the entire length. Of course, it is possible to configure Into this extruder, a bulk polymerization raw material containing mainly acrylic monomers and containing no solvent used in ordinary solution polymerization is continuously fed into the extruder from a supply port 2 at a constant rate, preferably after the atmosphere has been replaced with nitrogen in advance. The supplied raw materials are mixed by the rotation of the screw 5 and transported while the surface is renewed. At this time, for example, the heating controller 6 is used to gradually increase the temperature in the regions a1 to a2 so that the viscosity increases due to rapid polymerization in the first half region indicated by a in the figure during the transfer process from the supply port 2 to the discharge port 3. is raised, and the temperature is controlled by the heating controller 7 so that polymerization starts instantaneously in area a3 and the polymerization reaction proceeds rapidly. The polymerized content whose viscosity has increased in this way is further mixed and surface renewed while being transferred to the second half area b, where the polymerization reaction proceeds to the desired conversion rate while being temperature controlled by heating controllers 8 and 9, and finally It is continuously taken out from the take-out port 3 at the open end. In this example, the axis 4 of the single screw 5 is concentric between the screws 5, 5, but for the purpose of reaction control, each part of the barrel is configured to have a different diameter. The transfer amount may be varied. Further, in the above example, a single-screw extruder is used, but polymerization can also be carried out using a twin-screw extruder in the same manner as described above. In the case of a two-axis screw, each axis can be rotated in the same direction or in different directions. In these screw extruders, as mentioned above, the distance between the screw and the barrel is preferably set to about 0.5 to 2 mm, but the speed gradient, that is, [pi (π) × number of revolutions × The screw outer diameter/distance between barrel and screw] is generally 1000/min or more. In addition to the above-mentioned screw extruder, the reactor used in this invention may be any reactor that can continuously transfer the contents while renewing the surface and is equipped with a temperature control mechanism over the entire transfer process. can also be used. This surface renewal includes renewal of the contact surface between the contents and the reactor wall, and the resulting heat exchange between the two effectively controls the temperature of the reactants and suppresses side reactions. As the monomer component of the raw material used in this invention, any monomer component known as a polymer raw material for general acrylic pressure-sensitive adhesive compositions can be used, and usually acrylic acid and a carbon number of 2 to 14 are used. Monomers copolymerizable with esters with alcohols or derivatives thereof as main monomers, such as vinyl acetate, styrene, acrylonitrile, acrylic acid, methacrylic acid, methacrylic esters and derivatives thereof, acrylic acids other than the above main monomers. It is added with ester or its derivative. The polymerization raw material is a mixture of monomers mainly consisting of the above-mentioned acrylic monomers, which can make the formed polymer sticky at room temperature, and other additives such as a radical polymerization initiator and, if necessary, a molecular weight regulator. However, in this invention method, at least two kinds of radical polymerization initiators having different half-lives are used. That is, in the reactor described above, the polymerization initiator, which has a short half-life and therefore has a low decomposition temperature, is mainly consumed during the initial stage of radical polymerization or the early stage of the reaction, and the polymerization initiator, which has a long half-life and therefore has a low decomposition temperature, is consumed in the late stage of the reaction. By actively consuming the high-temperature polymerization initiator, the radical concentration can be kept as constant as possible during the process of the polymerization reaction while being continuously transferred, and the polymerization reaction can proceed uniformly. A bulk polymer with little gelation and high polymerization rate is obtained. On the other hand, when a single polymerization initiator is used, the polymerization initiator is rapidly consumed at the beginning of the reaction, causing the reaction to run out of control, making it difficult to control the temperature within the system, and causing deterioration due to gelation, etc. Furthermore, there is an extreme shortage of polymerization initiator remaining in the late stage of the reaction, which slows down the reaction rate and lowers the polymerization rate of the resulting polymer. This may lead to problems such as deterioration of production efficiency. As the polymerization initiator that can be used, a combination of at least two types may be selected from various compounds commonly used as polymerization initiators depending on the type of monomer, temperature conditions, reactor structure and operating conditions, etc. A typical polymerization initiator is benzoyl peroxide (half-life at 60°C in toluene).
t1/2 = 4100 min), cumene hydroperoxide (t1/2 = 1650 min), di-t-butyl peroxide (t1/2 = 2650000 min), lauroyl peroxide (halved in benzene at 60°C) Period t1/2
= 760 min) and 2,2'-azobisisobutyronitrile (half-life at 60°C in toluene).
