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Timestamp: 2017-07-25 13:41:08
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Patent US4911978 - Polyolefin resin foamed laminate sheet and double-side vacuum forming of the ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsA foamed laminate sheet suitable for thermoforming and a double-side vacuum forming process using the same are disclosed, said foamed laminate sheet being composed of a foamed interlayer comprising a polyolefin resin as a main resinous component and from 0.5 to 35 parts by weight of an inorganic filler...http://www.google.com/patents/US4911978?utm_source=gb-gplus-sharePatent US4911978 - Polyolefin resin foamed laminate sheet and double-side vacuum forming of the sameAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS4911978 APublication typeGrantApplication numberUS 07/358,110Publication dateMar 27, 1990Filing dateMay 30, 1989Priority dateMay 30, 1988Fee statusLapsedAlso published asCA1293913C, DE68918159D1, DE68918159T2, EP0344726A2, EP0344726A3, EP0344726B1Publication number07358110, 358110, US 4911978 A, US 4911978A, US-A-4911978, US4911978 A, US4911978AInventorsMasahiro Tsubone, Yoshinori Kajimoto, Toru YoshimiOriginal AssigneeSekisui Kaseihin Kogyo Kabushiki KaishaExport CitationBiBTeX, EndNote, RefManPatent Citations (3), Referenced by (41), Classifications (26), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetPolyolefin resin foamed laminate sheet and double-side vacuum forming of the same
US 4911978 AAbstract
A foamed laminate sheet suitable for thermoforming and a double-side vacuum forming process using the same are disclosed, said foamed laminate sheet being composed of a foamed interlayer comprising a polyolefin resin as a main resinous component and from 0.5 to 35 parts by weight of an inorganic filler per 100 parts by weight of the polyolefin resin, said foamed interlayer having a density of from 0.18 to 0.98 g/cm3, and a polyolefin film laminated on both sides of said foamed interlayer. The foamed laminate sheet exhibits excellent formability, and formings obtained therefrom have excellent heat resistance, oil resistance, heat insulating properties, and strength, with outstanding use in a microwave oven or as a retort food container.
1. A foamed laminate sheet suitable for thermoforming, which is composed of a foamed interlayer comprising a polyolefin resin as a main resinous component and from 0.5 to 35 parts by weight of an inorganic filler per 100 parts by weight of the polyolefin resin, said foamed interlayer having a density of from 0.18 to 0.98 g/cm3, and a polyolefin film laminated on both sides of said foamed interlayer.
9. A process of double-side vacuum forming as claimed in claim 7, wherein said male and female molds are set at a temperature of 50° C. or lower.
This invention relates to a foamed laminate sheet suited for thermoforming, particularly double-side vacuum forming, comprising a foamed interlayer composed mainly of a polyolefin resin and a polyolefin film laminated on both side thereof. It also relates to a process of double-side vacuum forming using such a foamed laminate sheet in which a relatively cheap polypropylene resin is used to provide heat resistant, oil resistant and thermally insulating food containers with high strength which can be used in a microwave oven or as a retort food container.
Known processes for obtaining containers and trays from a thermoplastic resin foamed sheet include a so-called single side vacuum forming technique in which a foamed sheet is heated to cause post-expansion and softening and the foamed sheet is vacuum-formed by the use of a female mold or a male mold to shape it in a desired formed article. However, the foamed sheet decreases with time and also scatters with changes of conditions of preparation of the sheet. Therefore, formings obtained by this process have a scattering thickness, which leads to insufficient strength or poor fitness when piled up, thus resulting in reduced yield of non-defectives.
