JPH023482A - Hot-melt pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE:To attain a good balance between hot melt applicability and tackiness and improve the adhesive strength and holding power to a polyolefin by conducting radical copolymn. of an alkyl (meth)acrylate, a particular polymerizable polymer, cyclohexyl acrylate and N-vinyl-2-pyrrolidone or methyl methacrylate. CONSTITUTION:100 pts.wt. alkyl (meth)acrylate of formula I (wherein R1 is H or CH3; and R2 is a 4-10C open-chain hydrocarbon residue), such as butyl (meth)acrylate, 5-30 pts.wt. polymerizable polymer of formula II [wherein R3 is H or CH3; and R4 is a nonpolymerizable polymer (e.g., PS) having a wt. average MW of 2000-50000 and a Tg of 50 deg.C or higher], 2-30 pts.wt. cyclohexyl acrylate and 3-30 pts.wt. N-vinyl-2-pyrrolidone or methyl methacrylate are mixed together, and the radical copolymn. of the mixture is conducted. In this copolymn., the soln. polymn. method, the bulk polymn. method or the like in which a peroxide initiator or radiation exposure is employed is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an acrylic true-melt pressure-sensitive adhesive composition that has excellent adhesive strength and cohesive strength to low-polar adherends such as polyolefin resins.

(Prior art) Solvent-type pressure-sensitive adhesives containing polymers of alkyl (meth)acrylates as main components have high adhesion, cohesiveness, transparency,
It has excellent performance such as aging resistance and has been used in many fields, but
Recently, there has been a strong demand for conversion from solvent-based coatings to solvent-free coatings that can be applied by hot melt coating.

Examples of solvent-free hot-melt acrylic pressure-sensitive adhesives include JP-A-60-23469, JP-A-59-75975, and JP-A-61-10397.
Publication No. 1 discloses a composition comprising an alkyl (meth)acrylate, a polymerizable polymer (a so-called macromonomer), and a polar monomer such as acrylic acid and acrylamide, and a pressure-sensitive adhesive sheet using the composition. ing.

In particular, JP-A No. 61-109371 discloses that by adding a plasticizer or tackifying resin to the above composition, adhesive physical properties such as hot meltability, tack, adhesive force, and cohesive force can be improved. A pressure sensitive adhesive having an excellent balance of the following is disclosed.

However, with the above-mentioned conventional adhesive compositions, it is very difficult to provide the physical property balance between heat meltability (hot melt properties) and tackiness required for acrylic hot melt adhesives.

In particular, JP-A-59-75975 and JP-A-60-
The composition disclosed in Publication No. 23469 had problems such as low adhesion to low polar substances (eg, polyethylene, etc.), particularly low adhesion at low temperatures.

Furthermore, as disclosed in JP-A No. 61-403971, when a composition containing a plasticizer is applied to a support such as paper, there is a problem that the plasticizer migrates to the support.

As mentioned above, acrylic adhesives have good adhesion, deterioration resistance,
Due to their excellent weather resistance, they are used in a variety of applications, but at present, liquid coating and drying adhesives such as solution or emulsion types are the mainstream, and hot-melt adhesives are becoming more popular due to the demand for solvent-free adhesives. Although attempts have been made, it has not been possible to obtain products with sufficient physical properties, making it difficult to put them into practical use.

(Problems to be Solved by the Invention) The hot melt adhesive composition of the present invention has been made to solve the above problems, and its purpose is to have good hot melt coating properties. Another object of the present invention is to provide a hot melt type acrylic pressure sensitive adhesive that has excellent adhesive strength and cohesive strength to low polarity adherends such as polyolefins.

(Means for Solving the Problems) The hot melt adhesive composition of the present invention comprises 100 parts by weight of an alkyl (meth)acrylate (A), 5 to 30 parts by weight of a polymerizable polymer (B), and cyclohexyl acrylate. (
C) 2 to 3 parts of N-vinyl-2-pyrrolidone (
The above object is achieved by radical copolymerization with D) or 3 to 20 parts by weight of methyl methacrylate (D').

