Foam cushioning material and manufacturing method therefor

Abstract

This foam cushioning material includes a cap film on which a plurality of protrusions are formed and a back film laminated on the back surface of the cap film, with gas sealed between the protrusions and the back film, and is molded from a resin composition containing 50 wt.% or more of a poly(3-hydroxyalkanoate)-based resin component. The resin composition may be melted and directly molded into the foam cushioning material, or a resin film may be manufactured by being molded from the resin composition, and then the resin film may be molded into the foam cushioning material.

Description

Bubble wrap and method for manufacturing the same 【0001】 The present invention relates to bubble wrap and a method for producing the same. 【0002】 Bubble wrap is a well-known packaging or packing material used to protect goods from impacts and other damage during transportation. Bubble wrap is composed of at least two resin films. Multiple protrusions are formed on the surface of one resin film by vacuum forming, and the other resin film is laminated to the back surface of the first resin film. This creates air pockets between the two film layers, which provide cushioning. 【0003】 Polyethylene is the main resin material known to constitute such bubble wrap (see, for example, Patent Document 1). 【0004】 Japanese Patent Publication No. 2018-167880 【0005】 Bubble wrap, especially under load, tends to lose its cushioning properties because the amount of air trapped in the air pockets decreases due to the gas barrier properties of the material or the rupture of bubbles. To suppress this decrease, bubble wrap needs to be able to easily maintain its thickness under load. In addition, to facilitate packaging or packing of goods, the bubble wrap as a whole needs to have a soft texture. 【0006】 Polyethylene, widely used as a resin in bubble wrap, is generally a material with low gas barrier properties. Therefore, in bubble wrap molded from polyethylene, air tends to escape easily from the air pockets, and the thickness of the bubble wrap tends to decrease, especially when held under load. 【0007】 On the other hand, polyethylene terephthalate is known as a material with high gas barrier properties. However, polyethylene terephthalate generally has a high modulus of elasticity, making it difficult to construct bubble wrap with a soft texture. 【0008】In view of the above situation, the present invention aims to provide a bubble cushioning material that maintains its thickness even under load and has a soft texture. 【0009】 As a result of diligent research to solve the above problems, the inventors of the present invention have found that by using a poly(3-hydroxyalkanoate) resin as the main resin, it is possible to construct a bubble cushioning material that maintains its thickness even under load and has a soft texture, thus completing the present invention. 【0010】 In other words, the present invention relates to a bubble cushioning material comprising a cap film having a plurality of protrusions formed thereon and a back film laminated on the back surface of the cap film, wherein gas is sealed between the protrusions and the back film, and the bubble cushioning material is molded from a resin composition containing 50% by weight or more of a poly(3-hydroxyalkanoate) resin component. The present invention also relates to a method for producing the bubble cushioning material, comprising the steps of melting the resin composition to form the bubble cushioning material, or molding a resin film molded from the resin composition into a bubble cushioning material. 【0011】 According to the present invention, it is possible to provide a bubble cushioning material that maintains its thickness even under load and has a soft texture. 【0012】 Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below, and various modifications are possible within the scope defined in the claims. Furthermore, the configurations described below can be combined in any way, and such combinations may also constitute an embodiment of the present invention. 【0013】 [Bubble wrap] Bubble wrap has a sheet-like form in which at least two resin films are laminated, and numerous air pockets filled with gas are formed between the layers of the films. These air pockets can absorb shock and provide cushioning. For this reason, bubble wrap is used as packaging or packing material to protect goods from shocks during transportation. 【0014】To describe the structure of the bubble wrap more specifically, the bubble wrap comprises at least a cap film with a plurality of protrusions formed on its surface, and a back film laminated to the back surface of the cap film. The protrusions are formed such that a part of the cap film protrudes (or is recessed when viewed from the back side), and the cap film has protrusions and non-protruding areas surrounding the protrusions. The back film may be a flat film or may also have protrusions. 【0015】 The cap film and back film are laminated with the back surface of the cap film facing the back film, and the non-protruding areas of the cap film and the back film are in close contact. The method for achieving this contact is not particularly limited, but it is usually heat fusion. The protrusions of the cap film and the back film are spaced apart, and gas (usually air) is sealed between the protrusions and the back film, forming an air pocket. 【0016】 The size of the protrusion is not particularly limited, but the width of the protrusion as viewed from the top surface of the film is usually about 1 mm to 5 cm. The height of the protrusion is also not particularly limited, and is usually about 1 mm to 3 cm. The shape of the protrusion is usually cylindrical, but the shape of the bottom surface of the protrusion is not limited to circular, and may be elliptical, square, or other shapes. 【0017】 The bubble wrap includes at least two resin films as described above, but the number of resin films is not limited to two and may include three or more. When there are three or more resin films, the configuration excluding the two resin films described above is not particularly limited and may be known. For example, this could include a configuration in which a third resin film is laminated on the upper surface of the protrusion of the cap film, a configuration in which a resin film is laminated between the cap film and the back film, or a configuration in which a third resin film is laminated on the back surface of the back film. 【0018】 Bubble wrap is in the form of a sheet, but it may also be a roll of sheets wound on a surface. Alternatively, the sheets may be further processed into shapes such as bags. 【0019】The bubble cushioning material relating to this disclosure maintains its thickness even under load and has a soft texture. 【0020】 In this application, the elastic modulus measured for the bubble wrap is used as a physical property value indicating the texture of the bubble wrap. The elastic modulus is determined as follows: A tensile test is performed on the bubble wrap under the conditions of a tensile speed of 500 mm / min and a sampling interval of 0.01 sec, and the obtained results are plotted on a graph with strain [mm] on the horizontal axis and test force [N] on the vertical axis. The slope of the curve is calculated for each plotting interval on this graph. From the obtained slope values, the maximum value is determined in the region where the strain is 5% or less (for example, when the distance between chucks is 40 mm, this corresponds to an elongation of 2 mm or less), and this is taken as the maximum slope [N / mm]. On the other hand, the basis weight (weight per unit area) [g / m²] of the same bubble wrap is determined. ２ Measure the elastic modulus of the bubble wrap [(N・m)]. Divide the maximum slope by the basis weight and use that value to determine the elastic modulus of the bubble wrap. ２ Let it be ) / (g・mm). 【0021】 The elastic modulus exhibited by the bubble cushioning material relating to this disclosure is 0.03 to 0.20 (N・m) in both the MD and TD directions. ２ It is preferable that the value is within the range of ) / (g・mm). Within this range, the bubble cushioning material can achieve both softness and rigidity suitable for packaging or packing materials. More preferably, it is within the range of 0.05 to 0.18 (N・m). ２ ) / (g・mm), and more preferably 0.07 to 0.16 (N・m ２ ) / (g・mm). 