JP7532196B2 - Styrenic resin extruded foam and its manufacturing method - Google Patents

Description

The present invention relates to an extruded styrene resin foam and a method for producing the same.

Styrenic resin extrusion foams are generally produced continuously by heating and melting a styrenic resin composition using an extruder or the like, then adding a blowing agent under high pressure conditions, cooling to a specified resin temperature, and then extruding the mixture into a low pressure region.

Traditionally, styrene-based resin extruded foams have been used, for example, as insulation for structures due to their good workability and insulating properties. With the current growing awareness of energy conservation, there is an increasing demand for insulation materials with better insulating performance.

As a method for producing a highly insulating foam, it has been proposed to control the bubble structure that constitutes the foam to produce a structure consisting of large bubbles and small bubbles (for example, Patent Document 1). In addition, a production method has been proposed in which graphite or titanium oxide is added in a specified range as a heat radiation inhibitor (for example, Patent Document 2), and a production method for extruded styrene resin foam using environmentally friendly fluorinated olefins (also known as hydrofluoroolefins, HFOs) that have an ozone depletion potential of zero and a small global warming potential (for example, Patent Document 3).

JP2004-175862A Special table 2010-511773 Patent Publication No. 2017-125121

However, the styrene-based resin extruded foam described in the above patent document has room for improvement in order to meet the high demands for energy saving in recent years and to obtain a heat insulating material that is easy to thicken.

The objective of the present invention is to provide an extruded styrene-based resin foam that has excellent heat insulation and thickness build-up properties.

As a result of intensive research into solving the above problems, the inventors have succeeded in achieving both excellent heat insulation and excellent thickness build-up properties by adding a specific amount of a heat radiation inhibitor and controlling the bubble structure, thus completing the present invention.

That is, the present invention relates to an extruded styrene-based resin foam containing a styrene-based resin, a heat radiation inhibitor, and a foaming agent, in which the content of the heat radiation inhibitor is 0.5 to 1.5 parts by weight per 100 parts by weight of the styrene-based resin, and in which, with regard to the cell structure of the foam, (A) cells having a cell diameter of 0.15 mm or less occupy 10 to 80% by area in the cross section of the extruded styrene-based resin foam, (B) cells having a cell diameter of 0.2 to 1.0 mm occupy 10 to 80% by area in the cross section of the extruded styrene-based resin foam, and (C) the proportion of cells having a cell diameter of 0.15 mm or less and cells having a cell diameter of 0.2 to 1.0 mm in the cross section of the extruded styrene-based resin foam is 90% or more (hereinafter, this may be referred to as the "extruded styrene-based resin foam according to the present invention"). In this specification, bubbles that make up the foam are referred to as small bubbles, and bubbles with a diameter of 0.15 mm or less are referred to as large bubbles, while bubbles with a diameter of 0.2 to 1.0 mm are referred to as large bubbles.

In the styrene-based resin extruded foam according to the present invention, it is preferable that the heat radiation inhibitor contains graphite.

In the styrene-based resin extruded foam according to the present invention, it is preferable that the foaming agent contains at least one selected from the group consisting of saturated hydrocarbons having 3 to 5 carbon atoms, dimethyl ether, water, and alcohols having 2 to 5 carbon atoms.

In the styrene-based resin extruded foam according to the present invention, it is preferable that the thermal conductivity of the styrene-based resin extruded foam is 0.0265 W/mK or less.

The present invention also relates to a method for producing an extruded styrene-based resin foam by extruding and foaming a styrene-based resin composition containing a styrene-based resin and a foaming agent, the method including the step of adding 0.5 to 1.5 parts by weight of a heat radiation suppressant containing graphite and 0.1 to 1.5 parts by weight of water to 100 parts by weight of the styrene-based resin.

According to the present invention, it is possible to obtain an extruded styrene-based resin foam that combines excellent heat insulation and thickness buildability.

One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to each of the configurations described below, and various modifications are possible within the scope of the claims. In addition, embodiments and/or examples obtained by appropriately combining the technical means disclosed in different embodiments and/or examples are also included in the technical scope of the present invention. In addition, all academic literature and patent documents described in this specification are incorporated herein by reference. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and smaller than B)."

The present inventors considered that the conventional techniques have the following problems in obtaining a styrene-based resin extruded foam that has both excellent heat insulation and thickness buildability. It has been known for a long time that a heat radiation inhibitor is used in a styrene-based resin extruded foam for the purpose of improving heat insulation, as described in Patent Document 2. It is also known that a heat radiation inhibitor, especially graphite, suppresses radiation heat transfer, while acting as a nucleating agent (nucleating agent), and therefore the bubbles constituting the foam become finer. For this reason, when graphite is used as a radiation inhibitor, there is a problem that the bubbles become finer, resulting in poor thickness buildability. In addition, in a styrene-based resin extruded foam, when a structure having different bubble diameters, large and small, is controlled as a cell structure exhibiting excellent heat insulation, as described in Patent Document 1, if a large amount of a heat radiation inhibitor is used for the purpose of further imparting heat insulation, the difference in the bubble diameters of the bubbles constituting the foam becomes smaller due to the finer bubbles, and the cell structure with high heat insulation cannot be maintained. For this reason, it was not anticipated that a heat radiation suppressant such as graphite could be added and that bubbles of different sizes could be formed.
As a result of intensive research, the present inventors have found that by setting the blending amount of the thermal radiation inhibitor within a specific range, it is possible to simultaneously achieve thickness buildability due to the cell structure while exerting the radiation suppression effect, and have arrived at the present invention. Specifically, in a styrene-based resin extruded foam obtained by heating and melting a styrene-based resin, adding a foaming agent, and extruding and foaming, the thermal radiation inhibitor is contained in an amount of 0.5 to 1.5 parts by weight per 100 parts by weight of the styrene-based resin, and the cells constituting the foam are mainly composed of cells with a cell diameter of 0.15 mm or less and cells with a cell diameter of 0.2 to 1.0 mm, whereby it is possible to achieve both excellent levels of heat insulation and thickness buildability. Here, "the bubbles constituting the foam are mainly composed of bubbles having a diameter of 0.15 mm or less and bubbles having a diameter of 0.2 to 1.0 mm" means that the foam has a bubble structure that at least satisfies the following requirements: (A) bubbles having a diameter of 0.15 mm or less occupy 10 to 80% of the cross section of the styrene-based resin extruded foam, (B) bubbles having a diameter of 0.2 to 1.0 mm occupy 10 to 80% of the cross section of the styrene-based resin extruded foam, and (C) bubbles having a diameter of 0.15 mm or less and bubbles having a diameter of 0.2 to 1.0 mm occupy 90% or more of the bubbles present in the styrene-based resin extruded foam. In addition, in the styrene-based resin extruded foam of the present invention, as described in Patent Document 3, it is possible to achieve both excellent levels of insulation and thickness development without using hydrofluoroolefin, which is a foaming agent that has high insulation performance but is expensive. In this specification, the "extruded foam" may be referred to as "foam".

