TWI842856B - Composition comprising fluororesin and methods of producing the composition and a fluororesin dispersion - Google Patents

Abstract

A composition, a method of producing the composition and a method of producing a fluororesin dispersion from the composition are provided, wherein the composition comprises: (i) a fluororesin having an average particle diameter of 1 μm or more and 5 μm or less and a maximum particle size of 10 μm or less; (ii) a dispersant; and (iii) an organic solvent, wherein percentage by mass of the organic solvent in the composition is 0.2% or less.

Description

Composition containing fluororesin and method for producing the composition and fluororesin dispersion

The present invention relates to a composition containing a fluororesin, and a method for preparing the composition and the fluororesin dispersion.

Fluororesins are used as coatings because they have chemical resistance, heat resistance, low friction coefficient, and electrical insulation properties. Specifically, fluororesins are used as coatings in high-frequency circuit boards due to their excellent dielectric properties. In a typical process for manufacturing high-frequency circuit boards, fluororesins are processed into fine particles, which are dispersed in a dispersion medium containing a base resin and then laminated with a conductor such as copper foil and the like. The resulting panel is then further processed by etching and similar processes to form a high-frequency circuit board.

Since the base resin commonly used in the above manufacturing process is soluble in a hydrocarbon solvent, the fluororesin must first be dispersed in the hydrocarbon solvent. However, due to its low interfacial tension, the fluororesin has poor wettability to hydrocarbon media and is difficult to disperse in the media.

Furthermore, considering the relatively high specific gravity of fluororesins, it is difficult to avoid separation in fluororesin dispersions. Conventionally, industrial responses must be made, such as maintaining the dispersion state by continuous stirring and setting a pot life after dispersion.

This separation problem is particularly evident during transportation. Another problem that may arise during the transportation of fluororesin dispersions is that handling organic solvents is often hazardous, which not only increases transportation costs but also increases transportation time.

Various methods have been proposed for dispersion techniques of fluororesins.

JP-A-2017-193655 discloses a fluororesin dispersion containing a dispersant having a thermally decomposable group of a specific oxyalkylene chain, fluororesin particles, and water or an organic solvent.

JP-A-1987-121700 discloses a fluorine resin dispersion characterized by dispersing a fluorine-containing resin powder having a particle size of 2 μm or less in an organic solvent.

Japanese Patent No. 2516241 discloses a technology for dispersing a fluorine-containing resin powder having a particle size of 2 μm or less in an aqueous medium in the presence of a non-ionic surfactant and a thickener.

Japanese Patent No. 4255169 discloses a dispersant having an organosiloxane structure that uniformly disperses fibrillated PTFE.

Japanese Patent No. 5195425 discloses a technology that brings a solution in which a fluororesin is substantially dispersed in an aqueous medium to an ion exchange resin, adds an electrolyte and an anionic emulsifier, and then performs phase separation and concentration to obtain an aqueous fluororesin solution.

JP-A-1998-176002 discloses a technique in which polymer particles insoluble in organic solvents are dispersed by using a polymer having an acrylic skeleton and a fluoroalkyl group in a side chain.

US 2013/0149540 discloses a charging roll composition for improving the copying quality of a dry copier, and in an example discloses a technique for dispersing polytetrafluoroethylene resin particles using a polymer having an acrylic backbone and fluoroalkyl groups in the side chains.

WO 2018070420 discloses a composition obtained by mixing a hydrous fluoropolymer having a specific sulfonic acid group and a carboxyl group in its structure with water, and filtering the mixture through a mesh size of 20 μm to obtain a composition having a dispersion of 50%. Drying at a work amount of 200 W or less to obtain a powder is disclosed.

As mentioned above, Japanese Patent No. 2516241 and Japanese Patent No. 5195425 disclose the use of water as a dispersion medium. However, since the latent heat of water evaporation is large, the use of water as a dispersion medium increases the time taken to apply the fluororesin coating to the substrate. Furthermore, the presence of a dispersing agent and a thickener used to stabilize the aqueous dispersion may cause the fluororesin to lose its dielectric properties.

