A preform structure conducive to stretch blow molding

Abstract

A bottle blank structure conducive to stretch blow molding comprises an integrally injection-molded bottle blank, wherein the bottle blank comprises a bottle mouth, a bottleneck, a blank body and a blank bottom which are connected in sequence, and the blank bottom is arranged as an upper bottom and a lower bottom which are connected, and the bottom end of the lower bottom is lower than the convergence point formed by the extension line of the upper bottom generatrix curve segment I, so that the blank bottom forms a downwardly protruding lower bottom on the basis of the upper bottom molding, and the lower bottom serves as a pre-stretching structure of the blank bottom, so that the blank bottom is fully expanded during the stretch blow molding process, so that serious material accumulation at the bottle bottom is avoided, and more material is distributed to the rest of the bottom of the bottle blank, so that when designing the bottle blank, the blank bottom wall thickness can be designed to be thinner, so as to achieve the purpose of lightweighting.

Description

Technical Field

[0001] The invention relates to the technical field of bottle preform structures, and in particular to a bottle preform structure which is conducive to stretch blow molding. Background Art

[0002] With the improvement of living standards, the containers made of glass, ceramics, metals, etc. that were commonly used in the past are gradually being replaced by plastic containers. Compared with containers made of glass, ceramics, metals, etc., plastic containers have the advantages of light weight, not easy to break, and low production and transportation costs.

[0003] Among beverage packaging containers, the most common is PET bottle, and PET bottles have also been widely used in various areas of life, such as food, chemical industry, medicine and many other fields, so the demand for PET bottles is very large. According to statistics, China's PET bottle consumption in 2018 has exceeded 10 million tons, and the demand is gradually increasing. Therefore, the lightweighting of PET bottles is an important part of environmental protection and energy saving. In the lightweight design of PET bottles, even if each PET bottle can be reduced by 0.1g, it is a historic breakthrough in environmental protection and energy saving in this field for the consumption of 10 million tons of PET bottles.

[0004] The manufacturing and molding of PET bottles is generally to first use an injection molding machine to inject the preform into a bottle, and then use a bottle blowing machine to stretch and blow mold the preform into a bottle. Figures 1 to 3 As shown, the bottom of the PET preform currently on the market is generally ellipsoidal, hemispherical and conical. In the process of stretch blow molding, the preform is stretched by a stretch rod and gas blown. The chemical bonds in the PET molecular chain are much stronger than the action between the molecular chains. In the stretching process, the chemical bonds in the molecule are mainly relied on to resist the external pulling force. The stretching of the PET material will greatly improve the strength of the PET material along the stretching direction. In this process, the larger the contact area between the bottom of the stretch rod and the bottom of the preform, the less likely the material in contact with the bottom will be stretched. Before pre-blowing, the stretch rod will stretch the preform, and a part of the bottom of the preform will envelop the stretch rod. This part is not easy to be stretched during the blow molding process. When the bottom of the preform reaches the bottom of the mold and contacts the mold, the material at the bottom of the preform is easy to cool too early, resulting in the bottom of the preform that has not been fully stretched being more difficult to stretch. All of the above reasons will lead to insufficient stretching of the material at the bottom of the preform. Bottles formed by stretch blow molding are prone to problems such as excessive accumulation of material at the bottom, too thick center point, and easy cracking of the bottom due to stress. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a bottle blank structure that is conducive to stretch blow molding.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A bottle blank structure conducive to stretch blow molding comprises an integral injection-molded bottle blank, the bottle blank comprising a bottle mouth, a bottleneck, a blank body and a blank bottom connected in sequence, a blank cavity is arranged in the bottle blank, the blank bottom comprises a connected upper bottom and a lower bottom, the construction lines of the corresponding upper bottom and lower bottom are connected curve segments I and curve segments II respectively, the upper bottom is formed by rotating 360° with curve segment I as a generatrix and a center line of the bottle blank as a rotation axis; the lower bottom is formed by rotating 360° with curve segment II as a generatrix and a center line of the bottle blank as a rotation axis; the bottommost end of the lower bottom is lower than the convergence point of the extension line of curve segment I.