t1/2=1300 minutes), 2・2'-Azobis-(2・4-
dimethylvaleronitrile) (t1/2 = 180 minutes),
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (same t1/2 = 7.5 minutes), dimethyl-2,2'-azobisisobutyrate (same t1/2)
2=1420 minutes), and two or more of these are used in combination. As a guideline for their combined use, the half-life of the polymerization initiator with the longest half-life to be used in combination with the polymerization initiator with the shortest half-life at 60℃ in toluene is approximately
A combination that is 30 to 2000 times more effective, more preferably about 100 to 1000 times more effective, is used. The combined ratio is preferably within a range where one of the above two is 50 times or less by weight of the other. The total amount of the polymerization initiator is preferably 0.01 to 1 part by weight per 100 parts by weight of the monomer. As the molecular weight regulator, a chain transfer agent such as thioglycolic acid, butyl mercaptan, lauryl mercaptan, and decyl mercaptan is used. In this invention, the solvent used in the above-mentioned normal solution polymerization, which is not allowed to exist in the polymerization system, is added to the raw materials before the start of the polymerization reaction for the purpose of facilitating control of the polymerization reaction, and is added to the resulting polymer. refers to inert organic solvents that are removed by volatilization when they are taken out, and are collected and reused for reasons of pollution prevention and cost. Examples include benzene, toluene, ethyl acetate, heptane, hexane, methanol, ethanol, water, and mixtures thereof. In the present invention, as described above, the above-mentioned solvent is not substantially used, but a monomer concentration adjusting agent that remains in the system even after coating and drying the tape support may be used. This monomer regulator is added mainly for the purpose of increasing the amount of polymer, improving coating properties, improving compatibility, etc., and is used as a plasticizer, various resins, etc.
Alternatively, bulk polymers synthesized by the above-mentioned polymerization method in this invention can be used. However, if a large amount of plasticizer or various resins is used, chain transfer and a decrease in the monomer concentration will occur, leading to a decrease in the polymerization rate and the molecular weight of the resulting polymer. % or less. Furthermore, when the bulk polymer synthesized by the above-mentioned polymerization method in this invention is used as a monomer concentration regulator, it does not cause a decrease in the polymerization rate, so it can be used in a relatively large amount, but the viscosity increases due to dissolution of the bulk polymer, resulting in a decrease in workability. Therefore, the amount used should be 25% by weight or less. The above-mentioned raw materials for polymerization may be continuously supplied all at once from the supply port of the reactor, or in some cases, a separate supply port may be provided in the middle of the transfer process of the reactor to supply them in parts. Furthermore, a method may be adopted in which some of the above-mentioned additive components, such as a polymerization initiator with a long half-life, are injected from an intermediate supply port. For example, numeral 10 in the figure is a supply port provided at a portion where the axis 4 of the screw 5 on the front stage side of the area a3 is tapered. Note that 11 is an exhaust port for low-molecular volatiles produced as a by-product in the polymerization reaction or generated by introducing arbitrary additives. In the continuous polymerization method described above, the heating temperature in each part of the reactor is appropriately controlled depending on the type of monomer and polymerization catalyst used, the amount of polymerization contents transferred to each part, etc. The temperature of the polymerized contents is 40-150℃, preferably
It is desirable to adjust the temperature within the range of 60 to 100°C. In particular, the heating temperature in the area where the viscosity is to be increased by rapid polymerization should be set depending on the type and amount of the polymerization catalyst, the structure of the reactor, and the transfer conditions. Incidentally, the conversion rate of the bulk polymer obtained by the method of this invention is usually 93 to 99% by weight. The bulk polymer that is sticky at room temperature obtained as described above can be used as a pressure-sensitive adhesive as it is, or it can be used with a tackifying resin such as a rosin-modified resin, a coumaron-indene resin, a polyfunctional isocyanate, or a polyfunctional adhesive. A pressure-sensitive adhesive composition is prepared by blending various commonly used additive components such as a functional epoxy, a crosslinking agent such as benzoyl peroxide, a filler, and a pigment. Furthermore, plasticizers such as phthalate esters and polyethers, which have already been described as being able to be added to the polymerization raw materials from the beginning, and various modifying resins can also be blended. In general, raw material polymers with low molecular weights or narrow molecular weight distributions have difficulty achieving both adhesion properties, especially tackiness and creep resistance. If the adhesive properties are increased, the adhesion properties, especially the tackiness, will be greatly reduced, and if the tackiness is emphasized, the cohesive force cannot be increased and the creep resistance will deteriorate. The pressure-sensitive adhesive obtained by this invention has a high monomer concentration and polymerization is completed in a short time, so the rate of chain transfer to the self-polymer is higher than when other polymerization methods are used, and the molecular weight is It is estimated that the distribution is wide and that there are more branched and entangled tangles than those obtained by other polymerization methods.