JP-A-1998-176002 and US 2013/0149540 disclose a technique for producing a non-aqueous dispersion by using a polymer having an acrylic backbone and having a fluoroalkyl group in a side chain. However, in the case where a non-fluorine portion exists in the polymer, in the application of high-frequency integrated circuits, it is possible that the properties possessed by the fluororesin may be disturbed.

WO 2018070420 discloses an ion exchange resin having a sulfonic acid group or a carboxyl group, which has a high affinity for water as a dispersion solvent itself, but cannot be used in high-frequency circuit boards that require electrical insulation. The possibility of dispersing the ion exchange resin in an organic solvent other than water is also suggested, but no examples are shown.

According to an example of the present disclosure, a composition comprising a fluororesin, a method for preparing the composition, and a method for preparing a fluororesin dispersion as claimed in an independent claim are provided. Some optional features are defined in the dependent claims.

101,201:Mixture

102:Filter

104: Composition

106,202:Dispersion liquid

204: Second solvent

FIG. 1A illustrates the steps of forming a composition according to an example of the present disclosure.

FIG. 1B illustrates the steps of preparing a fluororesin dispersion from the fluororesin composition of FIG. 1A.

Examples of the composition, the method for preparing the composition, and the method for preparing a fluororesin dispersion using the composition are described below.

FIG. 1A illustrates steps for forming an example of a composition 104 of the present disclosure. In this case, the composition 104 is a fluororesin composition. In this example, the fluororesin composition 104 is a dry solid. First, in step 1, the following components are mixed together: (a) fluororesin powder, (b) dispersant, (c) solvent, and (d) dispersion beads to form a mixture 101. In addition to dispersion beads, other suitable dispersing aids may also be used. In step 2, which is considered a dispersion step, the fluororesin powder in the mixture 101 is dispersed by mechanical action. Dispersion by mechanical action may include using a paint shaker to shake the mixture. Thereafter, in step 3, the dispersed beads are removed by filtering using a suitable filter 102 (in the example described in the example section below, see examples of such filters) to form a first fluororesin dispersion 106. Finally, in step 4, the first fluororesin dispersion 106 is dried to form a dry solid fluororesin composition 104 of this example.

The drying process of step 4 may be a continuous drying process with checkpoints during the process to confirm that the mass percentage of the organic solvent in the composition 104 is 0.2% or less. In another example, the drying process may be a process in which the first fluororesin dispersion 106 is dried more than once at the same temperature or fluctuating temperature, and wherein there are stop points or checkpoints between the more than one dryings to confirm that the mass percentage of the organic solvent in the composition 104 is 0.2% or less. 0.2% or less of the solvent ensures that the composition 104 is sufficiently dry. The confirmation step for ensuring that the mass percentage of the solvent in the composition 104 is 0.2% or less at each stop point or check point may be to perform a heating process on the composition 104 and determine the mass of the composition 104 before and after the heating process to verify that the mass change percentage of the composition 104 is 0.2% or less. After the drying process, finding that the mass change percentage of the composition 104 is 0.2% or less may lead to the conclusion that the mass percentage of the solvent in the composition 104 is 0.2% or less.

In the example of forming composition 104 as shown in FIG. 1A, the components are added in step 1 in the following parts per mass: 1 to 40 parts by mass of fluororesin; 1 to 10 parts by mass of dispersant; and 50 to 98 parts by mass of the first organic solvent, so that the total parts per mass of the components total 100.

Then, add 10 to 20 parts by mass of dispersion beads to every 100 parts of the mixture of fluororesin, dispersant and first organic solvent.

FIG. 1B illustrates the steps of making a second fluororesin dispersion from the dry solid fluororesin composition 104 made in the example of FIG. 1A. In step A, a second solvent 204 is first added to the dry solid fluororesin composition 104 of FIG. 1A to form a mixture 201. In step B, the mixture 201 is redistributed by mechanical action to redisperse the fluororesin in the mixture 201 to form a second fluororesin dispersion 202.

In the example of manufacturing the second dispersion 202 as shown in FIG. 1B , the components are added in step A in the following mass parts: 20 to 40 mass parts of the composition 104; and 60 to 80 mass parts of the second organic solvent, so that the total mass parts of the composition and the second organic solvent are 100.