In order to solve the problems associated with single-side vacuum forming, double-side vacuum forming of thermoplastic resin foamed sheets has been developed as disclosed in JP-B-59-1184 and JP-A-60-192615 (the term "JP-B" as used herein means an "examined published Japanese patent application" and the term "JP-A" means an "unexamined published Japanese patent application"), in which a pair of forming molds with a prescribed gap therebetween and having a clamping frame at the periphery thereof are used, the male mold being set at 50° to 60° C., a heated and plasticized thermoplastic resin foamed sheet is clamped between the male and female molds, the gap is evacuated from the both molds to thereby adibatically expand the sheet to the full of the gap to give a prescribed shape, the formed sheet is cooled, a gas is introduced into the mold cavity to raise the pressure to atmospheric pressure, the molds are opened, and the formed article is removed. The above-cited references describe that the double-side vacuum forming technique produces formings from a foamed sheet of a thermoplastic resin, such as polystyrene and polymers mainly comprising styrene, or a foamed laminate sheet composed of such a foamed sheet and a thermoplastic resin film.
One object of this invention is to eliminate the above-described disadvantages and to provide a polyolefin resin foamed laminate sheet which can provide formings, such as food containers and trays, excellent in heat resistance, oil resistance, thermal insulating properties, and strength.
FIG. 1 is a schematic cross section of a mold to be used for double-side vacuum forming.
The interlayer of the polyolefin resin foamed laminate sheet of the present invention is a foamed sheet comprising a polyolefin resin as a main resinous component. The polyolefin resin to be used includes polypropylene, polyethylene, polybutene, polymethyl-pentene, mixtures of these polymers, and olefin copolymers having an olefin content of at least 50% by weight, such as ethylene-vinyl acetate copolymers, ethylene-methacrylate copolymers, ethylene-propylene-terpolymers, and ethylene-propylene rubbers.
It is desirable that the foamed laminate sheet of the present invention has a percent heat shrinkage as small as possible so as to have high retention of dimension after heat shrinkage. It is also desirable that the shrinkage in the machine direction and that in the cross direction are substantially equal. For example, the foamed laminate sheet preferably has a percent retention of at least 50% and a residual dimension ratio of at least 0.7. The terminology "percent retention" as used herein means a percentage of the dimension after shrinkage to the original dimension in the machine or cross direction when the sheet is heated at 190° C. for 30 minutes. If the percent retention is less than 50%, the percent shrinkage on heating and softening becomes too great to make it difficult to form the sheet to shape. The terminology "residual dimension ratio" as used herein means a ratio of the shorter dimension after heat shrinkage in either the machine direction or the cross direction to the longer dimension in the other direction. If the residual dimension ratio is less than 0.7, the sheets tends to have poor stretchability on forming and the resulting formings tend to have defective appearance. These criteria can be adjusted by controlling the amount of the inorganic filler or the ratio of polyolefin to polystyrene in the foamed layer, the size of a mold, and the like.
The double-side vacuum forming in accordance with the present invention is illustrated below. The gap between the female and male molds is preferably set at 1.0 to 2.5 times, more preferably 2.0 times, the thickness of the heated and softened foamed laminate sheet. The foamed laminate sheet is clamped at the four corners and previously heated and softened at a temperature between 160° and 190° C. and then transferred to the open space between the molds. At this time, the gap between the molds is desirably 1.0 to 2.5 times, more desirably 2.0 times, the thickness of the heated and softened laminate sheet as stated above. This gap has an influence on strength of the resulting post-expanded and formed article. If it exceeds 2.5 times the thickness of the sheet, the degree of expansion becomes too high, resulting in extremely reduced bending strength. If it is less than 1.0 time, no contribution to improvement of bending strength can be obtained. The mold temperature is preferably 50° C. or lower. In the previously described double-side vacuum forming of polystyrene resin sheets, the mold temperature is set at 50° to 60° C. for evacuation from the mold surfaces to cause post-expansion and cooling. To the contrary, in the present invention in which the formable sheet is composed of a foamed sheet of polyolefin resins, e.g., polypropylene, laminated on both sides thereof a polyolefin film, since polypropylene resins have a large specific heat and poor cooling efficiency, mold temperatures of 50° C. or higher brings no increase of cycle speed but deformation of the laminate sheet. However, too a low mold temperature functions to cool the heated and softened sheet to lose plasticity, thus failing to achieve sufficient vacuum forming. From all these considerations, a suitable mold temperature ranges from about 35° to 45° C. The degree of vacuum in the cavity is usually 500 mmHg vac. or more.