An embodiment of the present invention will be described below.
[1. Extruded styrene resin foam]
The extruded styrene-based resin foam according to the present invention contains 0.5 to 1.5 parts by weight of a heat radiation inhibitor per 100 parts by weight of the styrene-based resin, and the cells constituting the foam are mainly composed of cells having a diameter of 0.15 mm or less and cells having a diameter of 0.2 to 1.0 mm. This allows both excellent heat insulation and thickness buildability to be achieved.

The styrene-based extruded foam of the present invention may further contain various additives as described below in appropriate amounts, if necessary. The styrene-based extruded foam of the present invention can be continuously produced by heating and melting the styrene-based resin composition containing the above-mentioned styrene-based resin and various additives as necessary using an extruder, adding a foaming agent under high pressure conditions, cooling to a predetermined resin temperature, and then extruding it into a low pressure region.

In the present invention,
The styrene resin is not particularly limited, but examples thereof include (i) homopolymers of styrene monomers such as styrene, methylstyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, bromostyrene, chlorostyrene, vinyltoluene, vinylxylene, etc., or copolymers of a combination of two or more styrene monomers, and (ii) copolymers of the styrene monomers with one or more other monomers such as divinylbenzene, butadiene, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, maleic anhydride, itaconic anhydride, acrylonitrile, etc. The other monomers such as acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, maleic anhydride, and itaconic anhydride to be copolymerized with the styrene monomer can be used in an amount that does not reduce the physical properties such as the compressive strength of the styrene resin extrusion foam. In addition, the styrene-based resin used in one embodiment of the present invention is not limited to the homopolymer or copolymer of the styrene-based monomer (hereinafter, the homopolymer or copolymer of the styrene-based monomer may be referred to as "polystyrene"), but may also include a blend of the homopolymer or copolymer of the styrene-based monomer and the homopolymer or copolymer of the other monomer. For example, the styrene-based resin used in one embodiment of the present invention may include a blend of the homopolymer or copolymer of the styrene-based monomer and a diene rubber reinforced polystyrene or an acrylic rubber reinforced polystyrene. Furthermore, the styrene-based resin used in the present invention may include a styrene-based (co)polymer having a branched structure for the purpose of adjusting the melt flow rate (hereinafter, referred to as MFR), the melt viscosity during molding, the melt tension, and the like.

In the present invention, the styrene resin is preferably a polymer having an MFR of 0.1 to 50 g/10 min, because (i) it has excellent moldability during extrusion foaming, (ii) it is easy to adjust the discharge amount during molding, the thickness, width, apparent density, and closed cell ratio of the styrene resin extrusion foam to the desired values, (iii) it has excellent foamability (ease of adjusting the thickness, width, apparent density, closed cell ratio, and surface properties of the foam to the desired conditions), (iv) it is possible to obtain an extrusion foam of a styrene resin having excellent appearance, and (v) it is possible to obtain an extrusion foam of a styrene resin having a good balance of properties (for example, mechanical strength such as compressive strength, bending strength, or bending deflection amount, toughness, etc.). Furthermore, the MFR is more preferably 0.3 to 30 g/10 min, and particularly preferably 0.5 to 25 g/10 min, from the viewpoint of the balance between moldability and foamability, and mechanical strength and toughness. In one embodiment of the present invention, MFR is measured according to Method A of JIS K7210-1 (2014).

In the present invention, it is particularly preferable that polystyrene is contained from the viewpoints of economy and processability. In addition, when higher heat resistance is required for the extruded foam, it is preferable to use (meth)acrylic acid copolymerized polystyrene or maleic anhydride modified polystyrene. In addition, when higher impact resistance is required for the extruded foam, it is preferable to use rubber-reinforced polystyrene. These may be used alone, or two or more styrene-based (co)polymers having different copolymerization components, molecular weights, molecular weight distributions, branched structures, and/or MFRs may be mixed and used.
In the present invention, the foaming agent preferably contains at least one selected from the group consisting of saturated hydrocarbons having a carbon number of 3 to 5, dimethyl ether, water, and alcohols having a carbon number of 2 to 5, which have a good plasticizing effect on the resin and good foaming properties. In particular, it is particularly preferable to contain water in order to easily obtain a characteristic bubble structure in which large and small bubbles are mixed.

