JPH0143792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a pressure-sensitive adhesive tape, and its purpose is to produce an acrylic pressure-sensitive adhesive tape with excellent properties at a lower cost and more consistently and continuously than the polymerization process of the adhesive polymer. The point is to provide a method for manufacturing.

Typical methods for producing pressure-sensitive adhesive tapes include applying a pressure-sensitive adhesive component diluted with water or an organic solvent onto a tape support using a roll coater and drying it, and applying a bulk pressure-sensitive adhesive to a calendar or T-shirt.
A method of spreading and coating the tape directly onto a tape support using a die or the like is known. The pressure-sensitive adhesive components used in the former method include emulsion polymers and solution polymers, but they require energy and man-hours for coating on the support and volatilizing the diluent, which is a factor in high costs. In addition to high costs, solvent-based products also pose environmental health problems and fire hazards. On the other hand, in the latter method, it is difficult to use emulsion polymers or solution polymers that have been made into lumps by some means as a bulk pressure-sensitive adhesive, which is problematic in practice. It can be said that it is most industrially advantageous to use the polymer obtained in .

However, 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 product. 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%. Recently, as a method for continuous polymerization of methyl methacrylate, for example, in Japanese Patent Publication No. 50-34071, a reactor consisting of a screw extruder is used, and a polymerization material mainly composed of methyl methacrylate is introduced from one end of the reactor into the reactor. is continuously press-fitted at a pressure higher than atmospheric pressure, 10 turns/
A method has been proposed in which the polymerization reaction is carried out while being transferred toward the other end at a low screw rotation speed of less than 1 minute, and the polymer is continuously taken out after removing unreacted monomers and volatile matter at the latter stage of the transfer process. There is.

On the other hand, acrylic acid alkyl ester monomers have a much larger calorific value during polymerization than the above-mentioned styrene, methyl methacrylate, etc., so not only continuous polymerization methods such as the above-mentioned methyl methacrylate, but also the above-mentioned styrene and methyl methacrylate are used. Even with such a pot-type polymerization method, 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 consisting of a single or twin screw extruder that can continuously transfer the contents while renewing the surface and has a temperature control function over the entire transfer process. The number of rotations was set at 50 revolutions per minute or more, and acrylic acid alkyl ester monomers (hereinafter referred to as acrylic monomers) were fed into the reactor at room temperature for 10 minutes.
Bulk polymerization raw materials having a viscosity below poise are continuously supplied under normal pressure, the viscosity is increased by rapid polymerization in the first half of the transfer process, and the bulk polymers that have reached a predetermined conversion rate in the subsequent polymerization progress are continuously fed. It is characterized by being removed from the reactor, making it possible to carry out bulk polymerization of acrylic monomers in a continuous manner, which was previously considered difficult.

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 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. Also,
In the above method, the contents are transferred while the surface is renewed, and the contact surface between the contents and the reactor wall is constantly renewed, so the efficiency of heat exchange between the two is good and the temperature distribution width of the contents is narrowed. , sufficient temperature control can be performed to prevent side reactions and runaway reactions from occurring.

This invention involves obtaining a bulk polymer that is sticky at room temperature by the above-mentioned continuous bulk polymerization method of acrylic monomers, and continuously molding this into a sheet shape.
This method involves a continuous process in which the molded product is applied onto a tape support, and the pressure-sensitive adhesive tape has excellent properties and appearance in a continuous process through the production of an adhesive polymer. We can manufacture tape.

In this invention, the monomer component of the polymerization raw material that is continuously supplied to the reactor in order to obtain a bulk polymer that is sticky at room temperature is an acrylic monomer that is known as a raw material for conventionally known acrylic pressure-sensitive adhesives. is used. That is, an acrylic acid alkyl ester consisting of an ester of acrylic acid and an alcohol having 2 to 14 carbon atoms is used alone, or this ester is used as the main monomer (that is, the ester is used in an amount of 50% by weight of the total monomers).
If necessary, monomers copolymerizable with the above esters, such as vinyl acetate, styrene, acrylic acid, methacrylic acid, acrylonitrile, acrylic acid alkyl esters and methacrylic acid alkyl esters other than the above-mentioned main monomers, are added. A mixture of monomers consisting of:

The polymerization raw material is mainly composed of the above-mentioned acrylic monomer, which can make the formed polymer sticky at room temperature, and is usually mixed with a radical polymerization catalyst and, if necessary, other additives such as a molecular weight regulator. ,
It is a liquid agent with a viscosity of 10 poise or less at room temperature.

