JP7565181B2 - Expandable polyvinyl chloride resin particles, expanded particles thereof, and polyvinyl chloride resin foam molded article using the same - Google Patents

Description

The present invention relates to expandable polyvinyl chloride resin particles, expanded particles thereof, and polyvinyl chloride resin foam molded articles using the same.

Resin foam molded products (foams) are lightweight, insulating, and shock-absorbing, and have been widely used as insulation materials for houses and heat-retaining materials for pipes. Among them, styrene resin foam molded products obtained using expandable styrene resin particles containing a foaming agent have a high degree of freedom in shape and are widely used as insulation materials that can be applied to areas where simple foam shapes such as board shapes obtained by extrusion foaming methods are difficult to apply. Although styrene resin is a flammable resin, flame retardants are added to styrene resin foam molded products to ensure a certain degree of flame retardancy. However, due to recent fire accidents at construction sites and fires in high-rise apartment buildings, there is a growing demand for higher flame retardancy than before for insulation materials for construction.

Examples of foams with excellent flame retardant properties include resin foam molded products that use vinyl chloride resin or chlorinated vinyl chloride resin, both of which have excellent flame retardant properties, as the base resin.

For example, Patent Documents 1 and 2 describe foams obtained by in-mold expansion molding of pre-expanded chlorinated polyvinyl chloride resin particles that contain a solvent compatible with chlorinated polyvinyl chloride resin and a blowing agent.

JP 64-132 A JP2-182735A

The object of the present invention is to provide expandable polyvinyl chloride resin particles with excellent expansion efficiency that can produce polyvinyl chloride resin foamed molded articles with a high expansion ratio.

As a result of intensive research conducted by the inventors of the present application to solve the above-mentioned problems, they have succeeded in producing novel expandable polyvinyl chloride resin particles that can give polyvinyl chloride resin foamed molded articles with excellent light weight (high expansion ratio) by adding a specific amount of plasticizer to the expandable polyvinyl chloride resin particles, thereby completing the present invention.

That is, the present invention provides:
[1] Expandable polyvinyl chloride resin particles comprising a polyvinyl chloride resin, a plasticizer, and a foaming agent, the content of the plasticizer being 1 part by weight or more and less than 10 parts by weight per 100 parts by weight of the polyvinyl chloride resin.
[2] The expandable polyvinyl chloride resin particles according to the above [1], wherein the plasticizer comprises at least one selected from the group consisting of a phthalic acid plasticizer, a phosphoric acid plasticizer, a trimellitic acid plasticizer, and an epoxy plasticizer.
[3] The expandable polyvinyl chloride resin particles according to the above [1] or [2], wherein the polyvinyl chloride resin contains a chlorinated polyvinyl chloride resin, and the chlorine content of the chlorinated polyvinyl chloride resin is 60% by weight or more and 75% by weight or less.
[4] The expandable polyvinyl chloride resin particles according to any one of [1] to [3] above, wherein the polyvinyl chloride resin comprises a chlorinated polyvinyl chloride resin, and the average polymerization degree of the chlorinated polyvinyl chloride resin is 400 or more and 1,500 or less.
[5] The expandable vinyl chloride resin particles according to any one of the above [1] to [4], which contain a physical foaming agent.
[6] The expandable polyvinyl chloride resin particles according to the above [5], wherein the physical foaming agent contains a saturated hydrocarbon having 4 to 6 carbon atoms.
[7] The expandable polyvinyl chloride resin particles according to the above [5] or [6], wherein the physical foaming agent contains a ketone.
[8] Expanded polyvinyl chloride resin particles obtained by pre-expanding the expandable polyvinyl chloride resin particles according to any one of [1] to [7] above.
[9] A polyvinyl chloride resin foamed article obtained by foaming the polyvinyl chloride resin foam particles according to [8] above.

The expandable vinyl chloride resin particles of the present invention, which have excellent expansion efficiency, can produce vinyl chloride resin foamed molded articles with a high expansion ratio.

Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more and B or less." Also, "A and/or B" means "A, B, and A and B."

(Expandable polyvinyl chloride resin particles)
The inventions described in the above Patent Documents 1 and 2 propose foamed molded articles that are excellent in flame retardancy and have a degree of freedom in shape by using a chlorinated polyvinyl chloride resin, which has better flame retardancy than polyvinyl chloride resin, as a base resin. However, in order to obtain the foamed molded article, many steps are required, resulting in poor productivity, and the method also requires the use of a large amount of solvent and a blowing agent with a high global warming potential, resulting in a manufacturing method that has a very large environmental load and is also problematic in terms of cost. Furthermore, although the details of the foaming efficiency of the obtained foam are not disclosed, it is about 0.6 to 1.9, and there is a problem in further improving the foaming efficiency.

As such, there is a strong need to improve the environmental compatibility and cost of the above foam molded products, so there is a need to provide new foam molded products that are lightweight and have shape-imparting properties while still taking advantage of the flame retardant properties of polyvinyl chloride resins and the like.

As a result of extensive research, the inventors discovered that the foaming efficiency of expandable polyvinyl chloride resin particles can be improved by adding a specific amount of plasticizer, which led to the successful development of the present invention.

That is, the expandable vinyl chloride resin particles of the present invention are characterized by containing 1 part by weight or more and less than 10 parts by weight of a plasticizer per 100 parts by weight of vinyl chloride resin. The expandable vinyl chloride resin particles of the present invention have excellent expansion efficiency, so that vinyl chloride resin foamed molded articles with a high expansion ratio can be obtained.

It is known that vinyl chloride resins maintain a very high viscosity due to dipole interactions even when the temperature is higher than the glass transition temperature. The viscosity at this time acts as a force resisting the foaming force during foaming. In order to increase the foaming efficiency and achieve a high foaming ratio, it is necessary to control this dipole interaction and make the vinyl chloride resin composition containing a foaming agent have a viscosity suitable for foaming. The present inventors have conducted extensive research and found that by adding 1 part by weight or more and less than 10 parts by weight of a plasticizer to 100 parts by weight of vinyl chloride resin in vinyl chloride resin particles containing a foaming agent, it is possible to make the vinyl chloride resin containing the foaming agent have a viscosity suitable for foaming, and a vinyl chloride resin foam with excellent foaming efficiency can be obtained.

