JPS6310750B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a method for producing a pressure-sensitive adhesive composition containing an acrylic acid alkyl ester-based bulk polymer as a main component and having excellent properties. Conventionally, solution polymerization method and emulsion polymerization method are known as methods for polymerizing the polymer component of an acrylic acid alkyl ester pressure-sensitive adhesive composition.
Since the former method uses a solvent, the lower the monomer concentration during polymerization, the more chain transfer to the solvent occurs, so it is important to improve both adhesive strength and cohesive strength, which are typical characteristics of pressure-sensitive adhesives. However, if a solvent such as benzene or ethyl acetate is selected to suppress this chain transfer to some extent, 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 terms of properties such as water resistance. In contrast, polymerization in the absence of a solvent, that is, bulk polymerization, solves the above problems, but this method has traditionally been considered inapplicable to acrylic acid alkyl ester polymers. Ta. 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 acid alkyl ester monomers generate a large amount of heat during polymerization, and even when using a pot-based polymerization method such as the above-mentioned styrene, it is difficult to control the temperature, and the above-mentioned drawbacks due to runaway reactions cannot be avoided. For this reason, the reality is that industrial bulk polymerization methods for acrylic acid alkyl ester monomers have not yet been put to practical use. The inventors have been conducting research on the bulk polymerization method of acrylic acid alkyl ester monomers for many years, and in the course of their research, they encountered the large-scale polymerization process during polymerization, which is an impediment to the application of the bulk polymerization method as described above. We investigated a method to continuously obtain homogeneous bulk polymers by taking advantage of the rapid viscosity that accompanies heat generation. The above method uses a reactor that can continuously transfer the contents while renewing the surface and has a temperature control function over the entire transfer process, and mainly contains acrylic acid alkyl ester monomers into the reactor. A raw material for bulk polymerization having a viscosity of 10 poise or less at room temperature is continuously supplied, the viscosity is increased by rapid polymerization in the first half of the transfer process, and the bulk polymer having a predetermined conversion rate is continuously supplied as the polymerization progresses thereafter. It is characterized by the fact that it can be taken out from the reactor in a continuous manner, making it possible to produce bulk polymerization of acrylic acid alkyl ester monomers, which was previously considered difficult, in a continuous manner, which was not possible with other ethylenic monomers. . In other words, in a reactor such as a single-screw or twin-screw extruder that can continuously transfer the contents while renewing the surface, stable transfer of a substance with a constant viscosity is extremely easy; If the product has a slope, the transfer force of the screw etc. will not be transmitted to the contents in the low viscosity range and will idle, causing stagnation or backflow of the contents and making stable transfer difficult. It is necessary to have a state where the viscosity gradient is small. As mentioned above, acrylic acid alkyl ester monomers tend to thicken due to the rapid progress of the polymerization reaction, which has been an obstacle to the application of bulk polymerization in the past, but when using the above reactor, the above properties can be improved. The advantage is that, at least in the first half of the transport process, the viscosity required for stable transport can be achieved by rapid polymerization. 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. This invention utilizes the continuous bulk polymerization method of the above-mentioned acrylic acid alkyl ester polymer,
A single-shaft or screw with a screw rotation speed of 15 revolutions per minute or more, which has a structure in which the continuously supplied contents are continuously transferred while renewing the surface, and which is heated and controlled to a predetermined temperature throughout the transfer process. In a reactor consisting of a twin-screw extruder, acrylic acid alkyl esters having an alkyl group of 2 to 14 carbon atoms were added.