Examples of the above radical polymerization catalysts include organic peroxides such as benzoyl peroxide, cumene hadroperoxide, di-t-butyl peroxide, and lauroyl peroxide, and azo compounds such as azobisisobutyronitrile. Can be widely used. These catalyst amounts are monomer
It is generally about 0.01 to 1 part by weight per 100 parts by weight. In addition to the above catalysts, it is also possible to use redox catalysts that can generate radicals at low temperatures.
As the molecular weight regulator, a chain transfer agent such as thioglycol, thioglycolic acid, butyl mercaptan, lauryl mercaptan, and decyl mercaptan is used.

In addition, in this invention, in order to impart appropriate properties to the produced bulk polymer, if desired, a small amount of solvent,
Plasticizers, polymers, etc. may be blended into the raw materials. This compounding amount is the total amount of these components and the monomer
It is desirable that the amount is 25 parts by weight or less per 100 parts by weight.

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,
Numerals 9 and 10 are heating controllers installed at each part of the entire length of the barrel, and each part can be controlled to an appropriate temperature, but it is of course possible to control the heating evenly over the entire length. It is.

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 under normal pressure, 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 the region a 1 using the heating controller 6, for example, 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 . area a ₂ with heating controller 7.
The temperature is controlled so that polymerization starts instantaneously and the polymerization reaction proceeds rapidly.

The polymer content whose viscosity has increased in this way is further mixed and surface renewed while being transferred to the second half area b via area a ₃ having a heating controller 8, and is heated to a desired temperature while being temperature controlled by heating controllers 9 and 10. The polymerization reaction is allowed to proceed until the conversion rate is reached, and finally the polymer is continuously taken out from the takeout 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 amount transferred may be varied.

Further, the radical polymerization catalyst and the molecular weight regulator may be added and mixed after the monomer is added alone to the reactor, instead of being mixed with the monomer from the beginning. 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. 11 in the diagram is the area
It is a supply port provided at the part where the axis 4 of the screw 5 on the previous stage side of a ₂ is tapered, and 12 is a supply port for small molecules that are by-produced in the polymerization reaction or generated by introducing arbitrary additives. It is an exhaust port for volatile substances. 1
3 is a supply port for additives, which will be described later.

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.

And the number of revolutions of the screw at this time [=
Velocity gradient/pi (π) x screw outer diameter x (gap between barrel and screw) In order to do so, as shown in the examples below,
High speed rotation of 50 revolutions/minute or more. That is,
Such high speed rotation makes it possible to carry out the continuous bulk polymerization of the present invention without any problems.

The bulk polymer, which is sticky at room temperature, obtained as described above is taken out of the reactor and then continuously formed into a sheet and coated as a bulk pressure-sensitive adhesive with a coating machine directly connected to the reactor. The tape is deposited onto the support.

In this case, for example, as shown by 13 in the figure, tackifier, plasticizer, pigment,
Desired components such as fillers can be continuously blended into the bulk polymer before being taken out, if necessary. A crosslinking agent can also be added depending on the conditions.

Generally, pressure sensitive adhesives are crosslinked to improve heat resistance, oil resistance, weather resistance, water resistance, etc. In this case, with conventional pressure sensitive adhesives diluted with water or organic solvents, various water-soluble or oil-soluble chemical crosslinking agents can be used with sufficient adjustment time due to the dilution effect, but as in the present invention, In bulk pressure-sensitive adhesives, even a slight crosslinking reaction causes problems in film formation. However, by appropriately selecting the temperature conditions during extrusion and further heating after forming into a sheet, it becomes possible to use a crosslinking agent.

