JPS5853975A - Production of pressure-sensitive adhesive tape - Google Patents

Abstract

PURPOSE:An acrylic monomer and an acidic group-containing unsaturated monomer are fed to a special reactor to form a bulk polymer, the polymer is neutralized with an aqueous alkali into a hydrosol and the hydrosol is spread on a support to produce the titled tape with high water resistance and a thin layer coated uniformly. CONSTITUTION:Raw materials for bulk polymerization of less than 10 poise at room temperature, consisting of an acrylic monomer as the major component and of an acidic group-containing unsaturated monomer as a copolymerization component, are fed into a reactor that can continuously transfer the contents, as being always renewing the surface of the contents, and is provided with a temperature control mechanism all over the transferring process, preferably a single- or twin-screw extruder to effect rapid polymerization in the first half under heat control until the polymerization conversion reaches 93-99wt% to form a bulk polymer that is tacky at room temperature. An alkali aqueous solution is continuously fed to the resultant polymer to effect neutralization and they are made into a hydrosol stably dispersed in water. The hydrosol is spread on a support to give the objective tape.

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing pressure sensitive adhesive tapes. Conventionally, pressure-sensitive adhesive tapes are produced using 1) suspension polymerization;
Poly obtained by emulsion polymerization or solution polymerization,
2) A method in which an adhesive composition consisting of a polymer dispersion or a polymer solution is reverse coated onto a support, or 2) a method in which a solid adhesive composition obtained by various polymerization methods is extrusion coated onto a support. Generally manufactured. However, in method 1) above, if a polymer dispersion is made, emulsifiers and dispersants are mixed in, resulting in poor water resistance, and the adhesive properties change due to blooming of emulsifiers and dispersants. Moreover, when used as a polymer solution, there are environmental health problems and cost disadvantages due to the use of organic solvents. In addition, in method 2) above, the viscosity of the adhesive composition is lowered by heating during extrusion coating, but the viscosity is lowered by 1 kg until a thin layer can be coated uniformly on the support, while giving a lower viscosity. Such a composition has poor heat resistance as a pressure-sensitive adhesive tape, and also has poor retention properties on a support. This invention overcomes the drawbacks of the conventional methods described above, does not cause changes in water resistance or adhesive properties caused by emulsifiers or dispersants, and also eliminates environmental hygiene problems and costs caused by organic solvents. It is an object of the present invention to provide a method for producing a pressure-sensitive adhesive tape that can be coated uniformly in a thin layer on a support while not causing any disadvantages in surface area. A reactor is used that is capable of continuous transfer and is equipped with a temperature control mechanism throughout the entire transfer process. A raw material for bulk polymerization with a viscosity of 10 poise or less at room temperature as a copolymerization component is continuously supplied, and while heating is controlled to a predetermined temperature throughout the entire transfer process, it is rapidly heated in the first half of the transfer process. When the viscosity is increased from the small polymerization number, the polymerization progresses after the 1st polymerization.

[Thus, a predetermined conversion rate is achieved, and in the second half of the transfer process, an alkaline aqueous solution is continuously supplied to the bulk polymer, which is sticky at room temperature and has the above-described predetermined conversion rate. A pressure-sensitive adhesive characterized in that the acidic groups are neutralized and the polymer is stably dispersed in water to form hydrosil, which is continuously removed from the reactor and then applied onto a support and dried. This relates to a method for manufacturing a tape. By the way, in the general bulk polymerization method, temperature control becomes difficult due to thickening caused by rapid reaction progress, and the reaction tends to run out of control. As a result, not only is the polymerization process dangerous, but it is also difficult to design the molecular weight of the polymer, gelling and deterioration products are likely to occur as by-products, and it is difficult to obtain a homogeneous polymer. There are some publications that cause processing problems during the process. □, 1 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 the polymer is either polymerized to a conversion rate of 30 to 70% in a well-formed prepolymerization vessel, and the remainder is demonomerized to produce a product, or the converted product is fed into an extruder (an extruder) in a gentle manner. Reactor trowel 95-96%
The reaction proceeds to a conversion rate of . On the other hand, acrylic monomers generate a large amount of heat during polymerization,
Even if a polymerization method using a regular type 1 such as the above-mentioned styrene is used, it is difficult to control the temperature, and the above-mentioned drawbacks due to runaway reactions cannot be avoided. For this reason, acrylic monomer (
The reality is that the difficult industrial bulk polymerization method has not yet been put into practical use. The inventors have continued to investigate the bulk commercial method of such acrylic yarn monomers for many years. We investigated a method to continuously obtain homogeneous bulk polymers by taking full advantage of the rapid viscosity that accompanies the large exothermic end of the process. In addition, the monomer composition of the bulk polymer obtained by this method (which allows it to have tackiness at room temperature) can be coated as it is by hot extrusion coating on a support in a thin, uniform layer. Since forming an adhesive layer is accompanied by a difficult problem, the above bulk polymer is further neutralized with an alkaline aqueous solution.