It has the advantage of being easy to balance adhesive properties, especially tackiness and creep resistance. Furthermore, since it is a pure product that does not contain emulsifiers or dispersants, it does not have the disadvantages of reduced water resistance and other disadvantages of compositions obtained by emulsion polymerization. Examples of the present invention will be described below, and all parts hereinafter mean parts by weight. Note that the present invention is not limited to these embodiments, and various modifications can be made without departing from the technical idea of the present invention. In addition, measurements of each characteristic in Examples and Comparative Examples were performed by the following method. The results are summarized in the table below. (1) Gel fraction: Dissolve the polymer before film formation in toluene and filter it to collect the insoluble matter (gelled material), and calculate the gel fraction relative to the polymer component from the weight after drying. Ta. (2) Creep resistance: Pressure-sensitive adhesive tape based on a 50 μm thick polyester film was attached to a Bakelite plate in an area of 10 mm x 20 mm, and a vertical load of 200 g was applied at a temperature of 40°C until it fell. The time was measured. (3) Adhesive strength: Measured according to JIS Z-1528. (4) Adhesive strength: Based on J.Dow's Rolling Ball Tack measurement method. Example 1 0.2 parts of lauroyl peroxide and 2,2'-azobis(4-methoxy -2,4-dimethylvaleronitrile) and 0.2 part of the mixture was thoroughly purged with nitrogen to obtain a raw material mixture.
Screw this mixture into a screw with an outer diameter of 40 mm and a barrel length of 40 mm.
1000 mm, the gap between the barrel and the screw ridge is 0.5 mm, and the barrel temperature inside the extruder is evened out by feeding at a speed of 50 cc/min into a twin-screw extruder (self-cleaning type) with a stirring speed gradient of 5000/min. divided 3
Bulk polymerization was carried out continuously by controlling the temperature so that the temperature of the zone was 60°C, 80°C, and 100°C from the supply port side.
The obtained bulk polymer had a polymer conversion rate of 97.8%, a weight average molecular weight (w) = 510,000, and a number average molecular weight (
It was homogeneous with n) = 88,000 and w/n = 5.8. This bulk polymer was sandwiched between release paper and heated to 120°C.
A film was formed by hot pressing at a temperature of 0.5 kg/cm ² at a pressure of 0.5 kg/cm 2 . Example 2 To 100 parts of a monomer mixture consisting of 60 parts of n-butyl acrylate, 40 parts of 2-ethylhexyl acrylate, and 4 parts of acrylic acid, 0.2 parts of 2.2'-azobisisobutyronitrile and 2. 2'-Azobis (2.4
-dimethylvaleronitrile) was added, and the mixture was sufficiently purged with nitrogen gas to obtain a raw material mixture. This raw material liquid is screwed into a screw with an outer diameter of 50 mm and a barrel length of 1000 mm.
mm, fed at a rate of 50 cc/min into a single screw extruder with a gap of 1 mm between the barrel and screw crest and a speed gradient of 7850/min, and the barrel temperature inside the extruder was controlled to 100°C over the entire length. Bulk polymerization was carried out continuously. The obtained bulk polymer had a polymer conversion rate of 98.0%, w = 540,000, n = 87,000,
It was homogeneous with Mw/n=6.2. This bulk polymer was diluted with toluene, and rosin modified resin in an amount of 20 parts and 2.0 parts of tolylene diisocyanate in an amount of 2.0 parts were added to 100 parts of the raw monomer mixture to create a pressure-sensitive adhesive. It was made into a drug composition. This was coated with a roll coater to a thickness of 50 μm.
The adhesive was applied onto a thick polyester film to a thickness of 50 μm and dried at 120° C. for 3 minutes to obtain a pressure-sensitive adhesive tape. Example 3 5 parts of dioctyl phthalate, 2,2'-azobisisobutyro Nitrile
0.2 parts and 2,2'-azobis(4-methoxy-
0.2 part of 2,4-dimethylvaleronitrile) was added, and the mixture was sufficiently purged with nitrogen gas to obtain a raw material mixture. When this mixed solution was polymerized in the same manner as in Example 1, the obtained bulk polymer had a polymer conversion rate of 95.4%, w = 400,000, n = 77,000, w/
It was a homogeneous polymer with n=5.2. This bulk polymer was made into a pressure-sensitive adhesive tape in the same manner as in Example 2. Comparative Example 1 0.1 part of 2,2'-azobisisobutyronitrile and 300 parts of benzene were added to 100 parts of a monomer mixture consisting of 60 parts of n-butyl acrylate, 40 parts of 2-ethylhexyl acrylate, and 4 parts of acrylic acid. A portion of the mixture was placed in a three-necked flask, and dissolved oxygen was sufficiently replaced with nitrogen gas while stirring, the temperature was raised to 62°C and polymerized for 4 hours, and then the temperature was further raised to 75°C and aged for 2 hours. The generated polymer is directly coated with a roll coater.