100% by weight and 50 to 0 monomers copolymerizable with this
% by weight of an acrylic acid alkyl ester monomer (hereinafter referred to as an acrylic monomer) and 0.01 to 1 part by weight of a radical polymerization initiator per 100 parts by weight of this monomer. A viscous polymerization raw material is continuously supplied under normal pressure in the absence of a solvent used in normal solution polymerization, and the initiator increases the viscosity by rapid polymerization in the first half of the transfer process, and the subsequent part is converted to a specified level. The present invention relates to a method for producing a pressure-sensitive adhesive composition, characterized in that a bulk polymer having adhesiveness at room temperature is obtained by polymerization progressing until the polymerization rate is reached, and this is used as the main component of the adhesive. . The monomer component of the raw material used in this invention is the acrylic monomer known as a polymer raw material for general acrylic acid alkyl ester pressure-sensitive adhesive compositions, and this monomer consists of acrylic acid and 2 carbon atoms. ~14 alcohols, that is, acrylic acid alkyl esters whose alkyl group has 2 to 14 carbon atoms, in a proportion of 50 to 100% by weight of all monomers, and if necessary, copolymerized with this ester as the main monomer. Possible proportions of 50 to 0% by weight of monomers, such as methacrylic acid alkyl esters or their derivatives, vinyl acetate, styrene, acrylonitrile, acrylic acid, methacrylic acid, acrylic acid alkyl esters or their derivatives other than the above-mentioned main monomers, etc. are added. It is something. The polymerization raw material is a mixture of the above-mentioned acrylic monomer, which can make the formed polymer sticky at room temperature, a radical polymerization initiator, and other additives such as a molecular weight regulator if necessary. It is a liquid agent with the following viscosity. Examples of the above radical polymerization initiators include organic peroxides such as benzoyl peroxide, cumene hydroperoxide, di-t-butyl peroxide, and lauroyl peroxide, and azo compounds such as azobisisobutyronitrile. Can be widely used. The amount of these initiators is generally about 0.01 to 1 part by weight per 100 parts by weight of monomer. In addition to the above-mentioned initiators, it is also possible to use redox-based initiators that can generate radicals at low temperatures. As a molecular weight regulator, thioglycol,
Chain transfer agents such as thioglycolic acid, butyl mercaptan, lauryl mercaptan, and decyl mercaptan are 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 volatilized and removed when they are removed, 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 method of this invention can be used. However, if a large amount of plasticizer or various resins is used, chain transfer or a decrease in monomer concentration will occur, leading to a decrease in the polymerization rate or the molecular weight of the resulting polymer. % or less. In addition, when the bulk polymer synthesized by the method of 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. However, the amount used should still be 25% by weight or less. Single-screw or twin-screw extruders are available as reactors that can continuously transfer the contents while renewing their surfaces, and the reactor of the present invention is equipped with a temperature control mechanism that covers the entire transfer process. It is. 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 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 installed 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 it is of course possible to have a configuration that controls the heating evenly over the entire length. . The raw material for bulk polymerization mainly consisting of acrylic monomers is continuously fed into this extruder from the feed port 2 at a constant rate, preferably after being 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, the temperature is gradually increased in region a 2 using, for example, the heating controller 6 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 take-out port ₃ . 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 to transfer the polymerization raw material or polymerization contents. The amount may be varied. In addition, radical polymerization initiators and molecular weight regulators are
Rather than mixing with the monomer from the beginning, the monomer may be added alone to the reactor and then added and mixed. For example, they can be introduced by providing a suitable feed port at a desired location in region a of the barrel of the single screw extruder shown. 10 in the figure is a supply port provided at the part where the axis 4 of the screw 5 on the front stage side of area _a3 is tapered, and 11 is a supply port for introducing by-products or arbitrary additives in the polymerization reaction. This is an exhaust port for low-molecular volatile substances generated as a result. Furthermore, although a single-screw extruder is used in the above example, polymerization can also be carried out using a twin-screw extruder in the same manner as 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/gap between barrel and screw] is generally 1000/min or more. The rotational speed of the screw at this time [velocity gradient/pi (π) x outer diameter of the screw x (gap between the barrel and the screw)] is determined to cope with the rapid thickening of the content. In order to enable continuous transport while renewing the surface, it is particularly preferable to rotate at a high speed of about 20 revolutions/minute or more, as shown in Examples 1 to 5 below. However, the rotation speed is 15 rotations/min, which is slightly lower than the above rotation speed (for example, the screw outer diameter of Example 5 described later is 40 mm).