【0022】In this application, the thickness retention rate measured by compression creep is used as a physical property value indicating the thickness retention of the bubble wrap. The value of the thickness retention rate by compression creep is determined as follows: Ten pieces of bubble wrap are stacked with paper in between each piece, and the overall height (thickness) is measured to obtain the initial height. Next, a load of 7 kg is placed on top and maintained for 7 days. After removing the load, the overall height is measured again to obtain the height after 7 days. The value of the thickness retention rate by compression creep (%) is obtained by dividing the height after 7 days by the initial height. The larger this value, the better the thickness of the bubble wrap is maintained. 【0023】 The thickness retention rate of the bubble cushioning material according to this disclosure is preferably 50% or more. Within this range, the bubble cushioning material can be said to be able to easily maintain its thickness even under load. More preferably it is 65% or more, and even more preferably 75% or more. 【0024】 In bubble wrap, uneven film thickness can occur in the protrusions formed by vacuum forming. Poly(3-hydroxyalkanoate) resins, in particular, generally have low melt tension, making them prone to thickness unevenness in the protrusions due to vacuum forming. Such thickness unevenness can lead to variations in quality or even punctures (bubble breakage) in the protrusions, so it is desirable to reduce thickness unevenness. However, in the bubble wrap according to a preferred embodiment of this disclosure, it is possible to suppress thickness unevenness in the protrusions. 【0025】 In this application, thickness deviation is used as a physical property value indicating thickness unevenness in the protrusions of the bubble wrap. To determine this, multiple protrusions contained in the bubble wrap were cut out, the film thickness at the tip of each protrusion was measured, and the thickness deviation was calculated from these measured values. 【0026】The bubble cushioning material according to a preferred embodiment of the present disclosure can achieve a thickness deviation of the cap film at the protrusion of 25 or less. Within this range, it can be said that the bubble cushioning material has little thickness unevenness at the protrusion. Preferably it is 20 or less, more preferably 15 or less, and even more preferably 10 or less. 【0027】 The thickness of each film constituting the bubble cushioning material is not particularly limited, and can be appropriately set in consideration of the strength, softness, thickness retention performance under load, etc. required for the bubble cushioning material. However, the thickness of the cap film is preferably about 10 to 100 μm as the thickness measured at the tip portion of the protrusion. More preferably, it is 12 to 60 μm, and even more preferably 14 to 50 μm. 【0028】 Also, the thickness of the back film is preferably about 10 to 80 μm as the thickness measured at the location facing the protrusion (the location not in close contact with the cap film). More preferably, it is 12 to 70 μm. 【0029】 The basis weight (weight per unit area) of the bubble cushioning material is not particularly limited and may be appropriately set in consideration of the strength, softness, thickness retention performance under load, etc. required for the bubble cushioning material, but it is preferably about 30 to 300 g / m ２ More preferably, it is 50 to 250 g / m ２ and even more preferably 80 to 200 g / m ２ is. 【0030】 [Poly(3-hydroxyalkanoate) resin] The bubble cushioning material according to the present disclosure is formed from a resin composition containing 50% by weight or more of a poly(3-hydroxyalkanoate) resin component (hereinafter, also referred to as the resin composition according to the present disclosure). 【0031】 The poly(3-hydroxyalkanoate) resin (hereinafter, may be referred to as "P3HA-based resin") is an aliphatic polyester having biodegradability (a polyester not containing an aromatic ring), and has the general formula: [-CHR-CH ２ -CO-O-] of the 3-hydroxyalkanoic acid repeating unit (wherein, R is C ｎ H２ｎ＋１ The polyhydroxyalkanoate contains an alkyl group represented by , where n is an integer between 1 and 15. In particular, it is preferable that the repeating unit is contained in an amount of 50 mol% or more relative to the total monomer repeating units (100 mol%), and more preferably 70 mol% or more. 【0032】 Among P3HA resins, poly(3-hydroxybutyrate) resins are particularly readily available and easy to process, making them a preferred choice. 【0033】 The poly(3-hydroxybutyrate) resin (hereinafter sometimes referred to as "P3HB resin") is a polyester resin containing 3-hydroxybutyrate as a repeating unit. The P3HB resin may be a poly(3-hydroxybutyrate) in which only 3-hydroxybutyrate is used as the repeating unit, or it may be a copolymer of 3-hydroxybutyrate and other hydroxyalkanoates. Furthermore, the P3HB resin may be a mixture of a homopolymer and one or more copolymers, or a mixture of two or more copolymers. 【0034】 Specific examples of the P3HB resins mentioned above include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter sometimes referred to as "P3HB3HH"), poly(3-hydroxybutyrate-co-3-hydroxyvariate) (hereinafter sometimes referred to as "P3HB3HV"), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Among these, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvariate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred because they are easy to produce industrially. 【0035】Furthermore, by changing the composition ratio of the repeating unit, the melting point and crystallinity can be changed, and physical properties such as Young's modulus and heat resistance can be changed. It is possible to impart physical properties between polypropylene and polyethylene. Also, from the perspective of being industrially easy to produce and being a physically useful plastic, P3HB3HH is preferred. In particular, among P3HB-based resins having the property of being easily thermally decomposed under heating at 180°C or higher, P3HB3HH is also preferred from the perspective of being able to lower the melting point and enabling molding processing at low temperatures. 【0036】 Examples of commercially available products of P3HB3HH include "Kaneka Biodegradable Polymer Green Planet" (registered trademark) of Kaneka Corporation. 【0037】 [Content ratio of P3HA-based resin component] The content ratio of the P3HA-based resin component in the resin composition according to the present disclosure (that is, the total content ratio of the P3HA-based resin) is 50% by weight or more. By setting the content ratio of the P3HA-based resin component to 50% by weight or more, since the P3HA-based resin has high gas barrier properties, it is possible to obtain the advantage that gas hardly escapes from the air pocket and the thickness retention performance of the bubble cushioning material is high. Also, due to the biodegradability exhibited by the P3HA-based resin, the biodegradability of the resin composition can be further improved. Preferably it is 60% by weight or more, more preferably 70% by weight or more, still more preferably 80% by weight or more, and particularly preferably 90% by weight or more. Also, the upper limit of the content ratio of the P3HA-based resin component is not particularly limited and may be 100% by weight or less, or may be 99% by weight or less. 【0038】 The P3HA-based resin component contained in the resin composition according to the present disclosure contains at least two P3HA-based resins having different types of constituent monomers and / or different content ratios of constituent monomers, and among all monomer units (the total of 3-hydroxybutyrate units and other hydroxyalkanoate units) contained in the entire P3HA-based resin component, the average molar fraction of 3-hydroxybutyrate units is preferably 70 mol% or more and less than 90 mol%. 【0039】By setting the average mole fraction of 3-hydroxybutyrate units in the entire P3HA resin component to less than 90 mol%, a softer texture can be imparted to the bubble wrap, making it suitable for packaging or packing goods. More preferably, it is 89% or less, and even more preferably 87% or less. Furthermore, by setting the average mole fraction of 3-hydroxybutyrate units to 70 mol% or more, it is possible to avoid the bubble wrap becoming excessively soft and to improve the productivity of the bubble wrap. More preferably, it is 74 mol% or more, even more preferably 78 mol% or more, and even more preferably 82 mol% or more. 【0040】 The average mole fraction of monomer units contained in the P3HA resin can be determined by methods known to those skilled in the art, for example, by the method described in paragraph