It was coated onto a 50 μm thick polyester to give an adhesive thickness of 50 μm, and dried at 120° C. for 3 minutes to obtain a pressure-sensitive adhesive tape. The above produced polymer has a conversion rate of 94.3
%, w=450,000, n=105,000, w/n=
It was 4.3. Comparative Example 2 A rosin modified resin and 2.0 parts of rosin modified resin were added to the produced polymer of Comparative Example 1 in an amount of 20 parts per 100 parts of the monomer mixture.
A pressure-sensitive adhesive tape was prepared in the same manner as in Comparative Example 1 by adding an amount of tolylene diisocyanate. Comparative Example 3 0.08 parts of lauryl mercaptan and 2 parts of a nonionic anionic emulsifier were added to 100 parts of a monomer mixture consisting of 60 parts of n-butyl acrylate, 40 parts of 2-ethylhexyl acrylate, and 4 parts of acrylic acid, and the mixture was purified. A monomer emulsion with a solid content concentration of 30% was prepared by pouring it into a three-necked flask containing water. Next, 0.15 parts of potassium persulfate was added to 100 parts of the above monomer mixture, and after purging with nitrogen gas for about 1 hour, the temperature was raised to 70°C, and a polymerization reaction was carried out at this temperature for 5 hours. The obtained polymer had a conversion rate of 98.5%, w = 490,000, n = 129,000, w/
n=3.8. This polymer emulsion was precipitated using a dilute hydrochloric acid-methanol system, washed, dried to form a lump, and redissolved in toluene to form a 40% solution. This polymer solution was coated onto a 50 μm thick polyester using a roll coater to form a pressure-sensitive adhesive tape. Comparative Example 4 Using the toluene solution polymer of Comparative Example 3, the same amount of the same additive as in Comparative Example 2 was added to obtain a pressure-sensitive adhesive tape. Comparative Example 5 0.4 part of 2,2'-azobisisobutyronitrile was mixed with a monomer mixture consisting of 60 parts of n-butyl acrylate, 40 parts of 2-ethylhexyl acrylate, and 4 parts of acrylic acid, and the mixture was heated with nitrogen gas. After sufficient substitution, the raw material mixture was polymerized in the same manner as in Example 1, and the obtained bulk polymer was w = 450,000,
Mn=39,000, w/n=11.5. This polymer was made into a pressure-sensitive adhesive tape in the same manner as in Example 2. Comparative Example 6 5 parts of dioctyl phthalate and 2,2'-azobisisobutyro were added to 100 parts of a monomer mixture consisting of 60 parts of n-butyl acrylate, 40 parts of 2-ethylhexyl acrylate, and 4 parts of acrylic acid. Nitrile
0.4 parts were mixed and the mixture was sufficiently replaced with nitrogen gas to obtain a raw material mixture. When this mixed solution was polymerized in the same manner as in Example 1, the obtained bulk polymer was
= 410,000, n = 38,000, w/n = 10.8. This polymer was made into a pressure-sensitive adhesive tape in the same manner as in Example 2.

[Table] (Note) * means cohesive failure of the pressure-sensitive adhesive From the results in the above table, the pressure-sensitive adhesive obtained by the method of this invention has typical characteristics as a pressure-sensitive adhesive. It can be seen that it shows satisfactory performance in both adhesive strength and cohesive strength, and is superior to those obtained according to the conventional method.

[Brief explanation of drawings]

The drawing is a sectional view of a single-screw extruder shown as an example of a reactor used in the present invention.

Claims (1)

[Claims] 1. Using a reactor that can continuously transfer the contents while renewing the surface and is equipped with a temperature control mechanism throughout the entire transfer process, the reactor contains mainly acrylic monomers. A polymerization raw material that does not contain the solvent used in normal solution polymerization is continuously supplied, and it is continuously polymerized using at least two types of radical polymerization initiators with different half-lives, and it becomes sticky at room temperature when a predetermined conversion rate is reached. 1. A method for producing a pressure-sensitive adhesive, which comprises continuously taking out a bulk polymer exhibiting properties from a reactor. 2. The method for producing a pressure-sensitive adhesive according to claim 1, which uses a single-screw or twin-screw extruder as a reactor.