[0008] As a further improvement of the present invention, the lower bottom includes a concave surface and a wave crest convexity for preventing material from piling up when the bottle bottom is formed, the concave surface is sunken toward the blank cavity, the wave crest convexity is convex toward the blank cavity, and the concave surface is arranged at the bottom of the blank cavity.

[0009] As a further improvement of the present invention, the bottle blank is provided with inner construction lines and outer construction lines respectively used to constitute the inner wall and outer wall of the bottle blank, the inner construction lines of the bottom of the blank are composed of arc lines I, arc lines II, arc lines III and arc lines IV connected in sequence, the concave surface is formed by rotating 360° with arc line IV as the generatrix and the center line of the bottle blank as the rotation axis; the wave crest convexity is formed by rotating 360° with arc line III as the generatrix and the center line of the bottle blank as the rotation axis.

[0010] As a further improvement of the present invention, the outer structural line of the bottom of the blank is composed of arc line i, arc line ii, arc line iii and arc line iv connected in sequence, and the arc line i, arc line ii, arc line iii and arc line iv are respectively arranged corresponding to the arc line i, arc line ii, arc line iii and arc line iv, and the arc line ii, arc line iii and arc line iv are respectively formed by the arc line ii, arc line iii and arc line iv offset outward by the same distance.

[0011] As a further improvement of the present invention, the centers of the arc line IV and the arc line iv coincide with each other and are both located on the center line of the preform.

[0012] As a further improvement of the present invention, the blank body includes a bottleneck transition part, a blank main part and a blank bottom transition part which are connected in sequence, the bottleneck transition part is a hollow cone shape, the blank main part is a hollow cylindrical shape, and the two ends of the blank bottom transition part are respectively connected to the blank main part and the blank bottom.

[0013] As a further improvement of the present invention, the inner construction line and the outer construction line of the bottleneck transition part are oblique line segment I and oblique line segment i respectively, and the angle between the extension line of the oblique line segment I and the center line of the bottle blank is greater than the angle between the extension line of the oblique line segment i and the center line of the bottle blank, so that the wall thickness of the bottleneck transition part gradually increases from near the bottleneck to near the main part of the blank.

[0014] As a further improvement of the present invention, the inner construction line and the outer construction line of the main body of the blank are respectively a straight line segment I and a straight line segment i which are parallel to each other.

[0015] As a further improvement of the present invention, the inner construction line and the outer construction line of the transition part of the bottom of the blank are respectively a straight line segment II and an arc line V.

[0016] As a further improvement of the present invention, the bottleneck is a circular ring structure, and the inner construction line and the outer construction line of the bottleneck are respectively a straight line segment III and a straight line segment ii which are parallel to each other.

[0017] The beneficial effects of the present invention are as follows: by setting the bottom of the blank as a connected upper bottom and a lower bottom, and the bottommost end of the lower bottom is lower than the convergence point formed by the extension line of the upper bottom generatrix curve segment I, the blank bottom forms a downwardly protruding lower bottom on the basis of the upper bottom molding, and the lower bottom serves as a pre-stretching structure of the blank bottom, so that the blank bottom can be fully expanded during the stretch blow molding process, thereby avoiding serious material accumulation at the bottle bottom, and more material is distributed to the rest of the bottom of the bottle blank, so that when designing the bottle blank, the wall thickness of the blank bottom can be designed to be thinner to achieve the purpose of lightweight; in addition, through the concave-convex surface design formed by the concave surface and the wave crest convexity in the blank bottom, during the bottle blowing process, the stretching rod can be positioned using the concave surface, and the wave crest convexity adjacent to the concave surface is used to prevent the blank bottom from enveloping the stretching rod, and the concave-convex surface design can reduce the contact area between the bottom of the bottle blank and the stretching rod, so that the bottom of the bottle blank can be fully expanded and the center of the bottle bottom is avoided from being too thick. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0019] Figure 1 It is a schematic diagram of the structure of a bottle blank with an ellipsoidal bottom in the prior art;