Alkyl (meth)acrylate (A) used in the present invention
In the formula, R8 is H or CH, and R2 is butyl carbon (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, (meth)acrylate. ) Octyl acrylate, (
Decyl meth)acrylate and the like are preferably used.

The polymerizable polymer (B) used in the present invention is a so-called macromonomer represented by -. In the formula, R1 represents H or CHs.

The non-polymerizable polymer represented by R4 has a Tg (glass transition temperature) of 50°C or higher and a weight average molecular weight of 2000-2000.
It is 50,000.

If Tg is less than 50°C, the obtained adhesive becomes soft and the cohesive force decreases, so it is limited to 50°C or higher.

Moreover, when the ζ weight average molecular weight becomes small, the adhesive becomes soft and the cohesive force decreases. Conversely, as the weight average molecular weight increases, the reactivity of the polymerizable polymer (B) decreases.
000 to 50,000, preferably 5,000 to 20,000.

As the polymerizable polymer, for example, polystyrene or a derivative thereof, or polymethyl methacrylate or a derivative thereof is preferably used.

The amount of the polymerizable polymer (B) is 5 to 30 parts by weight, preferably 8 to 15 parts by weight, based on 100 parts by weight of the alkyl (meth)acrylate (A).

Polymerizable polymer (B) is converted into alkyl (meth)acrylate (
Copolymerization with A) and other monomers can improve cohesive force, but if the amount of polymerizable polymer (B) is less than 5 parts by weight, sufficient cohesive force cannot be obtained; If it exceeds 20%, no tackiness develops.

The polymerizable polymer (B) described above is described in US Pat. No. 3.786.
Publication No. 116 and Publication No. 3.842.059 and JP-A No. 6
It can be manufactured by the method disclosed in Japanese Patent No. 0-133007.

The blending amount of cyclohexyl acrylate (C) is (meth)
Alkyl acrylate (A) 2 to 100 parts by weight
The amount is 30 parts by weight, preferably 5 to 25 parts by weight.

The amount of N-vinyl-2-pyrrolidone (D) or methyl methacrylate (Do) is 3 to 20 parts by weight, preferably 5 to 15 parts by weight, per 100 parts by weight of alkyl (meth)acrylate (A). Parts by weight.

In the present invention, cyclohexyl acrylate (C) and N-vinyl-2-pyrrolidone (D) or methyl methacrylate (D'') can be used with low polarity coatings such as polyethylene while maintaining sufficient cohesive force (retention force). They are used to increase the adhesion to materials; however, if each component is used alone, there is no effect; the desired performance can be achieved by using both components together.

Cyclohexyl (C) acrylate and N-vinyl-2-
If the amount of pyrrolidone (D) or methyl methacrylate (Do) is too small, the adhesiveness to low-polar adherends will not develop, and on the other hand, if the amount is too much, the adhesion will decrease, especially at temperatures below 0°C. The low-temperature adhesive strength of

Any method may be adopted as the radical copolymerization method for the hot melt adhesive composition of the present invention, such as solution polymerization,
Manufactured by bulk polymerization etc.

As the polymerization initiator, for example, peroxide type compounds, azo type compounds, etc. are used, but photopolymerization may be performed by irradiating with light or radiation.

Further, in order to adjust the molecular weight, a suitable chain transfer agent such as lauryl mercaptan may be used.

Furthermore, in order to obtain a wide range of adhesive properties, plasticizers, tackifier resins, deterioration inhibitors, etc. may be added as necessary.

In order for the pressure-sensitive adhesive composition of the present invention to have an optimum melt viscosity for hot melt coating, the weight average molecular weight is preferably in the range of 100,000 to 500,000, more preferably in the range of 150,000 to 350,000.

