JP5809895B2 - Polyphenylene sulfide foam and method for producing the same - Google Patents

Description

  The present invention relates to a polyphenylene sulfide foam excellent in basic characteristics such as heat resistance (including heat insulation and flame retardancy), low dielectric constant, and mechanical strength, and also excellent in secondary moldability, and a method for producing the same. It is.

Since polyphenylene sulfide resin is excellent in heat resistance, low dielectric constant, and mechanical strength, it is widely used as electronic / electric equipment part materials, transportation equipment parts materials such as automobiles, and chemical equipment parts materials.
In these fields, weight reduction of equipment has become an important issue, and it is required to reduce the weight of resin molded products, which are constituent parts, without damaging the excellent properties inherent in the resin. The case is increasing.
For example, Patent Document 1 discloses a polyarylene sulfide foam (polyphenylene sulfide foam) having a crystallinity of 20% or more and a foaming ratio of 2 times or more, and a method for producing the same. The characteristics such as low dielectric constant, mechanical strength and light weight are improved.

JP-A-7-224185

However, the foam described in Patent Document 1 has a problem that secondary moldability is low and it is difficult to process at the present stage (it is difficult to perform secondary molding).
In view of this point, the inventors of the present invention have found that the reason why it is difficult to secondary-mold the foam is that the crystallinity is as high as 20% or more.
Accordingly, a main object of the present invention is to provide a polyphenylene sulfide foam excellent in secondary moldability while maintaining basic characteristics such as heat resistance, low dielectric constant, and mechanical strength, and a method for producing the same. is there.

In order to solve the above problems, according to one aspect of the present invention,
A polyphenylene sulfide foam composed of a polyphenylene sulfide resin having a repeating unit represented by the general formula (a) and having a crystallinity of less than 20% ,
A crosslinking agent is added to the polyphenylene sulfide resin,
A polyphenylene sulfide foam in which the amount of the crosslinking agent added is 1.0 to 10 parts by mass with respect to 100 parts by mass of the polyphenylene sulfide resin .
-(Ar-S) -... (a)
In the general formula (a), “Ar” is an aryl group.

According to another aspect of the invention,
Adding 100 to 10 parts by mass of a crosslinking agent to 100 parts by mass of the polyphenylene sulfide resin having a repeating unit represented by the general formula (a);
A step of containing said polyphenylene sulfide resin of a mixture of the crosslinking agent, and held pressurized atmosphere by inert gas, the inert gas into the mixture,
Heating the mixture containing the inert gas under normal pressure and a temperature of 60 to 120 ° C. to foam;
A process for producing a polyphenylene sulfide foam comprising:
-(Ar-S) -... (a)
[In the general formula (a), “Ar” represents an aryl group. ]

According to the present invention, it is possible to improve secondary formability while maintaining basic characteristics such as heat resistance, low dielectric constant, and mechanical strength.
Such a secondary molded article made of the polyphenylene sulfide foam of the present invention is a resin foam molded article having excellent molding freedom and excellent viewpoints of heat resistance, low dielectric constant, mechanical strength and light weight. Utilizing these properties, the polyphenylene sulfide foam (secondary molded product) of the present invention is made of a material having electrical properties such as a heat insulating material for electronic and electrical parts such as motors, a sealing material such as adhesive tape and packing, and a capacitor. It can be suitably used as a molded article for tableware, containers, automobile parts and the like.

  Hereinafter, preferred embodiments of the present invention will be described.

(1) Polyphenylene sulfide foam (1.1) Polyphenylene sulfide resin The polyphenylene sulfide foam according to the present invention is mainly composed of a polyphenylene sulfide resin.
The polyphenylene sulfide resin has a repeating unit represented by the general formula (a).
-(Ar-S) -... (a)
In the general formula (a), “Ar” is an aryl group.
The polyphenylene sulfide resin is not particularly limited as long as it has a repeating unit represented by the general formula (a) and exhibits crystallinity.
A typical example of the polyphenylene sulfide resin is polyphenylene sulfide (hereinafter referred to as “PPS”) in which the aryl group (Ar) in the repeating unit represented by the general formula (a) is a phenyl group.

