JP2001055548A - Production of natural rubber for tackifier and natural rubber-based tackifier composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply obtain a natural rubber having a suitable molecular weight by lowering the molecular weight of an unmasticated natural rubber by the action of a peptizing agent while dissolving it in an organic solvent. SOLUTION: The natural rubber is exemplified by SMR, SVR, ribbed smoked sheet No. 1-6, or pale crepe Nos. 1-3. The organic solvent is exemplified by an aromatic hydrocarbon such as toluene or an aliphatic hydrocarbon such as heptane or hexane. The peptizing agent is desirably a mastication accelerator such as a disulfide or a mercaptan such as o,o-dibenzamidodiphenyl disulfide, 2-benzamidothiophenol zinc salt, 2-thionaphthol, thioxylenol, or pentachlorothiophenol. The natural rubber-based tackifier composition comprises a natural rubber having a weight-average molecular weight of at most 700,000 and obtained by the above process. It is desirable in the production of a pressure-sensitive adhesive tape that the composition has a viscosity of at most 80 Pa.s as measured at 30 deg.C with a Brookfield viscometer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a natural rubber for an adhesive, and a natural rubber-based adhesive composition comprising the natural rubber obtained by the method.

[0002]

2. Description of the Related Art Normally, a natural rubber-based pressure-sensitive adhesive is prepared by dissolving a natural rubber in an organic solvent such as toluene, hexane or heptane and then dissolving a compound such as a tackifier resin and a softener. However, since the molecular weight of unpulverized natural rubber is generally very high, it is difficult to dissolve it in an organic solvent as it is. On the other hand, if the molecular weight of the natural rubber is too high, the pressure-sensitive adhesive may lack flexibility and may not be able to obtain appropriate pressure-sensitive adhesive properties. Therefore, in order to avoid these problems, it is necessary to appropriately reduce the molecular weight of natural rubber before use in compounding.

[0003] As a method of reducing the molecular weight of natural rubber, it is common to mechanically masticate it beforehand by using a pressure kneader, a Banbury mixer, an open roll or the like before dissolving it in an organic solvent.

[0004]

However, the mechanical mastication step of adjusting the molecular weight of natural rubber consumes enormous amount of energy. In addition, natural rubber has a self-fusing property, so that the work load of the mastication process itself is very large, and particularly, the load of other processes such as handling and transport of the rubber after mastication is extremely large.

For example, natural rubber immediately after mechanical mastication is soft, and self-fusion is likely to occur due to contact, and if it fuses into a large lump, it will greatly hinder work in the next step. Will be. Generally, in order to prevent this, natural rubber is formed into a predetermined shape and size, and powder for preventing self-fusion is sprayed, or a release sheet is sandwiched. However, spraying the powder or using a release sheet in this way has many problems. For example, when powder is used, dust deteriorates the working environment and the powder is mixed into the product as impurities. Also,
When a release sheet is used, it takes time and effort to lay a large number of sheets, and the used sheet becomes an industrial waste. Furthermore, mastic natural rubber also adheres relatively strongly to a release sheet, and it often takes a great deal of effort to peel it off in the next step. Therefore, the mastication process has many disadvantageous elements in terms of manufacturing cost, work, and environment, and improvement has been desired.

[0006] As an environmental measure, when it is desired to lower the viscosity and increase the solid content in order to reduce the amount of the organic solvent used in the compounding of the adhesive, it is necessary to greatly reduce the molecular weight of natural rubber. In the method (1), there is a need to perform excessive mechanical mastication, and the load of the mechanical mastication step is further increased from the current state.