The process of the vacuum forming according to the present invention will be explained with reference to FIG. 2. Foamed laminate sheet 1 composed of a polypropylene resin foamed interlayer having adhered a polypropylene film to both sides thereof is heated and softened at 300° C. for 45 to 50 seconds by means of a far infrared heater. The heated foamed sheet is transferred to the open space between a pair of molds 2, 3 (FIG. 2-a). The molds used here are matching male and female molds. Female mold 2 is connected to a suction apparatus to perform straight vacuum forming (FIG. 2-b). The peripheries of the both molds are then matched (FIG. 2-c), and the cavity is evacuated from male mold 3 to cause expansion-in-mold to obtain a formed article 11 (FIG. 2-d). During the forming the mold temperature is kept at 50° C. or lower, preferably 40° C. After complete expansion, the pressure of the cavity is returned to atmospheric pressure, and the formed article 11 is removed from the molds.
TABLE 1__________________________________________________________________________                              MIDesig-                             Value Measurementnation    Kind of Polymer       Trade Name               Grade                    Manufacturer                              (g/10 min)                                    Method__________________________________________________________________________A   Polypropylene       Sumitomo               D-501                    Sumitomo  0.4   JIS K-6758       Noblen ® Chemical        230° C., 2.16 kg                    Co., Ltd.B   Polypropylene       Sumitomo               FH-1015                    Sumitomo  0.5   JIS K-6758       Noblen ® Chemical        230° C., 2.16 kg                    Co., Ltd.C   Styrene-maleic       More Max ®               UG-830                    Idemitsu  1.8   JIS K-7210    anhydride            Petrochemical   230° C., 2.16 kg    copolymer            Co., Ltd.D   Styrene-       AX Polymer               AX-T Asahi Chemical                              3.7   JIS K-7210    methacrylic     100  Industry Co., Ltd.                                    230° C., 2.16 kg    acid copolymerE   Polystyrene       Styron ®               8703 Asahi Chemical                              1.6   JIS K-6870                                    200° C., 5 kg                                    -    Industry Co.,                                    Ltd.  200° C., 5 kgF   &#945;-Methyl-       HS Polymer               HS-400                    Denki Kagaku                              2.1   Denka Method    styrene              Kogyo K.K.      250° C., 5 kgG   Saturated       Taftic ®               H-1011                    Asahi Chemical                              13.9  JIS K-7210    thermoplastic        Industry Co., Ltd.                                    230° C., 5 kg    elastomerH   Polypropylene       Sumitomo               FS-2011                    Sumitomo Chemical                              2.5   JIS K-6758       Noblen ® Co., Ltd.       230° C., 2.16 kgI   Polypropylene       Sumitomo               AD-571                    Sumitomo Chemical                              0.6   JIS K-6758       Noblen ® Co., Ltd.       230° C., 2.16 kgJ   Polyethylene       Yukalon ®               HE-30                    Mitsubishi                              0.27  ASTM D1238                    Petrochemical   190° C., 2.16 kg                    Co., Ltd.K   Polyethylene       Petrothene ®               172J Tosoh     0.38  ASTM D1238                    Corporation     190° C., 2.16 kgL   Polyethylene       Lumirror ®               F 86 Toray Industries,                              --    --    terephthalate        Inc.    filmM   Polypropylene/       Barielon ® CX               &#956; Asahi Chemical                              --    --    polyvinylidene       Industry Co., Ltd.    chloride/poly-    propylene__________________________________________________________________________
A polymer mixture consisting of 40 parts of a polypropylene resin A, 30 parts of a polypropylene resin B, 25 parts of a polystyrene resin C, and 5 parts of a saturated thermoplastic elastomer G was uniformly mixed with 12.5 parts of talc as an inorganic filler in an extruder. To the resin composition was added 0.6% by weight of butane (hereinafter abbreviated as "C4") as a blowing agent and the resulting foaming compound was supplied to an extruder. Separately, 55 parts of a polypropylene resin H and 45 parts of a block polypropylene resin I were uniformly mixed in an extruder to prepare a film-forming resin. The above-prepared foaming compound and the film-forming resin were co-extruded to obtain a foamed laminate sheet. The extrusion of the foaming compound was carried out at a resin temperature of 203° C. and at an output ratio of 90 kg/hr. The resulting foamed laminate sheet had a thickness of 1290 μm [50 μm/1185 μm (foamed interlayer)/55 μm] and a basis weight of 608 g/m2 [46/512 (foamed interlayer)/50 g/m2 ], and the foamed interlayer had a density of 0.41 g/cm3 and an open cell ratio of 52%.