The amount of plasticizer added is preferably 2 to 9.5 parts by weight, and more preferably 3 to 9 parts by weight. By setting the amount of plasticizer added within this range, the resistance of the resin viscosity during foaming can be reduced, resulting in high foaming efficiency, and by preventing the resin viscosity from dropping too low, it is possible to prevent the bubble film from breaking even when the bubble film becomes thin due to high-fold foaming, making high-fold foaming possible. If the resin viscosity drops too low, the bubble film will break during the foaming process, and the foaming agent will volatilize, causing the problem of not achieving the desired foaming ratio.

The plasticizer used in the present invention may be any known plasticizer, and is not particularly limited, but examples thereof include the following plasticizers. For example, phthalic acid plasticizers such as bis(2-ethylhexyl)phthalate (DOP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), and bis(2-ethylhexyl) terephthalate, adipic acid plasticizers, phosphoric acid plasticizers such as trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), tricresyl phosphate (TCP), and triphenyl phosphate, trimellitic acid plasticizers such as tris(2-ethylhexyl) trimellitate (TOTM), epoxy plasticizers such as epoxidized soybean oil, polyester plasticizers such as adipic acid polyester, fatty acid plasticizers, and compounds that have a plasticizing effect on vinyl chloride resins, such as chlorinated paraffin, may be used. These plasticizers may be used alone or in combination of two or more.

In one embodiment of the present invention, from the viewpoint of the gelling property of the vinyl chloride resin, the plasticizer is preferably a phthalic acid plasticizer, a phosphoric acid plasticizer, a trimellitic acid plasticizer, or an epoxy plasticizer, and more preferably a phthalic acid plasticizer or a phosphoric acid plasticizer. By using a plasticizer that has good gelling property of the vinyl chloride resin, the retention of the blowing agent tends to be improved, and a foam with a high expansion ratio tends to be easily obtained.

In one embodiment of the present invention, the plasticizer preferably contains an ester group. By containing an ester group, compatibility with vinyl chloride resins becomes good, and it tends to be easy to achieve a viscosity suitable for foaming. In addition, it is preferable that the boiling point is 210°C or higher. By having a boiling point of 210°C or higher, it remains in the resin without volatilizing even at the foaming temperature, making it possible to maintain a viscosity suitable for foaming during foaming. Furthermore, the ester group equivalent is preferably 97 or higher. By having an ester group equivalent of 97 or higher, affinity with the foaming agent becomes good, and it tends to be easy to achieve a high foaming rate.

The expandable polyvinyl chloride resin particles of the present invention have excellent expansion efficiency. In one embodiment of the present invention, the maximum expansion ratio (times)/volatile content during expansion (weight %) of the expandable polyvinyl chloride resin particles is preferably 2.0 or more, more preferably 2.3 or more, and even more preferably 2.6 or more. If the maximum expansion ratio (times)/volatile content during expansion (weight %) is within the above range, high expansion is possible with a small amount of foaming agent, and the expansion efficiency is excellent. The maximum expansion ratio here is the highest expansion ratio when the expansion evaluation is performed in a heated air atmosphere, and the volatile content during expansion is the weight change rate when the expandable polyvinyl chloride resin particles used in the expansion evaluation in a heated air atmosphere are heated at 150°C for 30 minutes, and can be determined specifically by the measurement method described below. Note that the volatile content in the expandable polyvinyl chloride resin particles changes over time, so the maximum expansion ratio and the volatile content during expansion are values measured on the same day.

(Vinyl chloride resin)
The expandable vinyl chloride resin particles of the present invention contain a vinyl chloride resin as a resin component, and any known vinyl chloride resin can be used. For example, polyvinyl chloride (vinyl chloride homopolymer); vinyl chloride-vinyl acetate copolymer, vinyl chloride-(meth)acrylic acid copolymer, vinyl chloride-methyl (meth)acrylate copolymer, vinyl chloride-ethyl (meth)acrylate copolymer, vinyl chloride-maleic acid ester copolymer, vinyl chloride-ethylene copolymer, vinyl chloride-propylene copolymer, vinyl chloride-styrene copolymer, vinyl chloride-isobutylene copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-styrene-maleic anhydride terpolymer, vinyl chloride-styrene-acrylonitrile terpolymer, vinyl chloride-butadiene copolymer, vinyl chloride-isoprene copolymer, vinyl chloride-chlorinated propylene copolymer, vinyl chloride-vinylidene chloride-vinyl acetate terpolymer, vinyl chloride-acrylonitrile copolymer, vinyl chloride-various vinyl ether copolymer, vinyl chloride copolymers of vinyl chloride and other monomers copolymerizable with vinyl chloride; post-chlorinated vinyl polymer, post-chlorinated polyvinyl chloride, post-chlorinated vinyl chloride copolymer, post-chlorinated chlorinated olefin, and the like vinyl polymers modified (chlorinated, etc.) can be mentioned. Furthermore, chlorinated polyolefins having a chemical structure similar to that of polyvinyl chloride, such as chlorinated polyethylenes having a chlorination degree of 40% by weight or more, may be included. As the vinyl chloride resin, one or a mixture of two or more of these may be used. In this specification, the term "vinyl chloride polymer" refers to polyvinyl chloride and/or vinyl chloride copolymer.

Chlorinated vinyl chloride polymers (hereinafter sometimes referred to as chlorinated vinyl chloride resins) are usually produced by using vinyl chloride polymers as raw materials, supplying chlorine to the vinyl chloride polymers dispersed in an aqueous medium, and chlorinating the polymers in an aqueous medium by irradiating them with a mercury lamp for photo-chlorination or by heating for chlorination, or by chlorinating vinyl chloride polymers in an air space by irradiating them with a mercury lamp.