On the other hand, as a technique for reducing the load of the mechanical mastication step as much as possible, a method of reducing the degree of mastication or shortening the mastication time can be considered. However, in this method, the molecular weight of the natural rubber is adjusted to a weight average molecular weight Mw of 700,000 to Mw of 1,000,000.
The limit is to reduce it to about 00, and a molecular weight lower than this cannot be obtained. In the case of this level of molecular weight, the properties as a pressure-sensitive adhesive tape are satisfactory, but when dissolved in an organic solvent, the viscosity becomes considerably high, so that a pressure-sensitive adhesive can be uniformly applied on a substrate in a thin layer during the production of the pressure-sensitive adhesive tape. It will be difficult. In producing the pressure-sensitive adhesive tape, the molecular weight of the natural rubber is adjusted to a weight average molecular weight Mw of 70 in order to keep the solution viscosity of the pressure-sensitive adhesive low while taking into account the amount of the organic solvent used.
It is preferred to be less than 000.

Accordingly, an object of the present invention is to provide a method for efficiently producing natural rubber for an adhesive by a simple operation without going through complicated steps. Another object of the present invention is to provide a method for easily producing a natural rubber for a pressure-sensitive adhesive having a desired appropriate molecular weight. Still another object of the present invention is to provide a natural rubber-based pressure-sensitive adhesive composition capable of lowering the viscosity even when the solid content concentration is high.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, when a specific treatment is applied to unsintered natural rubber, a mechanical mastication step is performed. The present inventors have found that it is possible to easily reduce the molecular weight to a desired molecular weight without any difficulty, and therefore, it is possible to easily obtain a natural rubber solution having a low viscosity even at a high solid content concentration, and it is possible to greatly reduce the amount of an organic solvent. Completed the invention.

[0010] That is, the present invention provides a method for producing a natural rubber for an adhesive, characterized in that the molecular weight is reduced by the action of a peptizer while dissolving the unpulverized natural rubber in an organic solvent. The present invention also provides a natural rubber-based pressure-sensitive adhesive composition comprising a natural rubber having a weight average molecular weight Mw of 700,000 or less obtained by the above method.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an unsintered natural rubber is prepared without adjusting the molecular weight in the step of mechanical mastication.
A natural rubber for pressure-sensitive adhesive is obtained by lowering the molecular weight by the action of a peptizing agent (chewing agent) while directly dissolving in an organic solvent.

As the natural rubber to be used, for example, stan
dard malaysian rubber (SMR), standard vietname
se rubber (SVR), ribbed smoked seat (RS
S) Nos. 1 to 6 and pale crepes 1 to 3 and the like, but are not limited thereto as long as they are of a general high molecular weight solid type.

The organic solvent used includes, for example, aromatic hydrocarbons such as toluene; and aliphatic hydrocarbons such as heptane and hexane. However, the organic solvent is not limited as long as it can dissolve natural rubber. .

[0014] The shredder refers to a reagent capable of chemically cleaving natural rubber molecules in an organic solvent. As a pouch disintegrator, it is known as a so-called mastication improver
o, o-dibenzamide diphenyl disulfide, 2-
Preferred are disulfides and mercaptans such as benzamide thiophenol zinc salt, 2-thionaphthol, thioxylenol, and pentachlorothiophenol, and may be those obtained by adding a metal catalyst thereto. Also, thiazoles such as 2-mercaptobenzothiazole; diacyl peroxides such as benzoyl peroxide; dialkyl peroxides such as dicumyl peroxide; and other organic peroxides may be used as a peptizer. .

As a special shredder, a compound containing a reactive functional group such as a hydroxyl group or a carboxyl group in the molecule of the above-mentioned shredder (hereinafter referred to as "functional group-introducing shredder") May be used. These may be used alone, or may be used in combination with the above-mentioned general shredder at any mixing ratio. By shredding natural rubber using such a functional group-introducing disintegrant, a reactive functional group can be introduced into the natural rubber molecular chain.

Among the functional group-introducing disintegrators, those having a hydroxyl group include 2-hydroxydiphenyl disulfide, 2-hydroxyethyl disulfide, mercaptophenol, 2-mercaptoethanol,
Examples thereof include mercapto-1,2-propanediol and the like. However, this is not limited as long as it has a structure containing a hydroxyl group in the molecule of the above general shredder.

Among the functional group-introducing disintegrating agents, those containing a carboxyl group include mercaptobenzoic acid, mercaptoacetic acid, mercaptopropionic acid and the like. It is not limited as long as it has a structure containing a carboxyl group.