A 100 mm-square piece was cut out of the foamed laminate sheet and heated in an oven at 190° C. for 30 minutes. The residual dimension was 56 mm in the machine direction (MD) and 58 mm in the transverse direction (TD), giving a residual dimension ratio MD/TD of 0.97. The foamed laminate sheet had a smooth surface with no bubbles due to gas entrapment.
The foamed laminate sheet as above produced was clamped at the four corners and heated and softened at 300° C. for about 50 seconds by means of a far infrared heater. The sheet heated and softened had a thickness of about 1.2 mm. The sheet heated and softened was double-side vacuum formed into a container by using matched male and female molds. The female mold had a cavity size of 157×124 mm and a depth of 30 mm, and the gap without clamping of the sheet between the male and female molds was 1.5 mm at the bottom part and 1.0 mm at the upright part. The sheet was first subjected to straight vacuum forming using the female mold set at 40° C. After the periphery of the female mold was matched with the periphery of the male mold also set at 40° C., the cavity was evacuated from the vacuum ports provided in both molds to a reduced pressure of 550 mmHg vac. for a matching time of 10 seconds to effect double-side vacuum forming. The sheet exhibited satisfactory formability.
The tray had a density of 0.33 g/cm3. When it was heated in a Geer oven set at 130° C. for 30 minutes, the dimensional change was within 2%, proving of excellent heat resistance of the tray. These results are shown in Table 2.
A foamed laminate sheet was produced in the same manner as in Example 1, except for changing the composition of the foaming compound for the foamed interlayer and the composition of the film-forming resin material as shown in Table 2. The properties of the foamed laminate sheet and formability in double-side vacuum forming as carried out in the same manner as in Example 1 are shown in Table 2.
In Example 15, polyethylene terephthalate films were coated on the both sides of a foamed layer in a separate step; in Example 16, a polypropylene/polyvinylidene chloride/polypropylene laminate film was laminated on one side of a film/foamed layer/film foamed laminate sheet in a separate step; and in Example 14, forming was carried out by use of a far infrared heater of 180° C. for about 50 seconds.
The abbreviate "H.C" for the blowing agent used in Examples 9 and 10 signifies Hydrocellol® (a mixture of sodium bicarbonate and citric acid, made by Beringer AG).
A foamed laminate sheet was produced in the same manner as in Example 1, except for using the inorganic filler in an amount less than (Comparative Example 1) or more than (Comparative Example 2) the range specified in the present invention. The properties of the resulting foamed laminate sheets and their formability in double-side vacuum forming as carried out in the same manner as in Example 1 are shown in Table 2.