A polyphenylene sulfide foam using this polyphenylene sulfide resin has a characteristic that the crystallinity of the foam is less than 20%.
Examples of foaming methods (foaming methods) include injection foaming methods, batch foaming methods, and extrusion foaming methods. The form of foaming is not particularly limited as long as pores are present in the foam sheet.

In addition, in the range that does not affect the characteristics, polyphenylene sulfide resin before foaming, antioxidant, antistatic agent, ultraviolet light inhibitor, light stabilizer, fluorescent brightener, pigment, dye, compatibilizer, lubricant, Reinforcing agents, flame retardants, crosslinking agents, thickeners, thickeners, reinforcing materials such as glass fibers and carbon fibers, various additives such as pigments and talc may be blended.
A resin containing the additive may be laminated on the obtained polyphenylene sulfide resin after foaming, or a coating containing the additive may be coated.

Specifically, the polyphenylene sulfide resin (A) constituting the polyphenylene sulfide foam of the present invention is a polymer having a repeating unit represented by the structural formula (I).
When all the units constituting the polyphenylene sulfide resin (A) are 100 mol%, the polyphenylene sulfide resin (A) preferably has 70 to 100 mol% of repeating units represented by the structural formula (I). contains.

  The polyphenylene sulfide resin (A) is composed of repeating units having the structural formula (II) in which less than 30 mol% of the repeating units are 100 mol% when all units constituting the polyphenylene sulfide resin (A) are 100 mol%. Is possible.

The polyphenylene sulfide foam of the present invention preferably contains 50% by mass or more and 99.99% by mass or less of the polyphenylene sulfide resin (A) in a total of 100% by mass of all the components constituting the foam.
A polyphenylene sulfide foam can contain various additives, such as resin other than polyphenylene sulfide resin, and inorganic filler as needed as components other than polyphenylene sulfide resin (A).
The polyphenylene sulfide foam of the present invention preferably contains 80% by mass or more and 99.99% by mass or less of the polyphenylene sulfide resin (A) in a total of 100% by mass of all the components constituting the foam.

The polyphenylene sulfide resin (A) constituting the polyphenylene sulfide foam of the present invention preferably satisfies both the following conditions 1 and 2.
Condition 1: 50,000 ≦ weight average molecular weight (Mw) ≦ 120,000
Condition 2: 2.6 ≦ molecular weight distribution (Mw / Mn) ≦ 5.5

This point will be described.
The weight average molecular weight Mw of the polyphenylene sulfide resin (A) constituting the polyphenylene sulfide foam of the present invention is not particularly limited, but is preferably 50,000 to 120,000 (measurement method: GPC).
When the weight average molecular weight Mw is 50,000 or more, the moldability is good and it is particularly possible to mold a mold having a large molding draw ratio.
On the other hand, it is preferable that the weight average molecular weight Mw is 120,000 or less because the expansion ratio can be easily increased and the density can be lowered and the weight can be reduced.
The weight average molecular weight Mw of the polyphenylene sulfide resin (A) is more preferably 60,000 to 100,000.

The molecular weight distribution state of the polyphenylene sulfide resin (A) constituting the polyphenylene sulfide foam of the present invention, that is, the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is not particularly limited, Preferably it is 2.6-5.5.
When the molecular weight distribution Mw / Mn is 2.6 or more, the molding condition width is widened, and it is particularly possible to mold a mold having a large molding ratio.
On the other hand, when the molecular weight distribution Mw / Mn is 5.5 or less, it is preferable from the point that uniform foaming occurs and stable production is possible and the surface appearance of the foam is improved.
The molecular weight distribution (Mw / Mn) of the polyphenylene sulfide resin (A) is more preferably 3.0 to 4.5.

The polyphenylene sulfide resin (A) constituting the polyphenylene sulfide foam of the present invention has a weight average molecular weight Mw of 50,000 to 120,000 and a molecular weight distribution (Mw / Mn) of 2.6 to 5.5. As a method for adjusting each, a polymerized and recovered by a known technique or the like can be used.
For example, a mixture containing at least a polyhalogenated aromatic compound typified by p-dichlorobenzene, an alkali metal sulfide typified by sodium sulfide, and an organic polar solvent typified by N-methyl-2-pyrrolidone is prepared. In general, the temperature is raised to the range of 200 to 290 ° C., usually after heat polymerization for about 0.5 to 50 hours, and then cooled to 220 ° C. or less, a by-product other than polyphenylene sulfide resin, water, The polyphenylene sulfide resin can be recovered from the mixed solution after the polymerization reaction of an alkali metal halide salt and an organic polar solvent using an eye such as a sieve. At that time, a technique of polymerizing in a branched manner using a crosslinking aid or the like may be carried out.