It is permissible up to the rotational speed when the gap between the screw and the barrel is 2 mm, which is the maximum value, and the speed gradient is 1000 minutes, which is the minimum value. That is, if the speed is 15 revolutions/minute or more, the continuous bulk polymerization of the present invention can be carried out without any problem by the above-mentioned operation. 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 addition, each of the above additive components can be added to the bulk polymer after obtaining the bulk polymer that is sticky at room temperature, or can be added at any stage of obtaining the bulk polymer, that is, at an appropriate location in the reactor. A drug supply port may be provided and the agent may be blended through the supply port. 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 composition of the present invention has a high monomer concentration and completes polymerization in a short time.
It is estimated that the rate of chain transfer to the self-polymer is higher than when using other polymerization methods, the molecular weight distribution is broader, and the number of branched entanglements is higher than that obtained using 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. Also,
Measurements of adhesive strength, adhesion strength, and holding strength in Examples were carried out by the following methods. The results are summarized in the table below. (1) Adhesive strength: Measured according to JIS Z-1528. (2) Adhesive strength: Based on J.Dow's Rolling Ball Tack measurement method. (3) Holding power: Pressure-sensitive adhesive tape based on a 50 μm thick polyester film was pasted on a Bakelite plate in an area of 10 mm x 20 mm, and a vertical load of 500 g was applied at a temperature of 40°C until it fell. The time was measured. Example 1 Lauryl mercaptan was added to 100 parts of a monomer mixture consisting of 70 parts of n-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, and 3 parts of acrylic acid.
Mix 0.02 part of azobisisobutyronitrile and 0.1 part of azobisisobutyronitrile, fully substitute with nitrogen gas, and reduce to 0.7 at room temperature.
The raw material mixture liquid had a viscosity of centipoise. This raw material liquid is screwed into a screw with an outer diameter of 50 mm and a barrel length of 1000 mm.
mm, the gap between the barrel and the screw crest was 1 mm, and the speed gradient was set at 7850/min, i.e., the screw rotation speed was 50 revolutions/min in a single screw extruder as shown in the figure at a speed of 50 c.c./min. The temperature of the barrel inside the extruder is controlled to 100℃ over the entire length.
Bulk polymerization was carried out continuously. The obtained bulk polymer had a polymer conversion rate of 97.8% and a weight average molecular weight (
w) 440,000, number average molecular weight (n) 39,000, w/
It showed Mn=11.3. 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 per 100 parts of the raw monomer mixture were added to create a pressure-sensitive adhesive. It was made into a drug composition. This was applied onto a 50 μm thick polyester film using a roll coater so that the glue thickness was 50 μm, and dried at 120° C. for 3 minutes to obtain a pressure sensitive adhesive tape. Example 2 0.1 part of azobisisobutyronitrile was mixed with 100 parts of a monomer mixture consisting of 70 parts of n-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, and 3 parts of acrylic acid, and the mixture was thoroughly heated with nitrogen gas. By replacing the mixture with Using this raw material liquid, a bulk polymerization reaction was carried out in the same manner as in Example 1, resulting in a polymer conversion rate of 98.5%, weight average molecular weight (w) 620,000, number average molecular weight (n) 48,000, and w/n. =12.9 bulk polymer was obtained. Using this, a pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and a pressure-sensitive adhesive tape was further obtained from this composition. Example 3 5 parts of dioctyl phthalate and 0.1 part of azobisisobutyronitrile to 100 parts of a monomer mixture consisting of 70 parts of n-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, and 3 parts of acrylic acid.
Mix the parts, thoroughly replace with nitrogen gas, and store at room temperature.