The present inventors discovered that the copolymer described above can be uniformly coated in a thin layer on a support by forming a hydrosil in which the copolymer is stably dispersed in water, leading to the completion of this invention. It is something. The drawing shows the cross-sectional structure of a single-screw extruder, which is an example of a reactor used in the present invention, and the method for manufacturing the pressure-sensitive adhesive tape 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. )<A plurality of screws 5 having a rotating shaft center 41 are formed inside the sill 1,
The polymerization raw material supplied by this screw 5 is
Move forward while mixing by rotating. The distance between the screw 5 and the barrel 1 is set appropriately in order to improve miscibility. The general distance is approximately 0.5 to 2 mm. 6.7
．． 8, 9, 10, and 11 are heating controllers installed at each part of the entire length of the barrel, and each part is configured to be able to control the temperature to an appropriate level. Of course, it is possible to do this.Into this extruder, from the supply port 2, a copolymerization component containing an acrylic monomer as a main component and an unsaturated monomer having acidic) The raw material for bulk polymerization is preferably replaced with nitrogen in advance and is continuously supplied at a constant rate.The supplied raw material is mixed by one rotation of the screw 5 and transferred while being updated. The transfer process from 1 to the take-out port 3 is indicated by a in the figure.
For example, the heating controller 6 gradually increases the viscosity in the area al-a2 so that the viscosity increases by rapid polymerization within one and a half areas, and the heating controller 7 instantly starts polymerization in the area a3. The temperature is controlled to allow the polymerization reaction to proceed rapidly. The polymerized contents whose viscosity has increased in this way are further mixed and
The surface is updated and transferred to the intermediate area. The polymerization reaction is allowed to proceed until the desired conversion rate is reached while the temperature is controlled by a heating controller 8.9. Next, the bulk polymer that has reached the desired conversion rate and is sticky at room temperature is transferred to the second half area C, where an alkaline aqueous solution is continuously supplied from the supply port 12 while the temperature of the trowel is controlled by a heating controller 10°111. The acidic groups in the bulk polymer molecules are neutralized, and the polymer is stably dispersed in water to form hydrosil, which is finally taken out continuously through the outlet 3 at the open end. The extracted hydrosil is coated onto a polyester film or other support using a conventionally known low-viscosity coating machine such as a roll coater or fountain coater and dried to produce a pressure-sensitive adhesive tape. In this example 1, the axis 4 of the single-screw 5 is concentric between each screw 5.5, but for the purpose of controlling the reaction, the diameter is different in each part of the barrel. The transfer amount of the polymerized contents may be changed by 1. Further, in the above example, a single-screw extruder is used, but polymerization can also be carried out using a twin-screw one-port extruder in the same manner as described above. In the case of a two-axis screw, each axis can be rotated once in the same direction or in different directions. In these screw extruders, as mentioned earlier, 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
)×rotation speed×screw outer diameter/gap between barrel and screw] is generally 1,0007 minutes or more. Furthermore, in addition to the above-mentioned screw extruder, the reactor used in the present invention is one that can continuously transfer the contents while renewing the surface and is equipped with a temperature control mechanism throughout the entire transfer process. You can use any of them if you have them. This surface renewal includes renewing the contact surface between the contents and the reactor wall, and by exchanging heat between the two, the temperature of the reactants is efficiently controlled and side reactions are suppressed. In the above method 1, it is very important in this invention method to rapidly advance the polymerization reaction in the half region of the barrel to increase the viscosity of the polymerized content. This is a requirement that enables stable transfer of materials and temperature control. That is, in the reactor used in this invention, such as the above-mentioned screw extruder, it is extremely easy to stably transport materials with a constant viscosity, but when the barrel has a large viscosity gradient in the longitudinal direction and the low viscosity region is long, For example, the screw in one of the screw extruders may become partially idle in the low viscosity region, causing accumulation or backflow of the contents, making stable transfer difficult. Therefore, it is important to maintain a state in which the viscosity gradient is small over as long a region as possible during the transfer process. As