[0047] of International Publication 2013 / 147139. 【0041】 The resin composition according to this disclosure preferably contains at least one highly crystalline P3HB resin and at least one low-crystalline P3HB resin as the P3HA resin. This improves the productivity of bubble wrap and imparts a softer texture to the bubble wrap. 【0042】 Generally, highly crystalline P3HB resins offer excellent productivity but poor mechanical strength, while low-crystalline P3HB resins have lower productivity but superior mechanical properties. By using both resins in combination, it is possible to achieve both strength and productivity in bubble wrap. 【0043】 Typically, highly crystalline P3HB resins have a higher proportion of 3-hydroxybutyrate units than the average proportion of 3-hydroxybutyrate units in the entire P3HA resin, while low-crystalline P3HB resins have a lower proportion of 3-hydroxybutyrate units than the average proportion of 3-hydroxybutyrate units in the entire P3HA resin. 【0044】As a low-crystallinity P3HB resin, a copolymer (A) of 3-hydroxybutyrate units and other hydroxyalkanoate units is preferred, wherein the mole fraction of other hydroxyalkanoate units in the total monomer units (sum of 3-hydroxybutyrate units and other hydroxyalkanoate units) contained in copolymer (A) is 24 mol% or more. By using a copolymer (A) having such a monomer composition, a softer texture can be imparted to the bubble wrap. 【0045】 The mole fraction of other hydroxyalkanoate units in copolymer (A) is preferably 24 to 99 mol%, more preferably 24 to 50 mol%, even more preferably 24 to 35 mol%, and particularly preferably 24 to 30 mol%. 【0046】 The content of copolymer (A) in the total P3HA-based resin components contained in the resin composition according to this disclosure is preferably 25% by weight or more, more preferably 30% by weight or more, even more preferably 35% by weight or more, and particularly preferably 40% by weight or more, from the viewpoint of improving the softness of the bubble wrap. The upper limit is preferably 60% by weight or less, and more preferably 50% by weight or less, from the viewpoint of avoiding the bubble wrap becoming excessively soft and from the viewpoint of the productivity of the bubble wrap. 【0047】 On the other hand, as a highly crystalline P3HB resin, a copolymer (B) of 3-hydroxybutyrate units and other hydroxyalkanoate units is preferred, wherein the mole fraction of other hydroxyalkanoate units in the total monomer units (sum of 3-hydroxybutyrate units and other hydroxyalkanoate units) contained in copolymer (B) is 1 to 7 mol%. By using a copolymer (B) having such a monomer composition, it is possible to impart appropriate rigidity to the bubble wrap, prevent the bubble wrap from becoming excessively soft, and also improve the productivity of the bubble wrap. A mole fraction of other hydroxyalkanoate units in copolymer (B) is more preferably 2 to 6 mol%. Within this mole fraction range, two or more copolymers (B) with different mole fractions from each other may be used in combination. 【0048】The content of copolymer (B) in the total P3HA-based resin components contained in the resin composition according to this disclosure is preferably 25 to 75% by weight, more preferably 35 to 65% by weight, and even more preferably 45 to 60% by weight, from the viewpoint of imparting appropriate rigidity to the bubble wrap. 【0049】 The total content ratio of copolymer (A) and copolymer (B) in the P3HA-based resin component contained in the resin composition according to this disclosure is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and particularly preferably 80% by weight or more, from the viewpoint of imparting softness and rigidity suitable for packaging or packing materials to the bubble cushioning material. The upper limit is not particularly limited and may be 100% by weight or less, or 99% by weight or less. 【0050】 The resin composition according to this disclosure may contain, in addition to copolymer (A) and copolymer (B), a copolymer (C) of 3-hydroxybutyrate units and other hydroxyalkanoate units whose crystallinity is intermediate between the two copolymers. According to this embodiment, it becomes easier to control the softness, rigidity and productivity of the bubble wrap. 【0051】 In copolymer (C), the mole fraction of other hydroxyalkanoate units among all monomer units (total of 3-hydroxybutyrate units and other hydroxyalkanoate units) is preferably 8 to 23 mol%, more preferably 9 to 20 mol%, and particularly preferably 10 to 15 mol%. 【0052】 When copolymer (C) is used, the content of copolymer (C) in the total P3HA-based resin components in the resin composition according to this disclosure may be set as appropriate, but is preferably 1 to 50% by weight, more preferably 5 to 40% by weight, and even more preferably 10 to 30% by weight. However, copolymer (C) may not be used. 【0053】Other hydroxyalkanoate units contained in copolymer (A), copolymer (B), and copolymer (C) include, as described above, 3-hydroxyhexanoate units, 3-hydroxyvariate units, 4-hydroxybutyrate units, 3-hydroxyoctanoate units, 3-hydroxyoctadecanoate units, and the like. Only one type of other hydroxyalkanoate unit may be included, or two or more types may be included. Furthermore, the other hydroxyalkanoate units contained in copolymer (A), copolymer (B), and copolymer (C) may be the same as or different from each other. In particular, it is preferable that the other hydroxyalkanoate units in at least one or all of copolymer (A), copolymer (B), and copolymer (C) are 3-hydroxyhexanoate. 【0054】 The method for obtaining a blend of two or more P3HA-based resins is not particularly limited and may be by microbial production or by chemical synthesis. Alternatively, the blend may be obtained by melting and kneading two or more resins using an extruder, kneader, Banbury mixer, rolls, etc., or by dissolving two or more resins in a solvent, mixing and drying them. 【0055】 The weight-average molecular weight of the P3HA-based resin components contained in the resin composition according to this disclosure is not particularly limited, but from the viewpoint of achieving both strength and productivity of the bubble wrap, it is preferably 200,000 to 2,000,000, more preferably 250,000 to 1,500,000, and even more preferably 300,000 to 1,000,000. 【0056】 Furthermore, the weight-average molecular weight of each polymer contained in the P3HA resin component is not particularly limited and can be appropriately selected from the above numerical range. In particular, from the viewpoint of improving the thickness retention of the bubble wrap, imparting a soft texture, and reducing thickness unevenness in the protrusions, the weight-average molecular weight of copolymer (A) and copolymer (B) is preferably 400,000 or more, more preferably 500,000 or more, and particularly preferably 600,000 or more. 【0057】The weight-average molecular weight of P3HA resins can be measured using gel permeation chromatography with a chloroform solution (HPLC GPC system manufactured by Shimadzu Corporation) and converted to polystyrene equivalent. A column suitable for measuring weight-average molecular weight should be used in the gel permeation chromatography. Note that the weight-average molecular weight of P3HA resins described above is the value measured for the P3HA resin before reaction with organic peroxides. 【0058】 The method for producing the P3HA resin is not particularly limited and may be a chemical synthesis method or a microbial method. Among these, the microbial method is preferred. The microorganism may be a natural microorganism, but a microorganism transformed to produce a specific P3HA resin can be suitably used. Known transformed microorganisms can be used for this purpose. 【0059】 [Modification with Organic Peroxides] The P3HA resin component contained in the resin composition according to this disclosure may consist only of unmodified P3HA resin, but it is preferable to include a P3HA resin modified with an organic peroxide (i.e., a reaction product of P3HA resin and organic peroxide). By using a modified P3HA resin, it becomes possible to suppress thickness unevenness at the protrusions of the bubble wrap more effectively. 