JPH021784A - Tacky adhesive - Google Patents

Abstract

PURPOSE:To provide a tacky adhesive composed of a copolymer of a main monomer (soft) component consisting of an acrylic acid ester and a comonomer (hard) component containing a crosslinking agent and having tackiness which is lost with heat to allow the adhesive to be easily peeled off from a work in the form of small pieces. CONSTITUTION:The objective tacky adhesive having an apparent glass transition point of -55 to -10 deg.C is composed of a copolymer of (A) an acrylic acid ester main monomer (preferably isobutyl acrylate) forming a soft segment having low glass transition point and (B) a comonomer component (preferably acrylic acid) forming a hard segment having high glass transition point and containing >=0.5 equivalent of a crosslinking agent based on 1 equivalent of the functional group of the monomer. The crosslinking agent is, e.g., an epoxy compound or na isocyanate compound.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an acrylic adhesive that loses its adhesive properties when heated.

(Prior Art) Generally, pressure-sensitive adhesives that easily adhere to adherends with pressure similar to finger pressure are known. Acrylic adhesives, which are a type of adhesive, consist of an acrylic acid ester raw monomer component that forms a soft segment with a low glass transition point to provide adhesive properties to the molecular chain, and a high It is a copolymer with a comonomer component that forms a hard segment having a glass transition point. The above comonomer components include aggregating components such as vinyl acetate that impart cohesive properties to molecular chains, and modifying components such as acrylic acid that improve the curability or adhesiveness of the polymer.

In other words, conventional pressure-sensitive adhesives are composed of a combination of the main monomer component and an agglomerated component, or a combination of the main monomer component, an agglomerated component, and a modifying component. Adhesive properties can be expected even when the temperature is relatively high.

(Problems to be Solved by the Invention) However, with conventional adhesives, when a workpiece is temporarily attached to an adherend, etc., and then it is peeled off from the adherend and used separately, The peeling operation is troublesome, and since the adhesive remaining on the workpiece has adhesive properties, this adhesive property may cause problems in the above-mentioned use.

In addition, when molding power transmission belts, the general method is to coat the canvas that forms the surface of the belt with friction rubber or adhesive rubber, place it tightly on a mold, wrap the rubber around it, and vulcanize it. It has been adopted. In this case, the above-mentioned friction rubber and glue rubber act as adhesives that adhere the canvas to the mold, but if such a belt uses an idler on the back or is transmitted through the back, the rubber of the canvas may When it slides against the pulley, it may turn into powder and fall, and when it adheres to the pulley, it may generate abnormal noises or vibrations.

In contrast, in manufacturing the power transmission belt, a temperature-sensitive adhesive is applied to the molding surface of the mold by spraying, etc., so that the canvas adheres well to the molding surface, and a tensile material is applied on top of it. Another method is to place an elastomer and heat it to harden the belt, and at the same time, the adhesive loses its tackiness, making it easier to cut out the belt. That is, the above-mentioned temperature-sensitive adhesive is a mixture of thermoplastic polymer substances, and when heated above a certain temperature, it melts and loses its adhesive properties, but it is easy to cut out the belt. However, since the above-mentioned adhesive hardens as it cools after die cutting and remains on the belt, problems such as falling of belt abrasion particles and adhesion occur during use of the belt, similar to the friction rubber and adhesive rubber mentioned above. It turns out.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides, by blending a predetermined amount of crosslinking agent in an acrylic pressure-sensitive adhesive,
To provide an adhesive that has adhesive properties at room temperature, but hardens and loses adhesive properties when heated, and easily falls apart and peels off from a workpiece.

That is, the adhesive according to the invention of claim (1) comprises an acrylic acid ester raw monomer component that forms a soft segment with a low glass transition point, and a comonomer that forms a hard segment with a high glass transition point. The comonomer component contains a monomer having a copolymerizable functional group, and a crosslinking agent is blended in a ratio of 0.5 equivalent or more to 1 functional group of this monomer. It is characterized by the presence of

As the raw monomer component, general acrylic esters can be used, such as ethyl acrylate, isobutyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isoamyl acrylate, etc. It is preferable to use an acrylic ester having a value of about 4 to 10.

Examples of monomers having a functional group as the comonomer component include methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylamino acid, etc. Ethyl methacrylate, acrylamide, methylol acrylamide, glycidyl methacrylate, maleic anhydride, and the like can be used.

