JPS5853969A - Pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:The titled composition having improved adhesiveness and cohesive force without causing reduction in water resistance and problems of environmental hygiene, comprising a bulk material obtained by continuous bulk polymerization of an acrylic monomer and a monomer for addition polymerization as a main component for adhesion. CONSTITUTION:The titled composition comprising a bulk polymer as a main component of adhesive. The bulk polymer is obtained by polymerizing quickly a polymerization raw material having a viscosity of <=10 poise at normal temperature, consisting essentially of an acrylic monomer capable of forming a polymer having adhesivity at normal temperature, by a radical polymerization initiator, to increase the viscosity of a polymer, polymerizing the polymer further to give an acrylic polymer having a given conversion, folowed by adding one or more ethylenic unsaturated monomers capable of providing a (co)polymer having a glass transition temperature of >=273 deg.K to the polymer by addition polymerization. The polymerization is carried out in a reactor having a structure to transfer continuously successively fed contents with renewing the surface of the contents, wherein the whole zone of transportation process is controlled at a given temperature by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure-sensitive adhesive composition containing an acrylic bulk polymer as the main component of the adhesive and having excellent properties.

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 lower the amount of solvent used. This makes it difficult to achieve good adhesion and cohesion, which are typical characteristics of pressure-sensitive adhesives. There are problems with toxicity and cost when selecting solvents such as , etc. On the other hand, with the latter method, it is difficult to obtain pure products due to residual additive components such as emulsifiers, and water resistance is affected by the influence of these residual components. This may cause problems in terms of characteristics such as

In contrast, polymerization in the absence of a solution, that is, bulk polymerization, solves the above-mentioned problems, but this method has hitherto been considered inapplicable to acrylic polymers.

Generally, in bulk polymerization, 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, and it is difficult to obtain a homogeneous polymer. This may cause processing problems in the process.

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 to a conversion rate of 30 to 70% in a pot-type prepolymerization vessel, and the remainder is demonomerized to produce a product, or the product with the above conversion rate is fed to an extruder and a gentle reaction is carried out. The reaction is allowed to proceed to a conversion rate of 95 to 96%.

On the other hand, acrylic monomers generate a large amount of heat during polymerization,
Even if a pot type polymerization method such as the above-mentioned styrene polymerization method is used, it is difficult to control the temperature, and the above-mentioned drawbacks due to runaway reactions cannot be avoided. 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 Hiko 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, We investigated a method to continuously obtain homogeneous bulk polymers by taking advantage of the accompanying rapid viscosity increase.

The above method uses a reactor that can continuously transfer the contents while renewing the surface and is equipped with a temperature control function over the entire transfer process. A raw material for bulk polymerization having a viscosity of 10 poise or less is continuously supplied, the viscosity is increased by rapid polymerization in the first half of the transfer process, and the bulk polymer that has reached a predetermined conversion rate as the polymerization progresses thereafter is continuously reacted. It is characterized by the fact that it can be taken out of the container, and it enables bulk polymerization of acrylic monomers, which was previously considered difficult, to be produced in a continuous manner, which has not been 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, it is extremely easy to stably transfer heavy viscosity materials; In the case of materials with a large viscosity gradient, the transfer force of the screw, etc. is not transmitted to the contents in the low viscosity range, and the contents run idly, causing stagnation or backflow of the contents, making stable transfer difficult. It is necessary to maintain a state in which the viscosity gradient is small over a long section. As mentioned above, acrylic monomers tend to thicken due to the rapid progress of the polymerization reaction, which was an obstacle to the application of the bulk polymerization method in the past, but the above properties are an advantage when using the above reactor. Therefore, the viscosity necessary for stable transfer can be achieved by rapid polymerization at least in the first half of the transfer process. In addition, in the above method, the contents are transferred while their 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 small. Therefore, sufficient temperature control can be performed to prevent side reactions and runaway reactions from occurring.

This invention further improves the cohesive strength of the acrylic polymer by adding a specific ethylenically unsaturated monomer in the same reactor to the acrylic polymer obtained using the continuous bulk polymerization method of the acrylic monomer described above. The present invention relates to a pressure-sensitive adhesive composition containing, as a main component of the adhesive, a bulk addition-polymerized polymer with improved properties.