【0060】Examples of organic peroxides include diisobutyl peroxide, cumyl peroxyneodecanoate, di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, t-butyl peroxy 2-ethylhexanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, bis(4-t-butylcyclohexyl) peroxydicarbonate, bis(2-ethylhexyl) peroxydicarbonate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, di(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide, 1,1,3,3-tetramethyl Examples include butyl peroxy-2-ethylhexanoate, disuccinate peroxide, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, t-hexyl peroxy-2-ethylhexanoate, di(4-methylbenzoyl) peroxide, dibenzoyl peroxide, t-butyl peroxy-2-ethylhexyl carbonate, t-butyl peroxyisopropyl carbonate, 1,6-bis(t-butylperoxycarbonyloxy)hexane, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxyacetate, t-butyl peroxybenzoate, t-amyl peroxy,3,5,5-trimethylhexanoate, 2,2-bis(4,4-di-t-butylperoxycyclohexy)propane, and 2,2-di-t-butylperoxybutane. Among these, t-butyl peroxy-2-ethylhexyl carbonate, t-butyl peroxyisopropyl carbonate, and t-butyl peroxy-2-ethylhexanoate are preferred. It is also possible to use two or more of these organic peroxides in combination. 【0061】The upper limit of the amount of organic peroxide used is preferably 0.8 parts by weight or less, more preferably 0.6 parts by weight or less, and particularly preferably 0.4 parts by weight or less, per 100 parts by weight of the modified P3HA resin. The lower limit is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, and particularly preferably 0.1 parts by weight or more. By using organic peroxide in amounts within the above ranges, it becomes possible to suppress thickness variations at the protrusions of the bubble wrap more effectively. 【0062】 The P3HA resin component contained in the resin composition according to this disclosure may consist only of a modified P3HA resin, which is a reaction product of a P3HA resin and an organic peroxide as described above, or it may contain both a modified P3HA resin and an unmodified P3HA resin. In such a combination, the proportion of the modified P3HA resin in the total of the modified and unmodified P3HA resins is preferably 20% by weight or more, more preferably 30% by weight or more, and particularly preferably 50% by weight or more. The upper limit is not particularly limited and may be 100% by weight or less. 【0063】 When the resin composition according to this disclosure contains copolymer (A), it is preferable that at least a portion of copolymer (A) is copolymer (A) modified with an organic peroxide, and more preferably that all of copolymer (A) is copolymer (A) modified with an organic peroxide. Similarly, when the resin composition according to this disclosure contains copolymer (B), it is preferable that at least a portion of copolymer (B) is copolymer (B) modified with an organic peroxide, and more preferably that all of copolymer (B) is copolymer (B) modified with an organic peroxide. The same applies to copolymer (C). 【0064】 [Other Resins] The resin composition according to this disclosure may contain resins other than P3HA resins (sometimes referred to as "other resins"). The other resins are not particularly limited as long as they do not significantly reduce compatibility, moldability, or mechanical properties, but if biodegradability is required for the resin composition, biodegradable resins are preferred. 【0065】Examples of such biodegradable resins include aliphatic polyesters, which have a structure formed by the polycondensation of aliphatic diols and aliphatic dicarboxylic acids, and aliphatic aromatic polyesters, which have both aliphatic and aromatic compounds as monomers. However, the resins are not limited to these. Examples of aliphatic polyesters include polylactic acid, polycaprolactone, polyethylene succinate, polybutylene succinate (PBS), polyhexamethylene succinate, polyethylene adipate, polybutylene adipate, polyhexamethylene adipate, polybutylene succinate adipate (PBSA), polyethylene sebacate, and polybutylene sebacate. Examples of aliphatic aromatic polyesters include poly(butylene adipate-co-butylene terephthalate) (PBAT), poly(butylene sebacate-co-butylene terephthalate), poly(butylene azelate-co-butylene terephthalate), and poly(butylene succinate-co-butylene terephthalate) (PBST). 【0066】 Other resins can be used individually or in combination of two or more types. 【0067】 The content of other resins in the resin composition according to this disclosure is not particularly limited, but is preferably 100 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 30 parts by weight or less, based on 100 parts by weight of the total amount of P3HA-based resin components. It may also be 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less. The lower limit of the content of other resins is not particularly limited and may be 0 parts by weight. 【0068】[Other Components (Additives)] The resin composition relating to this disclosure may contain other components (additives). Examples of such additives include colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolites, fragrances such as vanillin and dextrin, fillers, plasticizers, antioxidants, weather-resistant modifiers, ultraviolet absorbers, crystal nucleating agents, lubricants, mold release agents, water repellents, antibacterial agents, sliding properties modifiers, etc. Only one type of additive may be included, or two or more types may be included. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use. The crystal nucleating agents, lubricants, fillers, and plasticizers will be described in more detail below. 【0069】 (Crystal Nucleating Agent) The resin composition may also contain a crystal nucleating agent. Examples of crystal nucleating agents include polyhydric alcohols such as pentaerythritol, galactitol, and mannitol; orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among these, pentaerythritol is preferred because it is particularly effective in promoting the crystallization of P3HA resins. One type of crystal nucleating agent may be used, or two or more types may be used, and the ratio of use can be appropriately adjusted depending on the purpose. The amount of crystal nucleating agent used is not particularly limited, but it is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and even more preferably 0.7 to 1.5 parts by weight, per 100 parts by weight of the total amount of P3HA resin components. 【0070】(Lubricant) The resin composition may also contain a lubricant. Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearateamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislaurylamide, ethylenebiscaprateamide, p-phenylenebisstearateamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide or erucamide are preferred because they have particularly excellent lubricating effects on P3HA resins. One lubricant may be used, or two or more may be used, and the ratio of use can be appropriately adjusted depending on the purpose. The amount of lubricant used is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and even more preferably 0.1 to 1.5 parts by weight, per 100 parts by weight of the total amount of P3HA resin components. However, the resin composition does not need to contain a lubricant. 【0071】 (Filler) The resin composition may contain a filler. Including a filler can make the bubble wrap stronger. The filler may be either an inorganic filler or an organic filler, or both may be used in combination. The inorganic filler is not particularly limited, but examples include silicates, carbonates, sulfates, phosphates, oxides, hydroxides, nitrides, carbon black, etc. Only one type of inorganic filler may be used, or two or more types may be used in combination. 【0072】 The content of the filler is not particularly limited, but is preferably 0.1 to 100 parts by weight, more preferably 0.2 to 80 parts by weight, even more preferably 0.3 to 70 parts by weight, and still more preferably 0.5 to 60 parts by weight, based on 100 parts by weight of the total amount of P3HA resin components. However, the resin composition does not need to contain the filler. 【0073】(Plasticizer) The resin composition preferably contains a plasticizer. By incorporating a plasticizer, a softer texture can be imparted to the bubble wrap. The plasticizer is not particularly limited, but from the viewpoint of compatibility with P3HA resins, it is preferable to use an ester-based plasticizer having an ester bond in its molecule. 【0074】 Examples of ester-based plasticizers include modified glycerin compounds, dibasic acid ester compounds, adipic acid ester compounds, polyether ester compounds, benzoic acid ester compounds, phthalic acid ester compounds, citrate ester compounds, sebacate acid ester compounds, isosorbide ester compounds, and polycaprolactone compounds. Among these, modified glycerin compounds, dibasic acid ester compounds, adipic acid ester compounds, polyether ester compounds, citrate ester compounds, sebacate acid ester compounds, or isosorbide ester compounds are preferred, and modified glycerin compounds are particularly preferred. Furthermore, one type of ester-based plasticizer can be used alone, or two or more types can be used in combination. When two or more types are used in combination, the mixing ratio of these ester-based plasticizers can be adjusted as appropriate. 