[0020] Figure 2 It is a schematic diagram of the structure of a bottle blank with a hemispherical bottom in the prior art;

[0021] Figure 3 It is a schematic diagram of the structure of a bottle blank with a conical bottom in the prior art;

[0022] Figure 4 This is a schematic diagram of the external structure of the bottle blank structure of this embodiment;

[0023] Figure 5 This is a schematic diagram of the internal structure of the bottle blank structure of this embodiment;

[0024] Figure 6 This is a schematic structural diagram of the blank bottom of this embodiment;

[0025] Figure 7 It is a schematic diagram of the structure of the inner and outer structural lines of the bottle blank in this embodiment. DETAILED DESCRIPTION

[0026] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0027] Example:

[0028] like Figures 4 to 7As shown, this embodiment discloses a bottle blank structure that is conducive to stretch blow molding, including an integrally injection molded bottle blank, the bottle blank including a bottle mouth (1), a bottleneck (2), a blank body (3) and a blank bottom (4) connected in sequence, the axial length of the bottleneck (2) is preferably 5-6 mm. Since the bottle blank is used for bottle blow molding, the bottleneck (2) serves as a clamp during bottle blowing. For a standard thickness of the bottleneck (2) of about 4-4.5 mm, if the axial length of the bottleneck (2) is less than 5 mm, it is easy to cause the bottle blank to be clamped. If the axial length of the bottleneck (2) is greater than 6 mm, since the bottleneck (2) does not participate in the stretching during bottle blowing, it will cause excessive material waste. At the same time, the bottleneck transition part (31) produced by blow molding is prone to material accumulation, which affects the appearance of the bottle and market demand. In addition, in order to ensure that the molding effect of the bottom of the bottle preform after stretch blow molding is more integrated, the ratio of the axial length of the bottom of the preform (4) to the axial length of the bottle preform is 9% to 15%, and the ratio of the axial length of the bottom of the preform (4) to the axial length of the bottle preform cannot be too low. If the ratio of the axial length of the bottom of the preform (4) to the axial length of the bottle preform is less than 9%, when the bottle preform is stretched and blow molded, the bottom of the preform (4) and the body of the preform (3) do not have a sufficient axial length of stretching distance, so that visible stripes may appear at the connection between the two, affecting the appearance and pressure resistance of the bottle, and even causing the filling liquid in the bottle to be filled. Of course, the ratio of the axial length of the bottom of the preform (4) to the axial length of the preform cannot be too high. If the ratio of the axial length of the bottom of the preform (4) to the axial length of the preform is greater than 15%, it is easy to cause excessive accumulation of the bottle bottom material and waste of material. Because when the bottle preform is stretched and blow molded, the stretch rod enters along the bottle mouth direction and performs axial stretching along the center line of the bottle preform. The molding material of the bottom of the preform will be stretched as the stretch rod moves. Since the ratio of the axial length of the bottom of the preform to the axial length of the bottle preform is greater than 15%, the bottom of the preform cannot be fully stretched and the bottle bottom material is formed. The preform is provided with a preform cavity (5), and the preform bottom (4) includes a connected upper bottom (B) and a lower bottom (D), and the corresponding construction lines of the upper bottom (B) and the lower bottom (D) are connected curve segments I (b) and curve segments II (d), respectively. The upper bottom (B) is formed by rotating 360° with curve segment I (b) as the generatrix and the center line of the preform as the rotation axis; the lower bottom (D) is formed by rotating 360° with curve segment II (d) as the generatrix and the center line of the preform as the rotation axis; the bottom end of the lower bottom (D) is lower than the convergence point of the extension line of curve segment I (b). The curve segments I (b) and II (d) can be curve segments of any structural form, and the technical effect of the utility model can be achieved.By setting the blank bottom (4) as a connected upper bottom (B) and a lower bottom (D), and the bottommost end of the lower bottom (D) is lower than the convergence point formed by the extension line of the generatrix curve segment I (b) of the upper bottom (B), the blank bottom (4) forms a downwardly protruding lower bottom (D) on the basis of the upper bottom (B) being formed, and the lower bottom (D) serves as a pre-stretching structure of the blank bottom (4), so that the blank bottom (4) is fully expanded during the stretch blow molding process, thereby avoiding serious accumulation of material at the bottle bottom and distributing more material to the rest of the bottle blank bottom (4), so that when designing the bottle blank, the wall thickness of the blank bottom (4) can be designed to be thinner, thereby achieving the purpose of lightweighting.