mentioned above, acrylic monomers tend to thicken due to the rapid progress of the monopolymerization reaction, and this has hitherto been a problem for bulk polymerization, but in the present invention, this property is used to the contrary. In other words, even if the viscosity of the polymerization raw material mainly composed of acrylic monomers is 10 poise or less, the viscosity can be increased to the extent necessary for stable transfer in just a few minutes by rapid polymerization in at least the first half of the transfer process. Furthermore, since the method of the present invention transfers the surface while renewing it, it is possible to control the temperature according to the subdivided areas during the transfer process, so that the rapid polymerization can be sufficiently controlled to prevent it from reaching a runaway reaction. The viscosity required for the above stable transfer depends on the type and size of the reactor,
Although it varies depending on the type of acrylic monomer, the transfer rate of the polymerized contents, the desired properties of the bulk polymer, etc., it is generally in the range of 100 to several 1,000 poise. Further, although the region in which rapid polymerization is performed is region a3 in the first half region a of the transfer process in the above example, it goes without saying that it may be an earlier region, such as region a2 in the above example. In addition, in the conventional well-formed solution polymerization method in which acrylic monomer is diluted with an organic solvent, it takes a long time of 1 to 10 hours to obtain the conversion rate that provides the above-mentioned required viscosity. The polymerization raw material used in this invention, which has an acrylic monomer as a main component and an unsaturated monomer having an acidic group as a copolymerization component, has an alkyl ester of acrylic acid or methacrylic acid or a derivative thereof as a main monomer, and if necessary, A monomer mixture containing various ethylenically unsaturated monomers such as styrene, vinyl acetate, and acrylonitrile that can be copolymerized with this monomer, and an unsaturated monomer having an acidic group together with these monomers, can be made into a polymer at room temperature. It is a liquid agent consisting of a material exhibiting adhesive properties, which is a mixture of such monomers with a radical polymerization catalyst and, if necessary, a molecular weight regulator, etc., and has a viscosity of 10 poise or less at room temperature. Examples of unsaturated monomers having an acidic group in the hexamer mixture include unsaturated carboxylic acids having a carboxyl group as an acidic group, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, styrene sulfone, etc. Unsaturated sulfonic acids having a sulfonic group can be mentioned as acidic groups such as acids, acrylfroyloxypropanesulfonate, methallyls/\ sulfonate, acrylamide propanesulfonate, etc., and they may also have other acidic groups. , one or more of these may be used. The usage of the unsaturated monomer having an acidic group is preferably 1 to 20% by weight based on the total monomers. For example, in the case of unsaturated carboxylic acids, 5 to 15% by weight is suitable, and in the case of unsaturated sulfonic acids, 3 to 10% by weight is suitable. If too little of this type of monomer is used, good results are not obtained in the hydrosilation. Furthermore, since this type of monomer generally increases the glass transition temperature of the polymer, if too much of this monomer is present, a good pressure-sensitive adhesive cannot be obtained. Examples of radical polymerization catalysts that are one of the polymerization raw materials include organic peroxides such as benzoyl peroxide, cumene hydroperoxide, di[-butyl peroxide, and lauroyl peroxide, and azo compounds such as azobisisobutyronitrile. etc. can be widely used. The amount of these catalysts is generally about 0.01 to 1 part by weight per 100ffi of monomer. Further, it is also possible to use a redox catalyst that can generate radicals at a lower temperature than the above catalysts. As molecular weight regulators, thioglycol, thioglycolic acid, butyl mercaptan,
Chain transfer agents such as lauryl mercaptan and decyl mercaptan are used. The radical polymerization catalyst and molecular weight regulator may not be mixed with the monomer from the beginning, but may be added and mixed after the monomer is added alone to the reactor. For example, they can be introduced at a desired location in region a of the barrel of the single screw extruder shown by providing a suitable feed port. 13 in the figure is a supply port provided at the thinner part of the axis 4 of the screw 5 on the front stage side of the region a3, and 14 is a supply port for low molecular volatilization which is a by-product of the polymerization reaction or generated by the introduction of arbitrary additives. It is an exhaust port for things. Such polymerization raw materials are polymerized to a predetermined conversion rate in the first and middle regions of the transfer process, and the polymerization conversion rate at this time is usually 93 to 99% by