The average degree of polymerization of the vinyl chloride resin is not particularly limited, but the lower limit is preferably 300 or more, and more preferably 400 or more. On the other hand, the upper limit is preferably 3000 or less, and more preferably 1500 or less. If the average degree of polymerization is within the above range, a high expansion ratio tends to be obtained. The average degree of polymerization of the chlorinated vinyl chloride resin is regarded as the average degree of polymerization of the vinyl chloride resin before chlorination. The average degree of polymerization is measured in accordance with JIS K6720-2.

The weight average molecular weight of the chlorinated polyvinyl chloride resin is not particularly limited, but is preferably in the range of 30,000 to 400,000. If the weight average molecular weight is in this range, a high expansion ratio tends to be obtained. The weight average molecular weight is evaluated in terms of polystyrene by gel permeation chromatography.

From the viewpoint of ensuring foamability, the chlorine content of the chlorinated polyvinyl chloride resin is preferably in the range of 60% by weight to 75% by weight. More preferably, it is 64% by weight to 70% by weight. The higher the chlorine content, the higher the foaming ratio tends to be, but if the chlorine content is too high, the melt viscosity increases and the processability tends to be significantly impaired. The chlorine content of polyvinyl chloride resins, including chlorinated polyvinyl chloride resins, is measured in accordance with JIS K7385 B method.

As one embodiment of the present invention, a single type of chlorinated polyvinyl chloride resin with the same properties may be used, or two or more types with different properties may be used in combination.

In one embodiment of the present invention, from the viewpoint of foaming property and flame retardancy, it is preferable that the vinyl chloride resin contains a chlorinated vinyl chloride polymer, and more preferably contains mainly a chlorinated vinyl chloride polymer. Although not particularly limited, it is preferable that the chlorinated vinyl chloride polymer is contained in 100% by weight of the vinyl chloride resin, more preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and most preferably 80% by weight or more. On the other hand, the upper limit is preferably 100% by weight of the chlorinated vinyl chloride polymer in 100% by weight of the vinyl chloride resin.

(Foaming Agent)
The blowing agent contained in the expandable vinyl chloride resin particles of the present invention may be any known blowing agent, and is not particularly limited, but examples thereof include the following blowing agents: hydrocarbons such as normal butane, isobutane, normal pentane, isopentane, neopentane, cyclopentane, normal hexane, and cyclohexane; ethers such as dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, furfural, 2-methylfuran, tetrahydrofuran, and tetrahydropyran; ketones such as dimethyl ketone (acetone), methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl i-butyl ketone, methyl n-hexyl ketone, ethyl n-propyl ketone, and ethyl n-butyl ketone; saturated alcohols having 1 to 4 carbon atoms such as methanol, ethanol, propyl alcohol, i-propyl alcohol, butyl alcohol, i-butyl alcohol, and t-butyl alcohol; methyl formate, ethyl formate Examples of the foaming agents that can be used include carboxylic acid esters such as ter, propyl formate, butyl formate, amyl formate, methyl propionate, and ethyl propionate; alkyl halides such as methyl chloride and ethyl chloride; hydrofluoroolefins or chlorinated hydrofluoroolefins such as trans-1,3,3,3-tetrafluoropropene (trans-HFO-1234e), cis-1,3,3,3-tetrafluoropropene (cis-HFO-1234ze), 2,3,3,3-tetrafluoropropene (trans-HFO-1234yf), trans-1-chloro-3,3,3-trifluoropropene (trans-HCFO-1233zd), and cis-1-chloro-3,3,3-trifluoropropene (cis-HCFO-1233zd); physical foaming agents such as inorganic foaming agents such as water, carbon dioxide, and nitrogen; and chemical foaming agents such as azo compounds and tetrazole. These other foaming agents may be used alone or in combination of two or more.

In one embodiment of the present invention, a physical foaming agent is preferably contained as the foaming agent because it is easy to achieve a high foaming ratio, and a hydrocarbon is more preferable, and among them, a saturated hydrocarbon having 4 to 6 carbon atoms (4, 5, and 6 carbon atoms) is more preferable. If the foaming agent has 4 or more carbon atoms, the volatility is low and the foaming agent is less likely to escape from the expandable vinyl chloride resin particles, so that when actually used, a sufficient amount of foaming agent remains in the foaming process, making it possible to obtain sufficient foaming power and facilitating high foaming ratios, which is preferable. In addition, if the foaming agent has 6 or less carbon atoms, the boiling point of the foaming agent is not too high, so it is easy to obtain sufficient foaming power by heating during pre-foaming, and there is a tendency for high foaming to be easy. Examples of saturated hydrocarbons having 4 to 6 carbon atoms include normal butane, isobutane, normal pentane, isopentane, neopentane, cyclopentane, normal hexane, and cyclohexane. From the viewpoint of the solubility and retention of the foaming agent in the resin, it is preferable that at least pentane is contained as a saturated hydrocarbon having 4 to 6 carbon atoms.

As one embodiment of the present invention, it is preferable that a ketone is included as a foaming agent from the viewpoint of improving the solubility of the foaming agent. In particular, it is preferable that it is used in combination with a hydrocarbon. For example, by using a saturated hydrocarbon having 4 to 6 carbon atoms in combination with a ketone, the solubility of the saturated hydrocarbon having 4 to 6 carbon atoms in the resin can be further improved.

In one embodiment of the present invention, the content of the foaming agent is preferably 1 to 40% by weight based on 100% by weight of the expandable polyvinyl chloride resin particles. By controlling the content of the foaming agent within the above-mentioned range, it is possible to easily obtain foamed particles with a high expansion ratio and foamed molded products with excellent surface beauty. A more preferred range is 3 to 25% by weight, and even more preferably 5 to 20% by weight.