In the present invention, further, by using another foaming agent, a plasticizing effect and/or a co-foaming effect during foam production can be obtained, the extrusion pressure can be reduced, and a foam can be stably produced.
Other blowing agents include, for example, ethers such as diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, furfural, 2-methylfuran, tetrahydrofuran, and tetrahydropyran; ketones such as dimethyl ketone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl i-butyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone, ethyl n-propyl ketone, and ethyl n-butyl ketone; trans-1,3,3,3-tetrafluoropropene (trans-HFO-1234ze), cis ... Hydrofluoroolefins such as tetrafluoropropene (cis-HFO-1234ze), 2,3,3,3-tetrafluoropropene (trans-HFO-1234yf), and trans-1-chloro-3,3,3-trifluoropropene (trans-HCFO-1233zd); alkyl chlorides such as methyl chloride and ethyl chloride; organic foaming agents such as carboxylates such as methyl formate, ethyl formate, propyl formate, butyl formate, amyl formate, methyl propionate, and ethyl propionate; inorganic foaming agents such as carbon dioxide; azo compounds, chemical foaming agents such as tetrazole, and the like can be used. These other foaming agents may be used alone or in combination of two or more. Hydrofluoroolefins are expensive, and when used in large quantities, they have the effect of making the bubbles in the foam finer, making it difficult to form large bubbles. Therefore, when used as another foaming agent, it is preferable that the amount of the other foaming agents is 3 parts by weight or less relative to 100 parts by weight of the styrene-based resin, and it is more preferable that they are not used at all. Carbon dioxide also has the effect of making air bubbles finer, making it difficult for large bubbles to form. Therefore, when carbon dioxide is used as another foaming agent, it is preferable that the amount of carbon dioxide is 1.5 parts by weight or less per 100 parts by weight of the styrene-based resin, and it is more preferable that carbon dioxide is not used at all.

The amount of foaming agent added in the present invention is preferably 2 to 20 parts by weight, and more preferably 2 to 15 parts by weight, per 100 parts by weight of the styrene-based resin as a whole. If the amount of foaming agent added is less than 2 parts by weight, the expansion ratio will be low and the properties of the resin foam, such as light weight and heat insulation, may not be fully exhibited. If the amount of foaming agent added is more than 20 parts by weight, the excessive amount of foaming agent may cause defects such as voids in the foam.

In the present invention, when water and/or alcohols are used, it is preferable to add a water-absorbing substance in order to perform stable extrusion foam molding. Specific examples of water-absorbing substances include water-absorbing polymers such as polyacrylate polymers, starch-acrylic acid graft copolymers, polyvinyl alcohol polymers, vinyl alcohol-acrylate copolymers, ethylene-vinyl alcohol copolymers, acrylonitrile-methyl methacrylate-butadiene copolymers, polyethylene oxide copolymers, and derivatives thereof, as well as fine powders having hydroxyl groups on the surface such as anhydrous silica (silicon oxide) having silanol groups on the surface [for example, AEROSIL manufactured by Nippon Aerosil Co., Ltd. is commercially available]; water-absorbing or water-swelling layered silicates such as smectite and swelling fluoromica, and organically treated products thereof; and porous substances such as zeolite, activated carbon, alumina, silica gel, porous glass, activated clay, diatomaceous earth, and bentonite. The amount of water-absorbing substance added is adjusted as appropriate depending on the amount of water and/or alcohol added, but is preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, per 100 parts by weight of styrene-based resin.

In the method for producing an extruded styrene resin foam according to the present invention, the pressure at which the foaming agent is added or injected is not particularly limited, and may be any pressure higher than the internal pressure of the extruder, etc.

In the present invention, it is preferable to include a flame retardant in the styrene-based resin extruded foam. The content of the flame retardant is preferably 1.0 to 8.0 parts by weight per 100 parts by weight of the styrene-based resin. This allows the resulting styrene-based resin extruded foam to be flame-retardant. If the content of the flame retardant is less than 1.0 part by weight, it tends to be difficult to obtain good foam properties such as flame retardancy, while if it exceeds 8.0 parts by weight, the stability and surface properties during foam production may be impaired. However, it is more preferable that the content of the flame retardant is appropriately adjusted according to the foaming agent content, the apparent density of the foam, and the type or content of additives having a flame retardant synergistic effect so that the oxygen index measured in accordance with JIS K7201-2 (2007) is 26% or more.

As the flame retardant, a bromine-based flame retardant is preferably used. Specific examples of the bromine-based flame retardant in the present invention include hexabromocyclododecane, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether, tetrabromobisphenol A-bis(2,3-dibromopropyl)ether, tris(2,3-dibromopropyl)isocyanurate, and aliphatic bromine-containing polymers such as brominated styrene-butadiene block copolymers. These may be used alone or in combination of two or more.
Among these, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether, mixed brominated flame retardants consisting of tetrabromobisphenol A-bis(2,3-dibromopropyl)ether, brominated styrene-butadiene block copolymer, and hexabromocyclododecane are preferably used because they have good extrusion operation and do not adversely affect the heat resistance of the foam, etc. These substances may be used alone or as a mixture.

The content of the bromine-based flame retardant in the styrene-based resin extruded foam according to the present invention is preferably 1.0 to 8.0 parts by weight per 100 parts by weight of the styrene-based resin, more preferably 1.5 to 7.0 parts by weight per 100 parts by weight of the styrene-based resin, and even more preferably 2.0 to 6.0 parts by weight. If the content of the bromine-based flame retardant is less than 1.0 part by weight, it tends to be difficult to obtain good foam properties such as flame retardancy, while if it exceeds 8.0 parts by weight, the stability and surface properties during foam production may be impaired.

In the present invention, a radical generator can be used in combination with the styrene-based resin extrusion foam to improve the flame retardant performance. Specific examples of the radical generator include 2,3-dimethyl-2,3-diphenylbutane, poly-1,4-diisopropylbenzene, 2,3-diethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane, 3,4-diethyl-3,4-diphenylhexane, 2,4-diphenyl-4-methyl-1-pentene, and 2,4-diphenyl-4-ethyl-1-pentene. Peroxides such as dicumyl peroxide are also used. Among them, those that are stable under the resin processing temperature conditions are preferred, specifically 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropylbenzene, and the preferred amount of the radical generator to be added is 0.05 to 0.5 parts by weight per 100 parts by weight of the styrene-based resin.

