JPH04309509A - Polyvinyl acetal resin and adhesive containing the same - Google Patents

Abstract

PURPOSE:To obtain an adhesive which is lowly viscous, excellent in soldering- heat resistance and used for bonding a copper foil of a printed circuit board by specifying the structural units, the contents of the units and the average degree of polymerization. CONSTITUTION:A mixture of a carboxyl-modified polyvinyl acetal with optionally a non-carboxyl-modified mixed polyvinyl acetal resin in a weight ratio of (9-1):(1-9) is acetalized in the presence of an acid catalyst, and the catalyst is neutralized to obtain the title resin having an average degree of polymerization of 1500-2500 and comprising acetoacetal units and butylacetal units in a weight ratio of (3-7):(7-3), 14-21wt.% vinyl alcohol units, 5-13wt.% fatty acid/ vinyl ester units and 0.1-5wt.% units having a carboxyl group as the side chain.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a low-viscosity method for bonding metallic copper foil for printed circuits to a base material in the production of copper-clad laminates.
The present invention also relates to an adhesive having excellent adhesive strength and soldering heat resistance, and a polyvinyl acetal resin contained in the adhesive.

0002

[Prior Art] Conventionally, copper-clad laminates for printed circuits have been produced by coating one side of copper foil with an adhesive and drying it to form an adhesive-coated copper foil. It is manufactured by stacking the base materials impregnated with thermosetting resin so that they are in contact with each other, and then integrating them by heat and pressure bonding.The adhesive used is polyvinyl acetal resin, phenolic resin, and melamine. Adhesives containing thermosetting resins such as resins and epoxy resins are used.

[0003] The copper-clad laminate obtained as described above is
A printed circuit is provided by etching the copper foil, and circuit components are attached to the circuit by soldering, and are used in various electronic devices.

[0004] This copper-clad laminate is made by bonding a metallic copper foil to a non-conductive base material, and of course the bond must be strong, but it is also required to be etched. When attaching circuit components to the remaining copper foil, the immersion time in a high-temperature molten solder bath is becoming longer, and as a result, copper clad laminates with even better heat resistance are being used. Boards are now in demand.

[0005] In response to such demands, adhesives whose main component is a polyvinyl acetal resin having a specific composition, such as an acetoacetal-butylacetal mixed polyvinyl acetal resin having a degree of polymerization of 1500 to 2500, are available.
The weight ratio of the acetoacetal part and the butyl acetal part is 3:7 to 7:3, the vinyl alcohol part is 14 to 21% by weight, the vinyl acetate part is 3% by weight or less, and the acrylic acid part is 0.1 to 7:3. 1.9
Adhesive whose main component is polyvinyl acetal resin (Japanese Patent Application Laid-Open No. 58-98306), degree of polymerization 1
500 to 2500 acetoacetal-butyl acetal mixed polyvinyl acetal resin, the weight ratio of the acetoacetal part to the butyl acetal part is 3:7 to 7:3, and the vinyl alcohol part is 14 to 21% by weight, An adhesive whose main component is a polyvinyl acetal resin containing 4% by weight or less of vinyl acetate and 0.1 to 1.5% by weight of maleic acid has been proposed (Japanese Unexamined Patent Publication No. 58-98307). .

However, although the adhesives obtained using these polyvinyl acetal resins have good heat resistance and adhesive strength for copper-clad laminates to which copper foil is bonded using the adhesives, their high viscosity makes them difficult to use in various ways. There's a problem.

[0007] The above problems include, for example, 30 to 40
Since a small amount of highly viscous adhesive is applied to a thin and flexible copper foil on the order of microns, the application workability is low and it is difficult to apply it uniformly. In addition, since the adhesive is applied to one side of the copper foil, which has numerous fine protrusions about 10 microns in height that are electrodeposited on the surface, the adhesive has a high viscosity. It is difficult to penetrate deep into the fine gaps, which are the concave portions between the convex portions, and the adhesion between the rough surface of the copper foil and the adhesive tends to be insufficient.

Furthermore, adhesives with high viscosity are difficult to handle in terms of transport, measurement, mixing, etc.

[0009] In order to avoid such problems, attempts have been made to lower the viscosity of the adhesive by diluting it with a solvent or increasing the temperature of the adhesive. None of these methods are preferable because they involve problems such as requiring more heat energy and time to dry the adhesive and shortening the pot life of the adhesive.

0010

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned prior art, and provides a polyvinyl acetal resin and thermosetting resin that has low adhesive viscosity and excellent adhesive strength and soldering heat resistance. Adhesives containing synthetic resins and solvents,
Another object of the present invention is to provide a polyvinyl acetal resin that can be contained in the adhesive.

