JPS5928352B2 - adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adhesive composition containing synthetic cis-1,4-polyisoprene rubber as the main rubber component.

Conventionally, as rubber-based adhesive compositions (hereinafter referred to as adhesives), compositions made of natural rubber as a main material and blended with tackifiers, anti-aging agents, softeners, plasticizers, etc. have been known. ing.

The properties of the adhesive tape obtained by coating and drying such an adhesive on a tape support such as paper or plastic film are evaluated by adhesive strength, cohesive strength, and tack (adhesive strength). Because they have contradictory characteristics, it is difficult to improve one characteristic without degrading the other characteristics because of the need to balance them. It has drawbacks that require sacrifices. For example, if an inorganic substance is added for the purpose of improving cohesive force, the adhesive force will decrease, and conversely, if a large amount of tackifier or softener is added for the purpose of improving adhesive force, the decrease in cohesive force cannot be avoided. There isn't.

Since the physical properties of the rubber-like substance that constitutes the main material of the adhesive affect the basic characteristics of the adhesive, the selection of the rubber-like substance must be given the utmost importance. Natural rubber, which is well known as a rubber-like substance, has been commonly used as a material that can provide basic properties such as adhesive strength, cohesive force, and tack that are required for adhesive tapes in a relatively well-balanced manner. However, natural rubber has the disadvantage that its quality is not constant; it is often contaminated with dirt and impurities. Therefore, synthetic rubber 1,4-polyisoprene rubber (hereinafter referred to as IR) has a similar chemical structure to natural rubber.
Although IR is expected to be a substitute for natural rubber, it has the disadvantage of poor cohesive strength when used as a rubbery material in adhesives. Furthermore, it has the disadvantage that it lacks balance in overall adhesive properties such as adhesive strength and tack compared to natural rubber, making it difficult to completely replace natural rubber. Therefore, various proposals have been made for using IR in place of natural rubber.

It is known from French Patent No. 976073 that the cohesive force can be improved by adding polyisocyanate to a pressure-sensitive adhesive whose main component is natural rubber.
It has been thought that the addition of polyisocyanate alone has no effect on IR. In order to solve these difficulties, JP-A No. 507,830 proposes adding a Lewis acid as a third component.

Furthermore, JP-A-50-39335 proposes adding a delayed crosslinking tackifier.

Further, JP-A-50-135132 proposes adding a compound having two or more active hydrogens as a third component to a mixed solution of IR and polyisocyanate.

However, adhesives made by adding a third component to a system of IR and polyisocyanate often become cloudy, making it difficult to obtain a transparent adhesive tape, and the reaction is complicated, making the quality of the adhesive unstable. There are drawbacks such as not being able to do so.

What is more important is that basic properties such as adhesive strength, cohesive force, and tactile strength must be balanced as mentioned above, and at the same time, subtle properties that cannot be expressed by these properties or that can be ignored in practical terms must be maintained. For example, even if the surface of the paper becomes fuzzed, it must not impair its properties, such as its ability to adhere well at low temperatures. However, in the method described above, the third
Adding ingredients often impairs the balance of these properties and practical properties, and in order to solve this problem,
Instead, expensive compensatory measures must be taken, such as using special tackifiers that are expensive but have good performance. In order to overcome the characteristics and other constraints associated with the addition of the third component mentioned above, the present inventors have devised a method that produces characteristics very similar to those of natural rubber by simply subjecting IR and an isocyanate compound to a direct crosslinking reaction. As a result of extensive research, we discovered a composition for adhesive tapes that, by using a specific isocyanate compound, can exhibit particularly good cohesive strength and other good properties such as adhesive strength and tack. This led to the invention. That is, the present invention provides an adhesive composition containing pre-massified IR as a main rubber component, in which an isocyanate represented by the following general formula (n is an integer of 1 to 10) is added to 100 parts by weight of the rubber component. The present invention relates to an adhesive composition characterized in that 0.1 to 20 parts by weight of a polyisocyanate containing a compound is added.

According to the present invention, the IR to be used is masticated in advance with a roll, a Banbury mixer, etc., and active sites for crosslinking with the above-mentioned isocyanate compound are provided in the polymer molecules of the IR. This affects the degree of crosslinking and structure of the material, and it is preferable to masticate until the viscosity in the form of a 5% by weight toluene solution becomes 15 poise (3'C) or less. In addition, the rubber component in the present invention is not limited to the above-mentioned pre-masked IP alone, but natural rubber can be used as part of the IR (50% by weight).
Surprisingly, it has been found that even when the following compounds are replaced, it exhibits higher cohesive force and better tack than expected without impairing other properties. The natural rubber that can be replaced is preferably one that has been thoroughly masticated and has a viscosity of 10 poise (3'C) or less in the form of a 5% by weight toluene solution.
In the present invention, the polyisocyanate for crosslinking the rubber component and imparting suitable properties has three or more isocyanate groups in which n is an integer of 1 to 10, preferably 1 to 6 in the general formula. The effect of the present invention is that the isocyanate compound is contained as an essential component, and the isocyanate compound is contained in an amount of at least 50% by weight based on the total amount of other polyisocyanates that can be used. The other polyisocyanates mentioned above include P-phenylene diisocyanate, 2,4-tolylene diisocyanate, 4,4/-diphenylmethane diisocyanate, and 4,4'-diphenyl. Ether diisocyanate, hexamethylene diisocyanate, or their isomers are used, but these are not effective when used alone;
This compound can be used in combination with the above-mentioned isocyanate compound, which is an essential component. Commercially available polyisocyanates containing the above-mentioned specific isocyanate compounds include Millionate MR manufactured by Nippon Polyurethane Industries;
Product name: PAPI. PAPI-13
5 etc. can be mentioned. In the present invention, a polyisocyanate containing a specific isocyanate compound represented by the above general formula is added to 100 parts by weight of a rubber component mainly consisting of IR masticated in advance, depending on the degree of mastication of the rubber component. Generally 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight
It is added in a range of parts by weight.