weight, and the average molecular weight of the polymer is 100,000%. As mentioned above, the preferred value is 200,000 to 800,000. If the average molecular weight is too low, the cohesive force of the resulting pressure-sensitive adhesive tape will be poor; if it is too high, problems such as problems with hydrosilation may occur. In the latter half of the transfer process, an alkaline aqueous solution is supplied to the bulk polymer, which is sticky at room temperature once a predetermined conversion rate has been reached. Ammonia that can be volatilized quickly and has particularly good water and moisture resistance properties is desirable. Examples of other alkalis include nitrogen-containing compounds such as propylamine, aniline, and alkanolamines, and caustic alkali metals such as sodium hydroxide and potassium hydroxide. The amount of alkali to be used is usually 0.1 to 1.5 times the amount of acidic groups contained in the bulk polymer molecules. By supplying such an alkaline aqueous solution, part or all of the acidic groups contained in the bulk polymer are neutralized, and due to the phase inversion phenomenon caused by the introduction of water, hydrosil, that is, polymer particles, have a particle size of 0.01 to 0.1μ. A uniformly and stably dispersed dispersion in water is produced within this range. This hydrosil has a low viscosity that allows it to be coated with a roll coater or fan coater, but if necessary, it can be diluted to the desired viscosity by adding water after being taken out from the outlet of the reactor. You can also do that. The total proportion of water that can be added into the reactor and taken out from the reactor is generally set so that the solid content concentration is 10 to 60% by weight. The viscosity of the hydrosil at this time is usually 30 to 1,000 voids at 25°C. In the above production method, 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 polymerized contents transferred to each part, etc. The temperature of the polymerized content in the first half region and the middle region is 40 to 150°C, preferably 60 to 1
It is desirable to adjust the temperature within the range of 00°C, and in particular, the heating temperature in the area where the viscosity is increased by rapid polymerization should be set depending on the type of polymerization catalyst, the structure of the crucian carp, the structure of the carp reactor, and the transfer conditions. . In addition, in the latter half of the transfer process, the temperature of the contents is 20 to 100°C, preferably 40 to 8°C.
It is preferable to set it to 0°C1. In this invention, the hydrosil taken out from the reactor as described above is coated on a support and dried to obtain a pressure-sensitive adhesive tape. Various additives can be added in the latter half of the transfer process, that is, in the region where the alkaline aqueous solution is supplied, or in the intermediate region from Case 1. The aqueous alkali solution may be added at the same time from the supply port 12, or may be added by providing a separate supply port. Alternatively, a similar additive can be added after being removed from the hydrosyl-forming reactor. Examples of such additives include, for example, initial adhesion (
In order to further improve tack), we use liquid tackifying resins such as phenolic resins, petroleum resins, styrene resins, xylene resins, and terpene resins used in general pressure-sensitive adhesives, and polyether polyols. There are hydrophilic plasticizers such as The amount of these additives should be up to 50 parts by weight per 100 parts by weight of the polymer component in the hydrosil. If the amount is too large, properties such as cohesive strength and heat resistance may be impaired, and the stability of the hydrosil may be reduced. It is not desirable because it has a negative effect. Moreover, the average molecular weight which is liquid at room temperature is s, oo. ~200,000 low molecular weight polymers can also be added to improve initial adhesion. As such a low molecular weight polymer, an acrylic low molecular weight polymer having a similar composition to the acrylic monomer used in the present invention is preferable from the viewpoint of compatibility. The amount of these polymers added varies depending on the composition, but it is best to add up to 200 parts by weight per 100 parts by weight of the hydrosil polymer component; too much will impair properties such as cohesive strength and heat resistance. It also inhibits the stability of hydrosyl. Furthermore, in order to improve the cohesive force, an appropriate crosslinking agent such as a polyvalent metal salt such as calcium chloride or aluminum acetate, a water-soluble glycidyl compound, or a water-soluble melamine may be added. The amount added is usually up to 2 parts by weight, preferably within the range of 0.005 to 1 part by weight, per 100 parts by weight of the hydrosil polymer component. Pressure-sensitive adhesive tapes that can be produced according to this invention include:
Selecting the pressure-sensitive adhesive composition and support from general packaging tapes to double-sided adhesive tapes and electrical insulation tapes 1.