Furthermore, for the purpose of improving flame retardant performance, in other words as a flame retardant auxiliary, phosphorus-based flame retardants such as phosphate esters and phosphine oxides can be used in combination, as long as the thermal stability performance is not impaired. Examples of phosphate esters include triphenyl phosphate, tris(tributylbromoneopentyl)phosphate, tricresyl phosphate, trixylyleneyl phosphate, cresyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, tris(2-ethylhexyl)phosphate, tris(butoxyethyl)phosphate, and condensed phosphate esters, and triphenyl phosphate and tris(tributylbromoneopentyl)phosphate are particularly preferred. Furthermore, triphenylphosphine oxide is preferred as a phosphine oxide-type phosphorus-based flame retardant. These phosphate esters and phosphine oxides may be used alone or in combination of two or more. The preferred amount of phosphorus-based flame retardant to be added is 0.1 to 2 parts by weight per 100 parts by weight of styrene-based resin.

In the present invention, a stabilizer for the resin and/or the flame retardant can be used as necessary. Specific examples of stabilizers include, but are not limited to, (i) epoxy compounds such as bisphenol A diglycidyl ether type epoxy resins, cresol novolac type epoxy resins, and phenol novolac type epoxy resins; (ii) polyhydric alcohol esters, which are reaction products of polyhydric alcohols such as pentaerythritol, dipentaerythritol, and tripentaerythritol with monovalent carboxylic acids such as acetic acid and propionic acid, or divalent carboxylic acids such as adipic acid and glutamic acid, and which are mixtures of esters having one or more hydroxyl groups in the molecule and may contain a small amount of the raw material polyhydric alcohol; (iii) triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, pentaerythritol tetrakis[3-(3 ',5'-di-tert-butyl-4'-hydroxyphenyl)propionate] and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and (iv) phosphite stabilizers such as 3,9-bis(2,4-di-tert-butylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and tetrakis(2,4-di-tert-butyl-5-methylphenyl)-4,4'-biphenylene diphosphonite), are preferably used because they do not reduce the flame retardant performance of the foam and improve the thermal stability of the foam.

The styrene-based resin extrusion foam according to the present invention contains a heat radiation inhibitor to improve heat insulation. The heat radiation inhibitor refers to a substance that has the properties of reflecting, scattering, and absorbing light in the near infrared or infrared region. By containing a heat radiation inhibitor, the foam can have high heat insulation. Examples of heat radiation inhibitors include black particles such as graphite, carbon black, and activated carbon, and white particles such as titanium oxide, barium sulfate, zinc oxide, aluminum oxide, and antimony oxide. These may be used alone or in combination of two or more. Among these, graphite and carbon black are preferred as black particles, and graphite is more preferred, because they have a high heat radiation suppression effect. Also, titanium oxide and barium sulfate are preferred as white particles, and titanium oxide is more preferred.

The total content of the heat radiation inhibitor in the present invention is 0.5 to 1.5 parts by weight per 100 parts by weight of the styrene-based resin. If the total content of the heat radiation inhibitor is less than 0.5 parts by weight, the heat radiation inhibitor effect is poor, and if it is more than 1.5 parts by weight, the number of nucleation points increases, causing the bubbles in the foam to become finer, making it difficult to achieve the thickness of the extruded foam.

Examples of graphite in the present invention include scaly (flake) graphite, clayey graphite, spherical graphite, and artificial graphite. Among these, it is preferable to use graphite whose main component is scaly (flake) graphite because of its high heat radiation suppression effect. Graphite with a fixed carbon content of 80% or more is preferable, and graphite with a fixed carbon content of 85% or more is more preferable. By setting the fixed carbon content within the above range, a foam with high thermal insulation properties can be obtained.

The average particle size of the black particles in the present invention is not particularly limited, but for example, for graphite, it is preferably 15 μm or less, more preferably 10 μm or less. For carbon black, it is preferably 0.3 μm or less, more preferably 0.1 μm or less. By setting the average particle size within the above range, the specific surface area becomes large and the probability of collision with heat radiation increases, so that the heat radiation suppression effect is enhanced. The average particle size means the particle size when the cumulative volume of the total particle volume becomes 50% (volume average particle size by laser diffraction scattering method) when the particle size distribution is measured and analyzed by the laser diffraction scattering method based on the Mie theory in accordance with ISO13320:2009 and JIS Z8825:2013.

The average particle size of the white particles in the present invention is not particularly limited, but in consideration of effectively reflecting infrared rays and coloring properties in resin, for example, for titanium oxide, 0.1 to 10 μm is preferable, and 0.15 to 5 μm is more preferable.

In the present invention, further additives such as inorganic compounds such as silica, calcium silicate, wollastonite, kaolin, clay, mica, and calcium carbonate, processing aids such as sodium stearate, calcium stearate, magnesium stearate, barium stearate, liquid paraffin, olefin wax, and stearylamide compounds, phenolic antioxidants, phosphorus-based stabilizers, nitrogen-based stabilizers, sulfur-based stabilizers, light resistance stabilizers such as benzotriazoles and hindered amines, bubble size regulators such as talc, moldability improvers such as polyethylene glycol and polyhydric alcohol fatty acid esters, antistatic agents other than those mentioned above, and colorants such as pigments may be contained in the styrene resin as necessary, provided that the effects of the present invention are not impaired.

Methods and procedures for blending various additives with styrene resin include, for example, a method of adding various additives to styrene resin and mixing by dry blending, a method of adding various additives to molten styrene resin from a supply section provided midway through an extruder, a method of preparing a master batch in which various additives are incorporated into styrene resin at high concentrations using an extruder, kneader, Banbury mixer, rolls, etc., and mixing the master batch with styrene resin by dry blending, or a method of supplying various additives to an extruder using a supply facility separate from the styrene resin. For example, a procedure may be used in which various additives are added to styrene resin and mixed, then the mixture is supplied to an extruder to be heated and melted, and a foaming agent is further added and mixed, but the timing of adding various additives or foaming agent to styrene resin and the kneading time are not particularly limited.