About polyphenylene sulfide resin (A) which comprises the polyphenylene sulfide foam of this invention, you may post-process to the polyphenylene sulfide resin superposed | polymerized and collect | recovered.
As described above, the polymerized / recovered polyphenylene sulfide resin is likely to contain low molecular weight polyphenylene sulfide resin, by-products, and impurities. Therefore, the polyphenylene sulfide resin after polymerization / recovery may be subjected to hot water treatment or organic solvent treatment (washing with an organic solvent).
It is known as a known fact that these post-treatments may be applied to the polyphenylene sulfide resin after polymerization and recovery.

When performing hot water treatment, it is as follows.
Although there is no restriction | limiting in particular in the hot water used for a hot-water process, From the point of a washing | cleaning effect, Preferably the water to be used is distilled water or deionized water.
The hot water temperature is preferably 90 ° C. or higher.

When the organic solvent treatment is performed, it is as follows.
The organic solvent used in the organic solvent treatment is not particularly limited as long as it does not have an action of decomposing polyphenylene sulfide resin, and N-methyl-2-pyrrolidone, dimethylacetamide, 1,3-dimethylimidazolidinone, Polar solvents containing piperazinones containing nitrogen atoms, polar solvents containing halogen atoms such as methylene chloride, trichloroethylene, perchloroethylene, monochloroethane, dichloroethane, chloroform, chlorobenzene, ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, acetophenone, etc. Is mentioned.
Among these, it is particularly preferable to use N-methyl-2-pyrrolidone or acetone or chloroform.
These organic solvents may be used alone or in combination of two or more.
From the viewpoint of the cleaning effect, the cleaning temperature is preferably from room temperature to 200 ° C.

The polyphenylene sulfide foam of the present invention preferably has a high purity and is preferably mainly composed of the polyphenylene sulfide resin (A), but the polyphenylene sulfide foam of the present invention contains an alkali metal, an alkaline earth metal, It may contain halogen or the like. Alkali metals, alkaline earth metals, halogens, and the like are components that are considered to be mainly contained in the polymerization process and washing process of polyphenylene sulfide resin, and these often remain in the foam in the end. There is no restriction | limiting in particular in containing.
The alkali metal here refers to lithium, sodium, potassium, rubidium, cesium, francium and the like, and is not particularly limited, but sodium sulfide is preferably used in the polymerization process of the polyphenylene sulfide resin.
The alkaline earth metal as used herein refers to calcium, strontium, magnesium, barium and the like, and is not particularly limited. In the polyphenylene sulfide resin washing step, calcium acetate, calcium hydroxide, magnesium hydroxide is used. Etc. are preferably used.
Halogen here refers to fluorine, bromine, and iodine, and p-dichlorobenzene, m-dichlorobenzene, o-dichlorobenzene, and the like are often used in the polymerization process of the polyphenylene sulfide resin.
Among alkali metals, alkaline earth metals, halogens and the like, it is preferable to contain an alkaline earth metal, and the polyphenylene sulfide foam of the present invention has a calcium component of 30 to 2000 ppm (mass basis) with respect to 100 mass% of the foam. ) Is preferably contained.
In order for the polyphenylene sulfide foam of the present invention to contain a calcium component, the polyphenylene sulfide foam may contain a carboxylic acid salt containing calcium component, calcium hydroxide, or the like.
When the calcium component is less than 30 ppm (mass basis) with respect to 100% by mass of the foam, it may be difficult to obtain a high-quality foam having low yellowness and high whiteness.
On the other hand, when the calcium component is more than 2000 ppm (mass basis) with respect to 100% by mass of the foam, the strength of the molded product may be reduced, or the appearance of the molded product may be reduced.

The carboxylate containing a calcium component is not particularly limited.
Examples of the carboxylate containing a calcium component include calcium acetate, calcium propionate, calcium benzoate, calcium phthalate, calcium fumarate, and calcium maleate.
In consideration of productivity, the carboxylate containing a calcium component is preferably calcium acetate.
Two kinds of carboxylic acid containing these calcium components and calcium hydroxide can be used in combination.