(Processing aids)
As a preferred embodiment of the present invention, a processing aid may be contained. The processing aid may be any processing aid commonly used for vinyl chloride resins, and may include, for example, a copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units, such as a styrene-acrylonitrile copolymer, an impact resistance improver such as a methyl methacrylate-butadiene-styrene polymer, and chlorinated polyethylene. In order to easily obtain expanded particles and foamed molded articles with a high expansion ratio, it is preferable to contain at least one selected from the group consisting of a copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units, an acrylic resin, and a chlorinated polyethylene. Among them, from the viewpoint of improving the fluidity of the chlorinated vinyl chloride resin and improving the molding processability, it is more preferable to use a copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units and/or an acrylic resin in combination with chlorinated polyethylene.

In one embodiment of the present invention, a copolymer having structural units of an aromatic vinyl monomer and an unsaturated nitrile monomer is used in a vinyl chloride resin, which is excellent in the effect of easily obtaining foamed particles and foamed molded articles with high expansion ratios during pre-expansion and foam molding under steam heating conditions.

The aromatic vinyl monomer of the copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units includes styrene derivatives such as styrene, α-methylstyrene, ethylstyrene, and halogenated styrene. The unsaturated nitrile monomer includes acrylonitrile, methacrylonitrile, etc.

As long as the effect of the present invention is not impaired, the copolymer having structural units of an aromatic vinyl monomer and an unsaturated nitrile monomer may have structural units derived from monomers other than the aromatic vinyl monomer and the unsaturated nitrile monomer (other copolymerizable monomers). Examples of other copolymerizable monomers include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, N-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, (meth)acrylic acid, maleic anhydride, and N-substituted maleimide.

The preferred range of the unsaturated nitrile monomer in the copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units is 5 to 45% by weight, more preferably 8 to 35% by weight, and even more preferably 10 to 30% by weight, based on 100% by weight of the entire copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units. By being in this range, it is easy to obtain expanded beads and expanded molded products with a high expansion ratio.

A preferred example of a copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units is a styrene-acrylonitrile copolymer. The copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units may be used alone or in combination of two or more. In a preferred embodiment, a styrene-acrylonitrile copolymer is used as at least one of the copolymers having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units. It is preferable to use a copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units whose weight average molecular weight is higher than the weight average molecular weight of the vinyl chloride resin used, since it is easy to ensure a high expansion ratio. The weight average molecular weight of the copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units is evaluated in terms of polystyrene molecular weight by gel permeation chromatography. As a copolymer having an aromatic vinyl monomer and an unsaturated nitrile monomer as structural units, for example, Blendex 869 manufactured by Galata can be used.

Specific examples of acrylic resins include polymethyl methacrylate obtained by polymerizing methyl methacrylate, methacrylic acid alkyl esters having 2 to 8 carbon atoms in the alkyl group such as n-butyl methacrylate, acrylic acid alkyl esters having 1 to 8 carbon atoms in the alkyl group such as ethyl acrylate, and copolymers of at least one monomer copolymerizable with these, such as butylene, substituted styrene, and acrylonitrile. It is preferable to use an acrylic resin whose weight average molecular weight is higher than that of the vinyl chloride resin used, since this makes it easier to ensure a high expansion ratio. The weight average molecular weight of the acrylic resin is evaluated in terms of polystyrene molecular weight by gel permeation chromatography. For example, Kane Ace PA-40 manufactured by Kaneka can be used as the acrylic resin.

The chlorinated polyethylene may be any known chlorinated polyethylene used in polyvinyl chloride resins. The chlorine content of the chlorinated polyethylene is not limited to any particular range, but is measured in accordance with JIS K7385 B method.

The content of the processing aid is not particularly limited as long as it is within a range that does not impair the effects of the present invention, but is preferably 1 to 50 parts by weight, more preferably 5 to 50 parts by weight, and even more preferably 8 to 30 parts by weight, per 100 parts by weight of the vinyl chloride resin. If the content is 1 part by weight or more, it becomes easier to obtain expanded beads and/or expanded molded products with a high expansion ratio, and if it is 50 parts by weight or less, it becomes possible to obtain expanded beads and/or expanded molded products with excellent flame retardant performance.

(Other additives)
As long as the effects of the present invention are not impaired, the composition may contain, as necessary, flame retardants, stabilizers, lubricants, nucleating agents, foaming assistants, antistatic agents, radiation heat transfer inhibitors, solvents, and colorants such as pigments and dyes.

As the flame retardant, known flame retardants can be used, for example, bromine-based flame retardants, phosphorus-based flame retardants, boron-based flame retardants, intumescent flame retardants such as ammonium polyphosphate and melamine cyanurate, hydroxide compounds such as aluminum hydroxide and magnesium hydroxide, and flame retardant assistants such as antimony oxide, zinc oxide, and zinc borate.

As the stabilizer, those conventionally used for polyvinyl chloride resins can be used. Examples include tin-based stabilizers, antioxidants such as phenolic compounds, phosphorus-based compounds, and amine-based compounds, epoxy-based stabilizers, and zeolites. The amount of each stabilizer used is not particularly limited as long as it does not impair the effects of the present invention, but it is preferable that the amount is 10 parts by weight or less per 100 parts by weight of the polyvinyl chloride resin.

Examples of lubricants include waxes such as ester wax and polyethylene wax, and fatty acid metal salts such as calcium stearate and zinc stearate.

Nucleating agents include inorganic compounds such as silica, calcium silicate, wollastonite, kaolin, clay, mica, zinc oxide, calcium carbonate, sodium bicarbonate, zeolite, or talc.

Radiation heat transfer inhibitors include substances that have the property of reflecting, scattering, or absorbing light in the near-infrared or infrared region, such as graphite, graphene, carbon black, expanded graphite, titanium oxide, and aluminum.

Other resins (thermoplastic resins and thermosetting resins) may be used in combination with vinyl chloride resins as long as the effects of the present invention are not impaired. When using other resins in combination, the amount of the other resins is not particularly limited as long as the effects of the present invention are not impaired, but 0 to 99 parts by weight per 100 parts by weight of vinyl chloride resin is preferred.