[0029] As a preferred embodiment, the blank body (3) and the blank bottom (4) are tangentially connected, the lower bottom (B) comprises a concave surface (41) and a wave crest protrusion (42) for preventing material from being piled up when the bottle bottom is formed, the concave surface (41) is concave in the direction of the blank cavity (5), the wave crest protrusion (42) is convex in the direction of the blank cavity (5), the concave surface (41) and the wave crest protrusion (42) are tangentially connected, and the concave surface (41) is arranged at the bottom of the blank cavity (5). By arranging the wave crest protrusion (42) at the bottom of the preform and combining the tangent connection structure design between the preform body (3) and the preform bottom (4), the preform bottom (4) can be fully expanded during the stretch blow molding process, thereby avoiding serious material accumulation at the bottom of the bottle, and more material is distributed to the rest of the bottom of the preform. Therefore, when designing the preform, the wall thickness of the preform bottom (4) can be designed to be thinner, thereby achieving the purpose of lightweighting. In addition, through the concave surface (41) in the bottom of the preform (4) and the wave crest protrusion (42) formed by the concave surface (41) and the wave crest protrusion (42), during the bottle blowing process, the stretching rod can be positioned using the concave surface (41), and the wave crest protrusion (42) adjacent to the concave surface (41) is used to prevent the preform bottom (4) from enveloping the stretching rod. The concave surface design can reduce the contact area between the bottom of the bottle and the stretching rod, thereby allowing the bottom of the bottle to be fully expanded and avoiding the center of the bottle bottom being too thick.