[0011]

[Means for Solving the Problem] As a result of various studies, the present inventor has found that a carboxy-modified acetoacetal-butyl acetal mixed polyvinyl acetal resin with a specific composition and an adhesive containing the polyvinyl acetal resin achieve the object. Based on this knowledge, we have completed the present invention.

That is, the gist of the present invention is as follows.

(1) Acetoacetal unit (A),
It has a butyl acetal unit (B), a vinyl alcohol unit (C), a fatty acid vinyl ester unit (D), and a unit to which a carboxyl group is bonded as a side chain (E), and has an average degree of polymerization of 1500 to 2500, (A ) and (B
) is 3:7 to 7:3 by weight, and (C) is 14 to 21% by weight based on the total of (A), (B), (C), (D) and (E). , the proportion of (D) is 5 to 13% by weight on the same basis as (C), and the proportion of carboxyl groups bonded to (E) as a side chain is 0.1 to 5% by weight on the same basis as (C). Carboxy-modified acetoacetal-butyl acetal mixed polyvinyl acetal resin for copper foil adhesive for printed circuits, and (2) above (1)
An adhesive for bonding copper foil to a printed circuit, comprising the polyvinyl acetal resin, thermosetting resin, and solvent described above.

The present invention will be explained in detail below. In this specification, the acetoacetal-butyl acetal mixed polyvinyl acetal resin refers to acetoacetal units obtained by coexisting both acetaldehyde and butyraldehyde in the reaction system during the acetalization reaction.
It means a polyvinyl acetal resin having both units of A) and butyl acetal units (B).

The carboxy-modified acetoacetal-butyl acetal mixed polyvinyl acetal resin (hereinafter sometimes abbreviated as carboxy-modified mixed polyvinyl acetal resin) of the present invention will be explained below.

The average degree of polymerization of the carboxy-modified mixed polyvinyl acetal resin of the present invention is from 1,500 to 2,500, preferably from 1,600 to 2,300. Average degree of polymerization is 15
If it is less than 00, both adhesive strength and soldering heat resistance are insufficient.
If it exceeds 2,500, the viscosity of the adhesive containing the resin increases, particularly the coating workability and handling properties are reduced, and the soldering heat resistance is hardly improved.

The ratio of (A) and (B) in the carboxy-modified mixed polyvinyl acetal resin of the present invention (measured by an infrared spectrophotometer) is 3:7 to 7:3 by weight, preferably 6:4. ~4:6. If this weight ratio is less than 3:7, the soldering heat resistance of the adhesive will be insufficient, and if it exceeds 7:3, the solvent solubility of the resin will decrease, the resin will become hard and brittle, and it will not work on the copper foil. Cracks may occur in the adhesive layer after application and drying. The degree of acetalization [total of (A) and (B)] of this resin is (C),
As long as (D) and (E) satisfy their respective ranges, their content is preferably 65% by weight or more, preferably 70% by weight or more.

The proportion of vinyl alcohol units (C) remaining without being acetalized in the resin of the present invention is
14 to 21% by weight based on the total standard of (A), (B), (C), (D) and (E), and 14% by weight
If it is less than this, the reactivity with the thermosetting resin blended into the adhesive will be low, and the curing reaction will likely be insufficient. Also, 21% by weight
If the amount exceeds 100%, the solubility in organic solvents decreases.

One of the characteristics of the carboxy-modified mixed polyvinyl acetal resin of the present invention is that the proportion of fatty acid vinyl ester units (D) is higher than that of polyvinyl acetal resins conventionally used as a component of adhesives for copper foil. That's true.

Conventionally, this fatty acid vinyl ester unit is
Since it lowers the soldering heat resistance of the adhesive layer, it has been considered that the lower the ratio, the more preferable it is. However, in the adhesive containing the carboxy-modified mixed polyvinyl acetal resin and thermosetting resin of the present invention, even if the proportion of fatty acid vinyl ester units in the polyvinyl acetal resin is high, the soldering heat resistance hardly decreases, compared to the conventional adhesive. It is possible to obtain an adhesive with a lower viscosity than the adhesive.