That is, the pressure-sensitive adhesive composition of the present invention has a structure in which the continuously supplied contents are continuously transferred while renewing the surface, and the pressure-sensitive adhesive composition is heated to a predetermined temperature throughout the entire transfer process. In a reactor, a polymerization raw material having a viscosity of 10 poise or less at room temperature, which is mainly composed of acrylic monomers that can cause the formed polymer to be sticky at room temperature, is subjected to radical radical treatment in the absence of a solvent used in normal solution polymerization. Rapidly polymerize with a polymerization initiator to increase the viscosity and proceed with polymerization to obtain an acrylic polymer with a predetermined conversion rate, and further add to this polymer an ethylenically unsaturated monomer that can have a homopolymer or copolymer glass transition point of 273° or more. The main component of the adhesive is a bulk polymer obtained by addition polymerizing one or more types of adhesives.

The monomer components of the polymerization raw material mainly composed of acrylic monomers that can make the above-mentioned forming polymer sticky at room temperature include all those known for base polymers of general acrylic pressure-sensitive adhesives. Can be used, usually acrylic acid or methacrylic acid and 12 carbon atoms
It consists mainly of esters with the following alcohols or derivatives thereof, to which a modifying monomer is added if necessary.

Examples of the above-mentioned modifying monomers include vinyl chloride, vinyl propionate, mono- or diester maleic acid, acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, 2-hydroxyethyl acrylate, and 2-hydroxy acrylate. Propyl, 2-hydroxyethyl methacrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminoethyl methacrylate, N-1rt-butylaminoethyl acrylate,
Bis(N,N-dimethylaminoethyl)maleate, acrylamide, methacrylamide, N-methylolacrylamide, glycidyl acrylate, and the like.

On the other hand, ethylenically unsaturated monomers whose homopolymers or copolymers can have a glass transition point of 273° or higher,
It is used to further improve the cohesive force of the polymer formed from the acrylic monomer and is sticky at room temperature, and those having the glass transition point of 300° or more are particularly good. Here, if the glass transition point of the homopolymer or copolymer is lower than 273°, a sufficient effect of improving the cohesive force cannot be obtained.

In addition, among the two or more unsaturated monomers that can make the copolymer have a glass transition point of 273° or more, there are monomer mixtures that can make the homopolymer of each monomer have a glass transition point of 273° or more. It also includes a mixture of an unsaturated monomer whose homopolymer has a glass transition point of 273° or higher and an unsaturated monomer whose homopolymer has a glass transition point lower than 273°. The latter monomer mixture may be one that can exhibit a glass transition point of 273° or more when formed into a copolymer depending on its composition ratio.

Such unsaturated monomers include styrene, vinyl acetate,
The glass transition point of the homopolymer selected from the group of acrylonitrile and methacrylonitrile is 30.
0° or more, or unsaturated monomers that can be from the group of acrylic esters, methacrylic esters, or styrene derivatives (hereinafter, unsaturated monomers belonging to both groups are referred to as A). component monomers) are particularly preferred.

Specific examples of unsaturated monomers belonging to the latter group include cyclohexyl acrylate (289°K), methyl acrylate (279°K), butyl methacrylate (293°K),
N,N dimethylamine ethyl methacrylate (289°
K), hexadecyl methacrylate (288°K), 2-methoxyethyl methacrylate (286°K), 4-butylstyrene (279°K), and other unsaturated homopolymers whose glass transition point can be 273°K or higher. Monomers, and 2-butyl methacrylate (318°K), 3,3-dimethylbutyl methacrylate (318°K), 3,3-
dimethyl-2-butyl methacrylate (381°K),
Ethyl methane disulfurate (338°K), glycidyl methacrylate (319°K), isobornyl methacrylate (383°K), isobutyl methacrylate (326°K)
°K), isoboronyl methacrylate (354 °K),
Methyl methacrylate (378°K), phenyl methacrylate (378°K), n-propyl methacrylate (3
08°K), isoboronylacryle-1-(367°K
), 4-tert-butylstyrene (403°K
), 2,4-diisopropylstyrene (441°K),
2,5-dimethylstyrene (416°K), 3,4-diethylstyrene (3820IO12-hydroxymethylstyrene (433°K), 4-methylstyrene (366
There are unsaturated monomers whose homopolymer glass transition point can be 300° or higher, such as 2-methylstyrene (366°K) and 2-methylstyrene (366°K).

Among these unsaturated monomers belonging to the latter group, those whose homopolymer glass transition point can be 300° or more are desirable, and among these, methyl methacrylate is the most preferred.

In this invention, it is preferable to use one or more monomers of component A selected from one or both of the two groups depending on the type of acrylic polymer; An unsaturated monomer (hereinafter referred to as a component B monomer) which can co-electrify with the monomer and whose copolymer Δ − can have a glass transition point of 273° or more may be used together with the monomer.