Examples of crosslinking agents that can be used include melamine types such as ethyl etherified methylol melamine and butyl etherified methylol melamine, isocyanate types such as tolylene diisocyanate and hexamethylene diisocyanate, benzoyl peroxide, di-
Examples include peroxide systems such as t-butyl peroxide, and epoxy systems such as diglycidyl ether of bisphenol A. In addition, instead of these, triplet oxidation can be performed by ultraviolet absorption of anthraquinone, β-methylanthraquinone, 2-methyl-1,4-naphthoquinone, quinone dioxime, 1,4-benzoquinone, benzanthrone, benzophenone, etc. before forming the sheet. It is also possible to mix a component that exhibits a sensitizing effect and photo-crosslink it with ultraviolet rays having a wavelength of about 2800 to 4000 Å, for example, from a low-pressure to ultra-high pressure mercury lamp, xenon lamp, carbon arc lamp, etc. after forming the sheet. The above-mentioned crosslinking agent or sensitizer is used in an amount of 0.01 to 0.5 parts by weight per 100 parts by weight of the bulk polymer.

As for the coating machine, the suitable model is determined depending on the viscosity of the pressure-sensitive adhesive, and a roll coater or the like is used for low-viscosity pressure-sensitive adhesives, but the adhesive of this invention is lumpy and has a high viscosity. T-dies and calenders used in general plastic molding are suitable.

One of the features of the method of this invention is that the reactor for producing the pressure-sensitive adhesive and the coating machine are directly connected, and the produced bulk polymer can be directly led to the coating machine. When the polymer is taken out of the reactor, it is softened by the heat of reaction and is easily molded, so no additional man-hours or energy is required for molding. In contrast, ordinary adhesives require man-hours, energy, labor, time, etc. to form them into ribbons or pellets, and to heat them to improve moldability.

The final pressure-sensitive adhesive tape can be used for general packaging tape, double-sided adhesive tape, electrical insulation tape, etc. by appropriately selecting the composition of the bulk pressure-sensitive adhesive and the type of tape support. Various configurations are possible.

As described above, the method of the present invention enables the production of pressure-sensitive adhesive tapes using pressure-sensitive adhesives mainly composed of acrylic acid alkyl ester polymers in a shorter time, at lower cost, and more easily through a continuous process that is more consistent than the production of adhesives. It has the characteristic of being able to be manufactured and has extremely high utility value industrially.

The present invention will be specifically illustrated below with reference to Examples. In the examples, all parts mean parts by weight, and the adhesive strength and holding strength were measured by the following method.

<Adhesive Strength> 180 degree peeling adhesive strength (g/20 mm) was measured based on JISZ-1528.

<Holding force> A pressure-sensitive adhesive tape measuring 25 x 25 mm was attached to a Bakelite plate, a load of 1 kg was applied at 40°C, and the time (minutes) until the tape fell was measured.

Example 1 Screw outer diameter 40mm, barrel length 1250mm, gap between barrel and screw crest 1mm, A from front end side,
A single-screw type screw extruder is used, which is divided into five zones B, C, D, and E whose temperature can be controlled independently, and has a feed port at the front end of zones A and D to control the temperature of each zone. A, B, C, D,
E=100°C, 100°C, 100°C, 30°C, 30°C, and the speed gradient between the screw mountain and the barrel was set at 6280/min, that is, the screw rotation speed was set at 50 revolutions/min.

From the supply port of zone A of this reactor, 90 parts of 2-ethylhexyl acrylate and 10 parts of ethyl acrylate were added.
1 part, 2.5 parts of acrylic acid, and 0.15 parts of azobisisobutyronitrile, with a viscosity of 0.8 centipoise at room temperature, was mixed with 40 g/ml while purging with nitrogen gas.
Bulk polymerization reaction was carried out continuously by continuous feeding under normal pressure at a rate of 5 g/min, and an 8:2 dilution of dioctyl phthalate and butyl etherified methylol melamine was fed from the feed port of the D zone at a rate of 5 g/min. . The butyl etherified melamine was supplied in a feed ratio of 2.5 parts per 100 parts of polymer.