The proportion of units (D) in the carboxy-modified mixed polyvinyl acetal resin of the present invention is (C)
5 to 13% by weight, preferably 7 to 12% by weight on the same basis as
It is. When the proportion of (D) is less than 5% by weight, the viscosity of the adhesive decreases little, and when it exceeds 13% by weight, the soldering heat resistance decreases. As the fatty acid vinyl ester, vinyl acetate is preferred. The above ratio of fatty acid vinyl ester units can be determined by adding an aqueous solution of caustic soda to the resin dissolved in ethyl alcohol, heating it, and hydrolyzing the ester portion to generate fatty acid soda (the remaining caustic soda is neutralized with sulfuric acid). Then, a fatty acid different from the fatty acid of the fatty acid vinyl ester unit (D) (in the case of vinyl acetate, use propionic acid) and phosphoric acid are added to it as an internal standard substance, and the result is determined by gas chromatography. It can be determined by quantifying the amount of fatty acids and converting the amount of this fatty acid.

The proportion of carboxyl groups in the carboxy-modified mixed polyvinyl acetal resin of the present invention is such that the carboxyl groups (in terms of COOH) are the units (A), (
B), (C), (D) and (E) as a weight percentage relative to the total standard, and the ratio is 0.1
~5% by weight, especially 0.5~2.
5% by weight is preferred. The proportion of carboxyl groups is 0.1
If it is less than % by weight, adhesion to metal etc. is insufficient,
Moreover, if it exceeds 5% by weight, both normal adhesive strength and soldering heat resistance tend to decrease, and it is also uneconomical.

[0023] The amount of carboxyl groups possessed by the resin was determined by converting the carboxyl groups into sodium salts, quantifying the sodium using an atomic absorption spectrophotometer, and converting the value into carboxyl groups.

Next, a method for producing the carboxy-modified mixed polyvinyl acetal resin of the present invention will be explained.

[0025] The carboxy-modified mixed polyvinyl acetal resin of the present invention is produced by treating one or more carboxy-modified PVAs having carboxyl groups as side chains with both aldehydes, acetaldehyde and butyraldehyde, in a medium containing an acid catalyst. Obtained by acetalization.

The above-mentioned carboxy-modified PVA can be prepared by known methods such as Japanese Patent Publication No. 46-7605 and Japanese Unexamined Patent Publication No. 5
It can be obtained by the method described in JP 7-94002 and the like. Specifically, for example, one or more fatty acid vinyl esters (vinyl acetate, vinyl propionate, vinyl formate, etc.), unsaturated monocarboxylic acids (acrylic acid, methacrylic acid, crotonic acid, etc.), ethylenic monocarboxylic acids, etc. Saturated dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.), ethylenically unsaturated dicarboxylic anhydride (maleic anhydride), (meth)acrylic acid alkyl esters [methyl (meth)acrylate, ethyl (meth)acrylate , butyl (meth)acrylate, ethylhexyl (meth)acrylate, etc.), (meth)acrylonitrile, etc.], and (meth)acrylonitrile.

Furthermore, a monomer having a side chain that reacts with one or more fatty acid vinyl esters and an acid used as a catalyst when carrying out an acetalization reaction to convert into a carboxyl group [for example, acrylamide, methacrylamide, etc.] Modified PVA obtained by saponifying a copolymerized resin with one or more of the following can also be used as carboxy-modified PVA.

Furthermore, the above-mentioned carboxy-modified PVA includes, in addition to units having vinyl alcohol units, fatty acid vinyl ester units, and carboxyl groups (including groups having side chains that react with acids and convert into carboxyl groups).
It is also possible to use PVA in which about 10% by weight or less of units of other monomers copolymerizable with fatty acid vinyl ester are contained in the PVA by copolymerization. Other monomers copolymerizable with the above fatty acid vinyl ester include:
For example, monomers with glycidyl groups [allyl glycidyl ether, glycidyl (meth)acrylate, etc.], monomers with halogen atoms (vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, etc.), olefins (ethylene, propylene, etc.), alkyl vinyl ethers, etc.

The carboxyl group in the carboxy-modified PVA may be in the form of an acid, a salt, an acid amide, an alkyl ester, or a combination thereof.

The carboxy-modified PVA used as the raw material PVA to obtain the carboxy-modified mixed polyvinyl acetal resin of the present invention is determined by the proportion having carboxyl groups, the structure of carboxyl units, the shape of carboxyl groups, and the proportion having fatty acid vinyl ester units. Alternatively, two or more types having different average degrees of polymerization can also be used together.

Two or more types of carboxy-modified PV as raw materials
When used in combination with A, the combination is:
As long as the carboxy-modified mixed polyvinyl acetal resin of the present invention is obtained, the properties of the carboxy-modified PVA used as a raw material, such as average degree of polymerization, carboxyl groups, etc. The ratio of fatty acid vinyl ester units, the ratio of fatty acid vinyl ester units, etc. are not limited.