The shape of the expandable polyvinyl chloride resin particles of the present invention is not particularly important as long as the particles have a shape that allows the expandable resin particles to be pre-expanded and expanded as described below, but this includes not only general granular objects (for example, small rounded particles such as spherical, approximately spherical, convex lens-like, concave lens-like, and spindle-like), but also particles with indentations. The particle weight of the expandable polyvinyl chloride resin particles of the present invention is preferably 0.5 to 10 mg/particle, more preferably 1 to 8 mg/particle, and even more preferably 2.5 to 7 mg/particle, from the viewpoint of ensuring the fillability of the expanded particles into a molding die and thus the moldability such as the surface beauty of the expanded molded product.

From the viewpoint of reducing the rate at which the foaming agent escapes from the foamable vinyl chloride resin particles of the present invention or further improving the expansion ratio, the true density of the foamable vinyl chloride resin particles of the present invention is preferably 1100 kg/m ³ or more, more preferably 1150 kg/m ³ or more, even more preferably 1200 kg/m ³ or more, and particularly preferably 1250 kg/m ³ or more. The true density here can be determined by the measurement method described below.

(Method for producing expandable polyvinyl chloride resin particles)
The expandable vinyl chloride resin particles of the present invention can be obtained by a known production method, for example, the following two production methods.

The first method for producing expandable polyvinyl chloride resin particles (hereinafter sometimes referred to as the "first production method") involves heating, melting and mixing polyvinyl chloride resin, a plasticizer, and, if necessary, other additives in a known kneading machine such as an extruder, a roll processing machine, or a Banbury mixer, followed by granulation, and impregnating the resulting polyvinyl chloride resin particles with a blowing agent in an autoclave to obtain expandable polyvinyl chloride resin particles.

The second method for producing expandable polyvinyl chloride resin particles (hereinafter sometimes referred to as the "second production method") involves feeding polyvinyl chloride resin, a plasticizer, and optionally other additives to an extruder and melt-kneading them, dissolving and dispersing the foaming agent in the molten mixture using the extruder or a dispersing device downstream of the extruder, extruding the molten mixture of the foaming agent-containing polyvinyl chloride resin composition through a die with many small holes attached downstream of the extruder into a cutter chamber filled with pressurized circulating water, and immediately after extrusion, cutting the molten mixture with a rotating cutter in contact with the die and cooling and solidifying it with pressurized circulating water to obtain expandable polyvinyl chloride resin particles.

In both the first and second manufacturing methods, it is preferable to gel the vinyl chloride resin sufficiently. If gelation is not sufficient, when the resin is made into expandable resin particles, the rate at which the blowing agent escapes from the resin particles may increase, and the blowing agent may tend not to contribute to expansion. As a result, it may be difficult to obtain expanded particles and foamed molded articles with a high expansion ratio or a high closed cell ratio.

In the first and second manufacturing methods, the resin temperature during melt kneading (mixing) of the vinyl chloride resin, etc. is preferably 150°C or higher and lower than 250°C, and more preferably 160°C or higher and lower than 240°C, since this may affect the decomposition of the vinyl chloride resin and additives. If the resin temperature exceeds 250°C, there is a risk of decomposition of the vinyl chloride resin and additives, which may result in deterioration of the expandable vinyl chloride resin particles and lead to a decrease in the expandability.

(Conditions of granulation process)
The conditions for the granulation step of the (expandable) vinyl chloride resin particles in the first and second production methods will be described below.

In the first manufacturing method, an embodiment in which a sheet-shaped molten kneaded product is obtained using a roll processing machine or the like can be given, in which the obtained sheet is cooled and then granulated into sheet-shaped vinyl chloride resin particles using cutting equipment such as a cutter or shredder. The thickness of the sheet-shaped vinyl chloride resin particles can be adjusted by adjusting the clearance of the roll processing machine, which is the kneading equipment, or by further pressing the obtained sheet.

In the second manufacturing method, the temperature of the molten resin immediately before being extruded from the die is preferably Tg+20°C or higher, more preferably Tg+30°C to Tg+110°C, and even more preferably Tg+40°C to Tg+90°C, where Tg is the glass transition temperature of the resin (resin after blending in the case of a blend of multiple resins) without the foaming agent. Note that, for vinyl chloride resins, the glass transition temperature increases with an increase in the chlorine content, so it is preferable to adjust the temperature appropriately according to the chlorine content of the vinyl chloride resin used. If the temperature is Tg+20°C or higher, the viscosity of the extruded molten resin is low, small pore clogging is unlikely to occur, and there is no decrease in the actual small pore opening rate, so that it is possible to avoid a situation in which the shape of the resulting expandable vinyl chloride resin particles becomes distorted or irregular. On the other hand, if the temperature is Tg+110°C or lower, the extruded molten resin is easily solidified and is less likely to wrap around the rotary cutter, allowing for stable cutting.

The die used in the second manufacturing method preferably has many small holes with a diameter of 0.3 mm to 2.0 mm, more preferably 0.4 mm to 1.5 mm.

The cutting device for cutting the molten resin extruded into the circulating pressurized cooling water in the second manufacturing method is not particularly limited, but examples include a device in which the resin is cut into small pellets by a rotating cutter that comes into contact with a die, and then transported to a centrifugal dehydrator to be dehydrated and aggregated without foaming in the circulating pressurized cooling water.