【0075】 As the modified glycerin-based compound, glycerin ester compounds are preferred. As the glycerin ester compound, any of glycerin monoester, diester, or triester can be used, but from the viewpoint of compatibility with P3HA-based resin components, glycerin triesters are preferred. Among glycerin triesters, glycerin diacetone monoester is particularly preferred. Specific examples of glycerin diacetone monoesters include glycerin diacetone monolaurate, glycerin diacetone monooleate, glycerin diacetone monostearate, glycerin diacetone monocaprylate, and glycerin diacetone monodecanoate. Examples of the modified glycerin-based compound include Riken Vitamin Co., Ltd.'s "Rikemar" (registered trademark) PL series and "BIOCIZER" (registered trademark). 【0076】Specific examples of dibasic acid ester compounds include dibutyl adipate, diisobutyl adipate, bis(2-ethylhexyl) adipate, diisononyl adipate, diisodecyl adipate, bis[2-(2-butoxyethoxy)ethyl] adipate, bis[2-(2-butoxyethoxy)ethyl] adipate, bis(2-ethylhexyl) azelate, dibutyl sebacate, bis(2-ethylhexyl) sebacate, diethyl succinate, and mixed dibasic acid ester compounds. 【0077】 Examples of adipic acid ester compounds include diethylhexyl adipate, dioctyl adipate, and diisononyl adipate. 【0078】 Examples of polyether ester compounds include polyethylene glycol dibenzoate, polyethylene glycol dicaprylate, and polyethylene glycol diisostearate. 【0079】 Examples of citrate ester compounds include tributyl acetylcitrate. 【0080】 Examples of sebacate ester compounds include dibutyl sebacate. 【0081】 As an ester-based plasticizer, glycerin diesters are preferred, glycerin diacetone monoesters are more preferred, and glycerin diacetone monolaurates are preferred, particularly from the viewpoint of compatibility with P3HA resins. 【0082】 The amount of plasticizer added is preferably 0.1 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the total amount of P3HA-based resin components. Adding 0.1 parts by weight or more of plasticizer can improve the soft texture of the bubble wrap. Adding 20 parts by weight or less of plasticizer can improve the productivity of the bubble wrap or resin film. The lower limit is preferably 0.2 parts by weight or more, and more preferably 0.3 parts by weight or more. The upper limit is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 8 parts by weight or less. 【0083】[Method for Manufacturing Resin Composition] The resin composition according to this disclosure may be a blend of each component, or it may be a mixture of each component that has been heated and melted to form a homogenized product. The shape of the resin composition is not particularly limited and may be, for example, pellets or powder. A general-purpose kneader can be used for melt-kneading the resin composition. Such a kneader is not particularly limited, but for example, a single-screw or multi-screw extruder, a kneader, etc. can be used. 【0084】 When the P3HA resin component contains a reaction product of the P3HA resin and an organic peroxide, the reaction between the P3HA resin and the organic peroxide can be carried out by a process of melting and kneading the two in an extruder ("melt kneading process"). Alternatively, the reaction can also be carried out by a process of reacting the P3HA resin and the organic peroxide in a solution or aqueous dispersion of the P3HA resin ("submerged reaction process"). 【0085】 During the melt-kneading process, the organic peroxide can be added in various forms, such as solid or liquid. It may also be added in the form of a solution or dispersion of the organic peroxide diluted with a diluent. In particular, an organic peroxide that is liquid at room temperature (25°C) is preferred because it can be uniformly dispersed in the P3HA resin, making it easier to suppress local modification reactions in the resin composition. 【0086】 In the melt-kneading step, the P3HA resin and organic peroxide are put into an extruder and melt-kneaded. In addition to these components, other components such as the crystal nucleating agents, lubricants, fillers, and plasticizers mentioned above may also be added to the extruder and melt-kneaded. In this embodiment, it is preferable to perform melt-kneading without adding a crosslinking agent having two or more radical-reactive functional groups (e.g., epoxy groups or carbon-carbon double bonds) as disclosed in U.S. Patent No. 9,034,989. 【0087】In the aforementioned melt-mixing process, the P3HA resin, organic peroxide, and other components as needed may be added to the extruder individually, or the components may be mixed together before being added to the extruder. In particular, it is preferable to mix the organic peroxide and the P3HA resin before adding them to the extruder. This method of adding the components improves the dispersibility of the organic peroxide, making it less likely for blemishes to form in the resulting resin composition, bubble wrap, or film, thus facilitating the stable and high-quality production of these materials. 【0088】 In the melt-kneading step described above, all of the P3HA resin component may be reacted with the organic peroxide. Alternatively, a portion of the P3HA resin component may be reacted with the organic peroxide to form a reaction product, and the remaining P3HA resin may be added to this reaction product for further melt-kneading. In this case, the remaining P3HA resin added later will not react with the organic peroxide. From the standpoint of productivity and property improvement, it is preferable to react a portion of the P3HA resin component with the organic peroxide before adding the remaining P3HA resin. 【0089】 The melt-kneading process described above can be carried out according to known or conventional methods, for example, using a single-screw or multi-screw extruder, kneader, etc. The conditions for melt-kneading are not particularly limited and can be set as appropriate, but it is preferable to set the resin temperature and residence time so that the organic peroxide can complete its reaction during melt-kneading. Specifically, the resin temperature measured by the die thermometer is preferably in the range of 120 to 190°C, and more preferably 130 to 180°C. The residence time in the extruder is preferably in the range of 40 to 700 seconds, and more preferably 60 to 300 seconds. 【0090】In the liquid reaction step, the organic peroxide can be decomposed and the P3HA resin modified by heating a solution or aqueous dispersion containing the P3HA resin and an organic peroxide. This liquid reaction step allows for modification of the P3HA resin at a relatively lower temperature than the melt-kneading step, thus reducing energy consumption and suppressing thermal degradation of the P3HA resin. Furthermore, the modified P3HA resin obtained in the liquid reaction step can be added to the unmodified P3HA resin and melt-kneaded. 【0091】 [Method for Manufacturing Bubble Wrap] The bubble wrap according to this disclosure can be manufactured by known methods and is not particularly limited. The resin composition according to this disclosure may be melted and the bubble wrap directly molded, or the resin composition according to this disclosure may be melted to first produce a resin film, and then the resin film may be molded into bubble wrap. A resin film used to manufacture bubble wrap (also called a resin film for molding bubble wrap) also constitutes one aspect of the present invention. 【0092】 The method for manufacturing the bubble wrap is described below in detail. First, the resin composition according to this disclosure is put into an extruder and heated and melted, and the molten resin composition is extruded in a film shape from the T-die at the tip of the extruder. The molten resin composition may be cooled and solidified to form a resin film, or the bubble wrap may be manufactured directly without cooling and solidification. For extrusion molding, a single-screw extruder, a twin-screw extruder, etc. can be used as appropriate. 【0093】 The conditions for heating and melting the resin composition can be any conditions that allow the P3HA-based resin to melt, but it is preferable to set the outlet temperature of the T-die of the extruder to, for example, 165°C or higher and below the thermal decomposition temperature of the resin. 