There is no particular limitation on the method of incorporating these calcium components in the polyphenylene sulfide foam, but the method of adding the calcium component in the form of an aqueous solution during the polymerization of the polyphenylene sulfide resin or immediately after the polymerization, or washing the polyphenylene sulfide resin In this case, there is a method of washing with an aqueous solution containing a calcium component, but the latter is generally used.
The calcium component used in the latter method is not particularly limited, but preferably calcium hydroxide, calcium acetate and the like.

  The “calcium component” in the present invention refers to that detected by the following measurement method.

The calculation method of content of a calcium component is as follows.
The platinum dish is washed with pure water, calcined at 700 ° C. for 1 hour, and dried in a desiccator. A value obtained by precisely weighing the platinum dish to 0.1 mg is defined as “A (g)”.
Next, about 5 (g) of the polyphenylene sulfide foam of the present invention was collected in a platinum dish, and the total amount of the platinum dish and the sample was precisely weighed to 0.1 (mg) with a chemical balance. (G) ".
Thereafter, a platinum dish containing a foam is placed on a stainless steel bat, placed in a high-temperature oven set at 440 ° C., and baked for 5 hours. Thereafter, the temperature in the oven is raised to 500 ° C., and further baked for 5 hours.
After carrying out the firing treatment, after cooling to 300 ° C. or lower, the platinum dish is stored in a desiccator for 12 hours.

Thereafter, the platinum dish is taken out of the desiccator and placed in a muffle furnace stable at 538 ° C. and baked for 6 hours.
After the treatment, the platinum dish is taken out from the muffle furnace, and it is confirmed that the black carbide is completely removed from the sample.
In addition, baking is further implemented when presence of black carbide is recognized even a little.
After the completion of firing, the platinum dish is taken out from the muffle furnace and cooled in a desiccator for 30 minutes.

Next, 2 ml of pure water: hydrochloric acid (special grade) = 1: 1 (hereinafter referred to as 1: 1 hydrochloric acid) is added to the platinum dish.
Then, using a hot plate, a platinum dish containing pure water and hydrochloric acid is heated 1: 1 to the extent that boiling of the solution is confirmed. Stop heating before evaporating to dryness and cool the platinum dish to room temperature.
Thereafter, the contents of the platinum dish are divided into several times while being washed with ion-exchanged water, placed in a 50 ml volumetric flask, and aligned with the 50 ml mark of the volumetric flask.

Using the sample solution thus prepared, measurement is carried out using an atomic absorption measuring apparatus with ion-exchanged water as a blank.
As a method for determining the concentration value, the calcium component concentration is calculated by a calibration curve created using a standard solution containing the calcium component to be analyzed. If the measured value deviates from the calibration curve, collect the sample solution “X (ml)”, dilute with ion-exchanged water to “Y (ml)”, and adjust the concentration so that it is within the calibration curve range. Do. A value measured using the sample solution thus adjusted is defined as “C (ppm)”.
The calcium component concentration (ppm) is calculated using the above numerical values.
Calcium component concentration [ppm] = C (ppm) / (BA) × 50 × Y / X

(1.2) Crosslinking agent A crosslinking agent is preferably added to the polyphenylene sulfide resin.
The cross-linking agent used in the present invention is not particularly limited as long as it can cross-link polyphenylene sulfide resins, and the cross-linking agent here includes a chain extender having a pseudo-crosslinking function.
The cross-linking agent is preferably one in which the functional group of polyphenylene sulfide resin (thermoplastic resin) reacts with the cross-linking agent to form a thermoplastic resin network structure. It may be cross-linked.
For example, a styrene oxazoline group-containing polymer can be used as a crosslinking agent.
The addition amount of a crosslinking agent is 0.5-15 mass parts with respect to 100 mass parts of polyphenylene sulfide resin.
If the addition amount of the cross-linking agent is too small, the effect of miniaturizing the bubbles is low. Conversely, if the addition amount of the cross-linking agent is too large, it is difficult to uniformly cross-link and the bubbles become coarse.
In consideration of the effect of refining bubbles and uniformity of crosslinking, the amount of the crosslinking agent added is preferably 1.0 to 10 parts by mass with respect to 100 parts by mass of the thermoplastic resin.