[0030] As a preferred embodiment, the bottle blank is provided with inner construction lines and outer construction lines for forming the inner wall and outer wall of the bottle blank respectively, and the inner construction lines of the bottom (4) of the blank are composed of arc lines I (400), arc lines II (401), arc lines III (402) and arc lines IV (403) connected in sequence, preferably connected tangentially to each other, wherein the arc radius of the arc line I (400) is the largest, accounting for 80% to 90% of the inner diameter of the main body (32) of the blank, and the arc radius of the arc line I (400) cannot be too small. When the arc radius of the arc line I (400) accounts for less than 80% of the inner diameter of the main body (32) of the blank, the wall thickness of the bottom (4) of the blank is relatively thick, and the overall gram weight of the bottle blank will be increased. The bottle bottom (4) is enlarged, which does not meet the requirement of lightweight bottle blank. During the stretch blow molding process of the bottle blank, the material of this part will move inward as the stretching rod stretches. When the blank bottom (4) is stretched, there may be a phenomenon of enveloping the stretching rod, and even delamination from the blank body may occur, and a smooth inner wall cannot be formed, resulting in the bottle stretched out of the bottle blank being a defective product; the arc radius of arc line I (400) cannot be too large. When the arc radius of arc line I (400) accounts for more than 90% of the inner diameter of the blank main part (32), the wall thickness of the blank bottom (4) is thin, and the space occupied by arc line II (401), arc line III (402) and arc line IV (403) in the entire blank bottom will be compressed, resulting in insufficient pressure resistance of the formed bottle bottom. At this time, the concave surface (41) is formed by rotating 360° with the arc line IV (403) as the generatrix and the center line of the bottle blank as the rotation axis; the wave crest convexity (42) is formed by rotating 360° with the arc line III (402) as the generatrix and the center line of the bottle blank as the rotation axis. In this embodiment, in order to further optimize the molding structure of the blank bottom (4), the arc radius of the arc line IV (403) constituting the concave surface (41) is preferably 2 to 5 mm. The arc radius of the arc line IV (403) cannot be too small. When the arc radius of the arc line IV (403) is less than 2 mm, the concave surface serving as the positioning position of the stretching rod during stretching will be too small, resulting in the stretching rod being unable to be positioned or the positioning stability being low. Of course, the arc radius of the arc line IV (403) cannot be too large. When the arc radius of the arc line IV (403) is greater than 5 mm, the area of ​​the concave surface (41) formed will be too large, and the contact area between the stretching rod and the blank bottom will increase accordingly. The material in this part is not easy to be stretched, which easily leads to material accumulation at the bottom of the bottle. The arc radius of the arc line III (402) constituting the wave crest protrusion (42) is preferably 3 to 5 mm. The arc radius of the arc line III (402) cannot be too small. When the arc radius of the arc line III (402) is less than 3 mm, the distance between the wave crest protrusion (42) and the stretching rod is relatively close, and the wave crest protrusion (42) cannot prevent the blank bottom (4) from enveloping the stretching rod. When the arc radius of the arc line III (402) is greater than 5 mm, the gram weight of the blank bottom (4) will be greatly increased, and when the blank bottom (4) is stretched and blow molded to form a bottle bottom, material accumulation will be formed due to insufficient stretching.The distance between the bottom of the concave surface (41) and the top of the wave crest protrusion (42) is preferably 0.5 to 2 mm. The distance between the bottom of the concave surface (41) and the top of the wave crest protrusion (42) is the spatial distance of the axial length occupied by the concave surface (41) and the wave crest protrusion (42). If the distance between the bottom of the concave surface (41) and the top of the wave crest protrusion (42) is less than 0.5 mm, the stretching positioning and anti-wrapping rod structure formed by the concave surface (41) and the wave crest protrusion (42) is too small to form a sufficient positioning structure and anti-wrapping rod structure. The structure of the preform is different from that of the conventional The structure of the bottle blank with an ellipsoidal or spherical bottom is the same. During the stretch blow molding process, there will also be a problem that the contact area between the bottom of the blank (4) and the stretching rod is large, and the bottom of the blank (4) cannot be fully stretched. If the distance between the bottom of the concave surface (41) and the top of the wave crest protrusion (42) is greater than 2 mm, the concave surface (41) and the wave crest protrusion (42) will affect the molding of the entire bottle bottom after the bottom of the blank (4) is stretched and formed. After the bottle bottom is formed, the bottle bottom part still has obvious molding structures of the concave surface (41) and the wave crest protrusion (42), which affects the molding of the bottle bottom. The normal angle between the two ends of the arc line III (402) constituting the wave crest protrusion (42) is α, which is one of the factors controlling the size of the wave crest protrusion (42). The preferred range of α is 18° to 30°. If α is less than 18°, the wave crest protrusion (42) is too small, resulting in the wave crest protrusion (42) being unable to prevent the blank bottom (4) from enveloping the stretching rod. If α is greater than 30 degrees, the wave crest protrusion (42) is too large, and the gram weight of the blank bottom (4) will be greatly increased. Moreover, when the blank bottom (4) is stretched and blow molded to form a bottle bottom, material accumulation will be formed due to insufficient stretching.