A lip with a length of 40 mm and a gap that connects the bulk polymer continuously taken out from the above reactor directly to the reactor.
The paste was passed through a 0.5 mm die at 30°C and applied onto a 25μm thick polyester film by adjusting the take-up speed so that the glue was 25μm thick, and then passed through an oven at 130°C for 90 seconds to cross-link. The reaction was completed. The pressure-sensitive adhesive tape thus obtained had an adhesive strength of 720 g/20 mm and a retention strength of over 1000 minutes.

Example 2 Using the same reactor as Example 1, A, B, C,
The temperature in each zone of D and E is 80℃, 80℃, 100℃,
The conditions were the same except that they were set at 100°C and 120°C.
From the supply port of zone A of this reactor, 100 parts of 2-ethylhexyl acrylate, 40 parts of vinyl acetate, 3 parts of acrylic acid, and azobisisobutyronitrile were added.
70 g of a mixed solution containing 0.15 parts and having a viscosity of 0.6 centipoise at room temperature, which has been replaced with nitrogen gas in advance.
A pressure-sensitive adhesive tape was prepared according to Example 1, except that continuous feeding was carried out under normal pressure at a rate of 1.5 min, and the die temperature was 75°C. This tape has an adhesive strength of 850
g/min, and the holding power was 295 minutes.

Example 3 Two screws outer diameter 50mm, barrel length 1250
mm, the gap between the barrel and the screw ridge is 1 mm, and the temperature is divided into 5 zones A, B, C, D, and E that can be controlled independently from the front end. Using a twin-screw extruder with a feed port, the temperature of each zone was set to A, B, C, D, E = 80℃, 80℃, 100℃, 100℃.
℃, 100℃, and the speed gradient between the screw mountain and the barrel is 15700/min, that is, the screw rotation speed is 100.
It was set to revolutions/minute.

From the supply port of the A zone of this reactor, 90 parts of n-butyl acrylate, 10 parts of methyl methacrylate, 2
- 100 g of a mixture of 1.5 parts of hydroxyethyl acrylate and 0.2 parts of azobisisobutyronitrile with a viscosity of 0.9 centipoise at room temperature.
Bulk polymerization reaction is carried out continuously by continuous feeding under normal pressure at a rate of 20 g/min, and a dispersion of dioctyl phthalate: β-methylanthraquinone = 100:1 is fed from the supply port of the D zone at a rate of 20 g/min. did.

The bulk polymer continuously taken out from the above reactor is connected directly to the reactor with a lip length of 40 mm and a gap.
It was passed through a 0.2 mm die at a temperature of 75°C and applied to a 30 μm thick semi-rigid PVC sheet by adjusting the drawing speed to a thickness of 30 μm, and then applied to the surface using a 400 W high pressure mercury lamp with a wavelength of 2800 Å. Crosslinking was carried out by irradiating ultraviolet light for 3 minutes from a distance of 10 cm. The tape obtained in this way has an adhesive strength of 950 g/20 mm and a holding power.
It took 750 minutes.

[Brief explanation of drawings]

The drawing shows one example of a reactor used in this invention.
FIG. 2 is a cross-sectional view of a axial screw extruder.

Claims (1)

[Claims] 1. Using a reactor consisting of a single or twin screw extruder that can continuously transfer the contents while renewing the surface and is equipped with a temperature control mechanism over the entire transfer process, the screw rotation speed is set to 50. rotate/
Set the temperature to 10 minutes or more, and add the acrylic acid alkyl ester monomer mainly to the reactor for 10 minutes at room temperature.
Bulk polymerization raw materials with a viscosity below poise are continuously supplied under normal pressure, thickened by rapid polymerization in the first half of the transfer process, and polymerized to a predetermined conversion rate in the subsequent transfer process, resulting in viscosity at room temperature. 1. A method for producing a pressure-sensitive adhesive tape, which comprises a continuous step of producing a bulk polymer having the following properties, continuously taking it out of a reactor, forming it into a sheet, and applying the formed product onto a tape support.