If the above polyisocyanate is 0.1 part by weight or less, I
The properties of R remain as they are, making it impossible to obtain sufficient cohesive force as an adhesive, and if it exceeds 20 parts by weight, the adhesive strength and tack are significantly reduced, which is not preferable. The adhesive composition of the present invention can be provided as a solvent-free type or dissolved in various solvents, and in addition to the above-mentioned rubber component and polyisocyanate, it may contain compounding agents used in conventional natural rubber-based adhesives. If so, each can be used. For example, rosin, rosin ester, phenol resin, terpene resin, coumaron indene resin, petroleum resin, etc. are used as the tackifier, and these are used in an amount of 30 to 150 parts by weight per 100 parts by weight of the above rubber component.
It can be used within a range of parts by weight. Other compounding agents such as aging prevention agents, softeners, and inorganic fillers may be used as necessary. EXAMPLES The present invention will be specifically explained below with reference to Examples, in which parts refer to parts by weight.

In addition, the characteristic test results in the examples show values measured by the following method.

Tack test method J-DO magnetism [PrOc. Inst. RubberInd
．． , l, lO5 (1954)].

A sample tape with a length of 10 cTn is fixed with the adhesive layer facing up on a non-adhesive smooth plate at an angle of 30 degrees with respect to the horizontal plane, and 1/32 inch from a position 10 CTn from the top of the sample tape. Roll steel balls of various diameters in increments of 1/32 inch between 1 inch and 1 inch, and measure the adhesive force (tack) based on the diameter of the largest steel ball that stops on the tape.
For convenience, the 1/32 inch ball is shown as a 1/32 inch ball and the 1.1 inch ball is 32. Adhesion force measurement method According to JISC21O7, a sample tape with a width of 20m7n was attached to a stainless steel plate of SUS27, and a peeling angle of 180 degrees was applied at 20°C, 30 (7L/
It is expressed as the value of adhesive force (9/20m77!) when peeled off at a speed of 1/20m.

Cohesive force measurement method StJs27 stainless steel plate width 20mTfL x length 2
A 5 mm sample tape is attached, a load of 1k9 is applied to one end of the sample tape in an atmosphere of 400 C, and the time until the tape piece shifts and falls is measured.

Example 1 Synthetic cis-1,4-polyisoprene rubber was masticated with a roll until the toluene viscosity by weight became 1 poise at 30°C, and then various isocyanate compounds were used to form the composition shown in Table 1. A sticky adhesive was prepared and applied to a cellophane base material with a thickness of about 40 μm so that the adhesive layer thickness after drying would be about 30 μm, and dried at 100° C. for 3 minutes to obtain a sample tape.

Table 2 shows the results of the first characteristic test of the sample tape one week after manufacture. At this point, it is considered that the tape characteristics have reached a stable state. In Table 2, sample numbers 12 and 13 represent embodiments of the present invention, and sample numbers 1 to 11 and 14 are listed as comparative examples.

As is clear from Table 2 above, sample numbers 12 and 1
Sample No. 3 has a very good cohesive force compared to the comparative example, and at the same time has a well-balanced property of both adhesion and tack, indicating that the effects of the present invention are remarkable. Example 2 Synthetic cis-1,4-polyisoprene rubber was masticated with a roll until the viscosity of the toluene solution by weight became 5 poise (30°C), and then an adhesive solution having the composition shown in Table 3 was prepared. The adhesive layer was coated on a polyester film with a thickness of about 25 μm so that the thickness of the adhesive layer after drying was about 30 μm, and dried with 130 Agent C for 3 minutes to obtain a sample tape.

Table 4 shows the characteristics test results one week after the sample tape was manufactured. Note that the "variables" in Table 3 are as described in Table 4, and for sample numbers 1 to 4 showing embodiments of the present invention, natural rubber is RSSL class natural rubber with a viscosity of 5% by weight toluene solution. Sample No. 5, which shows a comparative example, is a natural rubber with a soft degree of mastication (5 weight Shima toluene solution viscosity is 30°C).
20 voices).

As is clear from Table 4, sample numbers 1 to 1 according to the present invention
It can be seen that Sample No. 4 has a well-balanced property, while Comparative Example Sample No. 5 has particularly poor tack properties.

Claims (1)

[Scope of Claims] 1. In an adhesive composition containing pre-masked synthetic cis-1,4-polyisoprene rubber as the main rubber component, an isocyanate represented by the following general formula per 100 parts by weight of the rubber component. An adhesive composition characterized in that 0.1 to 20 parts by weight of a polyisocyanate containing a compound is added. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (n is an integer from 1 to 10) 2 Synthetic cis-1,4-polyisoprene rubber has a viscosity of 15 poise or less (at 30°C) in the form of a 5% by weight toluene solution. Claim 1 which has been masticated in advance until it becomes
Adhesive composition described in Section 1. 3. As a rubber component, a part of the synthetic cis-1,4-polyisoprene rubber is replaced with natural rubber masticated in the form of a 5% by weight toluene solution until the viscosity is 10 poise (30°C) or less. The pressure-sensitive adhesive composition according to claim 1.