In this way, the component monomers include acrylic acid, methacrylic acid, itaconic acid, etc., whose homopolymers have a glass transition point of 273° or higher, and unsaturated 2-ethylhexyl acrylate, which has a homopolymer glass transition point of 273° or more. One or more monomers used in general acrylic pressure-sensitive adhesives, such as unsaturated monomers whose angle is lower than 273°, are used. The amount of these component B monomers used is one of the factors that determines the glass transition point of the copolymer, so it may be determined appropriately depending on the types of both component A and B monomers, taking this point into consideration.

In this invention, in a continuous transfer process, the contents are continuously supplied in a reactor having a structure in which the contents are continuously transferred while the surface is renewed, and the temperature is controlled to a predetermined temperature throughout the entire transfer process. First, the polymerization raw material mainly composed of the acrylic monomer is subjected to bulk polymerization, and when the reaction is almost completed, preferably when the conversion rate is 95% or more, the ethylenically unsaturated monomer is addition-polymerized.

Polymerization raw materials mainly composed of acrylic monomers are generally prepared with a radical polymerization initiator and, if necessary, other additives such as molecular weight regulators, in order to carry out bulk polymerization of the monomer components. Used as a liquid.

Examples of the above-mentioned radical polymerization initiators include organic peroxides such as benzoyl peroxide, cumeno-1-hydron-oxide, di-butyl peroxide, and lauroyl-oxide, and azoyl peroxides such as azobisisobutyronitrile. A wide variety of compounds can be used.

The amount of these initiators is generally about 0.01 to 1 part by weight per 100 parts by weight of the monomer. In addition to the above-mentioned initiators, it is also possible to use redox initiators 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.

The radical polymerization initiator and 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.

The reactor is one that is equipped with a means to continuously transfer the contents continuously supplied from the main raw material supply port through a take-out port while renewing the surface, such as a single or twin screw extruder. It is preferable to use a device that is equipped with a temperature control mechanism throughout the entire process and has at least one auxiliary raw material supply port in the middle of the transfer process.

The drawing shows the cross-sectional structure of a single screw extruder which is an example of the above reactor, and 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, in which a main raw material supply port 2 is provided at one end, a take-out port 3 for polymerized contents at the other end, and an auxiliary raw material supply port 4 in the middle part. . Inside the barrel 1, there are a plurality of screws 6 on the rotating axis 5.
is formed, and the polymerization raw material supplied from the main raw material supply port 2 is mixed by the rotation of the shaft center 5 by this screw 6, and is advanced while renewing the surface. screw 6 and barrel 1
The interval between them is set appropriately to improve miscibility.

Generally, about 0.5 to 2 cm is appropriate. 7,8°9.
10.11 is a heating controller installed at each part of the entire length of the barrel, and is designed to be able to control the temperature at an appropriate temperature for each part, but it is of course possible to control the heating evenly over the entire length. be.

A raw material for bulk polymerization containing acrylic monomer as a main component and having a viscosity of 10 poise or less at room temperature is continuously fed into this extruder from the supply port 2 at a constant rate. The supplied raw materials are mixed by 60 rotations of the screw and transferred while the surface is renewed. At this time, the temperature is gradually increased in the region al using the heating controller 7, 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. The temperature is controlled by the heating controller 8 so that polymerization starts instantaneously in region a2 and the polymerization reaction proceeds rapidly.

The polymerized content whose viscosity has increased in this way is the area b1.
At the position where the reaction has almost completed and a bulk polymer with a predetermined conversion rate has been obtained, the monomer component for addition polymerization consisting of an ethylenically unsaturated monomer is continuously supplied into the barrel from the auxiliary raw material supply port 4, and the monomer component for addition polymerization consisting of an ethylenically unsaturated monomer is continuously supplied into the barrel. ．． An addition polymerization reaction takes place while b3 is being transported while its surface is renewed, thereby increasing the cohesive force of the bulk polymer, and finally it is continuously taken out from the take-out port 3 at the open end.

In this example, the axis 5 of the single screw 6 is concentric between each screw 6.6, but for the purpose of reaction control, the diameter is different in each part of the barrel so that the polymerization raw material or polymerization contents The amount transferred 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 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 - 20 mm, but the speed gradient, The rotation speed (outer diameter of female screw/gap between barrel and screw) is generally preferably set to 1,0007 minutes or more.

In addition to the above-mentioned screw extruder, as a reactor,
It is possible to feed the polymerization raw material from one end, mix it and advance it, and then take out the polymerization contents from the other end, and it has one or more raw material supply ports in the middle, making it easy to control the temperature in between. Any of these can be applied.