[0031] As a preferred embodiment, the outer structural line of the blank bottom (4) is composed of arc line i (400'), arc line ii (401'), arc line iii (402') and arc line iv (403') connected in sequence, preferably connected tangentially to each other, and the arc line i (400'), arc line ii (401'), arc line iii (402') and arc line iv (403') are respectively connected to the arc line i (400), arc line ii (401'), arc line iii (402') and arc line iv (403'). Correspondingly, the arc line II (401'), the arc line III (402') and the arc line IV (403') are respectively formed by the arc line II (401), the arc line III (402) and the arc line IV (403) being offset outward by the same distance, so that the arc line II (401'), the arc line III (402') and the arc line IV (403') have the same shape as the arc line II (401), the arc line III (402) and the arc line IV (403), respectively, and the centers of the corresponding arcs are at the same position. Furthermore, the wall thickness of the blank bottom (4) is the distance from the normal line of each point on the inner surface of the blank bottom (4) to the outer surface of the blank bottom (4). By balancing the requirements of the injection molding pressure and the thickness of the bottle bottom, the preferred range of the blank bottom (4) wall thickness to the blank body wall thickness is 85% to 95%. If the blank bottom (4) wall thickness is too thin, the blank bottom (4) wall thickness accounts for less than 85% of the blank body wall thickness, the injection molding pressure of the bottle preform should not be too large, thereby affecting the injection speed during the injection molding of the bottle preform and affecting the appearance of the bottle preform; if the blank bottom (4) wall thickness is too thick, the blank bottom (4) wall thickness accounts for more than 95% of the blank body wall thickness, it is not conducive to the blank bottom (4) stretch blow molding process, the blank bottom is difficult to achieve sufficient stretching, and the gram weight of the blank bottom (4) will also increase accordingly.

[0032] As a preferred embodiment, the centers of the arc line IV (403) and the arc line IV (403') coincide and are both located on the center line of the preform. The radii of the arc line II (401) and the arc line III (402) are close. Due to the obstruction of the wave crest protrusion (42) and the larger arc radius of the arc line I (400), when the preform is stretched and blow molded, compared with the distance between the inner construction line and the stretching rod at this location of the conventional ellipsoidal or spherical preform bottom (4), the inner construction line of the transition part (33) of the preform bottom of the present invention is farther from the stretching rod, that is, farther from the contact end, and the material at the corner is easier to stretch without forming a stretching inflection point.

[0033] As a preferred embodiment, the blank body (3) comprises a bottleneck transition portion (31), a blank main portion (32) and a blank bottom transition portion (33) which are connected in sequence, the bottleneck transition portion (31) is in the shape of a hollow cone, the inner construction line and the outer construction line of the bottleneck transition portion (31) are oblique line segment I (310) and oblique line segment i (310') respectively, the angle between the extension line of the oblique line segment I (310) and the center line of the bottle blank is greater than the angle between the extension line of the oblique line segment i (310') and the center line of the bottle blank, so that the wall thickness of the bottleneck transition portion (31) gradually increases from the position close to the bottleneck (2) to the position close to the blank main portion (32).

[0034] As a preferred embodiment, the main body (32) of the blank is in the shape of a hollow cylinder, and the inner structural line and the outer structural line of the main body (32) of the blank are respectively parallel straight line segments I (320) and straight line segments i (320'). The two ends of the bottom transition portion (33) of the blank are respectively connected to the main body (32) of the blank and the bottom (4), preferably tangentially connected. In this embodiment, the axial length of the bottleneck transition portion (31) accounts for 15% to 22% of the axial length of the blank body (3). The bottleneck transition portion (31) corresponds to the conical portion of the bottle transitioning from the bottleneck (2) to the main body (32) of the blank. If the length is too short, the axial length of the bottleneck transition portion (31) accounts for less than 15% of the axial length of the blank body (3). Then, during blow molding, the transition portion is stretched unevenly, the transition portion close to the bottleneck (2) is thin and even easy to cause cracks, and the transition portion close to the main body (32) is easy to be thick, causing material accumulation. If the length is too long, the axial length of the bottleneck transition part (31) accounts for more than 22% of the axial length of the blank body (3), resulting in insufficient material at the upper end of the blank body (32) connected to the bottleneck transition part (31) and being too thin. Similarly, the axial length of the blank bottom transition part (33) accounts for 20% to 25% of the axial length of the blank body (3). The blank bottom transition part (33) corresponds to the portion of the bottle transitioning from the blank body (32) to the blank bottom. If the length is too short, the axial length of the blank bottom transition part (33) accounts for less than 20% of the axial length of the blank body (3), then the effect of the invention is not obvious, but the cost of parts processing is increased. If the length is too long, the axial length of the blank bottom transition part (33) accounts for more than 25% of the axial length of the blank body (3), it is easy to make the lower part of the bottle transition stretched and the wall thickness thin, affecting the performance and appearance of the bottle. The rest is the blank body (32).