Furthermore, the comonomer components include acrylic acid alkyl esters and methacrylic acid alkyl esters of lower alkyl groups, such as methyl acrylate and methyl methacrylate, as well as vinyl acetate, vinylidene chloride, styrene,
Copolymerizable monomers having a high glass transition point, such as acrylonitrile, acrylamide, and styrene, may be used together with the above monomers having functional groups.

As the crosslinking agent, an epoxy type, an isocyanate type, etc. can be applied, and for example, blocked isocyanates such as trimethylolpropane triglycidyl ether, phenol block isocyanate, caprolactam block isocyanate, oxime bucco isocyanate, or tolylene. An adduct of isocyanate is preferred.

The adhesive according to the invention of claim (2) is the adhesive according to the invention of claim (1).
) The apparent glass transition point of the adhesive is -55°C to -1
It is characterized by being set at 0°C. In addition, in this specification, the apparent glass transition point is the value of the adhesive as a whole before the crosslinking reaction with the crosslinking agent.

The adhesive according to the invention of claim (3) is the adhesive according to the invention of claim (1).
) or (2), wherein the raw monomer component of the adhesive is isobutyl acrylate, and the comonomer component is acrylic acid. term (1
) to (3), wherein the crosslinking agent of each of the adhesives is an epoxy-based adhesive according to the invention of claim (5).
) to (3), each of the adhesives is characterized in that the crosslinking agent is an isocyanate-based adhesive.

(Function) In the adhesive according to claim (1) above, there is virtually no crosslinking reaction by the crosslinking agent at room temperature, and the copolymer of raw monomer component and comonomer component is similar to conventional adhesives. It has adhesive properties. When the adhesive is heated, the functional groups in the comonomer components react with the crosslinking agent, causing it to harden, lose its adhesive properties, and become brittle.

In this case, if the amount of crosslinking agent is less than 0.5 equivalent, high reaction temperature and long reaction time are required for loss of adhesive properties, which is not preferable.

In the adhesive of claim (2), since the apparent glass transition point is 155°C or higher, the adhesive is reliably cured by the crosslinking reaction by the crosslinking agent and loses its adhesive properties. Moreover, since the glass transition point is equal to or lower than 10°C,
Good adhesiveness at room temperature. That is, if the glass transition point is less than 155°C, the adhesive property will not be sufficiently lost even if 1 equivalent of a crosslinking agent is mixed and a crosslinking reaction is carried out, and the above glass transition point is less than 110°C. If it exceeds 20%, it is not possible to expect much tackiness at room temperature.

Since the adhesive according to claim (3) is a combination of isobutyl acrylate and acrylic acid, the adhesive has good adhesion or compatibility with the adherend, and also crosslinks with acrylic acid during heating. It has good reactivity with agents and can reliably eliminate adhesive properties.

In the adhesive of claim (4), since the crosslinking agent is an epoxy type, the adhesive of claim (5) causes a crosslinking reaction when heated to a relatively high temperature and exhibits adhesive properties. Since the crosslinking agent in adhesives is isocyanate-based, crosslinking reactions occur even at relatively low temperatures, resulting in loss of adhesive properties.

(Effect of the invention) Therefore, according to the invention of claim (1), the adhesive properties of the adhesive can be lost by heating and the adhesive can be made brittle. When using the adhesive after peeling it off (for example, when using an adhesive as a temporary fixing means for a workpiece), heating the adhesive will allow the workpiece to be easily peeled off from the adherend, and the adhesive will be removed. The cured adhesive also peels off easily from the workpiece or adherend, allowing the workpiece to be used without being bothered by the above-mentioned adhesive properties, and eliminating the need to separate the adhesive. It becomes possible to improve work efficiency.

In addition, in the molding of the above-mentioned power transmission and moving belts,
By coating the canvas with the adhesive of the present invention, it becomes easier to adhere the canvas to the mold, and the adhesive properties of the adhesive are lost due to the heat during vulcanization. This makes it possible to improve the release properties of the belt from the mold, and the cured adhesive can easily peel off from the belt, exposing the canvas itself on the outer surface of the belt. Even if a belt is used as a back drive or an idler is used on the back of the belt, problems such as falling rubber powder, belt wear, vibration, and noise are eliminated.

According to the invention of claim (2), since the apparent glass transition point is set to -55°C to -10°C, the adhesive property is maintained at room temperature, and the adhesive property is improved by the crosslinking reaction with the crosslinking agent. It becomes possible to ensure that one loses one's sexuality.