(2) Properties of Polyphenylene Sulfide Foam (2.1) Crystallinity Polyphenylene sulfide resin is usually used with a crystallinity of 20% or more.
This is because the heat resistance is lowered when the crystallinity is less than 20%. In particular, in the use as a circuit board, if the crystallinity of the foam is low, deformation usually occurs in the step of immersing in a solder bath at about 260 ° C., making it unusable. Therefore, the crystallinity of the foam is preferably 20 to 40%.
On the other hand, the polyphenylene sulfide foam according to the present invention has a crystallinity of 0% or more and less than 20% before the secondary molding (see below). Improves formability.
The foam after the secondary molding obtained by using the polyphenylene sulfide foam of the present invention has a crystallinity of 20% or more due to the heat and stretch orientation during the secondary molding, and is the same as a normal polyphenylene sulfide foam. Furthermore, a polyphenylene sulfide foam having both heat resistance and the like is preferable.

(2.2) Foaming ratio The foaming ratio of the polyphenylene sulfide foam of the present invention is 2 times or more.
The reason why the expansion ratio is defined as 2 times or more is that weight reduction cannot be realized if the expansion ratio is less than 2 times. If the expansion ratio is less than 2 times, electrical characteristics and dielectric characteristics that are important particularly when used in electrical / electronic parts may be deteriorated.
Further, when the foaming ratio of the foam is 2 times or more, the dielectric constant ε is about 1.8 or less, and the polyphenylene sulfide foam can be put to practical use as a circuit board.
The expansion ratio is preferably 3 times or more.
Moreover, although an upper limit is not specifically limited, About 15 times which can be manufactured without a problem in particular is preferable.

(2.3) Average cell diameter With respect to the cell diameter of the foam, the average cell diameter of the cut surface is preferably 100 μm or less in terms of mechanical strength and appearance.
When the average bubble diameter exceeds 100 μm, not only the mechanical strength is lowered, but also the surface irregularities may be increased and the appearance may be deteriorated.
Furthermore, from the viewpoint of mechanical strength, the average cell diameter is preferably 20 μm or less.
The lower limit is not particularly limited, but about 1 μm is preferable as an average cell diameter that can be produced without any particular problem.

(3) Method for Producing Polyphenylene Sulfide Foam Although the method for producing the polyphenylene sulfide foam of the present invention is not particularly limited, for example, the following method is preferably used.

(3.1) Sheet Forming Step First, a polyphenylene sulfide resin is first formed into a sheet shape to produce a resin molded body having a crystallinity of less than 10%.
As the method, when extruding the resin, the temperature of the resin molded body (for example, a sheet) is rapidly cooled to Tg (about 80 ° C.) or less at the die outlet, and the resin is set to a mold set to a temperature of Tg or less. Examples include a method of injection and injection molding into a plate shape.
The reason why the degree of crystallinity of the resin molded body before foaming is defined as less than 10% is that the amount of gas penetration is insufficient in the step of infiltrating the gas that becomes bubbles when the degree of crystallinity exceeds 10% (see later). This is because the foam does not swell sufficiently.
In the sheet molding step, preferably, the cross-linking agent (B) is kneaded and dispersed in the polyphenylene sulfide resin (A) during the production of the resin molded body, and then strong shear is applied during T-die extrusion to promote the cross-linking agent dispersion. (Make it fine)

(3.2) Gas Infiltration Step and Foaming Step Next, a sheet-like resin molded body composed of the polyphenylene sulfide resin (A) (or a mixture of the polyphenylene sulfide resin (A) and the crosslinking agent (B)) is used as a separator. Are rolled to form a roll.
Thereafter, the roll is held in an atmosphere pressurized with an inert gas so that the sheet-like resin molded body contains (infiltrates) the inert gas, and then the pressure of the inert gas under the pressurized atmosphere is released. Then, the resin molded body containing the inert gas is heated and foamed under normal pressure and at 60 to 120 ° C. (60 ° C. or more and 120 ° C. or less).
The heating time at the time of heating and foaming is suitably about 60 seconds.
A polyphenylene sulfide foam can be manufactured by the process of the above process.