The composition 104 of FIG. 1A refers to a composition in which the composition comprises a fluororesin having an average particle diameter of 1 μm or more and 5 μm or less and a maximum particle size of 10 μm or less, a dispersant, and an organic solvent or residual organic solvent having a mass percentage of 0.2 mass % or less. The composition 104 of FIG. 1A may be in the form of a cake-like material, or more specifically, in the form of a dried or hardened solid block. In another example, the composition 104 of FIG. 1A may be in the form of a powder and not aggregated to form a cake-like material.

One of the advantages of the composition 104 of FIG. 1A is that transportation problems can be avoided because harmful organic solvents in the fluororesin dispersion are removed or substantially removed.

Another advantage of the composition 104 of FIG. 1A is that it can be easily returned to a dispersed state again through steps A and B of FIG. 1B. The size of the fluororesin powder after redispersion in step B of FIG. 1B is 10 μm or less. Another advantage is that the redispersion of the composition 104 in step A is performed without using dispersion beads. In addition, a suitable but different (different from the first organic solvent) solvent may be used in step A of FIG. 1B. The organic solvent used for the redispersion of the composition 104 is not limited to the first organic solvent.

One of the applications of the composition according to the example disclosed herein is for manufacturing high-frequency circuit boards. Therefore, the fluororesin in the composition 104 of FIG. 1A may be a perfluoro fluororesin having higher dielectric properties. Specifically, the fluororesin may be a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. Tetrafluoroethylene-hexafluoropropylene is another choice of fluororesin because it melts during the heating process. Therefore, the fluororesin may be one or two selected from the group consisting of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer and a tetrafluoroethylene-hexafluoropropylene copolymer.

In another example of the present disclosure, in order to improve the function of a high-frequency circuit board, the fluororesin in the composition 104 of FIG. 1A may contain 10 mol% or less of a monomer. For example, the fluororesin may contain itaconic anhydride and 5-norbornene-2,3-dicarboxylic anhydride to improve the adhesion of the base resin to the substrate of the high-frequency circuit board.

According to an example of the present disclosure, the size of the fluororesin powder in the second fluororesin dispersion 202 of FIG. 1B (after redispersion) is 10 μm or less. When it is 10 μm or more, it may have some negative effects on the smoothness of the substrate of the high-frequency circuit board and affect the dielectric properties of the substrate. This in turn may affect the performance of the high-frequency circuit. Especially in a multi-layer board with multiple substrates stacked, this problem of affecting the performance of the high-frequency circuit becomes significant. In order to obtain a redispersion state of no more than 10 μm, it is required that the average particle diameter in the composition 104 of FIG. 1A is 1 to 5 μm or less, and the maximum particle diameter is 10 μm or less. When the average particle diameter is 1 μm to 5 μm, the amount of dispersant and organic solvent used to redisperse the second fluororesin dispersion 202 does not adversely affect the electrical properties.

Regarding the organic solvent used in the first fluororesin dispersion 106 of FIG. 1A, one example is to volatilize the organic solvent under normal pressure or reduced pressure until the mass percentage of the organic solvent in the composition 104 is 0.2% or less. In the case of application to high-frequency circuit boards, the organic solvent is generally used based on the solubility in the base resin. Illustrative examples of such organic solvents include MEK (methyl ethyl ketone), toluene, xylene, DMF (dimethylformamide), NMP (N-methylpyrrolidone), DMAC (dimethylacetamide), CAN (cyclohexanone) and the like.

As for the dispersant in the composition 104 of FIG. 1A, an example is a oligomer of hexafluoropropene. Therefore, the dispersant may be a hexafluoropropylene trimer. The dispersant may contain one or more surfactants. The amount of the dispersant added varies depending on the organic solvent used, but is generally about 1 to 10 parts by mass per 100 parts of fluororesin.

Regarding the dispersion beads used to disperse the first fluororesin dispersion 106 of FIG. 1A, glass, ceramic beads, and oxide beads can be used.