Various tapes can be obtained from this. As detailed above, the present invention has discovered a method for bulk polymerization of acrylic monomers that solves the problems caused by conventional suspension polymerization, emulsion bed polymerization, or solution polymerization, while also adding alkali polymerization to the bulk polymerization obtained by this method. The aqueous solution is hydrosilated to enable uniform thin layer coating on the support, and by making these manufacturing steps continuous, it is ideal from the standpoint of quality stability and manufacturing efficiency. It is possible to provide a method for manufacturing a pressure-sensitive adhesive tape, which is extremely meaningful industrially. Next, examples of this invention will be described. In addition, the adhesive strength in the examples is JIS7. -1528, the 180 degree peeling strength (91720am) was measured, and the holding power (cohesive force) was measured at 25X on the Bakelite plate.
The time taken for the Bakelite plate to fall was measured by laminating the sheets to a thickness of 25 mm and applying a load of I kg at 40°C. Example 1 As a reactor, an extruder having a single internal screw type stirrer was used. In addition, the screw diameter is 40 mm, the barrel length is 1,250 mm, and zones A, B, C, D, and E]
The temperature can be adjusted independently for each zone, and there are supply ports in zones A and D, and the temperature is A:B:C:I):E=
100°C: ] 00'C: 100°C: 30°C: 30°C
I set one. The gap between the barrel and the screw thread is 1mm.
The velocity gradient between the screw mountain and the barrel is 6.280/
It was a minute. Using the above reactor, butyl acrylate:acrylic acid:azobisisobutyronitrile-90:10:0.15
A polymerization raw material of 0.8 centivoise consisting of (ili amount ratio) was quantitatively fed from the supply port of the A zone at a speed of 50 y/min. Furthermore, a 5% by weight ammonia aqueous solution and a 1% epoxy crosslinking agent aqueous solution were quantitatively fed from the supply port of the D zone at a speed of 100 y/min and 5 y/min, respectively. The resulting water-dispersed pressure-sensitive adhesive (hydrosil)
The polymer conversion rate is 98.5%, and the solid content is 30%.
, the average molecular weight of the polymer particles was 400,000. this,
After drying with a roll coater, the glue thickness was 50μ (coated with 25μ polyester film and heated at 130°C).
and dried for 5 minutes. The resulting tape has an adhesive strength of 820 y
/ 201 nm, and the holding force was more than i, ooo minutes. In addition, the melt viscosity at 200'C1 of the bulk polymer obtained without supplying the ammonia aqueous solution and the crosslinking agent aqueous solution from the supply port of the D zone in the above method 1 is 10.0
00 poise, it could not be applied in a uniform thin layer onto a polyester film by extrusion coating. Example 2 The reactor was the same as in Example 1, with A, B, C, D
, the temperature of E zone is 100℃, 120'C, 1, respectively.