The thermal conductivity of the styrene-based resin extruded foam according to the present invention is not particularly limited, but from the viewpoint of thermal insulation considering that the foam functions as, for example, a thermal insulation material for building, or a thermal insulation material for refrigerators or refrigerated vehicles, it is preferable that the thermal conductivity measured at an average temperature of 23°C one week after manufacture is 0.0265 W/mK or less.

The apparent density of the extruded styrene-based resin foam according to the present invention is preferably 20 kg/m3 or more, more preferably 25 kg/ ^m3 or more, from the viewpoint of heat insulation and light weight, taking into consideration the functioning of the foam as a heat insulating material for buildings, or a heat insulating material for refrigerators or refrigerated vehicles, for example. On the other hand, the apparent density is preferably 60 kg/ ^m3 or ^less , more preferably 50 kg/ ^m3 or less.

The closed cell ratio of the extruded styrene-based resin foam of the present invention is preferably 85% or more, and more preferably 90% or more. If the closed cell ratio is less than 85%, the foaming agent may dissipate from the extruded foam prematurely, resulting in reduced thermal insulation.

In the styrene-based resin extruded foam according to the present invention, the bubbles constituting the styrene-based resin extruded foam are mainly composed of bubbles with a bubble diameter of 0.15 mm or less and bubbles with a bubble diameter of 0.2 to 1.0 mm. The bubble diameters of the styrene-based resin extruded foam according to the present invention are preferably 0.01 to 0.15 mm for small bubbles and 0.2 to 1.0 mm for large bubbles, and more preferably 0.03 to 0.1 mm for small bubbles and 0.2 to 0.5 mm for large bubbles. In general, the smaller the average bubble diameter, the shorter the distance between the bubble walls of the foam, so that the range of movement of the bubbles of the extruded foam when giving a shape to the extruded foam during extrusion foaming is narrow, making deformation difficult, and it tends to be difficult to give the extruded foam a beautiful surface and to produce a thickness of the extruded foam. On the other hand, the larger the average bubble diameter, the fewer the number of bubbles per unit thickness, so that the insulation performance of the extruded foam tends to deteriorate. Furthermore, the difference between the average bubble diameter of small bubbles and the average bubble diameter of large bubbles is preferably 0.1 mm or more, and more preferably 0.15 mm or more.

The cell structure constituting the styrene-based resin extruded foam according to the present invention has cells with a cell diameter of 0.15 mm or less occupying 10 to 80% of the cross section of the styrene-based resin extruded foam, preferably 20 to 70%. This results in a sufficient number of small cells per unit thickness, and fully exerts the effect of reducing the thermal conductivity of the foam.

The cell structure constituting the styrene-based resin extruded foam according to the present invention has cells with a diameter of 0.2 to 1.0 mm occupying 10 to 80% of the cross section of the styrene-based resin extruded foam, preferably 20 to 80%, and more preferably 30 to 80%. If the area ratio of the cells with a diameter of 0.2 to 1.0 mm in the cross section of the styrene-based resin extruded foam is less than 10%, this adversely affects the foam's ability to be thickened, and if it is more than 80%, the effect of the small cells in reducing thermal conductivity is not fully exerted.

In the extruded styrene-based resin foam of the present invention, the ratio of the total area occupied by small bubbles to the total area occupied by large bubbles in the cross section of the extruded styrene-based resin foam (total area occupied by small bubbles:total area occupied by large bubbles) is preferably 20:80 to 50:50, and more preferably 20:80 to 40:60. By satisfying the above ratio, an excellent balance between excellent heat insulation properties and thickness buildability is achieved.

The average cell diameter of the extruded styrene resin foam according to the present invention is evaluated using a microscope (DIGITAL MICROSCOPE VHX-900, manufactured by KEYENCE LTD.) as follows.
A 10 mm square sample was cut out from the center of the width and thickness of the obtained extruded styrene-based resin foam, and observed with the microscope from three directions, namely, the extrusion direction, the width direction, and the thickness direction, and a 100x magnification photograph was taken. Small bubbles having a diameter of 0.15 mm or less and large bubbles having a diameter of 0.2 to 1.0 mm were selected from the magnified photograph, and the distance between two points in the vertical and horizontal directions of each of the small and large bubbles was measured so that the number of measurement points in each direction exceeded 30, and the average bubble diameter in each direction was calculated. The arithmetic mean of the obtained average bubble diameters in each direction was determined to be the average bubble diameter of the small and large bubbles of the extruded styrene-based resin foam.

The thickness of the styrene-based resin extruded foam according to the present invention is preferably 10 to 150 mm, more preferably 20 to 130 mm, and particularly preferably 20 to 120 mm, from the viewpoint of thermal insulation, bending strength, and compressive strength, taking into consideration the functioning of the foam as, for example, a thermal insulation material for buildings, or a thermal insulation material for refrigerators or refrigerated vehicles.

As described in the examples and comparative examples of the present invention, in the case of extruded styrene resin foams, after the foam is extruded to give it a shape, both surfaces of a plane perpendicular to the thickness direction may be cut to a depth of about 5 mm on each side in the thickness direction to obtain the product thickness. However, unless otherwise specified, the thickness of the extruded styrene resin foam of the present invention refers to the uncut thickness after the foam is extruded to give it a shape.

Thus, the present invention makes it possible to easily obtain extruded styrene resin foams with excellent heat insulation and thickness build-up properties.