By the way, in a general crystalline resin, fine crystal nuclei are generated during the gas permeation process, and fine crystals are formed during the foaming process at a high temperature (over 120 ° C.). Thanks to the fine crystals (due to the formation of fine crystals), the bubbles generated during foaming become fine.
However, in order to realize fine crystallization, it is necessary to foam at a high temperature, but when the foaming temperature is high, the degree of crystallinity of the obtained foam becomes high.
Polyphenylene sulfide resin does not crystallize during gas permeation and does not generate bubble nuclei. For this reason, when the foaming temperature is low, crystallization does not occur during foaming, and the degree of crystallization is low, but a sheet-like resin molded body with coarsened bubbles is formed. If the bubbles become too coarse, the bubbles become cracks and are easily broken during the secondary molding step (see later).

Therefore, in the present invention, the crosslinking agent (B) is preferably added to the polyphenylene sulfide resin (A).
If the crosslinking agent (B) is added, even if the foaming temperature is low, the crosslinking agent is finely dispersed in the sheet-like resin molded article, so that the crosslinking agent (B) is a bubble even if crystallization does not occur. Hinder growth. Therefore, when the crosslinking agent (B) is added, a foam having fine bubbles having an average cell diameter of 10 μm or less and a crystallinity of less than 10% can be obtained.
In general, when the degree of crystallinity is high, the elongation during the secondary molding process is reduced, and as a result, cracking may occur and the secondary moldability may be reduced. On the other hand, if the cross-linking agent (B) is added, the foam obtained thereby has a low crystallinity and fine bubbles, so that it has excellent secondary moldability with a crystallinity of less than 10%. It becomes a foam.

(3.2.1) Inert Gas Examples of the inert gas that can be used in the gas permeation process include helium, nitrogen, oxygen, carbon dioxide, argon, hydrogen, methane, and chlorofluorocarbon gases.
In view of gas permeability (rate, solubility), the inert gas is preferably carbon dioxide.
For example, if the pressure is about 60 kg / cm ² , the pressure and time in the gas infiltration step are preferably 8 hours or longer.
The inert gas permeation time and the inert gas permeation amount until the resin molded body is saturated vary depending on the type of resin to be foamed, the type of inert gas, the permeation pressure, and the thickness of the sheet.
In addition, in this method, before the roll which consists of a sheet-like resin molded object and a separator is hold | maintained in the atmosphere pressurized with inert gas and the said resin molded object contains an inert gas, the resin molded object May be contained in an organic solvent.
Examples of the organic solvent include benzene, toluene, methyl ethyl ketone, ethyl formate, acetone, acetic acid, dioxane, m-cresol, aniline, acrylonitrile, dimethyl phthalate, nitroethane, nitromethane, and benzyl alcohol.
Among these, from the viewpoints of handleability and economy, the organic solvent is preferably acetone.

(3.3) Cooling Step The polyphenylene sulfide foam may be cooled at a predetermined temperature as necessary after the foaming step.

(3.4) Secondary molding step The polyphenylene sulfide foam is subjected to secondary molding.
In such a case, the type of secondary molding is not particularly limited, and examples thereof include drawing, press molding, vacuum forming, and pressure forming.
The shape and structure of the foam according to the present invention are not limited, and can be appropriately set according to the purpose of use.For example, various shapes such as a circular shape in plan view, an elliptical shape in plan view, and a rectangular shape in plan view, Secondary molding can be performed into a flat plate having a plurality of protrusions on the surface, a flat plate having a plurality of depressions on the surface, a corrugated plate, or the like.
Since the polyphenylene sulfide foam of the present invention has a crystallinity of less than 20% before secondary molding, it has good elongation and excellent secondary moldability.
Furthermore, in the polyphenylene sulfide foam of the present invention, since the bubble diameter is small, the bubbles do not cause cracking as in the case of coarse bubbles, and the secondary moldability is further improved.
When the secondary formability is improved, not only the degree of freedom of the shape is increased, but also the merit such as the degree of freedom of deep drawing is increased.

Next, the present invention will be described more specifically by way of examples.
The present invention is not limited to the following examples.