【0094】When manufacturing a bubble wrap directly from the resin composition according to this disclosure, the molten resin composition in film form immediately after being extruded from the T-die is brought into contact with a molding roll for the bubble wrap. The molding roll for the bubble wrap is a temperature-controlled drum in which a plurality of recesses are formed on the surface of the roll, and minute vacuum holes exist within the recesses. When the resin composition comes into contact with the molding roll, the recesses are under reduced pressure, causing the film portion facing the recesses to deform along the recesses. This forms a protruding portion of the cap film. 【0095】 Immediately after forming the protrusions on the cap film, a film-like molten resin composition extruded from a T-die of another extruder is laminated onto the back surface of the cap film (the side not in contact with the molding roll), adheres tightly, and then peeled off from the molding roll. This allows for the production of a bubble wrap material in which the cap film and back film are heat-fused together. To ensure reliable heat fusion, it is desirable to sandwich the two films between the molding roll and another heating roll. 【0096】 Furthermore, it is also possible to manufacture a resin film using the resin composition according to this disclosure by an inflation method, a T-die extrusion method, or the like, and then mold the resin film into a bubble wrap. In this case, the resin film can be used as a raw material film, and the bubble wrap can be manufactured by vacuum molding using a molding roll for bubble wrap, as described above. 【0097】 The thickness of the resin film is not particularly limited, but it is preferably less than 100 μm from the viewpoint of softening the texture of the manufactured bubble wrap and from the viewpoint of suitably forming protrusions by vacuum forming. Preferably it is 10 to 80 μm, and more preferably 15 to 60 μm. 【0098】The elastic modulus of the resin film is preferably 100 to 1500 MPa in both the MD and TD directions of the resin film. A modulus of elasticity of 100 MPa or higher provides the bubble wrap with appropriate rigidity. More preferably, it is 150 MPa or higher, even more preferably 200 MPa or higher, and even more preferably 400 MPa or higher. Furthermore, a modulus of elasticity of 1500 MPa or lower provides the bubble wrap with a soft texture. More preferably, it is 1200 MPa or lower, and even more preferably 1000 MPa or lower. 【0099】 The bubble wrap material described herein contains P3HA-based resin components as its main component, and therefore can exhibit high biodegradability in natural environments such as seawater or soil. For this reason, it is extremely promising as a bubble wrap material to solve the problem of waste plastics or microplastics. 【0100】 The following items list preferred embodiments of the present disclosure, but the present invention is not limited to the following items. [Item 1] A bubble cushioning material comprising a cap film having a plurality of protrusions formed thereon and a back film laminated on the back surface of the cap film, wherein gas is sealed between the protrusions and the back film, and the bubble cushioning material is molded from a resin composition containing 50% by weight or more of a poly(3-hydroxyalkanoate) resin component. [Item 2] In a graph plotted with strain [mm] on the horizontal axis and test force [N] on the vertical axis in a tensile test performed on the bubble cushioning material, the maximum slope [N / mm] in the region of strain of 5% or less is defined as the basis weight [g / m] of the bubble cushioning material. ２ The value obtained by dividing by ] is between 0.03 and 0.20 (N・m ２[Item 3] The bubble cushioning material according to item 1, wherein the thickness deviation of the cap film at the protrusion is 25 or less. [Item 4] The bubble cushioning material according to any one of items 1 to 3, wherein the thickness of the cap film at the protrusion is 10 to 100 μm, and the thickness of the back film at the location facing the protrusion is 10 to 80 μm. [Item 5] The bubble cushioning material according to any one of items 1 to 4, wherein the thickness retention rate (%) measured after holding a load of 7 kg for 7 days by compression creep is 50% or more. [Item 6] The bubble cushioning material according to any one of items 1 to 5, wherein the average mole fraction of 3-hydroxybutyrate units among the total monomer units contained in the poly(3-hydroxyalkanoate) resin component is 70 mol% or more and less than 90 mol%. [Item 7] The foam cushioning material according to any one of Items 1 to 6, wherein the poly(3-hydroxyalkanoate) resin component comprises a copolymer (A) of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the mole fraction of other hydroxyalkanoate units is 24 mol% or more. [Item 8] The foam cushioning material according to Item 7, wherein the copolymer (A) accounts for 25% by weight or more of the poly(3-hydroxyalkanoate) resin component. [Item 9] A method for producing the foam cushioning material according to any one of Items 1 to 8, comprising the steps of melting the resin composition to form the foam cushioning material, or forming a resin film molded from the resin composition into a foam cushioning material. [Item 10] A method for manufacturing a bubble wrap according to Item 9, comprising the steps of: controlling the outlet temperature of the T-die of an extruder to 165°C or higher; bringing the resin composition extruded from the T-die into contact with a temperature-controlled drum having a plurality of recesses on its surface and vacuum holes in the recesses, thereby forming a cap film with a plurality of protrusions; and heat-sealing a back film to the back surface of the cap film. 【0101】 The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to these examples. 【0102】In the examples, the following raw materials were used. (Poly(3-hydroxyalkanoate) resin) As the P3HA resin, the following poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) resins A-1 to A-8 were used. Below, 3HB represents the 3-hydroxybutyrate repeating unit, and 3HH represents the 3-hydroxyhexanoate repeating unit. A-1: ​​P3HB3HH (average content ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%), weight-average molecular weight is 660,000 g / mol, glass transition temperature is 1°C) It was manufactured in accordance with the method described in Example 9 of International Publication No. 2019 / 142845. A-2: P3HB3HH (average content ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%), weight-average molecular weight 380,000 g / mol, glass transition temperature 1°C) A-3: P3HB3HH (average content ratio 3HB / 3HH = 97.2 / 2.8 (mol% / mol%), weight-average molecular weight 660,000 g / mol, glass transition temperature 6°C) Manufactured according to the method described in Example 2 of International Publication No. 2019 / 142845. A-4: P3HB3HH (average content ratio 3HB / 3HH = 97.2 / 2.8 (mol% / mol%), weight-average molecular weight 380,000 g / mol, glass transition temperature 6°C) Manufactured according to the method described in Example 2 of International Publication No. 2019 / 142845. A-5: P3HB3HH (average content ratio 3HB / 3HH = 89.5 / 10.5 (mol% / mol%), weight-average molecular weight 1,220,000 g / mol, glass transition temperature 5°C) Manufactured according to the method described in Comparative Example 1 of International Publication No. 2015 / 146195. A-6: P3HB3HH (average content ratio 3HB / 3HH = 89.4 / 10.6 (mol% / mol%), weight-average molecular weight 750,000 g / mol, glass transition temperature 5°C) Manufactured according to the method described in Comparative Example 1 of International Publication No. 2015 / 146195. A-7: P3HB3HH (average content ratio 3HB / 3HH = 95.0 / 5.0 (mol% / mol%), weight-average molecular weight is 560,000 g / mol, glass transition temperature is 2°C) Manufactured according to the method described in Example 1 of International Publication No. 2019 / 142845.A-8: P3HB3HH (average content ratio 3HB / 3HH = 94.7 / 5.3 (mol% / mol%), weight-average molecular weight 400,000 g / mol, glass transition temperature 2°C) was prepared according to the method described in Example 1 of International Publication No. 2019 / 142845. 【0103】 (Plasticizer) B-1: Biocizer (manufactured by Riken Vitamin Co., Ltd., ester-based plasticizer: glycerin diacetomolaurate) 【0104】 (Organic peroxide) C-1: Perbutyl I (t-butyl peroxyisopropyl carbonate, 1-minute half-life temperature: 159°C) manufactured by NOF Corporation 【0105】 (Crystal nucleating agent) D-1: Pentaerythritol (manufactured by Mitsubishi Chemical Corporation, Neulizer P) 【0106】 In each example and comparative example, the following evaluations were performed: [Melting viscosity] Using a Shimadzu capillary rheometer, the volumetric flow rate (Q) of 0.716 cm was measured from an orifice with a radius (d) of 0.05 cm and a capillary length (l) of 1 cm, connected to the end of a barrel with a barrel setting temperature of 170°C and a radius (D) of 0.4775 cm. ３ / min, shear rate 122sec －１ The molten resin composition was extruded, and the load (F) at that time was measured. The apparent melt viscosity (η) was calculated from the above formula (1). 