TABLE 2-(1)__________________________________________________________________________               Example 1                      Example 2                             Example 3                                    Example 4                                           Example__________________________________________________________________________                                           5Resin Composition:Foamed Interlayer (part)               A/B/C/G =                      B/C/G =                             B/C = 75/25                                    A/B/C/G =                                           A/B/C/G =               40/30/25/5                      70/25/5       40/45/10/5                                           40/5/50/5External Film Layer (part)               H/I = 55/45                      H/I = 55/45                             H/I = 55/45                                    H/I = 55/45                                           H/I = 55/45Amount of Talc (part)               12.5   0.5    0.5    12.5   12.5Blowing Agent (% by wt.)               C4 0.6                      C4 0.8                             C4 0.1                                    C4 0.5                                           C4 0.7Temp. of Foaming Resin (°C.)               203    202    202    201    200Extrusion Output (kg/hr)               90     90     91     89     92Total Thickness (&#956;m)               1290   2954   2428   1161   2659(Film/Foamed Layer/Film)               50/1185/55                      51/2847/55                             50/2326/52                                    49/1059/53                                           50/2555/54Total Basis Weight (g/cm3)               608    608    602    601    605(Film/Foamed Layer/Film)               46/512/50                      46/512/50                             45/510/47                                    44/509/48                                           45/511/49Density of Foamed Layer (g/cm3)               0.41   0.18   0.22   0.48   0.20Open Cell Ratio (%) 52     30     35     56     48Residual Dimension (190° C. × 30 min.):MD                  56     52     55     62     60TD                  58     74     71     63     72MD/TD               0.97   0.70   0.77   0.98   0.83Dimensional Change (130° C. × 30 min.)               within 2%                      within 2%                             within 2%                                    within 2%                                           within 2%Appearance of Sheet excellent                      good   good   excellent                                           excellentBubble              good   good   good   good   goodThickness of Formed Article (mm)bottom part         1.8    4.4    3.2    1.6    4.1upright part        1.2    2.9    2.2    1.1    2.7Density of Foamed Layer of               0.33   0.14   0.19   0.38   0.15Formed Article (g/cm3)Appearance of Formed Article               excellent                      good   good   excellent                                           excellent__________________________________________________________________________
TABLE 2-(2)__________________________________________________________________________               Example 6                      Example 7                             Example 8                                    Example 9                                           Example__________________________________________________________________________                                           10Resin Composition:Foamed Interlayer (part)               A/B/D/G =                      A/B/F/G =                             A/B/E/G =                                    B/C/G =                                           B/C/G =               40/30/25/5                      40/30/25/5                             40/30/25/5                                    70/25/5                                           70/25/5External Film Layer (part)               H/I = 55/45                      H/I = 55/45                             H/I = 55/45                                    H/I = 55/45                                           H/I = 55/45Amount of Talc (part)               12.5   12.5   12.5   0.5    0.5Blowing Agent (% by wt.)               C4 0.6                      C4 0.7                             C4 0.8                                    (H.C) 0.3                                           C4 0.6 + H.C 0.3Temp. of Foaming Resin (°C.)               202    202    201    208    201Extrusion Output (kg/hr)               91     90     92     89     90Total Thickness (&#956;m)               1442   1316   1263   1064   2783(Film/Foamed Layer/Film)               52/1336/54                      50/1214/52                             50/1160/53                                    48/964/52                                           52/2674/57Total Basis Weight (g/cm3)               604    603    604    601    606(Film/Foamed Layer/Film)               47/508/49                      46/510/47                             45/511/48                                    43/511/47                                           47/508/51Density of Foamed Layer (g/cm3)               0.38   0.42   0.44   0.53   0.19Open Cell Ratio (%) 54     58     61     31     53Residual Dimension (190° C. × 30 min.):MD                  54     56     57     61     54TD                  57     58     60     64     73MD/TD               0.95   0.97   0.95   0.95   0.74Dimensional Change (130° C. × 30 min.)               within 2%                      within 2%                             within 2%                                    within 2%                                           within 2%Appearance of Sheet excellent                      excellent                             good   excellent                                           excellentBubble              good   good   good   good   goodThickness of Formed Article (mm)bottom part         2.0    1.8    1.7    1.5    3.8upright part        1.3    1.2    1.1    1.0    2.5Density of Foamed Layer of               0.31   0.34   0.36   0.41   0.16Formed Article (g/cm3)Appearance of Foamed Article               excellent                      excellent                             good   excellent                                           excellent__________________________________________________________________________