2. Method for producing extruded styrene resin foam
The method for producing an extruded styrene-based resin foam according to the present invention is a method for producing an extruded styrene-based resin foam by extruding and foaming a styrene-based resin composition containing a styrene-based resin and a foaming agent, and includes a step of adding 0.5 to 1.5 parts by weight of a heat radiation inhibitor containing graphite and 0.1 to 1.5 parts by weight of water to 100 parts by weight of the styrene-based resin. According to the method according to the present invention, the bubbles constituting the obtained extruded styrene-based resin foam are composed of bubbles having a bubble diameter of 0.15 mm or less and bubbles having a bubble diameter of 0.2 to 1.0 mm. In addition, the obtained extruded styrene-based resin foam contains a specific amount of a heat radiation inhibitor containing graphite. Therefore, an extruded styrene-based resin foam having excellent heat insulation and thickness buildability can be easily obtained.

The method for producing a styrene-based resin extruded foam described below is one of the preferred embodiments used for producing the styrene-based resin extruded foam of the present invention. Among the components in the method for producing a styrene-based resin extruded foam, those already explained in [1. Styrene-based resin extruded foam] will not be explained here.

In a preferred embodiment of the method for producing a styrene-based resin extrusion foam, a styrene-based resin, a bromine-based flame retardant, and, if necessary, a stabilizer, a heat radiation suppressant, or other additives are supplied to a heat melting section of an extruder or the like. At this time, a foaming agent can be added to the styrene-based resin under high pressure conditions at any stage. The mixture containing the styrene-based resin, the bromine-based flame retardant, and the foaming agent is then made into a fluid gel, cooled to a temperature suitable for extrusion foaming, and the fluid gel is extruded through a die into a low pressure region to form a foam.

The heating temperature in the heat melting section may be equal to or higher than the temperature at which the styrene resin used melts, but is preferably a temperature at which molecular deterioration of the resin due to the influence of additives and the like is suppressed as much as possible, for example, about 150 to 260°C. The melt kneading time in the heat melting section cannot be uniquely defined because it differs depending on the amount of styrene resin extruded per unit time and/or the type of extruder used as the heat melting section and as the melt kneading section, and is appropriately set as the time required for the styrene resin, the foaming agent, and the additives to be uniformly dispersed and mixed.

The melt kneading section may be, for example, a screw-type extruder, but is not particularly limited as long as it is one that is used for normal extrusion foaming.

The foam molding method according to the present invention uses, for example, a slit die having a straight slit-shaped opening used for extrusion molding, which is used to release the extruded foam from a high-pressure region to a low-pressure region, and then molds the extruded foam into a plate-like foam with a large cross-sectional area using a molding die installed in close contact with or in contact with the slit die, and a molding roll installed adjacent to the downstream side of the molding die. By adjusting the flow surface shape of the molding die and the die temperature, the desired cross-sectional shape, surface properties, and foam quality can be obtained.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Furthermore, new technical features can be formed by combining the technical means disclosed in the respective embodiments.

Examples of the present invention will be described below. However, it goes without saying that the present invention is not limited to the following examples.
The raw materials used in the examples and comparative examples are as follows.

Base resin: styrene resin [PS Japan Co., Ltd., G9401; MFR 2.2 g/10 min]
Thermal radiation suppressant - graphite [Marutoyo Foundry Manufacturing Co., Ltd., M-885; scaly graphite, primary particle size 5.5 μm, fixed carbon content 89%]
Flame retardant: A mixed bromine-based flame retardant consisting of tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether and tetrabromobisphenol A-bis(2,3-dibromopropyl)ether [GR-125P, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.]
Brominated styrene-butadiene block polymer [Chemtura, EMERALD INNOVATION #3000]
Flame retardant synergist: Triphenylphosphine oxide [Sumitomo Shoji Chemicals]
Radical generator: Poly-1,4-diisopropylbenzene [UNITED INITIATORS, CCPIB]
Stabilizer: Bisphenol-A-glycidyl ether [ADEKA Corporation, EP-13]
・Cresol novolac epoxy resin [Huntsman Japan, ECN-1280]
Dipentaerythritol-adipic acid reaction mixture [Ajinomoto Fine-Techno Co., Ltd., Plainlyzer ST210]
Pentaerythritol tetrakis[3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate] [Chemtura, ANOX20]
3,9-bis(2,4-di-tert-butylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane [Chemtura, Ultranox 626]
Triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate [Songwon Japan Co., Ltd., Sonnox 2450FF]
Other additives
Talc [Talc Powder PK-Z, manufactured by Hayashi Kasei Co., Ltd.]
Calcium stearate [Sakai Chemical Industry Co., Ltd., SC-P]
Ethylene bis stearic acid amide [NOF Corporation, Alflow H-50S]
Bentonite [Hojun Co., Ltd., Bengelbright 11K]
Silica [Evonik Degussa Japan Co., Ltd., Carplex BS-304F]
○Foaming agent: Dimethyl ether [Iwatani Corporation]
- Isobutane [Mitsui Chemicals, Inc.]
・Water [Settsu City, Osaka Prefecture tap water]

The physical properties of the extruded foams in the Examples and Comparative Examples were evaluated according to the following methods: thickness (before cutting), apparent density, closed cell ratio, average cell diameter of large bubbles, average cell diameter of small bubbles, small cell ratio, thermal conductivity, and oxygen index of the extruded styrene resin foams.

(1) Thickness of extruded styrene resin foam (before cutting)
The thickness of the extruded styrene foam before cutting was measured at three points in total, namely, the center in the width direction and a point 20 mm from one end in the width direction to the opposite end (the same point on both ends in the width direction) using a caliper [M-type standard caliper N30, manufactured by Mitutoyo Corporation]. The average value of the three points was taken as the thickness of the extruded styrene foam before cutting.