[0035] As a preferred embodiment, the inner construction line and the outer construction line of the bottom transition part (33) are a straight line segment II (330) and an arc line V (330') respectively. By designing the inner construction line of the bottom transition part (33) as a straight line segment, it is easier to radially expand during the blow molding process, and the outer construction line of the bottom transition part (33) is designed as an arc line, so that the blank body (3) and the bottom (4) are smoothly connected, the flow resistance of the material during the transition is reduced, the wall thickness of the bottle formed by stretch blow molding is more uniform, and stress cracking of the bottle bottom is avoided.

[0036] As a preferred embodiment, the bottleneck (2) is a circular ring structure, and the inner structural line and the outer structural line of the bottleneck (2) are respectively a straight line segment III (200) and a straight line segment II (200') which are parallel to each other.

[0037] Compared with conventional bottle blanks with ellipsoidal, hemispherical and conical blank bottom (4) structures, the bottle blank structure of the present invention provides a concave surface (41) and a wave crest protrusion (42) on the blank bottom (4), and at the same time sets the arc radius of the arc line I (400) to 80% to 90% of the inner diameter of the blank main body (32). The blank bottom (4) portion formed by the arc line I (400) accounts for a relatively large proportion of the entire blank bottom (4), and an arc line II (401) with an arc radius close to that of the arc line III (402) is provided between the arc line III (402) forming the wave crest protrusion (42) and the arc line I (400) for transition, thereby making the blank bottom (4) structure of the present invention have better tensile properties than conventional blank bottom (4) structures. When the bottle blank structure of the present invention is subjected to stretch blow molding, the stretch rod enters the blank cavity (5), and the end of the stretch rod contacts the concave surface (41) to axially stretch the entire bottle blank. Under the blocking effect of the wave crest protrusion (42), only the concave surface (41) part of the stretch rod and the bottle blank is in contact, and the contact area is relatively reduced. In addition, the wave crest protrusion (42) is set as a structure protruding toward the blank cavity (5), so that the wave crest protrusion (42) of the blank bottom (4) provides an outward supporting anti-deformation force during the stretching process of the stretch rod, thereby preventing the wave crest protrusion (42) of the blank bottom (4) from contacting the stretch rod, reducing the contact area, and allowing more parts of the bottle blank to be stretched during the stretch blow molding process, so that the bottle blank is stretched more fully, and the center of the bottle bottom is prevented from being too thick. Therefore, when designing the bottle blank, the wall thickness of the blank bottom (4) can be designed to be thinner, thereby achieving the purpose of lightweighting.

[0038] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by substantially the same means belongs to the protection scope of the present invention.