The conditions of the pressurized circulating cooling water should be adjusted according to the resin, additives, foaming agent, and content used, but it is preferable that the foaming of the molten resin extruded from the die is suppressed and the resin is stably cut by the cutter. Specifically, the temperature condition of the pressurized circulating cooling water is preferably 40°C to 99°C, more preferably 60°C to 90°C. As for the pressure condition, it is preferable to adjust the pressure so that the expansion ratio of the obtained expandable polyvinyl chloride resin particles is 1.0 to 1.25 times. The expansion ratio of the expandable polyvinyl chloride resin particles refers to the value obtained by dividing the true density (kg/m3) of the base resin by the true density (kg/m3) of the expandable polyvinyl chloride resin particles. The true density of the base resin and the expandable polyvinyl chloride resin particles referred to here is calculated by immersing a weight W (kg) of polyvinyl chloride resin pellets or expandable polyvinyl chloride resin particles in a measuring cylinder containing ethanol, and determining the volume V (m3) from the rise in the liquid level of the measuring cylinder (submersion method). Specifically, it can be determined by the measurement method described below.

Although it depends on the type of foaming agent used, the pressure conditions are preferably 0.6 to 2.0 MPa, more preferably 0.7 to 1.7 MPa, and even more preferably 0.8 to 1.5 MPa.

The conditions for impregnation of the foaming agent in the first manufacturing method may be the same as those generally used and may be set appropriately.

(Polyvinyl chloride resin foam particles and their manufacturing method)
The expandable polyvinyl chloride resin particles of the present invention can be used for a foamed molded article after being pre-expanded 2 to 110 times by a heating medium such as heated air or steam to form expanded polyvinyl chloride resin particles. The steam that can be used may be saturated steam or superheated steam.

The heating temperature during foaming should be adjusted appropriately depending on the glass transition temperature and melting point of the resin, as well as the amount of foaming agent, but is preferably 90°C or higher, and more preferably 100°C or higher. On the other hand, from the viewpoint of suppressing the variation in the expansion ratio between the foamed beads and preventing the shrinkage of the foamed beads, it is preferably 150°C or lower, and more preferably 130°C or lower.

(Polyvinyl chloride resin foam molded product and its manufacturing method)
The obtained polyvinyl chloride resin foamed particles are molded (e.g., molded in a mold) using a conventional molding machine, for example, with steam to produce a polyvinyl chloride resin foamed molded article. Depending on the shape of the mold used, a molded article with a complex shape or a block-like molded article can be obtained.

The vinyl chloride resin foam particles and vinyl chloride resin foam molded products thereof of the present invention preferably have an average cell diameter of 70 to 1000 μm, more preferably 90 to 800 μm, and even more preferably 100 to 600 μm. By having an average cell diameter within the above range, a vinyl chloride resin foam molded product with higher thermal insulation properties is obtained. If the average cell diameter is 70 μm or more, it tends to be easier to increase the expansion ratio, and if it is 1000 μm or less, an increase in thermal conductivity, i.e., a deterioration in thermal insulation performance, can be avoided.

The vinyl chloride resin foamed beads and vinyl chloride resin foamed molded articles thereof of the present invention preferably have a closed cell ratio of 70% or more, more preferably 80% or more, and even more preferably 90% or more. When the closed cell ratio is within the above-mentioned range, the foamed beads are more likely to undergo secondary expansion during molding, improving the moldability of the foamed beads and improving the surface properties of the resulting foamed molded article. In addition, when the closed cell ratio is within the above-mentioned range, the strength of the foamed molded article, such as the compressive strength, tends to be increased.

(Applications of foamed molded products)
The foamed molded article formed using the expandable polyvinyl chloride resin particles of the present invention has a high expansion ratio and a high closed cell ratio, and is excellent in flame retardancy. Therefore, it is suitable for reducing the weight of products and components that require flame retardancy and fire resistance. For example, it is suitable for various applications such as building insulation materials, ceiling materials, core materials for metal sandwich panels, food container boxes, cold storage boxes, cushioning materials, agricultural and fishery boxes, bathroom insulation materials, and hot water tank insulation materials.

One embodiment of the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. An embodiment obtained by appropriately combining the technical means disclosed in different embodiments is also included in the technical scope of one embodiment of the present invention.

Below, an embodiment of the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to these.

The measurement and evaluation methods used in the following examples and comparative examples are as follows:

<Measurement of the amount of blowing agent (volatile matter) contained in expandable polyvinyl chloride resin particles>
The weight W ₁ (g) of the expandable polyvinyl chloride resin particles was measured, heated in an oven at 150° C. for 30 minutes, then cooled at room temperature in a desiccator for 30 minutes, and the weight W ₂ (g) was measured again. The weight difference (W ₁ -W ₂ ) before and after heating was taken as the foaming agent content in the expandable polyvinyl chloride resin particles. In this specification, this foaming agent content may be referred to as the volatile content. The volatile content was calculated using the following formula:
Volatile content (wt%)=(W ₁ −W ₂ )/W ₁ ×100
The value (volatile content) measured under the above conditions during foaming evaluation in a heated air atmosphere (on the same day as foaming evaluation) and calculated based on the above formula is referred to as the volatile content during foaming (wt %).

<Measurement of particle weight of expandable polyvinyl chloride resin particles>
Using an electronic balance capable of measuring to the nearest 0.01 mg, the weight of 100 randomly sampled expandable polyvinyl chloride resin particles was measured, and the particle weight was calculated using the following formula.
Particle weight (mg) = [Weight of 100 particles (mg)]/100

<Measurement of true density of expandable polyvinyl chloride resin particles>
The expandable polyvinyl chloride resin particles having a weight W (kg) were submerged in a measuring cylinder containing ethanol, and the volume V (m ³ ) was obtained from the rise in the liquid level of the measuring cylinder (submersion method) and calculated using the following formula.
True density of expandable polyvinyl chloride resin particles (kg/m ³ )=(W/V)

<Measurement of true density of polyvinyl chloride resin pellets (base resin)>
After blending vinyl chloride resin with auxiliary materials such as processing aids, stabilizers, and lubricants to obtain a uniform mixture, the mixture was melt-kneaded in an extruder, and the weight W (kg) of the obtained vinyl chloride resin pellets was submerged in a measuring cylinder containing ethanol, and the volume V ( ^m3 ) was calculated from the rise in the liquid level in the measuring cylinder (submersion method) and calculated using the following formula.
True density of polyvinyl chloride resin pellets (kg/m ³ )=(W/V)
The true density of the vinyl chloride resin pellets prepared in the Examples and Comparative Examples based on the above-mentioned method was 1,430 kg/ ^m3 , and this value was taken as the density of the base resin used in the Examples and Comparative Examples.