TABLE 2-(3)__________________________________________________________________________                                              Compara-                                                    Compara-                                              tive  tive        Example 11              Example 12                    Example 13                          Example 14                                Example 15                                       Example 16                                              Example                                                    Example__________________________________________________________________________                                                    2Resin Composition:Foamed Interlayer        B/C/G =              A/B/C =                    A/B/C =                          J = 100                                B/C/G =                                       A/B/C/G =                                              B/C/G                                                    A = 100(part)       70/25/5              40/35/25                    40/35/25                          70/25/5                                70/25/5                                       40/30/25/5External Film layer        H/I=55/45              H/I=55/45                    H/I=55/45                          K = 100                                L      H/I=55/45                                              H/I=55/45                                                    H/I=55/45(part)                                      M = 5Amount of Talc (part)        0.5   35    30    5     5      12.5   0.2   40Blowing Agent        C4 0.8              C4 0.5                    C4 0.6                          C4 0.5                                C4 0.8                                       C4 0.6                                              C4                                                    C4 0.5(% by wt.)Temp. of Foaming Resin        198   203   202   120   203    202    202   204(°C.)Extrusion Output (kg/hr)        93    90    91    91    91     90     90    89Total Thickness (&#956;m)        2414  626   1120  2235  2913   1355   2642  617(Film/Foamed Layer/        51/2305/58              52/514/60                    51/1010/59                          49/2126/60                                *25/2863/25                                       55/1185/                                              53/2530/59                                                    51/513/53Film)                                       55/60Total Basis Weight        605   605   604   605   585    666    607   602(g/cm3) (Film/Foamed        46/507/52              47/504/54                    46/505/53                          45/505/55                                35/515/35                                       50/512/                                              48/506/53                                                    46/508/48Layer/Film)                                 50/54Density of Foamed Layer        0.22  0.98  0.5   0.31  0.36   0.41   0.20  0.99(g/cm3)Open Cell Ratio (%)        35    95    91    33    30     52     22    98Residual Dimension(190° C. × 30 min.):MD           38    85    60    54    56     55     41    91                          (120° C. ×                                (200° C. ×                          30 min.)                                30 min.)TD           76    87    65    76    75     76     74    92MD/TD        0.50  0.98  0.92  0.71  0.75   0.72   0.55  0.99Dimensional Change        within 2%              within 2%                    within 2%                          within 2%                                within 2%                                       within 2%                                              within                                                    within 2%(130° C. × 30 min.)                          (80° C. ×                                (135° C. ×                          30 min.)                                30 min.)Appearance of Sheet        good  good  excellent                          good  good   excellent                                              poor  poorBubble       good  good  good  good  good   good   good  poorThickness of FormedArticle (mm)bottom part  3.4   0.9   1.5   3.4   4.4    1.8    3.6   0.9upright part 2.3   0.6   1.0   2.3   2.9    1.2    2.4   0.6Density of Foamed        0.18  0.67  0.39  0.23  0.28   0.32   0.17  0.70Layer of FormedArticle (g/cm3)Appearance of Foamed        fair  good  excellent                          good  good   excellent                                              poor  poorArticle__________________________________________________________________________
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ASSIGNORS INTEREST.;ASSIGNORS:TSUBONE, MASAHIRO;KAJIMOTO, YOSHINORI;YOSHIMI, TORU;REEL/FRAME:005085/0903Effective date: 19890522Sep 13, 1993FPAYFee paymentYear of fee payment: 4Sep 15, 1997FPAYFee paymentYear of fee payment: 8Oct 16, 2001REMIMaintenance fee reminder mailedMar 27, 2002LAPSLapse for failure to pay maintenance feesMay 21, 2002FPExpired due to failure to pay maintenance feeEffective date: 20020327RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services