According to the invention of claim (3), the combination of isobutyl acrylate and acrylic acid can improve the compatibility of the adhesive with the adherend and the crosslinking reactivity during heating.

According to the invention of claim (4), by using an epoxy-based crosslinking agent, the adhesive property is lost at a relatively high heating temperature, so even if the ambient temperature is slightly high, the adhesive property is maintained. Bonding work using adhesive can be performed smoothly.

According to the invention of claim (5), by using an isocyanate-based crosslinking agent, the adhesive property is lost at a relatively low heating temperature. Heating becomes easier.

(Example) Examples of the present invention will be described below in comparison with comparative examples.

Formulations and Manufacturing Methods The formulations (parts by weight) of Examples and Comparative Examples are shown in 1.2 of Table 1 and the upper column of Table 2, respectively.

Table 1-1 Table 1-2 Table 2 In the above formulation, the epoxy crosslinking agent is trimethylolpropane triglycidyl ether, and the isocyanate crosslinking agent is phenol block isocyanate. The amount of this crosslinking agent is expressed as the equivalent amount of acrylic acid having a copolymerizable functional group (carboxyl group) with respect to the above functional group. With this crosslinking agent removed, the acrylic monomer concentration is reduced to 30% by weight using ethyl acetate (solvent).
Then, 0.2% by weight of AIBN was added to the monomer as an initiator, and solution polymerization was carried out for 6 hours in a nitrogen stream at a temperature of 70°C and a volume of 500ml, and a crosslinking agent was mixed with the obtained polymer. An adhesive was obtained.

In addition, the apparent glass transition point of the obtained adhesive is the first
Tables 1, 2 and 2 are shown in the lower columns.

Adhesive strength test> An adhesive was applied to the surface of a cotton canvas, and the applied surface was bonded to a stainless steel plate (using a hand roller), and the adhesive strength before and after heating was determined to be 7Tp1.

Heating was at 150℃ for 15 minutes, and the adhesive strength was 50+A.
The measurement was performed by peeling off the cotton canvas at a speed of m/min. In this case, the crosslinking agent reacts with the carboxyl groups of acrylic acid. The results are shown in the lower columns of Tables 1 and 2.

Discussion> Examples 1 to 8 (1 in Table 1) used an epoxy crosslinking agent, and Examples 9 to 14 (2 in Table 1) used an incyanate crosslinking agent.

In Examples 1 to 3, isobutyl acrylate was used as the main monomer component, and the amount of the epoxy crosslinking agent was varied. The apparent glass transition point is -15°C. The adhesive strength before heating is 1.9 kg even with a large amount of crosslinking agent.
It is relatively high at r/25m+a. When molding a transmission belt using a mold, when canvas is coated with the adhesive of the present invention, the adhesive strength is 1.5 kgf/25n+
+n or more makes it easy to bring the canvas into close contact with the mold, so it can be seen that good moldability can be obtained in the above examples. On the other hand, the adhesive strength after heating is 0.5 kgr/2 even when the amount of crosslinking agent is small (0.5 equivalent).
It is as low as 5mm. In molding the power transmission belt, if the adhesive force is 0°5 kgf'/25Iaa+ or less, the canvas will easily peel off from the mold, so it can be seen that there is no problem with the demoldability in the above example. .

In Comparative Examples 1 to 3, which correspond to Examples 1 to 3 above, the amount of crosslinking agent was reduced, but although there was no problem with the adhesive strength before heating, the adhesive strength after heating was high. There is a problem with the above-mentioned demoldability. From this, it can be seen that the amount of crosslinking agent is preferably 0.5 equivalent or more.

Further, Examples 4 to 6 used n-butyl acrylate as the raw monomer component, and Examples 7 and 8 used a combination of isobutyl acrylate and n-butyl acrylate, and n-butyl acrylate and 2-butyl acrylate. - Concerning the combination with ethylhexyl. Although the apparent glass transition point is lower than those of Examples 1 to 3, there are no problems in terms of moldability or demoldability, and Example 8 (- 54°C), there is no problem in cutting out the mold.