<Measurement of expansion ratio of polyvinyl chloride resin expanded beads>
A polyvinyl chloride resin foamed particle having a weight W (kg) was submerged in a measuring cylinder containing ethanol, and the volume V ( ^m3 ) was obtained from the rise in the liquid level of the measuring cylinder (submersion method), and calculated using the following formula: The density of the base resin, 1430 kg/ ^m3, was used from the above-mentioned <Measurement of true density of polyvinyl chloride resin pellets (base resin)>.
Expansion ratio of polyvinyl chloride resin foam particles (times) = 1430 / (W / V)

<Measurement of bulk magnification of polyvinyl chloride resin foam beads>
The polyvinyl chloride resin foamed particles were filled into a container having an internal volume of 3250 cc, and the weight W (g) was measured and calculated using the following formula: The density of the base resin was 1.43 g/cc, as determined in the above-mentioned <Measurement of true density of polyvinyl chloride resin pellets (base resin)>.
Bulk magnification of polyvinyl chloride resin foamed particles (times) = 1.43 / (W / 3250)

<Evaluation of foaming under heated air atmosphere>
The expandable polyvinyl chloride resin particles were placed in an oven (forced convection constant temperature dryer SOFW-600, manufactured by AS ONE CORPORATION) heated to 130°C, and expanded under a heated air atmosphere at a temperature of 130°C while changing the heating time, to obtain expanded beads for each heating time. The heating time was changed at 30-second intervals, such as 30 seconds, 60 seconds, and 90 seconds after placing in the oven, and the particles were heated until shrinkage of the expanded beads due to overheating (decrease in the expanded bead magnification) or non-uniform expansion such as the formation of large cavities inside the expanded beads was confirmed. The maximum heating time was 30 minutes. The expansion ratio of the expanded beads obtained for each heating time was measured based on the above-mentioned <Expansion ratio measurement of polyvinyl chloride resin expanded beads>, and the highest expansion ratio in a state where no large cavities were generated inside was determined as the maximum expansion ratio of the polyvinyl chloride resin expanded beads. As described above in the section <Measurement of the amount of blowing agent (volatile content) contained in expandable polyvinyl chloride resin particles>, the volatile content was measured on the same day as the foaming evaluation in a heated air atmosphere, and this was recorded as the volatile content during foaming (% by weight).
Using the values measured here, the ratio of the maximum expansion ratio to the volatile matter during expansion (wt %) (maximum expansion ratio/volatile matter during expansion (wt %)) was calculated as the maximum expansion efficiency.

<Evaluation of foaming under water vapor atmosphere>
The expandable polyvinyl chloride resin particles were put into a pre-expansion machine (manufactured by Daikai Kogyo Co., Ltd.), 0.16 MPa water vapor was introduced into the pre-expansion machine, and the particles were expanded at a temperature of 90 to 110° C. inside the pre-expansion machine to obtain expanded particles (expanded polyvinyl chloride resin particles). The amount of the expandable polyvinyl chloride resin particles put into the pre-expansion machine was 1000 g. The expansion ratio of the obtained expanded particles was measured based on the above-mentioned <Bulk expansion ratio measurement of expanded polyvinyl chloride resin particles>.

<Molding evaluation of polyvinyl chloride resin foam beads>
The obtained foamed beads were filled into a mold for in-mold molding having a length of 400 mm, a width of 400 mm, and a thickness of 25 mm attached to a polystyrene foam molding machine, and 0.12 MPa water vapor was introduced into the mold for 30 seconds to cause in-mold foaming, and then water was sprayed into the mold for 20 seconds to cool. The vinyl chloride resin foam molded body was held in the mold until the pressure of the vinyl chloride resin foam molded body pressing the mold reached 0.05 MPa (gauge pressure), and then the vinyl chloride resin foam molded body was taken out to obtain a rectangular parallelepiped vinyl chloride resin foam molded body.

<Measurement of magnification of polyvinyl chloride resin foam molded body>
The longitudinal dimension X (mm), lateral dimension Y (mm), and thickness dimension Z (mm) of the foamed molded article were measured with a vernier caliper, and the weight W (g) of the foamed molded article was measured with an electronic balance, and the magnification of the foamed molded article was calculated from the following formula: The density of the base resin, 1430 kg/ ^m3, was used from the above-mentioned <Measurement of true density of vinyl chloride resin pellets (base resin)>.
Magnification of foamed molded article (times) = 1430/(W/(X x Y x Z) x ¹⁰⁶ )

The raw materials used in the examples and comparative examples are shown below.
(Vinyl chloride resin)
(A-1) Chlorinated polyvinyl chloride resin [Kaneka Corporation, H716S, average degree of polymerization 600, chlorine content 67.6% by weight]
(Plasticizer)
(B-1) Bis(2-ethylhexyl) phthalate (DOP) (manufactured by J-Plus)
(B-2) Tri(2-ethylhexyl) trimellitate (TOTM) (manufactured by J-Plus)
(B-3) Epoxidized soybean oil (manufactured by ADEKA, product name: O-130P)
(B-4) Triphenyl phosphate (TPP) (manufactured by Daihachi Chemical Industry Co., Ltd.)
(Foaming Agent)
(C-1) Normal pentane [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.]
(C-2) Acetone [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.]

Example 1
[Preparation of expandable polyvinyl chloride resin particles]
To 100 parts by weight of chlorinated polyvinyl chloride resin (A-1), 2 parts by weight of plasticizer (B-1), 13 parts by weight of styrene-acrylonitrile copolymer (Blendex 869 manufactured by Galata), 5 parts by weight of butyltin mercapto stabilizer, 3 parts by weight of lubricant (ester wax, polyethylene wax), and 5 parts by weight of chlorinated polyethylene having a chlorine content of 35% by weight were added, and the mixture was hand-blended to obtain a uniform mixture.