A carboxylic anhydride such as maleic anhydride may be used as the functional group-introducing shredder. An acid anhydride group can be introduced into the natural rubber molecular chain by using maleic anhydride or the like in combination with the above-mentioned peptizing agent at an arbitrary mixing ratio.

The natural rubber for an adhesive includes, for example, natural rubber,
It is obtained by charging an organic solvent, a peptizer and, if necessary, an appropriate additive into a dissolving tank at a predetermined mixing ratio and stirring the mixture at a predetermined reaction temperature for a predetermined time. The dissolution tank is not particularly limited as long as it is generally used in the dissolution step.

The molecular weight of the natural rubber can be controlled to a desired value by adjusting the amount of the peptizing agent. As for the timing of dispensing of the shaking agent, it may be introduced simultaneously with natural rubber or the like at the time of initial preparation, or may be introduced at an arbitrary timing. Also, it may be charged separately during the initial stage and during the reaction. This timing can also control the target molecular weight of the natural rubber.

The reaction temperature can be appropriately selected depending on the kind of the peptizing agent used and the target molecular weight of the natural rubber.
Usually, it is 70 ° C. or higher, and particularly preferably 80 to 120 ° C. The stirring / reaction time is defined as the time until the natural rubber is completely dissolved, all undissolved solids are eliminated, and the molecular weight can be reduced to a predetermined molecular weight.

According to the process of the present invention, the high-molecular-weight unpulverized natural rubber, which was initially a solid content, is dissolved in an organic solvent and, at the same time, is chemically cut by a shaking agent and thermal energy to form a molecule. Desired molecular weight suitable for the agent (eg, weight average molecular weight Mw of 700,000 or less)
Of natural rubber can be prepared.

It is a well-known fact that oxygen is usually required for the shredding reaction of natural rubber. However, in the present invention, it is also possible to accelerate the shredding reaction by blowing air into the reaction system. It is possible. When the method of the present invention is carried out at a high solid content, it is necessary to significantly reduce the molecular weight, so that it is preferable to blow air.

The viscosity of the natural rubber solution prepared in the present invention can be freely adjusted by controlling the molecular weight of the natural rubber using parameters such as a peptizing agent, a reaction temperature, a reaction time, and an oxygen concentration as parameters. For example,
A B-type viscometer having a viscosity at 30 ° C. of 80 Pa · s or less, preferably 40 Pa · s or less, can be used as it is for a pressure-sensitive adhesive composition.

The natural rubber-based pressure-sensitive adhesive composition of the present invention has a weight average molecular weight Mw of 70 obtained by the method of the present invention.
000 or less (for example, 200,000 to 700,0
00) of natural rubber.

In the process of producing a pressure-sensitive adhesive tape, in order to uniformly apply a natural rubber-based pressure-sensitive adhesive composition on a substrate in a thin layer, it is necessary to use B
80 Pa · s or less at 30 ° C. viscosity, preferably 4
It is desirably 0 Pa · s or less. When the weight average molecular weight Mw of the natural rubber in the pressure-sensitive adhesive exceeds 700,000, in order to reduce the solution viscosity to 40 Pa · s or less,
The solid concentration must be 20% by weight or less, which is not preferable because a large amount of an organic solvent is required.

The natural rubber-based pressure-sensitive adhesive composition may be added to the natural rubber solution obtained by the above-described method, if necessary, by adding a tackifier, a crosslinking agent, a softening agent, an antioxidant, a filler and the like. It can be produced by adding an agent and adjusting the concentration as necessary.

The tackifier is not particularly limited.
For example, rosin-based resins, terpene-based resins, petroleum resins (aliphatic, aromatic, alicyclic), cumarone / indene resins, styrene-based resins and the like can be mentioned. The amount of the tackifier used is, for example, 5 to 100 parts by weight of natural rubber.
It is 180 parts by weight, preferably about 70 to 130 parts by weight.