(Function) In the hot melt adhesive composition of the present invention, when the polymerizable polymer (B) is copolymerized with the alkyl (meth)acrylate (A) and other monomers, the terminal R4 of the polymerizable polymer is grafted. The synthesized adhesive has a higher-order structure in which the alkyl poly(meth)acrylate part and the R4 part are phase-separated, and exhibits a reversible physical crosslinking structure at around room temperature, which allows it to bond with the adherend. Adhesive firmly. In addition, at high temperatures, the physical crosslinking structure disappears and it has fluidity, so it can be easily coated.

(Example) Examples of the present invention will be described below.

Examples 1 to 10, Comparative Examples 1 to 8 1) Preparation of hot melt adhesive sheet Into the separable flask of 11, predetermined amounts of 2-ethylhexyl acrylate or n-butyl acrylate (A) shown in Table 1 were added. Polystyrene (B) with methacrylated terminals (Macromer 0-450 manufactured by Sartomer)
0, weight average molecular weight 13000, Tg 100℃)
, cyclohexyl acrylate (C), N-vinyl-2-
Pyrrolidone (D) or methyl methacrylate (D'
), and 118 parts by weight of ethyl acetate and 0.15 parts by weight of lauryl mercaptan were added and mixed uniformly, the temperature was raised, and 0.01 parts of azobisisobutyronitrile was added every hour under reflux of ethyl acetate. Part by weight was added dropwise and radical copolymerization was carried out for 6 hours to obtain a copolymer solution having a weight average molecular weight of 250,000.

The solvent of the obtained copolymer solution was evaporated to obtain the hot melt adhesive of the present invention, and the hot melt adhesive was placed on a 25 μm thick polyethylene terephthalate film so that the thickness of the adhesive layer was 20 μm. A hot melt adhesive sheet was obtained by coating at 160°C.

2) Measurement of physical properties of hot melt adhesive sheet The physical properties of the hot melt adhesive sheet prepared in 1) were measured according to the measuring method shown below, and the results are shown in Table 2.

1) Holding force at 40°C In accordance with JIS-20237, a hot melt adhesive sheet with an area of 25 cranes x 25 fins was attached to a stainless steel plate, and then a load of l k + r (
A weight was placed on the test piece, and the time until the weight fell was measured.

1i) SP Adhesive Strength The adhesive strength to a stainless steel plate was measured by 180 degree peeling according to J r S-20237.

iii) Adhesive strength to polyethylene The same method as for sp adhesive strength was used except that a polyethylene plate with a clean surface was used as the adherend, at temperatures of 23°C and 0°C.
Adhesion was measured by 180 degree peeling at , and -io<0>C.

IV) Using a 160°C melt viscosity enhancement type flow tester (manufactured by Kinsei Seisakusho),
The viscosity at °C was measured.

Conditions: load 10 kgf, die 1 φ x 10 m (margin below) Table (effects of the invention) The hot melt adhesive composition of the present invention, as described above,
Since the alkyl (meth)acrylate and the polymerizable polymer are copolymerized, it has an excellent performance balance between hot-melt coating properties and adhesive properties. Since methyl methacrylate is copolymerized, it has excellent adhesive strength and cohesive strength (holding power) even on non-polar adherends, such as polyolefin.
Even at low temperatures, there is little decline in adhesive strength or cohesive strength.

Claims (1)

[Claims] 1. General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (However, R_1 is H or CH_3, R_2 is carbon number 4
100 parts by weight of alkyl (meth)acrylate (A) represented by ~10 chain hydrocarbon groups) and the general formula ▲ Numerical formula, chemical formula, table, etc. ▼ (However, R_3 is H or CH_3, R_4 is a non-polymerizable polymer with a weight average molecular weight of 2000 to 50000 and a Tg of 50°C or higher) (B)
5 to 30 parts by weight and cyclohexyl (C) acrylate2
A hot melt adhesive composition obtained by radical copolymerization of ~30 parts by weight and 3 to 20 parts by weight of N-vinyl-2-pyrrolidone (D) or methyl methacrylate (D').