The bulk polymer obtained as described above is sticky at room temperature, but because it is an addition polymer in which the specific ethylenically unsaturated monomer is added to an acrylic polymer, its cohesive strength is low. It is also excellent.

In the pressure-sensitive adhesive composition of the present invention, the above-mentioned bulk polymer may be used as a trench adhesive, but generally the above-mentioned polymer is dissolved in a suitable solvent to form a solution. If necessary, rosin-modified resin, tackifier resin such as coumaron-indene resin, crosslinking agent such as polyfunctional incyanate, polyfunctional epoxy, benzoyl peroxy, de, etc., plasticizer such as heptatarate esters, polyethers, etc. ,filler,
A pressure-sensitive adhesive composition is prepared by blending various commonly used additive components such as pigments.

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 adhesive polymer component of the pressure-sensitive adhesive composition of the present invention is polymerized in a specific reactor at a high monomer concentration and in a short time, so that the rate of chain transfer to the self-polymer is lower than that of other polymerization methods. It is estimated that the molecular weight distribution is wider than that obtained using other polymerization methods, and that the number of branched entanglements is higher than that obtained by other polymerization methods. It has the advantage of being easy. Moreover, since it is an addition polymer in which an ethylenically unsaturated monomer is added to the acrylic polymer in the reaction system, it exhibits superior creep resistance compared to the acrylic polymer alone. Furthermore, since it is pure and does not contain any by-products, it does not have the disadvantages of a composition obtained by emulsion polymerization, such as a decrease in water resistance.

Examples of this invention will be described below. In the examples, all parts mean parts by weight, and the adhesive strength and holding strength were measured by the following method. Incidentally, the first liquid of each Example had a viscosity in the range of 0.5 to 1.0 centipoise at room temperature.

<Adhesive strength> Measured according to JIS Z-1528.

■ Paste together 20 pieces of sea bream size and heat at 40℃ for 5 minutes.
A vertical load of 0.001 was applied and the time taken to fall was measured.

Example 1 An extruder having one screw shaft was used as a reactor. This extruder has a screw outer diameter of 50cm.

The barrel is 1,250 mm long and is divided into 5 zones A, B, C, D, and E. Each zone can be controlled independently, and the set temperature of each zone is A, B, C
, D, E = 100°C, 100°C.

The temperatures were 100°C, 120°C, and 120°C. Furthermore, one supply port was provided in each of the A zone and the D zone, the gap between the barrel and the screw crest was IWII++, and the velocity gradient was 7,8507 minutes.

The first liquid is a mixed solution consisting of 100 parts of ethyl acrylate, 100 parts of 2-ethylhexyl acrylate, 10 parts of acrylic acid, and 01 part of benzoyl peroxide, and the mixture is made of 100 parts of styrene, 5 parts of acrylic acid, and 01 part of benzoyl peroxide. The mixed liquid was used as the second liquid. Both liquids were sufficiently purged with nitrogen gas in advance, and the first liquid was supplied from the A zone supply port at a rate of 502 parts, and the second liquid was supplied from the D zone supply port at a rate of 17.5 f/min. A bulk polymer was obtained in a total polymerization time of 5 minutes. This polymer was dissolved in toluene to a concentration of 30% by weight to obtain a pressure-sensitive adhesive composition of the present invention.

25 parts of the adhesive composition thus obtained were applied onto a 7 m thick polyester film to form a tape with a dry thickness of 25 μm, and its adhesive properties were investigated.
The adhesive strength was 800 f720 mm, and the holding strength was 1.000 minutes or more. In addition, when the first liquid reactant was extracted before supplying the first liquid and the conversion rate 1 weight average molecular weight and the adhesive force and holding force were measured in the same manner as above, they were 985% and Mw, respectively.
= 420,000.

It was 690 f/20 m, 38 minutes. Furthermore, the monomer mixture used in the second liquid has a glass transition point of 372° when made into a copolymer.

Example 2 A self-cleaning twin-screw extruder in which almost no reaction intermediates or finished products were retained was used as a reactor. This extruder has a screw outer diameter of 40 wIn and a barrel length of 1,000 mm.
It is divided into 4 zones A, B, C, and D, and each zone can be independently controlled, and the set temperature for each zone is A, B, C, D = 100℃, 120℃, 150℃,
The temperature was 150°C. In addition, there are 1 each in zones A and C.
There were two supply ports, and the gap between the barrel and the screw crest was 0.5 mm. Further, the velocity gradient was set to 5,000 parts.