Claims

1. A bottle blank structure that is conducive to stretch blow molding, comprising a bottle blank formed by integral injection molding, the bottle blank comprising a bottle mouth, a neck, a blank body and a blank bottom connected in sequence, and a blank cavity is provided in the bottle blank, characterized in that: The blank body comprises a bottleneck transition part, a blank main body part and a blank bottom transition part which are connected in sequence; the blank bottom comprises an upper bottom and a lower bottom which are connected; the construction lines of the upper bottom and the lower bottom are respectively connected curve segments I and II; the upper bottom is formed by rotating 360° with curve segment I as the generatrix and the center line of the bottle blank as the rotation axis; the lower bottom is formed by rotating 360° with curve segment II as the generatrix and the center line of the bottle blank as the rotation axis; the bottommost end of the lower bottom is lower than the convergence point of the extension line of curve segment I; The lower bottom portion includes a concave surface and a wave crest convex portion for preventing the material from being piled up during the bottle bottom molding, wherein the concave surface is sunken toward the blank cavity, the wave crest convex portion is convex toward the blank cavity, and the concave surface is arranged at the bottom of the blank cavity; The bottle blank is provided with inner construction lines and outer construction lines for forming the inner wall and outer wall of the bottle blank respectively. The inner construction lines of the bottom of the blank are composed of arc lines I, arc lines II, arc lines III and arc lines IV connected in sequence. The concave surface is formed by rotating 360° with arc line IV as the generatrix and the center line of the bottle blank as the rotation axis; the wave crest convexity is formed by rotating 360° with arc line III as the generatrix and the center line of the bottle blank as the rotation axis; the arc radius of arc line I is the largest, accounting for 80% to 90% of the inner diameter of the main part of the blank; the arc radius of arc line IV forming the concave surface is 2 to 5 mm; the distance between the bottom of the concave surface and the top of the wave crest convexity is 0.5 to 2 mm; the normal angle between the two ends of arc line III forming the wave crest convexity is α, and the range of α is 18° to 30°.

2. A preform structure for stretch blow molding according to claim 1, characterized in that: The outer structural line of the bottom of the blank is composed of arc line i, arc line ii, arc line iii and arc line iv connected in sequence. The arc line i, arc line ii, arc line iii and arc line iv are respectively arranged corresponding to the arc line i, arc line ii, arc line iii and arc line iv. The arc line ii, arc line iii and arc line iv are respectively formed by the arc line ii, arc line iii and arc line iv being offset outward by the same distance.

3. A preform structure conducive to stretch blow molding according to claim 2, characterized in that: The centers of the arc line IV and the arc line ⅳ coincide with each other and are both located on the center line of the preform.

4. A preform structure for stretch blow molding according to claim 1, characterized in that: The bottleneck transition part is in the shape of a hollow cone, the main body part of the billet is in the shape of a hollow cylinder, and two ends of the billet bottom transition part are respectively connected to the main body part of the billet and the billet bottom.

5. A preform structure for stretch blow molding according to claim 4, characterized in that: The inner construction line and the outer construction line of the bottleneck transition part are oblique line segment I and oblique line segment i respectively, and the angle between the extension line of the oblique line segment I and the center line of the bottle blank is greater than the angle between the extension line of the oblique line segment i and the center line of the bottle blank, so that the wall thickness of the bottleneck transition part gradually increases from near the bottleneck to near the main body of the blank.

6. A preform structure for stretch blow molding according to claim 4, characterized in that: The inner construction line and the outer construction line of the main body of the blank are respectively a straight line segment I and a straight line segment i which are parallel to each other.

7. A preform structure for stretch blow molding according to claim 4, characterized in that: The inner construction line and the outer construction line of the transition part of the bottom of the blank are respectively a straight line segment II and an arc line V.

8. A preform structure for stretch blow molding according to claim 1, characterized in that: The bottleneck is a circular ring structure, and the inner construction line and the outer construction line of the bottleneck are straight line segment III and straight line segment ii which are parallel to each other.

9. A preform structure for stretch blow molding according to claim 1, characterized in that: The axial length of the bottom of the blank accounts for 9% to 15% of the axial length of the bottle blank, the axial length of the bottleneck transition part accounts for 15% to 22% of the axial length of the blank body, and the axial length of the bottom of the blank accounts for 20% to 25% of the axial length of the blank body.

10. A preform structure for stretch blow molding according to claim 1, characterized in that: The wall thickness of the bottom of the billet accounts for 85% to 95% of the wall thickness of the main body of the billet.

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