【0107】 [Drawdown Time] When measuring the melt viscosity as described above, the time required for the molten resin composition dispensed from the orifice to fall 30 cm was measured and defined as the drawdown time (DT). 【0108】[Elastic Modulus of Resin Film] Resin pellets were fed into an extruder and extruded into a film with a thickness of 25 μm using a T-die. The film was then formed by contacting it with a molding roll at a set temperature of 60°C. The resulting resin film was cured for two weeks in an environment of 23°C and 50% RH. Then, a tensile test was performed using a tensile testing machine (Shimadzu Corporation: EZ-LX 1kN) in accordance with JIS K 7127, at a tensile speed of 100 mm / min. Based on the SS curve obtained from the tensile test, the elastic modulus of the resin film was calculated from the stress rise at the initial stage of tensile strain. The elastic modulus was obtained for both the MD and TD directions of the resin film. 【0109】 [Thickness of the resin film] The thickness of the resin film obtained in the measurement of the elastic modulus was measured at 20 locations using a contact-type thickness gauge. The average thickness was calculated from the obtained values. 【0110】 [Thickness and Thickness Deviation of Protrusions on Bubble Wrap Sheets] Twenty protrusions were cut out from a bubble wrap sheet. The thickness of the tip of each cut-out protrusion was measured using a contact-type thickness gauge. From the obtained values, the average and deviation of the protrusion thicknesses were calculated and recorded in the table. 【0111】 [Thickness of the bonded portion of the bubble wrap sheet] Using bubble wrap with the protrusions cut off, the thickness of the back film in the areas where the protrusions were removed (the thickness of the back film in the areas not in close contact with the cap film) was measured at 20 locations using a contact-type thickness gauge. The average value was calculated from the obtained values ​​and is listed in the table as the thickness of the bonded portion. 【0112】 [Basis weight of bubble wrap sheet] From the bubble wrap sheet, the area is 1 m ２ Cut out a sample for measurement, measure its weight, and determine the basis weight (g / m²) of the bubble wrap sheet. ２ ) 【0113】[Maximum Slope and Elastic Modulus during Tensile Test of Bubble Wrap Sheet] A test specimen measuring 80 mm in the longitudinal direction (MD direction) and 35 mm in the transverse direction (TD direction) was cut from a bubble wrap sheet. The distance between the chucks was set to 40 mm, and a tensile test was performed using a tensile testing machine (Shimadzu Corporation: EZ-LX) under the conditions of a tensile speed of 500 mm / min and a sampling interval of 0.01 sec. The obtained results were plotted on a graph with strain [mm] on the horizontal axis and test force [N] on the vertical axis. The slope of the curve was calculated for each plotting interval, and the value of the largest slope in the region of strain 5% or less (elongation 2 mm or less) was defined as the maximum slope during the tensile test [N / mm]. The obtained maximum slope during the tensile test was used in relation to the basis weight (g / m²) of the bubble wrap sheet. ２ The value obtained by dividing by ) is the elastic modulus of the bubble cushioning material [(N・m ２ The elastic modulus of the bubble wrap was set to ) / (g・mm). The above measurements were performed at 10 points in the MD direction and 10 points in the TD direction, and the average value of the obtained calculated values ​​is shown in the table. The smaller the value of the elastic modulus of the bubble wrap, the softer the texture of the bubble wrap sheet. In addition, air pockets in the bubble wrap sheet were not crushed during the tensile test, except for those that burst when the test piece was cut out. 【0114】 [Thickness retention rate (%) due to compression creep of bubble wrap sheets] Ten test pieces measuring 150 mm x 150 mm were cut from a bubble wrap sheet. Similarly, nine sheets of printing paper measuring 150 mm x 150 mm were cut. The ten bubble wrap sheets and nine sheets of printing paper were stacked alternately on a horizontal table, and a flat plate weighing just enough so as not to crush the air pockets in the bubble wrap sheets was placed on top. The height from the table surface to the bottom of the plate was measured to obtain the initial height. Next, with the bubble wrap sheets and printing paper still stacked alternately, a load of 7 kg was placed on the flat plate. After standing for 7 days in an environment of 23°C x 50% RH, the load was removed, and the height from the table surface to the bottom of the plate was measured again to obtain the height after 7 days. The height after 7 days was divided by the initial height to obtain the thickness retention rate (%). A higher thickness retention rate indicates that the thickness of the bubble wrap sheet is retained. 【0115】(Example 1) (Method for producing the resin composition) 45 parts by weight of poly(3-hydroxyalkanoate) resin A-1, 45 parts by weight of A-3, and 10 parts by weight of A-8 were dry-blended with 4.5 parts by weight of B-1 as a plasticizer, 0.135 parts by weight of C-1 as an organic peroxide, and 1.0 part by weight of D-1 as a crystal nucleating agent. The obtained resin material was put into a φ26 mm co-screw extruder hopper with the cylinder temperature and die temperature set to 150°C, and after the crosslinking reaction was carried out and completed in the extruder, it was further melt-kneaded, extruded from the die onto strands, passed through a water bath filled with 45°C water to solidify the strands, and cut with a pelletizer to obtain resin pellets P-1. The melt viscosity (η), drawdown time (DT), and DT / η of the obtained resin pellets are shown in Table 1. 【0116】 (Manufacturing of bubble wrap sheets) Two φ65 mm single-screw extruders, each connected to a 500 mm wide T-die, were set to a cylinder temperature of 160°C and connecting pipe and die temperatures of 165°C. The resin pellets P-1 were fed into each single-screw extruder and extruded into a film shape by the T-die. The cap film discharged from one T-die was vacuum-formed on a bubble wrap molding roll (a temperature-controlled drum with multiple recesses on its surface and vacuum holes within the recesses) connected to a vacuum pump at a set temperature of 60°C, forming numerous hollow, bulging protrusions on the cap film. Immediately afterward, a back film discharged from the other T-die was heat-fused to the back surface of the cap film to obtain a bubble wrap sheet with multiple air pockets containing air. The obtained bubble wrap sheets were evaluated. The evaluation results are shown in Table 1. 【0117】 (Example 2) A bubble wrap sheet was manufactured and evaluated in the same manner as in Example 1, except that the rotation speed of the extruder was changed so that the thickness of the protrusion portion was 46 μm and the thickness of the bonded portion was 61 μm. The evaluation results are shown in Table 1. 【0118】(Examples 3-4) Resin pellets and bubble wrap sheets were manufactured and evaluated in the same manner as in Example 1, except that the amounts of poly(3-hydroxyalkanoate) resin, plasticizer, organic peroxide, and crystal nucleating agent were changed as shown in Table 1. The evaluation results are shown in Table 1. 【0119】 (Comparative Examples 1-2) Except for using polyethylene resin pellets or polyethylene terephthalate resin pellets as the resin pellets, bubble wrap sheets were manufactured and evaluated using the method for manufacturing bubble wrap sheets described in Example 1. The evaluation results are shown in Table 1. 【0120】 【0121】 Table 1 shows that the bubble cushioning sheets of Examples 1 to 4 have small thickness deviation values ​​at the protrusions, suppressing thickness unevenness; have a small elastic modulus value, giving them a soft texture; and have a large thickness retention rate due to compression creep, indicating good thickness retention under load. 【0122】 On the other hand, the bubble cushioning sheet of Comparative Example 1, which uses polyethylene, has a soft texture, but its thickness retention rate is extremely low, indicating that it is significantly inferior in thickness retention under load. The bubble cushioning sheet of Comparative Example 2, which uses polyethylene terephthalate, has good thickness retention under load, but its elastic modulus is extremely high, indicating that it has a hard texture.