Azobisisobutylene was added to 100 parts of a monomer mixture consisting of 100 parts of n-butyl acrylate, 100 parts of 2-ethylhexyl acrylate, 20 parts of vinyl acetate, 5 parts of acrylic acid, and 10 parts of 2-hydroxyethyl acrylate. The first liquid was prepared by dissolving 0.03 parts of ronitrile, and 1 part of cumene hydroperoxide was added to 100 parts of a monomer mixture of 100 parts of methyl methacrylate and 3 parts of acrylic acid.
A second liquid was prepared. Both liquids were replaced with nitrogen gas in advance, and the first liquid was continuously supplied from the A zone supply port at a speed of 402 parts, and the second liquid was continuously supplied from the C zone supply port at a speed of 26.5 f/min. did.

Using the thus obtained bulk polymer, a pressure sensitive adhesive solution was obtained in the same manner as in Example 1, and this was made into a tape and its adhesive properties were investigated, and the adhesive strength was 810 f/20 snow,
The holding power was 1,000 minutes or more. In addition, the reaction product of the 1st liquid was extracted in the same manner as in Example 1, and the conversion rate 2 weight average molecular weight, adhesive force, and holding force were measured, and they were 98.7% and 98.7%, respectively.
Mw = 350,000.

It was 950 f/20 tan, 17 minutes.

Furthermore, the monomer mixture used in the second liquid has a glass transition point of 377° when made into a copolymer.

Example 3 A twin-screw self-cleaning extruder was used as a reactor. The screw outer diameter is 50 mm, the barrel length is 1,500 mm, and the A
, B, C, D, E, and F. The temperature of each zone can be controlled in the same manner as in Examples 1 and 2, and the set temperatures of each zone are A, B, and C.

1), E, F-8Q℃, 100℃, 120℃, 120℃
, 120°C, and 150°C, there are two supply ports each in zones A and D, and the gap between the barrel and the screw thread is 1. Own, the velocity gradient was 10.990/min.

A mixed solution of 100 parts of vinyl acetate and 10 parts of benzoyl peroxide was used as the second solution, and the first solution of Example 2 was used as the first solution in zone A.
Nitrogen gas is supplied from one supply port at 502/min, and at the same time from another supply port at 0.5t/, (D
Supply the second liquid from one supply port in the D zone at a speed of 2.
05t/min of nitrogen gas from other supply ports at a rate of 52/min.
Supplied at a rate of 1 minute.

Using the thus obtained bulk polymer, a pressure-sensitive adhesive solution was obtained in the same manner as in Example 1, and when the tape was formed and the adhesive properties were examined, the adhesive strength was 86 (1/20 morning, retention The force was more than i, ooo minutes.The conversion rate 1 weight average molecular weight, adhesive force, and holding force of the reactant of the first liquid were measured in the same manner as in Examples 1 and 2, and they were each 972%.
, Mw -380,000, 91 (1/20 theory, 28 minutes. Furthermore, the vinyl acetate used in the second liquid has a homopolymer glass transition point of 301°.

As is clear from the above examples, the pressure-sensitive adhesive composition of the present invention has as its adhesive main component a lump obtained by continuous bulk polymerization using an acrylic monomer and an addition polymerization monomer. It can be seen that adhesive strength and cohesive strength can be greatly improved without causing any of the problems encountered in conventional solution polymerization or emulsion polymerization, such as a decrease in water resistance and environmental hygiene problems.

[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. Patent Applicant Nitto Electric Industry Co., Ltd. Representative Patent Attorney Kunio Nemoto 5'

Claims (2)

[Claims] (1) The formed polymer is kept at room temperature in a reactor which has a structure in which the continuously supplied contents are continuously transferred while the surface is renewed, and which is heated to a predetermined temperature and sterilized throughout the transfer process. Polymerization raw materials that have a viscosity of 10 poise or less at room temperature and are mainly composed of acrylic monomers that can become sticky at room temperature are rapidly polymerized using a radical polymerization initiator in the absence of solvents used in normal solution polymerization. This polymer is made viscous and further polymerized to obtain an acrylic polymer with a predetermined conversion rate, and one or more ethylenically unsaturated monomers that can make the homopolymer or copolymer have a glass transition point of 273° or more are added to this polymer. A pressure-sensitive adhesive composition containing a bulk polymer obtained by addition polymerization as a main component of the adhesive. (2) The pressure-sensitive adhesive composition according to claim (1), which uses a single-screw or twin-screw extruder as a reactor.