The solid content of the natural rubber-based pressure-sensitive adhesive composition is as follows:
It is automatically determined by the target solution viscosity and the molecular weight of natural rubber. However, in view of global environmental issues, it is necessary to use as little solvent as possible, and the solid content concentration is 20% by weight.
It is desirable that the content be above (for example, about 20 to 75% by weight).

In the above method, if the molecular weight of the natural rubber after shattering is reduced, the viscosity and the solid content can be reduced accordingly, which can contribute to the reduction of the organic solvent. When such low viscosity and high solid content concentration are intended, it is preferable to use the above-described functional group-introduced shredder as the shredder. Normally, when the molecular weight of natural rubber decreases, the cohesive strength of the adhesive tends to decrease.However, when a reactive functional group is introduced into natural rubber molecules using a functional group-introducing disintegrant, the molecular weight becomes considerably lower. Even so, since the molecular chain can be efficiently extended by the cross-linking agent, it is possible to realize pressure-sensitive adhesive tape characteristics closer to a high molecular weight product, for example, in terms of cohesion and the like.

[0031]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

Example 1 In a flask, 100 parts by weight of natural rubber (SMR) and a peptizer (Noctizer SZ, manufactured by Ouchi Shinko Chemical Co., Ltd.)
0.3 parts by weight and 233 parts by weight of toluene
The mixture was stirred at 80 ° C. for 10 hours to obtain a shredded natural rubber solution. A tackifier (YS Resin P) is added to this natural rubber solution.
X1000, 100 parts by weight of Yasuhara Chemical Co., Ltd.) was added to prepare a natural rubber-based pressure-sensitive adhesive solution. The viscosity of the prepared natural rubber-based pressure-sensitive adhesive solution was measured at 30 ° C. using a B-type viscometer, and the solid content base was measured by a heating loss method. The molecular weight of the natural rubber was measured using GPC (gel permeation chromatography). The results are shown in Table 1. This natural rubber-based pressure-sensitive adhesive solution is mixed with an isocyanate-based crosslinking agent (Millionate MT).
L, manufactured by Nippon Polyurethane Industry Co., Ltd.) and coated on a biaxially stretched polypropylene film having a thickness of 40 μm, and the organic solvent was volatilized with hot air to obtain a thickness of 25 μm.
A natural rubber-based pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer was prepared.
The prepared pressure-sensitive adhesive tape was cut into a width of 25 mm, stuck on a stainless steel plate, pressed one reciprocally with a rubber roller weighing 2 kg, left at room temperature for 30 minutes, and then removed from the stainless steel plate 180.
° A peel test was performed to evaluate the adhesive strength of the adhesive tape to the stainless steel plate. Table 2 shows the results of the evaluation. In addition, the prepared adhesive tape was placed on a stainless steel plate at 25 mm × 25 m.
m, and reciprocatingly pressed with a rubber roller weighing 2 kg once, left at 40 ° C for 30 minutes, and then heated to 40 ° C.
A creep test on a stainless steel plate at 40 ° C. was performed by applying a load of 2 kg in the inside. The holding time until the adhesive tape dropped was evaluated. Table 2 shows the results of the evaluation. Also,
Similarly, the prepared adhesive tape was placed on a stainless steel plate for 25 minutes.
Paste to an area of mm × 25mm, weight 2k
After one reciprocal pressure bonding with a g roller, the sample was allowed to stand at 23 ° C. for 30 minutes, a load of 2 kg was applied at 23 ° C., and a creep test on a stainless steel plate at 23 ° C. was performed. The displacement distance of the adhesive tape 30 minutes after the start of the test was evaluated. Table 2 shows the results of the evaluation.

Example 2 In a flask, 100 parts by weight of natural rubber (SMR) and a peptizer (Noxeller M, manufactured by Ouchi Shinko Chemical Co., Ltd.) 1.0
Parts by weight and 163 parts by weight of toluene were added, and the mixture was stirred at 90 ° C. for 10 hours while blowing a small amount of air to obtain a shredded natural rubber solution. To this natural rubber solution, a tackifier (YS Resin PX1000, Yashara Chemical Co., Ltd.)
Was added to prepare a natural rubber-based pressure-sensitive adhesive solution. The viscosity and solid content of the prepared natural rubber-based pressure-sensitive adhesive solution were measured in the same manner as in Example 1. Further, the molecular weight of the natural rubber was measured in the same manner as in Example 1. The results are shown in Table 1. In the same manner as in Example 1, an adhesive tape was prepared,
° A peel test and a stainless steel plate creep test were performed.
Table 2 shows the results of the evaluation.