The temperature was set at 20°C, 80°C and 140°C. Other conditions are the same as in Example 1. The polymerization raw materials are phtyl acrylate: 2-ethylhexyl acrylate: acrylic acid: azobisisobutyronitrile -45:45:10:O,1
. Furthermore, a 25% by weight ammonia aqueous solution and a 1% epoxy crosslinking agent aqueous solution were quantitatively fed from the supply port of this D/- at a speed of 30 y/min and 7 y/min, respectively. Pressure adhesive (hydrosil)
The solid content is 30% by weight, and the polymer conversion rate is 98.7% by weight.
The average molecular resistance of the polymer particles was 350,000. This was made into a tape in the same way as in Example 1, and adhesive cuff 20
At gI/20 nm, the retention force was 1.000 minutes or more. Example 3 A twin-screw extruder having two internal screw shafts was used as the reactor. Barrel (total length 1.500 mm) is A
, B, C, D, E, and F are divided into 6 zones, each with a temperature of 100°C, 100°C, 100°C, 150°
C150°C180°C (This setting was made. Zones A, D and E each have a supply port, the screw diameter is 50 mm, and the gap between the barrel and the screw thread is I.
mm, the velocity gradient between the screw thread and the barrel is 9,
It was 980/min. The polymerization raw material was the same as in Example 1, and was supplied at a constant rate of 00 p/min from the supply port of the A zone. 1) Liquid xylene resin was supplied stationary at 20 y/min from the supply port of the zone, and 1.0 weight% thorium hydroxide aqueous solution and 1 wt% epoxy crosslinking agent aqueous solution were respectively supplied from the supply port of the E zone. The constant was supplied at a speed of 201'/min, 10y/min. The resulting water-dispersed pressure-sensitive adhesive (hydrosil)
The solid content was 30 tons 1 m%, the polymer conversion rate was 99%, and the average molecular weight of the polymer particles was 500,000. When this was made into a tape in the same manner as in Example 1, the adhesive strength was 9.
80 y/20 am, hold cuff 50 minutes. Comparative Example Compared to Example 1, butyl acrylate: acrylic acid: azobisisobutyronitrile = 100:10 was prepared in a Mitsuro Furaraco equipped with a barrel stirrer, nitrogen exchanger, and cooling pipe.
:0.15 (heavy elbow ratio) to (to) It is a sectional view of the single screw extruder shown. Add 500 y of polymerization raw material mixed with 40% market weight of toluene in 1 trowel, and after purging with nitrogen, polymerize for 6 hours while controlling the temperature at 60 to 65°C, and further mature at 80°C for 4 hours. Ta. A 1% Ichikawa epoxy crosslinking agent solution dissolved in methyl ethyl ketone was blended with the solution polymerized product thus obtained, and the same solution as in Example 1 was formed into a tape using a reverse coater. The obtained tape has an adhesive strength of 840f;'/20r
nm, and the holding power was 1,000 minutes. As is clear from the above Examples and Comparative Examples, the characteristics of the tape obtained from this invention are almost the same as those of organic solvent-based tapes, and since no organic solvent is used as a medium, it is environmentally friendly and cost effective. It is clear that it has superior water resistance and moisture resistance compared to those obtained by suspension polymerization or emulsion polymerization. This can be done easily.

[Brief explanation of the drawing]

The drawing shows the method of this invention (41 as an example of the reactor used). Patent applicant: Nitto Electric Industry Co., Ltd.

Claims (2)

[Claims] (1) Use 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, and transfer the material containing mainly acrylic monomers and acidic groups into the reactor. A raw material for bulk polymerization having a viscosity of 10 poise or less at room temperature and containing an unsaturated monomer having a The viscosity is increased by rapid polymerization in the region, and a predetermined conversion rate is achieved by the subsequent polymerization progress.Furthermore, in the second half of the transfer process, the bulk polymer, which is sticky at room temperature and has the above-mentioned predetermined conversion rate, is treated with an alkali. An aqueous solution is continuously supplied to neutralize the acidic groups in the molecules of the bulk polymer, and the polymer is turned into hydrosil, which is stably dispersed in water. 1. A method for producing a pressure-sensitive adhesive tape, which comprises applying the tape to a surface and drying it. (2) The method for producing a pressure-sensitive adhesive tape according to claim (1), wherein the reactor is a power-screw extruder or a twin-screw extruder.