(2) Apparent density (kg/ ^m3 )
A test piece having a thickness of 25 mm × length (in the extrusion direction) of 300 mm × width of 100 mm was cut out from the obtained styrene-based resin extruded foam, and the weight of the test piece was measured. The length, width and thickness of the test piece were also measured using a vernier caliper [Mitutoyo Corporation, M-type standard vernier caliper N30].
From the measured weight and each dimension, the foam density was calculated based on the following formula (5) and converted into kg/ ^m3 .
Apparent density (g/cm ³ )=foam weight (g)/foam volume (cm ³ ) (5)

(3) Closed Cell Ratio Test pieces of 25 mm thickness × 25 mm length (extrusion direction) × 25 mm width were cut out from a total of three locations of the width direction center of the obtained extruded styrene-based resin foam and a location 20 mm from one end in the width direction to the opposite end (the same locations on both ends in the width direction). Measurement was performed according to Procedure C of ASTM-D2856-70, and the closed cell ratio of each test piece was calculated using the following calculation formula (6). The average value of the three locations was regarded as the closed cell ratio of the extruded styrene-based resin foam.
Closed cell ratio (%) = (V1-W/ρ) x 100/(V2-W/ρ) (6)
Here, V1 (cm ³ ) is the true volume (excluding the volume of the portion that is not an independent cell) of the test piece measured using an air comparison type specific gravity meter [Tokyo Science Co., Ltd., air comparison type specific gravity meter, Model 1000]. V2 (cm ³ ) is the apparent volume calculated from the outer dimensions of the test piece measured using a caliper [M-type standard caliper N30, Mitutoyo Co., Ltd.]. W (g) is the total weight of the test piece. In addition, ρ (g/cm ³ ) is the density of the styrene-based resin constituting the extruded foam, and polystyrene is 1.05 (g/cm ³ ), and was calculated and used according to the weight ratio (wt %) of each contained in the styrene-based resin.

(4) (5) Average Cell Diameter of Small Cells and Large Cells The obtained extruded styrene resin foams were evaluated as described above.

(6) Small Cell Ratio For the resulting styrene-based extruded foam, the area ratio of bubbles having a diameter of 0.15 mm or less per cross-sectional area of the foam (small cell ratio) was determined as follows. Here, bubbles having a diameter of 0.15 mm or less are defined as bubbles having an equivalent circle diameter of 0.15 mm or less.
a) A 10 mm square sample is cut out from the center in the width direction and thickness direction of the obtained styrene-based resin extruded foam, and photographed at 100 times magnification using a microscope [DIGITAL MICROSCOPE VHX-900, manufactured by KEYENCE CORPORATION] from three directions, that is, the extrusion direction, the width direction, and the thickness direction.
b) The captured image is imported into image processing software [Dibas32], and the bubble membrane portion and large bubble portion (bubbles having a diameter of 0.2 to 1.0 mm) are filled in black, and the contrast is adjusted before binarization.
c) Histogram analysis is performed using image processing software to calculate the area ratio of white areas (small bubble ratio).
d) The above steps b and c are carried out for each cross-sectional direction, and the average value for the three directions is regarded as the small bubble ratio of the sample.

(7) Large Cell Ratio For the resulting styrene-based extruded foam, the area ratio of cells with a cell diameter of 0.2 to 1.0 mm per cross-sectional area of the foam (large cell ratio) was determined as follows. Here, cells with a cell diameter of 0.2 to 1.0 mm refer to cells with a circle equivalent diameter of 0.2 to 1.0 mm.
a) A 10 mm square sample is cut out from the center in the width direction and thickness direction of the obtained styrene-based resin extruded foam, and photographed at 100 times magnification using a microscope [DIGITAL MICROSCOPE VHX-900, manufactured by KEYENCE CORPORATION] from three directions, that is, the extrusion direction, the width direction, and the thickness direction.
b) The captured image is imported into image processing software [Dibas32], and the bubble film portion and small bubble portion (bubbles having a bubble diameter of 0.15 mm or less) are filled in black, and the contrast is adjusted before binarization.
c) Histogram analysis is performed using image processing software to calculate the area ratio of white areas (large bubble ratio).
d) The above steps b and c are carried out for each cross-sectional direction, and the average value for the three directions is determined as the large bubble ratio of the sample.

(8) Area Ratio of Small Cells and Large Cells The sum of the small cell ratio and the large cell ratio was defined as the area ratio of small cells and large cells in the extruded styrene resin foam.

(9) Thermal Conductivity According to JIS A 9521, three test pieces were cut to a thickness of 25 mm × length (extrusion direction) of 300 mm × width of 100 mm, and the thermal conductivity was measured at an average temperature of 23° C. using a thermal conductivity measuring device [Eiko Seiki Co., Ltd., HC-074]. After production of the styrene-based resin extruded foam, the test pieces were cut to the above dimensions, and the test pieces were left to stand under the conditions of standard temperature condition class 3 (23° C.±5° C.) and standard humidity condition class 3 (50 ^{+20, -10} % R.H.) specified in JIS K 7100, one week after production.

(10) Oxygen Index The oxygen index of the obtained styrene-based resin extruded foam was measured in accordance with JIS K7201-2 (2007). A test piece was cut from the width direction center of the styrene-based resin extruded foam to a size of 10 mm in thickness × 150 mm in length (extrusion direction) × 10 mm in width, and was preconditioned for 168 hours, and then conditioned for 88 hours under the conditions of standard temperature condition class 3 (23°C ± 5°C) and standard humidity condition class 3 (50 ^{+ 20, -10} % R.H.) specified in JIS K 7100.

For the examples and comparative examples, graphite was added using a masterbatch prepared according to the following method.