Example 3 In a flask, 100 parts by weight of natural rubber (SMR) and a peptizer (Noctizer SZ, manufactured by Ouchi Shinko Chemical Co., Ltd.)
0.1 parts by weight and 400 parts by weight of toluene
The mixture was stirred at 8 ° C. for 8 hours to obtain a shredded natural rubber solution. A tackifier (YS Resin PX100) is added to this natural rubber solution.
0, 100 parts by weight of Yashara Chemical Co., Ltd.) to prepare a natural rubber-based pressure-sensitive adhesive solution. The viscosity and solid content of the prepared natural rubber-based pressure-sensitive adhesive solution were measured in the same manner as in Example 1. Further, the molecular weight of the natural rubber was measured in the same manner as in Example 1. The results are shown in Table 1. An isocyanate-based crosslinking agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) is added to this natural rubber-based pressure-sensitive adhesive solution.
6 parts by weight, applied on a biaxially stretched polypropylene film having a thickness of 40 μm, the organic solvent is evaporated by hot air,
A natural rubber-based pressure-sensitive adhesive tape having a 25-μm-thick pressure-sensitive adhesive layer was produced. This adhesive tape was subjected to a 180 ° peel test on a stainless steel plate and a creep test on a stainless steel plate in the same manner as in Example 1. Table 3 shows the results of the evaluation.

Comparative Example 1 Natural rubber (RSS class 1) was previously passed through an open roll several times, and lightly mechanically masticated to reduce the molecular weight of the natural rubber. 100 parts by weight of the masticated natural rubber and 1000 parts by weight of toluene were charged into a flask, and dissolved without stirring at 80 ° C. for 8 hours without adding a peptizing agent. To this natural rubber solution was added 100 parts by weight of a tackifier (YS Resin PX1000, manufactured by Yasuhara Chemical Co., Ltd.) to prepare a natural rubber-based pressure-sensitive adhesive solution. The viscosity and solid content of the prepared natural rubber-based pressure-sensitive adhesive solution were measured in the same manner as in Example 1. Further, the molecular weight of the natural rubber was measured in the same manner as in Example 1. The results are shown in Table 1. To this natural rubber-based pressure-sensitive adhesive solution, 4 parts by weight of an isocyanate-based cross-linking agent (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added, and the solution was applied on a biaxially oriented polypropylene film having a thickness of 40 μm. To produce a natural rubber-based pressure-sensitive adhesive tape having a 25-μm-thick pressure-sensitive adhesive layer. This adhesive tape was subjected to a 180 ° peel test on a stainless steel plate and a creep test on a stainless steel plate in the same manner as in Example 1. Tables 2 and 3 show the results of the evaluation.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

Next, with respect to the natural rubber-based pressure-sensitive adhesive solutions of Example 1, Example 2, Example 3, and Comparative Example 1, the toluene necessary for producing the same amount of pressure-sensitive adhesive tape from the measured solid content base was measured. The amount used was calculated. Table 4 shows the amounts of toluene used in Examples 1, 2, and 3 when the amount of toluene used in Comparative Example 1 was 100.

[0040]

[Table 4]

In the production method of Comparative Example 1, a light mechanical mastication step using an open roll was performed. However, although the degree of mastication was reduced, a heavy natural rubber block was passed through the roll. It goes without saying that work not only consumes energy but also puts a great burden on workers. Moreover, since the thin natural rubber sheet immediately after mastication by an open roll is fused when it is placed one on top of another, it is necessary to sandwich a release sheet for each thin sheet to prevent contact between the natural rubber pieces. In dissolving the rubber in the next step, the release sheet needs to be peeled off and discarded. As described above, the use of this release sheet is not preferable in terms of an increase in the number of work steps and a problem of discharge of industrial waste.