This blend was kneaded with an 8-inch roll at 195° C. for 5 minutes, and the resulting sheet-like composition was cut with a cutter to obtain vinyl chloride resin particles with a particle weight of 6 mg.
[Preparation of expandable polyvinyl chloride resin particles]
100 parts by weight of the obtained vinyl chloride resin particles and 100 parts by weight of the foaming agent (C-1) were placed in a 100 cc pressure vessel and sealed, and then heated in an oil bath at 120°C for 3 hours, the pressure vessel was cooled, and the expandable vinyl chloride resin particles were taken out from the pressure vessel. The foaming agent content of the expandable vinyl chloride particles was 9.1% by weight.
[Preparation of polyvinyl chloride resin foam particles]
The resulting expandable polyvinyl chloride resin particles were stored at 4° C. for 10 days, and then the foaming evaluation was carried out according to the above-mentioned <Foaming evaluation in a heated air atmosphere>. The results are shown in Table 1.

(Examples 2 to 6, Comparative Examples 1 to 3)
The same procedure as in Example 1 was carried out, except that the formulation was changed to that shown in Table 1. The results are shown in Table 1.

(Example 7)
To 100 parts by weight of chlorinated vinyl chloride resin (A-1), 5 parts by weight of plasticizer (B-1), 13 parts by weight of styrene-acrylonitrile copolymer (Blendex 869 manufactured by Galata), 5 parts by weight of butyltin mercapto stabilizer, 3 parts by weight of lubricant (ester wax, polyethylene wax), and 5 parts by weight of chlorinated polyethylene with a chlorine content of 35% by weight were added, and the resulting mixture was blended to obtain a uniform mixture, which was then melt-kneaded in a co-rotating intermeshing twin screw extruder to obtain pellets with the above-mentioned blending ratio. The resulting pellets were melt-kneaded in a φ40 mm co-rotating intermeshing twin screw extruder at a feed rate of 40 kg/hr.
From the middle of the φ40 mm co-rotating intermeshing twin screw extruder, 8.7 parts by weight of normal pentane (C-1) and 3.8 parts by weight of acetone (C-2) were pressed into 100 parts by weight of the pellets. Thereafter, through a continuation pipe attached to the tip of the twin screw extruder, a single screw extruder, a gear pump, and a diverter valve, the pellets were extruded into pressurized circulating water at a temperature of 65° C. and 1.3 MPa at a discharge rate of 45 kg/hr from a die having 30 small holes with a diameter of 1.0 mm and a land length of 3.5 mm attached downstream of the diverter valve and set at 220° C. The extruder tip pressure at this time was 15 MPa, and the resin temperature of the melt (i.e., the resin temperature of the resin melt at the tip of the extruder) was 158° C. The extruded molten resin was cut and pelletized using a rotary cutter in contact with the die, and transferred to a centrifugal dehydrator to obtain foamable polyvinyl chloride resin particles with a particle weight of 5.7 mg.
The true density of the obtained expandable polyvinyl chloride resin particles was measured by the above-mentioned <Measurement of true density of expandable polyvinyl chloride resin particles>, and it was found to be 1350 kg/ ^m3 .

[Preparation of polyvinyl chloride resin foam particles]
The obtained expandable polyvinyl chloride resin particles were stored at 23°C for 1 day, and then the foaming evaluation was carried out by the above-mentioned <Foaming evaluation in a heated air atmosphere>. The results are shown in Table 1. Furthermore, the obtained expandable polyvinyl chloride resin particles were stored at 23°C for 19 days, and then the above-mentioned <Foaming evaluation in a water vapor atmosphere> method was used to obtain foamed particles for molding. The bulk ratio of the obtained expanded particles was 31 times.

[Preparation of polyvinyl chloride resin foam molded body]
The foamed beads for molding were stored in an atmosphere of 30° C. for 24 hours, and then a foamed molded product was obtained according to the above-mentioned <Molding evaluation of vinyl chloride resin>. The foamed molded product had an expansion ratio of 29 times.

Claims (8)

The composition includes a vinyl chloride resin, a plasticizer, and a foaming agent,
The content of the plasticizer is 1 part by weight or more and less than 10 parts by weight based on 100 parts by weight of the vinyl chloride resin,
The vinyl chloride resin includes a chlorinated vinyl chloride resin,
The chlorine content of the chlorinated vinyl chloride resin is 60% by weight or more and 75% by weight or less.
Expandable polyvinyl chloride resin particles. The composition includes a vinyl chloride resin, a plasticizer, and a foaming agent,
The content of the plasticizer is 1 part by weight or more and less than 10 parts by weight based on 100 parts by weight of the vinyl chloride resin,
The vinyl chloride resin includes a chlorinated vinyl chloride resin,
The average polymerization degree of the chlorinated vinyl chloride resin is 400 or more and 1500 or less.
Expandable polyvinyl chloride resin particles. 3. The expandable polyvinyl chloride resin particles according to claim 1, wherein the plasticizer comprises at least one selected from the group consisting of a phthalic acid plasticizer, a phosphoric acid plasticizer, a trimellitic acid plasticizer, and an epoxy plasticizer. The expandable polyvinyl chloride resin particles according to any one of claims 1 to 3 , which contain a physical foaming agent. 5. The expandable polyvinyl chloride resin particles according to claim 4 , wherein the physical foaming agent contains a saturated hydrocarbon having 4 to 6 carbon atoms. The expandable polyvinyl chloride resin particles according to claim 4 or 5 , wherein the physical foaming agent comprises a ketone. 7. A polyvinyl chloride resin foamed particle obtained by pre-expanding the expandable polyvinyl chloride resin particle according to claim 1. A polyvinyl chloride resin foamed article obtained by foam molding the polyvinyl chloride resin foamed particles according to claim 7 .