The raw material mixture liquid had a viscosity of 1.5 centipoise. This raw material mixture was polymerized in the same manner as in Example 1, and the polymer conversion rate was 95.6%, w = 420,000, n =
A homogeneous bulk polymer of 32,000 w/n = 13.1 was obtained. Using this, a pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and a pressure-sensitive adhesive tape was further obtained from this composition. Example 4 A raw material mixture having a viscosity of 10 poise at room temperature was obtained by adding the produced bulk polymer of Example 1 in an amount of 3 parts to 100 parts of the monomer mixture to the raw material mixture of Example 1. And so. This was polymerized in the same manner as in Example 1, with a polymer conversion rate of 98.2%, w = 650,000, n
= 54,000, w/n = 12 homogeneous bulk polymers were obtained. Using this, a pressure-sensitive adhesive composition was prepared in the same manner as in Example 1, and a pressure-sensitive adhesive tape was further obtained from this composition. Example 5 0.1 part of lauroyl peroxide was mixed with 100 parts of a monomer mixture consisting of 70 parts of n-butyl acrylate, 20 parts of 2-ethylhexyl acrylate, 10 parts of vinyl acetate, and 3 parts of acrylic acid, and nitrogen gas was added. The mixture was sufficiently replaced to obtain a raw material mixture having a viscosity of 0.8 centipoise at room temperature. This mixed solution was stirred at a stirring speed gradient of 5000/2 with a screw outer diameter of 40 mm, a barrel length of 1000 mm, and a gap of 0.5 mm between the barrel and the screw crest.
It is fed at a rate of 50 c.c./min into a twin-screw extruder (self-cleaning type) with a screw rotation speed of approximately 20 rpm, and the barrel temperature inside the extruder is maintained over the entire length. Bulk polymerization was carried out continuously by controlling the heating to 100°C. The obtained bulk polymer had a polymer conversion rate of 96.8%, w = 550,000, n = 47,000,
It showed Mw/n=11.7. A pressure-sensitive adhesive composition was prepared using this bulk polymer in the same manner as in Example 1, and a pressure-sensitive adhesive tape was obtained from this composition. Comparative Example 1 Three portions of 0.1 part of azobisisobutyronitrile and 300 parts of benzene were added to 100 parts of a monomer mixture consisting of 70 parts of n-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, and 3 parts of acrylic acid. The mixture was placed in a flask, the 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 3.0 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 70 parts of n-butyl acrylate, 30 parts of 2-ethylhexyl acrylate, and 3 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 Comparative Example 2 was added thereto to obtain a pressure-sensitive adhesive tape. The measurement results of the holding force, adhesive force, and adhesive force of each pressure-sensitive adhesive tape obtained in the above Examples and Comparative Examples are shown in the table below.

[Table] (Note) * means cohesive failure of pressure-sensitive adhesive.
From the results shown in the table above, the pressure-sensitive adhesive composition of the present invention exhibits satisfactory performance in both adhesive strength and cohesive strength, which are typical properties of pressure-sensitive adhesives, and can be obtained according to the conventional method. It can be seen that it is superior compared to the previous one.

[Brief explanation of the drawing]

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. A single shaft with a screw rotation speed of 15 revolutions per minute or more, which has a structure in which the continuously supplied contents are continuously transferred while renewing the surface, and which is heated and controlled to a predetermined temperature throughout the entire transfer process. Alternatively, in a reactor consisting of a twin-screw extruder, acrylic acid alkyl ester with an alkyl group having 2 to 14 carbon atoms is added.
~100% by weight and monomers copolymerizable with this ~50~
0% by weight of an acrylic acid alkyl ester monomer and 100 parts by weight of this monomer.
A polymerization raw material having a viscosity of 10 poise or less at room temperature and containing 0.01 to 1 part by weight of a radical polymerization initiator as an essential component is continuously fed under normal pressure in the absence of a solvent used in normal solution polymerization, and the above initiator is The viscosity is increased by rapid polymerization in the first half of the transfer process, and the subsequent polymerization is allowed to proceed until a predetermined conversion rate is reached to obtain a bulk polymer that is sticky at room temperature. A method for producing a pressure-sensitive adhesive composition, characterized in that it is used as a component.