On the other hand, in Example 1 according to the production method of the present invention,
In the second and third embodiments, the above-described problems are solved because no mechanical mastication step is performed. As shown in Table 1, the values of the solution viscosities of the natural rubber pressure-sensitive adhesives of Example 1, Example 2, Example 3 and Comparative Example 1 were all 20.
Pa · s, but the molecular weights were significantly different, and the molecular weight Mw of the natural rubber of Comparative Example 1 was 700,000.
Was exceeded.

As shown in Table 2, the characteristics of the pressure-sensitive adhesive tape were almost the same in Examples 1 and 2 and Comparative Example 1, and even when the production method of the present invention was used. ,
It can be seen that the same properties as those of the pressure-sensitive adhesive tape manufactured by the conventional method are obtained. In the examples, although the molecular weight of the natural rubber was low, the properties required for the pressure-sensitive adhesive tape were not impaired by selecting the type of the crosslinking agent. Further, as shown in Table 3, in Example 3, the balance of the flexibility and the cohesiveness of the pressure-sensitive adhesive was good, and better pressure-sensitive properties could be obtained as compared with Comparative Example 1.

The amount of the organic solvent used was determined in Example 1,
Example 2 and Example 3 are considerably different from Comparative Example 1. That is, the solid content base in Comparative Example 1 was 17% by weight, which was much lower than the solid content bases in Examples 1, 2 and 3, and the same amount of tackiness shown in Table 4 Very large amount of toluene used when producing tapes. As in Comparative Example 1, when the weight average molecular weight Mw could not be reduced to 700,000 or less by light mechanical mastication, the viscosity was 20 Pa · s.
In order to achieve the level, the solid content base of the pressure-sensitive adhesive becomes 20% by weight or less, and it is understood that a large amount of organic solvent is required. On the other hand, in the case of Example 1, Example 2, and Example 3, the used amount of toluene shown in Table 4 is a very small value with respect to the used amount of Comparative Example 1. If the molecular weight of natural rubber is reduced by the production method of the present invention, it is possible to smoothly produce a low-viscosity, high-solids-based pressure-sensitive adhesive solution, and it is possible to significantly reduce the amount of organic solvent. .

[0045]

According to the method of the present invention, a natural rubber-based adhesive having an arbitrary molecular weight of 700,000 or less and having a weight-average molecular weight Mw of 700,000 or less suitable for an adhesive without a mechanical mastication step of the natural rubber. An agent solution can be produced. The manufacturing method of the present invention, which can omit the mechanical mastication step, is very effective in all aspects of manufacturing cost, work, and environment. Further, if the molecular weight of the natural rubber is further reduced, a natural rubber-based pressure-sensitive adhesive having a low viscosity and a high solid content can be produced, and by appropriately selecting the type of the cross-linking agent, the necessary properties as a pressure-sensitive adhesive tape can be obtained. Without compromising
Significant reduction of organic solvents can be realized. further,
Since the molecular weight of the natural rubber can be arbitrarily controlled, it is easy to design an adhesive using the molecular weight as a parameter according to the tape properties.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hirose Sakae 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Toshishi Umehara 1-1-2, Shimohozumi, Ibaraki-shi, Osaka F-term in Nitto Denko Corporation (reference) 4J002 AC011 EV026 EV036 EV046 EV066 FD206 4J040 BA201 BA202 CA011 CA012 DB041 DB042 DK011 DK012 HB41 HD04 HD05 JB09 KA23 KA43 LA01 4J100 AS02P CA01 CA31 DA01 DA09 HA51 HC72 HC05 HC

Claims (2)

[Claims] 1. A method for producing a natural rubber for pressure-sensitive adhesive, characterized in that the molecular weight is reduced by the action of a peptizer while dissolving the unpulverized natural rubber in an organic solvent. 2. A natural rubber-based pressure-sensitive adhesive composition comprising a natural rubber having a weight average molecular weight Mw of 700,000 or less, obtained by the method according to claim 1.