Example

Preparation of dispersion in Example 1 (Ex.1)

25 g of tetrafluoroethylene-perfluoroalkylether copolymer (particle diameter D50: 2.1 μm) (fluororesin), 1 g of hexafluoropropylene trimer surfactant (dispersant), 75 g of methyl ethyl ketone (MEK) solvent (organic solvent) and 12.5 g of zirconia (ZrO ₂ ) beads (diameter 2 mm) as dispersed beads are added to a 300 ml glass jar. The glass jar is sealed with an inner lid and a jar lid. The sealed glass jar is placed in a paint shaker (Collomix AGIA 200) and shaken for 60 minutes. Then, the mixture in the jar is filtered once through a 185 μm filter (an example of the filter 102 in FIG. 1A ) to remove the zirconia beads. The particle size of the obtained dispersion was determined by a milling machine to be less than 10 μm.

Preparation of dispersion in Example 2 (Ex.2)

The dispersion was prepared as described in Example 1 except that acetone was used as the organic solvent instead of MEK. The particle size of the obtained dispersion was determined by a milling machine to be less than 10 μm.

Preparation of dispersion in Example 3 (Ex.3)

This example is intended as a comparative example. The dispersion was prepared as described in Example 1, except that no zirconium dioxide beads were added as dispersion beads. The particle size of the obtained dispersion was determined by a milling machine to be greater than 10 μm.

Preparation of dispersion in Example 4 (Ex.4)

This example is intended as a comparative example. The dispersion was prepared as described in Example 1, except that the shaking time was 45 minutes instead of 60 minutes. The particle size of the obtained dispersion was determined by a milling machine to be greater than 10 μm.

Table 1 shows a summary of the results of Examples 1 to 4. Desired results (i.e., particle sizes less than 10 μm) were found in Examples 1 and 2, while Examples 3 and 4 are comparative examples that did not produce the desired results.

Preparation of redispersion solution in Example I

The dispersion obtained in Example 1 above was dried by exposing it to ambient conditions (25°C) for 7 days, and the glass bottle was not sealed in an exhaust cabinet to obtain a cake-like material. The cake-like material was confirmed to be dried by heating it and verifying that the mass change percentage of the cake-like material was 0.2% or less. 20g of the cake-like material and 60g of acetone were added to a 300ml glass jar. The mass ratio of the redispersing solvent to the mass of the cake-like material was 3:1. The glass jar was sealed with an inner cover and a jar lid. The sealed glass jar was placed in a paint shaker (Collomix AGIA 200) and shaken for 60 minutes. The particle size of the obtained dispersion was determined by a grinder to be less than 10 μm.

Preparation of redispersion solution in Example II

The redispersion was prepared as described in Example I except that MEK was used as the redispersion solvent. The particle size of the obtained dispersion was determined by a milling machine to be less than 10 μm.

Preparation of redispersion solution in Example III

The redispersion was prepared as described in Example I, except that the cake-like material used was obtained by drying from Example 2 and MEK was used as the redispersion solvent. The particle size of the obtained dispersion was determined by a milling machine to be less than 10 μm.

Preparation of redispersion solution in Example IV

This example is intended as a comparative example. The redispersion was prepared as described in Example I, except that dimethylacetamide was used as the redispersion solvent. The particle size of the obtained dispersion was determined by a milling machine to be greater than 10 μm.

Preparation of redispersion solution in Example V

This example is intended as a comparative example. The redispersion was prepared as described in Example I, except that toluene was used as the redispersion solvent. The particle size of the obtained dispersion was determined by a milling machine to be greater than 10 μm.

Preparation of redispersion solution in Example VI

This example is intended as a comparative example. The redispersion solution was prepared as described in Example I, except that toluene was used as the redispersion solvent and the mass of the redispersion solvent was increased to 4:1 to the mass of the "cake-like material". The particle size of the obtained dispersion was determined by a grinder to be greater than 10 μm.

Preparation of redispersion solution in Example VII

This example is intended as a comparative example. The redispersion was prepared as described in Example I, except that toluene was used as the redispersion solvent and the redispersion method used was by stirring with a paint stirrer for 60 minutes. The particle size of the obtained dispersion was determined by a grinder to be greater than 10 μm.