Claims

1. A bubble wrap material comprising a cap film having a plurality of protrusions formed thereon and a back film laminated on the back surface of the cap film, wherein gas is sealed between the protrusions and the back film, and the bubble wrap material is molded from a resin composition containing 50% by weight or more of a poly(3-hydroxyalkanoate) resin component.

2. In the graph plotted in the tensile test conducted on the bubble cushioning material, with strain [mm] on the horizontal axis and test force [N] on the vertical axis, the maximum slope [N / mm] in the region of strain 5% or less is defined as the basis weight [g / m] of the bubble cushioning material. ２ The value obtained by dividing by ] is between 0.03 and 0.20 (N・m ２ The bubble wrap according to claim 1, wherein the volume is ) / (g・mm).

3. The bubble wrap according to claim 1, wherein the thickness deviation of the cap film at the projection is 25 or less.

4. The bubble wrap according to claim 1, wherein the thickness of the cap film at the projection is 10 to 100 μm, and the thickness of the back film at the portion facing the projection is 10 to 80 μm.

5. The bubble wrap according to claim 1, wherein the thickness retention rate (%) measured after holding a load of 7 kg for 7 days by compression creep is 50% or more.

6. The bubble wrap according to claim 1, wherein the average mole fraction of 3-hydroxybutyrate units among all monomer units contained in the poly(3-hydroxyalkanoate) resin component is 70 mol% or more and less than 90 mol%.

7. The foam buffer according to claim 1, wherein the poly(3-hydroxyalkanoate) resin component comprises a copolymer (A) of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the mole fraction of other hydroxyalkanoate units is 24 mol% or more.

8. The bubble wrap according to claim 7, wherein the proportion of copolymer (A) in the poly(3-hydroxyalkanoate) resin component is 25% by weight or more.

9. A method for producing a bubble cushioning material according to any one of claims 1 to 8, comprising the steps of: melting the resin composition to form a bubble cushioning material; or forming a resin film formed from the resin composition into a bubble cushioning material.

10. A method for producing a bubble wrap according to claim 9, comprising the steps of: controlling the outlet temperature of the T-die of an extruder to 165°C or higher; bringing the resin composition extruded from the T-die into contact with a temperature-controlled drum having a plurality of recesses on its surface and vacuum holes in the recesses, thereby forming a cap film with a plurality of protrusions; and heat-sealing a back film to the back surface of the cap film.

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