The carboxy-modified polyvinyl acetal resin of the present invention uses only carboxy-modified PVA as a raw material PVA.
It is preferable to use a mixture of a carboxy-modified mixed polyvinyl acetal resin and a non-carboxy-modified acetoacetal-butyl acetal mixed polyvinyl acetal resin. This mixed resin may be a mixture of one or more of the above resins, but during the acetalization reaction, both carboxy-modified PVA and non-carboxy-modified PVA are allowed to coexist as the raw material PVA. A method of obtaining the compound by chemical reaction is preferred.

Ratio (weight ratio) of carboxy-modified mixed polyvinyl acetal resin and non-carboxy-modified mixed polyvinyl acetal resin in the above mixed resin
is from 9:1 to 1:9, preferably from 8:2 to 2:8.

The carboxy-modified PVA used as a raw material to obtain the carboxy-modified mixed polyvinyl acetal resin of the present invention is PVA obtained by saponifying a copolymer resin of vinyl acetate and acrylamide or maleic acids.
VA is preferred.

The carboxy-modified mixed polyvinyl acetal resin of the present invention is not limited to its manufacturing method or conditions, and may be obtained, for example, by using an organic solvent, water, or a mixture thereof as a medium during the acetalization reaction. , dissolution method, precipitation method as methods of acetalization reaction,
There are those obtained by a homogeneous method or a combination of these methods.

The acetalization reaction is carried out in the presence of an acid catalyst, which is usually an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid, with hydrochloric acid being preferred.

Hydroxides, carbonates, etc. of alkali metals, alkaline earth metals, etc. can be used to neutralize the acid catalyst upon completion of the acetalization reaction, but these do not produce salts upon neutralization. However, if the adhesive contains a resin in which this salt remains, it may cause a decrease in the insulation properties of the adhesive layer. Use is preferred.

Next, the adhesive of the present invention will be explained.

The adhesive of the present invention contains one or more of the above carboxy-modified acetoacetal-butyl acetal mixed polyvinyl acetal resins, one or more thermosetting resins, and a solvent. .

[0040] Examples of the thermosetting resin contained in the adhesive of the present invention include phenolic resins and amino resins. Examples of phenolic resins include soluble phenol/formalin resins, which include novolac type and resol type. Also included are modified phenolic resins.

As the amino resin, modified melamine resins such as melamine resins and butylated melamine resins can also be used.

The content ratio (weight ratio) of carboxy-modified mixed polyvinyl acetal resin and thermosetting resin in the adhesive of the present invention is preferably 1:4 to 4:1, and 2:3 to 3.
: A range of 2 is desirable.

Examples of the solvent to be contained in the adhesive of the present invention include ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, alcohols such as methanol, ethanol, isopropanol and butanol, aromatics such as toluene and xylene, and acetic acid. Examples include esters such as methyl and ethyl acetate, and the solvent can be used alone or in combination of two or more, and the proportion of the solvent to be included in the adhesive can be arbitrarily selected.

[0044] The adhesive of the present invention may contain isocyanate, soluble polyurethane, various additives, and the like as components other than the above-mentioned carboxy-modified polyvinyl acetal resin, thermosetting resin, and solvent, if desired. The main additives mentioned above include known stabilizers, antioxidants, catalysts, and the like.

The adhesive of the present invention can be obtained by mixing and dispersing in a solvent a carboxy-modified mixed polyvinyl acetal resin, a thermosetting resin, and optionally contained substances other than the above resins. After each resin is dissolved and dispersed in the solvent used separately,
A method of mixing in liquid form is preferred in order to obtain a uniform adhesive. Furthermore, the adhesive of the present invention can be obtained using equipment and methods that are normally used for producing adhesives, paints, and the like.

[0046]

[Examples] The present invention will be explained below using Examples and Comparative Examples. In addition, unless otherwise specified, "part" and "%" are
Parts by weight and % by weight are shown, respectively.

Example 1 (Production of carboxy-modified mixed polyvinyl acetal resin) In a reactor equipped with a stirrer, reflux condenser and thermometer,
490 parts of methanol and 6 parts of 35% hydrochloric acid were charged, and then acrylamide copolymerized modified PVA (average degree of polymerization 17
30, residual vinyl acetate unit amount 16%, acrylamide content 4.7%) was added with stirring. Next, 41 parts of acetaldehyde and 38 parts of butyraldehyde were added thereto, and a mixed acetalization reaction was carried out at a temperature of 60° C. for 6 hours while stirring to obtain a methanol solution of a carboxy-modified mixed polyvinyl acetal resin. After this solution was cooled and neutralized with ethylene oxide, water was added with stirring to precipitate the resin. After washing with water and drying, a carboxy-modified mixed polyvinyl acetal resin in the form of white powder was obtained.