Table 2 below shows successful redispersion results by using a redispersion solvent different from the first dispersing solvent. A successful result is defined as redispersion to a particle size below 10 μm. Examples of successful redispersion are found in Examples I and III, while Examples II and IV to VII are comparative examples.

Details of the chemicals used

In the specification and patent application, unless the context clearly indicates otherwise, the term "comprising" has a non-exclusive meaning of the word in the sense of "including at least", rather than an exclusive meaning in the sense of "consisting only of". The same logic applies to other grammatical variations of the word, such as "comprise", "comprises", etc.

Although the present invention has been described in conjunction with several embodiments and implementations in this disclosure, the present invention is not limited thereto, but covers various obvious modifications and equivalent arrangements within the scope of the attached patent application. Although the features of the present invention are expressed in certain combinations in the patent application, it is expected that these features can be arranged in any combination and order.

101:Mixture

102:Filter

104: Composition

106: Dispersion liquid

Claims (13)

A dry solid composition comprising: (i) a fluororesin having an average particle diameter of 1 μm or more and 5 μm or less and a maximum particle size of 10 μm or less; (ii) a dispersant; and (iii) an organic solvent, wherein the mass percentage of the organic solvent in the dry solid composition is 0.2% or less, wherein the dry solid composition is dried from a first fluororesin dispersion and used for redispersion to form a second fluororesin dispersion. A dry solid composition as described in claim 1, wherein the fluororesin is selected from one or both of the group consisting of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer and tetrafluoroethylene-hexafluoropropylene copolymer. A dry solid composition as described in claim 1 or 2, wherein the fluororesin comprises 10 mol% or less of a monomer. A dry solid composition as described in claim 3, wherein the monomer is selected from the group consisting of itaconic anhydride and 5-norbornene-2,3-dicarboxylic anhydride. A dry solid composition as described in claim 1 or 2, wherein the dispersant is an oligomer. A dry solid composition as described in claim 5, wherein the oligomer is a hexafluoropropylene trimer. A dry solid composition as described in claim 1 or 2, wherein the organic solvent is selected from the group consisting of MEK (methyl ethyl ketone) and acetone. A dry solid composition as described in claim 1 or 2, wherein the dry solid composition is in a powder form or a cake-like material form. A method for producing a dry solid composition as described in claim 1 or 2, the method comprising: (i) a mixing step of mixing a fluororesin, a dispersant, an organic solvent and a dispersing aid to form a mixture; (ii) a dispersing step of dispersing the fluororesin in the mixture to form a dispersion; (iii) a filtering step of removing the dispersing aid in the dispersion; and (iv) a drying step of removing the organic solvent in the filtered dispersion so that the mass percentage of the organic solvent in the dry solid composition is 0.2% or less. The method as described in claim 9, wherein the mixing step comprises: (a) mixing the fluororesin, the dispersant and the organic solvent in the following weight parts: 1 to 40 weight parts of the fluororesin; 1 to 10 weight parts of the dispersant; and 50 to 98 weight parts of the organic solvent, so that the total weight parts of the fluororesin, the dispersant and the organic solvent are 100; (b) adding 10 to 20 weight parts of the dispersing aid for every 100 weight parts of the fluororesin, the dispersant and the organic solvent. A method for producing a fluororesin dispersion, the method comprising: (i) a mixing step of mixing a second solvent into the dry solid composition as described in claim 1 or 2 to form a mixture; and (ii) a dispersing step of dispersing the fluororesin in the mixture without using a dispersing aid to form the fluororesin dispersion, wherein the fluororesin in the fluororesin dispersion has an average particle diameter of 1 μm or more and 5 μm or less and a maximum particle size of 10 μm or less. The method as described in claim 11, wherein the mixing step comprises: adding 20 to 40 parts by weight of the dry solid composition and 60 to 80 parts by weight of the second solvent, so that the total parts by weight of the dry solid composition and the second solvent is 100. The method of claim 11 or 12, wherein the second solvent is selected from the group consisting of MEK (methyl ethyl ketone) and acetone.