(1) Sample preparation (1.1) Example 1
2. A styrene oxazoline group-containing polymer (Epocross RPS-1005 manufactured by Nippon Shokubai Co., Ltd.) is added to 100 parts by mass of polyphenylene sulfide resin (PY10 manufactured by Toray) having a weight average molecular weight of 78,400 and a molecular weight distribution Mw / Mn4.0. In addition, 0 parts by mass was melt-kneaded with a same-direction twin screw extruder (Technovel KZW15-30MG) set at 215 to 295 ° C. Each component was adjusted so as to contain 150 ppm (based on mass) of the calcium component with respect to 100% by mass of the finally obtained foam.
Thereafter, the kneaded sheet was pushed out from a T-die having a width of 120 mm and taken up with a roll set at about room temperature to obtain a sheet serving as a mother board.
Then, the above-mentioned mother board sheet was allowed to stand in a pressure vessel, filled with carbon dioxide gas at a pressure of 5.5 MPa at a temperature of 17 ° C., and left for 48 hours.
After elapse of a predetermined time, the mother board sheet was taken out from the pressure vessel, and the mother board sheet was heated and foamed for 1 minute in a thermostatic bath set at a temperature of 80 ° C. to obtain a foam.
In addition, the weight average molecular weight Mw and the number average molecular weight Mn were calculated | required using the gel permeation chromatography (GPC) on the following conditions.
Device name: SSC-7100 (manufactured by Senshu Chemical)
Column name: GPC3506 (manufactured by Senshu Chemical)
Eluent: 1-chloronaphthalene Detector: Differential refractive index detector Column temperature: 210 ° C (detector temperature is also 210 ° C)
Flow rate: 1.0 (ml / min)

(1.2) Example 2
In the sample preparation of Example 1, the temperature of the thermostat was set to 60 ° C.
Except that, a sample was prepared in the same manner as in Example 1.
(1.3) Example 3
In the sample preparation of Example 1, the temperature of the thermostatic bath was set to 120 ° C.
Otherwise, a sample was prepared in the same manner as in Example 1.

(1.4) Reference example 4
In the sample preparation of Example 1, the styrene oxazoline group-containing polymer as a crosslinking agent was not added.
Other than that, samples were prepared in the same manner as in Example 1.
(1.5) Example 5
In sample preparation of Example 1, the addition amount of the styrene oxazoline group-containing polymer as a crosslinking agent was 1% (parts by mass).
Otherwise, a sample was prepared in the same manner as in Example 1.
(1.6) Example 6
In the sample preparation of Example 1, the addition amount of the styrene oxazoline group-containing polymer as a crosslinking agent was 10% (parts by mass).
Otherwise, a sample was prepared in the same manner as in Example 1.
(1.7) Reference Example 7
In the sample preparation of Example 1, the addition amount of the styrene oxazoline group-containing polymer as a crosslinking agent was 20% (parts by mass).
Otherwise, a sample was prepared in the same manner as in Example 1.

(1.8) Example 8
In the sample preparation of Example 1, the additive was changed to a modified polyethylene (BF, trade name: Bond First 7M grade, manufactured by Sumitomo Chemical Co., Ltd.) instead of the styrene-based oxazoline group-containing polymer.
Otherwise, a sample was prepared in the same manner as in Example 1.
(1.9) Example 9
In the sample preparation of Example 1, the additive was changed to modified polyethylene (BF, trade name: Bond First 7M grade, manufactured by Sumitomo Chemical Co., Ltd.) instead of the styrene-based oxazoline group-containing polymer, and the addition amount was 10%. (Parts by mass).
Otherwise, a sample was prepared in the same manner as in Example 1.

(1.10) Comparative Example 1
In the sample preparation of Example 1, the temperature of the thermostatic bath was set to 150 ° C.
Except that, a sample was prepared in the same manner as in Example 1.

(2) Evaluation of sample The following evaluation was performed about each sample of the Example , the reference example, and the comparative example.
Each test and its evaluation were performed by the following methods.

(2.1) Crystallinity The crystallinity of the foam was measured at a rate of temperature increase of 10 ° C./min using a differential scanning calorimeter, and was determined by the following formula based on the thermal analysis result.
Note that the foam to be measured in this process is a foam before secondary molding.
χc = {(ΔHm−ΔHc) / ΔH0} × 100
Where χc: crystallinity [%]
ΔHm: calorific value of crystal melting peak [J / g]
ΔHc: exothermic peak during crystal growth [J / g]
H0: calorific value of melting endothermic peak of 100% crystal (= 146.2 ^* ) [J / g]
(*) Maemura E. et al. , Polym. Eng. Sci. , 29 (2), 140 (1989)

(2.2) Foaming ratio The ratio ρs / ρf between the specific gravity (ρf) of the sheet-like foam measured by the underwater substitution method and the specific gravity (ρs) of the resin before foaming is calculated, and this is calculated as the foaming ratio. It was.