The composition of the obtained resin was 16.4% vinyl alcohol units, 8.4% vinyl acetate units, and 1.6% carboxyl group content, and the content of the resin was measured using an infrared spectrophotometer. The ratio (weight ratio) of acetoacetal units to butyl acetal units was 5:5, and the degree of acetalization was 72.7%.

Furthermore, the viscosity of a 5% solution obtained by dissolving the resin in a mixed solvent of equal weights of ethanol and toluene is 20°C.
It was 58 cps. (manufacture of adhesive)

8 parts of the carboxy-modified mixed polyvinyl acetal resin produced above was mixed with an organic solvent [methyl ethyl ketone/methanol/xylene/toluene=50
/17/17/17 (weight ratio)], then mix 80 parts of this solution with 20 parts of phenol resin solution (resin content 60%, manufactured by Gunei Chemical Industry Co., Ltd., product name: PL-2205). and used it as an adhesive. The viscosity of this adhesive at 20°C was 4700 cps. (Preparation and physical property measurement of copper-clad laminate)

[0051] The adhesive produced as described above was applied to a metallic copper foil (
35g/solid content on the rough side of 35μm thick)
m2, and after drying naturally for 30 minutes at room temperature,
It was dried in a hot air dryer at 140° C. for 3 minutes to produce an adhesive-coated copper foil. This copper foil was placed so that the adhesive-coated surface was in contact with the upper surface of several sheets of phenolic resin-impregnated paper, and the two were heat-pressed at a temperature of 160°C and a pressure of 75 kg/cm2 for 1 hour to form a single piece. A sheet of copper-clad laminate was obtained. This laminate was cut into pieces of 25 x 100 mm to obtain test pieces for measuring physical properties. Using this test piece, normal (20°C) adhesive strength and soldering heat resistance (260°C) were measured. The measurement method was based on JIS C-6485. Table 2 shows the results.
Shown below.

[0052] The adhesive obtained in the example had a low viscosity;
Application to the copper foil surface and measurement were easy, and the adhesive-coated surface of the adhesive-coated copper foil was uniform.

Examples 2 to 13 and Comparative Examples 1 to 11 Table 1
A carboxy-modified mixed polyvinyl acetal resin and a non-carboxy-modified mixed polyvinyl acetal resin (Comparative Example 1) were obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in FIG. Table 2 shows the properties of the obtained resin. In addition, in the same manner as in Example 1, an adhesive containing the above-mentioned mixed polyvinyl acetal resin was manufactured, and a copper-clad laminate bonded using the adhesive was manufactured, and the physical properties of the copper-clad laminate were measured. The results are shown in Table 2.

The adhesives obtained in Examples 2 to 13 had low viscosity and were easy to apply to the copper foil surface and measure, and the adhesive-coated surface of the adhesive-coated copper foil was uniform. On the other hand, the adhesives obtained in Comparative Examples 2, 3, and 10 had high viscosity and were difficult to apply and measure, and the coating thickness remained uneven on the coated surface, resulting in lack of uniformity.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

Effects of the Invention The adhesive of the present invention containing the carboxy-modified mixed polyvinyl acetal resin, thermosetting resin, and solvent of the present invention has a low viscosity and is excellent in coating workability, ease of handling, and uniformity of the coating film. Moreover, the copper-clad laminate bonded using this adhesive has excellent normal adhesive strength and solder heat resistance.

Claims (2)

[Claims] [Claim 1] Acetoacetal unit (A), butyl acetal unit (B), vinyl alcohol unit (
C), having a fatty acid vinyl ester unit (D) and a unit to which a carboxyl group is bonded as a side chain (E),
Average degree of polymerization is 1500-2500, (A) and (B)
The weight ratio of (C) is 3:7 to 7:3, and the weight ratio of (C) is (
A), (B), (C), (D) and (E) 14 to 21% by weight, proportion of (D)
Copper foil adhesive for printed circuits in which the proportion of carboxyl groups bonded as side chains to (E) is 0.1 to 5% by weight based on the same standards as (C), and 5 to 13% by weight based on the same standards as (C). Carboxy-modified acetoacetal-butyl acetal mixed polyvinyl acetal resin. 2. An adhesive for adhering copper foil to a printed circuit, comprising the polyvinyl acetal resin described in (1) above, a thermosetting resin, and a solvent.