On the other hand, in Comparative Example 4, 2-ethylhexyl acrylate was used as the raw monomer component and the amount of the crosslinking agent was 1.0 equivalent, but the apparent glass transition point was as low as -61°C. In the case of Comparative Example 4, although there is no problem in terms of moldability, the adhesive strength after heating is high and there is a problem in terms of demoldability. This shows that even if the amount of crosslinking agent is increased, if the apparent glass transition point is too low, the adhesive will not be sufficiently cured and the adhesive strength after heating will become high.

Next, looking at Examples 9 to 14 in which an isocyanate-based crosslinking agent was used, moldability and demoldability were good in all cases. For example, in Example 12, the bone contact force before heating is low, but the value is still 1.5 kgr/25 mm,
There is no problem with the above moldability.

In addition, the adhesive strength after heating in Example 9 is slightly higher than that in the corresponding Example 3 using the same equivalent amount of epoxy crosslinking agent, but it is still less than 0.5 kgr/25ml11, and the above-mentioned demoldability is There is no problem in that respect either.

On the other hand, Comparative Examples 5 to 7 corresponding to Examples 10 to 12
In the case of , the adhesive strength after heating is high as a direct reflection of the small amount of crosslinking agent, and it can be seen that there is a problem in terms of demoldability. In addition, in Comparative Example 8, the amount of crosslinking agent was 1
Although the weight is equivalent, the adhesive strength before heating is low and there is a problem in moldability. This is because the apparent glass transition point is as high as +3.8° C. due to the inclusion of methyl methacrylate, and therefore it can be seen that a high glass transition point is not desirable.

Relationship between heating temperature and adhesive strength> For Example 1.3 and Comparative Example 1, a heating test was conducted at each temperature, and the adhesive strength of each was determined as apr. Heating time is 12 hours. The test results are shown in FIG.

From the figure, it can be seen that the adhesive strength decreases depending on the amount of crosslinking agent. In the case of the example, the adhesive strength was 0.0 when heated at 80°C. It is 2 kgf/25 mm or less, which shows that good demoldability can be obtained due to the loss of adhesive properties.

In addition, in the case of the example, the adhesive strength decreases to the above value even after heating at 170°C for 15 minutes, but at a temperature of 170°C or higher, the heating time required to reduce the adhesive strength to the above value is even longer. Becomes shorter. Furthermore, it goes without saying that even at a temperature of 80° C. or lower, if the time is longer, the adhesive strength will decrease to the above value.

Further, the isocyanate-based crosslinking agent is a blocked isocyanate and starts the reaction at a high temperature of 130 to 180°C, so it has good workability.

That is, FIG. 2 shows adhesive A using phenol block isocyanate and adhesive B using an adduct of tolylene diisocyanate at room temperature (21°C).
) is shown, and FIG. 3 shows the change in adhesive force over time at 150°C. As can be seen from both figures, in the case of phenol-blocked isocyanate,
At room temperature, the adhesive strength hardly changes after 6 days, but at 150℃ the adhesive strength decreases in a short period of time, so the hot life is long, the work can be completed in a short time, and it is easy to use. It can be said that.

In the above example, acrylic acid was used as a comonomer component having a copolymerizable functional group, but even if other comonomer components having a similar functional group are used, the temperature required for loss of adhesiveness or Basically, the same results as in the above embodiment can be obtained with only a slight change in time.

Furthermore, although the solvent in the above examples is ethyl acetate, it goes without saying that toluene and other solvents can be used.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the heating temperature and adhesive strength of the adhesive, Figure 2 is a graph showing the change in adhesive strength over time at room temperature (21°C), and Figure 3 is It is also a graph showing changes in adhesive strength over time at 150°C.

Claims (5)

[Claims] (1) A copolymer of an acrylic acid ester main monomer component that forms a soft segment with a low glass transition point and a comonomer component that forms a hard segment with a high glass transition point, wherein the comonomer component is An adhesive characterized in that it contains a monomer having a copolymerizable functional group, and a crosslinking agent is blended in a ratio of 0.5 equivalent or more to 1 functional group of the monomer. (2) The pressure-sensitive adhesive according to claim (1), which has an apparent glass transition point of -55°C to -10°C. (3) The main monomer component is isobutyl acrylate,
The pressure-sensitive adhesive according to claim 1 or 2, wherein the comonomer component is acrylic acid. (4) The adhesive according to any one of claims (1) to (3), wherein the crosslinking agent is an epoxy-based one. (5) Claim in which the crosslinking agent is an isocyanate type (
The adhesive according to any one of 1) to (3).