(Production Example 1) [Preparation of Graphite Masterbatch]
Into a Banbury mixer, 100 parts by weight of a styrene-based resin [PS Japan Co., Ltd., G9401; MFR 2.2 g/10 min] as a base resin, and 100 parts by weight of the styrene-based resin were charged with 102 parts by weight of graphite [Marutoyo Casting Manufacturing Co., Ltd., M-885] and 2.0 parts by weight of ethylene bisstearic acid amide [NOF Corp., Alflow H-50S], and melt-kneaded for 20 minutes without heating or cooling under a load of 5 kgf/cm ^2. At this time, the resin temperature was measured and found to be 185 ° C. The strand-shaped resin extruded at a discharge rate of 250 kg/hr through a die having a small hole attached to the tip of the ruder was cooled and solidified in a water tank at 30 ° C., and then cut to obtain a graphite master batch.

Example 1
[Preparation of resin mixture]
The mixture consisted of 100 parts by weight of a styrene-based resin (G9401, manufactured by PS Japan Co., Ltd.; MFR 2.2 g/10 min.) as a base resin, 1.0 part by weight of a graphite master batch as a radiation suppressant, 3.0 parts by weight of a mixed bromine-based flame retardant of tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether and tetrabromobisphenol A-bis(2,3-dibromopropyl)ether (GR-125P, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a flame retardant, and triphenylphosphine oxide as a flame retardant assistant. [Sumitomo Shoji Chemical] 1.0 part by weight, bisphenol-A-glycidyl ether [(Ltd.) ADEKA, EP-13] 0.20 part by weight as a stabilizer, dipentaerythritol-adipic acid reaction mixture [(Ltd.) ADEKA, EP-13] 0.10 part by weight, triethylene glycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl) propionate [(Ltd.) Songwon Japan, Sonox 2450FF] 0.20 part by weight, bentonite [(Ltd.) Hojun, Bengelbright 11K] 0.40 part by weight as a water absorbing medium, silica [(Ltd.) Evonik Degussa Japan, Carplex BS-304F] 0.4 part by weight, calcium stearate [(Ltd.) Sakai Chemical Industry, SC-P] 0.10 part by weight as a lubricant were dry blended to obtain a resin mixture.

[Preparation of extruded foam]
The obtained resin mixture was fed at 75 kg/hr to an extruder in which a single screw extruder (first extruder) with a diameter of 65 mm, a single screw extruder (second extruder) with a diameter of 90 mm, and a cooler were connected in series. The resin mixture fed to the first extruder was heated to a resin temperature of 220° C. to melt or plasticize and knead, and a foaming agent (3.2 parts by weight of isobutane, 2.1 parts by weight of dimethyl ether, and 0.8 parts by weight of water per 100 parts by weight of the base resin) was injected into the resin near the tip of the first extruder.

Then, in the second extruder and cooler connected to the first extruder, the resin temperature was cooled to 120°C, and extrusion foaming was performed into the atmosphere at a foaming pressure of 3.0 MPa from a die (slit die) with a rectangular cross section of 2 mm thick x 150 mm wide installed at the tip of the cooler. After that, an extruded foam board with a cross section of 42 mm thick x 150 mm wide was obtained using a molding die installed in close contact with the die and a molding roll installed downstream of it, and cut to a thickness of 35 mm x width of 130 mm x length of 1500 mm with a cutter. The cut product was used as a styrene resin extruded foam and was evaluated as described above. The evaluation results are shown in Table 1.

(Examples 2 to 4)
Extruded foams were obtained in the same manner as in Example 1, except that the types and amounts of various ingredients were changed as shown in Table 1. The physical properties of the extruded foams obtained are shown in Table 1.

(Comparative Examples 1 to 2)
Extruded foams were obtained in the same manner as in Example 1, except that the types, amounts, and/or production conditions of the various ingredients were changed as shown in Table 1. The physical properties of the obtained extruded foams are shown in the table.

Compared with Examples 1 to 3 and Comparative Examples 1 and 2, the use of a specific amount of graphite not only results in low thermal conductivity, but also excellent foam thickness buildability. In other words, it is clear that the styrene-based resin extruded foam of the present invention has the effect of achieving both excellent thermal insulation and thickness buildability. It is also clear that the styrene-based resin extruded foam of the present invention has a high oxygen index and is flame retardant.

According to the present invention, it is possible to obtain an extruded styrene-based resin foam having excellent heat insulation and thickness forming properties. The extruded styrene-based resin foam is suitable for use as a heat insulating material for houses or structures.

Claims (5)

A styrene-based resin extruded foam containing a styrene-based resin, a heat radiation inhibitor, and a foaming agent, the content of the heat radiation inhibitor being 0.5 to 1.5 parts by weight per 100 parts by weight of the styrene-based resin, and having the following cell structures (A), (B), and (C):
(A) bubbles having a diameter of 0.15 mm or less occupy 10 to 80% of the cross section of the extruded styrene-based resin foam;
(B) bubbles having a diameter of 0.2 to 1.0 mm occupy 10 to 80% of the cross section of the extruded styrene-based resin foam;
(C) The proportion of bubbles having a diameter of 0.15 mm or less and bubbles having a diameter of 0.2 to 1.0 mm in the cross-sectional area of the extruded styrene resin foam is 90% or more. The extruded styrene-based resin foam according to claim 1, wherein the heat radiation inhibitor contains graphite. The extruded styrene-based resin foam according to any one of claims 1 to 2, wherein the foaming agent contains at least one selected from the group consisting of saturated hydrocarbons having 3 to 5 carbon atoms, dimethyl ether, water, and alcohols having 2 to 5 carbon atoms. The extruded styrene-based resin foam according to any one of claims 1 to 3, wherein the thermal conductivity of the extruded styrene-based resin foam is 0.0265 W/mK or less. 5. A method for producing the extruded styrene-based resin foam according to any one of claims 1 to 4, by extruding and foaming a styrene-based resin composition containing a styrene-based resin and a foaming agent, the method comprising the steps of: adding 0.5 to 1.5 parts by weight of a heat radiation inhibitor containing graphite and 0.1 to 1.5 parts by weight of water per 100 parts by weight of the styrene-based resin.