(2.3) Average bubble diameter It calculated | required according to ASTMD3576-77.
Specifically, a SEM photograph of a cross section of the sheet-like foam was taken, a straight line was drawn on the SEM photograph in the horizontal direction and the vertical direction, and the length t of the bubble chords that the straight line crossed was averaged.
Assuming that the magnification of the photograph is M, the average bubble diameter d was determined by substituting it into the following equation.
d = t / (0.616 × M)

(2.4) Secondary moldability After the foam is heated to a temperature at which it is softened using an infrared heater, it is press-molded using a circular mold, and a cup-shaped light reflecting molded body having a circular shape in plan view is obtained. Obtained.
Thereafter, the state (appearance) of the cup-shaped molded body was observed and evaluated according to the following criteria.
“◎”: Very good (the edge (ridgeline) from the bottom to the side of the cup is sharp and the cup is not cracked)
"Good": Good (the cup has no cracks, although the edge from the bottom to the side is slightly rounded)
“△”: No problem in practical use (the edge from the bottom to the side of the cup is rounded or wrinkled on the bottom of the cup)
“×”: defective (there is a crack on the bottom of the cup)

(3) Summary As shown in Table 1, the sample of Example 1 had a crystallinity after foaming of 10%, an expansion ratio of 2.5 times, and an average cell diameter of 3 μm. In the sample of Example 1, the foam after the secondary molding (secondary molded product) was free from cracks and the secondary moldability was very good. In the sample of Example 1, the degree of crystallinity of the secondary molded body was also 25%.
Even in the samples of Examples 2-3, 5-6, 8-9, and Reference Examples 4 and 7 , the crystallinity after foaming was less than 20%, and the secondary moldability was excellent.
On the other hand, in the sample of Comparative Example 1, the crystallinity after foaming was 22%, the crystallinity before secondary molding was high, the elongation was not excellent, the secondary moldability was inferior, and cracks occurred.
From the above, it can be seen that setting the crystallinity to less than 20% in the polyphenyl sulfide foam after foaming and before secondary molding is useful for improving secondary moldability.

Claims (6)

A polyphenylene sulfide foam composed of a polyphenylene sulfide resin having a repeating unit represented by the general formula (a) and having a crystallinity of less than 20% ,
A crosslinking agent is added to the polyphenylene sulfide resin,
The polyphenylene sulfide foam whose addition amount of the said crosslinking agent is 1.0-10 mass parts with respect to 100 mass parts of said polyphenylene sulfide resin.
-(Ar-S) -... (a)
[In the general formula (a), “Ar” represents an aryl group. ] In the polyphenylene sulfide foam according to claim 1,
A polyphenylene sulfide foam in which the crosslinking agent is a styrene-based oxazoline group-containing polymer or modified polyethylene. In the polyphenylene sulfide foam according to claim 1 or 2 ,
A polyphenylene sulfide foam having an expansion ratio of 2 times or more. In the polyphenylene sulfide foam according to any one of claims 1 to 3 ,
A polyphenylene sulfide foam having an average cell diameter of 20 μm or less. Adding 100 to 10 parts by mass of a crosslinking agent to 100 parts by mass of the polyphenylene sulfide resin having a repeating unit represented by the general formula (a);
A step of containing said polyphenylene sulfide resin of a mixture of the crosslinking agent, and held pressurized atmosphere by inert gas, the inert gas into the mixture,
Heating the mixture containing the inert gas under normal pressure and a temperature of 60 to 120 ° C. to foam;
A process for producing a polyphenylene sulfide foam comprising:
-(Ar-S) -... (a)
[In the general formula (a), “Ar” represents an aryl group. ] In the manufacturing method of the polyphenylene sulfide foam of Claim 5 ,
The manufacturing method of the polyphenylene sulfide foam whose said crosslinking agent is a styrene-type oxazoline group containing polymer or modified polyethylene.